Monday, October 16, 2017

Exoplanet Transits as the Foundation of an Interstellar Communications Network

Exoplanet Transits as the Foundation of an Interstellar Communications Network

Author:

Forgan

Abstract:


Two fundamental problems for extraterrestrial intelligences (ETIs) attempting to establish interstellar communication are timing and energy consumption. Humanity's study of exoplanets via their transit across the host star highlights a means of solving both problems. An ETI 'A' can communicate with ETI 'B' if B is observing transiting planets in A's star system, either by building structures to produce artificial transits observable by B, or by emitting signals at B during transit, at significantly lower energy consumption than typical electromagnetic transmission schemes.

This can produce a network of interconnected civilisations, establishing contact via observing each other's transits. Assuming that civilisations reside in a Galactic Habitable Zone (GHZ), I conduct Monte Carlo Realisation simulations of the establishment and growth of this network, and analyse its properties in the context of graph theory.

I find that at any instant, only a few civilisations are correctly aligned to communicate via transits. However, we should expect the true network to be cumulative, where a "handshake" connection at any time guarantees connection in the future via e.g. electromagnetic signals. In all our simulations, the cumulative network connects all civilisations together in a complete network. If civilisations share knowledge of their network connections, the network can be fully complete on timescales of order a hundred thousand years. Once established, this network can connect any two civilisations either directly, or via intermediate civilisations, with a path much less than the dimensions of the GHZ.

A Wideband Data Recorder System for the Robert C. Byrd Green Bank Telescope

The Breakthrough Listen Search for Intelligent Life: A Wideband Data Recorder System for the Robert C. Byrd Green Bank Telescope

Authors:


MacMahon et al

Abstract:
The Breakthrough Listen Initiative is undertaking a comprehensive search for radio and optical signatures from extraterrestrial civilizations. An integral component of the project is the design and implementation of wide-bandwidth data recorder and signal processing systems. The capabilities of these systems, particularly at radio frequencies, directly determine survey speed; further, given a fixed observing time and spectral coverage, they determine sensitivity as well. Here, we detail the Breakthrough Listen wide-bandwidth data recording system deployed at the 100-m aperture Robert C. Byrd Green Bank Telescope. The system digitizes up to 6 GHz of bandwidth at 8 bits for both polarizations, storing the resultant 24 GB/s of data to disk. This system is among the highest data rate baseband recording systems in use in radio astronomy. A future system expansion will double recording capacity, to achieve a total Nyquist bandwidth of 12 GHz in two polarizations. In this paper, we present details of the system architecture, along with salient configuration and disk-write optimizations used to achieve high-throughput data capture on commodity compute servers and consumer-class hard disk drives.

Sunday, October 15, 2017

A Millimeter Continuum Size-Luminosity Relationship for Protoplanetary Disks

A Millimeter Continuum Size-Luminosity Relationship for Protoplanetary Disks

Authors:


Tripathi et al

Abstract:
We present a sub-arcsecond resolution survey of the 340 GHz dust continuum emission from 50 nearby protoplanetary disks, based on new and archival observations with the Submillimeter Array. The observed visibility data were modeled with a simple prescription for the radial surface brightness profile. The results were used to extract intuitive, empirical estimates of the emission "size" for each disk, Reff, defined as the radius that encircles a fixed fraction of the total continuum luminosity, Lmm. We find a significant correlation between the sizes and luminosities, such that Reff∝L0.5mm, providing a confirmation and quantitative characterization of a putative trend that was noted previously. This correlation suggests that these disks have roughly the same average surface brightness interior to their given effective radius, ~0.2 Jy arcsec−2 (or 8 K in brightness temperature). The same trend remains, but the 0.2dex of dispersion perpendicular to this relation essentially disappears, when we account for the irradiation environment of each disk with a crude approximation of the dust temperatures based on the stellar host luminosities. We consider two (not mutually exclusive) explanations for the origin of this size-luminosity relationship. Simple models of the growth and migration of disk solids can account for the observed trend for a reasonable range of initial conditions, but only on timescales that are much shorter than the nominal ages present in the sample. An alternative scenario invokes optically thick emission concentrated on unresolved scales, with filling factors of a few tens of percent, that are perhaps manifestations of localized particle traps.

Magnetic fields in circumstellar disks: The potential of Zeeman observations


Authors:

Brauer et al

Abstract:

Context.

Recent high angular resolution polarimetric continuum observations of circumstellar disks provide new insights into their magnetic field. However, direct constraints are limited to the plane of sky component of the magnetic field. Observations of Zeeman split spectral lines are a potential approach to enhance these insights by providing complementary information.

Aims.

We investigate which constraints for magnetic fields in circumstellar disks can be obtained from Zeeman observations of the 113 GHz CN lines. Furthermore, we analyze the requirements to perform these observations and their dependence on selected quantities.

Methods.

We simulate the Zeeman splitting with the radiative transfer (RT) code POLARIS (Reissl et al. 2016) extended by our Zeeman splitting RT extension ZRAD (Brauer et al. 2017), which is based on the line RT code Mol3D (Ober et al. 2015).

Results.

We find that Zeeman observations of the 113 GHz CN lines provide significant insights into the magnetic field of circumstellar disks. However, with the capabilities of recent and upcoming instrument/observatories, even spatially unresolved observations would be challenging. Nevertheless, these observations are feasible for the most massive disks with a strong magnetic field and high abundance of CN/H. The most restrictive quantity is the magnetic field strength, which should be at least in the order of ∼1 mG. In addition, the inclination of the disk should be around 60deg to preserve the ability to derive the line-of-sight (LOS) magnetic field strength and to obtain a sufficiently high circularly polarized flux.

A precessing Be disk as a possible model for occultation events in GX 304-1

A precessing Be disk as a possible model for occultation events in GX 304-1

Authors:


Kühnel et al

Abstract:

We report on the RXTE detection of a sudden increase in the absorption column density, NH, during the 2011 May outburst of GX 304-1. The NH increased up to ∼16×1022 atoms cm−2, which is a factor of 3-4 larger than what is usually measured during the outbursts of GX 304-1 as covered by RXTE. Additionally, an increase in the variability of the hardness ratio as calculated from the energy resolved RXTE-PCA light curves is measured during this time range. We interpret these facts as an occultation event of the neutron star by material in the line of sight. Using a simple 3D model of an inclined and precessing Be disk around the Be type companion, we are able to qualitatively explain the NH evolution over time. We are able to constrain the Be-disk density to be on the order of 10−11 g cm−3. Our model strengthens the idea of inclined Be disks as origin of double-peaked outbursts as the derived geometry allows accretion twice per orbit under certain conditions.

Saturday, October 14, 2017

Magnetically Induced Disk Winds and Transport in the HL Tau Disk

Magnetically Induced Disk Winds and Transport in the HL Tau Disk

Authors:


Hasegawa et al

Abstract:
The mechanism of angular momentum transport in protoplanetary disks is fundamental to understand the distributions of gas and dust in the disks. The unprecedented, high spatial resolution ALMA observations taken toward HL Tau and subsequent radiative transfer modeling reveal that a high degree of dust settling is currently achieved at the outer part of the HL Tau disk. Previous observations however suggest a high disk accretion rate onto the central star. This configuration is not necessarily intuitive in the framework of the conventional viscous disk model, since efficient accretion generally requires a high level of turbulence, which can suppress dust settling considerably. We develop a simplified, semi-analytical disk model to examine under what condition these two properties can be realized in a single model. Recent, non-ideal MHD simulations are utilized to realistically model the angular momentum transport both radially via MHD turbulence and vertically via magnetically induced disk winds. We find that the HL Tau disk configuration can be reproduced well when disk winds are properly taken into account. While the resulting disk properties are likely consistent with other observational results, such an ideal situation can be established only if the plasma β at the disk midplane is β0≃2×104 under the assumption of steady accretion. Equivalently, the vertical magnetic flux at 100 au is about 0.2 mG. More detailed modeling is needed to fully identify the origin of the disk accretion and quantitatively examine plausible mechanisms behind the observed gap structures in the HL Tau disk.

Generation of inclined protoplanetary discs and misaligned planets through mass accretion I: Coplanar secondary discs

Generation of inclined protoplanetary discs and misaligned planets through mass accretion I: Coplanar secondary discs

Authors:


Xiang-Gruess et al

Abstract:

We study the three-dimensional evolution of a viscous protoplanetary disc which accretes gas material from a second protoplanetary disc during a close encounter in an embedded star cluster. The aim is to investigate the capability of the mass accretion scenario to generate strongly inclined gaseous discs which could later form misaligned planets. We use smoothed particle hydrodynamics to study mass transfer and disc inclination for passing stars and circumstellar discs with different masses. We explore different orbital configurations to find the parameter space which allows significant disc inclination generation. Thies et al. (2011) suggested that significant disc inclination and disc or planetary system shrinkage can generally be produced by the accretion of external gas material with a different angular momentum. We found that this condition can be fullfilled for a large range of gas mass and angular momentum. For all encounters, mass accretion from the secondary disc increases with decreasing mass of the secondary proto-star. Thus, higher disc inclinations can be attained for lower secondary stellar masses. Variations of the secondary disc’s orientation relative to the orbital plane can alter the disc evolution significantly. The results taken together show that mass accretion can change the three-dimensional disc orientation significantly resulting in strongly inclined discs. In combination with the gravitational interaction between the two star-disc systems, this scenario is relevant for explaining the formation of highly inclined discs which could later form misaligned planets.

