- ID:
- ivo://CDS.VizieR/J/A+A/653/A53
- Title:
- DEATHSTAR. II. The S-type
- Short Name:
- J/A+A/653/A53
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- We present the re-calibrated and re-imaged fits-cubes of the second set of data from the DEATHSTAR project (DEtermining Accurate mass-loss rates for THermally pulsing AGB STARs, www.astro.uu.se/deathstar): the S-type stars. Fifteen S-type southern AGB stars were mapped in Bands 6 and 7 with the Atacama Compact Array (ACA). The generated beams have sizes of 4-8 and 3-6-arcseconds in Band 6 and 7, respectively. The rms noise level reached is typically 50-70 and 100-150mJy/beam in Band 6 and 7, respectively. The beam sizes and rms values for each source are listed in the paper together with the description of the reduction process, the analysis of the cubes and tentative line detections.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/640/A133
- Title:
- DEATHSTAR. Nearby AGB stars with ALMA ACA
- Short Name:
- J/A+A/640/A133
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the re-calibrated and re-imaged fits-cubes of the first set of data from the DEATHSTAR project (DEtermining Accurate mass-loss rates for THermally pulsing AGB STARs, www.astro.uu.se/deathstar). Forty-two southern AGB stars, 21 carbon stars and 21 M-type stars, were mapped in Bands 6 and 7 with the Atacama Compact Array (ACA). Source selection, detected line emission, data calibration procedures etc. are described in detail in the paper. The beams are typically 4-8 and 3-5-arcseconds in Band 6 and 7, respectively. The rms noise level reached is typically 50-70 and 100-150mJy/beam in Band 6 and 7, respectively. More exact beam sizes and rms values for each source are listed in the paper together with tentative line detections.
- ID:
- ivo://CDS.VizieR/J/A+A/593/A51
- Title:
- Debris discs around nearby FGK stars
- Short Name:
- J/A+A/593/A51
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Debris discs are a consequence of the planet formation process and constitute the fingerprints of planetesimal systems. Their counterparts in the solar system are the asteroid and Edgeworth-Kuiper belts. The aim of this paper is to provide robust numbers for the incidence of debris discs around FGK stars in the solar neighbourhood. The full sample of 177 FGK stars with d>=20pc proposed for the DUst around NEarby Stars (DUNES) survey is presented. Herschel/PACS observations at 100 and 160{mu}m were obtained, and were complemented in some cases with data at 70{mu}m and at 250, 350, and 500{mu}m SPIRE photometry. The 123 objects observed by the DUNES collaboration were presented in a previous paper. The remaining 54 stars, shared with the Disc Emission via a Bias-free Reconnaissance in IR and Sub-mm (DEBRIS) consortium and observed by them, and the combined full sample are studied in this paper. The incidence of debris discs per spectral type is analysed and put into context together with other parameters of the sample, like metallicity, rotation and activity, and age. The subsample of 105 stars with d>=15pc containing 23 F, 33 G, and 49 K stars is complete for F stars, almost complete for G stars, and contains a substantial number of K stars from which we draw solid conclusions on objects of this spectral type. The incidence rates of debris discs per spectral type are 0.26^+0.21^_-0.14_ (6 objects with excesses out of 23 F stars), 0.21^+0.17^_-0.11_ (7 out of 33 G stars), and 0.20^0.14^_-0.09_ (10 out of 49 K stars); the fraction for all three spectral types together is 0.22^+0.08^_-0.07_ (23 out of 105 stars). The uncertainties correspond to a 95% confidence level. The medians of the upper limits of L_dust_/L* for each spectral type are 7.8x10^-7^ (F), 1.4x10^-6^ (G), and 2.2x10^-6^ (K); the lowest values are around 4.0x10^-7^. The incidence of debris discs is similar for active (young) and inactive (old) stars. The fractional luminosity tends to drop with increasing age, as expected from collisional erosion of the debris belts.
