- ID:
- ivo://CDS.VizieR/J/AJ/111/439
- Title:
- Chromospheric emission in late-type stars.
- Short Name:
- J/AJ/111/439
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- More than 800 southern stars within 50pc have been observed for chromospheric emission in the cores of the Ca II H and K lines. Most of the sample targets were selected to be G dwarfs on the basis of colors and spectral types. The bimodal distribution in stellar activity first noted in a sample of northern stars by Vaughan and Preston (1980PASP...92..385V) is confirmed, and the percentage of active stars, about 30%, is remarkably consistent between the northern and southern surveys. This is especially compelling given that we have used an entirely different instrumental setup and stellar sample than used in the previous study. Comparisons to the Sun, a relatively inactive star, show that most nearby solar-type stars have a similar activity level, and presumably a similar age. We identify two additional subsamples of stars -- a very active group, and a very inactive group. The very active group may be made up of young stars near the Sun, accounting for only a few percent of the sample, and appears to be less than ~0.1Gyr old. Included in this high-activity tail of the distribution, however, is a subset of very close binaries of the RS CVn or W UMa types. The remaining members of this population may be undetected close binaries or very young single stars. The very inactive group of stars, contributing ~5%-10% to the total sample, may be those caught during a Maunder Minimum type phase. If the observations of the survey stars are considered to be a sequence of snapshots of the Sun during its life, we might expect that the Sun will spend about 10% of the remainder of its main sequence life in a Maunder Minimum phase.
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Search Results
- ID:
- ivo://CDS.VizieR/J/MNRAS/414/418
- Title:
- Chromospheric Mg II h+k flux of evolved stars
- Short Name:
- J/MNRAS/414/418
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Of a total of 177 cool G, K and M giants and supergiants, we measured the MgII h+k line emission of extended chromospheres in high-resolution (LWR) International Ultraviolet Explorer (IUE) spectra by using the IUE final data archive at the Space Telescope Science Institute (STScI) and derived the respective stellar surface fluxes. They represent the chromospheric radiative energy losses presumably related to basal heating by the dissipation of acoustic waves, plus a highly variable contribution due to magnetic activity.
- ID:
- ivo://CDS.VizieR/J/A+A/579/A20
- Title:
- Circumstellar debris discs
- Short Name:
- J/A+A/579/A20
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Tentative correlations between the presence of dusty circumstellar debris discs and low-mass planets have recently been presented. In parallel, detailed chemical abundance studies have reported different trends between samples of planet and non-planet hosts. Whether these chemical differences are indeed related to the presence of planets is still strongly debated. We aim to test whether solar-type stars with debris discs show any chemical peculiarity that could be related to the planet formation process. We determine in a homogeneous way the metallicity, [Fe/H], and abundances of individual elements of a sample of 251 stars including stars with known debris discs, stars harbouring simultaneously debris discs and planets, stars hosting exclusively planets, and a comparison sample of stars without known discs or planets. High-resolution echelle spectra (R~57000) from 2-3m class telescopes are used. Our methodology includes the calculation of the fundamental stellar parameters (T_eff_, logg, microturbulent velocity, and metallicity) by applying the iron ionisation and equilibrium conditions to several isolated Fe i and Fe ii lines, as well as individual abundances of C, O, Na, Mg, Al, Si, S, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, and Zn.
- ID:
- ivo://CDS.VizieR/J/A+A/600/A71
- Title:
- C17O and C18O spectra of nine AGB stars
- Short Name:
- J/A+A/600/A71
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We seek to investigate the ^17^O/^18^O ratio for a sample of AGB stars containing M-, S-, and C-type stars. These ratios are evaluated in relation to fundamental stellar evolution parameters: the stellar initial mass and pulsation period. Circumstellar ^13^C^16^O, ^12^C^17^O, and ^12^C^18^O line observations were obtained for a sample of nine stars with various singledish long-wavelength facilities. Line intensity ratios are shown to relate directly to the surface ^17^O/^18^O abundance ratio. Stellar evolution models predict the ^17^O/^18^O ratio to be a sensitive function of initial mass and to remain constant throughout the entire TP-AGB phase for stars initially less massive than 5 solar masses. This makes the measured ratio a probe of the initial stellar mass. Observed ^17^O/^18^O ratios are found to be well in the range predicted by stellar evolution models that do not consider convective overshooting. From this, accurate initial mass estimates are calculated for seven sources. For the remaining two sources, there are two mass solutions, although there is a larger probability that the low-mass solution is correct. Finally, we present hints at a possible separation between M/S- and C-type stars when comparing the ^17^O/^18^O ratio to the stellar pulsation period.
- ID:
- ivo://CDS.VizieR/J/A+AS/99/291
- Title:
- CO and HCN observations of circumstellar envelopes
- Short Name:
- J/A+AS/99/291
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have searched the literature for all observations of the ^12^CO(1-0), ^12^CO(2-1), and HCN(1-0) lines in circumstellar envelopes of late type stars published between January 1985 and September 1992. We report data for 1361 observations (stellar velocity, expansion velocity, peak intensity, integrated area, noise level). This CO-HCN sample now contains 444 sources. 184 are identified as oxygen-rich, 205 as carbon-rich, and there are 9 S stars. About 85% of the sources are AGB stars. There are 32 planetary nebulae and about thirty post-AGB stars candidates. Besides results of millimeter observations, we also list identifications, coordinates, IRAS data, chemical and spectral types for every source. For AGB stars, we have estimated (or compiled) bolometric fluxes and distances for 349 sources, and mass loss rates deduced from CO results for 324 sources, taking into account the influence of the CO photodissociation radius. We also list mass loss rates derived from detailed models of CO emission which we could find in the literature.
