Context. 55 Cnc e is a transiting super-Earth orbiting a solar-like star with an orbital period of ~17.7 h. In 2011, using the Microvariability and Oscillations in Stars (MOST) space telescope, a ...quasi-sinusoidal modulation in flux was detected with the same period as the planetary orbit. The amplitude of this modulation was too large to be explained as the change in light reflected or emitted by the planet. Aims. The MOST telescope continued to observe 55 Cnc e for a few weeks per year over five years (from 2011 to 2015), covering 143 individual transits. This paper presents the analysis of the observed phase modulation throughout these observations and a search for the secondary eclipse of the planet. Methods. The most important source of systematic noise in MOST data is due to stray-light reflected from the Earth, which is modulated with both the orbital period of the satellite (101.4 min) and the Earth’s rotation period. We present a new technique to deal with this source of noise, which we combined with standard detrending procedures for MOST data. We then performed Markov chain Monte Carlo analyses of the detrended light curves, modeling the planetary transit and phase modulation. Results. We find phase modulations similar to those seen in 2011 in most of the subsequent years; however, the amplitude and phase of maximum light are seen to vary, from year to year, from 113 to 28 ppm and from 0.1 to 3.8 rad. The secondary eclipse is not detected, but we constrain the geometric albedo of the planet to less than 0.47 (2σ). Conclusions. While we cannot identify a single origin of the observed optical modulation, we propose a few possible scenarios. Those include star-planet interaction, such as coronal rains and spots rotating with the motion of the planet along its orbit, or the presence of a transiting circumstellar torus of dust. However, a detailed interpretation of these observations is limited by their photometric precision. Additional observations at optical wavelengths could measure the variations at higher precision, contribute to uncovering the underlying physical processes, and measure or improve the upper limit on the albedo of the planet.
The benchmark hot Jupiter HD 189733 b has been a key target, used to lay out the foundations of comparative planetology for giant exo-planets. As such, HD 189733 b has been extensively studied across ...the electromagnetic spectrum. Here we report the observation and analysis of three transit light curves of HD 189733 b obtained with
Hubble/
STIS in the near-ultraviolet (NUV), the last remaining unexplored spectral window to be probed with present-day instrumentation for this planet. The NUV is a unique window for atmospheric mass-loss studies owing to the strong resonance lines and large photospheric flux. Overall, from a low-resolution analysis (
R
= 50) we found that the planet’s NUV spectrum is well characterized by a relatively flat baseline, consistent with the optical-infrared transmission, plus two regions at ~2350 and ~2600 Å that exhibit a broad and significant excess absorption above the continuum. From an analysis at a higher resolution (
R
= 4700), we found that the transit depths at the core of the magnesium resonance lines are consistent with the surrounding continuum. We discarded the presence of Mg
II
absorption in the upper atmosphere at a ~2–4
σ
confidence level, whereas we could place no significant constraint for Mg I absorption. These broad absorption features coincide with the expected location of Fe II bands; however, solar-abundance hydrodynamic models of the upper atmosphere are not able to reproduce the amplitude of these features with iron absorption. This scenario would require a combination of little to no iron condensation in the lower atmosphere super-solar metallicities and a mechanism to enhance the absorption features (such as zonal wind broadening). The true nature of this feature remains to be confirmed.
The K2-33 planetary system hosts one transiting ~5
R
⊕
planet orbiting the young M-type host star. The planet’s mass is still unknown, with an estimated upper limit of 5.4
M
J
. The extreme youth of ...the system (<20 Myr) gives the unprecedented opportunity to study the earliest phases of planetary evolution, at a stage when the planet is exposed to an extremely high level of high-energy radiation emitted by the host star. We perform a series of 1D hydrodynamic simulations of the planet’s upper atmosphere considering a range of possible planetary masses, from 2 to 40
M
⊕
, and equilibrium temperatures, from 850 to 1300 K, to account for internal heating as a result of contraction. We obtain temperature profiles mostly controlled by the planet’s mass, while the equilibrium temperature has a secondary effect. For planetary masses below 7–10
M
⊕
, the atmosphere is subject to extremely high escape rates, driven by the planet’s weak gravity and high thermal energy, which increase with decreasing mass and/or increasing temperature. For higher masses, the escape is instead driven by the absorption of the high-energy stellar radiation. A rough comparison of the timescales for complete atmospheric escape and age of the system indicates that the planet is more massive than 10
M
⊕
.
