- ID:
- ivo://CDS.VizieR/J/A+A/549/A57
- Title:
- Young, massive star candidates in Sgr A*
- Short Name:
- J/A+A/549/A57
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Nuclear star clusters (NSCs) are ubiquitous at the centers of galaxies. They show mixed stellar populations and the spectra of many NSCs indicate recent events of star formation. However, it is impossible to resolve external NSCs in order to examine the relevant processes. The Milky Way NSC, on the other hand, is close enough to be resolved into its individual stars and presents therefore a unique template for NSCs in general. Young, massive stars have been found by systematic spectroscopic studies at projected distances R<~0.5pc from the supermassive black hole, Sagittarius A* (Sgr A*). In recent years, increasing evidence has been found for the presence of young, massive stars also at R>0.5pc. Our goal in this work is a systematic search for young, massive star candidates throughout the entire region within R~2.5pc of the black hole.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+AS/139/393
- Title:
- Young Massive Star Clusters. II.
- Short Name:
- J/A+AS/139/393
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Table 4 lists photometric data for Young Massive Star Clusters identified in a sample of 21 nearby galaxies. The photometric data have been corrected for Galactic foreground extinction. Each cluster is identified by the abbreviated NGC number of its host galaxy and an object number: nxxx-yyy is object number yyy in the galaxy NGC xxx. Effective cluster radii have been obtained by modeling the cluster images as MOFFAT15 functions convolved with the point-spread function measured on the CCD images.
- ID:
- ivo://CDS.VizieR/J/ApJ/841/92
- Title:
- Young massive star clusters in 2 LEGUS galaxies
- Short Name:
- J/ApJ/841/92
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a study of the effective (half-light) radii and other structural properties of a systematically selected sample of young, massive star clusters (>=5x10^3^M_{sun}_ and <=200Myr) in two nearby spiral galaxies, NGC 628 and NGC 1313. We use Hubble Space Telescope (HST) WFC3/UVIS and archival ACS/WFC data obtained by the Legacy Extragalactic UV Survey (LEGUS), an HST Treasury Program. We measure effective radii with GALFIT, a two- dimensional image-fitting package, and with a new technique to estimate effective radii from the concentration index of observed clusters. The distribution of effective radii from both techniques spans ~0.5-10pc and peaks at 2-3pc for both galaxies. We find slight positive correlations between effective radius and cluster age in both galaxies, but no significant relationship between effective radius and galactocentric distance. Clusters in NGC 1313 display a mild increase in effective radius with cluster mass, but the trend disappears when the sample is divided into age bins. We show that the vast majority of the clusters in both galaxies are much older than their dynamical times, suggesting they are gravitationally bound objects. We find that about half of the clusters in NGC 628 are underfilling their Roche lobes, based on their Jacobi radii. Our results suggest that the young, massive clusters in NGC 628 and NGC 1313 are expanding, due to stellar mass loss or two-body relaxation, and are not significantly influenced by the tidal fields of their host galaxies.
- ID:
- ivo://CDS.VizieR/J/ApJ/695/511
- Title:
- Young massive stars in LHA 120-N 44
- Short Name:
- J/ApJ/695/511
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The HII complex N44 in the Large Magellanic Cloud (LMC) provides an excellent site to perform a detailed study of star formation in a mild starburst, as it hosts three regions of star formation at different evolutionary stages, and it is not as complicated and confusing as the 30 Doradus giant HII region. We have obtained Spitzer Space Telescope observations and complementary ground-based 4m uBVIJK observations of N44 to identify candidate massive young stellar objects (YSOs). We further classify the YSOs into Types I, II, and III, according to their spectral energy distributions (SEDs). In our sample of 60 YSO candidates, ~65% of them are resolved into multiple components or extended sources in high-resolution ground-based images.
- ID:
- ivo://CDS.VizieR/J/ApJ/699/649
- Title:
- Young M dwarfs within 25pc. I.
- Short Name:
- J/ApJ/699/649
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have completed a high-resolution (R~60000) optical spectroscopic survey of 185 nearby M dwarfs identified using ROSAT data to select active, young objects with fractional X-ray luminosities comparable to or greater than Pleiades members. Our targets are drawn from the "NStars" 20pc census and the "Moving-M" sample with distances determined from parallaxes or spectrophotometric relations. We limited our sample to 25pc from the Sun, prior to correcting for pre-main-sequence overluminosity or binarity. Nearly half of the resulting M dwarfs are not present in the Gliese catalog and have no previously published spectral types. We identified 30 spectroscopic binaries (SBs) from the sample, which have strong X-ray emission due to tidal spin-up rather than youth.
