28 research outputs found
Characterization of the K2-38 planetary system: Unraveling one of the densest planets known to date
.-- Toledo-Padrón, B. et al.Context. An accurate characterization of the known exoplanet population is key to understanding the origin and evolution of planetary systems. Determining true planetary masses through the radial velocity (RV) method is expected to experience a great improvement thanks to the availability of ultra-stable echelle spectrographs. Aims. We took advantage of the extreme precision of the new-generation echelle spectrograph ESPRESSO to characterize the transiting planetary system orbiting the G2V star K2-38 located at 194 pc from the Sun with V 11.4. This system is particularly interesting because it could contain the densest planet detected to date. Methods. We carried out a photometric analysis of the available K2 photometric light curve of this star to measure the radius of its two known planets, K2-38b and K2-38c, with Pb = 4.01593 ± 0.00050 d and Pc = 10.56103 ± 0.00090 d, respectively. Using 43 ESPRESSO high-precision RV measurements taken over the course of 8 months along with the 14 previously published HIRES RV measurements, we modeled the orbits of the two planets through a Markov chain Monte Carlo analysis, significantly improving their mass measurements. Results. Using ESPRESSO spectra, we derived the stellar parameters, Teff = 5731 ± 66, log g = 4.38 ± 0.11 dex, and [Fe/H] = 0.26 ± 0.05 dex, and thus the mass and radius of K2-38, Ma = 1.03-0.02+0.04 MaS and Ra = 1.06-0.06+0.09 RaS. We determine new values for the planetary properties of both planets. We characterize K2-38b as a super-Earth with RP = 1.54 ± 0.14 RaS and Mp = 7.3-1.0+1.1 MaS, and K2-38c as a sub-Neptune with RP = 2.29 ± 0.26 RaS and Mp = 8.3-1.3+1.3 MaS. Combining the radius and mass measurements, we derived a mean density of ρp = 11.0-2.8+4.1 g cm-3 for K2-38b and ρp = 3.8-1.1+1.8 g cm-3 for K2-38c, confirming K2-38b as one of the densest planets known to date. Conclusions. The best description for the composition of K2-38b comes from an iron-rich Mercury-like model, while K2-38c is better described by a rocky-model with H2 envelope. The maximum collision stripping boundary shows how giant impacts could be the cause for the high density of K2-38b. The irradiation received by each planet places them on opposite sides of the radius valley. We find evidence of a long-period signal in the RV time-series whose origin could be linked to a 0.25-3 MJ planet or stellar activity.With funding from the Spanish government through the "María de Maeztu Unit of Excellence" accreditation (MDM-2017-0737
ESPRESSO: The next European exoplanet hunter
The acronym ESPRESSO stems for Echelle SPectrograph for Rocky Exoplanets and
Stable Spectroscopic Observations; this instrument will be the next VLT high
resolution spectrograph. The spectrograph will be installed at the
Combined-Coud\'e Laboratory of the VLT and linked to the four 8.2 m Unit
Telescopes (UT) through four optical Coud\'e trains. ESPRESSO will combine
efficiency and extreme spectroscopic precision. ESPRESSO is foreseen to achieve
a gain of two magnitudes with respect to its predecessor HARPS, and to improve
the instrumental radial-velocity precision to reach the 10 cm/s level. It can
be operated either with a single UT or with up to four UTs, enabling an
additional gain in the latter mode. The incoherent combination of four
telescopes and the extreme precision requirements called for many innovative
design solutions while ensuring the technical heritage of the successful HARPS
experience. ESPRESSO will allow to explore new frontiers in most domains of
astrophysics that require precision and sensitivity. The main scientific
drivers are the search and characterization of rocky exoplanets in the
habitable zone of quiet, nearby G to M-dwarfs and the analysis of the
variability of fundamental physical constants. The project passed the final
design review in May 2013 and entered the manufacturing phase. ESPRESSO will be
installed at the Paranal Observatory in 2016 and its operation is planned to
start by the end of the same year.Comment: 12 pages, figures included, accepted for publication in Astron. Nach
Atmospheric Rossiter-McLaughlin effect and transmission spectroscopy of WASP-121b with ESPRESSO
WASP-121b is one of the most studied Ultra-hot Jupiters: many recent analyses
of its atmosphere report interesting features at different wavelength ranges.
