- ID:
- ivo://CDS.VizieR/J/ApJS/239/26
- Title:
- NOFS astrometric measurements for distant WDs
- Short Name:
- J/ApJS/239/26
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper presents new trigonometric parallaxes and proper motions for 214 stars. The measurements were made at the US Naval Observatory Flagstaff Station between 1989 and 2017, and the average uncertainty in the parallax values is 0.6mas. We find good agreement with Gaia Data Release 2 measurements for the stars in common, although there may be a small systematic offset similar to what has been found by other investigators. The sample is matched to catalogs and the literature to create a photometric data set that spans the ultraviolet to the mid-infrared. New mid-infrared photometry is obtained for 19 stars from archived Spitzer mosaics. New optical spectroscopy is presented for seven systems and additional spectra were obtained from the literature. We identify a subsample of 179 white dwarfs (WDs) at distances of 25-200pc. Their spectral energy distributions (SEDs) are analyzed using model atmospheres. The models reproduce the entire flux-calibrated SED very well and provide the atmospheric chemical composition, temperature, surface gravity, mass, and cooling age of each WD. Twenty-six WDs are newly classified, and 12 systems are presented as candidate unresolved binaries. We confirm one WD+red dwarf system and identify two WDs as candidate dust disk systems. Twelve old and high-velocity systems are identified as candidate thick disk or halo objects. The WDs in the sample generally have Galactic disk-like ages of <8Gyr and masses close to the canonical 0.6M_{sun}_.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/813/42
- Title:
- O and B type stars in W3: first results
- Short Name:
- J/ApJ/813/42
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first results from our survey of the star-forming complex W3, combining VRI photometry with multiobject spectroscopy to identify and characterize the high-mass stellar population across the region. With 79 new spectral classifications, we bring the total number of spectroscopically confirmed O- and B-type stars in W3 to 105. We find that the high-mass slope of the mass function in W3 is consistent with a Salpeter IMF, and that the extinction toward the region is best characterized by an R_V_ of approximately 3.6. B-type stars are found to be more widely dispersed across the W3 giant molecular cloud (GMC) than previously realized: they are not confined to the high-density layer (HDL) created by the expansion of the neighboring W4 H ii region into the GMC. This broader B-type population suggests that star formation in W3 began spontaneously up to 8-10 Myr ago, although at a lower level than the more recent star formation episodes in the HDL. In addition, we describe a method of optimizing sky subtraction for fiber spectra in regions of strong and spatially variable nebular emission.
- ID:
- ivo://CDS.VizieR/J/AJ/161/164
- Title:
- Observation of 186 TESS stars with NESSI (WYIN)
- Short Name:
- J/AJ/161/164
- Date:
- 09 Mar 2022 22:00:00
- Publisher:
- CDS
- Description:
- We present high-resolution speckle interferometric imaging observations of TESS exoplanet host stars using the NN-EXPLORE Exoplanet and Stellar Speckle Imager instrument at the 3.5m WIYN telescope. Eight TESS objects of interest that were originally discovered by Kepler were previously observed using the Differential Speckle Survey Instrument. Speckle observations of 186 TESS stars were carried out, and 45 (24%) likely bound companions were detected. This is approximately the number of companions we would expect to observe given the established 46% binarity rate in exoplanet host stars. For the detected binaries, the distribution of stellar mass ratio is consistent with that of the standard Raghavan distribution and may show a decrease in high-q systems as the binary separation increases. The distribution of binary orbital periods, however, is not consistent with the standard Ragahavan model, and our observations support the premise that exoplanet-hosting stars with binary companions have, in general, wider orbital separations than field binaries. We find that exoplanet-hosting binary star systems show a distribution peaking near 100 au, higher than the 40-50au peak that is observed for field binaries. This fact led to earlier suggestions that planet formation is suppressed in close binaries.
- ID:
- ivo://CDS.VizieR/J/AJ/154/29
- Title:
- Observation of 148 young stars toward NGC 1980
- Short Name:
- J/AJ/154/29
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- NGC1980 is a young cluster that is located about 0.5{deg} south of the Orion Nebula Cluster (ONC). Recent studies by Bouy et al. and Pillitteri et al. have suggested that NGC1980 contains an older population of stars compared to a much younger ONC, and that it belongs to a foreground population that may be located in front of the Orion A molecular gas by as much as 40pc. In this work, we present low-resolution spectra toward 148 young stars found toward the NGC1980 region. We determine the spectral types of these stars, examine accretion signatures and measure the extinction toward them. We determine that based on these observations, the age of the population of NGC1980 is indistinguishable from L1641, estimated to be ~3Myr, comparable with the study by Fang et al.
