A Multi-planet System of Rapidly Rotating F-Star HD 106315

A Multi-planet System Transiting the V = 9 Rapidly Rotating F-Star HD 106315

Authors:

Rodriguez et al

Abstract:

We report the discovery of a multi-planet system orbiting HD 106315, a rapidly rotating mid F-type star, using data from the K2 mission. HD 106315 hosts a 2.51 ± 0.12 R ⊕ sub-Neptune in a 9.5-day orbit and a ${4.31}_{-0.27}^{+0.24}\,{R}_{\oplus }$ super-Neptune in a 21-day orbit. The projected rotational velocity of HD 106315 (12.9 km s−1) likely precludes precise measurements of the planets' masses but could enable a measurement of the sky-projected spin–orbit obliquity for the outer planet via Doppler tomography. The eccentricities of both planets were constrained to be consistent with 0, following a global modeling of the system that includes a Gaia distance and dynamical arguments. The HD 106315 system is one of few multi-planet systems hosting a Neptune-sized planet for which orbital obliquity measurements are possible, making it an excellent test-case for formation mechanisms of warm-Neptunian systems. The brightness of the host star also makes HD 106315 c a candidate for future transmission spectroscopic follow-up studies.

HD 106315c: a SubSaturn Detected by K2

Two Small Transiting Planets and a Possible Third Body Orbiting HD 106315

Authors:

Crossfield et al

Abstract:

The masses, atmospheric makeups, spin–orbit alignments, and system architectures of extrasolar planets can be best studied when the planets orbit bright stars. We report the discovery of three bodies orbiting HD 106315, a bright (V = 8.97 mag) F5 dwarf targeted by our K2 survey for transiting exoplanets. Two small transiting planets are found to have radii ${2.23}_{-0.25}^{+0.30}\,{R}_{\oplus }$ and ${3.95}_{-0.39}^{+0.42}\,{R}_{\oplus }$ and orbital periods 9.55 days and 21.06 days, respectively. A radial velocity (RV) trend of 0.3 ± 0.1 m s−1 day−1 indicates the likely presence of a third body orbiting HD 106315 with period gsim160 days and mass gsim45 M ⊕. Transits of this object would have depths gsim0.1% and are definitively ruled out. Although the star has v sin i = 13.2 km s−1, it exhibits a short-timescale RV variability of just 6.4 m s−1. Thus, it is a good target for RV measurements of the mass and density of the inner two planets and the outer object's orbit and mass. Furthermore, the combination of RV noise and moderate v sin i makes HD 106315 a valuable laboratory for studying the spin–orbit alignment of small planets through the Rossiter–McLaughlin effect. Space-based atmospheric characterization of the two transiting planets via transit and eclipse spectroscopy should also be feasible. This discovery demonstrates again the power of K2 to find compelling exoplanets worthy of future study.

K2-98 b: A 32 Earth Mass Neptune-sized Exoplanet in a 10-day orbit around an F8 star

K2-98 b: A 32-M⊕ Neptune-sized planet in a 10-day orbit transiting an F8 star

Authors:

Barragán et al

Abstract:

We report the discovery of K2-98 b (EPIC 211391664 b), a transiting Neptune-sized planet monitored by the K2 mission during its campaign 5. We combine the K2 time-series data with ground-based photometric and spectroscopic follow-up observations to confirm the planetary nature of the object and derive its mass, radius, and orbital parameters. K2-98 b is a warm Neptune-like planet in a 10-day orbit around a V=12.2~mag F-type star with M⋆=1.074±0.042, R⋆=1.311+0.083−0.048, and age of 5.2+1.2−1.0~Gyr. We derive a planetary mass and radius of Mp=32.2±8.1 and Rp=4.3+0.3−0.2. K2-98 b joins the relatively small group of Neptune-sized planets whose both mass and radius have been derived with a precision better than 25 %. We estimate that the planet will be engulfed by its host star in ∼3~Gyr, due to the evolution of the latter towards the red giant branch.