In this paper we analyze one transit of WASP-121b acquired with the
high-resolution spectrograph ESPRESSO at VLT in 1-telescope mode, and one
partial transit taken during the commissioning of the instrument in 4-telescope
mode. We investigate the anomalous in-transit radial velocity curve and study
the transmission spectrum of the planet. By analysing the in-transit radial
velocities we were able to infer the presence of the atmospheric
Rossiter-McLaughlin effect. We measured the height of the planetary atmospheric
layer that correlates with the stellar mask (mainly Fe) to be 1.0520.015
Rp and we also confirmed the blueshift of the planetary atmosphere. By
examining the planetary absorption signal on the stellar cross-correlation
functions we confirmed the presence of a temporal variation of its blueshift
during transit, which could be investigated spectrum-by-spectrum. We detected
significant absorption in the transmission spectrum for Na, H, K, Li, CaII, Mg,
and we certified their planetary nature by using the 2D tomographic technique.
Particularly remarkable is the detection of Li, with a line contrast of
0.2% detected at the 6 level. With the cross-correlation
technique we confirmed the presence of FeI, FeII, CrI and VI. H and
CaII are present up to very high altitudes in the atmosphere (1.44 Rp and
2 Rp, respectively), and also extend beyond the transit-equivalent Roche
lobe radius of the planet. These layers of the atmosphere have a large line
broadening that is not compatible with being caused by the tidally-locked
rotation of the planet alone, and could arise from vertical winds or
high-altitude jets in the evaporating atmosphere.Comment: 15 pages, 19 figures. Accepted for publication in A&
WASP-127b: A misaligned planet with a partly cloudy atmosphere and tenuous sodium signature seen by ESPRESSO
The study of exoplanet atmospheres is essential to understand the formation,
evolution and composition of exoplanets. The transmission spectroscopy
technique is playing a significant role in this domain. In particular, the
combination of state-of-the-art spectrographs at low- and high-spectral
resolution is key to our understanding of atmospheric structure and
composition. Two transits of the close-in sub Saturn-mass planet,WASP-127b,
have been observed with ESPRESSO in the frame of the Guaranteed Time
Observations Consortium. Transit observations allow us to study simultaneously
the system architecture and the exoplanet atmosphere. We found that this planet
is orbiting its slowly rotating host star (veq sin(i)=0.53+/-0.07 km/s) on a
retrograde misaligned orbit (lambda=-128.41+/-5.60 deg). We detected the sodium
line core at the 9-sigma confidence level with an excess absorption of
0.3+/-0.04%, a blueshift of 2.7+/-0.79 km/s and a FWHM of 15.18+/-1.75 km/s.
However, we did not detect the presence of other atomic species but set
upper-limits of only few scale heights. Finally, we put a 3-sigma upper limit,
to the average depth of the 1600 strongest water lines at equilibrium
temperature in the visible band, of 38 ppm. This constrains the cloud-deck
pressure between 0.3 and 0.5 mbar by combining our data with low-resolution
data in the near-infrared and models computed for this planet. To conclude,
WASP-127b, with an age of about 10 Gyr, is an unexpected exoplanet by its
orbital architecture but also by the small extension of its sodium atmosphere
(~7 scale heights). ESPRESSO allows us to take a step forward in the detection
of weak signals, thus bringing strong constraints on the presence of clouds in
exoplanet atmospheres. The framework proposed in this work can be applied to
search for molecular species and study cloud-decks in other exoplanets.Comment: Accepted in A&A, 19 pages, 20 figure
Revisiting Proxima with ESPRESSO
We aim to confirm the presence of Proxima b using independent measurements
obtained with the new ESPRESSO spectrograph, and refine the planetary
parameters taking advantage of its improved precision. We analysed 63
spectroscopic ESPRESSO observations of Proxima taken during 2019. We obtained
radial velocity measurements with a typical radial velocity photon noise of 26
cm/s. We ran a joint MCMC analysis on the time series of the radial velocity
and full-width half maximum of the cross-correlation function to model the
planetary and stellar signals present in the data, applying Gaussian process
regression to deal with stellar activity. We confirm the presence of Proxima b
independently in the ESPRESSO data. The ESPRESSO data on its own shows Proxima
b at a period of 11.218 0.029 days, with a minimum mass of 1.29
0.13 Me. In the combined dataset we measure a period of 11.18427 0.00070
days with a minimum mass of 1.173 0.086 Me. We find no evidence of
stellar activity as a potential cause for the 11.2 days signal. We find some
evidence for the presence of a second short-period signal, at 5.15 days with a
semi-amplitude of merely 40 cm/s. If caused by a planetary companion, it would
correspond to a minimum mass of 0.29 0.08 Me. We find that the FWHM of
the CCF can be used as a proxy for the brightness changes and that its gradient
with time can be used to successfully detrend the radial velocity data from
part of the influence of stellar activity. The activity-induced radial velocity
signal in the ESPRESSO data shows a trend in amplitude towards redder
wavelengths. Velocities measured using the red end of the spectrograph are less
affected by activity, suggesting that the stellar activity is spot-dominated.