- ID:
- ivo://CDS.VizieR/J/ApJ/822/L5
- Title:
- Observed red supergiants in the inner Galaxy
- Short Name:
- J/ApJ/822/L5
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this Letter, we present a search for Galactic red supergiant stars (RSGs) in the direction of the inner Galaxy. A total of 94 targets selected from the 2MASS (Cat. VII/233) and GLIMPSE I North (Benjamin et al. 2003, Cat. II/293; Churchwell et al. 2009PASP..121..213C) catalogs - via their blue extinction-free Q1 and Q2 colors - were spectroscopically observed at infrared wavelengths (in the H- and K-bands at R~1000), and an extraordinary high detection rate of RSGs (>61%) was found. We identified spectroscopically 58 RSGs, based on their flat continua and large equivalent widths of the CO-band at 2.293 {mu}m (EW>45 {AA}). This increase corresponds to about 25% of previously known RSGs in the Galactic region 10{deg}<l<60{deg}, -1.1{deg}<b<1.1{deg}. In order to confirm the location of the new RSGs in the inner Galaxy, distances were estimated for a subsample of 47 stars with the clump method and found to range from 3.6+/-0.4 to 8.6+/-0.7 kpc. The large new sample will allow us to investigate Galactic metallicity gradients as a function of galactocentric distances and azimuthal angles. Such information is currently an highly disputed issue to constrain models of Galaxy formation and evolution.
- ID:
- ivo://CDS.VizieR/J/ApJS/241/32
- Title:
- OB stars from the LAMOST DR5 spectra
- Short Name:
- J/ApJS/241/32
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present 22901 OB spectra of 16032 stars identified from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope data release 5 (LAMOST DR5) data set. A larger sample of OB candidates are first selected from the distributions in the spectral line indices' space. Then, all 22901 OB spectra are identified by manual inspection. Based on a subsample validation, we find that the completeness of the OB spectra reaches about 89+/-22% for the stars with spectral types earlier than B7, while around 57+/-16% B8-B9 stars are identified. The smaller completeness for late B stars will lead to the difficulty in discriminating them from A0-A1-type stars. The subclasses of the OB samples are determined using the software package MKCLASS. With a careful validation using 646 subsamples, we find that MKCLASS can give fairly reliable subtypes and luminosity classes for most of the OB stars. The uncertainty of the spectral subtype is around 1 subtype, and the uncertainty of the luminosity class is around 1 level. However, about 40% of the OB stars fail to be assigned to any class by MKCLASS, and a few spectra are significantly misclassified by MKCLASS. This is likely because the template spectra of MKCLASS are selected from nearby stars in the solar neighborhood, while the OB stars in this work are mostly located in the outer disk and may have lower metallicities. The rotation of the OB stars may also be responsible for the misclassifications. Moreover, we find that the spectral and luminosity classes of the OB stars located in the Galactic latitude larger than 20{deg} are substantially different with those located in the latitude smaller than 20{deg}, which may either be due to the observational selection effect or may hint a different origin of the high Galactic latitude OB stars.
- ID:
- ivo://CDS.VizieR/J/A+A/657/A62
- Title:
- OB stars spectral classification automated tool
- Short Name:
- J/A+A/657/A62
- Date:
- 17 Mar 2022 14:50:02
- Publisher:
- CDS
- Description:
- As an increasing number of spectroscopic surveys become available, an automated approach to spectral classification becomes necessary. Due to the significance of the massive stars, it is of great importance to identify the phenomenological parameters of these stars (e.g., the spectral type), which can be used as proxies to their physical parameters (e.g., mass and temperature). In this work, we aim to use the random forest (RF) algorithm to develop a tool for the automated spectral classification of OB-type stars according to their sub-types. We used the regular RF algorithm, the probabilistic RF (PRF), which is an extension of RF that incorporates uncertainties, and we introduced the KDE-RF method which is a combination of the kernel-density estimation and the RF algorithm. We trained the algorithms on the equivalent width (EW) of characteristic absorption lines measured in high-quality spectra (Signal-to-Noise (S/N)>50) from large Galactic (LAMOST, GOSSS) and extragalactic surveys (2dF, VFTS) with available spectral types and luminosity classes. By following an adaptive binning approach, we grouped the labels of these data in 11 spectral classes within the O2-B9 range. We examined which of the characteristic spectral lines (features) are more important for the classification based on a number of feature selection methods, and we searched for the optimal hyperparameters of the classifiers to achieve the best performance. From the feature-screening process, we find that the full set of 17 spectral lines is needed to reach the maximum performance per spectral class. We find that the overall accuracy score is ~70%, with similar results across all approaches. We apply our model in other observational data sets providing examples of the potential application of our classifier to real science cases. We find that it performs well for both single massive stars and for the companion massive stars in Be X-ray binaries, especially for data of similar quality to the training sample. In addition, we propose a reduced ten-features scheme that can be applied to large data sets with lower S/N~20-50. The similarity in the performances of our models indicates the robustness and the reliability of the RF algorithm when it is used for the spectral classification of early-type stars. The score of ~70% is high if we consider (a) the complexity of such multiclass classification problems (i.e., 11 classes), (b) the intrinsic scatter of the EW distributions within the examined spectral classes, and (c) the diversity of the training set since we use data obtained from different surveys with different observing strategies. In addition, the approach presented in this work is applicable to products from different surveys in terms of quality (e.g., different resolution) and different formats (e.g., absolute or normalized flux), while our classifier is agnostic to the luminosity class of a star, and, as much as possible, it is metallicity independent.