- ID:
- ivo://CDS.VizieR/J/ApJ/758/56
- Title:
- Young M dwarfs within 25pc. II. Kinematics
- Short Name:
- J/ApJ/758/56
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have conducted a kinematic study of 165 young M dwarfs with ages of <~300Myr. Our sample is composed of stars and brown dwarfs with spectral types ranging from K7 to L0, detected by ROSAT and with photometric distances of <~25pc assuming that the stars are single and on the main sequence. In order to find stars kinematically linked to known young moving groups (YMGs), we measured radial velocities for the complete sample with Keck and CFHT optical spectroscopy and trigonometric parallaxes for 75 of the M dwarfs with the CAPSCam instrument on the du Pont 2.5m Telescope. Due to their youthful overluminosity and unresolved binarity, the original photometric distances for our sample underestimated the distances by 70% on average, excluding two extremely young (<~3Myr) objects found to have distances beyond a few hundred parsecs. We searched for kinematic matches to 14 reported YMGs and identified 10 new members of the AB Dor YMG and 2 of the Ursa Majoris group. Additional possible candidates include six Castor, four Ursa Majoris, two AB Dor members, and one member each of the Her-Lyr and {beta} Pic groups. Our sample also contains 27 young low-mass stars and 4 brown dwarfs with ages <~150Myr that are not associated with any known YMG. We identified an additional 15 stars that are kinematic matches to one of the YMGs, but the ages from spectroscopic diagnostics and/or the positions on the sky do not match. These warn against grouping stars together based only on kinematics and that a confluence of evidence is required to claim that a group of stars originated from the same star-forming event.
- ID:
- ivo://CDS.VizieR/J/A+A/599/A70
- Title:
- Young moving group M-dwarf multiplicity
- Short Name:
- J/A+A/599/A70
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The solar galactic neighbourhood contains a number of young co-moving associations of stars (so-called 'young moving groups') with ages of ~10-150 Myr, which are prime targets for a range of scientific studies, including direct imaging planet searches. The late-type stellar population of such groups still remain in their pre-main sequence phase, and are thus well suited for purposes such as isochronal dating. Close binaries are particularly useful in this regard, since they allow for a model-independent dynamical mass determination. Here we present a dedicated effort to identify new close binaries in nearby young moving groups, through high-resolution imaging with the AstraLux Sur Lucky Imaging camera. We surveyed 181 targets, resulting in the detection of 61 companions or candidates, of which 38 are new discoveries.
- ID:
- ivo://CDS.VizieR/J/MNRAS/454/593
- Title:
- Young moving groups in solar neighbourhood
- Short Name:
- J/MNRAS/454/593
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a self-consistent, absolute isochronal age scale for young (<~200Myr), nearby (<~100pc) moving groups in the solar neighbourhood based on homogeneous fitting of semi-empirical pre-main-sequence model isochrones using the {tau}^2^ maximum-likelihood fitting statistic of Naylor & Jeffries (2006MNRAS.373.1251N) in the M_V_, V-J colour-magnitude diagram. The final adopted ages for the groups are as follows: 149^+51^_-19_Myr for the AB Dor moving group, 24+/-3Myr for the {beta} Pic moving group (BPMG), 45^+11^_-7_Myr for the Carina association, 42^+6^_-4_Myr for the Columba association, 11+/-3Myr for the {eta} Cha cluster, 45+/-4Myr for the Tucana-Horologium moving group (Tuc-Hor), 10+/-3Myr for the TW Hya association and 22^+4^_-3_Myr for the 32 Ori group. At this stage we are uncomfortable assigning a final, unambiguous age to the Argus association as our membership list for the association appears to suffer from a high level of contamination, and therefore it remains unclear whether these stars represent a single population of coeval stars. Our isochronal ages for both the BPMG and Tuc-Hor are consistent with recent lithium depletion boundary (LDB) ages, which unlike isochronal ages, are relatively insensitive to the choice of low-mass evolutionary models. This consistency between the isochronal and LDB ages instils confidence that our self-consistent, absolute age scale for young, nearby moving groups is robust, and hence we suggest that these ages be adopted for future studies of these groups. Software implementing the methods described in this study is available from http://www.astro.ex.ac.uk/people/timn/tau-squared/.
- ID:
- ivo://CDS.VizieR/J/PAZh/25/689
- Title:
- Young open clusters kinematical parameters
- Short Name:
- J/PAZh/25/689
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Kinematic data of 117 open clusters younger than 100 million years with proper motions reduced to the HIPPARCOS reference system are presented.
- ID:
- ivo://CDS.VizieR/J/PAZh/25/10
- Title:
- Young open clusters space-age distribution
- Short Name:
- J/PAZh/25/10
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Based on published photoelectric and CCD photometry and using the empirical ZAMS of Kholopov (1980, AZh, 57, 12) and the evolutionary-deviation curves obtained from the grid of isochrones computed by Maeder and Meynet (1991A&AS...89..451M), we determine the distances, color excesses, and ages for 203 Galactic open clusters with logt<8.2. The validity of the derived distance scale is corroborated by the Hipparcos trigonometric parallaxes of seven clusters. The age distribution of the clusters is distorted by observational selection, which is enhanced with increasing heliocentric distance and which is virtually independent of interstellar extinction. As a result, the youngest (logt<=7.5) clusters are represented almost exclusively at heliocentric distances >2kpc, and the mean age of the cataloged clusters with logt<=100Myr decreases from 50Myr in the solar neighborhood down to 15Myr at heliocentric distances >2.4kpc.
