- ID:
- ivo://CDS.VizieR/J/ApJ/835/61
- Title:
- Chromospherically active stars in RAVE. II.
- Short Name:
- J/ApJ/835/61
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A large sample of over 38000 chromospherically active candidate solar-like stars and cooler dwarfs from the RAVE survey is addressed in this paper. An improved activity identification with respect to the previous study was introduced to build a catalog of field stars in the solar neighborhood with an excess emission flux in the calcium infrared triplet wavelength region. The central result of this work is the calibration of the age-activity relation for main-sequence dwarfs in a range from a few 10Myr up to a few Gyr. It enabled an order of magnitude age estimation of the entire active sample. Almost 15000 stars are shown to be younger than 1Gyr and ~2000 younger than 100Myr. The young age of the most active stars is confirmed by their position off the main sequence in the J-K versus N_UV_-V diagram showing strong ultraviolet excess, mid-infrared excess in the J-K versus W_1_-W_2_ diagram, and very cool temperatures (J-K>0.7). They overlap with the reference pre-main-sequence RAVE stars often displaying X-ray emission. The activity level increasing with the color reveals their different nature from the solar-like stars and probably represents an underlying dynamo-generating magnetic fields in cool stars. Of the RAVE objects from DR5, 50% are found in the TGAS catalog and supplemented with accurate parallaxes and proper motions by Gaia. This makes the database of a large number of young stars in a combination with RAVE's radial velocities directly useful as a tracer of the very recent large-scale star formation history in the solar neighborhood.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJS/152/261
- Title:
- Chromospheric Ca II emission in nearby stars
- Short Name:
- J/ApJS/152/261
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present chromospheric CaII H and K activity measurements, rotation periods, and ages for ~1200 F, G, K, and M type main-sequence stars from ~18000 archival spectra taken at Keck and Lick Observatories as a part of the California and Carnegie Planet Search Project. We have calibrated our chromospheric S-values against the Mount Wilson chromospheric activity data. From these measurements we have calculated median activity levels and derived R'_HK_, stellar ages, and rotation periods from general parameterizations for 1228 stars, ~1000 of which have no previously published S-values. We also present precise time series of activity measurements for these stars.
- ID:
- ivo://CDS.VizieR/J/AJ/131/1674
- Title:
- Close binary systems from SDSS DR4
- Short Name:
- J/AJ/131/1674
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a spectroscopic sample of 746 detached close binary systems from the Sloan Digital Sky Survey (SDSS) Fourth Data Release (2006ApJS..162...38A). The majority of these binaries consist of a white dwarf primary and a low-mass secondary (typically M dwarf) companion. We have determined the temperature and gravity for 496 of the white dwarf primaries and the spectral type and magnetic activity properties for 661 of the low-mass secondaries. We have estimated the distances for each of the white dwarf-main-sequence star binaries and use white dwarf evolutionary grids to establish the age of each binary system from the white dwarf cooling times.
