- ID:
- ivo://CDS.VizieR/J/ApJ/686/1280
- Title:
- Discovery of hot subdwarf companion to FY CMa
- Short Name:
- J/ApJ/686/1280
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The rapid rotation of Be stars may be caused in some cases by past mass and angular momentum accretion in an interacting binary in which the mass donor is currently viewed as a small, hot subdwarf stripped of its outer envelope. Here we report on the spectroscopic detection of such a subdwarf in the Be binary system FY Canis Majoris from the analysis of data acquired by the IUE spacecraft and KPNO Coude Feed Telescope over the course of 16 and 21yr, respectively. We present a double-lined spectroscopic orbit for the binary based on radial velocities from the IUE spectra and use the orbital solutions with a Doppler tomography algorithm to reconstruct the components' UV spectra. The subdwarf is hot (T_eff_=45+/-5kK) and has a mass of about 1.3M_{sun}_ and a radius of about 0.6R_{sun}_. It contributes about 4% as much flux as the Be star does in the FUV. We also present observations of the H{alpha} and HeI{lambda}6678 emission features that are formed in the circumstellar disk of the Be star.
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- ID:
- ivo://CDS.VizieR/J/A+A/309/787
- Title:
- DX Eri variability
- Short Name:
- J/A+A/309/787
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results of nearly simultaneous monitoring of uvby light and HeI667.81nm line-profile variations of the equatorial Be star DX Eri in November 1991. They are analysed along with numerous uvby photometry in the period 1986-1995.
- ID:
- ivo://CDS.VizieR/III/17B
- Title:
- Early-Type Emission-Line Stars
- Short Name:
- III/17B
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The catalog contains 5326 early-type emission-line stars. Of these, 1424 have no spectral classification but are assumed to be of early type. Some 71 percent of the stars listed here can also be found in the Mount Wilson and the Mount Wilson-Michigan survey catalogs. The catalog contains numerous cross identifications to other designations (name, HD, DM, LS, MWC, TON, HIL, WRA, HEN, etc.), spectroscopic type, magnitudes (visual and blue), equatorial (B1900 and B1950), and galactic coordinates.
- ID:
- ivo://CDS.VizieR/J/A+A/506/95
- Title:
- Fourier analysis of HD 49330 CoRoT light curve
- Short Name:
- J/A+A/506/95
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Be stars undergo outbursts producing a circumstellar disk from the ejected material. The beating of non-radial pulsations has been put forward as a possible mechanism of ejection. We analyze the pulsational behavior of the early B0.5IVe star HD 49330 observed during the first CoRoT long run towards the Galactical anticenter (LRA1). This Be star is located close to the lower edge of the {beta} Cephei instability strip in the HR diagram and showed a 0.03mag outburst during the CoRoT observations. It is thus an ideal case for testing the aforementioned hypothesis.
- ID:
- ivo://CDS.VizieR/J/A+A/451/1053
- Title:
- Fundamental parameters of Be stars
- Short Name:
- J/A+A/451/1053
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In preparation for the COROT space mission, we determined the fundamental parameters (spectral type, temperature, gravity, vsini) of the Be stars observable by COROT in its seismology fields (64 Be stars). We applied a careful and detailed modeling of the stellar spectra, taking into account the veiling caused by the envelope, as well as the gravitational darkening and stellar flattening due to rapid rotation. Evolutionary tracks for fast rotators were used to derive stellar masses and ages. The derived parameters will be used to select Be stars as secondary targets (i.e. observed for 5 consecutive months) and short-run targets of the COROT mission. Furthermore, we note that the main part of our stellar sample is falling in the second half of the main sequence life time, and that in most cases the luminosity class of Be stars is inaccurate in characterizing their evolutionary status.
- ID:
- ivo://CDS.VizieR/J/ApJ/765/2
- Title:
- FUV radial velocities of 59 Cyg
- Short Name:
- J/ApJ/765/2
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on the detection of a hot subdwarf component in the Be binary system, 59 Cygni. The spectral signature is found in cross-correlation functions of photospheric model spectra with far-ultraviolet spectra obtained by the International Ultraviolet Explorer Satellite, and we used radial velocities from the cross-correlation functions to determine a double-lined spectroscopic orbit. The individual spectra of the binary components were extracted using a Doppler tomography algorithm. The flux of the system is dominated by the rapidly rotating Be star. However, the subdwarf contributes approximately 4% of the UV flux, and its spectrum bears a strong resemblance to that of the hot sdO star BD +75{deg}325. Based on the appearance of the UV spectrum and the orbital elements, we present estimates for the stellar masses, radii, and temperatures. The presence of the hot companion causes excess emission from the outer part of the Be disk facing the companion. We present a set of red spectra that show the orbital phase variations of the He I {lambda}6678 emission formed in the heated region of the disk, which probably occurs near the disk outer boundary. 59 Cygni, FY Canis Majoris, and {phi} Persei comprise the known set of Be binaries with detected hot evolved companions, which are the stripped down remains of mass transfer. Their properties demonstrate that some fraction of Be stars were spun up through angular momentum transfer by Roche lobe overflow.