Kepler-21b/HD 179070b: a Terrestrial Exoplanet Around an F Dwarf Star

Kepler-21b: A rocky planet around a V = 8.25 magnitude star

Authors:

Lopez-Morales et al

Abstract:

HD 179070, aka Kepler-21, is a V = 8.25 F6IV star and the brightest exoplanet host discovered by Kepler. An early detailed analysis by Howell et al. (2012) of the first thirteen months (Q0 - Q5) of Kepler light curves revealed transits of a planetary companion, Kepler-21b, with a radius of about 1.60 +/- 0.04 R_earth and an orbital period of about 2.7857 days. However, they could not determine the mass of the planet from the initial radial velocity observations with Keck-HIRES, and were only able to impose a 2-sigma upper limit of 10 M_earth. Here we present results from the analysis of 82 new radial velocity observations of this system obtained with HARPS-N, together with the existing 14 HIRES data points. We detect the Doppler signal of Kepler-21b with a radial velocity semi-amplitude K = 2.00 +/- 0.65 m/s, which corresponds to a planetary mass of 5.1 +/- 1.7 M_earth. We also measure an improved radius for the planet of 1.639 (+0.019, -0.015) R_earth, in agreement with the radius reported by Howell et al. (2012). We conclude that Kepler-21b, with a density of 6.4 +/- 2.1 g/cm^3, belongs to the population of terrestrial planets with iron, magnesium silicate interiors, which have lost the majority of their envelope volatiles via stellar winds or gravitational escape. The radial velocity analysis presented in this paper serves as example of the type of analysis that will be necessary to confirm the masses of TESS small planet candidates.

EPIC 211391664b: A 32-M⊕ Neptune-sized planet in a 10-day orbit around an F8 star

EPIC 211391664b: A 32-M⊕ Neptune-sized planet in a 10-day orbit transiting an F8 star

Authors:

Barragán et al

Abstract:

We report the discovery of EPIC 211391664b, a transiting Neptune-sized planet monitored by the K2 mission during its campaign 5. We combine the K2 time-series data with ground-based photometric and spectroscopic follow-up observations to confirm the planetary nature of the object and derive its mass, radius, and orbital parameters. EPIC 211391664 b is a warm Neptune-like planet in a 10-day orbit around a V=12.2~mag F-type star with M⋆=1.074±0.042M⊙, R⋆=1.311+0.083−0.048R⊙, and age of 5.2+1.2−1.0~Gyr. We derive a planetary mass and radius of Mp=32.2±8.1M⊕ and Rp=4.3+0.3−0.2R⊕. EPIC 211391664b joins the relatively small group of Neptune-sized planets whose mass and radius have been derived with a precision better than 3-σ. We estimate that the planet will be engulfed by EPIC 211391664 in ∼3~Gyr, due to the evolution of the host star towards the red giant branch.

WASP-94AB: a Binary Star System With Each Star Having a hot Jupiters

The Curious Case of Elemental Abundance Differences in the Dual Hot Jupiter Hosts WASP-94AB

Authors:

Teske et al

Abstract:

Binary stars provide an ideal laboratory for investigating the potential effects of planet formation on stellar composition. Assuming the stars formed in the same environment/from the same material, any compositional anomalies between binary components might indicate differences in how material was sequestered in planets, or accreted by the star in the process of planet formation. We present here a study of the elemental abundance differences between WASP-94AB, a pair of stars that each host a hot Jupiter exoplanet. The two stars are very similar in spectral type (F8 and F9), and their ~2700 AU separation suggests their protoplanetary disks were likely not influenced by stellar interactions, but WASP-94Ab's orbit -- misaligned with the host star spin axis and likely retrograde -- points towards a dynamically active formation mechanism, perhaps different than that of WASP-94Bb, which is not misaligned and has nearly circular orbit. Based on our high-quality spectra and strictly relative abundance analysis, we detect a depletion of volatiles (~-0.02 dex, on average) and enhancement of refractories (~0.01 dex) in WASP-94A relative to B (standard errors are ~0.005 dex). This is different than every other published case of binary host star abundances, in which either no significant abundance differences are reported, or there is some degree of enhancement in all elements, including volatiles. Several scenarios that may explain the abundance trend are discussed, but none can be definitively accepted or rejected. Additional high-contrast imaging observations to search for companions that may be dynamically affecting the system, as well as a larger sample of binary host star studies, are needed to better understand the curious abundance trends we observe in WASP-94AB.

