91 research outputs found
The RoPES project with HARPS and HARPS-N. I. A system of super-Earths orbiting the moderately active K-dwarf HD 176986
We report the discovery of a system of two super-Earths orbiting the
moderately active K-dwarf HD 176986. This work is part of the RoPES RV program
of G- and K-type stars, which combines radial velocities (RVs) from the HARPS
and HARPS-N spectrographs to search for short-period terrestrial planets. HD
176986 b and c are super-Earth planets with masses of 5.74 and 9.18
M, orbital periods of 6.49 and 16.82 days, and distances of 0.063
and 0.119 AU in orbits that are consistent with circular. The host star is a
K2.5 dwarf, and despite its modest level of chromospheric activity (log(R'hk) =
- 4.90 +- 0.04), it shows a complex activity pattern. Along with the discovery
of the planets, we study the magnetic cycle and rotation of the star. HD 176986
proves to be suitable for testing the available RV analysis technique and
further our understanding of stellar activity.Comment: 21 pages, 24 figures, 7 table
A super-Earth orbiting the nearby M-dwarf GJ 536
We report the discovery of a super-Earth orbiting the star GJ 536 based on
the analysis of the radial-velocity time series from the HARPS and HARPS-N
spectrographs. GJ 536 b is a planet with a minimum mass M sin of 5.36 +-
0.69 Me with an orbital period of 8.7076 +- 0.0025 days at a distance of
0.066610(13) AU, and an orbit that is consistent with circular. The host star
is the moderately quiet M1 V star GJ 536, located at 10 pc from the Sun. We
find the presence of a second signal at 43 days that we relate to stellar
rotation after analysing the time series of Ca II H&K and H alpha spectroscopic
indicators and photometric data from the ASAS archive. We find no evidence
linking the short period signal to any activity proxy. We also tentatively
derived a stellar magnetic cycle of less than 3 years.Comment: 14 pages, 14 figures, 5 tables, Accepted in A&
HADES RV Programme with HARPS-N at TNG VI. GJ 3942 b behind dominant activity signals
Short- to mid-term magnetic phenomena on the stellar surface of M-type stars
cannot only resemble the effects of planets in radial velocity data, but also
may hide them. We analyze 145 spectroscopic HARPS-N observations of GJ 3942
taken over the past five years and additional photometry to disentangle stellar
activity effects from genuine Doppler signals as a result of the orbital motion
of the star around the common barycenter with its planet. To achieve this, we
use the common methods of pre-whitening, and treat the correlated red noise by
a first-order moving average term and by Gaussian-process regression following
an MCMC analysis. We identify the rotational period of the star at 16.3 days
and discover a new super-Earth, GJ 3942 b, with an orbital period of 6.9 days
and a minimum mass of 7.1 Me. An additional signal in the periodogram of the
residuals is present but we cannot claim it to be related to a second planet
with sufficient significance at this point. If confirmed, such planet candidate
would have a minimum mass of 6.3 Me and a period of 10.4 days, which might
indicate a 3:2 mean-motion resonance with the inner planet
The HADES RV Programme with HARPS-N@TNG II. Data treatment and simulations
The distribution of exoplanets around low-mass stars is still not well
understood. Such stars, however, present an excellent opportunity of reaching
down to the rocky and habitable planet domains. The number of current
detections used for statistical purposes is still quite modest and different
surveys, using both photometry and precise radial velocities, are searching for
planets around M dwarfs. Our HARPS-N red dwarf exoplanet survey is aimed at the
detection of new planets around a sample of 78 selected stars, together with
the subsequent characterization of their activity properties. Here we
investigate the survey performance and strategy. From 2700 observed spectra, we
compare the radial velocity determinations of the HARPS-N DRS pipeline and the
HARPS-TERRA code, we calculate the mean activity jitter level, we evaluate the
planet detection expectations, and we address the general question of how to
define the strategy of spectroscopic surveys in order to be most efficient in
the detection of planets. We find that the HARPS-TERRA radial velocities show
less scatter and we calculate a mean activity jitter of 2.3 m/s for our sample.