- ID:
- ivo://CDS.VizieR/J/ApJ/719/550
- Title:
- Deep NIR imaging of {rho} Oph cloud core
- Short Name:
- J/ApJ/719/550
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A search for young substellar objects in the {rho} Oph cloud core region has been made with the aid of multiband profile-fitting point-source photometry of the deep-integration Combined Calibration Scan images of the 2MASS extended mission in the J, H, and Ks bands, and Spitzer IRAC images at 3.6, 4.5, 5.8, and 8.0um. The field of view of the combined observations was 1{deg}x9.3', and the 5{sigma} limiting magnitude at J was 20.5. Comparison of the observed spectral energy distributions with the predictions of the COND and DUSTY models, for an assumed age of 1Myr, supports the identification of many of the sources with brown dwarfs and enables the estimation of effective temperature, T_eff_. The cluster members are then readily distinguishable from background stars by their locations on a plot of flux density versus T_eff_. The range of estimated T_eff_ values extends down to ~750K which, based on the COND model, would suggest the presence of objects of sub-Jupiter mass. The results also suggest that the mass function for the {rho} Oph cloud resembles that of the {sigma} Orionis cluster based on a recent study, with both rising steadily toward lower masses. The other main result from our study is the apparent presence of a progressive blueward skew in the distribution of J-H and H-Ks colors, such that the blue end of the range becomes increasingly bluer with increasing magnitude. We suggest that this behavior might be understood in terms of the "ejected stellar embryo" hypothesis, whereby some of the lowest-mass brown dwarfs could escape to locations close to the front edge of the cloud, and thereby be seen with less extinction.
- ID:
- ivo://CDS.VizieR/J/MNRAS/489/5301
- Title:
- DES Y3 substellar LT and M catalogs
- Short Name:
- J/MNRAS/489/5301
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper we present a catalogue of 11745 brown dwarfs with spectral types ranging from L0 to T9, photometrically classified using data from the Dark Energy Survey (DES) year 3 release matched to the Vista Hemisphere Survey (VHS) DR3 and Wide-field Infrared Survey Explorer (WISE) data, covering ~2400deg^2^ up to i_AB_=22. The classification method follows the same photo-type method previously applied to SDSS-UKIDSS-WISE data. The most significant difference comes from the use of DES data instead of SDSS, which allow us to classify almost an order of magnitude more brown dwarfs than any previous search and reaching distances beyond 400 parsecs for the earliest types. Next, we also present and validate the GalmodBD simulation, which produces brown dwarf number counts as a function of structural parameters with realistic photometric properties of a given survey. We use this simulation to estimate the completeness and purity of our photometric LT catalogue down to i_AB_=22, as well as to compare to the observed number of LT types. We put constraints on the thin disk scale height for the early L (L0-L3) population to be around 450 parsecs, in agreement with previous findings. For completeness, we also publish in a separate table a catalogue of 20863 M dwarfs that passed our colour cut with spectral types greater than M6. Both the LT and the late M catalogues are found at https://des.ncsa.illinois.edu/releases/other/y3-mlt.
