arXiv subjects

Ignas A. G. Snellen

Publications and source records attributed to Ignas A. G. Snellen.

At least 19 recordsLinked to original sources

arXiv2024

The ESO SupJup Survey III: Confirmation of 13CO in YSES 1 b and Atmospheric Detection of YSES 1 c with CRIRES+

High-resolution spectroscopic characterization of young super-Jovian planets enables precise constraints on elemental and isotopic abundances of their atmospheres. As part of the ESO SupJup Survey, we present high-resolution spectral observations of two wide-orbit super-Jupiters in YSES 1 (or TYC 8998-760-1) using the upgraded VLT/CRIRES+ (R~100,000) in K-band. We carry out free atmospheric retrieval analyses to constrain chemical and isotopic abundances, temperature structures, rotation velocities, and radial velocities. We confirm the previous detection of 13CO in YSES 1 b at a higher significance of 12.6σ, but point to a higher 12CO/13CO ratio of 88+/-13 (1σ confidence interval), consistent with the primary's isotope ratio 66+/-5. We retrieve a solar-like composition in YSES 1 b with a C/O=0.57+/-0.01, indicating a formation via gravitational instability or core accretion beyond the CO iceline. Additionally, the observations lead to detections of H2O and CO in the outer planet YSES 1 c at 7.3σ and 5.7σ, respectively. We constrain the atmospheric C/O ratio of YSES 1 c to be either solar or subsolar (C/O=0.36+/-0.15), indicating the accretion of oxygen-rich solids. The two companions have distinct vsini, 5.34+/-0.14 km/s for YSES 1 b and 11.3+/-2.1 km/s for YSES 1 c, despite their similar natal environments. This may indicate different spin axis inclinations or effective magnetic braking by the long-lived circumplanetary disk around YSES 1 b. YSES 1 represents an intriguing system for comparative studies of super-Jovian companions and linking present atmospheres to formation histories.

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arXiv2024

Peering above the clouds of the warm Neptune GJ 436b with CRIRES+

Exoplanets with masses between Earth and Neptune are amongst the most commonly observed, yet their properties are poorly constrained. Their transmission spectra are often featureless, which indicate either high-altitude clouds or a high atmospheric metallicity. The archetypical warm Neptune GJ 436b is such a planet showing a flat transmission spectrum in observations with the Hubble Space Telescope (HST). Ground-based high-resolution spectroscopy (HRS) effectively probes exoplanet atmospheres at higher altitudes and can therefore be more sensitive to absorption coming from above potential cloud decks. In this paper we aim to investigate this for the exoplanet GJ 436b. We present new CRIRES+ HRS transit data of GJ 436b. Three transits were observed, but since two were during bad weather conditions, only one transit was analyzed. The radiative transfer code petitRADTRANS was used to create atmospheric models for cross-correlation and signal-injection purposes, including absorption from H$_2$O, CH$_4$, and CO. No transmission signals were detected, but atmospheric constraints can be derived. Injection of artificial transmission signals indicate that if GJ 436b would have a cloud deck at pressures P>10 mbar and a <300$\times$ solar metallicity, these CRIRES+ observations should have resulted in a detection. We estimate that the constraints presented here from one ground-based HRS transit are slightly better than those obtained with four HST transits. Combining HRS data from multiple transits is an interesting avenue for future studies of exoplanets with high-altitude clouds.

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arXiv2023

Observability of silicates in volatile atmospheres of super-Earths and sub-Neptunes

Many of the confirmed short period super-Earths and smaller sub-Neptunes are sufficiently irradiated for the surface silicates to be sustained in a long-lasting molten state. While there is no direct evidence of magma ocean influence on exoplanets, theory suggests that due to outgassing and diverse evolution paths, a wide range of resulting atmospheric compositions should be possible. Atmospheric contamination caused by the outgassing of the underlying magma ocean is potentially detectable using low resolution spectroscopy. The James Webb Space Telescope provides the necessary spectral coverage and sensitivity to characterise smaller planets, including lava worlds. In this light, we assess observability of outgassed silicates submerged in volatile atmospheres on the edge of the evaporation valley. By placing a hypothetical 2 R${_\oplus}$ planet around a Sun-like star, we self-consistently model, in 1-D, a wide range of potential atmospheric compositions, including thermal structure and outgassing. We focus on atmospheres rich in H, C and N. We assess diverse chemistry of silicates and volatiles, and what features of outgassed species could be detected via emission spectroscopy using MIRI LRS. Results indicate that even for substantial volatile envelopes, strong in infrared opacity, the presence of silicates causes deep thermal inversions, affecting emission. Similar to pure lava worlds, SiO remains the only outgassed species with major infrared, 5 and 9 \textmu m, bands. However, even a small amount of volatiles, especially of H2O and H-, may hinder its observability. We also find that the C/O ratio plays a large role in determining the abundance of SiO. Detecting SiO on a strongly irradiated planet could indicate an atmosphere with high metallicity and a low C/O ratio, which may be a result of efficient interaction between the atmosphere and the underlying melt.

