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1. A deep catalogue of classical Be stars
ID:
ivo://CDS.VizieR/J/MNRAS/446/274
Title:
A deep catalogue of classical Be stars
Short Name:
J/MNRAS/446/274
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a catalogue of 247 photometrically and spectroscopically confirmed fainter classical Be stars (13<r<16) in the direction of the Perseus Arm of the Milky Way (1{deg}<b<+4{deg}, 120{deg}<l<140{deg}). The catalogue consists of 181 IPHAS-selected new classical Be stars, in addition to 66 objects that we studied in our previous work more closely, and three stars identified as classical Be stars in earlier work. This study more than doubles the number known in the region. Photometry spanning 0.6-5um, spectral types, and interstellar reddenings are given for each object. The spectral types were determined from low-resolution spectra ({lambda}/{Delta}_{lambda}~800-2000), to a precision of 1-3 subtypes. The interstellar reddenings are derived from the (r-i) colour, using a method that corrects for circumstellar disc emission. The colour excesses obtained range from E(B-V)=0.3 up to 1.6 a distribution that modestly extends the range reported in the literature for Perseus-Arm open clusters. For around half the sample, the reddenings obtained are compatible with measures of the total sightline Galactic extinction. Many of these are likely to lie well beyond the Perseus Arm.
2. Angular differential imaging of MCW 758
ID:
ivo://CDS.VizieR/J/A+A/611/A74
Title:
Angular differential imaging of MCW 758
Short Name:
J/A+A/611/A74
Date:
21 Oct 2021
Publisher:
CDS
Description:
Transition disks offer the extraordinary opportunity to look for newly born planets and investigate the early stages of planet formation. In this context we observed the Herbig A5 star MWC 758 with the L'-band vector vortex coronagraph installed in the near infrared camera and spectrograph NIRC2 at the Keck II telescope, with the aim of unveiling the nature of the spiral structure by constraining the presence of planetary companions in the system. Our high-contrast imaging observations show a bright ({Delta}L'=7.0+/-0.3mag) point-like emission, south of MWC 758 at a deprojected separation of ~20au (r=0.111"+/-0.004") from the central star. We also recover the two spiral arms (south-east and north-west), already imaged by previous studies in polarized light, and discover a third one to the south-west of the star. No additional companions were detected in the system down to 5 Jupiter masses beyond 0.6" from the star. We propose that the bright L' band emission could be caused by the presence of an embedded and accreting protoplanet, although the possibility of it being an asymmetric disk feature cannot be excluded. The spiral structure is probably not related to the protoplanet candidate, unless on an inclined and eccentric orbit, and it could be due to one (or more) yet undetected planetary companions at the edge of or outside the spiral pattern. Future observations and additional simulations will be needed to shed light on the true nature of the point-like source and its link with the spiral arms.
3. A study of the H{alpha} variability of Be stars
ID:
ivo://CDS.VizieR/J/AJ/156/61
Title:
A study of the H{alpha} variability of Be stars
Short Name:
J/AJ/156/61
Date:
21 Oct 2021
Publisher:
CDS
Description:
This paper presents the results of 4 years of high-resolution spectral observations of 69 emission-line stars, 54 of them being newly discovered sources. We classified the stars on the basis of their position in the two-color IR diagram and some additional criteria: shape and width of the H{alpha} profile, presence of He lines, proper motion and parallax, membership to open cluster and associations. Sixty of our targets turned out to be Be stars. We also found four late giants, four pre-MS stars, and one late dwarf. The H{alpha} emission profiles of our Be stars range from single peaked to typical shell profiles that can also be highly asymmetric or single-peaked profiles with a narrow absorption core. The emission profiles appear almost constant with time or highly variable in intensity and in their V/R ratio. The detected long-term variability of the H{alpha} emission is important for investigating the on/off switch phenomenon of Be stars. Our study led to an increase of the number of the emission-line stars of 16 open clusters.