- ID:
- ivo://CDS.VizieR/J/A+A/591/A43
- Title:
- Differential rotation in solar-like stars
- Short Name:
- J/A+A/591/A43
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Surface differential rotation (SDR) plays a key role in dynamo models and determines a lower limit on the accuracy of stellar rotation period measurements. SDR estimates are therefore essential to constrain theoretical models and infer realistic rotation period uncertainties. We measure a lower limit to SDR in a sample of solar-like stars belonging to young loose stellar associations with the aim of investigating how SDR depends on global stellar parameters in the age range (4-95Myr). The rotation period of a solar-like star can be recovered by analyzing the flux modulation caused by dark spots and stellar rotation. The SDR and the latitude migration of dark-spots induce a modulation of the detected rotation period. We employed long-term photometry to measure the amplitude of such a modulation and to compute the quantity {Delta}{Omega}_phot_=2{pi}/P_min_-2{pi}/P_max_ that is a lower limit to SDR. We find that {Delta}{Omega}_phot_ increases with the stellar effective temperature and with the global convective turn-over timescale tau_c_, which is the characteristic time for the rise of a convective element through the stellar convection zone. We find that {Delta}{Omega}_phot_ is proportional to T_eff_^2.18+/-0.65^ in stars recently settled on the ZAMS. This power law is less steep than those found by previous authors, but closest to recent theoretical models. We investigate how {Delta}{Omega}_phot_ changes in time in a 1M_{sun}_ star. We find that {Delta}{Omega}_phot_ steeply increases between 4 and 30Myr and that it is almost constant between 30 and 95Myr. We find also that the relative shear increases with the Rossby number Ro. Although our results are qualitatively in agreement with hydrodynamical mean-field models, our measurements are systematically higher than the values predicted by these models. The discrepancy between {Delta}{Omega}_phot_ measurements and theoretical models is particularly large in stars with periods between 0.7 and 2d. Such a discrepancy, together with the anomalous SDR measured by other authors for HD 171488 (rotating in 1.31d), suggests that the rotation period could influence SDR more than predicted by the models.
- ID:
- ivo://CDS.VizieR/J/A+A/630/A104
- Title:
- Disk and halo stars C, O and Fe abundances
- Short Name:
- J/A+A/630/A104
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The abundances of carbon, oxygen, and iron in late-type stars are important parameters in exoplanetary and stellar physics, as well as key tracers of stellar populations and Galactic chemical evolution. However, standard spectroscopic abundance analyses can be prone to severe systematic errors, by the assumption that the stellar atmosphere is one-dimensional (1D) and hydrostatic, and by ignoring departures from local thermodynamic equilibrium (LTE). To address this, we carry out 3D non-LTE radiative transfer calculations for CI and OI, and 3D LTE radiative transfer calculations for FeII, across the stagger-grid of 3D hydrodynamic model atmospheres. The absolute 3D non-LTE versus 1D LTE abundance corrections can be as severe as ~0.3dex for CI lines in low-metallicity F dwarfs, and ~0.6dex for OI lines in high-metallicity F dwarfs. The 3D LTE versus 1D LTE abundance corrections for FeII lines are less severe, typically less than +0.15dex. We use the corrections in a re-analysis of carbon, oxygen, and iron in 187 F and G dwarfs in the Galactic disk and halo. Applying the differential 3D non-LTE corrections to 1D LTE abundances visibly reduces the scatter in the abundance plots. The thick disk and high- halo population rise in carbon and oxygen with decreasing metallicity, reaching a maximum of [C/Fe]~=0.2 and a plateau of [O/Fe]~=0.6 at [Fe/H]~=~1.0. The low- halo population is qualitatively similar, albeit offset towards lower metallicities and with larger scatter. Nevertheless, these populations overlap in the [C/O] versus [O/H] plane, decreasing to a plateau of [C/O]~=0.6 below [O/H]~=1.0. In the thin-disk, stars having confirmed planet detections tend to have higher values of C/O at given [O/H]; this potential signature of planet formation is only apparent after applying the abundance corrections to the 1D LTE results. Our grids of line-by-line abundance corrections are publicly available and can readily be used to improve the accuracy of spectroscopic analyses of late-type stars.
- ID:
- ivo://CDS.VizieR/J/A+A/478/507
- Title:
- Distances and atmospheric parameters of MSU stars
- Short Name:
- J/A+A/478/507
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Recent analyses of low-mass eclipsing binary stars have unveiled a significant disagreement between the observations and the predictions of stellar structure models. Results show that theoretical models underestimate the radii and overestimate the effective temperatures of low-mass stars but yield luminosities that accord with observations. A hypothesis based upon the effects of stellar activity was put forward to explain the discrepancies. Here we study the existence of the same trend in single active stars and provide a consistent scenario to explain systematic differences between active and inactive stars in the H-R diagram reported earlier. The analysis is done using single field stars of spectral types late-K and M and computing its bolometric magnitudes and temperatures through infrared colours and spectral indices. The properties of the stars in samples of active and inactive stars are compared statistically to reveal systematic differences. After accounting for a number of possible bias effects, active stars are shown to be cooler than inactive stars of similar luminosity therefore implying a larger radius as well, in proportions that are in excellent agreement with those found from eclipsing binaries. The present results generalise the existence of strong radius and temperature dependences on stellar activity to the entire population of low-mass stars, regardless of their membership in close binary systems.
