- ID:
- ivo://CDS.VizieR/J/ApJ/768/128
- Title:
- K-band calibrated visibilities of 24 Be stars
- Short Name:
- J/ApJ/768/128
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on a high angular resolution survey of circumstellar disks around 24 northern sky Be stars. The K-band continuum survey was made using the CHARA Array long baseline interferometer (baselines of 30-331m). The interferometric visibilities were corrected for the flux contribution of stellar companions in those cases where the Be star is a member of a known binary or multiple system. For those targets with good (u, v) coverage, we used a four-parameter Gaussian elliptical disk model to fit the visibilities and to determine the axial ratio, position angle, K-band photospheric flux contribution, and angular diameter of the disk's major axis. For the other targets with relatively limited (u, v) coverage, we constrained the axial ratio, inclination angle, and/or disk position angle where necessary in order to resolve the degeneracy between possible model solutions. We also made fits of the ultraviolet and infrared spectral energy distributions (SEDs) to estimate the stellar angular diameter and infrared flux excess of each target. The mean ratio of the disk diameter (measured in K-band emission) to stellar diameter (from SED modeling) is 4.4 among the 14 cases where we reliably resolved the disk emission, a value which is generally lower than the disk size ratio measured in the higher opacity H{alpha} emission line. We estimated the equatorial rotational velocity from the projected rotational velocity and disk inclination for 12 stars, and most of these stars rotate close to or at the critical rotational velocity.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/A+AS/129/289
- Title:
- Long-term spectrophotometry of Be stars
- Short Name:
- J/A+AS/129/289
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The long-term spectrophotometric variations of 49 Be stars are studied using the U and V magnitudes of the UBV system, the total Balmer discontinuity D and the visible gradient {Phi}_rb_. BCD (Barbier-Chalonge-Divan, see Chalonge & Divan, 1952AnAp...15..201C) spectrophotometric and photometric data in five different photometric systems, obtained in most cases since 1950 and reduced to the BCD system, were used. The (U,D), (V,D), ({Phi}_rb_,D) and ({Phi}_rb_,V) correlations obtained differ from star to star and they can be single or double-valued. They differ clearly for Be phases or Be-shell phases. Be stars with small V.sin(i) showing the "spectrophotometric shell behaviour": D>D*, were found. This finding implies either that strongly flattened models of circumstellar envelopes are in doubt for these stars, or that not all Be stars are rapid rotators. Comparison of observed variations with those predicted for model Be stars with spherical circumstellar envelopes of variable densities and dimensions implies that spectrophotometric patterns of Be phases are due to circumstellar envelopes in low opacity regimes, while those of spectrophotometric shell phases are due to circumstellar envelopes in high opacity regimes. In a given star, the envelope regions responsible for the observed variations of D and {Phi}_rb_ in spectrophotometric shell phases seem to be smaller and denser than those producing the observed variations of these parameters in spectrophotometric Be phases. The high positive RV found in strong shell phases might favor the formation of compact circumstellar layers near the star.
- ID:
- ivo://CDS.VizieR/J/A+A/641/A42
- Title:
- Main-sequence companions to massive Be stars
- Short Name:
- J/A+A/641/A42
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- About 20% of all B-type stars are classical Be stars. The Be phenomenon is strongly correlated with rapid rotation, the origin of which remains unclear. It may be rooted in single- or binary-star evolution. In the framework of the binary channel, the initially more massive star transfers mass and angular momentum to the original secondary, which becomes a Be star. The system then evolves into a Be binary with a post-main-sequence companion, which may later be disrupted in a supernova event. Hence, if the binary channel dominates the formation of Be stars, one may expect a strong lack of close Be binaries with main sequence (MS) companions. Through an extensive, star-by-star review of the literature of a magnitude-limited sample of Galactic early-type Be stars, we investigate whether Be binaries with MS companions are known to exist. Our sample is constructed from the BeSS database and cross-matched with all available literature on the individual stars. Out of an initial list of 505 Be stars, we compile a final sample of 287 Galactic Be stars earlier than B1.5 with V<=12mag. Out of those, 13 objects were reported as Be binaries with known post-MS companions and 11 as binaries with unknown, uncertain or debated companions. We find no confirmed reports of Be binaries with MS companions. For the remaining 263 targets, no significant reports of multiplicity exist in the literature, implying that they are either Be binaries with faint companions, or truly single. The clear lack of reported MS companions to Be stars, which stands in contrast to the high number of detected B+B MS binaries, strongly supports the hypothesis that early-type Be stars are binary interaction products that spun up after mass and angular momentum transfer from a companion star. Taken at face value, our results may suggest that a large majority of the early-type Be stars have formed through binary mass-transfer.
