Context.
Clouds are ubiquitous in exoplanet atmospheres and they represent a challenge for the model interpretation of their spectra. When generating a large number of model spectra, complex cloud ...models often prove too costly numerically, whereas more efficient models may be overly simplified.
Aims.
We aim to constrain the atmospheric properties of the directly imaged planet HR 8799e with a free retrieval approach.
Methods.
We used our radiative transfer code petitRADTRANS for generating the spectra, which we coupled to the PyMultiNest tool. We added the effect of multiple scattering which is important for treating clouds. Two cloud model parameterizations are tested: the first incorporates the mixing and settling of condensates, the second simply parameterizes the functional form of the opacity.
Results.
In mock retrievals, using an inadequate cloud model may result in atmospheres that are more isothermal and less cloudy than the input. Applying our framework on observations of HR 8799e made with the GPI, SPHERE, and GRAVITY, we find a cloudy atmosphere governed by disequilibrium chemistry, confirming previous analyses. We retrieve that C/O = 0.60
−0.08
+0.07
. Other models have not yet produced a well constrained C/O value for this planet. The retrieved C/O values of both cloud models are consistent, while leading to different atmospheric structures: either cloudy or more isothermal and less cloudy. Fitting the observations with the self-consistent Exo-REM model leads to comparable results, without constraining C/O.
Conclusions.
With data from the most sensitive instruments, retrieval analyses of directly imaged planets are possible. The inferred C/O ratio of HR 8799e is independent of the cloud model and thus appears to be a robust. This C/O is consistent with stellar, which could indicate that the HR 8799e formed outside the CO
2
or CO iceline. As it is the innermost planet of the system, this constraint could apply to all HR 8799 planets.
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. If the ...orbital velocity of the planet could be determined, the masses of both star and planet could be calculated using Newton’s law of gravity, just as in the case of stellar double-line eclipsing binaries. Here we report high-dispersion ground-based spectroscopy of a transit of the extrasolar planet HD 209458b. We see a significant wavelength shift in absorption lines from carbon monoxide in the planet’s atmosphere, which we conclude arises from a change in the radial component of the planet’s orbital velocity. The masses of the star and planet are 1.00 ± 0.22MSun and 0.64 ± 0.09MJup respectively. A blueshift of the carbon monoxide signal of approximately 2 km s−1 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 carbon monoxide mixing ratio of (1–3) × 10−3 in this planet’s upper atmosphere.
The spin of a planet arises from the accretion of angular momentum during its formation, but the details of this process are still unclear. In the Solar System, the equatorial rotation velocities ...and, consequently, spin angular momenta of most of the planets increase with planetary mass; the exceptions to this trend are Mercury and Venus, which, since formation, have significantly spun down because of tidal interactions. Here we report near-infrared spectroscopic observations, at a resolving power of 100,000, of the young extrasolar gas giant planet β Pictoris b (refs 7, 8). The absorption signal from carbon monoxide in the planet's thermal spectrum is found to be blueshifted with respect to that from the parent star by approximately 15 kilometres per second, consistent with a circular orbit. The combined line profile exhibits a rotational broadening of about 25 kilometres per second, meaning that β Pictoris b spins significantly faster than any planet in the Solar System, in line with the extrapolation of the known trend in spin velocity with planet mass.
Context. The cross-correlation technique is a well-tested method for exoplanet characterization, having lead to the detection of various molecules, to constraints on atmospheric temperature profiles, ...wind speeds, and planetary spin rates. A new, potentially powerful application of this technique is the measurement of atmospheric isotope ratios. In particular D/H can give unique insights into the formation and evolution of planets, and their atmospheres. Aims. In this paper we aim to study the detectability of molecular isotopologues in the high-dispersion spectra of exoplanet atmospheres, to identify the optimal wavelength ranges to conduct such studies, and to predict the required observational efforts – both with current and future ground-based instrumentation. Methods. High-dispersion (R = 100 000) thermal emission spectra, and in some cases reflection spectra, were simulated by self-consistent modeling of the atmospheric structures and abundances of exoplanets over a wide range of effective temperatures. These were synthetically observed with a telescope equivalent to the VLT and/or ELT, and analyzed using the cross-correlation technique, resulting in signal-to-noise ratio predictions for the 13CO, HDO, and CH3D isotopologues. Results. We find that for the best observable exoplanets, 13CO is well in range of current telescopes. We predict it will be most favorably detectable at 2.4 μm, just longward of the wavelength regions probed by several high-dispersion spectroscopic observations presented in the literature. CH3D can be best targeted at 4.7 μm, and may be detectable using 40 m-class telescopes for planets below 600 K in equilibrium temperature. In this case, the sky background becomes the dominating noise source for self-luminous planets. HDO is best targeted at 3.7 μm, and is less affected by sky background noise. 40 m-class telescopes may lead to its detection for planets with Tequ below 900 K. It could already be in the range of current 8 m-class telescopes in the case of quenched methane abundances. Finally, if Proxima Cen b is water-rich, the HDO isotopologue could be detected with the ELT in ~1 night of observing time in its reflected-light spectrum. Conclusions. Isotopologues will soon be a part of the exoplanet characterisation tools. Measuring D/H in exoplanets, and ratios of other isotopes, could become a prime science case for the first-light instrument METIS on the European ELT, especially for nearby temperate rocky and ice giant planets. This can provide unique insights in their history of icy-body enrichment and atmospheric evaporation processes.
