- ID:
- ivo://CDS.VizieR/J/ApJ/684/1143
- Title:
- BHB candidates in the Milky Way
- Short Name:
- J/ApJ/684/1143
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We derive new constraints on the mass of the Milky Way's dark matter halo, based on 2401 rigorously selected blue horizontal-branch halo stars from SDSS DR6. This sample enables construction of the full line-of-sight velocity distribution at different galactocentric radii. To interpret these distributions, we compare them to matched mock observations drawn from two different cosmological galaxy formation simulations designed to resemble the Milky Way. This procedure results in an estimate of the Milky Way's circular velocity curve to ~60kpc, which is found to be slightly falling from the adopted value of 220km/s at the Sun's location, and implies M(<60kpc)=(4.0+/-0.7)x10^11^M_{sun}_.
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- ID:
- ivo://CDS.VizieR/J/AJ/108/1722
- Title:
- Blue horizontal branch stars
- Short Name:
- J/AJ/108/1722
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A complete sample of blue horizontal branch (BHB) stars in the magnitude range 13.0<V<16.5 is isolated in two Galactic fields that have previously been searched for RR Lyrae variables: SA 57 in the Northern Polar Cap and the Lick Astrograph field RR 7 in the Anticenter (l=183{deg}, b=+37{deg}). These BHB stars are a subset of the AF stars found in the Case Low-Dispersion Northern Survey; lists of these AF stars were made available by the late Nick Sanduleak. The completeness of the sample was confirmed by reference to the photometric survey of SA 57 by Stobie & Ishida (1987AJ93..... 624S) that is complete to fainter than V=18. In the color range 0.00<(B-V)_0_<+0.20, we can distinguish the BHB stars among these AF stars by comparing them both with well known local field horizontal branch (FHB) stars and also the BHB members of the halo globular clusters M3 and M92. The criteria for this comparison include (1) a (u-B)_K_ color index (derived from photoelectric observations using the Stromgren u filter and the Johnson B and V filters) that measures the size of the Balmer jump, (2) a spectrophotometric index A that measures the steepness of the Balmer jump, and (3) a parameter D_0.2_ that is the mean width of the H{gamma} and H{delta} Balmer lines measured at 20 percent of the continuum level. These criteria give consistent results in separating BHB stars from higher gravity main sequence AF stars in the color range 0.00<(B-V)_0_<+0.20. All three photometric and spectrophotometric criteria were measured for 35 stars in the SA 57 field and 37 stars in the RR 7 field that are in the color range (B-V)_0_<+0.23 and in the magnitude range 13.0<V<16.5. For a small number of additional stars only (u-B)_K_ was obtained. Among the AF stars that are fainter than B=13 and bluer than (B-V)_0_=+0.23, about half of those in the SA 57 field and about one third of those in the lower latitude RR 7 field are BHB stars. Isoabundance contours were located empirically in plots of the pseudoequivalent width versus (B-V)_0_ for the lines of Mg II A4481{AA}, Ca II A3933 {AA} and Fe I A4272{AA}. Solar abundances were defined by the data from main sequence stars in the Pleiades and Coma open clusters. Data from the BHB stars in M3 and M92 defined the [Fe/H]=1.5 and -2.2 isoabundance contours, respectively. Metallicities of all stars were estimated by interpolating the measured pseudoequivalent widths in these diagrams at the observed (B-V)_0_. The distribution of [Fe/H] found for the BHB stars in this way is very similar to that which we found for the RR Lyrae stars in the same fields using the Preston AS method. The space densities of these BHB stars were analyzed both separately and together with earlier observations of field BHB stars given by Arnold & Gilmore (1992MNRAS.257..225A), Sommer-Larsen & Christensen (1986MNRAS.219..537S), and