- ID:
- ivo://CDS.VizieR/J/AJ/144/93
- Title:
- Close white dwarf + M dwarf binaries (WD+dM)
- Short Name:
- J/AJ/144/93
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a study of close white dwarf and M dwarf (WD+dM) binary systems and examine the effect that a close companion has on the magnetic field generation in M dwarfs. We use a base sample of 1602 white dwarf main-sequence binaries from Rebassa-Mansergas et al. to develop a set of color cuts in GALEX, SDSS, UKIDSS, and 2MASS color space. Then using the SDSS Data Release 8 spectroscopic database, we construct a sample of 1756 WD+dM high-quality pairs from our color cuts and previous catalogs. We separate the individual WD and dM from each spectrum using an iterative technique that compares the WD and dM components to best-fit templates. Using the absolute height above the Galactic plane as a proxy for age, and the H{alpha} emission line as an indicator for magnetic activity, we investigate the age-activity relation for our sample for spectral types <=M7. Our results show that early-type M dwarfs (<=M4) in close binary systems are more likely to be active and have longer activity lifetimes compared to their field counterparts. However, at a spectral type of M5 (just past the onset of full convection in M dwarfs), the activity fraction and lifetimes of WD+dM binary systems become more comparable to that of the field M dwarfs. One of the implications of having a close binary companion is presumed to be increased stellar rotation through disk disruption, tidal effects, or angular momentum exchange. Thus, we interpret the similarity in activity behavior between late-type dMs in WD+dM pairs and late-type field dMs to be due to a decrease in sensitivity in close binary companions (or stellar rotation), which has implications for the nature of magnetic activity in fully convective stars. Using the WD components of the pairs, we find WD cooling ages to use as an additional constraint on the age-activity relation for our sample. We find that, on average, active early-type dMs tend to be younger and that active late-type dMs span a much broader age regime making them indistinguishable from the inactive late-type population. We also show that magnetic strength, as measured by H{alpha}, is comparable between paired and field M dwarfs until a spectral type of M6/M7 where M dwarf activity for stars with close companions becomes much stronger. In addition, we present 37 very close candidate pairs with fast-moving orbits that display radial velocity changes over hour timescales.
- ID:
- ivo://CDS.VizieR/J/A+A/524/A44
- Title:
- CN and CH line strengths in 12 globulars
- Short Name:
- J/A+A/524/A44
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Globular clusters show star-to-star abundance variations for light elements that are not yet well understood. The preferred explanation involves a self-enrichment scenario, within which two subsequent generations of stars co-exist in globular clusters. Observations of chemical abundances in the main sequence and sub-giant branch stars allow us to investigate the signature of this chemically processed material without the complicating effects caused by stellar evolution and internal mixing. Our main goal is to investigate the carbon-nitrogen anti-correlation with low-resolution spectroscopy of 20-50 stars fainter than the first dredge-up in seven Galactic globular clusters (NGC288, NGC1851, NGC5927, NGC6352, NGC6388, and Pal12) with different properties. We complemented our observations with 47Tuc archival data, with four additional clusters from the literature (M15, M22, M55, NGC362), and with additional literature data on NGC288.
- ID:
- ivo://CDS.VizieR/J/AJ/153/165
- Title:
- Collisions of terrestrial worlds
- Short Name:
- J/AJ/153/165
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of an investigation into the occurrence and properties (stellar age and mass trends) of low- mass field stars exhibiting extreme mid-infrared (MIR) excesses (LIR/L*~>~0.01). Stars for the analysis were initially selected from the Motion Verified Red Stars (MoVeRS) catalog of photometric stars with Sloan Digital Sky Survey, 2MASS, and WISE photometry and significant proper motions. We identify 584 stars exhibiting extreme MIR excesses, selected based on an empirical relationship for main-sequence W1-W3 colors. For a small subset of the sample, we show, using spectroscopic tracers of stellar age (H{alpha} and LiI) and luminosity class, that the parent sample is most likely comprised of field dwarfs (>1Gyr). We also develop the Low-mass Kinematics (LoKi) galactic model to estimate the completeness of the extreme MIR excess sample. Using Galactic height as a proxy for stellar age, the completeness-corrected analysis indicates a distinct age dependence for field stars exhibiting extreme MIR excesses. We also find a trend with stellar mass (using r-z color as a proxy). Our findings are consistent with the detected extreme MIR excesses originating from dust created in a short-lived collisional cascade (<100000-years) during a giant impact between two large planetismals or terrestrial planets. These stars with extreme MIR excesses also provide support for planetary collisions being the dominant mechanism in creating the observed Kepler dichotomy (the need for more than a single mode, typically two, to explain the variety of planetary system architectures Kepler has observed), rather than different formation mechanisms.
- ID:
- ivo://CDS.VizieR/J/AJ/139/1808
- Title:
- Colors and kinematics of SDSS L dwarfs
- Short Name:
- J/AJ/139/1808
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a sample of 484 L dwarfs, 210 of which are newly discovered from the Sloan Digital Sky Survey (SDSS) Data Release 7 spectroscopic database. We combine this sample with known L dwarfs to investigate their izJHKS colors. We present photometric distance relations based on i-z and i-J colors and derive distances to our L dwarf sample. We combine the distances with SDSS/2MASS proper motions in order to examine the tangential velocities.