For the hot exoplanets CoRoT-24b and CoRoT-24c, observations have provided transit radii R
T of 3.7 ± 0.4R
⊕ and 4.9 ± 0.5R
⊕, and masses of ≤5.7M
⊕ and 28 ± 11M
⊕, respectively. We study their upper ...atmosphere structure and escape applying an hydrodynamic model. Assuming R
T ≈ R
PL, where R
PL is the planetary radius at the pressure of 100 mbar, we obtained for CoRoT-24b unrealistically high thermally driven hydrodynamic escape rates. This is due to the planet's high temperature and low gravity, independent of the stellar EUV flux. Such high escape rates could last only for <100 Myr, while R
PL shrinks till the escape rate becomes less than or equal to the maximum possible EUV-driven escape rate. For CoRoT-24b, R
PL must be therefore located at ≈1.9–2.2R
⊕ and high altitude hazes/clouds possibly extinct the light at R
T. Our analysis constraints also the planet's mass to be 5–5.7M
⊕. For CoRoT-24c, R
PL and R
T lie too close together to be distinguished in the same way. Similar differences between R
PL and R
T may be present also for other hot, low-density sub-Neptunes.
The GAPS Programme at TNG Guilluy, G.; Giacobbe, P.; Carleo, I. ...
Astronomy and astrophysics (Berlin),
09/2022, Letnik:
665
Journal Article
Recenzirano
Odprti dostop
Context.
The field of exo-atmospheric characterisation is progressing at an extraordinary pace. Atmospheric observations are now available for tens of exoplanets, mainly hot and warm inflated gas ...giants, and new molecular species continue to be detected, revealing a richer atmospheric composition than previously expected. Thanks to its warm equilibrium temperature (963 ± 18 K) and low density (0.219 ± 0.031 g cm
−3
), the close-in gas giant WASP-69b represents a golden target for atmospheric characterisation.
Aims.
With the aim of searching for molecules in the atmosphere of WASP-69b and investigating its properties, we performed high-resolution transmission spectroscopy with the GIANO-B near-infrared spectrograph at the Telescopio Nazionale Galileo.
Methods.
We observed three transit events of WASP-69b. During a transit, the planetary lines are Doppler-shifted due to the large change in the planet’s radial velocity, allowing us to separate the planetary signal from the quasi-stationary telluric and stellar spectrum.
Results.
Considering the three nights together, we report the detection of CH
4
, NH
3
, CO, C
2
H
2
, and H
2
O, at more than a 3.3a- level. We did not identify the presence of HCN or CO
2
with confidence a level higher than 3a. This is the first time that five molecules have been simultaneously detected in the atmosphere of a warm giant planet. These results suggest that the atmosphere of WASP-69b is possibly carbon-rich and characterised by the presence of disequilibrium chemistry.
We analyzed the combined near-infrared spectrum of a star-planet system with thermal emission atmospheric models, based on the composition and physical parameters of the system. The main objective of ...this work is to obtain the inclination of the orbit, the mass of the exoplanet, and the planet-to-star flux ratio. We present the results of our routines on the planetary system HD 217107, which was observed with the high-resolution spectrograph Phoenix at 2.14 μm. We revisited and tuned a correlation method to directly search for the high-resolution signature of a known non-transiting extrasolar planet. We could not detect the planet with our current data, but we present sensitivity estimates of our method and the respective constraints on the planetary parameters. With a confidence level of 3-σ we constrain the HD 217107 b planet-to-star flux ratio to be less than 5 × 10-3. We also carried out simulations on other planet candidates to assess the detectability limit of atmospheric water on realistically simulated data sets for this instrument, and we outline an optimized observational and selection strategy to increase future probabilities of success by considering the optimal observing conditions and the most suitable candidates.
We report on the confirmation and mass determination of a transiting planet orbiting the old and inactive G7 dwarf star HD 219666 (M⋆ = 0.92 ± 0.03 M⊙, R⋆ = 1.03 ± 0.03 R⊙, τ⋆ = 10 ± 2 Gyr). With a ...mass of Mb = 16.6 ± 1.3 M⊕, a radius of Rb = 4.71 ± 0.17 R⊕, and an orbital period of Porb ≃ 6 days, HD 219666 b is a new member of a rare class of exoplanets: the hot-Neptunes. The Transiting Exoplanet Survey Satellite (TESS) observed HD 219666 (also known as TOI-118) in its Sector 1 and the light curve shows four transit-like events, equally spaced in time. We confirmed the planetary nature of the candidate by gathering precise radial-velocity measurements with the High Accuracy Radial velocity Planet Searcher (HARPS) at ESO 3.6 m. We used the co-added HARPS spectrum to derive the host star fundamental parameters (Teff = 5527 ± 65 K, log g⋆ = 4.40 ± 0.11 (cgs), Fe/H= 0.04 ± 0.04 dex, log R′HK $\log R^{\prime}_{\textrm{HK}}$ log R HK ′ = −5.07 ± 0.03), as well as the abundances of many volatile and refractory elements. The host star brightness (V = 9.9) makes it suitable for further characterisation by means of in-transit spectroscopy. The determination of the planet orbital obliquity, along with the atmosphericmetal-to-hydrogen content and thermal structure could provide us with important clues on the formation mechanisms of this class of objects.
