- ID:
- ivo://CDS.VizieR/J/ApJ/764/154
- Title:
- Stellar populations in the central 0.5pc. I.
- Short Name:
- J/ApJ/764/154
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new high angular resolution near-infrared spectroscopic observations of the nuclear star cluster surrounding the Milky Way's central supermassive black hole. Using the integral-field spectrograph OSIRIS on Keck II behind the laser-guide-star adaptive optics system, this spectroscopic survey enables us to separate early-type (young, 4-6Myr) and late-type (old, >1Gyr) stars with a completeness of 50% down to K'=15.5mag, which corresponds to ~10M_{sun}_ for the early-type stars. This work increases the radial extent of reported OSIRIS/Keck measurements by more than a factor of three from 4" to 14" (0.16 to 0.56pc), along the projected disk of young stars. For our analysis, we implement a new method of completeness correction using a combination of star-planting simulations and Bayesian inference. We assign probabilities for the spectral type of every source detected in deep imaging down to K'=15.5mag using information from spectra, simulations, number counts, and the distribution of stars. The inferred radial surface-density profiles, {Sigma}(R){prop.to}R^-{Gamma}^, for the young stars and late-type giants are consistent with earlier results ({Gamma}_early_=0.93+/-0.09, {Gamma}_late_=0.16+/-0.07). The late-type surface-density profile is approximately flat out to the edge of the survey. While the late-type stellar luminosity function is consistent with the Galactic bulge, the completeness-corrected luminosity function of the early-type stars has significantly more young stars at faint magnitudes compared with previous surveys with similar depth. This luminosity function indicates that the corresponding mass function of the young stars is likely less top-heavy than that inferred from previous surveys.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/733/L9
- Title:
- Stellar rotation for 71 NGC 6811 members
- Short Name:
- J/ApJ/733/L9
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present rotation periods for 71 single dwarf members of the open cluster NGC 6811 determined using photometry from NASA's Kepler mission. The results are the first from The Kepler Cluster Study, which combines Kepler's photometry with ground-based spectroscopy for cluster membership and binarity. The rotation periods delineate a tight sequence in the NGC 6811 color-period diagram from ~1 day at mid-F to ~11 days at early-K spectral type. This result extends to 1Gyr similar prior results in the ~600Myr Hyades and Praesepe clusters, suggesting that rotation periods for cool dwarf stars delineate a well-defined surface in the three-dimensional space of color (mass), rotation, and age. It implies that reliable ages can be derived for field dwarf stars with measured colors and rotation periods, and it promises to enable further understanding of various aspects of stellar rotation and activity for cool stars.
- ID:
- ivo://CDS.VizieR/J/ApJ/695/679
- Title:
- Stellar rotation in M35
- Short Name:
- J/ApJ/695/679
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a five month photometric time-series survey for stellar rotation over a 40'x40' field centered on the 150Myr open cluster M35 (=NGC 2168). We report rotation periods for 441 stars within this field and determine their cluster membership and binarity based on a decade-long radial velocity survey, proper-motion measurements, and multiband photometric observations. We find that 310 of the stars with measured rotation periods are late-type members of M35. The distribution of rotation periods for cluster members span more than 2 orders of magnitude from ~0.1 to 15 days, not constrained by the sampling frequency and the timespan of the survey. With an age between the zero-age main sequence and the Hyades, and with ~6 times more rotation periods than measured in the Pleiades, M35 permit detailed studies of early rotational evolution of late-type stars. Nearly 80% of the 310 rotators lie on two distinct sequences in the color-period plane, and define clear relations between stellar rotation period and color (mass). The M35 color-period diagram enables us to determine timescales for the transition between the two rotational states, of ~60Myr and ~140Myr for G and K dwarfs, respectively.
- ID:
- ivo://CDS.VizieR/J/A+A/581/A28
- Title:
- Stellar X-ray flares from the 2XMM catalog
- Short Name:
- J/A+A/581/A28
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a uniform, large-scale survey of X-ray flare emission, based on the XMM-Newton Serendipitous Source Catalogue and its associated data products. Our survey comprises both XMM-targeted active stars and those observed serendipitously in the field-of-view of each observation. The 2XMM Catalogue and the associated time-series ('light-curve') data products have been used as the basis for the survey of X-ray flares from cool stars in the Hipparcos Tycho-2 catalogue. Our sample contains ~130 flares with well-observed profiles; they originate from ~70 stars.
- ID:
- ivo://CDS.VizieR/J/ApJ/725/480
- Title:
- Stellar X-ray sources in the COSMOS survey
- Short Name:
- J/ApJ/725/480
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an analysis of the X-ray properties of a sample of solar- and late-type field stars identified in the Chandra Cosmic Evolution Survey (COSMOS), a deep (160ks) and wide (~0.9deg^2^) extragalactic survey. The sample of 60 sources was identified using both morphological and photometric star/galaxy separation methods. We determine X-ray count rates, extract spectra and light curves, and perform spectral fits to determine fluxes and plasma temperatures. Complementary optical and near-IR photometry is also presented and combined with spectroscopy for 48 of the sources to determine spectral types and distances for the sample. We find distances ranging from 30pc to ~12kpc, including a number of the most distant and highly active stellar X-ray sources ever detected. Overall the sample is typically more luminous than the active Sun, representing the high-luminosity end of the disk and halo X-ray luminosity functions. The halo population appears to include both low-activity spectrally hard sources that may be emitting through thermal bremsstrahlung, as well as a number of highly active sources in close binaries.