- ID:
- ivo://CDS.VizieR/J/other/NewA/10.325
- Title:
- 2MASS observations of Be stars
- Short Name:
- J/other/NewA/10.
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A catalogue of almost all known Galactic Be stars in the 2MASS (<II/246>) database (1185 in total) and in the MSX (<V/114>) database (225 in total) is presented in this paper. From the color-color diagrams and spectral indexes, it is found that the IR excesses for many samples are due to free-free and free-bound emission from the ionized material around a Be star as suggested previously and that the mean spectral index derived for the samples is 1.50+/-0.34 between J to K bands and 1.14+/-0.42 between K to A bands, respectively. However, it is also found that there are eight Be stars that have large near infrared excess emission with spectral index values outside the range expected for freefree and freebound emission. This is likely attributed to circumstellar dust emission.
- ID:
- ivo://CDS.VizieR/J/A+AS/104/315
- Title:
- Member of Herbig Ae/Be stellar group
- Short Name:
- J/A+AS/104/315
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- An up-to-date catalogue of Herbig Ae/Be (HAEBE) stars and related objects is listed in five tables, containing 287 objects. Table 1 contains all Ae and Be stars which historically are recognized as true HAEBE stars or potential candidate members. Table 2 gives the stars of spectral type Fe, and emission line stars with very uncertain or unknown spectral type. In Table 3 are given all known Extreme Emission Line Objects (EELOs), of which most have not been identified to belong to any specific group. Table 4a and b list other Bep or B[e] stars with strong IR-excess and unknown spectral type. Table 5 contains the non-emission line possible young objects. Furthermore, Table 6 contains 35 stars rejected from former published lists of HAEBE stars. In these tables we are including coordinates, spectral types, visual magnitudes, ranges in photometric variability and references of several key publications related to each object. Relevant remarks, such as the presence of a nebula in the vicinity of an object, are also given.
- ID:
- ivo://CDS.VizieR/J/A+A/629/A136
- Title:
- MWC 922 ALMA maps and datacubes
- Short Name:
- J/A+A/629/A136
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present interferometric observations with the Atacama Large Millimeter Array (ALMA) of the free-free continuum and recombination line emission at 1 and 3mm of the Red Square Nebula surrounding the B[e]-type star MWC922. The distance to the source, which is unknown, is usually taken to be d=1.7-3kpc. The unprecedented angular resolution (up to ~0.02") and exquisite sensitivity of these data reveal for the first time the structure and kinematics of the nascent compact ionized region at its center. We imaged the line emission of H30{alpha} and H39{alpha}, previously detected with single-dish observations, and of H51{epsilon}, H55{gamma}, and H63{delta}, detected for the first time in this work. The line emission is seen over a full velocity range of ~180km/s arising in a region of diameter <0.14" (less than a few hundred au) in the maser line H30{alpha}, which is the most intense transition reported here. We resolve the spatio-kinematic structure of a nearly edge-on disk rotating around a central mass of ~10M_{sun}_ (d=1.7kpc) or ~18M_{sun}_ (d=3kpc), assuming Keplerian rotation. Our data also reveal a fast (~100km/s) bipolar ejection (possibly a jet) orthogonal to the disk. In addition, a slow (<15km/s) wind may be emanating from the disk. Both, the slow and the fast winds are found to be rotating in a similar manner to the ionized layers of the disk. This represents the first empirical proof of rotation in a bipolar wind expanding at high velocity (~100km/s).