Gas Giants HD 60532b & HD 60532c are in a 3:1 Orbital Resonance

Dynamics of the 3/1 planetary mean-motion resonance. An application to the HD60532 b-c planetary system

Authors:

Alves et al

Abstract:

In this paper, we use a semi-analytical approach to analyze the global structure of the phase space of the planar planetary 3/1 mean-motion resonance, in cases where the outer planet is more massive than its inner companion. We show that the resonant dynamics can be described using only two fundamental parameters, the total angular momentum and the scaling parameter. The topology of the Hamiltonian function describing the resonant behaviour is studied on the representative planes that allows us to investigate a large domain of the phase space of the three-body problem without time-expensive numerical integrations of the equations of motion, and without any restriction on the magnitude of the planetary eccentricities. The families of the well known Apsidal Corotation Resonances (ACR) parameterized by the planetary mass ratio are obtained and their stability is analyzed. The main dynamical features in the domains around ACR are also investigated in detail by means of spectral analysis techniques, which allow us to detect the regions of different regimes of motion of resonant systems. The construction of dynamical maps for various values of the total angular momentum shows the evolution of domains of stable motion with the eccentricities, identifying possible configurations suitable for exoplanetary systems.

M Dwarfs Have Less Massive Protoplanetary Disks, but More Mass in Their Exoplanets

An Increase in the Mass of Planetary Systems around Lower-Mass Stars

Authors:

Mulders et al

Abstract:

Trends in the planet population with host star mass provide an avenue to constrain planet formation theories. We derive the planet radius distribution function for Kepler stars of different spectral types, sampling a range in host star masses. We find that M dwarf stars have 3.5 times more small planets (1.0-2.8 R_Earth) than main-sequence FGK stars, but two times fewer Neptune-sized and larger planets (>2.8 R_Earth). We find no systematic trend in the planet size distribution between spectral types F, G, and K to explain the increasing occurrence rates. Taking into account the mass-radius relationship and heavy-element mass of observed exoplanets, and assuming those are independent of spectral type, we derive the inventory of the heavy-element mass locked up in exoplanets at short orbits. The overall higher planet occurrence rates around M stars are not consistent with the redistribution of the same mass into more, smaller planets. At the orbital periods and planet radii where Kepler observations are complete for all spectral types, the average heavy-element mass locked up in exoplanets increases roughly inversely with stellar mass from 4 M_Earth in F stars to 5 M_Earth in G and K stars to 7 M_Earth in M stars. This trend stands in stark contrast with observed protoplanetary disk masses that decrease towards lower mass stars, and provides a challenge for current planet formation models. Neither models of in situ formation nor migration of fully-formed planets are consistent with these results. Instead, these results are indicative of large-scale inward migration of planetary building blocks --- either through type-I migration or radial drift of dust grains --- that is more efficient for lower mass stars, but does not result in significantly larger or smaller planets.

Did F Dwarf KIC 8462852 Have a Comet Breakup?

Planet Hunters X. KIC 8462852 - Where's the Flux?

Authors:

Boyajian et al

Abstract:

Over the duration of the Kepler mission, KIC 8462852 was observed to undergo irregularly shaped, aperiodic dips in flux down to below the 20% level. The dipping activity can last for between 5 and 80 days. We characterize the object with high-resolution spectroscopy, spectral energy distribution fitting, and Fourier analyses of the Kepler light curve. We determine thatKIC 8462852 is a main-sequence F3 V/IV star, with a rotation period ~0.88 d, that exhibits no significant IR excess. In this paper, we describe various scenarios to explain the mysterious events in the Kepler light curve, most of which have problems explaining the data in hand. By considering the observational constraints on dust clumps orbiting a normal main-sequence star, we conclude that the scenario most consistent with the data is the passage of a family of exocomet fragments, all of which are associated with a single previous breakup event. We discuss the necessity of future observations to help interpret the system.