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arXiv2022

Occurrence rate of hot Jupiters orbiting red giant stars

Hot Jupiters form an enigmatic class of object with yet unclear formation pathways. Determination of their occurrence rates as function orbit, planet and stellar mass, and system age, can be an important ingredient for understanding how they form. To date, various Hot Jupiters have been discovered orbiting red giant stars and deriving their incidence would be highly interesting. In this study we aim to determine the number of Hot Jupiters in a well-defined sample of red giants, estimate their occurrence rate and compare it with that for A, F and G-type stars. A sample of 14474 red giant stars, with estimated radii between 2 and 5 $R_\odot$, was selected using Gaia to coincide with observations by the NASA TESS mission. Subsequently, the TESS light curves were searched for transits from Hot Jupiters. The detection efficiency was determined using injected signals, and the results further corrected for the geometric transit probability to estimate the occurrence rate. Three previously confirmed Hot Jupiters were found in the TESS data, in addition to one other TESS Object of Interest, and two M-dwarf companions. This results in an occurrence rate of $0.37^{+0.29}_{-0.09}$%. Due to the yet large uncertainties, this cannot be distinguished from that of A-, F- and G-type stars. We argue that it is unlikely that planet engulfment in expanding red giants plays yet an important role in this sample.

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arXiv2022

Transmission spectroscopy of the ultra-hot Jupiter MASCARA-4 b: Disentangling the hydrostatic and exospheric regimes of ultra-hot Jupiters

Ultra-hot Jupiters (UHJs), rendering the hottest planetary atmospheres, offer great opportunities of detailed characterisation with high-resolution spectroscopy. MASCARA-4 b is a recently discovered close-in gas giant belonging to this category. In order to refine system and planet parameters, we carried out radial velocity measurements and transit photometry with the CORALIE spectrograph and EulerCam at the Swiss 1.2m Euler telescope. We observed two transits of MASCARA-4 b with the high-resolution spectrograph ESPRESSO at ESO's Very Large Telescope. We searched for atomic, ionic, and molecular species via individual absorption lines and cross-correlation techniques. These results are compared to literature studies on UHJs characterised to date. With CORALIE and EulerCam observations, we updated the mass of MASCARA-4 b (1.675 +/- 0.241 Jupiter masses) as well as other system and planet parameters. In the transmission spectrum derived from ESPRESSO observations, we resolve excess absorption by H$α$, H$β$, Na D1 & D2, Ca+ H & K, and a few strong individual lines of Mg, Fe and Fe+. We also present the cross-correlation detection of Mg, Ca, Cr, Fe and Fe+. The absorption strength of Fe+ significantly exceeds the prediction from a hydrostatic atmospheric model, as commonly observed in other UHJs. We attribute this to the presence of Fe+ in the exosphere due to hydrodynamic outflows. This is further supported by the positive correlation of absorption strengths of Fe+ with the H$α$ line. Comparing transmission signatures of various species in the UHJ population allows us to disentangle the hydrostatic regime (as traced via the absorption by Mg and Fe) from the exospheres (as probed by H$α$ and Fe+) of the strongly irradiated atmospheres.