Detecting Water's Dissociation in Protoplanetary Disks

The 1600 Angstrom Emission Bump in Protoplanetary Disks: A Spectral Signature of H2O Dissociation

Authors:


France et al

Abstract:

The FUV continuum spectrum of many accreting pre-main sequence stars, Classical T Tauri Stars (CTTSs), does not continue smoothly from the well-studied Balmer continuum emission in the NUV, suggesting that additional processes contribute to the short-wavelength emission in these objects. The most notable spectral feature in the FUV continuum of some CTTSs is a broad emission approximately centered at 1600~\AA, which has been referred to as the "1600 A Bump". The origin of this feature remains unclear. We have assembled archival FUV spectra of 37 disk-hosting systems observed by the {\it Hubble Space Telescope}. Clear 1600 A Bump emission is observed above the smooth, underlying 1100-1800 A continuum spectrum in 19/37 Classical T Tauri disks in the HST sample, with the detection rate in transition disks (8/8) being much higher than in primordial or non-transition sources (11/29). We describe a spectral deconvolution analysis to separate the Bump (spanning 1490~--~1690 A) from the underlying FUV continuum, finding an average Bump luminosity, L(Bump7 x 10^{29} erg s^{-1}. We find that the 1600 A Bump is characterized by a peak wavelength of 1598.6 +/- 3.3 A.
Contrary to previous studies, we find that this feature is inconsistent with models of H2 excited by electron-impact. We show that this Bump emits roughly 10-80% of the total fluorescent H2 luminosity for stars with well-defined Bump features. Energetically, this suggests that the carrier of the 1600 A Bump emission is powered by Ly-a photons. We argue that the most likely mechanism is Ly-a-driven dissociation of H2O in the inner disk, r < 2 AU. We demonstrate that non-thermally populated H2O fragments can qualitatively account for the observed emission (discrete and continuum), and find that the average Ly-a-driven H2O dissociation rate is 1.7x 10^{42} water molecules s^{-1}.

Friday, October 13, 2017

Emission lines in the atmosphere of the irradiated brown dwarf WD0137-349B

Emission lines in the atmosphere of the irradiated brown dwarf WD0137-349B

Authors:

Longstaff et al

Abstract:

We present new optical and near-infrared spectra of WD0137-349; a close white dwarf - brown dwarf non-interacting binary system with a period of ≈114 minutes. We have confirmed the presence of Hα emission and discovered He, Na, Mg, Si, K, Ca, Ti, and Fe emission lines originating from the brown dwarf atmosphere. This is the first brown dwarf atmosphere to have been observed to exhibit metal emission lines as a direct result of intense irradiation. The equivalent widths of many of these lines show a significant difference between the day and night sides of the brown dwarf. This is likely an indication that efficient heat redistribution may not be happening on this object, in agreement with models of hot Jupiter atmospheres. The Hα line strength variation shows a strong phase dependency as does the width. We have simulated the Ca II emission lines using a model that includes the brown dwarf Roche geometry and limb darkening and we estimate the mass ratio of the system to be 0.135±0.004. We also apply a gas-phase equilibrium code using a prescribed DRIFT-PHOENIX model to examine how the chemical composition of the brown dwarf upper atmosphere would change given an outward temperature increase, and discuss the possibility that this would induce a chromosphere above the brown dwarf atmosphere.

HH1165: The First Large-scale Herbig–Haro Jet Driven by a Proto-brown Dwarf

First Large-scale Herbig–Haro Jet Driven by a Proto-brown Dwarf

Authors:


Riaz et al

Abstract:

We report the discovery of a new Herbig–Haro jet, HH 1165, in SOAR narrow-band imaging of the vicinity of the σ Orionis cluster. HH 1165 shows a spectacular extended and collimated spatial structure, with a projected length of 0.26 pc, a bent C-shaped morphology, multiple knots, and fragmented bow shocks at the apparent ends of the flow. The Hα image shows a bright halo with a clumpy distribution of material seen around the driving source, and curved reflection nebulosity tracing the outflow cavities. The driving source of HH 1165 is a Class I proto-brown dwarf, Mayrit 1701117 (M1701117), with a total (dust+gas) mass of ~36 M Jup and a bolometric luminosity of ~0.1 L ⊙. High-resolution VLT/UVES spectra of M1701117 show a wealth of emission lines indicative of strong outflow and accretion activity. SOAR/Goodman low-resolution spectra along the jet axis show an asymmetrical morphology for HH 1165. We find a puzzling picture wherein the northwest part exhibits a classical HH jet running into a pre-dominantly neutral medium, while the southern part resembles an externally irradiated jet. The C-shaped bending in HH 1165 may be produced by the combined effects from the massive stars in the ionization front to the east, the σ Orionis core to the west, and the close proximity to the B2-type star HR 1950. HH 1165 shows all of the signatures to be considered as a scaled-down version of parsec-length HH jets, and can be termed as the first sub-stellar analog of a protostellar HH jet system.

OGLE-2016-BLG-0693LB: Probing the Brown Dwarf Desert with Microlensing

OGLE-2016-BLG-0693LB: Probing the Brown Dwarf Desert with Microlensing

Authors:


Ryu et al

Abstract:

We present an analysis of microlensing event OGLE-2016-BLG-0693, based on the survey-only microlensing observations by the OGLE and KMTNet groups. In order to analyze the light curve, we consider the effects of parallax, orbital motion, and baseline slope, and also refine the result using a Galactic model prior. From the microlensing analysis, we find that the event is a binary composed of a low-mass brown dwarf (49+-20 MJ) companion and a K- or G-dwarf host, which lies at a distance 5.0+-0.6 kpc toward the Galactic bulge. The projected separation between the brown dwarf and its host star is less than ~5 AU, and thus it is likely that the brown dwarf companion is located in the brown dwarf desert.

Thursday, October 12, 2017

Estimating the magnetic field strength in hot Jupiters

Estimating the magnetic field strength in hot Jupiters

Authors:


Yadav et al

Abstract:
A large fraction of known Jupiter like exoplanets are inflated as compared to Jupiter. These "hot" Jupiters orbit close to their parent star and are bombarded with intense starlight. Many theories have been proposed to explain their radius inflation and several suggest that a small fraction of the incident starlight is injected in to the planetary interior which helps to puff up the planet. How will such energy injection affect the planetary dynamo? In this Letter, we estimate the surface magnetic field strength of hot Jupiters using scaling arguments that relate energy available in planetary interiors to the dynamo generated magnetic fields. We find that if we take into account the energy injected in the planetary interior that is sufficient to inflate hot Jupiters to observed radii, then the resulting dynamo should be able generate magnetic fields that are more than an order of magnitude stronger than the Jovian values. Our analysis highlights the potential fundamental role of the stellar light in setting the field strength in hot Jupiters.

Water Clouds in hot Jupiter HAT-P-32b's Atmosphere

Near-IR Transmission Spectrum of HAT-P-32b using HST/WFC3

Authors:


Damiano et al

Abstract:
We report here the analysis of the near-infrared transit spectrum of the hot Jupiter HAT-P-32b, which was recorded with the Wide Field Camera 3 (WFC3) on board the Hubble Space Telescope. HAT-P-32b is one of the most inflated exoplanets discovered, making it an excellent candidate for transit spectroscopic measurements. To obtain the transit spectrum, we have adopted different analysis methods, both parametric and non-parametric (Independent Component Analysis, ICA), and compared the results. The final spectra are all consistent within 0.5σ. The uncertainties obtained with ICA are larger than those obtained with the parametric method by a factor of ~1.6–1.8. This difference is the trade-off for higher objectivity due to the lack of any assumption about the instrument systematics compared to the parametric approach. The ICA error bars are therefore worst-case estimates. To interpret the spectrum of HAT-P-32b we used ${ \mathcal T }$-REx, our fully Bayesian spectral retrieval code. As for other hot Jupiters, the results are consistent with the presence of water vapor (${\mathrm{log}{\rm{H}}}_{2}{\rm{O}}=-{3.45}_{-1.65}^{+1.83}$), clouds (top pressure between 5.16 and 1.73 bar). Spectroscopic data over a broader wavelength range are needed to de-correlate the mixing ratio of water vapor from clouds and identify other possible molecular species in the atmosphere of HAT-P-32b.

A hot Saturn on an eccentric orbit around the giant star EPIC228754001

A hot Saturn on an eccentric orbit around the giant star EPIC228754001

Authors:

Jones et al

Abstract:

Although the majority of radial velocity detected planets have been found orbiting solar-type stars, a fraction of them have been discovered around giant stars. These planetary systems have revealed different orbital properties when compared to solar-type stars companions. In particular, radial velocity surveys have shown that there is a lack of giant planets in close-in orbits around giant stars, in contrast to the known population of hot-Jupiters orbiting solar-type stars. The reason of this distinctive feature in the semimajor-axis distribution has been theorized to be the result of the stellar evolution and/or due to the effect of a different formation/evolution scenario for planets around intermediate-mass stars. However, in the past few years, a handful of transiting short-period planets (P≲ 10 days) have been found around giant stars, thanks to the high precision photometric data obtained initially by the Kepler mission, and later by its two-wheels extension K2. These new discoveries, have allowed us for the first time to study the orbital properties and physical parameters of these intriguing and elusive sub-stellar companions. In this paper we report on an independent discovery of a transiting planet in field 10 of the K2 mission, also reported recently by Grunblatt et al. (2017). The main orbital parameters of EPIC\,228754001\,b, obtained with all the available data for the system, are the following: P = 9.1708 ± 0.0025 d, e = 0.290 ± 0.049, Mp = 0.495 ± 0.007 Mjup \,and Rp = 1.089 ± 0.006 Rjup. This is the fifth known planet orbiting any giant star with a less than 0.1, and the most eccentric one among them, making EPIC\,228754001\,b a very interesting object.

