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- ID:
- ivo://CDS.VizieR/J/AJ/103/1205
- Title:
- Stellar Content of LH 9 and 10 in the LMC
- Short Name:
- J/AJ/103/1205
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present CCD photometry and spectroscopy for stars in Lucke-Hodge 9 and 10, two adjacent OB association in the northwest corner of the LMC. Our catalog contains UBV photometry (complete to ~18mag in all three filters) for 795 stars and BV-only photometry (complete to ~19mag in both filters) for an additional 434 stars.
- ID:
- ivo://CDS.VizieR/J/AJ/98/1305
- Title:
- Stellar content of NGC 346
- Short Name:
- J/AJ/98/1305
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using CCD UBV photometry and spectroscopy, we have investigated the stellar content of NGC 346, the brightest H II region in the SMC. Spectra of 42 stars confirm that 33 are of O type, of which 11 are of type O6.5 or earlier; this is as many early-type O stars as is known in the rest of the SMC. From the spectroscopy and photometry we are able to construct an H-R diagram which is essentially complete down to ~10M_{sun}_. We find an initial mass-function slope {GAMMA}=-1.9, similar to that found for massive stars near the Sun and in the LMC: the presence of six stars in the mass range 40-85M_{sun}_ suggests that the upper-mass limit of the IMF is also not appreciably lower in the SMC than it is in the Galaxy. Our photometry has identified five probable red supergiants of which one was previously known. These stars, plus two B supergiants, are evolved stars of considerably lower mass (15M_{sun}_) than many of the unevolved cluster members. Most of these lower-mass, evolved stars form a spatially distinct subgroup; we believe that NGC 346 thus provides an example of sequential star formation in the SMC. We also have identified a background field population of 5M_{sun}_ stars. We find that the ionizing flux from the hot stars is consistent with the previously known Half nebular luminosity. Finally, we discuss the enigmatic W-R binary HD 5980, which our point-spread-function fitting has identified as a close visual double.
- ID:
- ivo://CDS.VizieR/J/AJ/105/980
- Title:
- Stellar content of Tr 14 and Tr 16
- Short Name:
- J/AJ/105/980
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The stellar content of the region around {eta} Car is investigated using CCD photometry and spectroscopy.
- ID:
- ivo://CDS.VizieR/J/ApJ/757/112
- Title:
- Stellar diameters. II. K and M-stars
- Short Name:
- J/ApJ/757/112
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present interferometric angular diameter measurements of 21 low-mass, K- and M-dwarfs made with the CHARA Array. This sample is enhanced by adding a collection of radius measurements published in the literature to form a total data set of 33 K-M-dwarfs with diameters measured to better than 5%. We use these data in combination with the Hipparcos parallax and new measurements of the star's bolometric flux to compute absolute luminosities, linear radii, and effective temperatures for the stars. We develop empirical relations for ~K0 to M4 main-sequence stars that link the stellar temperature, radius, and luminosity to the observed (B-V), (V-R), (V-I), (V-J), (V-H), and (V-K) broadband color index and stellar metallicity [Fe/H]. These relations are valid for metallicities ranging from [Fe/H]=-0.5 to +0.1dex and are accurate to ~2%, ~5%, and ~4% for temperature, radius, and luminosity, respectively. Our results show that it is necessary to use metallicity-dependent transformations in order to properly convert colors into stellar temperatures, radii, and luminosities.
- 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.
- 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.
- ID:
- ivo://CDS.VizieR/J/A+A/657/A41
- Title:
- Stellar halo of NGC 5128 (Centaurus A)
- Short Name:
- J/A+A/657/A41
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- The extended stellar halos of galaxies contain important clues for investigating their assembly history and evolution. We investigate the resolved stellar content and the extended halo of NGC 5128 as a function of galactocentric distance, and trace the halo outward to its currently detectable limits. We used Hubble Space Telescope images obtained with the WFPC2, ACS, and WFC3 cameras equipped with F606W and F814W filters to resolve individual red giant branch (RGB) stars in 28 independent pointings across the halo of NGC 5128. The stellar halo analysis for 14 of these pointings is presented here for the first time. Star counts from deep VI color-magnitude diagrams reaching at least 1.5mag below the tip of the RGB are used to derive the surface density distribution of the halo. The contamination by Milky Way stars is assessed with a new control field, with models, and by combining optical and near-IR photometry. We present a new calibration of the WFC3 F606W + F814W photometry to the ground-based VI photometric system. The photometry shows that the stellar halo of NGC 5128 is dominated by old RGB stars that are present in all fields. The V-band surface brightness of fields changes from 23 to 32mag/arcsec^2^ between the innermost field only 8.3kpc from the galaxy center to our outermost halo fields, which are located 140 kpc away from the center along the major axis and 92 kpc along the minor axis. Within the inner ~30kpc, we also find evidence for a 2-3Gyr old population traced by asymptotic giant branch stars that are brighter than the tip of the RGB. This population contributes only up to 10% in total stellar mass if it is 2Gyr old, but a larger fraction of 30-40% is required if its age is 3Gyr. The stellar surface density profile is well fit by a classic r^1/4^ curve or a simple power-law form ~r^-3.1^ over the full radial range, with no obvious break in the slope, but with large field-to-field scatter. The ellipticity measured from integrated-light photometry in the inner parts, e=(b/a)=0.77, flattens to e=0.54+/-0.02 beyond 30kpc. Considering the flattening of the outer halo, the projection of the elliptical isophote on the semimajor axis for our most distant field reaches nearly 30 effective radii.
- ID:
- ivo://CDS.VizieR/J/ApJ/786/L10
- Title:
- Stellar IMF mass normalization for z~1 galaxies
- Short Name:
- J/ApJ/786/L10
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The stellar initial mass function (IMF) is a key parameter for studying galaxy evolution. Here we measure the IMF mass normalization for a sample of 68 field galaxies in the redshift range 0.7-0.9 within the Extended Groth Strip. To do this we derive the total (stellar + dark matter) mass-to-light [(M/L)] ratio using axisymmetric dynamical models. Within the region where we have kinematics (about one half-light radius), the models assume (1) that mass follows light, implying negligible differences between the slope of the stellar and total density profiles, (2) constant velocity anisotropy ({beta}_z_=1-{sigma}_z_^2^/{sigma}_R_^2^=0.2), and (3) that galaxies are seen at the average inclination for random orientations (i.e., i=60{deg}, where i=90{deg} represents edge-on). The dynamical models are based on anisotropic Jeans equations, constrained by Hubble Space Telescope/Advanced Camera for Surveys imaging and the central velocity dispersion of the galaxies, extracted from good-quality spectra taken by the DEEP2 survey. The population (M/L) are derived from full-spectrum fitting of the same spectra with a grid of simple stellar population models. Recent dynamical modeling results from the ATLAS^3D^ project and numerical simulations of galaxy evolution indicate that the dark matter fraction within the central regions of our galaxies should be small. This suggests that our derived total (M/L) should closely approximate the stellar M/L. Our comparison of the dynamical (M/L) and the population (M/L) then implies that for galaxies with stellar mass M_*_>~10^11^ M_{sun}_, the average normalization of the IMF is consistent with a Salpeter slope, with a substantial scatter. This is similar to what is found within a similar mass range for nearby galaxies.