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arXiv2021

Characterizing the protolunar disk of the accreting companion GQ Lupi B

GQ Lup B is a young and accreting, substellar companion that appears to drive a spiral arm in the circumstellar disk of its host star. We report high-contrast imaging observations of GQ Lup B with VLT/NACO at 4-5 $μ$m and medium-resolution integral field spectroscopy with VLT/MUSE. The optical spectrum is consistent with an M9 spectral type, shows characteristics of a low-gravity atmosphere, and exhibits strong H$α$ emission. The $H-M'$ color is $\gtrsim$1 mag redder than field dwarfs with similar spectral types and a detailed analysis of the spectral energy distribution (SED) from optical to mid-infrared wavelengths reveals excess emission in the $L'$, NB4.05, and $M'$ bands. The excess flux is well described by a blackbody component with $T_\mathrm{disk} \approx 460$ K and $R_\mathrm{disk} \approx 65\,R_\mathrm{J}$ and is expected to trace continuum emission from small grains in a protolunar disk. We derive an extinction of $A_V \approx 2.3$ mag from the broadband SED with a suspected origin in the vicinity of the companion. We also combine 15 yr of astrometric measurements and constrain the mutual inclination with the circumstellar disk to $84 \pm 9$ deg, indicating a tumultuous dynamical evolution or a stellar-like formation pathway. From the measured H$α$ flux and the estimated companion mass, $M_\mathrm{p} \approx 30\,M_\mathrm{J}$, we derive an accretion rate of $\dot{M} \approx 10^{-6.5}\,M_\mathrm{J}\,\mathrm{yr}^{-1}$. We speculate that the disk is in a transitional stage in which the assembly of satellites from a pebble reservoir has opened a central cavity while GQ Lup B is in the final stages of its formation.

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arXiv2021

Measuring titanium isotope ratios in exoplanet atmospheres

[abridged] Measurements of relative isotope abundances can provide unique insights into the formation and evolution histories of celestial bodies. The five stable isotopes of titanium are used to study the early history of the solar system and constrain Galactic chemical models. The minor isotopes of titanium are relatively abundant compared to those of other elements, making them more accessible for challenging observations. We assessed the feasibility of performing titanium isotope measurements in exoplanet atmospheres, and in particular, whether processing techniques used for high-resolution spectroscopy affect the derived isotope ratios. We used an archival high-dispersion CARMENES spectrum of the M-dwarf GJ 1002 as a proxy for an exoplanet observed at very high signal-to-noise. Spectral retrievals using petitRADTRANS models were performed on both narrow (7045-7090 Å) and wide (7045-7500 Å) wavelength regions, resulting in isotope ratios and uncertainties. These retrievals were repeated on the spectrum with its continuum removed to mimic typical high-dispersion exoplanet observations. The relative abundances of all minor Ti isotopes are found to be slightly enhanced compared to terrestrial values. Loss of continuum information from broadband spectral filtering has little effect on the isotope ratios. The CARMENES spectrum was subsequently degraded by adding varying levels of Gaussian noise to estimate the signal-to-noise requirements for future exoplanet atmospheric observations. For the wide wavelength range, a spectrum with signal-to-noise of 5 is required to determine the isotope ratios with relative errors $\lesssim$10%. Super Jupiters at large angular separations from their host star are the most accessible exoplanets, requiring about an hour of observing time on 8-meter-class telescopes, and less than a minute of observing time with the future Extremely Large Telescope.

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arXiv2021

The 12CO/13CO isotopologue ratio of a young, isolated brown dwarf. Possibly distinct formation pathways of super-Jupiters and brown dwarfs

Linking atmospheric characteristics of planets to their formation pathways is a central theme in the study of extrasolar planets. Although the 12C/13C isotope ratio shows little variation in the solar system, the atmosphere of a super-Jupiter was recently shown to be rich in 13CO, possibly as a result of dominant ice accretion beyond the CO snowline during its formation. In this paper we aim to measure the 12CO/13CO isotopologue ratio of a young, isolated brown dwarf. While the general atmospheric characteristics of young, low mass brown dwarfs are expected to be very similar to those of super-Jupiters, their formation pathways may be different, leading to distinct isotopologue ratios. We analyse archival K-band spectra of the L dwarf 2MASS J03552337+1133437 taken with NIRSPEC at the Keck telescope. A free retrieval analysis is applied to the data to determine the isotopologue ratio 12CO/13CO in its atmosphere. The isotopologue 13CO, is detected in the atmosphere through the cross-correlation method at a signal-to-noise of ~8.4. The detection significance is determined to be ~9.5 sigma using Bayesian model comparison between two retrieval models. We retrieve an isotopologue ratio 12CO/13CO of 97(+25/-18), marginally higher than the local interstellar standard. Its C/O ratio of ~0.56 is consistent with the solar value. Although only one super-Jupiter and one brown dwarf have now a measured 12CO/13CO ratio, it is intriguing that they are different, possibly hinting to distinct formation pathways. Albeit spectroscopic similarities, isolated brown dwarfs may experience a top-down formation via gravitational collapse, which resembles star formation, while giant exoplanets favorably form through core accretion, which potentially alters isotopologue ratios in their atmospheres depending on the material they accrete from protoplanetary disks. (abridged)

