74 research outputs found
Spectroscopic characterisation of CARMENES target candidates from FEROS, CAFE and HRS high-resolution spectra
CARMENES (Calar Alto high-Resolution search for M dwarfs with Exoearths with
Near-infrared and optical Echelle Spectrographs) started a new planet survey on
M-dwarfs in January this year. The new high-resolution spectrographs are
operating in the visible and near-infrared at Calar Alto Observatory. They will
perform high-accuracy radial-velocity measurements (goal 1 m s-1) of about 300
M-dwarfs with the aim to detect low-mass planets within habitable zones. We
characterised the candidate sample for CARMENES and provide fundamental
parameters for these stars in order to constrain planetary properties and
understand star-planet systems. Using state-of-the-art model atmospheres
(PHOENIX-ACES) and chi2-minimization with a downhill-simplex method we
determine effective temperature, surface gravity and metallicity [Fe/H] for
high-resolution spectra of around 480 stars of spectral types M0.0-6.5V taken
with FEROS, CAFE and HRS. We find good agreement between the models and our
observed high-resolution spectra. We show the performance of the algorithm, as
well as results, parameter and spectral type distributions for the CARMENES
candidate sample, which is used to define the CARMENES target sample. We also
present first preliminary results obtained from CARMENES spectra
The CARMENES search for exoplanets around M dwarfs - Photospheric parameters of target stars from high-resolution spectroscopy
The new CARMENES instrument comprises two high-resolution and high-stability
spectrographs that are used to search for habitable planets around M dwarfs in
the visible and near-infrared regime via the Doppler technique. Characterising
our target sample is important for constraining the physical properties of any
planetary systems that are detected. The aim of this paper is to determine the
fundamental stellar parameters of the CARMENES M-dwarf target sample from
high-resolution spectra observed with CARMENES. We also include several M-dwarf
spectra observed with other high-resolution spectrographs, that is CAFE, FEROS,
and HRS, for completeness. We used a {chi}^2 method to derive the stellar
parameters effective temperature T_eff, surface gravity log g, and metallicity
[Fe/H] of the target stars by fitting the most recent version of the
PHOENIX-ACES models to high-resolution spectroscopic data. These stellar
atmosphere models incorporate a new equation of state to describe spectral
features of low-temperature stellar atmospheres. Since T_eff, log g, and [Fe/H]
show degeneracies, the surface gravity is determined independently using
stellar evolutionary models. We derive the stellar parameters for a total of
300 stars. The fits achieve very good agreement between the PHOENIX models and
observed spectra. We estimate that our method provides parameters with
uncertainties of {sigma} T_eff = 51 K, {sigma} log g = 0.07, and {sigma} [Fe/H]
= 0.16, and show that atmosphere models for low-mass stars have significantly
improved in the last years. Our work also provides an independent test of the
new PHOENIX-ACES models, and a comparison for other methods using
low-resolution spectra. In particular, our effective temperatures agree well
with literature values, while metallicities determined with our method exhibit
a larger spread when compared to literature results
The CARMENES search for exoplanets around M dwarfs: Nine new double-line spectroscopic binary stars
Context. The CARMENES spectrograph is surveying ~300 M dwarf stars in search
for exoplanets. Among the target stars, spectroscopic binary systems have been
discovered, which can be used to measure fundamental properties of stars. Aims.
Using spectroscopic observations, we determine the orbital and physical
properties of nine new double-line spectroscopic binary systems by analysing
their radial velocity curves. Methods. We use two-dimensional cross-correlation
techniques to derive the radial velocities of the targets, which are then
employed to determine the orbital properties. Photometric data from the
literature are also analysed to search for possible eclipses and to measure
stellar variability, which can yield rotation periods. Results. Out of the 342
stars selected for the CARMENES survey, 9 have been found to be double-line
spectroscopic binaries, with periods ranging from 1.13 to ~8000 days and orbits
with eccentricities up to 0.54. We provide empirical orbital properties and
minimum masses for the sample of spectroscopic binaries. Absolute masses are
also estimated from mass-luminosity calibrations, ranging between ~0.1 and ~0.6
Msol . Conclusions. These new binary systems increase the number of double-line
M dwarf binary systems with known orbital parameters by 15%, and they have
lower mass ratios on average.Comment: Accepted for publication in A&A. 17 pages, 4 figure
The CARMENES search for exoplanets around M dwarfs -- Planet occurrence rates from a subsample of 71 stars
The CARMENES exoplanet survey of M dwarfs has obtained more than 18 000
spectra of 329 nearby M dwarfs over the past five years as part of its
guaranteed time observations (GTO) program. We determine planet occurrence
rates with the 71 stars from the GTO program for which we have more than 50
observations. We use injection-and-retrieval experiments on the radial-velocity
(RV) time series to measure detection probabilities. We include 27 planets in
21 planetary systems in our analysis. We find 0.06+0.04-0.03 giant planets (100
M_Earth < M_pl sin i < 1000 M_Earth) per star in periods of up to 1000 d, but
due to a selection bias this number could be up to a factor of five lower in
the whole 329-star sample. The upper limit for hot Jupiters (orbital period of
less than 10 d) is 0.03 planets per star, while the occurrence rate of planets
with intermediate masses (10 M_Earth < M_pl sin i < 100 M_Earth) is
0.18+0.07-0.05 planets per star. Less massive planets with 1 M_Earth < M_pl sin
i < 10 M_Earth are very abundant, with an estimated rate of 1.32+0.33-0.31
planets per star for periods of up to 100 d. When considering only late M
dwarfs with masses M_star < 0.34 M_sol, planets more massive than 10 M_Earth
become rare. Instead, low-mass planets with periods shorter than 10 d are
significantly overabundant. For orbital periods shorter than 100 d, our results
confirm the known stellar mass dependences from the Kepler survey: M dwarfs
host fewer giant planets and at least two times more planets with M_pl sin i <
10 M_Earth than G-type stars. In contrast to previous results, planets around
our sample of very low-mass stars have a higher occurrence rate in short-period
orbits of less than 10 d. Our results demonstrate the need to take into account
host star masses in planet formation models.Comment: 15 pages, 12 figures. Accepted for publication in Astronomy &
Astrophysic
The CARMENES search for exoplanets around M dwarfs: Convective shift and starspot constraints from chromatic radial velocities
Context. Variability caused by stellar activity represents a challenge to the
discovery and characterization of terrestrial exoplanets and complicates the
interpretation of atmospheric planetary signals.