Preston et al. (1991ApJ...375..121P). This analysis supports a two-component model for the halo of our Galaxy that is similar in many respects to that proposed by Hartwick [The Galaxy (Reidel, Dordrecht 1987)] although our discussion refers only to the region outside the solar circle. For Z>=35kpc, a classical spherical halo dominates which follows a R_gal_^-3.5^ space-density law and which has a HB morphology like that of the globular cluster M3 (i.e., approximately equal numbers of BHB and RR Lyrae stars). Closer to the galactic plane, there is an additional component with a much flatter galactic distribution (scale height ~2.2kpc near the Sun). The stars of the two components do not have significantly different metallicity distributions but do have slightly different distributions of the A parameter which measures the steepness of the Balmer jump; this is the only physical criterion (independent of spatial or kinematic considerations) which distinguishes between the two components. If present estimates of the local RR Lyrae star space density are correct, then the ratio of BHB stars to RR Lyrae stars is higher in the flatter halo component. The flat component would then have a bluer HB morphology (which could be interpreted as making it older) than the spherical component. In the solar neighborhood about 80 percent of the BHB stars come from the flat component and about 20 percent from the spherical component. More than half of the AF stars with V>13.0 and (B-V)_0_<+0.23 are not BHB stars but have surface gravities that are more like those expected for main sequence stars. Their measured metallicities lie in the range -0.2<[Fe/H]<-2.3. The more metal-poor of these stars are probably similar to the blue metal-poor stars that have been discussed by Preston et al. (1994AJ....108..538P) which, while they probably include globular cluster blue stragglers as a subset, must also comprise stars of other types.
- ID:
- ivo://CDS.VizieR/J/A+A/475/539
- Title:
- BV photometry and Li abundances in NGC3960
- Short Name:
- J/A+A/475/539
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Old open clusters are very useful targets to investigate mechanisms responsible for lithium (Li) depletion during the main sequence. Comparison of the Li abundances in clusters of different age allows us to understand the efficiency of the Li destruction process. To determine the membership and Li abundance in a sample of candidate members of the open cluster NGC 3960 (age ~1Gyr), aiming to fill the gap between 0.6 and 2Gyr in the empirical description of the behavior of the average Li abundance as a function of the stellar age. We use VLT/FLAMES Giraffe spectra to determine the radial velocities and thus the membership of a sample of 113 photometrically selected candidate cluster members. From the analysis of the Li line we derive Li abundances for both cluster members and non-members. 39 stars have radial velocities consistent with membership, with an expected fraction of contaminating field stars of about 20%. Li is detected in 29 of the radial velocity members; we consider these stars as cluster members, while we make the reasonable assumption that the remaining 10 radial velocity members without Li are among the contaminating stars. Li abundances of the stars hotter than about 6000K are similar to those of stars in the Hyades, while they are slightly smaller for cooler stars. This confirms that NGC 3960 is older than the Hyades. The average Li abundance of stars cooler than about 6000K indicates that the Li Pop. I plateau might start at ~1Gyr, rather than 2Gyr, which is the upper limit previously derived in the literature. We also find that the fraction of field stars with high Li abundance (>1.5) is about one third of the whole sample, which is in agreement with previous estimates. The fraction of contaminating field stars is consistent with that previously derived by us from photometry.
