Search

Start Over Subject optical astronomy Capability Type Simple Cone Search
2601. Stellar-mass black holes in the SDSS
ID:
ivo://CDS.VizieR/J/ApJ/596/437
Title:
Stellar-mass black holes in the SDSS
Short Name:
J/ApJ/596/437
Date:
21 Oct 2021
Publisher:
CDS
Description:
We search for nearby, isolated, accreting, "stellar-mass" (3-100M_{sun}_) black holes. Models suggest a synchrotron spectrum in visible wavelengths and some emission in X-ray wavelengths. Of 3.7 million objects in the Sloan Digital Sky Survey Early Data Release, Cat. <J/AJ/123/567>, about 150,000 objects have colors and properties consistent with such a spectrum, and 87 of these objects are X-ray sources from the ROSAT All-Sky Survey (Cat. <IX/10> and <IX/29>). Thirty-two of these have been confirmed not to be black holes using optical spectra. We give the positions and colors of these 55 black hole candidates and quantitatively rank them on their likelihood to be black holes. We discuss uncertainties in the expected number of sources and the contribution of black holes to local dark matter.
2602. Stellar masses and rest-frame u-g colors of SNIa
ID:
ivo://CDS.VizieR/J/ApJ/867/108
Title:
Stellar masses and rest-frame u-g colors of SNIa
Short Name:
J/ApJ/867/108
Date:
03 Dec 2021 00:48:50
Publisher:
CDS
Description:
Recent analyses suggest that distance residuals measured from Type Ia supernovae (SNe Ia) are correlated with local host galaxy properties within a few kiloparsecs of the SN explosion. However, the well-established correlation with global host galaxy properties is nearly as significant, with a shift of 0.06mag across a low to high mass boundary (the mass step). Here, with 273 SNe Ia at z<0.1, we investigate whether the stellar masses and rest-frame u-g colors of regions within 1.5kpc of the SN Ia explosion site are significantly better correlated with SN distance measurements than global properties or properties measured at random locations in SN hosts. At >~2{sigma} significance, local properties tend to correlate with distance residuals better than properties at random locations, though despite using the largest low-z sample to date, we cannot definitively prove that a local correlation is more significant than a random correlation. Our data hint that SNe observed by surveys that do not target a pre-selected set of galaxies may have a larger local mass step than SNe from surveys that do, an increase of 0.071+/-0.036mag (2.0{sigma}). We find a 3{sigma} local mass step after global mass correction, evidence that SNe Ia should be corrected for their local mass, but we note that this effect is insignificant in the targeted low-z sample. Only the local mass step remains significant at >2{sigma} after global mass correction, and we conservatively estimate a systematic shift in H0 measurements of -0.14km/s/Mpc with an additional uncertainty of 0.14km/s/Mpc, ~10% of the present uncertainty.
2603. Stellar multiplicity rate of M dwarfs within 25 pc
ID:
ivo://CDS.VizieR/J/AJ/157/216
Title:
Stellar multiplicity rate of M dwarfs within 25 pc
Short Name:
J/AJ/157/216
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present results of the largest, most comprehensive study ever done of the stellar multiplicity of the most common stars in the Galaxy, the red dwarfs. We have conducted an all-sky volume-limited survey for stellar companions to 1120 M dwarf primaries known to lie within 25 pc of the Sun via trigonometric parallaxes. In addition to a comprehensive literature search, stars were explored in new surveys for companions at separations of 2"-300". A reconnaissance of wide companions to separations of 300" was done via blinking archival images. I-band images were used to search our sample for companions at separations of 2"-180". Various astrometric and photometric methods were used to probe the inner 2" to reveal close companions. We report the discovery of 20 new companions and identify 56 candidate multiple systems. We find a stellar multiplicity rate of 26.8+/-1.4% and a stellar companion rate of 32.4+/-1.4% for M dwarfs. There is a broad peak in the separation distribution of the companions at 4-20 au, with a weak trend of smaller projected linear separations for lower mass primaries. A hint that M-dwarf multiplicity may be a function of tangential velocity is found, with faster moving, presumably older, stars found to be multiple somewhat less often. We calculate that stellar companions make up at least 17% of mass attributed to M dwarfs in the solar neighborhood, with roughly 11% of M-dwarf mass hidden as unresolved companions. Finally, when considering all M-dwarf primaries and companions, we find that the mass distribution for M dwarfs increases to the end of the stellar main sequence.