Aims. We aim to use a detailed modeling tool to reproduce the effect of
active regions on radial velocity measurements, which aids the identification
of the key parameters that have an impact on the induced variability.
Methods. We analyzed the effect of stellar activity on radial velocities as a
function of wavelength by simulating the impact of the properties of spots,
shifts induced by convective motions, and rotation. We focused our modeling
effort on the active star YZ CMi (GJ 285), which was photometrically and
spectroscopically monitored with CARMENES and the Telescopi Joan Or\'o.
Results. We demonstrate that radial velocity curves at different wavelengths
yield determinations of key properties of active regions, including spot
filling factor, temperature contrast, and location, thus solving the degeneracy
between them. Most notably, our model is also sensitive to convective motions.
Results indicate a reduced convective shift for M dwarfs when compared to
solar-type stars (in agreement with theoretical extrapolations) and points to a
small global convective redshift instead of blueshift.
Conclusions. Using a novel approach based on simultaneous chromatic radial
velocities and light curves, we can set strong constraints on stellar activity,
including an elusive parameter such as the net convective motion effect.Comment: A&A, in pres
The CARMENES search for exoplanets around M dwarfs -- A deep learning approach to determine fundamental parameters of target stars
Existing and upcoming instrumentation is collecting large amounts of
astrophysical data, which require efficient and fast analysis techniques. We
present a deep neural network architecture to analyze high-resolution stellar
spectra and predict stellar parameters such as effective temperature, surface
gravity, metallicity, and rotational velocity. With this study, we firstly
demonstrate the capability of deep neural networks to precisely recover stellar
parameters from a synthetic training set. Secondly, we analyze the application
of this method to observed spectra and the impact of the synthetic gap (i.e.,
the difference between observed and synthetic spectra) on the estimation of
stellar parameters, their errors, and their precision. Our convolutional
network is trained on synthetic PHOENIX-ACES spectra in different optical and
near-infrared wavelength regions. For each of the four stellar parameters,
, , [M/H], and , we constructed a neural
network model to estimate each parameter independently. We then applied this
method to 50 M dwarfs with high-resolution spectra taken with CARMENES (Calar
Alto high-Resolution search for M dwarfs with Exo-earths with Near-infrared and
optical Echelle Spectrographs), which operates in the visible (520-960 nm) and
near-infrared wavelength range (960-1710 nm) simultaneously. Our results are
compared with literature values for these stars. They show mostly good
agreement within the errors, but also exhibit large deviations in some cases,
especially for [M/H], pointing out the importance of a better understanding of
the synthetic gap
Спостереження як метод державного фінансового контролю за сплатою податків суб'єктами малого підприємництва
У статті проаналізовано особливості державного контролю за діяльністю суб’єктів малого підприємництва. Наведено авторське визначення методу спостереження в державному фінансовому контролі за сплатою податків та обґрунтовано доцільність його застосування в перспективі.
(The features of state control over the activities of small businesses are analyzed. The author’s definition of the method of monitoring in the state financial control over tax payments is given, and the expedience for its use in the prospects is grounded.