Seeing double with K2: Testing re-inflation with two remarkably similar planets around red giant branch stars

Seeing double with K2: Testing re-inflation with two remarkably similar planets around red giant branch stars

Authors:


Grunblatt et al

Abstract:

Determining the mechanism that causes anomalously large radii of strongly irradiated exoplanets has remained a puzzle since before the radius of an exoplanet was first measured. Here, we report the discovery of a new inflated gas giant planet found with the NASA K2 Mission, EPIC2287.01, and a revised mass for the previously discovered inflated gas giant K2-97b. These planets orbit at moderate (~9 day) orbital distances around host stars which recently evolved into red giants. We constrain the irradiation history of these systems using a model constrained by parameters determined by asteroseismology and Keck/HIRES spectroscopy and radial velocity measurements. We find that both planets resided near the planet inflation irradiation threshold during their main sequence lifetimes. We also find that the current irradiation of these planets is typical for the population of planets with similar radii, but the main sequence irradiation of these planets would have been atypically small for the population of planets inflated to their size. Our precise constraints of the masses and radii of the stars and planets in this system allow us to constrain the planetary heating efficiencies of both systems to 0.03% +0.03%/-0.02%. These results are consistent with a planet re-inflation scenario, but suggest the efficiency of planet re-inflation is significantly lower than previously theorized. Finally, we discuss the similarity of both planetary systems (agreement within 10% of stellar masses and radii, and planet masses, radii, and orbital periods) and speculate that this may be due to selection bias in searching for planets around evolved stars.

Wednesday, October 11, 2017

Models of Warm Jupiter Atmospheres: Observable Signatures of Obliquity

Models of Warm Jupiter Atmospheres: Observable Signatures of Obliquity


Author:


Rauscher

Abstract:
We present three-dimensional atmospheric circulation models of a hypothetical "warm Jupiter" planet, for a range of possible obliquities from 0-90 degrees. We model a Jupiter-mass planet on a 10-day orbit around a Sun-like star, since this hypothetical planet sits at the boundary between planets for which we expect that tidal forces should have aligned their rotation axes with their orbital axes (i.e., ones with zero obliquity) and planets whose timescale for tidal alignment is longer than the typical age of an exoplanet system. In line with observational progress, which is pushing atmospheric characterization to planets on longer orbital periods, we calculate the observable signatures of obliquity for a transiting warm Jupiter: in orbital phase curves of thermal emission and in the hemispheric flux gradients that could be measured by eclipse mapping. For both of these predicted measurements, the signal that we would see depends strongly on our viewing geometry relative to the orientation of the planet's rotation axis, and we thoroughly identify the degeneracies that result. We compare these signals to the predicted sensitivities of current and future instruments and determine that the James Webb Space Telescope should be able to constrain the obliquities of nearby warm Jupiters to be small (if less than or equal to 10 degrees) or to directly measure them if significantly non-zero (greater than or equal to 30 degrees), using the technique of eclipse mapping. For a bright target and assuming photon-limited precision, this could be done with a single secondary eclipse observation.

Hot Start Giant Planets Form With Radiative Interiors

Hot Start Giant Planets Form With Radiative Interiors

Authors:


Berardo et al

Abstract:
In the hot-start core accretion formation model for gas giants, the interior of a planet is usually assumed to be fully convective. By calculating the detailed internal evolution of a planet assuming hot start outer boundary conditions, we show that such a planet will in fact form with a radially increasing internal entropy profile, so that its interior will be radiative instead of convective. For a hot outer boundary, there is a minimum value for the entropy of the internal adiabat Smin below which the accreting envelope does not match smoothly onto the interior, but instead deposits high entropy material onto the growing interior. One implication of this would be to at least temporarily halt the mixing of heavy elements within the planet, which are deposited by planetesimals accreted during formation. The compositional gradient this would impose could subsequently disrupt convection during post-accretion cooling, which would alter the observed cooling curve of the planet. However even with a homogeneous composition, for which convection develops as the planet cools, the difference in cooling timescale will change the inferred mass of directly-imaged gas giants.

Polarized scattered light from self-luminous exoplanets

Polarized scattered light from self-luminous exoplanets

Authors:


Stolker et al

Abstract:
Direct imaging has paved the way for atmospheric characterization of young and self-luminous gas giants. Scattering in a horizontally-inhomogeneous atmosphere causes the disk-integrated polarization of the thermal radiation to be linearly polarized, possibly detectable with the newest generation of high-contrast imaging instruments. We aim to investigate the effect of latitudinal and longitudinal cloud variations, circumplanetary disks, atmospheric oblateness, and cloud particle properties on the integrated degree and direction of polarization in the near-infrared. We have developed a three-dimensional Monte Carlo radiative transfer code (ARTES) for scattered light simulations in (exo)planetary atmospheres. The code is applicable to calculations of reflected light and thermal radiation in a spherical grid with a parameterized distribution of gas, clouds, hazes, and circumplanetary material. The disk-integrated degree of polarization of a horizontally-inhomogeneous atmosphere is maximal when the planet is flattened, the optical thickness of the equatorial clouds is large compared to the polar clouds, and the clouds are located at high altitude. For a flattened planet, the integrated polarization can both increase or decrease with respect to a spherical planet which depends on the horizontal distribution and optical thickness of the clouds. The direction of polarization can be either parallel or perpendicular to the projected direction of the rotation axis when clouds are zonally distributed. Rayleigh scattering by submicron-sized cloud particles will maximize the polarimetric signal whereas the integrated degree of polarization is significantly reduced with micron-sized cloud particles as a result of forward scattering. The presence of a cold or hot circumplanetary disk may also produce a detectable degree of polarization (≲1%) even with a uniform cloud layer in the atmosphere.

Tuesday, October 10, 2017

Analytical model of multi-planetary resonant chains and constraints on migration scenarios

Analytical model of multi-planetary resonant chains and constraints on migration scenarios


Author:


Delisle

Abstract:

Resonant chains are groups of planets for which each pair is in resonance, with an orbital period ratio locked at a rational value (2/1, 3/2, etc.). Such chains naturally form as a result of convergent migration of the planets in the proto-planetary disk. In this article, I present an analytical model of resonant chains of any number of planets. Using this model, I show that a system captured in a resonant chain can librate around several possible equilibrium configurations. The probability of capture around each equilibrium depends on how the chain formed, and especially on the order in which the planets have been captured in the chain. Therefore, for an observed resonant chain, knowing around which equilibrium the chain is librating allows for constraints to be put on the formation and migration scenario of the system. I apply this reasoning to the four planets orbiting Kepler-223 in a 3:4:6:8 resonant chain. I show that the system is observed around one of the six equilibria predicted by the analytical model. Using N-body integrations, I show that the most favorable scenario to reproduce the observed configuration is to first capture the two intermediate planets, then the outermost, and finally the innermost.

Accounting for planet-shaped planetary nebulae

Accounting for planet-shaped planetary nebulae

Authors:


Sabach et al

Abstract:

By following the evolution of several observed exoplanetary systems we show that by lowering the mass loss rate of single solar-like stars during their two giant branches, these stars will swallow their planets at the tip of their asymptotic giant branch (AGB) phase. This will most likely lead the stars to form elliptical planetary nebulae (PNe). Under the traditional mass loss rate these stars will not form PNe. Stars with a lower mass loss rate as we propose, about 15 per cent of the traditional mass loss rate of single stars, leave the AGB with much higher luminosities than what traditional evolution produces. Hence, the assumed lower mass loss rate might also account for the presence of bright PNe in old stellar populations. We present the evolution of four exoplanetary systems that represent stellar masses in the range of 0.9-1.3 Mo. The justification for this low mass loss rate is our assumption that the stellar samples that were used to derive the traditional average single-star mass loss rate were contaminated by stars that suffer binary interaction.

Unsupervised Method for Correlated Noise Removal for Multi-wavelength Exoplanet Transit Observations

Unsupervised Method for Correlated Noise Removal for Multi-wavelength Exoplanet Transit Observations

Authors:


Firoozabadi et al

Abstract:

Exoplanetary atmospheric observations require an exquisite precision in the measurement of the relative flux among wavelengths. In this paper, we aim to provide a new adaptive method to treat light curves before fitting transit parameters in order to minimize systematic effects that affect, for instance, ground-based observations of exo-atmospheres. We propose a neural-network-based method that uses a reference built from the data itself with parameters that are chosen in an unsupervised fashion. To improve the performance of proposed method, K-means clustering and Silhouette criteria are used for identifying similar wavelengths in each cluster. We also constrain under which circumstances our method improves the measurement of planetary-to-stellar radius ratio without producing significant systematic offset. We tested our method in high quality data from WASP-19b and low quality data from GJ-1214. We succeed in providing smaller error bars for the former when using JKTEBOP, but GJ-1214 light curve was beyond the capabilities of this method to improve as it was expected from our validation tests.

Monday, October 9, 2017

Terrestrial Exoplanets Without Plate Tectonics can be Habitable

The habitability of a stagnant-lid Earth

Authors:


Tosi et al

Abstract:
Plate tectonics is a fundamental component for the habitability of the Earth. Yet whether it is a recurrent feature of terrestrial bodies orbiting other stars or unique to the Earth is unknown. The stagnant lid may rather be the most common tectonic expression on such bodies. To understand whether a stagnant-lid planet can be habitable, i.e. host liquid water at its surface, we model the thermal evolution of the mantle, volcanic outgassing of H2O and CO2, and resulting climate of an Earth-like planet lacking plate tectonics. We used a 1D model of parameterized convection to simulate the evolution of melt generation and the build-up of an atmosphere of H2O and CO2 over 4.5 Gyr. We then employed a 1D radiative-convective atmosphere model to calculate the global mean atmospheric temperature and the boundaries of the habitable zone (HZ). The evolution of the interior is characterized by the initial production of a large amount of partial melt accompanied by a rapid outgassing of H2O and CO2. At 1 au, the obtained temperatures generally allow for liquid water on the surface nearly over the entire evolution. While the outer edge of the HZ is mostly influenced by the amount of outgassed CO2, the inner edge presents a more complex behaviour that is dependent on the partial pressures of both gases. At 1 au, the stagnant-lid planet considered would be regarded as habitable. The width of the HZ at the end of the evolution, albeit influenced by the amount of outgassed CO2, can vary in a non-monotonic way depending on the extent of the outgassed H2O reservoir. Our results suggest that stagnant-lid planets can be habitable over geological timescales and that joint modelling of interior evolution, volcanic outgassing, and accompanying climate is necessary to robustly characterize planetary habitability.