- ID:
- ivo://CDS.VizieR/II/19
- Title:
- Colors of F and G dwarfs
- Short Name:
- II/19
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Synthetic spectra have been computed for F and G dwarf stars, using a number of values of chemical abundances, Doppler broadening velocity and damping constants. Filter transmission function have been convolved with thee spectra to yield color indices in 3 photometric systems.
- ID:
- ivo://CDS.VizieR/J/ApJ/792/119
- Title:
- Companions to nearby stars from Pan-STARRS 1
- Short Name:
- J/ApJ/792/119
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the discovery of 57 wide (>5'') separation, low-mass (stellar and substellar) companions to stars in the solar neighborhood identified from Pan-STARRS 1 (PS1) data and the spectral classification of 31 previously known companions. Our companions represent a selective subsample of promising candidates and span a range in spectral type of K7-L9 with the addition of one DA white dwarf. These were identified primarily from a dedicated common proper motion search around nearby stars, along with a few as serendipitous discoveries from our Pan-STARRS 1 brown dwarf search. Our discoveries include 23 new L dwarf companions and one known L dwarf not previously identified as a companion. The primary stars around which we searched for companions come from a list of bright stars with well-measured parallaxes and large proper motions from the Hipparcos catalog (8583 stars, mostly A-K dwarfs) and fainter stars from other proper motion catalogs (79170 stars, mostly M dwarfs). We examine the likelihood that our companions are chance alignments between unrelated stars and conclude that this is unlikely for the majority of the objects that we have followed-up spectroscopically. We also examine the entire population of ultracool (>M7) dwarf companions and conclude that while some are loosely bound, most are unlikely to be disrupted over the course of ~10 Gyr. Our search increases the number of ultracool M dwarf companions wider than 300 AU by 88% and increases the number of L dwarf companions in the same separation range by 82%. Finally, we resolve our new L dwarf companion to HIP 6407 into a tight (0.13'', 7.4 AU) L1+T3 binary, making the system a hierarchical triple. Our search for these key benchmarks against which brown dwarf and exoplanet atmosphere models are tested has yielded the largest number of discoveries to date.
- ID:
- ivo://CDS.VizieR/J/A+A/654/A168
- Title:
- Convective blueshifts for solar-type stars
- Short Name:
- J/A+A/654/A168
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- The detection of earth-mass exoplanets in the habitable zone around solar-mass stars using the radial velocity technique requires extremely high- precision of the order of 10cm/s. This puts the required noise floor below the intrinsic variability of even relatively inactive stars, like the Sun. One such variable is convective blueshift varying temporally, spatially and between spectral lines. We develop a novel approach to measure convective blueshift and determine the strength of convective blueshift for 810 stars observed by the HARPS spectrograph, spanning spectral types from late-F, G, K to early-M. We derive a model to infer blueshift velocity for lines of any depth in later-type stars of any effective temperature. Using a custom list of spectral lines, covering a wide range of absorption depths, we create a model for the line-core shift as a function of line depth, commonly known as the third signature of granulation. For this we utilize an extremely high-resolution solar spectrum (R~1.000.000) to empirically account for the non-linear nature of the third signature. The solar third signature is then scaled to all 810 stars. Through this we obtain a measure of the convective blueshift relative to the Sun as a function of stellar effective temperature. We confirm the general correlation of increasing convective blueshift with effective temperature and establish a tight, cubic relation between the two that strongly increases for stars above ~5800K. For stars between ~4100K and ~4700K we show for the first time a plateau in convective shift and a possible onset of a plateau for stars above 6000K. Stars below ~4000K show neither blue or red shift. We provide a table listing expected blueshift velocities for each spectral subtype in the data set to quickly access the intrinsic noise floor through convective blueshift for the RV technique.