- ID:
- ivo://CDS.VizieR/J/A+AS/93/121
- Title:
- CO emission from a sample of IRAS sources
- Short Name:
- J/A+AS/93/121
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The first results from a survey of circumstellar CO(1-0) emission are presented. The sources were selected from the IRAS point source catalog according to the IRAS color criteria described in van der Veen and Habing (1988A&A...194..125V). The sources have good quality fluxes at 12, 25, and 60 microns, flux densities larger than 20Jy at 25{mu}m, and are situated more than 5{deg} away from the Galactic plane. The survey is undertaken to study the relationship between mass loss rates, dust properties, and the evolution along the AGB. The sample consists of 787 sources and contains both oxygen and carbon-rich stars, including Mira variables, OH/IR objects, protoplanetary nebulae, planetary nebulae, and 60-micron excess sources. So far, 519 objects, situated on both the northern and the southern sky, have been observed; 163 sources were found to have circumstellar CO emission, and in 58 of these CO emission has not previously been detected.
- 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/J/A+A/551/A46
- Title:
- Compiled photometry for Cham I and II members
- Short Name:
- J/A+A/551/A46
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a proper motion study aiming at providing further evidence on the origin of the proposed stellar members of the Chamaeleon I and II clouds and to identify interlopers from the foreground young clusters {epsilon} Cha and {eta} Cha. We compiled lists of spectroscopically confirmed members of the four associations, and of background objects in the same line of sight. Using Virtual Observatory tools, we cross-matched these lists with the UCAC3 (Cat. I/315) catalogue to get proper motions for the objects. In the vector point diagram, we identified the different moving groups, and used this information to study the membership of proposed candidate members of the associations from the literature. For those objects with available radial velocities, we computed their Galactic space velocities. We compiled photometry from public data archives and from the literature for the Cha I and II objects. We looked for correlations between the properties of the objects and their proper motions.
- ID:
- ivo://CDS.VizieR/J/A+A/557/A104
- Title:
- CO observations of post-AGB stars
- Short Name:
- J/A+A/557/A104
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- There is a group of binary post-AGB stars that show conspicuous near infrared (NIR) excess, which is usually assumed to arise from hot dust in very compact possibly rotating disks. These stars are surrounded by significantly fainter nebulae than the standard, well studied protoplanetary and planetary nebulae (PPNe, PNe). We aim to identify and study extended rotating disks around these stars and shed light on the role of disks in the formation and shaping of planetary nebulae. We present high-sensitivity mm-wave observations of CO lines in 24 objects of this type. The resulting CO lines are compared with profiles expected to arise from rotating disks, from both theoretical and observational grounds. We derive simple formulae that allow us to determine the mass of the CO-emitting gas and estimate its extent. The reliability and uncertainty of the methods are also widely discussed. CO emission is detected in most observed sources, and the line profiles show that the emissions very probably come from disks in rotation. We derive typical values of the disk mass between 10^-3^ and 10^-2^M_{sun}_, about two orders of magnitude lower than the (total) masses of standard PPNe. The high-detection rate (upper limits being not very significant) clearly confirm that the NIR excess of these stars arises from compact disks in rotation, which are likely the inner parts of those found here. Low-velocity outflows are also found in about eight objects with moderate expansion velocities of ~10km/s, to be compared with the velocities of about 100km/s often found in standard PPNe. Except for two sources with complex profiles, the outflowing gas in our objects represents a minor nebular component. Our simple estimates of the typical disk sizes yields values ~0.5-1arcsec, which is between 5x10^15^ and 3x10^16^cm. Estimates of the linear momenta carried by the outflows, which can only be performed in a few well studied objects, also yield moderate values when compared to the linear momenta that can be released by the stellar radiation pressure (contrary, again, to the case of the very massive and fast bipolar outflows in $standard$ PPNe that are strongly overluminous). The mass and dynamics of nebulae around various classes of post-AGB stars differ very significantly, and we can expect the formation of PNe with very different properties.
- ID:
- ivo://CDS.VizieR/J/ApJ/597/323
- Title:
- Cool stars at the Galactic Center
- Short Name:
- J/ApJ/597/323
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present {lambda}/{Delta}{lambda}=550-1200 near-infrared H and K spectra for a magnitude-limited sample of 79 asymptotic giant branch and cool supergiant stars in the central ~5pc (diameter) of the Galaxy. We use a set of similar spectra obtained for solar neighborhood stars with known Teff and Mbol that is in the same range as the Galactic center (GC) sample to derive Teff and Mbol for the GC sample. We then construct the H-R diagram for the GC sample. Using an automated maximum likelihood routine, we derive a coarse star formation history of the GC.
