- ID:
- ivo://CDS.VizieR/J/MNRAS/507/1699
- Title:
- Blue straggler stars in open clusters with Gaia
- Short Name:
- J/MNRAS/507/1699
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Blue straggler stars (BSSs) are the most massive stars in a cluster formed via binary or higher-order stellar interactions. Though the exact nature of such formation scenarios is difficult to pin down, we provide observational constraints on the different possible mechanism. In this quest, we first produce a catalogue of BSSs using Gaia DR2 data. Among the 670 clusters older than 300Myr, we identified 868 BSSs in 228 clusters and 500 BSS candidates in 208 clusters. In general, all clusters older than 1Gyr and massive than 1000M_{sun}_ have BSSs. The average number of BSSs increases with cluster age and mass, and there is a power-law relation between the cluster mass and the maximum number of BSSs in the cluster. We introduce the term fractional mass excess (Me) for BSSs. We find that at least 54% of BSSs have Me<0.5 (likely to have gained mass through a binary mass transfer (MT)), 30% in the 1.0<Me<0.5 range (likely to have gained mass through a merger) and up to 16% with Me>1.0 (likely from multiple mergers/MT). We also find that the percentage of low Me BSSs increases with age, beyond 1-2Gyr, suggesting an increase in formation through MT in older clusters. The BSSs are radially segregated, and the extent of segregation depends on the dynamical relaxation of the cluster. The statistics and trends presented here are expected to constrain the BSS formation models in open clusters.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/623/A83
- Title:
- Blue stragglers Wd1-27 and Wd1-30a spectra
- Short Name:
- J/A+A/623/A83
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Recent observational studies indicate that a large number of OB stars are found within binary systems which may be expected to interact during their lifetimes. Significant mass transfer or indeed merger of both components is expected to modify evolutionary pathways, facilitating the production of exceptionally massive stars which will present as blue stragglers. Identification and characterisation of such objects is crucial if the efficiency of mass transfer is to be established; a critical parameter in determining the outcomes of binary evolutionary channels. The young and coeval massive cluster Westerlund 1 hosts a rich population of X-ray bright OB and Wolf-Rayet stars where the emission is attributed to shocks in the wind collision zones of massive binaries. Motivated by this, we instigated a study of the extremely X-ray luminous O supergiants Wd1-27 and -30a. We subjected a multi-wavelength and -epoch photometric and spectroscopic dataset to quantitative non-LTE model atmosphere and time-series analysis in order to determine fundamental stellar parameters and search for evidence of binarity. A detailed examination of the second Gaia data release was undertaken to establish cluster membership. Both stars were found to be early/mid-O hypergiants with luminosities, temperatures and masses significantly in excess of other early stars within Wd1, hence qualifying as massive blue stragglers. The binary nature of Wd1-27 remains uncertain but the detection of radial velocity changes and the X-ray properties of Wd1-30a suggest that it is a binary with an orbital period <=10 days. Analysis of Gaia proper motion and parallactic data indicates that both stars are cluster members; we also provide a membership list for Wd1 based on this analysis. The presence of hypergiants of spectral types O to M withinWd1 cannot be understood solely via single-star evolution. We suppose that the early-B and mid-O hypergiants formed via binary-induced mass-stripping of the primary and mass-transfer to the secondary, respectively. This implies that for a subset of objects massive star-formation may be regarded as a two-stage process, with binary-driven mass-transfer or merger yielding stars with masses significantly in excess of their initial 'birth' mass.
- ID:
- ivo://CDS.VizieR/J/A+A/559/A70
- Title:
- Blue wing of the 2p-1s He_2_ line
- Short Name:
- J/A+A/559/A70
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The shape and broadening of He lines affects radiative transport in dense, He-rich, stellar atmospheres. At wavelengths inaccessible for direct observation, we rely on theoretical calculations of self-broadening to support stellar structure and spectral modeling. In this work, we examine lines of He due to 1s-2p and 2p-3s transitions. The line profiles are analyzed in terms of a unified theory of spectral line broadening using ab initio potential energies that have been recently determined. For temperatures up to 20000K, the linear dependence of width and shift on gas density and the non-linear dependence on temperature of the Lorentzian core of the resonance line are described. Beyond the conventional symmetrical Lorentzian core, we show that they are asymmetrical and have significant additional contributions on the short wavelength side. This blue asymmetry is a consequence of maxima in the corresponding He2 potential energy difference curves at short and intermediate internuclear distance. Over a limited range of density and temperature, laboratory measurements in the visible and near infrared can be used to validate the potentials that underlie the spectral line profile theory, which is useful for modeling spectra over the extreme ranges of temperature and density encountered in stellar and planetary atmospheres.
- ID:
- ivo://CDS.VizieR/J/AN/338/453
- Title:
- BM CVn V-band differential light curve
- Short Name:
- J/AN/338/453
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We perform detailed time series analysis for V-band photometry of BM CVn to investigate the characteristics of its magnetic activity in both long and short time scale and also to estimate its differential rotation.