2604. Stellar parameters and abundances in NGC 6752
ID:
ivo://CDS.VizieR/J/A+A/567/A72
Title:
Stellar parameters and abundances in NGC 6752
Short Name:
J/A+A/567/A72
Date:
21 Oct 2021
Publisher:
CDS
Description:
Abundance trends in heavier elements with evolutionary phase have been shown to exist in the globular cluster NGC 6752. These trends are a result of atomic diffusion and additional (non-convective) mixing. Studying such trends can provide us with important constraints on the extent to which diffusion modifies the internal structure and surface abundances of solar-type, metal-poor stars. Taking advantage of a larger data sample, we investigate the reality and the size of these abundance trends and address questions and potential biases associated with the various stellar populations that make up NGC 6752. We perform an abundance analysis by combining photometric and spectroscopic data of 194 stars located between the turnoff point and the base of the red giant branch. Stellar parameters are derived from uvby Stromgren photometry. Using the quantitative-spectroscopy package SME, stellar surface abundances for light elements such as Li, Na, Mg, Al, and Si as well as heavier elements such as Ca, Ti, and Fe are derived in an automated way by fitting synthetic spectra to individual lines in the stellar spectra, obtained with the VLT/FLAMES-GIRAFFE spectrograph. Based on uvby Stromgren photometry, we are able to separate three stellar populations in NGC 6752 along the evolutionary sequence from the base of the red giant branch down to the turnoff point. We find weak systematic abundance trends with evolutionary phase for Ca, Ti, and Fe which are best explained by stellar-structure models including atomic diffusion with efficient additional mixing. We derive a new value for the initial lithium abundance of NGC 6752 after correcting for the effect of atomic diffusion and additional mixing which falls slightly below the predicted standard BBN value. We find three stellar populations by combining photometric and spectroscopic data of 194 stars in the globular cluster NGC 6752. Abundance trends for groups of elements, differently affected by atomic diffusion and additional mixing, are identified. Although the statistical significance of the individual trends is weak, they all support the notion that atomic diffusion is operational along the evolutionary sequence of NGC 6752.
2605. Stellar parameters and extinction
ID:
ivo://CDS.VizieR/J/MNRAS/411/435
Title:
Stellar parameters and extinction
Short Name:
J/MNRAS/411/435
Date:
21 Oct 2021
Publisher:
CDS
Description:
Astrometric surveys provide the opportunity to measure the absolute magnitudes of large numbers of stars, but only if the individual line-of-sight extinctions are known. Unfortunately, extinction is highly degenerate with stellar effective temperature when estimated from broad band optical/infrared photometry. To address this problem, I introduce a Bayesian method for estimating the intrinsic parameters of a star and its line-of-sight extinction.
2606. Stellar parameters for 13196 Kepler dwarfs
ID:
ivo://CDS.VizieR/J/AJ/160/90
Title:
Stellar parameters for 13196 Kepler dwarfs
Short Name:
J/AJ/160/90
Date:
21 Oct 2021
Publisher:
CDS
Description:
The rotational evolution of cool dwarfs is poorly constrained after ~1-2Gyr due to a lack of precise ages and rotation periods for old main-sequence stars. In this work, we use velocity dispersion as an age proxy to reveal the temperature-dependent rotational evolution of low-mass Kepler dwarfs and demonstrate that kinematic ages could be a useful tool for calibrating gyrochronology in the future. We find that a linear gyrochronology model, calibrated to fit the period-Teff relationship of the Praesepe cluster, does not apply to stars older than around 1Gyr. Although late K dwarfs spin more slowly than early-K dwarfs when they are young, at old ages, we find that late K dwarfs rotate at the same rate or faster than early-K dwarfs of the same age. This result agrees qualitatively with semiempirical models that vary the rate of surface-to-core angular momentum transport as a function of time and mass. It also aligns with recent observations of stars in the NGC6811 cluster, which indicate that the surface rotation rates of K dwarfs go through an epoch of inhibited evolution. We find that the oldest Kepler stars with measured rotation periods are late K and early M dwarfs, indicating that these stars maintain spotted surfaces and stay magnetically active longer than more massive stars. Finally, based on their kinematics, we confirm that many rapidly rotating GKM dwarfs are likely to be synchronized binaries.
