- ID:
- ivo://CDS.VizieR/J/ApJS/166/249
- Title:
- Stellar dynamics and proper motions in 47Tuc
- Short Name:
- J/ApJS/166/249
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have used HST imaging of the central regions of the globular cluster 47 Tucanae (=NGC 104), taken with the WFPC2 and ACS instruments between 1995 and 2002, to derive proper motions and U- and V-band magnitudes for 14366 stars within 100 (about 5 core radii) of the cluster center. This represents the largest set of member velocities collected for any globular cluster. The stars involved range in brightness from just fainter than the horizontal branch of the cluster to more than 2.5mag below the main-sequence turnoff. In the course of obtaining these kinematic data, we also use a recent set of ACS images to define a list of astrometrically calibrated positions (and F475W magnitudes) for nearly 130000 stars in a larger, 3x3 central area. We describe our data reduction procedures in some detail and provide the full position, photometric, and velocity data.
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Search Results
- ID:
- ivo://CDS.VizieR/J/MNRAS/394/1338
- Title:
- Stellar effective magnetic fields. II.
- Short Name:
- J/MNRAS/394/1338
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the second catalog of averaged quadratic effective magnetic fields <B_e_> of 1212 main sequence and giant stars, and 11 white dwarfs. Our sample includes a subset of 610 chemically peculiar early-type stars. Some stars in the sample are members of several open clusters. The catalog was derived from measurements of the longitudinal magnetic field strength B_e_ for stars, which were scattered in the published sources.
- ID:
- ivo://CDS.VizieR/J/ApJ/766/136
- Title:
- Stellar encounter rates in Galactic GCs
- Short Name:
- J/ApJ/766/136
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The high stellar densities in the cores of globular clusters cause significant stellar interactions. These stellar interactions can produce close binary mass-transferring systems involving compact objects and their progeny, such as X-ray binaries and radio millisecond pulsars. Comparing the numbers of these systems and interaction rates in different clusters drives our understanding of how cluster parameters affect the production of close binaries. In this paper we estimate stellar encounter rates ({Gamma}) for 124 Galactic globular clusters based on observational data as opposed to the methods previously employed, which assumed "King-model" profiles for all clusters. By deprojecting cluster surface brightness profiles to estimate luminosity density profiles, we treat "King-model" and "core-collapsed" clusters in the same way. In addition, we use Monte Carlo simulations to investigate the effects of uncertainties in various observational parameters (distance, reddening, surface brightness) on {Gamma}, producing the first catalog of globular cluster stellar encounter rates with estimated errors. Comparing our results with published observations of likely products of stellar interactions (numbers of X-ray binaries, numbers of radio millisecond pulsars, and {gamma}-ray luminosity) we find both clear correlations and some differences with published results.
- ID:
- ivo://CDS.VizieR/J/MNRAS/454/3267
- Title:
- Stellar encounters with long-period comets
- Short Name:
- J/MNRAS/454/3267
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Solar system's Oort cloud can be perturbed by the Galactic tide and by individual passing stars. These perturbations can inject Oort cloud objects into the inner parts of the Solar system, where they may be observed as the long-period comets (periods longer than 200yr). Using dynamical simulations of the Oort cloud under the perturbing effects of the tide and 61 known stellar encounters, we investigate the link between long-period comets and encounters. We find that past encounters were responsible for injecting at least 5 percent of the currently known long-period comets. This is a lower limit due to the incompleteness of known encounters. Although the Galactic tide seems to play the dominant role in producing the observed long-period comets, the non-uniform longitude distribution of the cometary perihelia suggests the existence of strong - but as yet unidentified - stellar encounters or other impulses. The strongest individual future and past encounters are probably HIP 89825 (Gliese 710) and HIP 14473, which contribute at most 8 and 6 percent to the total flux of long-period comets, respectively. Our results show that the strength of an encounter can be approximated well by a simple proxy, which will be convenient for quickly identifying significant encounters in large data sets. Our analysis also indicates a smaller population of the Oort cloud than is usually assumed, which would bring the mass of the solar nebula into line with planet formation theories.
- ID:
- ivo://CDS.VizieR/J/ApJ/764/21
- Title:
- Stellar evolutionary models with 13-120Msun
- Short Name:
- J/ApJ/764/21
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first set of a new generation of models of massive stars with a solar composition extending between 13 and 120M_{sun}_, computed with and without the effects of rotation. We included two instabilities induced by rotation: the meridional circulation and the shear instability. We implemented two alternative schemes to treat the transport of the angular momentum: the advection-diffusion formalism and the simpler purely diffusive one. The full evolution from the pre-main sequence up to the pre-supernova stage is followed in detail with a very extended nuclear network. The explosive yields are provided for a variety of possible mass cuts and are available at the Web site http://www.iasf-roma.inaf.it/orfeo/public_html. We find that both the He and the CO core masses are larger than those of their non-rotating counterparts. Also the C abundance left by the He burning is lower than in the non-rotating case, especially for stars with an initial mass of 13-25M_{sun}_, and this affects the final mass-radius relation, basically the final binding energy, at the pre-supernova stage. The elemental yields produced by a generation of stars rotating initially at 300km/s do not change substantially with respect to those produced by a generation of non-rotating massive stars, the main differences being a slight overproduction of the weak s-component and a larger production of F. Since rotation also affects the mass-loss rate, either directly or indirectly, we find substantial differences in the lifetimes as O-type and Wolf-Rayet subtypes between the rotating and non-rotating models. The maximum mass exploding as Type IIP supernova ranges between 15 and 20M _{sun}_ in both sets of models (this value depends basically on the larger mass-loss rates in the red supergiant phase due to the inclusion of the dust-driven wind). This limiting value is in remarkably good agreement with current estimates.
