- ID:
- ivo://CDS.VizieR/J/other/PASA/32.36
- Title:
- lambda Boo star membership evaluations
- Short Name:
- J/other/PASA/32.
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The literature on the {lambda} Boo stars has grown to become somewhat heterogenous, as different authors have applied different criteria across the UV, optical and infrared regions to determine the membership status of {lambda} Boo candidates. We aim to clear up the confusion by consulting the literature on 212 objects that have been considered as {lambda} Boo candidates, and subsequently evaluating the evidence in favour of their admission to the {lambda} Boo class. We obtained new spectra of ~90 of these candidates and classified them on the MK system to aid in the membership evaluations. The re-evaluation of the 212 objects resulted in 64 members and 103 non-members of the {lambda} Boo class, with a further 45 stars for which membership status is unclear. We suggest observations for each of the stars in the latter category that will allow them to be confidently included or rejected from the class. Our reclassification facilitates homogeneous analysis on group members, and represents the largest collection of confirmed {lambda} Boo stars known.
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- ID:
- ivo://CDS.VizieR/J/AJ/154/31
- Title:
- {lambda} Bootis stars: the southern survey I.
- Short Name:
- J/AJ/154/31
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The {lambda} Boo stars are a class of chemically peculiar Population I A-type stars characterized by under-abundances of the refractory elements, but near-solar abundances of carbon, nitrogen, oxygen, and sulfur. There is some evidence that {lambda} Boo stars have higher frequencies of "bright" debris disks than normal A-type stars. The discovery of four exoplanets orbiting HR8799, a {lambda} Boo star with a resolved debris disk, suggests that the {lambda} Boo phenomenon may be related to the presence of a dynamic debris disk, perhaps perturbed by migrating planets. However, only 64 {lambda} Boo stars are known, and those stars were discovered with different techniques, making it problematic to use that sample for statistical purposes, including determining the frequency of debris disks. The purpose of this paper is to derive a new sample of {lambda} Boo stars using a technique that does not lead to biases with respect to the presence of infrared excesses. Through spectroscopic observations in the southern hemisphere, we have discovered 33 {lambda} Boo stars and have confirmed 12 others. As a step toward determining the proportion of {lambda} Boo stars with infrared excesses, we have used WISE data to examine the infrared properties of this sample out to 22{mu}m. On this basis, we cannot conclude that {lambda} Boo stars have a greater tendency than normal A-type stars to show infrared excesses. However, observing this sample at longer wavelengths may change that conclusion, as many {lambda} Boo debris disks are cool and do not radiate strongly at 22{mu}m.
- ID:
- ivo://CDS.VizieR/J/other/RAA/16.138
- Title:
- LAMOST catalog of early-type emission-line stars
- Short Name:
- J/other/RAA/16.1
- Date:
- 10 Dec 2021 14:42:33
- Publisher:
- CDS
- Description:
- We present a catalog including 11204 spectra of 10436 early-type emission-line stars from LAMOST DR2, among which 9752 early-type emission-line spectra are newly discovered. For these early-type emission-line stars, we discuss the morphological and physical properties of their low-resolution spectra. In this spectral sample, the H{alpha} emission profiles display a wide variety of shapes. Based on the H{alpha} line profiles, these spectra are categorized into five distinct classes: single-peak emission, single-peak emission in absorption, double-peak emission, double-peak emission in absorption, and P-Cygni profiles. To better understand what causes the H{alpha} line profiles, we divide these objects into four types from the perspective of physical classification, which include classical Be stars, Herbig Ae/Be stars, close binaries and spectra contaminated by HII regions. The majority of Herbig Ae/Be stars and classical Be stars are identified and separated using a (H-K, K-W1) color-color diagram.We also discuss 31 binary systems that are listed in the SIMBAD on-line catalog and identify 3600 spectra contaminated by HII regions after cross-matching with positions in the Dubout-Crillon catalog (1976, Cat. J/A+AS/25/25. A statistical analysis of line profiles versus classifications is then conducted in order to understand the distribution of H{alpha} profiles for each type in our sample. Finally, we also provide a table of 172 spectra with FeII emission lines and roughly calculate stellar wind velocities for seven spectra with P-Cygni profiles.
- ID:
- ivo://CDS.VizieR/III/68
- Title:
- List of Early-Type Chemically Peculiar Stars
- Short Name:
- III/68
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This catalogue is a subset of the "CATALOGUE OF STELLAR GROUPS" (CSG, Jaschek M. and Egret D., 1981BICDS..20...36J). It provides a list of identifications, positions, UBV photometry, subgroup and references for chemically peculiar stars corresponding to the following groups: Table 1: Helium abnormal stars Table 2: Ap stars Table 3: Am stars A bibliography file is also included.
