- ID:
- ivo://CDS.VizieR/J/A+A/531/A8
- Title:
- Activity indices and velocities for 890 stars
- Short Name:
- J/A+A/531/A8
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this work we present chromospheric activity indices, kinematics, radial-velocities, and rotational velocities for more than 850 FGK-type dwarfs and subgiant stars in the southern hemisphere and test how best to calibrate and measure S -indices from echelle spectra. We measured our parameters using the high-resolution and high-S/N FEROS echelle spectra acquired for this purpose. Results. We confirm the bimodal distribution of chromospheric activities for such stars and highlight the role that the more active K-dwarfs play in biasing the number of active stars. We show that the age-activity relationship does appear to continue to ages older than the Sun if we simply compare main sequence stars and subgiant stars with an offset of around 2.5Gyr between the peaks of both distributions. Also we show evidence of an increased spin-down timescale for cool K dwarfs compared with earlier F and G type stars. We highlight that activities drawn from low-resolution spectra (R<2.500') significantly increase the rms scatter when calibrating onto common systems of measurements like the Mt. Wilson system. Also we show that older and widely used catalogues of activities in the south appear to be offset compared to more recent works at the ~0.1dex level in logR'HK through calibrator drift. In addition, we show how kinematics can be used to preselect inactive stars for future planet search projects. We see the well known trend between projected rotational velocity and activity, however we also find a correlation between kinematic space velocity and chromospheric activity. It appears that after the Vaughan-Preston gap there is a quick step function in the kinematic space motion towards a significantly broader spread in velocities. We speculate on reasons for this correlation and provide some model scenarios to describe the bimodal activity distribution through magnetic saturation, residual low level gas accretion, or accretion by the star of planets or planetesimals. Finally, we provide a new empirical measurement for the disk-heating law, using the latest age-activity relationships to reconstruct the age-velocity distribution for local disk stars. We find a value of 0.337+/-0.045 for the exponent of this power law, in excellent agreement with those found using isochrone fitting methods and with theoretical disk-heating models.
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- ID:
- ivo://CDS.VizieR/J/MNRAS/372/163
- Title:
- Activity indices for southern stars
- Short Name:
- J/MNRAS/372/163
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have acquired high-resolution echelle spectra of 225 F6-M5 type stars in the Southern hemisphere. The stars are targets or candidates to be targets for the Anglo-Australian Planet Search. CaII H&K line cores were used to derive activity indices for all of these objects. The indices were converted to the Mt. Wilson system of measurements and logR'_HK_ values determined. A number of these stars had no previously derived activity indices. In addition, we have also included the stars from Tinney et al. (2002MNRAS.332..759T) using our Mt. Wilson calibration. The radial-velocity instability (also known as jitter) level was determined for all 21 planet-host stars in our data set. We find the jitter to be at a level considerably below the radial-velocity signatures in all but one of these systems. 19 stars from our sample were found to be active (logR'_HK_>-4.5) and thus have high levels of jitter. Radial-velocity analysis for planetary companions to these stars should proceed with caution.
- ID:
- ivo://CDS.VizieR/J/ApJ/697/1578
- Title:
- A debris disk study of Praesepe
- Short Name:
- J/ApJ/697/1578
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present 24um photometry of the intermediate-age open cluster Praesepe. We assemble a catalog of 193 probable cluster members that are detected in optical databases, the Two Micron All Sky Survey (2MASS), and at 24um, within an area of ~2.47deg^2^. Mid-IR excesses indicating debris disks are found for one early-type and for three solar-type stars. Corrections for sampling statistics yield a 24um excess fraction (debris disk fraction) of 6.5%+/-4.1% for luminous and 1.9%+/-1.2% for solar-type stars. The incidence of excesses is in agreement with the decay trend of debris disks as a function of age observed for other cluster and field stars.
- ID:
- ivo://CDS.VizieR/J/A+A/377/911
- Title:
- Age-metallicity relation in solar neighbourhood
- Short Name:
- J/A+A/377/911
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We derive stellar ages, from evolutionary tracks, and metallicities, from Stroemgren photometry, for a sample of 5828 dwarf and sub-dwarf stars from the Hipparcos (Cat. <I/239>) Catalogue. This stellar disk sample is used to investigate the age-metallicity diagram in the solar neighbourhood. Such diagrams are often used to derive a so called age-metallicity relation. Because of the size of our sample, we are able to quantify the impact on such diagrams, and derived relations, due to different selection effects. Some of these effects are of a more subtle sort, giving rise to erroneous conclusions. In particular we show that [1] the age-metallicity diagram is well populated at all ages and especially that old, metal-rich stars do exist, [2] the scatter in metallicity at any given age is larger than the observational errors, [3] the exclusion of cooler dwarf stars from an age-metallicity sample preferentially excludes old, metal-rich stars, depleting the upper right-hand corner of the age-metallicity diagram, [4] the distance dependence found in the Edvardsson et al. (1993, Cat. <J/A+A/275/101>) sample by Garnett & Kobulnicky (2000ApJ...532.1192G) is an expected artifact due to the construction of the original sample. We conclude that, although some of it can be attributed to stellar migration in the galactic disk, a large part of the observed scatter is intrinsic to the formation processes of stars.
- ID:
- ivo://CDS.VizieR/J/A+A/348/897
- Title:
- Ages of main-sequence stars
- Short Name:
- J/A+A/348/897
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have determined the age of a sample of nearby main-sequence stars with spectral types B9-K9. We have derived the stellar ages from five different age estimators: the location in the HR diagram compared to theoretical isochrones, the rotational velocity, the strength of chromospheric calcium emission lines, the stellar metallicity, and their space velocity. New calibrations consistent with recent theoretical isochrones are provided for the last four indicators. For hot stars, isochrones are the best indicator, while stellar rotation is best for cool stars. However, many stars require in fact a combination of different methods to properly bracket their actual age. We also discuss the uncertainties involved, in particular those in using isochrones, and we find that these uncertainties are often underestimated in the literature.