Hot Jupiters are a class of extrasolar planet that orbit their parent stars at very short distances. They are expected to be tidally locked, which can lead to a large temperature difference between ...their daysides and nightsides. Infrared observations of eclipsing systems have yielded dayside temperatures for a number of transiting planets. The day-night contrast of the transiting extrasolar planet HD 189733b was 'mapped' using infrared observations. It is expected that the contrast between the daysides and nightsides of hot Jupiters is much higher at visual wavelengths, shorter than that of the peak emission, and could be further enhanced by reflected stellar light. Here we report the analysis of optical photometric data obtained over 36 planetary orbits of the transiting hot Jupiter CoRoT-1b. The data are consistent with the nightside hemisphere of the planet being entirely black, with the dayside flux dominating the optical phase curve. This means that at optical wavelengths the planet's phase variation is just as we see it for the interior planets in the Solar System. The data allow for only a small fraction of reflected light, corresponding to a geometric albedo of <0.20.
We report the detection of water absorption features in the day side spectrum of the first-known hot Jupiter, 51 Peg b, confirming the star-planet system to be a double-lined spectroscopic binary. We ...use high-resolution ( 100,000), spectra taken with CRIRES/VLT to trace the radial-velocity shift of the water features in the planet's day side atmosphere during 4 hr of its 4.23 day orbit after superior conjunction. We detect the signature of molecular absorption by water at a significance of at a systemic velocity of km s−1, coincident with the 51 Peg host star, with a corresponding orbital velocity km s−1. This translates directly to a planet mass of , placing it at the transition boundary between Jovian and Neptunian worlds. We determine upper and lower limits on the orbital inclination of the system of . We also provide an updated orbital solution for 51 Peg b, using an extensive set of 639 stellar radial velocities measured between 1994 and 2013, finding no significant evidence of an eccentric orbit. We find no evidence of significant absorption or emission from other major carbon-bearing molecules of the planet, including methane and carbon dioxide. The atmosphere is non-inverted in the temperature-pressure region probed by these observations. The deepest absorption lines reach an observed relative contrast of with respect to the host star continuum flux at an angular separation of 3 milliarcseconds. This work is consistent with a previous tentative report of K-band molecular absorption for 51 Peg b by Brogi et al.
Abstract
Ultrahot Jupiters are gas giants that orbit so close to their host star that they are tidally locked, causing a permanent hot dayside and a cooler nightside. Signatures of their nonuniform ...atmospheres can be observed with high-resolution transit transmission spectroscopy by resolving time-dependent velocity shifts as the planet rotates and varying areas of the evening and morning terminator are probed. These asymmetric shifts were seen for the first time in iron absorption in WASP-76b. Here, we search for other atoms/ions in the planets transmission spectrum and study the asymmetries in their signals. We detect Li
i
, Na
i
, Mg
i
, Ca
ii
, V
i
, Cr
i
, Mn
i
, Fe
i
, Ni
i
, and Sr
ii
, and tentatively detect H
i
, K
i
, and Co
i
, of which V, Cr, Ni, Sr
ii
, and Co have not been reported before. We notably do not detect Ti or Al, even though these species should be readily observable, and hypothesize this could be due to condensation or cold trapping. We find that the observed signal asymmetries in the detected species can be explained in different ways. We find a relation between the expected condensation or ionization temperatures and the strength of the observed asymmetry, which could indicate rain-out or recombination on the nightside. However, we also find a dependence on the signal broadening, which could imply a two-zoned atmospheric model, in which the lower atmosphere is dominated by a day-to-night wind, while the upper atmosphere is dominated by a vertical wind or outflow. These observations provide a new level of modeling constraint and will aid our understanding of atmospheric dynamics in highly irradiated planets.
Context. 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 separate the planet signal from telluric and stellar contaminants. Aims. We apply high-resolution spectroscopy to probe molecular absorption in the day-side spectrum of the bright transiting hot Jupiter HD 189733b. Methods. We observed HD 189733b with the CRIRES high-resolution near-infrared spectograph on the Very Large Telescope during three nights, targeting possible absorption from carbon monoxide, water vapour, methane, and carbon dioxide, at 2.0 and 2.3 μm. Results. We detect a 5-σ absorption signal from CO at a contrast level of ~4.5 × 10-4 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 0.846+0.068-0.049M⊙ and Mp = 1.162+0.058-0.039 MJup. No significant absorption is detected from H2O, CO2, or CH4 and we determine upper limits on their line contrasts. Conclusions. 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 μm 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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