- ID:
- ivo://CDS.VizieR/J/MNRAS/499/5379
- Title:
- Longitudinal magnetic field of 6 B stars
- Short Name:
- J/MNRAS/499/5379
- Date:
- 02 Feb 2022 09:52:06
- Publisher:
- CDS
- Description:
- Rapidly rotating early-type stars with strong magnetic fields frequently show H{alpha} emission originating in centrifugal magnetospheres (CMs), circumstellar structures in which centrifugal support due to magnetically enforced corotation of the magnetically confined plasma enables it to accumulate to high densities. It is not currently known whether the CM plasma escapes via centrifugal breakout (CB), or by an unidentified leakage mechanism. We have conducted the first comprehensive examination of the H{alpha} emission properties of all stars currently known to display CM-pattern emission. We find that the onset of emission is dependent primarily on the area of the CM, which can be predicted simply by the value B_K_ of the magnetic field at the Kepler corotation radius R_K_. Emission strength is strongly sensitive to both CM area and B_K_. Emission onset and strength are not dependent on effective temperature, luminosity, or mass-loss rate. These results all favour a CB scenario; however, the lack of intrinsic variability in any CM diagnostics indicates that CB must be an essentially continuous process, i.e. it effectively acts as a leakage mechanism. We also show that the emission profile shapes are approximately scale-invariant, i.e. they are broadly similar across a wide range of emission strengths and stellar parameters. While the radius of maximum emission correlates closely as expected to R_K_, it is always larger, contradicting models that predict that emission should peak at R_K_.
- ID:
- ivo://CDS.VizieR/J/MNRAS/373/13
- Title:
- Lower main-sequence stars fundamental param.
- Short Name:
- J/MNRAS/373/13
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We derive an empirical effective temperature and bolometric luminosity calibration for G and K dwarfs, by applying our own implementation of the Infrared Flux Method to multiband photometry. Our study is based on 104 stars for which we have excellent BV(RI)_C_ JHK_s_ photometry, excellent parallaxes and good metallicities. Colours computed from the most recent synthetic libraries (ATLAS9 and MARCS) are found to be in good agreement with the empirical colours in the optical bands, but some discrepancies still remain in the infrared. Synthetic and empirical bolometric corrections also show fair agreement.
- ID:
- ivo://CDS.VizieR/J/A+A/650/A112
- Title:
- Mapping hot luminous stars in the Galaxy
- Short Name:
- J/A+A/650/A112
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Luminous hot stars (M_Ks_<~0mag and Teff>~8000K) dominate the stellar energy input to the interstellar medium (ISM) throughout cosmological time, are used as laboratories to test theories of stellar evolution and multiplicity, and serve as luminous tracers of star formation in the Milky Way and other galaxies. Massive stars occupy well-defined loci in colour-colour and colour-magnitude spaces, enabling selection based on the combination of Gaia EDR3 astrometry and photometry and 2MASS photometry, even in the presence of substantive dust extinction. In this paper we devise an all-sky sample of such luminous OBA-type stars, which was designed to be complete rather than very pure, providing targets for spectroscopic follow-up with the SDSS-V survey. To estimate the purity and completeness of our catalogue, we derive stellar parameters for the stars in common with LAMOST DR6 and we compare the sample to other O and B-type star catalogues. We estimate `astro-kinematic' distances by combining parallaxes and proper motions with a model for the expected velocity and density distribution of young stars; we show that this adds useful constraints on the distances and therefore luminosities of the stars. With these distances we map the spatial distribution of a more stringently selected subsample across the Galactic disc, and find it to be highly structured, with distinct over- and under-densities. The most evident over-densities can be associated with the presumed spiral arms of the Milky Way, in particular the Sagittarius-Carina and Scutum-Centaurus arms. Yet, the spatial picture of the Milky Way's young disc structure emerging in this study is complex, and suggests that most young stars in our Galaxy (t_age_<t_dyn_) are not neatly organised into distinct spiral arms. The combination of the comprehensive spectroscopy to come from SDSS-V (yielding velocities, ages, etc.) with future Gaia data releases will be crucial in order to reveal the dynamical nature of the spiral arms themselves.
