ABSTRACT
We present the first release of GTC OSIRIS broad-band data archive. This is an effort conducted in the framework of the Spanish Virtual Observatory to help optimize science from the Gran ...Telescopio Canarias Archive. Data Release 1 includes 6788 broad-band images in the Sloan griz filters obtained between 2009 April and 2014 January and the associated catalogue with roughly 6.23 million detections of more than 630 000 unique sources. The catalogue contains standard PSF and Kron aperture photometry with a mean accuracy better than 0.09 and 0.15 mag, respectively. The relative astrometric residuals are always better than 30 mas and better than 15 mas in most cases. The absolute astrometric uncertainty of the catalogue is of 0.12 arcsec. In this paper we describe the procedure followed to build the image archive and the associated catalogue, as well as the quality tests carried out for validation. To illustrate some of the scientific potential of the catalogue, we also provide two examples of its scientific exploitation: discovery and identification of asteroids and cool dwarfs.
We determined effective temperatures, surface gravities, and metallicities for a sample of 343 M dwarfs observed with CARMENES, the double-channel, high-resolution spectrograph installed at the 3.5 m ...telescope at Calar Alto Observatory. We employed S
TE
P
AR
S
YN
, a Bayesian spectral synthesis implementation particularly designed to infer the stellar atmospheric parameters of late-type stars following a Markov chain Monte Carlo approach. We made use of the BT-Settl model atmospheres and the radiative transfer code
turbospectrum
to compute a grid of synthetic spectra around 75 magnetically insensitive Fe
I
and Ti
I
lines plus the TiO
γ
and
ϵ
bands. To avoid any potential degeneracy in the parameter space, we imposed Bayesian priors on
T
eff
and log
g
based on the comprehensive, multi-band photometric data available for the sample. We find that this methodology is suitable down to M7.0 V, where refractory metals such as Ti are expected to condense in the stellar photospheres. The derived
T
eff
, log
g
, and Fe/H range from 3000 to 4200 K, 4.5 to 5.3 dex, and −0.7 to 0.2 dex, respectively. Although our
T
eff
scale is in good agreement with the literature, we report large discrepancies in the Fe/H scales, which might arise from the different methodologies and sets of lines considered. However, our Fe/H is in agreement with the metallicity distribution of FGK-type stars in the solar neighbourhood and correlates well with the kinematic membership of the targets in the Galactic populations. Lastly, excellent agreement in
T
eff
is found for M dwarfs with interferometric angular diameter measurements, as well as in the Fe/H between the components in the wide physical FGK+M and M+M systems included in our sample.
Abstract
The nature and physical properties of asteroids, in particular those orbiting in the near-Earth space, are of scientific interest and practical importance. Exoplanet surveys can be excellent ...resources to detect asteroids, both already known and new objects. This is due to their similar observing requirements: large fields of view, long sequences, and short cadence. If the targeted fields are not located far from the ecliptic, many asteroids will cross the field of view occasionally. We present two complementary methodologies to identify asteroids serendipitously observed in large-area astronomical surveys. One methodology focuses on detecting already known asteroids using the Virtual Observatory tool SkyBoT, which predicts their positions and motions in the sky at a specific epoch. The other methodology applies the ssos pipeline, which is able to identify known and new asteroids based on their apparent motion. The application of these methods to the 6.4 deg2 of the sky covered by the Wide-Field CAMera Transit Survey in the J-band is described. We identified 15 661 positions of 1821 different asteroids. Of them, 182 are potential new discoveries. A publicly accessible online, Virtual Observatory compliant catalogue was created. We obtained the shapes and periods for five of our asteroids from their light curves built with additional photometry taken from external archives. We demonstrated that our methodologies are robust and reliable approaches to find, at zero cost of observing time, asteroids observed by chance in astronomical surveys. Our future goal is to apply them to other surveys with adequate temporal coverage.
We present the discovery and characterisation of two transiting planets observed by the Transiting Exoplanet Survey Satellite (TESS) orbiting the nearby (d⋆ ≈ 22 pc), bright (J ≈ 9 mag) M3.5 dwarf ...LTT 3780 (TOI–732). We confirm both planets and their association with LTT 3780 via ground-based photometry and determine their masses using precise radial velocities measured with the CARMENES spectrograph. Precise stellar parameters determined from CARMENES high-resolution spectra confirm that LTT 3780 is a mid-M dwarf with an effective temperature of T(eff) = 3360 ± 51 K, a surface gravity of log g⋆ = 4.81 ± 0.04 (cgs), and an iron abundance of Fe/H = 0.09 ± 0.16 dex, with an inferred mass of M⋆ = 0.379 ± 0.016M⊙ and a radius of R⋆ = 0.382 ± 0.012R⊙. The ultra-short-period planet LTT 3780 b (P(b) = 0.77 d) with a radius of 1.35(−0.06,+0.06) R⊕, a mass of 2.34(−0.23,+0.24) M⊕, and a bulk density of 5.24(−0.81,+0.94) g/cu.cm joins the population of Earth-size planets with rocky, terrestrial composition. The outer planet, LTT 3780 c, with an orbital period of 12.25 d, radius of 2.42(−0.10,+0.10) R⊕, mass of 6.29(−0.61,+0.63) M⊕, and mean density of 2.45(−0.37,+0.44) g/cu.cm belongs to the population of dense sub-Neptunes. With the two planets located on opposite sides of the radius gap, this planetary system is an excellent target for testing planetary formation, evolution, and atmospheric models. In particular, LTT 3780 c is an ideal object for atmospheric studies with the James Webb Space Telescope (JWST).