- ID:
- ivo://CDS.VizieR/J/A+A/523/A88
- Title:
- A Jupiter-mass companion around HD 109246
- Short Name:
- J/A+A/523/A88
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the detection of a Jupiter-mass planet discovered with the SOPHIE spectrograph mounted on the 1.93-m telescope at the Haute-Provence Observatory. The new planet orbits HD 109246, a G0V star slightly more metallic than the Sun. HD 109246b has a minimum mass of 0.77M_{jup}_, an orbital period of 68 days, and an eccentricity of 0.12. It is placed in a sparsely populated region of the period distribution of extrasolar planets. We also present a correction method for the so-called seeing effect that affects the SOPHIE radial velocities. We complement this discovery announcement with a description of some calibrations that are implemented in the SOPHIE automatic reduction pipeline. These calibrations allow the derivation of the photon-noise radial velocity uncertainty and some useful stellar properties (vsini, [Fe/H], log R'hk) directly from the SOPHIE data.
- ID:
- ivo://CDS.VizieR/J/AJ/142/138
- Title:
- All-sky catalog of bright M dwarfs
- Short Name:
- J/AJ/142/138
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an all-sky catalog of M dwarf stars with apparent infrared magnitude J<10. The 8889 stars are selected from the ongoing SUPERBLINK survey of stars with proper motion pm>40mas/yr, supplemented on the bright end with the Tycho-2 catalog.
- ID:
- ivo://CDS.VizieR/J/A+A/492/277
- Title:
- Analysis of Collinder 69 stars with VOSA
- Short Name:
- J/A+A/492/277
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The physical properties of almost any kind of astronomical object can be derived by fitting synthetic spectra or photometry extracted from theoretical models to observational data. We want to develop an automatic procedure to perform this kind of fitting to a relatively large sample of members of a stellar association and apply this methodology to the case of Collinder 69. We combine the multiwavelength data of our sources and follow a work-flow to derive the physical parameters of the sources. The key step of the work-flow is performed by a new VO-tool, VOSA. All the steps in this process are done in a VO environment.
- ID:
- ivo://CDS.VizieR/J/AJ/146/156
- Title:
- APOGEE M-dwarf survey. I. First year velocities
- Short Name:
- J/AJ/146/156
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We are carrying out a large ancillary program with the Sloan Digital Sky Survey, SDSS-III, using the fiber-fed multi-object near-infrared APOGEE spectrograph, to obtain high-resolution H-band spectra of more than 1200 M dwarfs. These observations will be used to measure spectroscopic rotational velocities, radial velocities, physical stellar parameters, and variability of the target stars. Here, we describe the target selection for this survey, as well as results from the first year of scientific observations based on spectra that will be publicly available in the SDSS-III DR10 data release. As part of this paper we present radial velocities and rotational velocities of over 200 M dwarfs, with a vsini precision of ~2km/s and a measurement floor at vsini=4km/s. This survey significantly increases the number of M dwarfs studied for rotational velocities and radial velocity variability (at ~100-200m/s), and will inform and advance the target selection for planned radial velocity and photometric searches for low-mass exoplanets around M dwarfs, such as the Habitable Zone Planet Finder, CARMENES, and TESS. Multiple epochs of radial velocity observations enable us to identify short period binaries, and adaptive optics imaging of a subset of stars enables the detection of possible stellar companions at larger separations. The high-resolution APOGEE spectra, covering the entire H band, provide the opportunity to measure physical stellar parameters such as effective temperatures and metallicities for many of these stars. At the culmination of this survey, we will have obtained multi-epoch spectra and radial velocities for over 1400 stars spanning the spectral range M0-L0, providing the largest set of near-infrared M dwarf spectra at high resolution, and more than doubling the number of known spectroscopic vsini values for M dwarfs. Furthermore, by modeling telluric lines to correct for small instrumental radial velocity shifts, we hope to achieve a relative velocity precision floor of 50m/s for bright M dwarfs. With three or more epochs, this precision is adequate to detect substellar companions, including giant planets with short orbital periods, and flag them for higher-cadence followup. We present preliminary, and promising, results of this telluric modeling technique in this paper.
- ID:
- ivo://CDS.VizieR/J/AJ/159/182
- Title:
- APOGEE Net, YSOs parameters through deep learning
- Short Name:
- J/AJ/159/182
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Machine learning allows for efficient extraction of physical properties from stellar spectra that have been obtained by large surveys. The viability of machine-learning approaches has been demonstrated for spectra covering a variety of wavelengths and spectral resolutions, but most often for main-sequence (MS) or evolved stars, where reliable synthetic spectra provide labels and data for training. Spectral models of young stellar objects (YSOs) and low-mass MS stars are less well-matched to their empirical counterparts, however, posing barriers to previous approaches to classify spectra of such stars. In this work, we generate labels for YSOs and low-mass MS stars through their photometry. We then use these labels to train a deep convolutional neural network to predict logg, Teff, and Fe/H for stars with Apache Point Observatory Galactic Evolution Experiment (APOGEE) spectra in the DR14 data set. This "APOGEE Net" has produced reliable predictions of logg for YSOs, with uncertainties of within 0.1dex and a good agreement with the structure indicated by pre-MS evolutionary tracks, and it correlates well with independently derived stellar radii. These values will be useful for studying pre-MS stellar populations to accurately diagnose membership and ages.
