Evidence against a strong thermal inversion in HD 209458 b from high-dispersion spectroscopy

Broadband secondary-eclipse measurements of hot Jupiters have indicated the existence of atmospheric thermal inversions, but their presence is difficult to determine from broadband measurements because of degeneracies between molecular abundances and temperature structure. We apply high-resolution (R = 100 000) infrared spectroscopy to probe the temperature-pressure profile of HD 209458 b. This bright, transiting hot-Jupiter has long been considered the gold standard for a hot Jupiter with an inversion layer, but this has been challenged in recent publications. We observed the thermal dayside emission of HD 209458 b with CRIRES / VLT during three nights, targeting the carbon monoxide band at 2.3 microns. Thermal inversions give rise to emission features, which means that detecting emission lines in the planetary spectrum, as opposed to absorption lines, would be direct evidence of a region in which the temperature increases with altitude. We do not detect any significant absorption or emission of CO in the dayside spectrum of HD 209458 b, although cross-correlation with template spectra either with CO absorption lines or with weak emission at the core of the lines show a low-significance correlation signal with a signal-to-noise ratio of 3 - 3.5. Models with strong CO emission lines show a weak anti-correlation with similar or lower significance levels. Furthermore, we found no evidence of absorption or emission from H2O at these wavelengths. The non-detection of CO in the dayside spectrum of HD 209458 b is interesting in light of a previous CO detection in the transmission spectrum. That there is no signal indicates that HD 209458 b either has a nearly isothermal atmosphere or that the signal is heavily muted. Assuming a clear atmosphere, we can rule out a full-disc dayside inversion layer in the pressure range 1 bar to 1 mbar.Comment: 11 pages, 6 figures, accepted for publication in Astronomy & Astrophysic

Finding extraterrestrial life using ground-based high-resolution spectroscopy

Exoplanet observations promise one day to unveil the presence of extraterrestrial life. Atmospheric compounds in strong chemical disequilibrium would point to large-scale biological activity just as oxygen and methane do in the Earth's atmosphere. The cancellation of both the Terrestrial Planet Finder and Darwin missions means that it is unlikely that a dedicated space telescope to search for biomarker gases in exoplanet atmospheres will be launched within the next 25 years. Here we show that ground-based telescopes provide a strong alternative for finding biomarkers in exoplanet atmospheres through transit observations. Recent results on hot Jupiters show the enormous potential of high-dispersion spectroscopy to separate the extraterrestrial and telluric signals making use of the Doppler shift of the planet. The transmission signal of oxygen from an Earth-twin orbiting a small red dwarf star is only a factor 3 smaller than that of carbon monoxide recently detected in the hot Jupiter tau Bootis b, albeit such a star will be orders of magnitude fainter. We show that if Earth-like planets are common, the planned extremely large telescopes can detect oxygen within a few dozen transits. Ultimately, large arrays of dedicated flux collector telescopes equipped with high-dispersion spectrographs can provide the large collecting area needed to perform a statistical study of life-bearing planets in the solar neighborhood.Comment: 22 pages, 3 figures; published in Ap

Low-mass eclipsing binaries in the WFCAM Transit Survey : The persistence of the M-dwarf radius inflation problem

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society. © 2018 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.We present the characterization of five new short-period low-mass eclipsing binaries (LMEBs) from the WFCAM Transit Survey. The analysis was performed by using the photometric WFCAM J-mag data and additional low- and intermediate-resolution spectroscopic data to obtain both orbital and physical properties of the studied sample. The light curves and the measured radial velocity curves were modelled simultaneously with the JKTEBOP code, with Markov chain MonteCarlo simulations for the error estimates. The best-model fit have revealed that the investigated detached binaries are in very close orbits, with orbital separations of 2.9 ≤ a ≤ 6.7R⊙ and short periods of 0.59 ≤ Porb ≤ 1.72 d, approximately. We have derived stellar masses between 0.24 and 0.72M⊙ and radii ranging from 0.42 to 0.67 R⊙. The great majority of the LMEBs in our sample has an estimated radius far from the predicted values according to evolutionary models. The components with derived masses of M < 0.6M⊙ present a radius inflation of ~9 per cent or more. This general behaviour follows the trend of inflation for partially radiative stars proposed previously. These systems add to the increasing sample of low-mass stellar radii that are not well-reproduced by stellarmodels. They further highlight the need to understand the magnetic activity and physical state of small stars. Missions like TESS will provide many such systems to perform high-precision radius measurements to tightly constrain low-mass stellar evolution models.Peer reviewe