- ID:
- ivo://CDS.VizieR/J/A+A/299/755
- Title:
- Stellar evolution. II. Post-AGB
- Short Name:
- J/A+A/299/755
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a set of evolutionary tracks for central stars of planetary nebulae in the range from 0.53 to 0.94M_{sun}_. These models are based on extensive stellar evolution calculations for initial masses between 1 and 7M_{sun}_ which have been carried out all the way from the main sequence through the AGB towards the stage of white dwarfs.
- ID:
- ivo://CDS.VizieR/J/MNRAS/298/525
- Title:
- Stellar evolution models for Z = 0.0001 to 0.03
- Short Name:
- J/MNRAS/298/525
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have calculated a grid of empirically well tested evolutionary tracks with masses M between 0.5 and 50M_{sun}_, spaced by approximately 0.1 in log M, and with metallicities Z=0.0001, 0.0003, 0.001, 0.004, 0.01, 0.02 and 0.03. We use a robust and fast evolution code with a self-adaptive non-Lagrangian mesh, which employs the mixing-length theory but treats convective mixing as a diffusion process, solving simultaneously for the structure and the chemical composition. The hydrogen and helium abundances are chosen as functions of the metallicity: X=0.76-3.0Z and Y=0.24+2.0Z. Two sets of models were computed, one without and one with a certain amount of enhanced mixing or 'overshooting'.
- ID:
- ivo://CDS.VizieR/J/A+A/557/A128
- Title:
- Stellar [Fe/H] and [Na/H] in NGC6752
- Short Name:
- J/A+A/557/A128
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new method to estimate the fraction of stars with chemical composition of first and second(s) generation(s) currently hosted in Galactic globular clusters (GCs). We compare cluster and field stars of similar metallicity in the [Fe/H]-[Na/H] plane. Since the phenomenon of multiple populations is only restricted to the cluster environment, the number of GC stars whose location coincides with that of field stars provides the fraction of first generation stars in that cluster. By exclusion, the fraction of second generation stars is derived. We assembled a dataset of 1891 field stars of the thin disk, thick disk, and halo of the Milky Way in the metallicity range -3.15<=[Fe/H]<=+0.48dex and with Na abundance from high resolution spectra. They are mostly dwarfs, but include also giants. Considering only the range in metallicity spanned by most GCs extensively studied for the Na-O anticorrelation (-2.36<=[Fe/H]<=-0.33dex), we have 804 stars. The total sample is homogeneized by offsets in [Fe/H] and [Na/H] with respect to a reference sample using the same line list and NLTE correction for Na adopted in a recent extensive survey of GC stars. This fully accounts for offsets among analyses due to different temperature scales, line lists, adopted (or neglected) corrections for departures from LTE. We illustrate our method estimating the fraction of first and second generation stars in the well studied GC NGC 6752. As a by-product, the comparison of [Na/H] values in GC and field stars suggests that at least two classes of old stellar systems probably contributed to the halo assembly: one group with characteristics similar to the currently existing GCs, and the other more similar to the present-day dwarf satellite galaxies.
- ID:
- ivo://CDS.VizieR/J/AJ/151/166
- Title:
- Stellar flares and variables from 2009-2010 CSTAR
- Short Name:
- J/AJ/151/166
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Chinese Small Telescope Array (CSTAR) carried out high-cadence time-series observations of ~20.1 square degrees centered on the South Celestial Pole during the 2008, 2009, and 2010 winter seasons from Dome A in Antarctica. The nearly continuous six months of dark conditions during each observing season allowed for >10^6^ images to be collected through gri and clear filters, resulting in the detection of >10^4^ sources over the course of three years of operation. The nearly space-like conditions in the Antarctic plateau are an ideal testbed for the suitability of very small-aperture (<20cm) telescopes to detect transient events, variable stars, and stellar flares. We present the results of a robust search for such objects using difference image analysis of the data obtained during the 2009 and 2010 winter seasons. While no transients were found, we detected 29 flaring events and find a normalized flaring rate of 5+/-4*10^-7^flare/hr for late-K dwarfs, 1+/-1*10^-6^flare/hr for M dwarfs and 7+/-1*10^-7^flare/hr for all other stars in our sample. We suggest future small-aperture telescopes planned for deployment at Dome A would benefit from a tracking mechanism, to help alleviate effects from ghosting, and a finer pixel scale, to increase the telescope's sensitivity to faint objects. We find that the light curves of non-transient sources have excellent photometric qualities once corrected for systematics, and are limited only by photon noise and atmospheric scintillation.
- ID:
- ivo://CDS.VizieR/J/ApJ/829/23
- Title:
- Stellar flares from Q0-Q17 Kepler LCs
- Short Name:
- J/ApJ/829/23
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A homogeneous search for stellar flares has been performed using every available Kepler light curve. An iterative light curve de-trending approach was used to filter out both astrophysical and systematic variability to detect flares. The flare recovery completeness has also been computed throughout each light curve using artificial flare injection tests, and the tools for this work have been made publicly available. The final sample contains 851168 candidate flare events recovered above the 68% completeness threshold, which were detected from 4041 stars, or 1.9% of the stars in the Kepler database. The average flare energy detected is ~10^35^erg. The net fraction of flare stars increases with g-i color, or decreasing stellar mass. For stars in this sample with previously measured rotation periods, the total relative flare luminosity is compared to the Rossby number. A tentative detection of flare activity saturation for low-mass stars with rapid rotation below a Rossby number of ~0.03 is found. A power-law decay in flare activity with Rossby number is found with a slope of -1, shallower than typical measurements for X-ray activity decay with Rossby number.