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arXiv2020

Is TiO emission present in the ultra-hot Jupiter WASP-33b? A reassessment using the improved ExoMol Toto line list

[abridged] Efficient absorption of stellar UV and visible radiation by TiO and VO is predicted to drive temperature inversions in the upper atmospheres of hot Jupiters. However, few inversions or detections of TiO or VO have been reported, and results are often contradictory. Using the improved ExoMol Toto line list, we searched for TiO emission in the dayside spectrum of WASP-33b using the same data in which the molecule was previously detected with an older line list at 4.8$σ$. We intended to confirm the molecular detection and quantify the signal improvement offered by the ExoMol Toto line list. Data from the High Dispersion Spectrograph on the Subaru Telescope was extracted and reduced in an identical manner to the previous study. Stellar and telluric contamination were then removed. High-resolution TiO emission models of WASP-33b were created using the radiative transfer code petitRADTRANS and cross-correlated with the data. We measure a 4.3$σ$ TiO emission signature using the ExoMol Toto models, corresponding to a WASP-33b orbital velocity semi-amplitude of $K_\mathrm{p}=252.9^{+5.0}_{-5.3}\ \mathrm{km\ s^{-1}}$ and a system velocity of $v_\mathrm{sys}=-23.0^{+4.7}_{-4.6}\ \mathrm{km\ s^{-1}}$. Injection-recovery tests using models based on the new and earlier line lists indicate that if the new models provide a perfect match to the planet spectrum, the significance of the TiO detection should have increased by a factor of $\sim$2. Although the TiO signal we find is statistically significant, comparison with previous works makes our result too ambiguous to claim a clear-cut detection. Unexpectedly, the new ExoMol Toto models provide a weaker signal than that found previously, which is offset in $K_\mathrm{p}$-$v_\mathrm{sys}$ space. This sheds some doubt on both detections, especially in light of a recently published TiO non-detection using a different dataset.

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arXiv2020

Diffraction-limited integral-field spectroscopy for extreme adaptive optics systems with the Multi-Core fiber-fed Integral-Field Unit

Direct imaging instruments have the spatial resolution to resolve exoplanets from their host star. This enables direct characterization of the exoplanets atmosphere, but most direct imaging instruments do not have spectrographs with high enough resolving power for detailed atmospheric characterization. We investigate the use of a single-mode diffraction-limited integral-field unit that is compact and easy to integrate into current and future direct imaging instruments for exoplanet characterization. This achieved by making use of recent progress in photonic manufacturing to create a single-mode fiber-fed image reformatter. The fiber-link is created with 3D printed lenses on top of a single-mode multi-core fiber that feeds an ultrafast laser inscribed photonic chip that reformats the fiber into a pseudo-slit. We then couple it to a first-order spectrograph with a triple stacked volume phase holographic grating for a high efficiency over a large bandwidth. The prototype system has had a successful first-light observing run at the 4.2 meter William Herschel Telescope. The measured on-sky resolving power is between 2500 and 3000, depending on the wavelength. With our observations we show that single-mode integral-field spectroscopy is a viable option for current and future exoplanet imaging instruments.