Observing F Dwarf ε Aurigae's Protoplanetary Disk for 14 Years

Interferometry of ε Aurigae: Characterization of the asymmetric eclipsing disk

Authors:

Kloppenborg et al

Abstract:

We report on a total of 106 nights of optical interferometric observations of the ϵ Aurigae system taken during the last 14 years by four beam combiners at three different interferometric facilities. This long sequence of data provides an ideal assessment of the system prior to, during, and after the recent 2009-2011 eclipse. We have reconstructed model-independent images from the 10 in-eclipse epochs which show that a disk-like object is indeed responsible for the eclipse. Using new 3D, time-dependent modeling software, we derive the properties of the F-star (diameter, limb darkening), determine previously unknown orbital elements (Ω, i), and access the global structures of the optically thick portion of the eclipsing disk using both geometric models and approximations of astrophysically relevant density distributions. These models may be useful in future hydrodynamical modeling of the system. Lastly, we address several outstanding research questions including mid-eclipse brightening, possible shrinking of the F-type primary, and any warps or sub-features within the disk.

Hunting for Gas Giant Exoplanets Around A & F Class Stars

Searching for gas giant planets on Solar System scales - A NACO/APP L'-band survey of A- and F-type Main Sequence stars

Authors:

Meshkat et al

Abstract:

We report the results of a direct imaging survey of A- and F-type main sequence stars searching for giant planets. A/F stars are often the targets of surveys, as they are thought to have more massive giant planets relative to solar-type stars. However, most imaging is only sensitive to orbital separations greater than 30 AU, where it has been demonstrated that giant planets are rare. In this survey, we take advantage of the high-contrast capabilities of the Apodizing Phase Plate coronagraph on NACO at the Very Large Telescope. Combined with optimized principal component analysis post-processing, we are sensitive to planetary-mass companions (2 to 12 MJup) at Solar System scales (≤30 AU). We obtained data on 13 stars in L'-band and detected one new companion as part of this survey: an M6.0±0.5 dwarf companion around HD 984. We re-detect low-mass companions around HD 12894 and HD 20385, both reported shortly after the completion of this survey. We use Monte Carlo simulations to determine new constraints on the low-mass (less than 80 MJup) companion frequency, as a function of mass and separation. Assuming solar-type planet mass and separation distributions, normalized to the planet frequency appropriate for A-stars, and the observed companion mass-ratio distribution for stellar companions extrapolated to planetary masses, we derive a truncation radius for the planetary mass companion surface density of less than 135 AU at 95% confidence.

The UV Enviroment of ExoEarths Around Alternate Stars

UV SURFACE ENVIRONMENT OF EARTH-LIKE PLANETS ORBITING FGKM STARS THROUGH GEOLOGICAL EVOLUTION

Authors:

Rugheimer et al

Abstract:

The UV environment of a host star affects the photochemistry in the atmosphere, and ultimately the surface UV environment for terrestrial planets and therefore the conditions for the origin and evolution of life. We model the surface UV radiation environment for Earth-sized planets orbiting FGKM stars in the circumstellar Habitable Zone for Earth through its geological evolution. We explore four different types of atmospheres corresponding to an early-Earth atmosphere at 3.9 Gyr ago and three atmospheres covering the rise of oxygen to present-day levels at 2.0 Gyr ago, 0.8 Gyr ago, and modern Earth. In addition to calculating the UV flux on the surface of the planet, we model the biologically effective irradiance, using DNA damage as a proxy for biological damage. We find that a pre-biotic Earth (3.9 Gyr ago) orbiting an F0V star receives 6 times the biologically effective radiation as around the early Sun and 3520 times the modern Earth–Sun levels. A pre-biotic Earth orbiting GJ 581 (M3.5 V) receives 300 times less biologically effective radiation, about 2 times modern Earth–Sun levels. The UV fluxes calculated here provide a grid of model UV environments during the evolution of an Earth-like planet orbiting a range of stars. These models can be used as inputs into photo-biological experiments and for pre-biotic chemistry and early life evolution experiments.