The high-resolution, dual channel, visible and near-infrared spectrograph CARMENES offers exciting opportunities for stellar and exoplanetary research on M dwarfs. In this work we address the ...challenge of reaching the highest radial velocity precision possible with a complex, actively cooled, cryogenic instrument, such as the near-infrared channel. We describe the performance of the instrument and the work flow used to derive precise Doppler measurements from the spectra. The capability of both CARMENES channels to detect small exoplanets is demonstrated with the example of the nearby M5.0 V star CD Cet (GJ 1057), around which we announce a super-Earth (4.0 ± 0.4
M
⊕
) companion on a 2.29 d orbit.
CARMENES input catalog of M dwarfs Perdelwitz, V.; Mittag, M.; Tal-Or, L. ...
Astronomy and astrophysics (Berlin),
08/2021, Volume:
652
Journal Article
Peer reviewed
Context.
Radial-velocity (RV) jitter caused by stellar magnetic activity is an important factor in state-of-the-art exoplanet discovery surveys such as CARMENES. Stellar rotation, along with ...heterogeneities in the photosphere and chromosphere caused by activity, can result in false-positive planet detections. Hence, it is necessary to determine the stellar rotation period and compare it to any putative planetary RV signature. Long-term measurements of activity indicators such as the chromospheric emission in the Ca
II
H&K lines (
R
HK
′
) enable the identification of magnetic activity cycles.
Aims.
In order to determine stellar rotation periods and study the long-term behavior of magnetic activity of the CARMENES guaranteed time observations (GTO) sample, it is advantageous to extract
R
HK
′
time series from archival data, since the CARMENES spectrograph does not cover the blue range of the stellar spectrum containing the Ca
II
H&K lines.
Methods.
We have assembled a catalog of 11 634 archival spectra of 186 M dwarfs acquired by seven different instruments covering the Ca
II
H&K regime: ESPaDOnS, FEROS, HARPS, HIRES, NARVAL, TIGRE, and UVES. The relative chromospheric flux in these lines,
R
HK
′
, was directly extracted from the spectra by rectification with PHOENIX synthetic spectra via narrow passbands around the Ca
II
H&K line cores.
Results.
The combination of archival spectra from various instruments results in time series for 186 stars from the CARMENES GTO sample. As an example of the use of the catalog, we report the tentative discovery of three previously unknown activity cycles of M dwarfs.
Conclusions.
We conclude that the method of extracting $ R_{\mathrm{HK}}^\prime $
with the use of model spectra yields consistent results for different instruments and that the compilation of this catalog will enable the analysis of long-term activity time series for a large number of M dwarfs.
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 Oró
.
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.
Context . Deep learning (DL) techniques are a promising approach among the set of methods used in the ever-challenging determination of stellar parameters in M dwarfs. In this context, transfer ...learning could play an important role in mitigating uncertainties in the results due to the synthetic gap (i.e. difference in feature distributions between observed and synthetic data). Aims . We propose a feature-based deep transfer learning (DTL) approach based on autoencoders to determine stellar parameters from high-resolution spectra. Using this methodology, we provide new estimations for the effective temperature, surface gravity, metallicity, and projected rotational velocity for 286 M dwarfs observed by the CARMENES survey. Methods . Using autoencoder architectures, we projected synthetic PHOENIX-ACES spectra and observed CARMENES spectra onto a new feature space of lower dimensionality in which the differences between the two domains are reduced. We used this low-dimensional new feature space as input for a convolutional neural network to obtain the stellar parameter determinations. Results . We performed an extensive analysis of our estimated stellar parameters, ranging from 3050 to 4300 K, 4.7 to 5.1 dex, and −0.53 to 0.25 dex for T eff , log , and Fe/H, respectively. Our results are broadly consistent with those of recent studies using CARMENES data, with a systematic deviation in our T eff scale towards hotter values for estimations above 3750 K. Furthermore, our methodology mitigates the deviations in metallicity found in previous DL techniques due to the synthetic gap. Conclusions . We consolidated a DTL-based methodology to determine stellar parameters in M dwarfs from synthetic spectra, with no need for high-quality measurements involved in the knowledge transfer. These results suggest the great potential of DTL to mitigate the differences in feature distributions between the observations and the PHOENIX-ACES spectra.
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