4. Be and Bn stars Balmer discontinuity
ID:
ivo://CDS.VizieR/J/A+A/634/A18
Title:
Be and Bn stars Balmer discontinuity
Short Name:
J/A+A/634/A18
Date:
21 Oct 2021
Publisher:
CDS
Description:
A significant number of Be stars show a second Balmer discontinuity (sBD) attributed to an extended circumstellar envelope (CE). The fast rotational velocity of Be stars undoubtedly plays a significant role in the formation of the CE. However, Bn stars, which are also B-type rapidly rotating stars, do not all present clear evidence of being surrounded by circumstellar material. We aim to characterize the populations of Be and Bn stars, and discuss the appearance of the sBD as a function of the stellar parameters. We expect to find new indices characterizing the properties of CEs in Be stars and properties relating Be and Bn stars. We obtained low- and high-resolution spectra of a sample of Be and Bn stars, derived stellar parameters, characterized the sBD, and measured the emission in the H{alpha} line. Results. Correlations of the aspect and intensity of the sBD and the emission in the H{alpha} line with the stellar parameters and the Vsini are presented. Some Bn stars exhibit the sBD in absorption, which may indicate the presence of rather dense CEs. Six Bn stars show emission in the H{alpha} line, so they are reclassified as Be stars. The sBD in emission appears in Be stars with Vsini<=250km/s, and in absorption in both Be and Bn stars with Vsini>=50km/s Low-mass Be and Bn stars share the same region in the Hertzsprung-Russell diagram. The distributions of rotational to critical velocity ratios of Be and Bn stars corresponding to the current stellar evolutionary stage are similar, while distributions inferred for the zero-age main sequence have different skewness. We found emission in the H{alpha} line and signs of a CE in some Bn stars, which motivated us to think that Bn and Be stars probably belong to the same population. It should be noted that some of the most massive Bn stars could display the Be phenomenon at any time. The similarities found among Be and Bn stars deserve to be more deeply pursued.
5. BeSOS Be stars stellar parameters
ID:
ivo://CDS.VizieR/J/MNRAS/474/5287
Title:
BeSOS Be stars stellar parameters
Short Name:
J/MNRAS/474/5287
Date:
07 Dec 2021 13:16:10
Publisher:
CDS
Description:
The Be phenomenon is present in about 20 per cent of B-type stars. Be stars show variability on a broad range of time-scales, which in most cases is related to the presence of a circumstellar disc of variable size and structure. For this reason, a time-resolved survey is highly desirable in order to understand the mechanisms of disc formation, which are still poorly understood. In addition, a complete observational sample would improve the statistical significance of the study of stellar and disc parameters. The 'Be Stars Observation Survey' (BeSOS) is a survey containing reduced spectra obtained using the Pontifica Universidad Catolica High Echelle Resolution Optical Spectrograph (PUCHEROS) with a spectral resolution of 17000 in the range 4260-7300{AA}. BeSOS's main objective is to offer consistent spectroscopic and time-resolved data obtained with one instrument. The user can download or plot the data and obtain stellar parameters directly from the website. We also provide a star-by-star analysis based on photometric, spectroscopic and interferometric data, as well as general information about the whole BeSOS sample. Recently, BeSOS led to the discovery of a new Be star HD 42167 and facilitated study of the V/R variation of HD 35165 and HD 120324, the steady disc of HD 110335 and the Be shell status of HD 127972. Optical spectra used in this work, as well as the stellar parameters derived, are available online at http://besos.ifa.uv.cl.
6. Be star candidates in Magellanic Clouds
ID:
ivo://CDS.VizieR/J/MNRAS/469/4175
Title:
Be star candidates in Magellanic Clouds
Short Name:
J/MNRAS/469/4175
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a proper motion investigation of a sample of Be star candidates towards the Magellanic Clouds, which has resulted in the identification of separate populations, in the Galactic foreground and in the Magellanic background. Be stars are broadly speaking B-type stars that have shown emission lines in their spectra. In this work, we studied a sample of 2446 and 1019 Be star candidates towards the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC), respectively, taken from the literature and proposed as possible Be stars due to their variability behaviour in the OGLE-II I band. JHKs magnitudes from the InfraRed Survey Facility catalogue and proper motions from the Southern Proper Motion 4 catalogue were obtained for 1188 and 619 LMC and SMC Be stars candidates, respectively. Colour-colour and vector-point diagrams were used to identify different populations amongst the Be star candidates. In the LMC sample, two populations with distinctive infrared colours and kinematics were found, the bluer sample is consistent with being in the LMC and the redder one with belonging to the Milky Way disc. This settles the nature of the redder sample that had been described in previous publications as a possible unknown subclass of stars amongst the Be candidates in the LMC. In the SMC sample, a similar but less evident result was obtained, since this apparent unknown subclass was not seen in this galaxy. We confirm that in the selection of Be stars by their variability, although generally successful, there is a higher risk of contamination by Milky Way objects towards redder B-V and V-I colours.