HAT-P-56b: An Inflated Hot Jupiter Around an F Dwarf

An inflated massive Hot Jupiter transiting a bright F star followed up with K2.0 observations

Authors:

Huang et al

Abstract:

We report the discovery of HAT-P-56b by the HATNet survey, an inflated hot Jupiter transiting a bright F type star in Field 0 of NASA's K2 mission. We combine ground-based discovery and follow-up light curves with high precision photometry from K2, as well as ground-based radial velocities from TRES on the FLWO~1.5m telescope to determine the physical properties of this system. HAT-P-56b has a mass of Mp≈2.18MJ, radius of Rp≈1.47RJ, and transits its host star on a near-grazing orbit with a period of P≈ 2.7908 d. The radius of HAT-P-56b is among the largest known for a planet with Mp>2MJ. The host star has a V-band magnitude of 10.9, mass of 1.30 M⊙, and radius of 1.43 R⊙. The periodogram of the K2 light curve suggests the star is a γ Dor variable. HAT-P-56b is an example of a ground-based discovery of a transiting planet, where space-based observations greatly improve the confidence in the confirmation of its planetary nature, and also improve the accuracy of the planetary parameters.

3D Climate Modeling of Terrestrial Class Exoplanets Around Different Classes of Stars

3D climate modeling of Earth-like extrasolar planets orbiting different types of host stars

Authors:

Godolt et al

Abstract:

The potential habitability of a terrestrial planet is usually defined by the possible existence of liquid water on its surface, since life as we know it needs liquid water at least during a part of its life cycle. The potential presence of liquid water on a planetary surface depends on many factors such as, most importantly, surface temperatures. The properties of the planetary atmosphere and its interaction with the radiative energy provided by the planet's host star are thereby of decisive importance.

In this study we investigate the influence of different main-sequence stars (F, G, and K-type stars) upon the climate of Earth-like extrasolar planets and their potential habitability by applying a state-of-the-art three-dimensional (3D) Earth climate model accounting for local and dynamical processes. The calculations have been performed for planets with Earth-like atmospheres at orbital distances (and corresponding orbital periods) where the total amount of energy received from the various host stars equals the solar constant. In contrast to previous 3D modeling studies, we include the effect of ozone radiative heating upon the vertical temperature structure of the atmospheres. The global orbital mean results obtained have been compared to those of a one-dimensional (1D) radiative convective climate model to investigate the approximation of global mean 3D results by those of 1D models.

The different stellar spectral energy distributions lead to different surface temperatures and due to ozone heating to very different vertical temperature structures. As previous 1D studies we find higher surface temperatures for the Earth-like planet around the K-type star, and lower temperatures for the planet around the F-type star compared to an Earth-like planet around the Sun. However, this effect is more pronounced in the 3D model results than in the 1D model because the 3D model accounts for feedback processes such as the ice-albedo and the water vapor feedback. Whether the 1D model may approximate the global mean of the 3D model results strongly depends on the choice of the relative humidity profile in the 1D model, which is used to determine the water vapor profile. Hence, possible changes in the hydrological cycle need to be accounted for when estimating the potential habitability of an extrasolar planet.

There are some oddities in the paper.  They come up with K class stars making their planets hotter than the exoplanets around F class stars.  hm.

Habitability of Possible Exomoons in Observed F-star ExoPlanetary Systems From the Impact of Ultraviolet Light

UV Habitability of Possible Exomoons in Observed F-star Planetary Systems

Authors:

Sato et al

Abstract:

In the present study we explore the astrobiological significance of F-type stars of spectral type between F5 V and F9.5 V, which possess Jupiter-type planets within or close to their climatological habitable zones. These planets, or at least a subset of them, may also possess rocky exomoons, which potentially offer habitable environments. Our work considers eight selected systems. The Jupiter-type planets in these systems are in notably different orbits with eccentricities ranging from 0.08 to 0.72. Particularly, we consider the stellar UV environments provided by the photospheric stellar radiation in regard to the circumstellar habitability of the system. According to previous studies, DNA is taken as a proxy for carbon-based macromolecules following the paradigm that extraterrestrial biology might be based on hydrocarbons. Thus, the DNA action spectrum is utilized to represent the impact of the stellar UV radiation. Atmospheric attenuation is taken into account based on parameterized attenuation functions. We found that the damage inflicted on DNA is notably different for the range of systems studied, and also varies according to the orbit of the Jupiter-type planet, especially in systems of high ellipticity. For some systems large values of damage are attained compared to an Earth-type planet at Earth-like positions in the solar system. A highly protective exomoon atmosphere would be required in most systems to foster habitable environments, notwithstanding extremophiles or systems based on nonstandard exobiology, which are beyond the scope of the present study.

KELT-7b: A hot Jupiter Around a Fast Rotating F Class Star

KELT-7b: A hot Jupiter transiting a bright V=8.54 rapidly rotating F-star

Authors:

Bieryla et al

Abstract:

We report the discovery of KELT-7b, a transiting hot Jupiter with a mass of 1.28±0.18 MJ, radius of 1.53+0.046−0.047 RJ, and an orbital period of 2.7347749±0.0000039 days. The bright host star (HD33643; KELT-7) is an F-star with V=8.54, Teff =6789+50−49 K, [Fe/H] =0.139+0.075−0.081, and logg=4.149±0.019. It has a mass of 1.535+0.066−0.054 Msun, a radius of 1.732+0.043−0.045 Rsun, and is the fifth most massive, fifth hottest, and the ninth brightest star known to host a transiting planet. It is also the brightest star around which KELT has discovered a transiting planet. Thus, KELT-7b is an ideal target for detailed characterization given its relatively low surface gravity, high equilibrium temperature, and bright host star. The rapid rotation of the star (73±0.5 km/s) results in a Rossiter-McLaughlin effect with an unusually large amplitude of several hundred m/s. We find that the orbit normal of the planet is likely to be well-aligned with the stellar spin axis, with a projected spin-orbit alignment of λ=9.7±5.2 degrees. This is currently the most rapidly rotating star to have a reflex signal (and thus mass determination) due to a planetary companion measured.

Exoplanet System Demographics are Highly Tied to Host Star Type

A STELLAR-MASS-DEPENDENT DROP IN PLANET OCCURRENCE RATES

Authors:

Mulders et al

Abstract:

The Kepler spacecraft has discovered a large number of planets with up to one-year periods and down to terrestrial sizes. While the majority of the target stars are main-sequence dwarfs of spectral type F, G, and K, Kepler covers stars with effective temperatures as low as 2500 K, which corresponds to M stars. These cooler stars allow characterization of small planets near the habitable zone, yet it is not clear if this population is representative of that around FGK stars. In this paper, we calculate the occurrence of planets around stars of different spectral types as a function of planet radius and distance from the star and show that they are significantly different from each other. We further identify two trends. First, the occurrence of Earth- to Neptune-sized planets (1-4 R ⊕) is successively higher toward later spectral types at all orbital periods probed by Kepler; planets around M stars occur twice as frequently as around G stars, and thrice as frequently as around F stars. Second, a drop in planet occurrence is evident at all spectral types inward of a ~10 day orbital period, with a plateau further out. By assigning to each spectral type a median stellar mass, we show that the distance from the star where this drop occurs is stellar mass dependent, and scales with semi-major axis as the cube root of stellar mass. By comparing different mechanisms of planet formation, trapping, and destruction, we find that this scaling best matches the location of the pre-main-sequence co-rotation radius, indicating efficient trapping of migrating planets or planetary building blocks close to the star. These results demonstrate the stellar-mass dependence of the planet population, both in terms of occurrence rate and of orbital distribution. The prominent stellar-mass dependence of the inner boundary of the planet population shows that the formation or migration of planets is sensitive to the stellar parameters.