- ID:
- ivo://CDS.VizieR/J/A+A/498/527
- Title:
- Calibration of Stromgren phot. for late-type stars
- Short Name:
- J/A+A/498/527
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The use of model atmospheres for deriving stellar fundamental parameters, such as Teff, log(g), and [Fe/H], will increase as we find and explore extreme stellar populations where empirical calibrations are not yet available. Moreover, calibrations for upcoming large satellite missions of new spectrophotometric indices, similar to the uvby-Hbeta system, will be needed. We aim to test the power of theoretical calibrations based on a new generation of MARCS models by comparisons with observational photometric data. We calculated synthetic uvby-Hbeta colour indices from synthetic spectra. A sample of 367 field stars, as well as stars in globular clusters, is used for a direct comparison of the synthetic indices versus empirical data and for scrutizing the possibilities of theoretical calibrations for temperature, metallicity, and gravity. We show that the temperature sensitivity of the synthetic (b-y) colour is very close to its empirical counterpart, whereas the temperature scale based upon Hbeta shows a slight offset. The theoretical metallicity sensitivity of the m1 index (and for G-type stars its combination with c1) is somewhat higher than the empirical one, based upon spectroscopic determinations. The gravity sensitivity of the synthetic c1 index shows satisfactory behaviour when compared to observations of F stars. For stars cooler than the sun, a deviation is significant in the c1-(b-y) diagram. The theoretical calibrations of (b-y), (v-y), and c1 seem to work well for Pop II stars and lead to effective temperatures for globular cluster stars supporting recent claims that atomic diffusion occurs in stars near the turnoff point of NGC 6397. Synthetic colours of stellar atmospheres can indeed be used, in many cases, to derive reliable fundamental stellar parameters. The deviations seen when compared to observational data could be due to incomplete linelists but are possibly also due to the effects of assuming plane-parallel or spherical geometry and LTE.
- ID:
- ivo://CDS.VizieR/J/other/PASA/37.22
- Title:
- Calibration sample UBV and GALEX photometry
- Short Name:
- J/other/PASA/37.
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We derive transformation equations between GALEX and UBV colours by using the reliable data of 556 stars. We present two sets of equations: as a function of (only) luminosity class and as a function of both luminosity class and metallicity. The metallicities are provided from the literature, while the luminosity classes are determined by using the PARSEC mass tracks in this study. Small colour residuals and high squared correlation coefficients promise accurate derived colours. The application of the transformation equations to 70 stars with reliable data shows that the metallicity plays an important role in estimation of more accurate colours.
- ID:
- ivo://CDS.VizieR/J/MNRAS/492/3073
- Title:
- CALIFA galaxies hosting an AGN
- Short Name:
- J/MNRAS/492/3073
- Date:
- 02 Feb 2022 07:33:25
- Publisher:
- CDS
- Description:
- We study the presence of optically-selected Active Galactic Nuclei (AGNs) within a sample of 867 galaxies extracted from the extended Calar-Alto Legacy Integral Field spectroscopy Area (eCALIFA) spanning all morphological classes. We identify 10 Type-I and 24 Type-II AGNs, amounting to ~4 per cent of our sample, similar to the fraction reported by previous explorations in the same redshift range. We compare the integrated properties of the ionized and molecular gas, and stellar population of AGN hosts and their non-active counterparts, combining them with morphological information. The AGN hosts are found in transitory parts (i.e. green-valley) in almost all analysed properties which present bimodal distributions (i.e. a region where reside star-forming galaxies and another with quiescent/retired ones). Regarding morphology, we find AGN hosts among the most massive galaxies, with enhanced central stellar-mass surface density in comparison to the average population at each morphological type. Moreover, their distribution peaks at the Sab-Sb classes and none are found among very late-type galaxies (>Scd). Finally, we inspect how the AGN could act in heir hosts regarding the quenching of star-formation. The main role of the AGN in the quenching process appears to be the removal (or heating) of molecular gas, rather than an additional suppression of the already observed decrease of the star-formation efficiency from late-to-early type galaxies.
- ID:
- ivo://CDS.VizieR/J/AJ/156/264
- Title:
- California-Kepler Survey. VII. Planet radius gap
- Short Name:
- J/AJ/156/264
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The distribution of planet sizes encodes details of planet formation and evolution. We present the most precise planet size distribution to date based on Gaia parallaxes, Kepler photometry, and spectroscopic temperatures from the California-Kepler Survey. Previously, we measured stellar radii to 11% precision using high-resolution spectroscopy; by adding Gaia astrometry, the errors are now 3%. Planet radius measurements are, in turn, improved to 5% precision. With a catalog of ~1000 planets with precise properties, we probed in fine detail the gap in the planet size distribution that separates two classes of small planets, rocky super-Earths and gas-dominated sub-Neptunes. Our previous study and others suggested that the gap may be observationally under-resolved and inherently flat-bottomed, with a band of forbidden planet sizes. Analysis based on our new catalog refutes this; the gap is partially filled in. Two other important factors that sculpt the distribution are a planet's orbital distance and its host-star mass, both of which are related to a planet's X-ray/UV irradiation history. For lower-mass stars, the bimodal planet distribution shifts to smaller sizes, consistent with smaller stars producing smaller planet cores. Details of the size distribution including the extent of the "sub-Neptune desert" and the width and slope of the gap support the view that photoevaporation of low-density atmospheres is the dominant evolutionary determinant of the planet size distribution.