Detection of the secondary eclipse of Qatar-1b in the Ks band

Qatar-1b is a close-orbiting hot Jupiter ($R_p\simeq 1.18$ $R_J$, $M_p\simeq 1.33$ $M_J$) around a metal-rich K-dwarf, with orbital separation and period of 0.023 AU and 1.42 days. We have observed the secondary eclipse of this exoplanet in the Ks band with the objective of deriving a brightness temperature for the planet and providing further constraints to the orbital configuration of the system. We obtained near-infrared photometric data from the ground by using the OMEGA2000 instrument at the 3.5 m telescope at Calar Alto (Spain) in staring mode, with the telescope defocused. We have used principal component analysis (PCA) to identify correlated systematic trends in the data. A Markov chain Monte Carlo analysis was performed to model the correlated systematics and fit for the secondary eclipse of Qatar-1b using a previously developed occultation model. We adopted the prayer bead method to assess the effect of red noise on the derived parameters. We measured a secondary eclipse depth of $0.196\%^{+0.071\%}_{-0.051\%}$, which indicates a brightness temperature in the Ks band for the planet of $1885^{+212}_{-168}$ K. We also measured a small deviation in the central phase of the secondary eclipse of $-0.0079^{+0.0162}_{-0.0043}$, which leads to a value for $e\cos{\omega}$ of $-0.0123^{+0.0252}_{-0.0067}$. However, this last result needs to be confirmed with more data.Comment: 6 pages, 6 figures, accepted for publication in A&

Combining high-dispersion spectroscopy (HDS) with high contrast imaging (HCI): Probing rocky planets around our nearest neighbors

Aims: In this work, we discuss a way to combine High Dispersion Spectroscopy and High Contrast Imaging (HDS+HCI). For a planet located at a resolvable angular distance from its host star, the starlight can be reduced up to several orders of magnitude using adaptive optics and/or coronography. In addition, the remaining starlight can be filtered out using high-dispersion spectroscopy, utilizing the significantly different (or Doppler shifted) high-dispersion spectra of the planet and star. In this way, HDS+HCI can in principle reach contrast limits of ~1e-5 x 1e-5, although in practice this will be limited by photon noise and/or sky-background. Methods: We present simulations of HDS+HCI observations with the E-ELT, both probing thermal emission from a planet at infrared wavelengths, and starlight reflected off a planet atmosphere at optical wavelengths. For the infrared simulations we use the baseline parameters of the E-ELT and METIS instrument, with the latter combining extreme adaptive optics with an R=100,000 IFS. We include realistic models of the adaptive optics performance and atmospheric transmission and emission. For the optical simulation we also assume R=100,000 IFS with adaptive optics capabilities at the E-ELT. Results: One night of HDS+HCI observations with the E-ELT at 4.8 um (d_lambda = 0.07 um) can detect a planet orbiting alpha Cen A with a radius of R=1.5 R_earth and a twin-Earth thermal spectrum of T_eq=300 K at a signal-to-noise (S/N) of 5. In the optical, with a Strehl ratio performance of 0.3, reflected light from an Earth-size planet in the habitable zone of Proxima Centauri can be detected at a S/N of 10 in the same time frame. Recently, first HDS+HCI observations have shown the potential of this technique by determining the spin-rotation of the young massive exoplanet beta Pictoris b. [abridged]Comment: 9 pages, A&A in press: A movie of the simulation can be found at http://www.strw.leidenuniv.nl/~snellen/simulation.mpe

Detection of carbon monoxide in the high-resolution day-side spectrum of the exoplanet HD 189733b

[Abridged] After many attempts over more than a decade, high-resolution spectroscopy has recently delivered its first detections of molecular absorption in exoplanet atmospheres, both in transmission and thermal emission spectra. Targeting the combined signal from individual lines in molecular bands, these measurements use variations in the planet radial velocity to disentangle the planet signal from telluric and stellar contaminants. In this paper we apply high resolution spectroscopy to probe molecular absorption in the day-side spectrum of the bright transiting hot Jupiter HD 189733b. We observed HD 189733b with the CRIRES high-resolution near-infrared spectograph on the Very Large Telescope during three nights. We detect a 5-sigma absorption signal from CO at a contrast level of ~4.5e-4 with respect to the stellar continuum, revealing the planet orbital radial velocity at 154+4/-3 km s-1. This allows us to solve for the planet and stellar mass in a similar way as for stellar eclipsing binaries, resulting in Ms= 0.846+0.068/-0.049 Msun and Mp= 1.162+0.058/-0.039 MJup. No significant absorption is detected from H2O, CO2 or CH4 and we determined upper limits on their line contrasts here. The detection of CO in the day-side spectrum of HD 189733b can be made consistent with the haze layer proposed to explain the optical to near-infrared transmission spectrum if the layer is optically thin at the normal incidence angles probed by our observations, or if the CO abundance is high enough for the CO absorption to originate from above the haze. Our non-detection of CO2 at 2.0 micron is not inconsistent with the deep CO2 absorption from low resolution NICMOS secondary eclipse data in the same wavelength range. If genuine, the absorption would be so strong that it blanks out any planet light completely in this wavelength range, leaving no high-resolution signal to be measured.Comment: A&A, accepted for publication. Fig.1 reduced in qualit