For a general radial velocity survey with limited observing time, the number of
observations per star is key for the detection efficiency. In the case of an
early M-type target sample, we conclude that approximately 50 observations per
star with exposure times of 900 s and precisions of about 1 m/s maximizes the
number of planet detections
HADES RV Programme with HARPS-N at TNG. VII. Rotation and activity of M-Dwarfs from time-series high-resolution spectroscopy of chromospheric indicators
We aim to investigate the presence of signatures of magnetic cycles and
rotation on a sample of 71 early M-dwarfs from the HADES RV programme using
high-resolution time-series spectroscopy of the Ca II H & K and Halpha
chromospheric activity indicators, the radial velocity series, the parameters
of the cross correlation function and the V-band photometry. We used mainly
HARPS-N spectra, acquired over four years, and add HARPS spectra from the
public ESO database and ASAS photometry light-curves as support data, extending
the baseline of the observations of some stars up to 12 years. We provide
log(R'hk) measurements for all the stars in the sample, cycle length
measurements for 13 stars, rotation periods for 33 stars and we are able to
measure the semi-amplitude of the radial velocity signal induced by rotation in
16 stars. We complement our work with previous results and confirm and refine
the previously reported relationships between the mean level of chromospheric
emission, measured by the log(R'hk), with the rotation period, and with the
measured semi-amplitude of the activity induced radial velocity signal for
early M-dwarfs. We searched for a possible relation between the measured
rotation periods and the lengths of the magnetic cycle, finding a weak
correlation between both quantities. Using previous v sin i measurements we
estimated the inclinations of the star's poles to the line of sight for all the
stars in the sample, and estimate the range of masses of the planets GJ 3998 b
and c (2.5 - 4.9 Mearth and 6.3 - 12.5 Mearth), GJ 625 b (2.82 Mearth), GJ 3942
b (7.1 - 10.0 Mearth) and GJ 15A b (3.1 - 3.3 Mearth), assuming their orbits
are coplanar with the stellar rotation.Comment: 19 pages, 16 figures, 10 table
Catalog for the ESPRESSO blind radial velocity exoplanet survey
One of the main scientific drivers for ESPRESSO,\'Echelle SPectrograph, is
the detection and characterization of Earth-class exoplanets. With this goal in
mind, the ESPRESSO Guaranteed Time Observations (GTO) Catalog identifies the
best target stars for a blind search for the radial velocity (RV) signals
caused by Earth-class exoplanets. Using the most complete stellar catalogs
available, we screened for the most suitable G, K, and M dwarf stars for the
detection of Earth-class exoplanets with ESPRESSO. For most of the stars, we
then gathered high-resolution spectra from new observations or from archival
data. We used these spectra to spectroscopically investigate the existence of
any stellar binaries, both bound or background stars. We derived the activity
level using chromospheric activity indexes using , as well as the
projected rotational velocity . For the cases where planet
companions are already known, we also looked at the possibility that additional
planets may exist in the host's habitable zone using dynamical arguments. We
estimated the spectroscopic contamination level, , activity,
stellar parameters and chemical abundances for 249 of the most promising
targets. Using these data, we selected 45 stars that match our criteria for
detectability of a planet like Earth. The stars presented and discussed in this
paper constitute the ESPRESSO GTO catalog for the RV blind search for
Earth-class planets. They can also be used for any other work requiring a
detailed spectroscopic characterization of stars in the solar neighborhood.Comment: Corrected a typo in references. Corrected typo in table B.