- ID:
- ivo://CDS.VizieR/J/A+A/620/A128
- Title:
- Gaia DR2 study of Herbig Ae/Be stars
- Short Name:
- J/A+A/620/A128
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use Gaia Data Release 2 (DR2, Cat. I/345) to place 252 Herbig Ae/Be stars in the HR diagram and investigate their characteristics and properties. For all known Herbig Ae/Be stars with parallaxes in Gaia DR2, we collected their atmospheric parameters and photometric and extinction values from the literature. To these data we added near- and mid-infrared photometry, collected Halpha emission line properties such as equivalent widths and line profiles, and their binarity status. In addition, we developed a photometric variability indicator from Gaia's DR2 information. We provide masses, ages, luminosities, distances, photometric variabilities and infrared excesses homogeneously derived for the most complete sample of Herbig Ae/Be stars to date. We find that high mass stars have a much smaller infrared excess and have much lower optical variabilities compared to lower mass stars, with the break at around 7M_{sun}_. Halpha emission is generally correlated with infrared excess, with the correlation being stronger for infrared emission at wavelengths tracing the hot dust closest to the star. The variability indicator as developed by us shows that approximately 25% of all Herbig Ae/Be stars are strongly variable. We observe that the strongly variable objects display doubly peaked Halpha line profiles, indicating an edge-on disk. The fraction of strongly variable Herbig Ae stars is close to that found for A-type UX Ori stars. It had been suggested that this variability is in most cases due to asymmetric dusty disk structures seen edge-on. The observation here is in strong support of this hypothesis. Finally, the difference in dust properties occurs at 7M_{sun}_, while various properties traced at UV/optical wavelengths differ at a lower mass, 3M_{sun}_. The latter has been linked to different accretion mechanisms at work whereas the differing infrared properties and photometric variabilities are related to different or differently acting (dust-)disk dispersal mechanisms.
- ID:
- ivo://CDS.VizieR/J/MNRAS/500/4849
- Title:
- GALAH emission-line stars
- Short Name:
- J/MNRAS/500/4849
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a neural network autoencoder structure that is able to extract essential latent spectral features from observed spectra and then reconstruct a spectrum from those features. Because of the training with a set of unpeculiar spectra, the network is able to reproduce a spectrum of high signal-to-noise ratio that does not show any spectral peculiarities, even if they are present in an observed spectrum. Spectra generated in this manner were used to identify various emission features among spectra acquired by multiple surveys using the HERMES spectrograph at the Anglo-Australian telescope. Emission features were identified by a direct comparison of the observed and generated spectra. Using the described comparison procedure, we discovered 10364 candidate spectra with varying intensities (from partially filled-in to well above the continuum) of the H{alpha}/H{beta} emission component, produced by different physical mechanisms. A fraction of these spectra belong to the repeated observation that shows temporal variability in their emission profile. Among the emission spectra, we find objects that feature contributions from a nearby rarefied gas (identified through the emission of [NII] and [SII] lines) that was identified in 4004 spectra, which were not all identified as having H{alpha} emission. The positions of identified emission-line objects coincide with multiple known regions that harbour young stars. Similarly, detected nebular emission spectra coincide with visually prominent nebular clouds observable in the red all-sky photographic composites.
- ID:
- ivo://CDS.VizieR/J/A+A/540/A53
- Title:
- {gamma} Cas radial velocity curve
- Short Name:
- J/A+A/540/A53
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- {gamma} Cas is the prototypical classical Be star and is recently best known for its variable hard X-ray emission. To elucidate the reasons for this emission, we mounted a multiwavelength campaign in 2010 centered around four XMM-Newton observations. The observational techniques included long baseline optical interferometry (LBOI) from two instruments at CHARA, photometry carried out by an automated photometric telescope and H{alpha} observations. Because {gamma} Cas is also known to be in a binary, we measured radial velocities from the H{alpha} line and redetermined its period as 203.55+/-0.20 days and its eccentricity as near zero.
- ID:
- ivo://CDS.VizieR/J/A+A/550/A79
- Title:
- H{alpha} and H{beta} lines of northern Be stars
- Short Name:
- J/A+A/550/A79
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Be stars are fast rotating early-type emission line stars. It is generally assumed that observed emission is generated in a rotating disk- like envelope, as supported by the observed correlation between the stellar projected rotational velocity v sin i and the width of the emission lines. Then, high resolution spectroscopic observations of Balmer lines profiles play an important role in putting constrains on Be stars modeling. We present Balmer lines spectroscopy for a sample of 48 Be stars. For most of them, H{alpha} and H{beta} have been observed more than two times, in a total period spanning almost two years between 2008 and 2009. Spectral synthesis of the H{alpha} profile has been performed following two steps: photospheric contribution has been computed by using Kurucz's code ATLAS9 and SYNTHE, and disk emission have been derived by the approach of Hummel & Vrancken (1995A&A...302..751H). For 26 out of 48 stars, a modeling of the total H{alpha} emission, i.e. photospheric absorption plus disk net emission, has been attempted. By this modeling we derived an estimation of the disk radius, as well as the inclination angle between rotational axis and line of sight and the base density at the stellar equator. We also discussed, for the stars observed more than once, the variability of H{alpha} and H{beta} for what concerns both the equivalent width and the spectral profile. We found 16 stars with variable equivalent width and 7 stars with clear sign of profile variations. For all the stars of our sample we derive all the fundamental astrophysical quantities, such as: effective temperature, gravity, and projected rotational velocity. We found 13 stars which equivalent width is variable with a confidence level greater than 80% and 7 object for which spectral profiles show change with time. According to the classification scheme commonly used in literature, we classified 16 stars as belonging to class 1, 13 to class 2, 11 are shell stars, 6 objects do not show net emission, and 2 stars display transition from class 1 and 2. For the class 1 stars, we confirm the correlation between vsini and peak separation. concerning the geometry of the disk, we derived the inclination angle between rotational axis and line of sight, the base density at the stellar equator, and the radius. The maximum concentration of stars occur for disk dimensions ranging in the interval of 6 to 8 stellar radii and for inclination angles going from 23{deg} to 35{deg}.
