- 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.
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Search Results
- 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.
17978. Stellar groups in IC 2574
- ID:
- ivo://CDS.VizieR/J/AJ/144/182
- Title:
- Stellar groups in IC 2574
- Short Name:
- J/AJ/144/182
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Dissolving stellar groups are very difficult to detect using traditional surface photometry techniques. We have developed a method to find and characterize non-compact stellar systems in galaxies where the young stellar population can be spatially resolved. By carrying out photometry on individual stars, we are able to separate the luminous blue stellar population from the star field background. The locations of these stars are used to identify groups by applying the HOP algorithm, which are then characterized using color-magnitude and stellar density radial profiles to estimate age, size, density, and shape. We test the method on Hubble Space Telescope Advanced Camera for Surveys archival images of IC 2574 and find 75 dispersed stellar groups. Of these, 20 highly dispersed groups are good candidates for dissolving systems. We find few compact systems with evidence of dissolution, potentially indicating that star formation in this galaxy occurs mostly in unbound clusters or groups. These systems indicate that the dispersion rate of groups and clusters in IC 2574 is at most 0.45pc/Myr. The location of the groups found with HOP correlate well with HI contour map features. However, they do not coincide with HI holes, suggesting that those holes were not created by star-forming regions.
- ID:
- ivo://CDS.VizieR/J/ApJS/254/20
- Title:
- Stellar groups in Taurus field from Gaia DR2 & LAMOST
- Short Name:
- J/ApJS/254/20
- Date:
- 17 Jan 2022 14:18:37
- Publisher:
- CDS
- Description:
- In this work, we present a systematic search for stellar groups in the Taurus field by applying the DBSCAN algorithm to the data from Gaia DR2. We find 22 groups, consisting of 8 young groups (Groups 1-8) at ages of 2-4Myr and distances of ~130-170pc, and 14 old groups (Groups 9-22) at ages of 8-49Myr and distances of ~110-210pc. We characterize the disk properties of group members and find 19 new disk-bearing stars, 8 of which are in the young groups with 11 others belonging to the comparatively old groups at the ages of 8-11Myr. We characterize the accretion properties of the group members with H{alpha} emission lines in their Large Sky Area Multi-Object Fibre Spectroscopic Telescope spectra, and discover one source in Group 10 at an age of 10Myr which still shows accretion activity. We investigate the kinematic relations among the old groups, find that Group 9 is kinematically related to the known Taurus members, and exclude any kinematic relations between Groups 10-22 and the known Taurus members.
- ID:
- ivo://CDS.VizieR/J/AZh/87/853
- Title:
- Stellar groups of Orion's Sword region
- Short Name:
- J/AZh/87/853
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The region of Orion's Sword with coordinates RA=83.79{deg}, DE=-5.20{deg} and a size of 1.0{deg}x2.5{deg} is analyzed. We compiled a master catalog of stars observed in the optical, containing positions, proper motions, and UBV photometry for 1634 stars. Using the nearest-neighbor-distance technique, we subdivided the region into stellar groups with different numbers of members. The positions of five groups coincide with known clusters, and two groups coincide with aggregates of stars with H{alpha} emission. We have identified groups with low membership that are moving away from the system. We also considered the kinematic structure of the groups using the AD-diagram method we developed earlier. Most of the stellar clusters and groups display similar kinematics, with the exception of the group OMC-2, which is moving toward its own apex. We also confirmed the existence of the kinematic star group 189 discovered earlier; its position is close to the cluster NGC 1977, and it is probably a component of its corona.