- ID:
- ivo://CDS.VizieR/J/A+A/540/A57
- Title:
- Mass function of Quintuplet cluster
- Short Name:
- J/A+A/540/A57
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The stellar mass function is a probe for a potential dependence of star formation on the environment. Only a few young clusters are known to reside within the central molecular zone and can serve as test-beds for star formation under the extreme conditions in this region. We determine the present-day mass function of the Quintuplet cluster, a young massive cluster in the vicinity of the Galactic centre. We use two epochs of high resolution near infrared imaging data obtained with NAOS/CONICA at the ESO VLT to measure the individual proper motions of stars in the Quintuplet cluster in the cluster reference frame. An unbiased sample of cluster members within a radius of 0.5pc from the cluster centre was established based on their common motion with respect to the field and a subsequent colour-cut. Initial stellar masses were inferred from four isochrones covering ages from 3 to 5Myr and two sets of stellar evolution models. For each isochrone, the present-day mass function of stars was determined for the full sample of main sequence cluster members using an equal number binning scheme. We find the slope of the present-day mass function in the central part of the Quintuplet cluster to be alpha=-1.68^+0.13^_-0.09_ for an approximate mass range from 5 to 40M_{sun}_, which is significantly flatter than the Salpeter slope of alpha=-2.35. The flattening of the present-day mass function may be caused by rapid dynamical evolution of the cluster in the strong Galactic centre tidal field. The derived mass function slope is compared to the values found in other young massive clusters in the Galaxy.
- ID:
- ivo://CDS.VizieR/J/A+A/597/A22
- Title:
- Massive O- and B-type stars velocities
- Short Name:
- J/A+A/597/A22
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The term macroturbulent broadening is commonly used to refer to a certain type of non-rotational broadening acting the spectral line profiles of O- and B-type stars. It has been proposed to be a spectroscopic signature of the presence of stellar oscillations; however, we still lack a definitive confirmation of this hypothesis. We aim to provide new empirical clues about macroturbulent spectral line broadening in O- and B-type stars to evaluate its physical origin. We used high-resolution spectra of 430 stars with spectral types in the range O4-B9 (all luminosity classes) compiled in the framework of the IACOB project. We characterized the line broadening of adequate diagnostic metal lines using a combined Fourier transform and goodness-of-fit technique. We performed a quantitative spectroscopic analysis of the whole sample using automatic tools coupled with a huge grid of FASTWIND models to determine their effective temperatures and gravities. We also incorporated quantitative information about line asymmetries into our observational description of the characteristics of the line profiles, and performed a comparison of the shape and type of line-profile variability found in a small sample of O stars and B supergiants with still undefined pulsational properties and B main-sequence stars with variable line profiles owing to a well-identified type of stellar oscillations or to the presence of spots in the stellar surface.
- ID:
- ivo://CDS.VizieR/J/A+A/638/A157
- Title:
- Massive O-type stars near ZAMS elusive detection
- Short Name:
- J/A+A/638/A157
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The apparent lack of massive O-type stars near the Zero Age Main Sequence, or ZAMS, (at ages <2Myr) has been a topic widely discussed in the last 40 years. Different explanations for the elusive detection of these young massive stars have been proposed from both the observational and theoretical side, but no firm conclusions have been reached yet. The aim of this work is to perform a reassessment of this empirical result benefiting from the high quality spectroscopic observations of (more than 400) Galactic O-type stars gathered by the IACOB and OWN surveys. We use effective temperatures and surface gravities resulting from a homogeneous, semi-automatized, IACOB-GBAT/FASTWIND spectroscopic analysis to locate our sample of stars in the Kiel and spectroscopic Hertzsprung-Russell (HR) diagrams. We evaluate the completeness of our magnitude limited sample of stars - as well as the existence of potential observational biases affecting the compiled sample - using information from the Galactic O star catalog (GOSC). We discuss limitations and possible systematics of our analysis methodology, and compare our results with other recent studies using smaller samples of Galactic O-type stars. We mainly base our discussion on the distribution of stars in the spectroscopic HR diagram in order to avoid the use of still uncertain distances to most of the stars in our sample. However, we also perform a more detailed study of the young cluster Trumpler-14 as an illustrative example of how Gaia cluster distances can help to construct the associated classical HR diagram. We find that the apparent lack of massive O-type stars near the zero-age main sequence with initial evolutionary masses in the range between ~30 and 70M_{sun}_ still persist despite using spectroscopic results from a large, non-biased sample of stars. We do not find any correlations between the dearth of stars close to the ZAMS and obvious observational biases, limitations of our analysis methodology, and/or the use of one example spectroscopic HR diagram instead of the classical one. Finally, by investigating the impact of the efficiency of mass accretion during the formation process of massive stars, we conclude that an adjustment of the mass accretion rate towards lower values than canonically assumed could reconcile the hotter boundary of the empirical distribution of optically detected O-type stars in the spectroscopic HR diagram and the theoretical birthline for stars with masses above 30M_{sun}_. Last, we also discuss how the presence of a small sample of O2-O3.5 stars found much closer to the ZAMS than the main distribution of Galactic O-type star could be explained in the context of this scenario taking also into account the effect of non-standard star evolution (e.g. binary interaction, mergers, and/or homogeneous evolution).
