- ID:
- ivo://CDS.VizieR/J/A+A/440/121
- Title:
- K magnitudes of OB stars in UCHIIs
- Short Name:
- J/A+A/440/121
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have obtained high resolution (R=10000) K-band spectra of candidate young massive stars deeply embedded in (ultra-) compact HII regions (UCHIIs). These objects were selected from a near-infrared survey of 44 fields centered on IRAS sources with UCHII colours. Often, the near-infrared counterpart of the IRAS source is a young embedded cluster hosting massive stars. In these clusters, three types of objects are identified. The first type (38 objects) consists of "naked" OB stars whose K-band spectra are dominated by photospheric emission. We classify the K-band spectra of the OB-type cluster members using near-infrared classification criteria. A few of them have a very early (O3-O4 V) spectral type, consistent with a young age of the embedded clusters. The spectral classification provides an important constraint on the distance to the embedded cluster.
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- ID:
- ivo://CDS.VizieR/J/A+A/584/A2
- Title:
- KMOS view of the Galactic centre. I.
- Short Name:
- J/A+A/584/A2
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Galactic centre hosts a crowded, dense nuclear star cluster with a half-light radius of 4pc. Most of the stars in the Galactic centre are cool late-type stars, but there are also >=100 hot early-type stars in the central parsec of the Milky Way. These stars are only 3-8Myr old. Our knowledge of the number and distribution of early-type stars in the Galactic centre is incomplete. Only a few spectroscopic observations have been made beyond a projected distance of 0.5pc of the Galactic centre. The distribution and kinematics of early-type stars are essential to understand the formation and growth of the nuclear star cluster.
- 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.
- 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/MNRAS/475/5144
- Title:
- Magnetic early B-type stars. I.
- Short Name:
- J/MNRAS/475/5144
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The rotational and magnetic properties of many magnetic hot stars are poorly characterized, therefore the MiMeS and BinaMIcS collaborations have collected extensive high-dispersion spectropolarimetric datasets of these targets. We present longitudinal magnetic field measurements <B_Z_> for 52 early B-type stars (B5 to B0), with which we attempt to determine their rotational periods Prot. Supplemented with high-resolution spectroscopy, low-resolution DAO circular spectropolarimetry, and archival Hipparcos photometry, we determined Prot for 10 stars, leaving only 5 stars for which Prot could not be determined. Rotational ephemerides for 14 stars were refined via comparison of new to historical magnetic measurements. The distribution of Prot is very similar to that observed for the cooler Ap/Bp stars. We also measured vsini and v_mac_ for all stars. Comparison to non-magnetic stars shows that vsini is much lower for magnetic stars, an expected consequence of magnetic braking. We also find evidence that v_mac_ is lower for magnetic stars. LSD profiles extracted using single-element masks revealed widespread, systematic discrepancies in <B_Z_> between different elements: this effect is apparent only for chemically peculiar stars, suggesting it is a consequence of chemical spots. Sinusoidal fits to H line <B_Z_> measurements (which should be minimally affected by chemical spots), yielded evidence of surface magnetic fields more complex than simple dipoles in 6 stars for which this has not previously been reported; however, in all 6 cases the second- and third-order amplitudes are small relative to the first-order (dipolar) amplitudes.
- 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.