- ID:
- ivo://CDS.VizieR/J/A+A/650/A146
- Title:
- Distant, pulsating red giants in southern halo
- Short Name:
- J/A+A/650/A146
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- To investigate the asymptotic giant branch (AGB) population in the Galactic halo, we search for pulsating AGB stars at a heliocentric distance over 50kpc. Our research is based on the Catalina Southern Survey (CSS) catalogue of variables, comprising 1286 long-period variables (LPVs) with declination less than -20{deg}. We first focus on the 77 stars in the cap abs(b)>30deg for which spectral M-type or C-type classification can be derived from Hamburg-ESO objective prism spectra. Most of these are oxygen-rich (M-type) and very few are carbon rich. The periods are in the range 100-500 days, and CSS amplitudes are up to 3mag. In this small sample, no halo AGB star is fainter than Ks0=12.5. This may be due to the scarcity of AGBs in the outer halo, or insufficient instrumental depth. Leaving aside spectral information, we then searched for even fainter pulsators (Ks>12.5) in the entire CSS catalogue. Gaia astrometry makes it possible to identify some contaminants. Our final result is the identification of ten candidate distant LPVs. If these ten stars obey the fundamental mode K-band period luminosity relation used for Miras and small-amplitude Miras, their distances are between 50 and 120kpc from the Sun. In a diagram showing distance versus Gaia tangential velocity, these ten stars have positions similar to those of other objects in the halo, such as globular clusters and dwarf galaxies. We also detect some underluminous AGBs that deserve further study. A detailed catalogue of the 77 high-latitude M or C stars will be made available at the CDS.
- ID:
- ivo://CDS.VizieR/J/A+A/615/A139
- Title:
- 3D non-LTE Balmer line formation
- Short Name:
- J/A+A/615/A139
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Hydrogen Balmer lines are commonly used as spectroscopic effective temperature diagnostics of late-type stars. However, reliable inferences require accurate model spectra, and the absolute accuracy of classical methods that are based on one-dimensional (1D) hydrostatic model atmospheres and local thermodynamic equilibrium (LTE) is still unclear. To investigate this, we carry out 3D non-LTE calculations for the Balmer lines, performed, for the first time, over an extensive grid of 3D hydrodynamic STAGGER model atmospheres. For H{alpha}, H{beta}, and H{gamma} we find significant 1D non-LTE versus 3D non-LTE differences (3D effects): the outer wings tend to be stronger in 3D models, particularly for H{gamma}, while the inner wings can be weaker in 3D models, particularly for H{alpha}. For H{alpha}, we also find significant 3D LTE versus 3D non-LTE differences (non-LTE effects): in warmer stars (Teff~~6500K) the inner wings tend to be weaker in non-LTE models, while at lower effective temperatures (Teff~~4500K) the inner wings can be stronger in non-LTE models; the non-LTE effects are more severe at lower metallicities. We test our 3D non-LTE models against observations of well-studied benchmark stars. For the Sun, we infer concordant effective temperatures from H{alpha}, H{beta}, and H{gamma}; however the value is too low by around 50K which could signal residual modelling shortcomings. For other benchmark stars, our 3D non-LTE models generally reproduce the effective temperatures to within 1{sigma} uncertainties. For H{alpha}, the absolute 3D effects and non-LTE effects can separately reach around 100K, in terms of inferred effective temperatures. For metal-poor turn-off stars, 1D LTE models of H{alpha} can underestimate effective temperatures by around 150K. Our 3D non-LTE model spectra are publicly available, and can be used for more reliable spectroscopic effective temperature determinations.