Transit Timing and Duration Variations for the Discovery and Characterization of Exoplanets

Transit Timing and Duration Variations for the Discovery and Characterization of Exoplanets

Authors:


Agol et al

Abstract:


Transiting exoplanets in multi-planet systems have non-Keplerian orbits which can cause the times and durations of transits to vary. The theory and observations of transit timing variations (TTV) and transit duration variations (TDV) are reviewed. A watershed since the last review is that the Kepler spacecraft has detected several hundred perturbed planets. In a few cases, these data have been used to discover additional planets, which has historical resonance with how Neptune was discovered in our own Solar System. However, the more impactful aspect of TTV and TDV studies has been characterization of planetary systems in which multiple planets transit. After addressing the equations of motion and parameter scalings, the main dynamical mechanisms for TTV and TDV are described, with citations to the observational literature for real examples. We describe parameter constraints, particularly how the mass/eccentricity degeneracy comes about and is overcome by the high-frequency component of the signal. On the observational side, derivation of timing precision and introduction to the timing diagram are given. Science results are reviewed, with an emphasis on mass measurements of transiting sub-Neptunes and super-Earths, which allows access to the mass-radius diagram and hence inference of bulk compositions.

Only 1/3 of Stars may Host Terrestrial Worlds Capable of Sustained Plate Tectonics

Stellar Chemical Clues As To The Rarity of Exoplanetary Tectonics

Authors:


Unterborn et al

Abstract:
Earth's tectonic processes regulate the formation of continental crust, control its unique deep water and carbon cycles, and are vital to its surface habitability. A major driver of steady-state plate tectonics on Earth is the sinking of the cold subducting plate into the underlying mantle. This sinking is the result of the combined effects of the thermal contraction of the lithosphere and of metamorphic transitions within the basaltic oceanic crust and lithospheric mantle. The latter of these effects is dependent on the bulk composition of the planet, e.g., the major, terrestrial planet-building elements Mg, Si, Fe, Ca, Al, and Na, which vary in abundance across the Galaxy. We present thermodynamic phase-equilibria calculations of planetary differentiation to calculate both melt composition and mantle mineralogy, and show that a planet's refractory and moderately-volatile elemental abundances control a terrestrial planet's likelihood to produce mantle-derived, melt-extracted crusts that sink. Those planets forming with a higher concentration of Si and Na abundances are less likely to undergo sustained tectonics compared to the Earth. We find only 1/3 of the range of stellar compositions observed in the Galaxy is likely to host planets able to sustain density-driven tectonics compared to the Sun/Earth. Systems outside of this compositional range are less likely to produce planets able to tectonically regulate their climate and may be inhospitable to life as we know it.

Sunday, October 8, 2017

NanoRocks: Design and Performance of an Experiment Studying Planet Formation on the International Space Station

NanoRocks: Design and Performance of an Experiment Studying Planet Formation on the International Space Station

Authors:


Brissett et al

Abstract:

In an effort to better understand the early stages of planet formation, we have developed a 1.5U payload that flew on the International Space Station (ISS) in the NanoRacks NanoLab facility between September 2014 and March 2016. This payload, named NanoRocks, ran a particle collision experiment under long-term microgravity conditions. The objectives of the experiment were (a) to observe collisions between mm-sized particles at relative velocities of less than 1~cm/s, and (b) to study the formation and disruption of particle clusters for different particle types and collision velocities. Four types of particles were used: mm-sized acrylic, glass, and copper beads, and 0.75 mm-sized JSC-1 lunar regolith simulant grains. The particles were placed in sample cells carved out of an aluminum tray. This tray was attached to one side of the payload casing with three springs. Every 60~s, the tray was agitated and the resulting collisions between the particles in the sample cells were recorded by the experiment camera.

During the 18 months the payload stayed on ISS, we obtained 158 videos, thus recording a great number of collisions. The average particle velocities in the sample cells after each shaking event were around 1 cm/s. After shaking stopped, the inter-particle collisions damped the particle kinetic energy in less than 20~s, reducing the average particle velocity to below 1 mm/s, and eventually slowing them to below our detection threshold. As the particle velocity decreased, we observed the transition from bouncing to sticking collisions. We recorded the formation of particle clusters at the end of each experiment run. This paper describes the design and performance of the NanoRocks ISS payload.

Determining Empirical Stellar Masses and Radii from Transits and Gaia Parallaxes as Illustrated by Spitzer Observations of KELT-11b

Determining Empirical Stellar Masses and Radii from Transits and Gaia Parallaxes as Illustrated by Spitzer Observations of KELT-11b 

Authors:


Beatty et al

Abstract:
Using the Spitzer Space Telescope, we observed a transit at 3.6 μm of KELT-11b. We also observed three partial planetary transits from the ground. We simultaneously fit these observations, ground-based photometry from Pepper et al., radial velocity data from Pepper et al., and a spectral energy distribution (SED) model using catalog magnitudes and the Hipparcos parallax to the system. The only significant difference between our results and those of Pepper et al. is that we find the orbital period to be shorter by 37 s, 4.73610 ± 0.00003 versus 4.73653 ± 0.00006 days, and we measure a transit center time of ${\mathrm{BJD}}_{\mathrm{TDB}}$ 2457483.4310 ± 0.0007, which is 42 minutes earlier than predicted. Using our new photometry, we precisely measure the density of the star KELT-11 to 4%. By combining the parallax and catalog magnitudes of the system, we are able to measure the radius of KELT-11b essentially empirically. Coupled with the stellar density, this gives a parallactic mass and radius of 1.8 ${M}_{\odot }$ and 2.9 ${R}_{\odot }$, which are each approximately 1σ higher than the adopted model-estimated mass and radius. If we conduct the same fit using the expected parallax uncertainty from the final Gaia data release, this difference increases to 4σ. The differences between the model and parallactic masses and radii for KELT-11 demonstrate the role that precise Gaia parallaxes, coupled with simultaneous photometric, radial velocity, and SED fitting, can play in determining stellar and planetary parameters. With high-precision photometry of transiting planets and high-precision Gaia parallaxes, the parallactic mass and radius uncertainties of stars become 1% and 3%, respectively. TESS is expected to discover 60–80 systems where these measurements will be possible. These parallactic mass and radius measurements have uncertainties small enough that they may provide observational input into the stellar models themselves.

Inclination Evolution of Protoplanetary Disks Around Eccentric Binaries

Inclination Evolution of Protoplanetary Disks Around Eccentric Binaries

Authors:


Zanazzi et al

Abstract:
It is usually thought that viscous torque works to align a circumbinary disk with the binary's orbital plane. However, recent numerical simulations suggest that the disk may evolve to a configuration perpendicular to the binary orbit ("polar alignment") if the binary is eccentric and the initial disk-binary inclination is sufficiently large. We carry out a theoretical study on the long-term evolution of inclined disks around eccentric binaries, calculating the disk warp profile and dissipative torque acting on the disk. For disks with aspect ratio H/r larger than the viscosity parameter α, bending wave propagation effectively makes the disk precess as a quasi-rigid body, while viscosity acts on the disk warp and twist to drive secular evolution of the disk-binary inclination. We derive a simple analytic criterion (in terms of the binary eccentricity and initial disk orientation) for the disk to evolve toward polar alignment with the eccentric binary. For typical protoplanetary disk parameters, the timescale of the inclination evolution is shorter than the disk lifetime, suggesting that highly-inclined disks and planets may exist orbiting eccentric binaries.

Saturday, October 7, 2017

The Disk Physical Conditions of 48 Persei Constrained by Contemporaneous Hα Spectroscopy and Interferometry

The Disk Physical Conditions of 48 Persei Constrained by Contemporaneous Hα Spectroscopy and Interferometry

Authors:


Jones et al

Abstract:
We utilize a multi-step modeling process to produce synthetic interferometric and spectroscopic observables, which are then compared to their observed counterparts. Our extensive set of interferometric observations of the Be star 48 Per, totaling 291 data points, were obtained at the Navy Precision Optical Interferometer from 2006 November 07 to 23. Our models were further constrained by comparison with contemporaneous Hα line spectroscopy obtained at the John S. Hall Telescope at the Lowell Observatory on 2006 November 1. Theoretical spectral energy distributions, SEDs, for 48 Per were confirmed by comparison with observations over a wavelength regime of 0.4–60 μm from Touhami et al. and Vieira et al. Our best-fitting combined model from Hα spectroscopy, Hα interferometry, and SED fitting has a power-law density fall off, n, of 2.3 and an initial density at the stellar surface of ${\rho }_{0}=1.0\times {10}^{-11}$ ${\rm{g}}\,{\mathrm{cm}}^{-3}$ with an inclination constrained by Hα spectroscopy and interferometry of ${45}^{^\circ }\pm 5^\circ $. The position angle for the system, measured east from north, is 114° ± 18°. Our best-fit model shows that the disk emission originates in a moderately large disk with a radius of 25 R *, which is consistent with a disk mass of approximately 5 × 1024 g or 3 × 10−10 M *. Finally, we compare our results with previous studies of 48 Per by Quirrenbach et al. and find agreement, whereas our disk size does not agree with Delaa et al., based on a much smaller visibility set.