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arXiv2020

A weak spectral signature of water vapour in the atmosphere of HD 179949 b at high spectral resolution in the L-band

High resolution spectroscopy (R > 20,000) is currently the only known method to constrain the orbital solution and atmospheric properties of non-transiting hot Jupiters. It does so by resolving the spectral features of the planet into a forest of spectral lines and directly observing its Doppler shift while orbiting the host star. In this study, we analyse VLT/CRIRES (R = 100,000) L-band observations of the non-transiting giant planet HD 179949 b centred around 3.5 microns. We observe a weak (3.0 sigma, or S/N = 4.8) spectral signature of H2O in absorption contained within the radial velocity of the planet at superior-conjunction, with a mild dependence on the choice of line list used for the modelling. Combining this data with previous observations in the K-band, we measure a detection significance of 8.4 sigma for an atmosphere that is most consistent with a shallow lapse-rate, solar C/O ratio, and with CO and H2O being the only major sources of opacity in this wavelength range. As the two sets of data were taken three years apart, this points to the absence of strong radial-velocity anomalies due, e.g., to variability in atmospheric circulation. We measure a projected orbital velocity for the planet of KP = (145.2 +- 2.0)kms^{-1} (1 sigma) and improve the error bars on this parameter by ~70%. However, we only marginally tighten constraints on orbital inclination (66.2 +3.7 -3.1 degrees) and planet mass (0.963 +0.036 -0.031 Jupiter masses), due to the dominant uncertainties of stellar mass and semi-major axis. Follow ups of radial-velocity planets are thus crucial to fully enable their accurate characterisation via high resolution spectroscopy.

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arXiv2020

No Massive Companion to the Coherent Radio-Emitting M Dwarf GJ 1151

The recent detection of circularly polarized, long-duration (>8 hr) low-frequency (~150 MHz) radio emission from the M4.5 dwarf GJ 1151 has been interpreted as arising from a star-planet interaction via the electron cyclotron maser instability. The existence or parameters of the proposed planets have not been determined. Using 20 new HARPS-N observations, we put 99th-percentile upper limits on the mass of any close companion to GJ 1151 at Msini < 5.6 M earth. With no stellar, brown dwarf, or giant planet companion likely in a close orbit, our data are consistent with detected radio emission emerging from a magnetic interaction between a short-period terrestrial-mass planet and GJ 1151.

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arXiv2019

Testing the Detectability of Extraterrestrial $\mathrm{O}_2$ with the ELTs using Real Data with Real Noise

The future extremely large telescopes (ELTs) are expected to be powerful tools to probe the atmospheres of extrasolar planets using high-dispersion spectroscopy, with the potential to detect molecular oxygen in Earth-like planets transiting nearby, late-type stars. So far, simulations have concentrated on the optical 7600 Å A-band of oxygen using synthetic noise distributions. In this paper, we build upon previous work to predict the detectability of molecular oxygen in nearby, temperate planets by using archival, time-series data of Proxima Centauri from the high-dispersion UVES spectrograph on ESO's Very Large Telescope (VLT). The brightest transiting M-dwarfs are expected to be about 25 times fainter than Proxima, a factor that is similar to the difference in light-gathering power between the VLT and the future ELTs. By injecting synthetic oxygen transmission signals into the UVES data, the $\mathrm{O}_2$ detectability can be studied in the presence of real data with real noise properties. Correcting for the relatively low throughput ($\sim$4%) of the Proxima spectra to an assumed 20% throughput for a high-dispersion spectrograph on the European ELT, we find that the molecular oxygen signature of an Earth-twin transiting a nearby ($d \approx 7 \,\mathrm{pc}$) M5V star can be detected in 20-50 transits (a total of 70-175 hours of observing time). This estimate using more realistic simulations is close to previous predictions. Novel concepts that increase the instrumental throughput can further reduce the time span over which such observations need to be taken.

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arXiv2018

Ground-based detection of an extended helium atmosphere in the Saturn-mass exoplanet WASP-69b

Hot gas giant exoplanets can lose part of their atmosphere due to strong stellar irradiation, affecting their physical and chemical evolution. Studies of atmospheric escape from exoplanets have mostly relied on space-based observations of the hydrogen Lyman-α line in the far ultraviolet which is strongly affected by interstellar absorption. Using ground-based high-resolution spectroscopy we detect excess absorption in the helium triplet at 1083 nm during the transit of the Saturn-mass exoplanet WASP-69b, at a signal-to-noise ratio of 18. We measure line blue shifts of several km/s and post transit absorption, which we interpret as the escape of part of the atmosphere trailing behind the planet in comet-like form. [Additional notes by authors: Furthermore, we provide upper limits for helium signals in the atmospheres of the exoplanets HD 209458b, KELT-9b, and GJ 436b. We investigate the host stars of all planets with detected helium signals and those of the three planets we derive upper limits for. In each case we calculate the X-ray and extreme ultraviolet flux received by these planets. We find that helium is detected in the atmospheres of planets (orbiting the more active stars and) receiving the larger amount of irradiation from their host stars.]