- ID:
- ivo://CDS.VizieR/J/AJ/161/295
- Title:
- Obs. with Differential Speckle Survey Instrument. X.
- Short Name:
- J/AJ/161/295
- Date:
- 09 Mar 2022 22:00:00
- Publisher:
- CDS
- Description:
- This paper details speckle observations of binary stars taken at the Lowell Discovery Telescope, the WIYN telescope, and the Gemini telescopes between 2016 January and 2019 September. The observations taken at Gemini and Lowell were done with the Differential Speckle Survey Instrument (DSSI), and those done at WIYN were taken with the successor instrument to DSSI at that site, the NN-EXPLORE Exoplanet Star and Speckle Imager (NESSI). In total, we present 378 observations of 178 systems, and we show that the uncertainty in the measurement precision for the combined data set is ~2mas in separation, ~1{deg}-2{deg} in position angle depending on the separation, and ~0.1mag in magnitude difference. Together with data already in the literature, these new results permit 25 visual orbits and one spectroscopic- visual orbit to be calculated for the first time. In the case of the spectroscopic-visual analysis, which is done on the ternary star HD173093, we calculate masses with a precision of better than 1% for all three stars in that system. Twenty-one of the visual orbits calculated have a K-dwarf as the primary star; we add these to the known orbits of K-dwarf primary stars and discuss the basic orbital properties of these stars at this stage. Although incomplete, the data that exist so far indicate that binaries with K-dwarf primaries tend not to have low-eccentricity orbits at separations of one to a few tens of astronomical units, that is, on solar system scales.
- ID:
- ivo://CDS.VizieR/J/ApJ/753/13
- Title:
- OI equivalent widths in Be stars
- Short Name:
- J/ApJ/753/13
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The possibility of the Ly{beta} fluorescence mechanism being operational in classical Be (CBe) stars and thereby contributing to the strength of the OI{lambda}8446 line has been recognized for long. However, this supposition needs to be quantified by comparing observed and predicted OI line ratios. In the present work, optical and near-infrared spectra of CBe stars are presented. We analyze the observed strengths of the OI{lambda}7774, {lambda}8446, {lambda}11287, and {lambda}13165 lines, which have been theoretically proposed as diagnostics for identifying the excitation mechanism. We have considered and examined the effects of Ly{beta} fluorescence, collisional excitation, recombination, and continuum fluorescence on these O I line strengths. From our analysis it appears that the Ly{beta} fluorescence process is indeed operative in Be stars.
- ID:
- ivo://CDS.VizieR/J/AJ/106/591
- Title:
- OP Survey of Halo early-type stars
- Short Name:
- J/AJ/106/591
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The results are reported of an objective-prism survey of stars, mostly earlier than spectral type F5, for two fields at (l;b) = (90 deg and 270 deg; -45 deg). The fields, each of approximately 70 square degrees, are examined on plates taken with the Schmidt Telescope of the Anglo-Australian Observatory. The brightness range of the stars classified is 10 < V < 15. The prism combination used provides a dispersion of 600 A/mm at Hgamma. The spectral classification presented is defined by the equality of equivalent widths of Ca II K and Hdelta at type "F0" and the absence of Ca II K in stars with significant Balmer lines at type "A0". Positions listed in the catalog were measured on the Stromlo PDS microdensitometer. Most stars were subsequently identified with objects in the ST ScI-NASA-ESO Hubble Space Telescope Guide Star Catalog in which positions have an accuracy of near +/- 1.0 arcsec.