The data collected excludes the presence of extra companions with masses above
0.6 Me at periods shorter than 50 days.Comment: 25 pages, 26 figure
A precise architecture characterization of the Men planetary system
The bright star Men was chosen as the first target for a radial
velocity follow-up to test the performance of ESPRESSO, the new high-resolution
spectrograph at the ESO's Very-Large Telescope (VLT). The star hosts a
multi-planet system (a transiting 4 M planet at 0.07 au, and a
sub-stellar companion on a 2100-day eccentric orbit) which is
particularly appealing for a precise multi-technique characterization. With the
new ESPRESSO observations, that cover a time span of 200 days, we aim to
improve the precision and accuracy of the planet parameters and search for
additional low-mass companions. We also take advantage of new photometric
transits of Men c observed by TESS over a time span that overlaps with
that of the ESPRESSO follow-up campaign. We analyse the enlarged spectroscopic
and photometric datasets and compare the results to those in the literature. We
further characterize the system by means of absolute astrometry with Hipparcos
and Gaia. We used the spectra of ESPRESSO for an independent determination of
the stellar fundamental parameters. We present a precise characterization of
the planetary system around Men. The ESPRESSO radial velocities alone
(with typical uncertainty of 10 cm/s) allow for a precise retrieval of the
Doppler signal induced by Men c. The residuals show an RMS of 1.2 m/s,
and we can exclude companions with a minimum mass less than 2 M
within the orbit of Men c). We improve the ephemeris of Men c using
18 additional TESS transits, and in combination with the astrometric
measurements, we determine the inclination of the orbital plane of Men b
with high precision ( deg). This leads to the precise
measurement of its absolute mass M, and
shows that the planetary orbital planes are highly misaligned.Comment: Accepted for publication on A&
Nightside condensation of iron in an ultra-hot giant exoplanet
Ultra-hot giant exoplanets receive thousands of times Earth's insolation.
Their high-temperature atmospheres (>2,000 K) are ideal laboratories for
studying extreme planetary climates and chemistry. Daysides are predicted to be
cloud-free, dominated by atomic species and substantially hotter than
nightsides. Atoms are expected to recombine into molecules over the nightside,
resulting in different day-night chemistry. While metallic elements and a large
temperature contrast have been observed, no chemical gradient has been measured
across the surface of such an exoplanet. Different atmospheric chemistry
between the day-to-night ("evening") and night-to-day ("morning") terminators
could, however, be revealed as an asymmetric absorption signature during
transit. Here, we report the detection of an asymmetric atmospheric signature
in the ultra-hot exoplanet WASP-76b. We spectrally and temporally resolve this
signature thanks to the combination of high-dispersion spectroscopy with a
large photon-collecting area. The absorption signal, attributed to neutral
iron, is blueshifted by -11+/-0.7 km s-1 on the trailing limb, which can be
explained by a combination of planetary rotation and wind blowing from the hot
dayside. In contrast, no signal arises from the nightside close to the morning
terminator, showing that atomic iron is not absorbing starlight there. Iron
must thus condense during its journey across the nightside.Comment: Published in Nature (Accepted on 24 January 2020.) 33 pages, 11
figures, 3 table
ELT-HIRES, the high resolution spectrograph for the ELT: results from the Phase A study
We present the results from the phase A study of ELT-HIRES, an optical-infrared High Resolution Spectrograph for ELT, which has just been completed by a consortium of 30 institutes from 12 countries forming a team of about 200 scientists and engineers. The top science cases of ELT-HIRES will be the detection of life signatures from exoplanet atmospheres, tests on the stability of Nature's fundamental couplings, the direct detection of the cosmic acceleration. However, the science requirements of these science cases enable many other groundbreaking science cases. The baseline design, which allows to fulfil the top science cases, consists in a modular fiber- fed cross-dispersed echelle spectrograph with two ultra-stable spectral arms providing a simultaneous spectral range of 0.4-1.8 μm at a spectral resolution of 100,000. The fiber-feeding allows ELT-HIRES to have several, interchangeable observing modes including a SCAO module and a small diffraction-limited IFU