Applications of a Gaussian process framework for modelling of high-resolution exoplanet spectra

Observations of exoplanet atmospheres in high resolution have the potential to resolve individual planetary absorption lines, despite the issues associated with ground-based observations. The removal of contaminating stellar and telluric absorption features is one of the most sensitive steps required to reveal the planetary spectrum and, while many different detrending methods exist, it remains difficult to directly compare the performance and efficacy of these methods. Additionally, though the standard cross-correlation method enables robust detection of specific atmospheric species, it only probes for features that are expected a priori. Here we present a novel methodology using Gaussian process regression to directly model the components of high-resolution spectra, which partially addresses these issues. We use two archival CRIRES/VLT datasets as test cases, observations of the hot Jupiters HD 189733 b and 51 Pegasi b, recovering injected signals with average line contrast ratios of ∼4.37 × 10−3 and ∼1.39 × 10−3, and planet radial velocities ΔKp = 1.45 ± 1.53 km s−1 and ΔKp = 0.12 ± 0.12 km s−1 from the injection velocities respectively. In addition, we demonstrate an application of the GP method to assess the impact of the detrending process on the planetary spectrum, by implementing injection-recovery tests. We show that standard detrending methods used in the literature negatively affect the amplitudes of absorption features in particular, which has the potential to render retrieval analyses inaccurate. Finally, we discuss possible limiting factors for the non-detections using this method, likely to be remedied by higher signal-to-noise data

Detection of the secondary eclipse of WASP-10b in the Ks-band

WASP-10b, a non-inflated hot Jupiter, was discovered around a K-dwarf in a near circular orbit ($\sim$$0.06$). Since its discovery in 2009, different published parameters for this system have led to a discussion about the size, density, and eccentricity of this exoplanet. In order to test the hypothesis of a circular orbit for WASP-10b, we have observed its secondary eclipse in the Ks-band, where the contribution of planetary light is high enough to be detected from the ground. Observations were performed with the OMEGA2000 instrument at the 3.5-meter telescope at Calar Alto (Almer\'ia, Spain), in staring mode during 5.4 continuous hours, with the telescope defocused, monitoring the target during the expected secondary eclipse. A relative light curve was generated and corrected from systematic effects, using the Principal Component Analysis (PCA) technique. The final light curve was fitted using a transit model to find the eclipse depth and a possible phase shift. The best model obtained from the Markov Chain Monte Carlo analysis resulted in an eclipse depth of $\Delta F$ of $0.137\%^{+0.013\%}_{-0.019\%}$ and a phase offset of $\Delta \phi$ of $-0.0028^{+0.0005}_{-0.0004}$. The eclipse phase offset derived from our modeling has systematic errors that were not taken into account and should not be considered as evidence of an eccentric orbit. The offset in phase obtained leads to a value for $|e\cos{\omega}|$ of $0.0044$. The derived eccentricity is too small to be of any significance.Comment: 8 pages, 10 figure

Prospects for Characterizing the Haziest Sub-Neptune Exoplanets with High Resolution Spectroscopy

Observations to characterize planets larger than Earth but smaller than Neptune have led to largely inconclusive interpretations at low spectral resolution due to hazes or clouds that obscure molecular features in their spectra. However, here we show that high-resolution spectroscopy (R $\sim$ 25,000 to 100,000) enables one to probe the regions in these atmospheres above the clouds where the cores of the strongest spectral lines are formed. We present models of transmission spectra for a suite of GJ1214b-like planets with thick photochemical hazes covering 1 - 5 $\mu$m at a range of resolutions relevant to current and future ground-based spectrographs. Furthermore, we compare the utility of the cross-correlation function that is typically used with a more formal likelihood-based approach, finding that only the likelihood based method is sensitive to the presence of haze opacity. We calculate the signal-to-noise of these spectra, including telluric contamination, required to robustly detect a host of molecules such as CO, CO$_{2}$, H$_{2}$O, and CH$_{4}$, and photochemical products like HCN, as a function of wavelength range and spectral resolution. Spectra in M band require the lowest S/N$_{res}$ to detect multiple molecules simultaneously. CH$_{4}$ is only observable for the coolest models ($T_{\rm{eff}} =$ 412 K) and only in the L band. We quantitatively assess how these requirements compare to what is achievable with current and future instruments, demonstrating that characterization of small cool worlds with ground-based high resolution spectroscopy is well within reach.Comment: Submitted to AAS Journals, revised to reflect referee comments. Posting of this manuscript on the arXiv was coordinated with S. Ghandi et a