7. Be star omega CMa V light curve & polarimetry
ID:
ivo://CDS.VizieR/J/ApJ/909/149
Title:
Be star omega CMa V light curve & polarimetry
Short Name:
J/ApJ/909/149
Date:
21 Oct 2021
Publisher:
CDS
Description:
The fact that the emission lines seen in the optical spectra of the Be stars originate from a Keplerian circumstellar disk surrounding the central star is gaining more and more observational and theoretical supports. Among all the proposed models explaining the physics of such disks, the Viscous Decretion Disk (VDD) paradigm matches best with the observations. In this work, we challenge the VDD model by applying it to the variety of data of the Be star {omega} CMa observed by different techniques. We find that the VDD model explains the data well, qualitatively. However, we see some quantitative discrepancies that in turn are clues for better understanding the underlying physics of the Be disks. We investigate the possibilities of existing an undetected binary companion, and a radially variable viscous parameter, {alpha} to explain the mismatch between the data and the model.
8. Be star rotational velocities distribution
ID:
ivo://CDS.VizieR/J/A+A/595/A132
Title:
Be star rotational velocities distribution
Short Name:
J/A+A/595/A132
Date:
21 Oct 2021
Publisher:
CDS
Description:
Among intermediate-mass and massive stars, Be stars are the fastest rotators in the main sequence (MS) and, as such, these stars are a cornerstone to validate models of structure and evolution of rotating stars. Several phenomena, however, induce under- or overestimations either of their apparent Vsini, or true velocity V. In the present contribution we aim at obtaining distributions of true rotational velocities corrected for systematic effects induced by the rapid rotation itself, macroturbulent velocities, and binarity. We study a set of 233 Be stars by assuming they have inclination angles distributed at random. We critically discuss the methods of Cranmer and Lucy-Richardson, which enable us to transform a distribution of projected velocities into another distribution of true rotational velocities, where the gravitational darkening effect on the Vsini parameter is considered in different ways. We conclude that iterative algorithm by Lucy-Richardson responds at best to the purposes of the present work, but it requires a thorough determination of the stellar fundamental parameters. We conclude that once the mode of ratios of the true velocities of Be stars attains the value V/Vc~0.77 in the main-sequence (MS) evolutionary phase, it remains unchanged up to the end of the MS lifespan. The statistical corrections found on the distribution of ratios V/Vc for overestimations of Vsini due to macroturbulent motions and binarity, produce a shift of this distribution toward lower values of V/Vc when Be stars in all MS evolutionary stages are considered together. The mode of the final distribution obtained is at V/Vc~0.65. This distribution has a nearly symmetric distribution and shows that the Be phenomenon is characterized by a wide range of true velocity ratios 0.3<V/Vc<0.95. It thus suggests that the probability that Be stars are critical rotators is extremely low. The corrections attempted in the present work represent an initial step to infer indications about the nature of the Be-star surface rotation that will be studied in the second paper of this series.
9. Be Stars Catalog
ID:
ivo://vopdc.obspm/lesia/BeStars/BeSC
Title:
Be Stars Catalog
Short Name:
BeSC
Date:
10 Jan 2017
Publisher:
Paris Astronomical Data Centre - LESIA
Description:
The BeSC database contains the complete catalogue of classical Be stars with some of their fundamental stellar parameters.
10. Be Stars Database
ID:
ivo://vopdc.obspm/lesia/BeStars
Title:
Be Stars Database
Short Name:
BeStars
Date:
10 Jan 2017
Publisher:
Paris Astronomical Data Centre - LESIA
Description:
The BeStars project contains (1) the complete catalogue of classical Be stars, BeSC, with some of their fundamental stellar parameters, and (2) a database, BeSS, which assembles classical Be star spectra obtained by professional and amateur astronomers at any wavelength, epoch, and spectral resolution.