Radio Emission from the Exoplanetary System ε Eridani

Radio Emission from the Exoplanetary System ε Eridani

Authors:


Bastian et al

Abstract:

As part of a wider search for radio emission from nearby systems known or suspected to contain extrasolar planets ϵ Eridani was observed by the Jansky Very Large Array (VLA) in the 2-4 GHz and 4-8 GHz frequency bands. In addition, as part of a separate survey of thermal emission from solar-like stars, ϵ Eri was observed in the 8-12 GHz and the 12-18 GHz bands of the VLA. Quasi-steady continuum radio emission from ϵ Eri was detected in the three high-frequency bands at levels ranging from approximately 55-83 μJy. The emission in the 2-4 GHz emission is shown to be the result of a radio flare of a few minutes in duration that is up to 50% circularly polarized -- no radio emission is detected following the flare. Both the K2V star and a possible Jupiter-like planet are considered as the source of the radio emission. While a planetary origin for the radio emission cannot be definitively ruled out, given that ϵ Eri is known to be a moderately active "young Sun", we conclude that the observed radio emission likely originates from the star.

Exoplanets as probes of the winds of host stars: the case of the M dwarf GJ 436

Exoplanets as probes of the winds of host stars: the case of the M dwarf GJ 436

Authors:


Vidotto et al

Abstract:
Winds of cool dwarfs are difficult to observe, with only a few M dwarfs presenting observationally-derived mass-loss rates (Mdot), which span several orders of magnitude. Close-in exoplanets are conveniently positioned in the inner regions of stellar winds and can, thus, be used to probe the otherwise-unobservable local properties of their host-stars' winds. Here, we use local stellar wind characteristics observationally-derived in the studies of atmospheric evaporation of the warm-neptune GJ436 b to derive the global characteristics of the wind of its M-dwarf host. Using an isothermal wind model, we constrain the stellar wind temperature to be in the range [0.36,0.43] MK, with Mdot=[0.5,2.5] x 10^{-15} Msyn/yr. By computing the pressure balance between the stellar wind and the interstellar medium, we derive the size of the astrophere of GJ436 to be around 25 au, significantly more compact than the heliosphere. We demonstrate in this paper that transmission spectroscopy, coupled to planetary atmospheric evaporation and stellar wind models, can be a useful tool for constraining the large-scale wind structure of planet-hosting stars. Extending our approach to future planetary systems discoveries will open new perspectives for the combined characterisation of planetary exospheres and winds of cool dwarf stars.

Friday, October 6, 2017

ALMA Observations of the Young Substellar Binary System 2M1207

ALMA Observations of the Young Substellar Binary System 2M1207

Authors:


Ricci et al

Abstract:

We present ALMA observations of the 2M1207 system, a young binary made of a brown dwarf with a planetary-mass companion at a projected separation of about 40 au. We detect emission from dust continuum at 0.89 mm and from the $J=3-2$ rotational transition of CO from a very compact disk around the young brown dwarf. The small radius found for this brown dwarf disk may be due to truncation from the tidal interaction with the planetary-mass companion. Under the assumption of optically thin dust emission, we estimate a dust mass of 0.1 M ⊕ for the 2M1207A disk and a 3σ upper limit of ~1 M Moon for dust surrounding 2M1207b, which is the tightest upper limit obtained so far for the mass of dust particles surrounding a young planetary-mass companion. We discuss the impact of this and other non-detections of young planetary-mass companions for models of planet formation that predict circumplanetary material to surround these objects.

The GAPS Programme with HARPS-N at TNG XV. A substellar companion around a K giant star identified with quasi-simultaneous HARPS-N and GIANO measurements

The GAPS Programme with HARPS-N at TNG XV. A substellar companion around a K giant star identified with quasi-simultaneous HARPS-N and GIANO measurements

Authors:


González-Álvarez et al

Abstract:

Context.

Identification of planetary companions of giant stars is made difficult because of the astrophysical noise, that may produce radial velocity (RV) variations similar to those induced by a companion. On the other hand any stellar signal is wavelength dependent, while signals due to a companion are achromatic.

Aims.

Our goal is to determine the origin of the Doppler periodic variations observed in the thick disk K giant star TYC 4282-605-1 by HARPS-N at the Telescopio Nazionale Galileo (TNG) and verify if they can be due to the presence of a substellar companion.

Methods.

Several methods have been used to exclude the stellar origin of the observed signal including detailed analysis of activity indicators and bisector and the analysis of the photometric light curve. Finally we have conducted an observational campaign to monitor the near infrared (NIR) RV with GIANO at the TNG in order to verify whether the NIR amplitude variations are comparable with those observed in the visible.

Results.

Both optical and NIR RVs show consistent variations with a period at 101 days and similar amplitude, pointing to the presence of a companion orbiting the target. The main orbital properties obtained for our giant star with a derived mass of M=0.97+-0.03M_sun are M_Psini=10.78+-0.12MJ;P=101.54+-0.05days;e=0.28+-0.01 and a=0.422+-0.009AU. The chemical analysis shows a significant enrichment in the abundance of Nai, Mgi, Ali and S i while the rest of analyzed elements are consistent with the solar value demonstrating that the chemical composition corresponds with an old K giant (age = 10.1 Gyr) belonging to local thick disk.

Conclusions.

We conclude that the substellar companion hypothesis for this K giant is the best explanation for the observed periodic RV variation. This study also shows the high potential of multi-wavelength RV observations for the validation of planet candidates.

Two white dwarfs in ultrashort binaries with detached, eclipsing, likely substellar companions detected by K2

Two white dwarfs in ultrashort binaries with detached, eclipsing, likely substellar companions detected by K2

Authors:


Parsons et al

Abstract:
Using data from the extended Kepler mission in K2 Campaign 10 we identify two eclipsing binaries containing white dwarfs with cool companions that have extremely short orbital periods of only 71.2 min (SDSS J1205−0242, a.k.a. EPIC 201283111) and 72.5 min (SDSS J1231+0041, a.k.a. EPIC 248368963). Despite their short periods, both systems are detached with small, low-mass companions, in one case a brown dwarf, and the other case either a brown dwarf or a low-mass star. We present follow-up photometry and spectroscopy of both binaries, as well as phase-resolved spectroscopy of the brighter system, and use these data to place preliminary estimates on the physical and binary parameters. SDSS J1205−0242 is composed of a 0.39 ± 0.02M⊙ helium-core white dwarf which is totally eclipsed by a 0.049 ± 0.006M⊙ (51 ± 6MJ) brown dwarf companion, while SDSS J1231+0041 is composed of a 0.56 ± 0.07M⊙ white dwarf which is partially eclipsed by a companion of mass ≲ 0.095M⊙. In the case of SDSS J1205−0242 we look at the combined constraints from common-envelope evolution and brown dwarf models; the system is compatible with similar constraints from other post common-envelope binaries given the current parameter uncertainties, but has potential for future refinement.

Thursday, October 5, 2017

Hot Jupiter WASP-12b is Black as Coal and Egg Shaped?


An exoplanet twice the size of Jupiter is hot, egg-shaped and coal-black.

Wasp-12b is a gas giant orbiting around a Sun-like star some 1,400 light-years away. It makes a complete orbit around its sun in just 24 hours because it lies so close to its star, and the proximity pushes the temperature to around 4,700 degrees Fahrenheit. It’s so hot that molecules there are broken down into atomic hydrogen and helium, and the extreme conditions give it an albedo of just .064, making the planet’s atmosphere even darker than asphalt.

Structure and Evolution of Internally Heated Hot Jupiters

Structure and Evolution of Internally Heated Hot Jupiters

Authors:


Komacek et al

Abstract:
Hot Jupiters receive strong stellar irradiation, producing equilibrium temperatures of 1000−2500 Kelvin. Incoming irradiation directly heats just their thin outer layer, down to pressures of ∼0.1 bars. In standard irradiated evolution models of hot Jupiters, predicted transit radii are too small. Previous studies have shown that deeper heating -- at a small fraction of the heating rate from irradiation -- can explain observed radii. Here we present a suite of evolution models for HD 209458b where we systematically vary both the depth and intensity of internal heating, without specifying the uncertain heating mechanism(s). Our models start with a hot, high entropy planet whose radius decreases as the convective interior cools. The applied heating suppresses this cooling. We find that very shallow heating -- at pressures of 1−10 bars -- does not significantly suppress cooling, unless the total heating rate is ≳10% of the incident stellar power. Deeper heating, at 100 bars, requires heating at only 1% of the stellar irradiation to explain the observed transit radius of 1.4RJup after 5 Gyr of cooling. In general, more intense and deeper heating results in larger hot Jupiter radii. Surprisingly, we find that heat deposited at 104 bars -- which is exterior to ≈99% of the planet's mass -- suppresses planetary cooling as effectively as heating at the center. In summary, we find that relatively shallow heating is required to explain the radii of most hot Jupiters, provided that this heat is applied early and persists throughout their evolution.

Muti-band characterization of the hot Jupiters: WASP-5b, WASP-44b, and WASP-46b

Muti-band characterization of the hot Jupiters: WASP-5b, WASP-44b, and WASP-46b

Authors:


Moyano et al

Abstract:

We have carried out a campaign to characterize the hot Jupiters WASP-5b, WASP-44b, and WASP-46b using multi-band photometry collected at the Observatório do Pico Dos Dias in Brazil. We have determined the planetary physical properties and new transit ephemerides for these systems. The new orbital parameters and physical properties of WASP-5b and WASP-44b are consistent with previous estimates. In the case of WASP-46b, there is some quota of disagreement between previous results. We provide a new determination of the radius of this planet and help clarify the previous differences. We also studied the transit time variations including our new measurements. No clear variation from a linear trend was found for the systems WASP-5b and WASP-44b. In the case of WASP-46b, we found evidence of deviations indicating the presence of a companion but statistical analysis of the existing times points to a signal due to the sampling rather than a new planet. Finally, we studied the fractional radius variation as a function of wavelength for these systems. The broadband spectrums of WASP-5b and WASP-44b are mostly flat. In the case of WASP-46b we found a trend, but further measurements are necessary to confirm this finding.