Automatic model-based telluric correction for the ESPRESSO data reduction software. Model description and application to radial velocity computation
Ground-based high-resolution spectrographs are key instruments for several
astrophysical domains. Unfortunately, the observed spectra are contaminated by
the Earth's atmosphere. While different techniques exist to correct for
telluric lines in exoplanet atmospheric studies, in radial velocity (RV)
studies, telluric lines with an absorption depth of >2% are generally masked,
which poses a problem for faint targets and M dwarfs as most of their RV
content is present where telluric contamination is important. We propose a
simple telluric model to be embedded in the ESPRESSO DRS. The goal is to
provide telluric-free spectra and enable RV measurements, including spectral
ranges where telluric lines fall. The model is a line-by-line radiative
transfer code that assumes a single atmospheric layer. We use the sky
conditions and the physical properties of the lines from HITRAN to create the
telluric spectrum. A subset of selected telluric lines is used to robustly fit
the spectrum through a Levenberg-Marquardt minimization algorithm. When applied
to stellar spectra from A0- to M5-type stars, the residuals of the strongest
H2O lines are below 2% for all spectral types, with the exception of M dwarfs,
which are within the pseudo-continuum. We then determined the RVs from the
telluric-corrected ESPRESSO spectra of Tau Ceti and Proxima. We created
telluric-free masks and compared the obtained RVs with the DRS RVs. In the case
of Tau Ceti, we identified that micro-telluric lines introduce systematics up
to an amplitude of 58 cm/s and with a period of one year. For Proxima, the gain
in spectral content at redder wavelengths is equivalent to a gain of 25% in
photon noise. This leads to better constraints on the semi-amplitude and
eccentricity of Proxima d. We showcase that our model can be applied to other
molecules, and thus to other wavelength regions observed by other
spectrographs, such as NIRPS.Comment: 18 pages, 18 figures, accepted to A&
Detection of barium in the atmospheres of the ultra-hot gas giants WASP-76b and WASP-121b
Context. High-resolution spectroscopy studies of ultra-hot Jupiters have been key in our understanding of exoplanet atmospheres. Observing into the atmospheres of these giant planets allows for direct constraints on their atmospheric compositions and dynamics while laying the groundwork for new research regarding their formation and evolution environments.
Aims. Two of the most well-studied ultra-hot Jupiters are WASP-76b and WASP-121b, with multiple detected chemical species and strong signatures of their atmospheric dynamics. We take a new look at these two exceptional ultra-hot Jupiters by reanalyzing the transit observations taken with ESPRESSO at the Very Large Telescope and attempt to detect additional species.
Methods. To extract the planetary spectra of the two targets, we corrected for the telluric absorption and removed the stellar spectrum contributions. We then exploited new synthetic templates that were specifically designed for ultra-hot Jupiters in combination with the cross-correlation technique to unveil species that remained undetected by previous analyses.
Results. We add a novel detection of Ba+ to the known atmospheric compositions of WASP-76b and WASP-121b, the heaviest species detected to date in any exoplanetary atmosphere, with additional new detections of Co and Sr+ and a tentative detection of Ti+ for WASP-121b. We also confirm the presence of Ca+, Cr, Fe, H, Li, Mg, Mn, Na, and V on both WASP-76b and WASP-121b, with the addition of Ca, Fe+, and Ni for the latter. Finally, we also confirm the clear asymmetric absorption feature of Ca+ on WASP-121b, with an excess absorption at the bluer wavelengths and an effective planet radius beyond the Roche lobe. This indicates that the signal may arise from the escape of planetary atmosphere.
Key words: planets and satellites: atmospheres / planets and satellites: composition / planets and satellites: gaseous planets / techniques: spectroscopic / planets and satellites: individual: WASP-76b / planets and satellites: individual: WASP-121
The atmosphere of HD 209458b seen with ESPRESSO. No detectable planetary absorptions at high resolution
We observed two transits of the iconic gas giant HD 209458b between 380 and
780 nm, using the high-resolution ESPRESSO spectrograph. The derived planetary
transmission spectrum exhibits features at all wavelengths where the parent
star shows strong absorption lines, for example, NaI, MgI, FeI, FeII, CaI, VI,
H, and KI. We interpreted these features as the signature of the
deformation of the stellar line profiles due to the Rossiter-McLaughlin effect,
combined with the centre-to-limb effects on the stellar surface, which is in
agreement with similar reports recently presented in the literature. We also
searched for species that might be present in the planetary atmosphere but not
in the stellar spectra, such as TiO and VO, and obtained a negative result.
Thus, we find no evidence of any planetary absorption, including previously
reported NaI, in the atmosphere of HD 209458b. The high signal-to-noise ratio
in the transmission spectrum allows us to compare the modelled deformation of
the stellar lines in assuming different one-dimensional stellar atmospheric
models. We conclude that the differences among various models and observations
remain within the precision limits of the data. However, the transmission light
curves are better explained when the centre-to-limb variation is not included
in the computation and only the Rossiter-McLaughlin deformation is considered.
This demonstrates that ESPRESSO is currently the best facility for spatially
resolving the stellar surface spectrum in the optical range using transit
observations and carrying out empirical validations of stellar models.Comment: 21 pages, 19 figures. Accepte
- …