- ID:
- ivo://CDS.VizieR/J/A+A/638/A21
- Title:
- New Herbig Ae/Be and classical Be stars catalog
- Short Name:
- J/A+A/638/A21
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The intermediate-mass pre-main sequence (PMS) Herbig Ae/Be stars are key to understanding the differences in formation mechanisms between low- and high-mass stars. The study of the general properties of these objects is hampered by the lack of a well-defined, homogeneous sample, and because few and mostly serendipitously discovered sources are known. Our goal is to identify new Herbig Ae/Be candidates to create a homogeneous and well defined catalogue of these objects. We have applied machine learning techniques to 4150983 sources with data from Gaia DR2, 2MASS, WISE, and IPHAS or VPHAS+. Several observables were chosen to identify new Herbig Ae/Be candidates based on our current knowledge of this class, which is characterised by infrared excesses, photometric variabilities, and Halpha emission lines. Classical techniques are not efficient for identifying new Herbig Ae/Be stars mainly because of their similarity with classical Be stars (CBe), with which they share many characteristics. By focusing on disentangling these two types of objects, our algorithm has also identified new classical Be stars. We have obtained a large catalogue of 8470 new pre-main sequence candidates and another catalogue of 693 new classical Be candidates with a completeness of 78.8+/-1.4% and 85.5+/-1.2%, respectively. Of the catalogue of pre-main sequence candidates, at least 1361 sources are potentially new Herbig Ae/Be candidates according to their position in the Hertzsprung-Russell diagram. In this study we present the methodology used, evaluate the quality of the catalogues, and perform an analysis of their flaws and biases. For this assessment, we make use of observables that have not been accounted for by the algorithm and hence are selection-independent, such as coordinates and parallax based distances. The catalogue of new Herbig Ae/Be stars that we present here increases the number of known objects of the class by an order of magnitude.
- ID:
- ivo://CDS.VizieR/J/A+A/472/577
- Title:
- NGC 330 Be stars and binaries
- Short Name:
- J/A+A/472/577
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Observations of hot stars belonging to the young cluster SMC-NGC 330 and its surrounding region were obtained with the VLT-GIRAFFE facilities in MEDUSA mode. We investigated the B and Be star properties and proportions in this environment of low metallicity. We also searched for rapid variability in Be stars using photometric databases. Using spectroscopic measurements, we characterized the emission and properties of Be stars. By cross-correlation with photometric databases such as MACHO and OGLE, we searched for binaries in our sample of hot stars, as well as for short-term variability in Be stars. We report on the global characteristics of the Be star sample.
- ID:
- ivo://CDS.VizieR/J/MNRAS/471/3398
- Title:
- Nitrogen abundances for Be and B stars
- Short Name:
- J/MNRAS/471/3398
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Photospheric nitrogen abundances for a sample of 26 Be stars and 16 normal B stars were found using high-resolution spectra from the Magnetism in Massive Stars (MiMeS) spectroscopic survey. Nitrogen abundances were obtained using non-local-thermodynamic-equilibrium equivalent widths and line profiles, and Monte Carlo simulation was used to determine the error bounds of the measured nitrogen abundances due to uncertainties in the adopted stellar parameters, continuum normalization and atomic data. In addition, the effects of gravitational darkening and disc contamination on the measured Be star nitrogen abundances were investigated. About one third of the sample of Be stars and half of the normal B-type stars have nitrogen enrichment that may be due to rotational mixing in these rapidly rotating objects. Corrections for gravitational darkening and disc contamination do not significantly change the overall results for the Be star sample. The average nitrogen abundance of the B and Be star samples coincides with the solar abundance, although the dispersion in the nitrogen abundances is much larger in the Be star sample. The Be star sample also has a significant fraction of sub-solar nitrogen abundance objects that are not present in significant numbers in the B star sample. This may point to yet unresolved systematic errors in the analysis of the Be stars.
- ID:
- ivo://CDS.VizieR/J/A+A/384/473
- Title:
- O, B and Be stars equivalent widths
- Short Name:
- J/A+A/384/473
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an atlas of spectra of O- and B-type stars, obtained with the Short Wavelength Spectrometer (SWS) during the Post-Helium program of the Infrared Space Observatory (ISO). This program is aimed at extending the Morgan & Keenan (1973ARA&A..11...29M) classification scheme into the near-infrared. Later type stars will be discussed in a separate publication. The observations consist of 57 SWS Post-Helium spectra from 2.4 to 4.1{mu}m, supplemented with 10 spectra acquired during the nominal mission with a similar observational setting. For B-type stars, this sample provides ample spectral coverage in terms of subtype and luminosity class. For O-type stars, the ISO sample is coarse and therefore is complemented with 8 UKIRT L'-band observations. In terms of the presence of diagnostic lines, the L'-band is likely the most promising of the near-infrared atmospheric windows for the study of the physical properties of B stars. Specifically, this wavelength interval contains the Br{alpha}, Pf{gamma}, and other Pfund lines which are probes of spectral type, luminosity class and mass loss. Here, we present simple empirical methods based on the lines present in the 2.4 to 4.1{mu}m interval that allow the determination of i) the spectral type of B dwarfs and giants to within two subtypes; ii) the luminosity class of B stars to within two classes; iii) the mass-loss rate of O stars and B supergiants to within 0.25dex.
