Near-IR Emission Spectrum of hot Jupiter WASP-103b

Near-IR Emission Spectrum of WASP-103b using Hubble Space Telescope/Wide Field Camera 3

Authors:

Cartier et al

Abstract:

We present here our observations and analysis of the dayside emission spectrum of the hot Jupiter WASP-103b. We observed WASP-103b during secondary eclipse using two visits of the Hubble Space Telescope with the G141 grism on Wide Field Camera 3 in spatial scan mode. We generated secondary eclipse light curves of the planet in both blended white-light and spectrally binned wavechannels from 1.1-1.7 micron and corrected the light curves for flux contamination from a nearby companion star. We modeled the detector systematics and secondary eclipse spectrum using Gaussian process regression and found that the near-IR emission spectrum of WASP-103b is featureless across the observed near-IR region to down to a sensitivity of 175 ppm, and shows a shallow slope towards the red. The atmosphere has a single brightness temperature of T_B = 2890 K across this wavelength range. This region of the spectrum is indistinguishable from isothermal, but may not manifest from a physically isothermal system, i.e. pseudo-isothermal. A Solar-metallicity profile with a thermal inversion layer at 10^-2 bar fits WASP-103b's spectrum with high confidence, as do an isothermal profile with Solar metallicity and a monotonically decreasing atmosphere with C/O>1. The data rule out a monotonically decreasing atmospheric profile with Solar composition, and we rule out a low-metallicity decreasing profile as non-physical for this system. The pseudo-isothermal profile could be explained by a thermal inversion layer just above the layer probed by our observations, or by clouds or haze in the upper atmosphere. Transmission spectra at optical wavelengths would allow us to better differentiate between potential atmospheric models.

Precise Near-Infrared Radial Velocities

Precise Near-Infrared Radial Velocities

Authors:

Plavchan et al

Abstract:

We present the results of two 2.3 micron near-infrared radial velocity surveys to detect exoplanets around 36 nearby and young M dwarfs. We use the CSHELL spectrograph (R ~46,000) at the NASA InfraRed Telescope Facility, combined with an isotopic methane absorption gas cell for common optical path relative wavelength calibration. We have developed a sophisticated RV forward modeling code that accounts for fringing and other instrumental artifacts present in the spectra. With a spectral grasp of only 5 nm, we are able to reach long-term radial velocity dispersions of ~20-30 m/s on our survey targets.

A High-Precision NIR Survey for RV Variable Low-Mass Stars

A High-Precision NIR Survey for RV Variable Low-Mass Stars

Authors:

Gagné et al

Abstract:

We present the results of a precise near-infrared (NIR) radial velocity (RV) survey of 32 low-mass stars with spectral types K2-M4 using CSHELL at the NASA IRTF in the K-band with an isotopologue methane gas cell to achieve wavelength calibration and a novel iterative RV extraction method. We surveyed 14 members of young (≈ 25-150 Myr) moving groups, the young field star ε Eridani as well as 18 nearby (< 25 pc) low-mass stars and achieved typical single-measurement precisions of 8-15 m s−1 with a long-term stability of 15-50 m s−1. We obtain the best NIR RV constraints to date on 27 targets in our sample, 19 of which were never followed by high-precision RV surveys. Our results indicate that very active stars can display long-term RV variations as low as ∼ 25-50 m s−1 at ≈ 2.3125 μm, thus constraining the effect of jitter at these wavelengths. We provide the first multi-wavelength confirmation of GJ 876 bc and independently retrieve orbital parameters consistent with previous studies. We recovered RV variability for HD 160934 AB and GJ 725 AB that are consistent with their known binary orbits, and nine other targets are candidate RV variables with a statistical significance of 3-5σ. Our method combined with the new iSHELL spectrograph will yield long-term RV precisions of ≲ 5 m s−1 in the NIR, which will allow the detection of Super-Earths near the habitable zone of mid-M dwarfs.

Radial velocity information content of M dwarf spectra in the near-infrared

Radial velocity information content of M dwarf spectra in the near-infrared

Authors:

Figuera et al

Abstract:

Aims:

We evaluate the radial velocity (RV) information content and achievable precision on M0-M9 spectra covering the ZYJHK bands. We do so while considering both a perfect atmospheric transmission correction and discarding areas polluted by deep telluric features, as done in previous works.


Methods:

To simulate the M-dwarf spectra, PHOENIX-ACES model spectra were employed; they were convolved with rotational kernels and instrumental profiles to reproduce stars with a v.sini of 1.0, 5.0, and 10.0 km/s when observed at resolutions of 60 000, 80 000, and 100 000. We considered the RV precision as calculated on the whole spectra, after discarding strongly polluted areas, and after applying a perfect telluric correction. In our simulations we paid particular attention to the details of the convolution and sampling of the spectra, and we discuss their impact on the final spectra.

Results:

Our simulations show that the most important parameter ruling the difference in attainable precision between the considered bands is the spectral type. For M0-M3 stars, the bands that deliver the most precise RV measurements are the Z, Y, and H band, with relative merits depending on the parameters of the simulation. For M6-M9 stars, the bands show a difference in precision that is within a factor of ∼2 and does not clearly depend on the band; this difference is reduced to a factor smaller than ∼1.5 if we consider a non-rotating star seen at high resolution. We also show that an M6-M9 spectrum will deliver a precision about two times better as an M0-M3 spectra with the same signal-to-noise ratio. Finally, we note that the details of modelling the Earth atmosphere and interpreting the results have a significant impact on which wavelength regions are discarded when setting a limit threshold at 2-3%.