- ID:
- ivo://CDS.VizieR/J/A+AS/143/409
- Title:
- Stock 2 CCD photometry and proper motions
- Short Name:
- J/A+AS/143/409
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of the first CCD BVRI photometric and proper motion study of late-type stars in the young open cluster Stock 2. Twenty-one fields of approximately 5'x5' size have been observed photometrically, from which we have identified 118 candidate members based on their positions on colour-magnitude diagrams relative to theoretical isochrones. From a comparison of the known star density of the Pleiades, we estimate the contamination of this selection process due to background stars to be as large as ~50%. However, only 22 of those 118 candidate members have proper motions consistent with membership, suggesting that the contamination is of the order of 80%. Additional candidate members were found by means of a proper motion analysis of Schmidt plate material for a 3{deg}x3{ deg} field containing the cluster. The cluster proper motion allows us to separate members from background and foreground stars. We have found 634 stars with a membership probability >=50% down to a limiting magnitude of B=~20, corresponding to late-M dwarfs at the distance of Stock 2.
- ID:
- ivo://CDS.VizieR/II/46
- Title:
- Strong cyanogen stars
- Short Name:
- II/46
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A cyanogen index for late-type giants, insensitive to surface gravity but sensitive to metallicity, is presented in the David Dunlap Observatory (DDO) photometric system. Observations were made using conventional single-channel photometers with 1P21 photomultiplier tubes on the 40cm and 90cm telescopes of Kitt Peak National Observatory. The original DDO filter set C was used (see Paper I, 1968AJ.....73..313M). Table 1 contains DDO photometry on 52 bright late-type giants for calibration. Most G8 to M0 stars, luminosity class III, V<4.0mag, north of {delta}=-10{deg}, supplement the original stars from Paper I. Table 4 includes both DDO and UBV photometry for stars from Schmitt (1967 thesis, Univ. Michigan, Ann Arbor) and Spinrad and Taylor (1967AJ.....72S.320S). Reddening values were computed using the method of McClure and Racine (1969AJ.....74.1000M).
- ID:
- ivo://CDS.VizieR/J/A+A/390/179
- Title:
- Study of FK Comae Berenices. IV.
- Short Name:
- J/A+A/390/179
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Doppler imaging techniques have earlier been used to study the starspots and their evolution over a four year period in a single, late-type star FK Com. In the present work we publish new photometric observations of FK Com for the year 2001 and analyse them together with the previously published photometry obtained since 1966. The observations for 2001 have been carried out at the Phoenix 10 automatic photometric telescope in Arizona, USA. Observations contain measurements at the Johnson U, B and V bands. The observations are differential photometry in respect to the primary comparison star HD 117567. In table1, 99.000 means that no observations were available at that time at that band or that the error in the magnitude was larger than 0.02.
- ID:
- ivo://CDS.VizieR/J/MNRAS/430/1171
- Title:
- Sub-stellar birth rate from UKIDSS
- Short Name:
- J/MNRAS/430/1171
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new sample of mid-L to mid-T dwarfs with effective temperatures of 1100-1700K selected from the UKIDSS Large Area Survey (LAS) and confirmed with infrared spectra from X-shooter/Very Large Telescope. This effective temperature range is especially sensitive to the formation history of Galactic brown dwarfs and allows us to constrain the form of the sub-stellar birth rate, with sensitivity to differentiate between a flat (stellar like) birth rate and an exponentially declining form. We present the discovery of 63 new L and T dwarfs from the UKIDSS LAS DR7, including the identification of 12 likely unresolved binaries, which form the first complete sub-set from our programme, covering 495 square degrees of sky, complete to J=18.1. We compare our results for this sub-sample with simulations of differing birth rates for objects of masses 0.10-0.03M_{sun}_ and ages 1-10Gyr. We find that the more extreme birth rates (e.g. a halo type form) can likely be excluded as the true form of the birth rate. In addition, we find that although there is substantial scatter we find a preference for a mass function, with a power-law index {alpha} in the range -1<{alpha}<0 that is consistent (within the errors) with the studies of late T dwarfs.
- ID:
- ivo://CDS.VizieR/J/MNRAS/491/215
- Title:
- Supplementary data for 146 candidate young stars
- Short Name:
- J/MNRAS/491/215
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The past two decades have seen dramatic progress in our knowledge of the population of young stars of age <200Myr that lie within 150pc of the Sun. These nearby, young stars, most of which are found in loose, comoving groups, provide the opportunity to explore (among many other things) the dissolution of stellar clusters and their diffusion into the field star population. Here, we exploit the combination of astrometric and photometric data from Gaia and photometric data from GALEX (UV) and 2MASS (near-IR) in an attempt to identify additional nearby, young, late-type stars. Specifically, we present a sample of 146 GALEX UV-selected late-type (predominantly K-type) field stars with Gaia-based distances <125pc (based on Gaia Data Release 1) that have isochronal ages <80Myr even if equal-components binaries. We investigate the spectroscopic and kinematic properties of this sample. Despite their young isochronal ages, only ~10 per cent of stars among this sample can be confidently associated with established nearby, young moving groups (MGs). These candidate MG members include five stars newly identified in this study. The vast majority of our sample of 146 nearby young star candidates have anomalous kinematics relative to the known MGs. These stars may hence represent a previously unrecognized population of young stars that has recently mixed into the older field star population. We discuss the implications and caveats of such a hypothesis - including the intriguing fact that, in addition to their non-young-star-like kinematics, the majority of the UV-selected, isochronally young field stars within 50pc appear surprisingly X-ray faint.