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arXiv2016

The slow spin of the young sub-stellar companion GQ Lupi b and its orbital configuration

The spin of a planet or brown dwarf is related to the accretion process, and therefore studying spin can help promote our understanding of the formation of such objects. We present the projected rotational velocity of the young sub-stellar companion GQ Lupi b, along with its barycentric radial velocity. The directly imaged exoplanet or brown dwarf companion joins a small but growing ensemble of wide-orbit sub-stellar companions with a spin measurement. The GQ Lupi system was observed at high spectral resolution (R ~ 100000), and in the analysis we made use of both spectral and spatial filtering to separate the signal of the companion from that of the host star. We detect both CO (S/N=11.6) and H2O (S/N=7.7) in the atmosphere of GQ Lupi b by cross-correlating with model spectra, and we find it to be a slow rotator with a projected rotational velocity of $5.3^{+0.9}_{-1.0}$ km/s. The slow rotation is most likely due to its young age of < 5 Myr, as it is still in the process of accreting material and angular momentum. We measure the barycentric radial velocity of GQ Lupi b to be $2.0 \pm 0.4$ km/s, and discuss the allowed orbital configurations and their implications for formation scenarios for GQ Lupi b.

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arXiv2013

Identifying new opportunities for exoplanet characterisation at high spectral resolution

[Abridged] Recently, there have been a series of detections of molecules in the atmospheres of extrasolar planets using high spectral resolution (R~100,000) observations, mostly using the CRyogenic high-resolution InfraRed Echelle Spectrograph (CRIRES) on the Very Large Telescope. These measurements are able to resolve molecular bands into individual absorption lines. Observing many lines simultaneously as their Doppler shift changes with time allows the detection of specific molecules in the atmosphere of the exoplanet. We performed simulations of high-resolution CRIRES observations of a planet's thermal emission and transit between 1-5 micron and performed a cross-correlation analysis on these results to assess how well the planet signal can be extracted. We also simulated day-side and night-side spectra at high spectral resolution for planets with and without a day-side temperature inversion, based on the cases of HD 189733b and HD 209458b. Several small wavelength regions in the L-band promise to yield cross-correlation signals from the thermal emission of hot Jupiters that can exceed those of the current detections by up to a factor of 2-3 for the same integration time. For transit observations, the H-band is also attractive, with the H, K, and L-band giving cross-correlation signals of similar strength. High-resolution night-side spectra of hot Jupiters can give cross-correlation signals as high as the day-side, or even higher. We show that there are many new possibilities for high-resolution observations of exoplanet atmospheres that have expected planet signals at least as high as those already detected. Hence, high-resolution observations at well-chosen wavelengths and at different phases can improve our knowledge about hot Jupiter atmospheres significantly, already with currently available instrumentation.

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arXiv2013

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.

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arXiv2010

The orbital motion, absolute mass, and high-altitude winds of exoplanet HD209458b

For extrasolar planets discovered using the radial velocity method, the spectral characterization of the host star leads to a mass-estimate of the star and subsequently of the orbiting planet. In contrast, if also the orbital velocity of the planet would be known, the masses of both star and planet could be determined directly using Newton's law of gravity, just as in the case of stellar double-line eclipsing binaries. Here we report on the detection of the orbital velocity of extrasolar planet HD209458b. High dispersion ground-based spectroscopy during a transit of this planet reveals absorption lines from carbon monoxide produced in the planet atmosphere, which shift significantly in wavelength due to the change in the radial component of the planet orbital velocity. These observations result in a mass determination of the star and planet of 1.00+-0.22 Msun and 0.64+-0.09 Mjup respectively. A ~2 km/sec blueshift of the carbon monoxide signal with respect to the systemic velocity of the host star suggests the presence of a strong wind flowing from the irradiated dayside to the non-irradiated nightside of the planet within the 0.01-0.1 mbar atmospheric pressure range probed by these observations. The strength of the carbon monoxide signal suggests a CO mixing ratio of 1-3x10-3 in this planet's upper atmosphere.

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