TW Hydrae's Protoplanetary Disk has a "Puffed up" Inner Rim

The Effects of Self-Shadowing by a Puffed up Inner Rim in Scattered Light Images of Protoplanetary Disks

Author:

Dong

Abstract:

We explore whether protoplanetary disks with self-shadowing from puffed up inner rims exhibit observable features in scattered light images. We use both self-consistent hydrostatic equilibrium calculations and parameterized models to produce the vertically puffed up inner rims. We find that, in general, the transition between the shadowed and flared regions occurs in a smooth manner over a broad radius range, and no sudden jump exists at the outer edge of the shadow in either the disk temperature or density structures. As a result, a puffed up rim cannot create sharp ring/arc/spiral-arm-like features in the outer disk as have been detected in recent direct NIR imaging of disks. On the other hand, if the puffed up rim has a sharp edge in the vertical direction, the shadowing effect can produce a distinct 3-stage broken power law in the radial intensity profile of the scattered light, with 2 steep surface brightness radial profiles in the inner and outer disk joined by a shallow transition region around the shadow edge. These types of scattered light profiles may have already been observed, such as in the recent Subaru direct imaging of the TW Hydrae system.

A New Method for Characterizing Very-Low-Mass Companions (ie Brown and Red Dwarfs)

A New Method for Characterizing Very-Low-Mass Companions with Low Resolution Near-Infrared Spectroscopy

Authors:

Rice et al

Abstract:

We present a new and computationally efficient method for characterizing very low mass companions using low resolution (R∼30) near-infrared (YJH) spectra from high contrast imaging campaigns with integral field spectrograph (IFS) units. We conduct a detailed quantitative comparison of the efficacy of this method through tests on simulated data comparable in spectral coverage and resolution to the currently operating direct imaging systems around the world. In particular, we simulate Project 1640 data as an example of the use, accuracy, and precision of this technique. We present results from comparing simulated spectra of M, L, and T dwarfs with a large and finely-sampled grid of synthetic spectra using Markov Chain Monte Carlo techniques. We determine the precision and accuracy of effective temperature and surface gravity inferred from fits to PHOENIX dusty and cond, which we find reproduce the low-resolution spectra of all objects within the adopted flux uncertainties. Uncertainties in effective temperature decrease from ±100-500 K for M dwarfs to as small as ±30 K for some L and T spectral types. Surface gravity is constrained to within 0.2-0.4 dex for mid-L through T dwarfs, but uncertainties are as large as 1.0 dex or more for M dwarfs. Results for effective temperature from low-resolution YJH spectra generally match predictions from published spectral type-temperature relationships except for L-T transition objects and young objects. Single-band spectra (i.e., narrower wavelength coverage) result in larger uncertainties and often discrepant results, suggesting that high contrast IFS observing campaigns can compensate for low spectral resolution by expanding the wavelength coverage for reliable characterization of detected companions.

Using Near IR Spectroscopy to Characterize Transiting Exoplanets

Using near infra-red spectroscopy for characterization of transiting exoplanets

Authors:

Aronson et al

Abstract:

We propose a method for observing transiting exoplanets with near-infrared high-resolution spectrometers. We aim to create a robust data analysis method for recovering atmospheric transmission spectra from transiting exoplanets over a wide wavelength range in the near infrared. By using an inverse method approach, combined with stellar models and telluric transmission spectra, the method recovers the transiting exoplanet's atmospheric transmittance at high precision over a wide wavelength range. We describe our method and have tested it by simulating observations. This method is capable of recovering transmission spectra of high enough accuracy to identify absorption features from molecules such as O2, CH4, CO2, and H2O. This accuracy is achievable for Jupiter-size exoplanetsat S/N that can be reached for 8m class telescopes using high-resolution spectrometers (R>20 000) during a single transit, and for Earth-size planets and super-Earths transiting late K or M dwarf stars at S/N reachable during observations of less than 10 transits. We also analyse potential error sources to show the robustness of the method. Detection and characterization of atmospheres of both Jupiter-size planets and smaller rocky planets looks promising using this set-up.

Methane and Ammonia in the Near-infrared Spectra of Late T Dwarf Atmospheres

Methane and Ammonia in the near-infrared spectra of late T dwarfs

Authors:

Canty et al

Abstract:

Analysis of T dwarfs using model atmospheres has been hampered by the absence of reliable line lists for methane and ammonia. Newly computed high temperature line lists for both of these important molecules are now available, so it is timely to investigate the appearance of the various absorption features in T dwarfs in order to better understand their atmospheres and validate the new line lists. We present high quality R~5000 Gemini/NIFS 1.0-2.4 microns spectra of the T8 standard 2MASS 0415-0935 and the T9 standard UGPS 0722-0540. We use these spectra to identify numerous methane and ammonia features not previously seen and we discuss the implications for our understanding of T dwarf atmospheres. Among our results, we find that ammonia is the dominant opacity source between ~1.233-1.266 microns in UGPS 0722-0540, and we tentatively identify several absorption features in this wavelength range in the T9's spectrum which may be due entirely to ammonia opacity. Our results also suggest that water rather than methane is the dominant opacity source in the red half of the J-band of the T8 dwarf. Water appears to be the main absorber in this wavelength region in the T9 dwarf until ~1.31 microns, when methane starts to dominate.