Li Abundances in F Class Exoplanetary Host Stars

Li abundances in F stars: planets, rotation and galactic evolution

Authors:

Delgado Mena et al

Abstract:

We find that hot jupiter host stars within the Teff range 5900-6300K show lower Li abundances, by 0.14 dex, than stars without detected planets. This offset has a significance at the level 7σ, pointing to a stronger effect of planet formation on Li abundances when the planets are more massive and migrate close to the star. However, we also find that the average v \textit{sin}i of (a fraction of) stars with hot jupiters is higher on average than for single stars in the same Teff region, suggesting that rotationally-induced mixing (and not the presence of planets) might be the cause for a greater depletion of Li. We confirm that the mass-metallicity dependence of the Li dip is extended towards [Fe/H] ∼ 0.4 dex (beginning at [Fe/H] ∼ -0.4 dex for our stars) and that probably reflects the mass-metallicity correlation of stars of the same Teff on the Main Sequence. We find that for the youngest stars (less than 1.5 Gyr) around the Li dip, the depletion of Li increases with v \textit{sin}i values, as proposed by rotationally-induced depletion models. This suggests that the Li dip consists of fast rotators at young ages whereas the most Li-depleted old stars show lower rotation rates (probably caused by the spin-down during their long lifes). We have also explored the Li evolution with [Fe/H] taking advantage of the metal-rich stars included in our sample. We find that Li abundance reaches its maximum around solar metallicity but decreases in the most metal-rich stars, as predicted by some models of Li Galactic production.

Evolution of Angular-momentum-losing Exoplanetary Systems

Evolution of angular-momentum-losing exoplanetary systems: Revisiting Darwin stability

Authors:

Damiani et al

Abstract:

We aim at assessing the importance of tidal evolution and its interplay with magnetic braking in the population of hot-Jupiter planetary systems. By minimizing the total mechanical energy of a given system under the constraint of stellar angular momentum loss, we rigorously find the conditions for the existence of dynamical equilibrium states. We estimate their duration, in particular when the wind torque spinning down the star is almost compensated by the tidal torque spinning it up. We introduce dimensionless variables to characterize the tidal evolution of observed hot Jupiter systems and discuss their spin and orbital states using generalized Darwin diagrams based on our new approach. We show that their orbital properties are related to the effective temperature of their host stars. The long-term evolution of planets orbiting F- and G-type stars is significantly different owing to the combined effect of magnetic braking and tidal dissipation. The existence of a quasi-stationary state, in the case of short-period planets, can significantly delay their tidal evolution that would otherwise bring the planet to fall into its host star. Most of the planets known to orbit F-type stars are presently found to be near this stationary state, probably in a configuration not too far from that they had when their host star settled on the zero-age main sequence. Estimates of the engulfment timescale based on the conservation of the total angular momentum of a star-planet system must be revised and angular momentum loss has to be taken into account when constraining tidal evolution in close planetary systems. Considering the importance of angular momentum loss in the early stages of stellar evolution, our results indicate that it has to be taken into account also to properly test the migration scenarios of planetary system formation.

One Hot Saturn, One Hot Jupiter and One Eccentric Hot Jupiter Found by WASP-South

Three WASP-South transiting exoplanets: WASP-74b, WASP-83b & WASP-89b

Authors:

Hellier et al

Abstract:

We report the discovery of three new transiting hot Jupiters by WASP-South together with the TRAPPIST photometer and the Euler/CORALIE spectrograph.

WASP-74b orbits a star of V = 9.7, making it one of the brighter systems accessible to Southern telescopes. It is a 0.95 M_Jup planet with a moderately bloated radius of 1.5 R_Jup in a 2-d orbit around a slightly evolved F9 star.

WASP-83b is a Saturn-mass planet at 0.3 M_Jup with a radius of 1.0 R_Jup. It is in a 5-d orbit around a fainter (V = 12.9) G8 star.

WASP-89b is a 6 M_Jup planet in a 3-d orbit with an eccentricity of e = 0.2. It is thus similar to massive, eccentric planets such as XO-3b and HAT-P-2b, except that those planets orbit F stars whereas WASP-89 is a K star. The V = 13.1 host star is magnetically active, showing a rotation period of 20.2 d, while star spots are visible in the transits. There are indications that the planet's orbit is aligned with the stellar spin. WASP-89 is a good target for an extensive study of transits of star spots.