Kelt-9b: A giant planet undergoing extreme ultraviolet irradiation by its hot massive-star host

A giant planet undergoing extreme ultraviolet irradiation by its hot massive-star host 
Authors:

Gaudi et al

Abstract:

The amount of ultraviolet irradiation and ablation experienced by a planet depends strongly on the temperature of its host star. Of the thousands of extra-solar planets now known, only four giant planets have been found that transit hot, A-type stars (temperatures of 7300-10,000K), and none are known to transit even hotter B-type stars. WASP-33 is an A-type star with a temperature of ~7430K, which hosts the hottest known transiting planet; the planet is itself as hot as a red dwarf star of type M. The planet displays a large heat differential between its day-side and night-side, and is highly inflated, traits that have been linked to high insolation. However, even at the temperature of WASP-33b's day-side, its atmosphere likely resembles the molecule-dominated atmospheres of other planets, and at the level of ultraviolet irradiation it experiences, its atmosphere is unlikely to be significantly ablated over the lifetime of its star. Here we report observations of the bright star HD 195689, which reveal a close-in (orbital period ~1.48 days) transiting giant planet, KELT-9b. At ~10,170K, the host star is at the dividing line between stars of type A and B, and we measure the KELT-9b's day-side temperature to be ~4600K. This is as hot as stars of stellar type K4. The molecules in K stars are entirely dissociated, and thus the primary sources of opacity in the day-side atmosphere of KELT-9b are likely atomic metals. Furthermore, KELT-9b receives ~700 times more extreme ultraviolet radiation (wavelengths shorter than 91.2 nanometers) than WASP-33b, leading to a predicted range of mass-loss rates that could leave the planet largely stripped of its envelope during the main-sequence lifetime of the host star.

Wednesday, October 4, 2017

30 Meter Telescope Gets Go Ahead...Again

Hawaii’s board of land and natural resources granted a fresh construction permit to the Thirty Meter Telescope (TMT) on 28 September, reviving the fortunes of the US$1.4-billion observatory — at least temporarily.

The permit moves the international project closer towards restarting construction near the summit of the Hawaiian mountain of Mauna Kea. Some Native Hawaiians oppose the TMT, saying that its construction would further violate a sacred mountain that is already home to multiple telescopes.

The board’s decision effectively puts the TMT project back where it was before protestors halted the telescope’s construction in April 2015, just days after it had begun, by blocking the road up Mauna Kea. That December, following months of challenges, Hawaii’s supreme court invalidated the telescope’s first construction permit. The court ruled that the state land board had not followed appropriate procedures because it had approved the first permit, in 2011, before it held a set of public hearings on the case.

How Expanded Ionospheres of Hot Jupiters Can Prevent Escape of Radio Emission Generated by the Cyclotron Maser Instability

How Expanded Ionospheres of Hot Jupiters Can Prevent Escape of Radio Emission Generated by the Cyclotron Maser Instability

Authors:


Weber et al

Abstract:
We present a study of plasma conditions in the atmospheres of the Hot Jupiters HD 209458b and HD 189733b and for an HD 209458b-like planet at orbit locations between 0.2-1 AU around a Sun-like star. We discuss how these conditions influence the radio emission we expect from their magnetospheres. We find that the environmental conditions are such that the cyclotron maser instability (CMI), the process responsible for the generation of radio waves at magnetic planets in the solar system, most likely will not operate at Hot Jupiters. Hydrodynamically expanding atmospheres possess extended ionospheres whose plasma densities within the magnetosphere are so large that the plasma frequency is much higher than the cyclotron frequency, which contradicts the condition for the production of radio emission and prevents the escape of radio waves from close-in exoplanets at distances less than 0.05 AU from a Sun-like host star. The upper atmosphere structure of gas giants around stars similar to the Sun changes between 0.2 and 0.5 AU from the hydrodynamic to a hydrostatic regime and this results in conditions similar to solar system planets with a region of depleted plasma between the exobase and the magnetopause where the plasma frequency can be lower than the cyclotron frequency. In such an environment, a beam of highly energetic electrons accelerated along the field lines towards the planet can produce radio emission. However, even if the CMI could operate the extended ionospheres of Hot Jupiters are too dense to let the radio emission escape from the planets.

Supervised Learning Detection of Sixty Non-Transiting Hot Jupiter Candidates

Supervised Learning Detection of Sixty Non-Transiting Hot Jupiter Candidates

Authors:


Millholland et al

Abstract:
The optical, full-phase photometric variations of a short-period planet provide a unique view of the planet's atmospheric composition and dynamics. The number of planets with optical phase curve detections, however, is currently too small to study them as an aggregate population, motivating an extension of the search to non-transiting planets. Here we present an algorithm for the detection of non-transiting, short-period giant planets in the Kepler field. The procedure uses the phase curves themselves as evidence for the planets' existence. We employ a supervised learning algorithm to recognize the salient time-dependent properties of synthetic phase curves; we then search for detections of signals that match these properties. After demonstrating the algorithm's capabilities, we classify 142,630 FGK Kepler stars without confirmed planets or KOIs and, for each one, assign a probability of a phase curve of a non-transiting planet being present. We identify 60 high-probability non-transiting hot Jupiter candidates. We also derive constraints on the candidates' albedos and offsets of the phase curve maxima. These targets are strong candidates for follow-up radial velocity confirmation and characterization. Once confirmed, the atmospheric information content in the phase curves may be studied in yet greater detail.

LAMOST Reveals Neptune-size Cousins of hot Jupiters, preferentially in "(metal-)rich" and "one-child" Kepler families


Authors:

Dong et al

Abstract:

WWe discover a new population of short-period, Neptune-size planets sharing key similarities with hot Jupiters: both populations are preferentially hosted by metal-rich stars, and both are preferentially found in Kepler systems with single transiting planets. We use accurate LAMOST DR4 stellar parameters for main-sequence stars to study the distributions of short-period (1d less than P less than 10d) Kepler planets as a function of host star metallicity. The radius distribution of planets around metal-rich stars is more "puffed up" as compared to that around metal-poor hosts. In two period-radius regimes, planets preferentially reside around metal-rich stars, while there are scantily any planets around metal-poor stars. One is the well-known hot Jupiters, and the other is a new population of Neptune-size planets (2 R_Earth less than R_p less than 6 R_Earth), dubbed as "Hoptunes". Also like hot Jupiters, Hoptunes occur more frequently in systems with single transiting planets than in multiple transiting planetary systems. About 1% of solar-type stars host "Hoptunes", and the frequencies of Hoptunes and hot Jupiters increase with consistent trends as a function of [Fe/H]. In the planet radius distribution, hot Jupiters and Hoptunes are separated by a "valley" at approximately Saturn size (in the range of 6 R_Earth less than approximately R_p less than approximately 10 R_Earth), and this "hot-Saturn valley" represents an approximately order-of-magnitude decrease in planet frequency compared to hot Jupiters and Hoptunes. The empirical "kinship" between Hoptunes and hot Jupiters suggests likely common processes (migration and/or formation) responsible for their existence.

Tuesday, October 3, 2017

An Investigation into Exoplanet Transits and Uncertainties

An Investigation into Exoplanet Transits and Uncertainties


Authors:


Ji et al

Abstract:
A simple transit model is described along with tests of this model against published results for 4 exoplanet systems (Kepler-1, 2, 8, and 77). Data from the Kepler mission are used. The Markov Chain Monte Carlo (MCMC) method is applied to obtain realistic error estimates. Optimization of limb darkening coefficients is subject to data quality. It is more likely for MCMC to derive an empirical limb darkening coefficient for light curves with S/N (signal to noise) above 15. Finally, the model is applied to Kepler data for 4 Kepler candidate systems (KOI 760.01, 767.01, 802.01, and 824.01) with previously unpublished results. Error estimates for these systems are obtained via the MCMC method.

The California-Kepler Survey V. Peas in a Pod: Planets in a Kepler Multi-planet System are Similar in Size and Regularly Spaced

The California-Kepler Survey V. Peas in a Pod: Planets in a Kepler Multi-planet System are Similar in Size and Regularly Spaced

Authors:


Weiss et al

Abstract:
We have established precise planet radii, semi-major axes, incident stellar fluxes, and stellar masses for 909 planets in 355 multi-planet systems discovered by Kepler. We find that planets within a single multi-planet system tend to be closer in size than planets drawn randomly from the collection of multi-planet systems. This is true even when considering systems with similar host stars; we find, at most, a weak correlation between planet radius and stellar mass. Evidently, it is not the stellar mass but some other property or process that enforces the similarity of planet sizes. When adjacent planets in a multi-planet system are not similar in size, the inner planet is smaller in 65±6\% of cases. The tendency for the inner planet to be smaller is especially pronounced when the inner planet has a short period (≲10 days) or equivalently, high radiation flux (≳150 times the Earth's insolation). This could be the result of photoevaporation. We also find that adjacent planets within a given system tend to be spaced in a regular geometric progression, with a typical semi-major axis ratio of 1.5. Using empirical mass-radius relationships, we estimate the mutual Hill separations of planet pairs. We find that 93\% of the planet pairs are at least 10 mutual Hill radii apart, and that a spacing of 10-30 mutual Hill radii is most common

Mean Motion Resonances at High Eccentricities: The 2:1 and the 3:2 Interior Resonances

Mean Motion Resonances at High Eccentricities: The 2:1 and the 3:2 Interior Resonances

Authors:


Wang et al

Abstract:
Mean motion resonances (MMRs) play an important role in the formation and evolution of planetary systems and have significantly influenced the orbital properties and distribution of planets and minor planets in the solar system and in exoplanetary systems. Most previous theoretical analyses have focused on the low- to moderate-eccentricity regime, but with new discoveries of high-eccentricity resonant minor planets and even exoplanets, there is increasing motivation to examine MMRs in the high-eccentricity regime. Here we report on a study of the high-eccentricity regime of MMRs in the circular planar restricted three-body problem. Numerical analyses of the 2:1 and the 3:2 interior resonances are carried out for a wide range of planet-to-star mass ratio μ, and for a wide range of eccentricity of the test particle. The surface-of-section technique is used to study the phase space structure near resonances. We find that new stable libration zones appear at higher eccentricity at libration centers that are shifted from those at low eccentricities. We provide physically intuitive explanations for these transitions in phase space, and we present novel results on the mass and eccentricity dependence of the resonance widths. Our results show that MMRs have sizable libration zones at high eccentricities, comparable to those at lower eccentricities.