- ID:
- ivo://CDS.VizieR/J/ApJS/234/31
- Title:
- Carbon stars from LAMOST using machine learning
- Short Name:
- J/ApJS/234/31
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this work, we present a catalog of 2651 carbon stars from the fourth Data Release (DR4) of the Large Sky Area Multi-Object Fiber Spectroscopy Telescope (LAMOST). Using an efficient machine-learning algorithm, we find these stars from more than 7 million spectra. As a by-product, 17 carbon-enhanced metal- poor turnoff star candidates are also reported in this paper, and they are preliminarily identified by their atmospheric parameters. Except for 176 stars that could not be given spectral types, we classify the other 2475 carbon stars into five subtypes: 864 C-H, 226 C-R, 400 C-J, 266 C-N, and 719 barium stars based on a series of spectral features. Furthermore, we divide the C-J stars into three subtypes, C-J(H), C-J(R), and C-J(N), and about 90% of them are cool N-type stars as expected from previous literature. Besides spectroscopic classification, we also match these carbon stars to multiple broadband photometries. Using ultraviolet photometry data, we find that 25 carbon stars have FUV detections and that they are likely to be in binary systems with compact white dwarf companions.
- ID:
- ivo://CDS.VizieR/J/AJ/153/95
- Title:
- Catalog of Suspected Nearby Young Stars
- Short Name:
- J/AJ/153/95
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new nearby young moving group (NYMG) kinematic membership analysis code, LocAting Constituent mEmbers In Nearby Groups (LACEwING), a new Catalog of Suspected Nearby Young Stars, a new list of bona fide members of moving groups, and a kinematic traceback code. LACEwING is a convergence-style algorithm with carefully vetted membership statistics based on a large numerical simulation of the Solar Neighborhood. Given spatial and kinematic information on stars, LACEwING calculates membership probabilities in 13 NYMGs and three open clusters within 100 pc. In addition to describing the inputs, methods, and products of the code, we provide comparisons of LACEwING to other popular kinematic moving group membership identification codes. As a proof of concept, we use LACEwING to reconsider the membership of 930 stellar systems in the Solar Neighborhood (within 100 pc) that have reported measurable lithium equivalent widths. We quantify the evidence in support of a population of young stars not attached to any NYMGs, which is a possible sign of new as-yet-undiscovered groups or of a field population of young stars.
- ID:
- ivo://CDS.VizieR/J/AJ/156/171
- Title:
- Cepheid abund.: multiphase results & spatial gradients
- Short Name:
- J/AJ/156/171
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Parameters and abundances have been derived for 435 Cepheids based on an analysis of 1127 spectra. Results from five or more phases are available for 52 of the program stars. The latter set of stars span periods between 1.5 and 68 days. The parameters and abundances show excellent consistency across phase. For iron, the average range in the determined abundance is 0.11 from these 52 stars. For 163 stars with more than one phase available the average range is 0.07. The variation in effective temperature tracks well with phase, as does the total broadening velocity. The gravity and microturbulent velocity follow phase, but with less variation and regularity. Abundance gradients have been derived using Gaia DR2 (Cat. I/345) parallax data, as well as Bayesian distance estimates based upon Gaia DR2 from Bailer-Jones et al. (2018, Cat. I/347). The abundance gradient derived for iron is d[Fe/H]/dR=-0.05 dex/kpc, similar to gradients derived in previous studies.