The James Webb Space Telescope (JWST) is expected to revolutionize the field of exoplanets. The broad wavelength coverage and the high sensitivity of its instruments will allow characterization of ...exoplanetary atmospheres with unprecedented precision. Following the Call for the Cycle 1 Early Release Science Program, the Transiting Exoplanet Community was awarded time to observe several targets, including WASP-43b. The atmosphere of this hot Jupiter has been intensively observed but still harbors some mysteries, especially concerning the day-night temperature gradient, the efficiency of the atmospheric circulation, and the presence of nightside clouds. We will constrain these properties by observing a full orbit of the planet and extracting its spectroscopic phase curve in the 5-12 m range with JWST/MIRI. To prepare for these observations, we performed extensive modeling work with various codes: radiative transfer, chemical kinetics, cloud microphysics, global circulation models, JWST simulators, and spectral retrieval. Our JWST simulations show that we should achieve a precision of 210 ppm per 0.1 m spectral bin on average, which will allow us to measure the variations of the spectrum in longitude and measure the nightside emission spectrum for the first time. If the atmosphere of WASP-43b is clear, our observations will permit us to determine if its atmosphere has an equilibrium or disequilibrium chemical composition, eventually providing the first conclusive evidence of chemical quenching in a hot Jupiter atmosphere. If the atmosphere is cloudy, a careful retrieval analysis will allow us to identify the cloud composition.
ABSTRACT
High-resolution Doppler-resolved spectroscopy has opened up a new window into the atmospheres of both transiting and non-transiting exoplanets. Here, we present VLT/UVES observations of a ...transit of WASP-121b, an ‘ultra-hot’ Jupiter previously found to exhibit a temperature inversion and detections of multiple species at optical wavelengths. We present initial results using the blue arm of UVES (≈3700–5000 Å), recovering a clear signal of neutral Fe in the planet’s atmosphere at >8$\, \sigma$, which could contribute to (or even fully explain) the temperature inversion in the stratosphere. However, using standard cross-correlation methods, it is difficult to extract physical parameters such as temperature and abundances. Recent pioneering efforts have sought to develop likelihood ‘mappings’ that can be used to directly fit models to high-resolution data sets. We introduce a new framework that directly computes the likelihood of the model fit to the data, and can be used to explore the posterior distribution of parametrised model atmospheres via MCMC techniques. Our method also recovers the physical extent of the atmosphere, as well as account for time- and wavelength-dependent uncertainties. We measure a temperature of $3710^{+490}_{-510}$ K, indicating a higher temperature in the upper atmosphere when compared to low-resolution observations. We also show that the Fe i signal is physically separated from the exospheric Fe ii. However, the temperature measurements are highly degenerate with aerosol properties; detection of additional species, using more sophisticated atmospheric models, or combining these methods with low-resolution spectra should help break these degeneracies.
WASP-18 hosts a massive, very close-in Jupiter-like planet. Despite its young age (<1 Gyr), the star presents an anomalously low stellar activity level: the measured activity parameter lies slightly ...below the basal level; there is no significant time-variability in the value; there is no detection of the star in the X-rays. We present results of far-UV observations of WASP-18 obtained with COS on board of Hubble Space Telescope aimed at explaining this anomaly. From the star's spectral energy distribution, we infer the extinction ( 0.01 mag) and then the interstellar medium (ISM) column density for a number of ions, concluding that ISM absorption is not the origin of the anomaly. We measure the flux of the four stellar emission features detected in the COS spectrum (C ii, C iii, C iv, Si iv). Comparing the C ii/C iv flux ratio measured for WASP-18 with that derived from spectra of nearby stars with known age, we see that the far-UV spectrum of WASP-18 resembles that of old (>5 Gyr), inactive stars, in stark contrast with its young age. We conclude that WASP-18 has an intrinsically low activity level, possibly caused by star-planet tidal interaction, as suggested by previous studies. Re-scaling the solar irradiance reference spectrum to match the flux of the Si iv line, yields an XUV integrated flux at the planet orbit of 10.2 erg s−1 cm−2. We employ the rescaled XUV solar fluxes to models of the planetary upper atmosphere, deriving an extremely low thermal mass-loss rate of 10−20 MJ Gyr−1. For such high-mass planets, thermal escape is not energy limited, but driven by Jeans escape.
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