Monday, October 2, 2017

NASA's Next Space Telescope (JWST) is Delayed

NASA announced Sept. 28 that the launch of the James Webb Space Telescope mission, which had been planned for next fall, will now be delayed until the spring of 2019.

In a statement posted on the agency’s website, NASA said that an assessment of overall work needed to complete integration and testing of the $8 billion spacecraft led to the decision to postpone the launch by about half a year.

“The change in launch timing is not indicative of hardware or technical performance concerns,” Thomas Zurbuchen, NASA associate administrator for science, said in the statement. “Rather, the integration of the various spacecraft elements is taking longer than expected.”

The release noted that testing of the telescope and its instruments “continues to go well and on schedule” in a thermal vacuum chamber at the Johnson Space Center but that the spacecraft bus and sunshield, being assembled at a Northrop Grumman facility in California, were suffering delays.

Do the Trappist-1 Worlds Have Water?

An international team of astronomers used the NASA/ESA Hubble Space Telescope to estimate whether there might be water on the seven earth-sized planets orbiting the nearby dwarf star TRAPPIST-1. The results suggest that the outer planets of the system might still harbour substantial amounts of water. This includes the three planets within the habitable zone of the star, lending further weight to the possibility that they may indeed be habitable.

 Link.

Can we Detect the Auroras of Proxima B?

The Detectability of Radio Auroral Emission from Proxima B

Authors:


Burkhart et al

Abstract:

Magnetically active stars possess stellar winds whose interaction with planetary magnetic fields produces radio auroral emission. We examine the detectability of radio auroral emission from Proxima b, the closest known exosolar planet orbiting our nearest neighboring star, Proxima Centauri. Using the Radiometric Bode's Law, we estimate the radio flux produced by the interaction of Proxima Centauri's stellar wind and Proxima b's magnetosphere for different planetary magnetic field strengths. For plausible planetary masses, Proxima b produces 6-83 mJy of auroral radio flux at frequencies of 0.3-0.8 MHz for planetary magnetic field strengths of 1-3 B⊕. According to recent MHD models that vary the orbital parameters of the system, this emission is expected to be highly variable. This variability is due to large fluctuations in the size of Proxima b's magnetosphere as it crosses the equatorial streamer regions of the dense stellar wind and high dynamic pressure. Using the MHD model of Garraffo et al. 2016 for the variation of the magnetosphere radius during the orbit, we estimate that the observed radio flux can vary nearly by an order of magnitude over the 11.2 day period of Proxima b. The detailed amplitude variation depends on the stellar wind, orbital, and planetary magnetic field parameters. We discuss observing strategies for proposed future space-based observatories to reach frequencies below the ionospheric cut off (∼10 MHz) as would be required to detect the signal we investigate.

All Eyes on Proxima b

Inner Workings: All eyes on Proxima Centauri b

Author:


Mann

Extract:
An Earth-sized planet next door: that was the startling announcement last August. Astronomers had found an exoplanet orbiting the sun’s closest stellar neighbor, a cool red dwarf star called Proxima Centauri (1). Even better, the nearby world orbited within its parent star’s habitable zone, meaning liquid water could exist on the planet’s surface, which raised the prospects for its harboring life. 
But aside from its mass—at least 1.3 times that of Earth’s—and the length of its year—a zippy 11 days—little was known about the new exoplanet, called Proxima Centauri b. Almost immediately, a rush of papers appeared, presenting ways to estimate Proxima b’s temperature, atmospheric composition and thickness, and even whether a worldwide ocean spans its surface. The proposed methods are extraordinarily tricky, pushing the boundary of what’s possible. 
“This planet is so good, so optimum, and so close to us, that using state-of-the-art technology we [can] demonstrate that it’s not science fiction to do these observations,” says astronomer Christophe Lovis of the University of Geneva in Switzerland. With two recently discovered systems garnering ample headlines—the potentially habitable planets near the star TRAPPIST-1 and a super-Earth orbiting the red dwarf LHS 1140—Proxima b offers a test case for how astronomers might take the first steps toward closer inspection of planets that seem to be prime candidates for life.

Sunday, October 1, 2017

Magnetism and activity of planet hosting stars

Magnetism and activity of planet hosting stars


Authors:


Wright et al

Abstract:
The magnetic activity levels of planet host stars may differ from that of stars not known to host planets in several ways. Hot Jupiters may induce activity in their hosts through magnetic interactions, or through tidal interactions by affecting their host's rotation or convection. Measurements of photospheric, chromospheric, or coronal activity might then be abnormally high or low compared to control stars that do not host hot Jupiters, or might be modulated at the planet's orbital period. Such detections are complicated by the small amplitude of the expected signal, by the fact that the signals may be transient, and by the difficulty of constructing control samples due to exoplanet detection biases and the uncertainty of field star ages. We review these issues, and discuss avenues for future progress in the field.

Recurring sets of recurring starspot occultations on exoplanet-host Qatar-2

Recurring sets of recurring starspot occultations on exoplanet-host Qatar-2


Authors:


Močnik et al

Abstract:

We announce the detection of recurring sets of recurring starspot occultation events in the short-cadence K2 lightcurve of Qatar-2, a K dwarf star transited every 1.34 d by a hot Jupiter. In total we detect 34 individual starspot occultation events, caused by five different starspots, occulted in up to five consecutive transits or after a full stellar rotation. The longest recurring set of recurring starspot occultations spans over three stellar rotations, setting a lower limit for the longest starspot lifetime of 58 d. Starspot analysis provided a robust stellar rotational period measurement of 18.0 ± 0.2 d and indicates that the system is aligned, having a sky-projected obliquity of 0 ± 8°. A pronounced rotational modulation in the lightcurve has a period of 18.2 ± 1.6 d, in agreement with the rotational period derived from the starspot occultations. We tentatively detect an ellipsoidal modulation in the phase-curve, with a semi-amplitude of 18 ppm, but cannot exclude the possibility that this is the result of red noise or imperfect removal of the rotational modulation. We detect no transit-timing and transit-duration variations with upper limits of 15 s and 1 min, respectively. We also reject any additional transiting planets with transit depths above 280 ppm in the orbital period region 0.5–30 d.

MOVES I. The evolving magnetic field of the planet-hosting star HD189733

MOVES I. The evolving magnetic field of the planet-hosting star HD189733


Authors:


Fares et al

Abstract:
HD189733 is an active K dwarf that is, with its transiting hot Jupiter, among the most studied exoplanetary systems. In this first paper of the Multiwavelength Observations of an eVaporating Exoplanet and its Star (MOVES) program, we present a 2-year monitoring of the large-scale magnetic field of HD189733. The magnetic maps are reconstructed for five epochs of observations, namely June-July 2013, August 2013, September 2013, September 2014, and July 2015, using Zeeman-Doppler Imaging. We show that the field evolves along the five epochs, with mean values of the total magnetic field of 36, 41, 42, 32 and 37 G, respectively. All epochs show a toroidally-dominated field. Using previously published data of Moutou et al. 2007 and Fares et al. 2010, we are able to study the evolution of the magnetic field over 9 years, one of the longest monitoring campaign for a given star. While the field evolved during the observed epochs, no polarity switch of the poles was observed. We calculate the stellar magnetic field value at the position of the planet using the Potential Field Source Surface extrapolation technique. We show that the planetary magnetic environment is not homogeneous over the orbit, and that it varies between observing epochs, due to the evolution of the stellar magnetic field. This result underlines the importance of contemporaneous multi-wavelength observations to characterise exoplanetary systems. Our reconstructed maps are a crucial input for the interpretation and modelling of our MOVES multi-wavelength observations.

Saturday, September 30, 2017

Decoupling of Magnetic Fields in Collapsing Protostellar Envelopes and Disk Formation and Fragmentation

Decoupling of Magnetic Fields in Collapsing Protostellar Envelopes and Disk Formation and Fragmentation

Authors:


Zhao et al

Abstract:
Efficient magnetic braking is a formidable obstacle to the formation of rotationally supported disks (RSDs) around protostars in magnetized dense cores. We have previously shown, through 2D (axisymmetric) non-ideal MHD simulations, that removing very small grains (VSGs: ~10 \AA to few 100 \AA) can greatly enhance ambipolar diffusion and enable the formation of RSDs. Here we extend the simulations of disk formation enabled by VSG removal to 3D. We find that the key to this scenario of disk formation is that the infall speed of ions (and thus the magnetic field lines tied to them) almost vanishes in the 102-103 AU-scale "pseudo-disk" where the field lines are most severely pinched and most of protostellar envelope mass infall occurs. As a result, the bulk neutral envelope matter can collapse without dragging much magnetic flux into the disk-forming region, which lowers the magnetic braking efficiency. We find that the initial disks enabled by VSG removal tend to be Toomre-unstable, which leads to the formation of prominent spiral structures that function as centrifugal barriers. The piling-up of infall material near the centrifugal barrier often produces dense fragments of tens of Jupiter masses, especially in cores that are not too strongly magnetized. Some fragments accrete onto the central stellar object, producing bursts in mass accretion rate. Others are longer lived, although whether they can survive long-term to produce multiple systems remains to be ascertained. Our results highlight the importance of dust grain evolution in determining the formation and properties of protostellar disks and potentially multiple systems.