2607. Stellar parameters from the 1st release of the MaSTar
ID:
ivo://CDS.VizieR/J/ApJ/899/62
Title:
Stellar parameters from the 1st release of the MaSTar
Short Name:
J/ApJ/899/62
Date:
14 Mar 2022 07:12:49
Publisher:
CDS
Description:
We report the stellar atmospheric parameters for 7503 spectra contained in the first release of the Mapping Nearby Galaxies at Apache Point Observatory survey (MaNGA) stellar library (MaStar) in Sloan Digital Sky Survey DR15. The first release of MaStar contains 8646 spectra measured from 3321 unique stars, each covering the wavelength range 3622-10354{AA} with a resolving power of R~1800. In this work, we first determined the basic stellar parameters: effective temperature (Teff), surface gravity (logg), and metallicity ([Fe/H]), which best fit the data using an empirical interpolator based on the Medium-resolution Isaac Newton Telescope library of empirical spectra (MILES), as implemented by the University of Lyon Spectroscopic analysis Software package. While we analyzed all 8646 spectra from the first release of MaStar, since MaStar has a wider parameter-space coverage than MILES, not all of these fits are robust. In addition, not all parameter regions covered by MILES yield robust results, likely due to the nonuniform coverage of the parameter space by MILES. We tested the robustness of the method using the MILES spectra itself and identified a proxy based on the local density of the training set. With this proxy, we identified 7503 MaStar spectra with robust fitting results. They cover the range from 3179 to 20517K in effective temperature (Teff), from 0.40 to 5.0 in surface gravity (logg), and from -2.49 to +0.73 in metallicity ([Fe/H]).
2608. Stellar parameters in Ophiuchus Stream with MMT
ID:
ivo://CDS.VizieR/J/AJ/159/287
Title:
Stellar parameters in Ophiuchus Stream with MMT
Short Name:
J/AJ/159/287
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present new kinematic data for the Ophiuchus stellar stream. Spectra have been taken of member candidates at the Multiple Mirror Telescope (MMT) using Hectospec, Hectochelle, and Binospec, which provide more than 1800 new velocities. Combined with proper-motion measurements of stars in the field by the Gaia-DR2 catalog, we have derived stream membership probabilities, resulting in the detection of more than 200 likely members. These data show the stream extends to more than three times the length shown in the discovery data. A spur to the main stream is also detected. The high-resolution spectra allow us to resolve the stellar velocity dispersion, found to be 1.6{+/-}0.3km/s.
2609. Stellar parameters of G and K giant stars
ID:
ivo://CDS.VizieR/J/A+A/475/1003
Title:
Stellar parameters of G and K giant stars
Short Name:
J/A+A/475/1003
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present results of a spectroscopic analysis of 366 G and K giant stars. For 112 stars this is the first spectroscopic analysis. The stars were selected for a radial velocity survey, which is currently carried out at Lick observatory, using the Coude Auxiliary Telescope in conjunction with the Hamilton Echelle spectrograph. For each star a high signal to noise spectrum is available, which is used for the present analysis. The Teff, logg and iron abundance are determined by imposing excitation and ionisation equilibrium through stellar models. The micro turbulence is obtained by requiring no dependence of Fe I against equivalent width. The rotational velocity is obtained from a comparison with data from Gray (1989ApJ...347.1021G) and the macro turbulence is derived using Gray (2005PASP..117..711G).
2610. Stellar parameters of giants in {omega} Cen
ID:
ivo://CDS.VizieR/J/MNRAS/427/1153
Title:
Stellar parameters of giants in {omega} Cen
Short Name:
J/MNRAS/427/1153
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have determined stellar parameters and abundances for 221 giant branch stars in the globular cluster omega Centauri. A combination of photometry and lower-resolution spectroscopy was used to determine temperature, gravity, metallicity, [C/Fe], [N/Fe] and [Ba/Fe]. These abundances agree well with those found by previous researchers and expand the analysed sample of the cluster. k-means clustering analysis was used to group the stars into four homogeneous groups based upon these abundances. These stars show the expected anticorrelation in [C/Fe] to [N/Fe]. We investigated the distribution of CN-weak/strong stars on the colour-magnitude diagram. Asymptotic giant branch stars, which were selected from their position on the colour-magnitude diagram, were almost all CN-weak. This is in contrast to the red giant branch where a large minority were CN-strong. The results were also compared with cluster formation and evolution models. Overall, this study shows that statistically significant elemental and evolutionary conclusions can be obtained from lower resolution spectroscopy.