Mass and density of the transiting hot and rocky super-Earth LHS 1478 b (TOI-1640 b)
One of the main objectives of the Transiting Exoplanet Survey Satellite
({TESS}) mission is the discovery of small rocky planets around relatively
bright nearby stars. Here, we report the discovery and characterization of the
transiting super-Earth planet orbiting LHS~1478 (TOI-1640). The star is an
inactive red dwarf (\,mag and spectral type m3\,V) with mass and
radius estimates of \, and \,,
respectively, and an effective temperature of \,K.It was observed by
\tess in four sectors. These data revealed a transit-like feature with a period
of 1.949 days. We combined the TESS data with three ground-based transit
measurements, 57 radial velocity (RV) measurements from CARMENES, and 13 RV
measurements from IRD, determining that the signal is produced by a planet with
a mass of \, and a radius of
\,. The resulting bulk density of this planet
is 6.67\,g\,cm, which is consistent with a rocky planet with an Fe- and
MgSiO-dominated composition. Although the planet would be too hot to
sustain liquid water on its surface (its equilibrium temperature is about
595\,K, suggesting a Venus-like atmosphere), spectroscopic metrics based
on the capabilities of the forthcoming James Webb Space Telescope and the fact
that the host star is rather inactive indicate that this is one of the most
favorable known rocky exoplanets for atmospheric characterization.Comment: 14 pages, 10 figures, 6 tables, accepted for publication in A&
Precise mass determination for the keystone sub-Neptune planet transiting the mid-type M dwarf G 9-40
Context. Despite being a prominent subset of the exoplanet population discovered in the past three decades, the nature and provenance of sub-Neptune-sized planets is still one of the open questions in exoplanet science. Aims. For planets orbiting bright stars, precisely measuring the orbital and planet parameters of the system is the best approach to distinguish between competing theories regarding their formation and evolution. Methods. We obtained 69 new radial velocity observations of the mid-M dwarf G 9-40 with the CARMENES instrument to measure for the first time the mass of its transiting sub-Neptune planet, G 9-40 b, discovered in data from the K2 mission. Results. Combined with new observations from the TESS mission during Sectors 44, 45, and 46, we are able to measure the radius of the planet to an uncertainty of 3.4% (R-b = 1.900 +/- 0.065 R-circle plus) and determine its mass with a precision of 16% (M-b = 4.00 +/- 0.63 M-circle plus). The resulting bulk density of the planet is inconsistent with a terrestrial composition and suggests the presence of either a water-rich core or a significant hydrogen-rich envelope. Conclusions. G 9-40 b is referred to as a keystone planet due to its location in period-radius space within the radius valley. Several theories offer explanations for the origin and properties of this population and this planet is a valuable target for testing the dependence of those models on stellar host mass. By virtue of its brightness and small size of the host, it joins L 98-59 d as one of the two best warm (T-eq similar to 400 K) sub-Neptunes for atmospheric characterization with JWST, which will probe cloud formation in sub-Neptune-sized planets and break the degeneracies of internal composition models
An ultra-short-period transiting super-Earth orbiting the M3 dwarf TOI-1685
Funding: We acknowledge financial support from the Agencia Estatal de Investigación of the Ministerio de Ciencia, Innovación y Universidades and the ERDF through projects PID2019-109522GB-C5[1:4]/AEI/10.13039/501100011033, PGC2018-098153-B-C33, and the Centre of Excellence “Severo Ochoa” and “María deMaeztu” awards to the Instituto de Astrofísica de Canarias (SEV-2015-0548), Instituto de Astrofísica de Andalucía (SEV-2017-0709), and Centro de Astro-biología (MDM-2017-0737), the Generalitat de Catalunya/CERCA programme,“la Caixa” Foundation (100010434), European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 847648 (LCF/BQ/PI20/11760023), a University Research Support Grant from the National Astronomical Observatory of Japan, JSPS KAKENHI (JP15H02063, JP18H01265, JP18H05439, JP18H05442, and JP22000005), JSTPRESTO (JPMJPR1775), UK Science and Technology Facilities Council (ST/R000824/1), and NASA (NNX17AG24G).Dynamical histories of planetary systems, as well as the atmospheric evolution of highly irradiated planets, can be studied by characterizing the ultra-short-period planet population, which the TESS mission is particularly well suited to discover. Here, we report on the follow-up of a transit signal detected in the TESS sector 19 photometric time series of the M3.0 V star TOI-1685 (2MASS J04342248+4302148). We confirm the planetary nature of the transit signal, which has a period of Pb = 0.6691403−0.0000021+0.0000023 d, using precise radial velocity measurements taken with the CARMENES spectrograph. From the joint photometry and radial velocity analysis, we estimate the following parameters for TOI-1685 b: a mass of Mb = 3.78−0.63+0.63 M⊕, a radius of Rb = 1.70−0.07+0.07 R⊕, which together result in a bulk density of ρb = 4.21−0.82+0.95 g cm−3, and an equilibrium temperature of Teq = 1069−16+16 K. TOI-1685 b is the least dense ultra-short-period planet around an M dwarf known to date. TOI-1685 b is also one of the hottest transiting super-Earth planets with accurate dynamical mass measurements, which makes it a particularly attractive target for thermal emission spectroscopy. Additionally, we report with moderate evidence an additional non-transiting planet candidate in the system, TOI-1685 [c], which has an orbital period of Pc = 9.02−0.12+0.10 d.Publisher PDFPeer reviewe
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