Improved Constraints on the Disk Around MWC 349A from the 23-Meter LBTI

Improved Constraints on the Disk Around MWC 349A from the 23-Meter LBTI 
Authors:

Sallum et al

Abstract:
We present new spatially resolved observations of MWC 349A from the Large Binocular Telescope Interferometer (LBTI), a 23-meter baseline interferometer made up of two, co-mounted 8-meter telescopes. MWC 349A is a B[e] star with an unknown evolutionary state. Proposed scenarios range from a young stellar object (YSO), to a B[e] supergiant, to a tight binary system. Radio continuum and recombination line observations of this source revealed a sub-arcsecond bipolar outflow surrounding a ~100 mas circumstellar disk. Followup infrared studies detected the disk, and suggested that it may have skew and an inner clearing. Our new infrared interferometric observations, which have more than twice the resolution of previously-published datasets, support the presence of both skew and a compact infrared excess. They rule out inner clearings with radii greater than ~14 mas. We show the improvements in disk parameter constraints provided by LBTI, and discuss the inferred disk parameters in the context of the posited evolutionary states for MWC 349A.

An Incipient Debris Disk in the Chamaeleon I Cloud

An Incipient Debris Disk in the Chamaeleon I Cloud

Authors:


Espaillat et al

Abstract:
The point at which a protoplanetary disk becomes a debris disk is difficult to identify. To better understand this, here we study the ∼40~AU separation binary T~54 in the Chamaeleon I cloud. We derive a K5 spectral type for T~54~A (which dominates the emission of the system) and an age of ∼2~Myr. However, the dust disk properties of T~54 are consistent with those of debris disks seen around older and earlier-type stars. At the same time, T~54 has evidence of gas remaining in the disk as indicated by [Ne II], [Ne III], and [O I] line detections. We model the spectral energy distribution of T~54 and estimate that ∼3×10−3 Earth-masses of small dust grains (<0 .25="" along="" an="" are="" at="" circumbinary="" disk="" earth-masses="" in="" larger="" least="" m="" of="" optically="" present="" thin="" with="">10~μm) grains within a circumprimary disk. Assuming a solar-like mixture, we use Ne line luminosities to place a minimum limit on the gas mass of the disk (∼3×10−4 Earth-masses) and derive a gas-to-dust mass ratio of ∼0.1. We do not detect substantial accretion, but we do see Hα in emission in one epoch, suggestive that there may be intermittent dumping of small amounts of matter onto the star. Considering the low dust mass, the presence of gas, and young age of T~54, we conclude that this system is on the bridge between the protoplanetary and debris disk stages.

Friday, September 29, 2017

Auroral Radio Emission from Ultracool Dwarfs: a Jovian Model

Auroral Radio Emission from Ultracool Dwarfs: a Jovian Model

Authors:


Turnpenney et al

Abstract:
A number of fast-rotating ultra cool dwarfs (UCDs) emit pulsed coherent radiation, attributed to the electron cyclotron maser instability, a phenomenon that occurs in the solar system at planets with strong auroral emission. In this paper we examine magnetosphere-ionosphere coupling currents in UCDs, adopting processes used in models of Jovian emission. We consider the angular velocity gradient arising from a steady outward flux of angular momentum from an internal plasma source, as analogous to the jovian main oval current system, as well as the interaction of a rotating magnetosphere with the external medium. Both of these mechanisms are seen in the solar system to be responsible for the production of radio emission. We present the results of an investigation over a range of relevant plasma and magnetosphere-ionosphere coupling parameters to determine regimes consistent with observed UCD radio luminosities. Both processes are able to explain observed UCD luminosities with ionospheric Pedersen conductances of ∼1 − 2 mho, either for a closed magnetosphere with a plasma mass outflow rate of ∼105 kg s−1, i.e. a factor of ∼100 larger than that observed at Jupiter’s moon Io, or for a dwarf with an open magnetosphere moving through the interstellar medium at ∼50 km s−1 and a plasma mass outflow rate of ∼1000 kg s−1. The radio luminosity resulting from these mechanisms have opposing dependencies on the magnetic field strength, a point which may be used to discriminate between the two models as more data become available.

Ultracool dwarf benchmarks with Gaia primaries

Ultracool dwarf benchmarks with Gaia primaries

Authors:


Marocco et al

Abstract:
We explore the potential of Gaia for the field of benchmark ultracool/brown dwarf companions, and present the results of an initial search for metal-rich/metal-poor systems. A simulated population of resolved ultracool dwarf companions to Gaia primary stars is generated and assessed. Of order ∼24,000 companions should be identifiable outside of the Galactic plane (|b| > 10 deg) with large-scale ground- and space-based surveys including late M, L, T, and Y types. Our simulated companion parameter space covers 0.02 ≤ M/M⊙ ≤ 0.1, 0.1 ≤ age/Gyr ≤ 14, and −2.5 ≤ [Fe/H] ≤ 0.5, with systems required to have a false alarm probability less than 10−4, based on projected separation and expected constraints on common-distance, common-proper motion, and/or common-radial velocity. Within this bulk population we identify smaller target subsets of rarer systems whose collective properties still span the full parameter space of the population, as well as systems containing primary stars that are good age calibrators. Our simulation analysis leads to a series of recommendations for candidate selection and observational follow-up that could identify ∼500 diverse Gaia benchmarks. As a test of the veracity of our methodology and simulations, our initial search uses UKIDSS and SDSS to select secondaries, with the parameters of primaries taken from Tycho-2, RAVE, LAMOST and TGAS. We identify and follow-up 13 new benchmarks. These include M8-L2 companions, with metallicity constraints ranging in quality, but robust in the range −0.39 ≤ [Fe/H] ≤ +0.36, and with projected physical separation in the range 0.6 less than s/kau less than 76. Going forward, Gaia offers a very high yield of benchmark systems, from which diverse sub-samples may be able to calibrate a range of foundational ultracool/sub-stellar theory and observation.

A new statistical method for characterizing the atmospheres applied to brown dwarf GJ 758B

A new statistical method for characterizing the atmospheres of extrasolar planets

Authors:


Henderson et al

Abstract:

By detecting light from extrasolar planets,we can measure their compositions and bulk physical properties. The technologies used to make these measurements are still in their infancy, and a lack of self-consistency suggests that previous observations have underestimated their systemic errors.We demonstrate a statistical method, newly applied to exoplanet characterization, which uses a Bayesian formalism to account for underestimated errorbars. We use this method to compare photometry of a substellar companion, GJ 758b, with custom atmospheric models. Our method produces a probability distribution of atmospheric model parameters including temperature, gravity, cloud model (fsed), and chemical abundance for GJ 758b. This distribution is less sensitive to highly variant data, and appropriately reflects a greater uncertainty on parameter fits.

Thursday, September 28, 2017

EPIC 228735255b: an eccentric 6.57 day transiting hot Jupiter in Virgo

EPIC 228735255b - An eccentric 6.57 day transiting hot Jupiter in Virgo

Authors:


Giles et al

Abstract:

We present the discovery of EPIC 228735255b, a P= 6.57 days Jupiter-mass (MP=1.019±0.070 MJup) planet transiting a V=12.5 (G5-spectral type) star in an eccentric orbit (e=0.120+0.056−0.046) detected using a combination of K2 photometry and ground-based observations. With a radius of 1.095±0.018RJup the planet has a bulk density of 0.726±0.062ρJup. The host star has a [Fe/H] of 0.12±0.045, and from the K2 light curve we find a rotation period for the star of 16.3±0.1 days. This discovery is the 9th hot Jupiter from K2 and highlights K2's ability to detect transiting giant planets at periods slightly longer than traditional, ground-based surveys. This planet is slightly inflated, but much less than others with similar incident fluxes. These are of interest for investigating the inflation mechanism of hot Jupiters.

Ground-based photometry of the 21-day Neptune HD 106315c

Ground-based photometry of the 21-day Neptune HD106315c

Authors:

Lendl et al

Abstract:
Space-based transit surveys such as K2 and TESS allow the detection of small transiting planets with orbital periods beyond 10 days. Few of these warm Neptunes are currently known around stars bright enough to allow for detailed follow-up observations dedicated to their atmospheric characterization. The 21-day period and 3.95 R⊕ planet HD106315c has been discovered based on the observation of two of its transits by K2. We have observed HD106315 using the 1.2m Euler telescope equipped with the EulerCam camera on two instances to confirm the transit using broad band photometry and refine the planetary period. Based on two observed transits of HD106315c, we detect its ∼1 mmag transit and obtain a precise measurement of the planetary ephemerids, which are critical for planning further follow-up observations. We have used the attained precision together with the predicted yield from the TESS mission to evaluate the potential for ground-based confirmation of Neptune-sized planets found by TESS. We find that 1-meter-class telescopes on the ground equipped with precise photometers could substantially contribute to the follow-up of 162 TESS candidates orbiting stars with magnitudes of V≤14. Out of these, 74 planets orbit stars with V≤12 and 12 planets orbit V≤10, which makes these candidates high-priority objects for atmospheric characterization with high-end instrumentation.