- ID:
- ivo://CDS.VizieR/J/A+A/488/1221
- Title:
- BMW-Chandra source catalog
- Short Name:
- J/A+A/488/1221
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the BMW-Chandra source catalogue drawn from essentially all Chandra ACIS-I pointed observations with an exposure time in excess of 10ks public as of March 2003 (136 observations). Using the wavelet detection algorithm developed by Lazzati et al. (1999ApJ...524..414) and Campana et al. (1999ApJ...524..423C), which can characterise both point-like and extended sources, we identified 21325 sources. Among them, 16758 are serendipitous, i.e. not associated with the targets of the pointings, and do not require a non-automated analysis. This makes our catalogue the largest compilation of Chandra sources to date. The 0.5-10keV absorption corrected fluxes of these sources range from ~3x10^-16^ to 9x10^-12^erg/cm^2^/s with a median of 7x10^-15^erg/cm^2^/s.
- ID:
- ivo://CDS.VizieR/J/AN/336/590
- Title:
- Bochum Galactic Disk Survey: II
- Short Name:
- J/AN/336/590
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper is the second in a series describing the southern Galactic Disk Survey (GDS) performed at the Universitatssternwarte Bochum near Cerro Armazones in Chile. Haas et al. (2012, Cat. J/AN/333/706, Paper I) presented the survey design and the characteristics of the observations and data. They identified ~2200 variable stars in an area of 50 square degrees with more than 50 observations in 2011. Here we present the first complete version of the GDS covering all 268 fields with 1323 square degrees along the Galactic disk including revised data from Paper I. The individual fields were observed up to 272 times and comprise a maximum time span between September 2010 and May 2015. We detect a total of 64151 variable sources, which are presented in a catalog including some of their properties and their light curves. A comparison with the International Variable Star Index (VSX) and All Sky Automated Survey (ASAS) indicates that 56794 of these sources are previously unknown variables. Furthermore, we present U, B, V, r', i', z' photometry for all sources within the GDS, resulting in a new multi-color catalog of nearly 16x10^6^ sources detected in at least one filter. Both the GDS and the near-infrared VISTA Variables in the Via Lactea survey (VVV) complement each other in the overlap area of about 300 square degrees enabling future comparison studies.
- ID:
- ivo://CDS.VizieR/J/AN/333/706
- Title:
- Bochum survey of the southern Galactic disk
- Short Name:
- J/AN/333/706
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We are monitoring a 6{deg} wide stripe along the southern Galactic disk simultaneously in the r and i bands, using a robotic 15-cm twin telescope of the Universitatsternwarte Bochum near Cerro Armazones in Chile. Utilising the telescope's 2.7{deg} field of view, the survey aims at observing a mosaic of 268 fields once per month and to monitor dedicated fields once per night. The survey reaches a sensitivity from 10m down to 18m (AB system), with a completeness limit of r~15.5m and i~14.5m which - due to the instrumental pixel size of 2.4" - refers to stars separated by >3". This brightness range is ideally suited to examine the intermediately bright stellar population supposed to be saturated in deep variability surveys with large telescopes. To connect to deep surveys or to explore faint long term variables, coadded images of several nights reach a depth of ~20m. The astrometric accuracy is better than 1", as determined from the overlap of neighbouring fields. We describe the survey design, the data properties and our procedures to derive the light curves and to extract variable stars. We present a list of ~2200 variable stars identified in 50 square degrees with 50-80 observations between May and October 2011. For bright stars the variability amplitude A reaches down to A~0.05m, while at the faint end variations of A>1m are detected. About 200 stars were known to be variable, and their amplitudes and periods - as far as determinable from our six month monitoring - agree with literature values, demonstrating the performance of the Bochum Galactic Disk Survey.
- ID:
- ivo://CDS.VizieR/J/A+A/597/A118
- Title:
- Bok globule BHR 160 radio lines spectra
- Short Name:
- J/A+A/597/A118
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- BHR160 is a virtually unstudied cometary globule within the Sco OB4 association in Scorpius at a distance of 1600pc. It is part of a system of cometary clouds which face the luminous O star HD155806. BHR160 is special because it has an intense bright rim. We attempt to derive physical parameters for BHR160 and to understand its structure and the origin of its peculiar bright rim. BHR160 was mapped in the ^12^CO, ^13^CO and C^18^O (2-1) and (1-0) and CS (3-2) and (2-1) lines. These data, augmented with stellar photometry derived from the ESO VVV survey, were used to derive the mass and distribution of molecular material in BHR160 and its surroundings. Archival mid-infrared data from the WISE satellite was used to find IR excess stars in the globule and its neighbourhood.
- ID:
- ivo://CDS.VizieR/J/AJ/152/180
- Title:
- Bolometric fluxes of eclipsing binaries in Tycho-2
- Short Name:
- J/AJ/152/180
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present fits to the broadband photometric spectral energy distributions (SEDs) of 158 eclipsing binaries (EBs) in the Tycho-2 catalog. These EBs were selected because they have highly precise stellar radii, effective temperatures, and in many cases metallicities previously determined in the literature, and thus have bolometric luminosities that are typically good to <~10%. In most cases the available broadband photometry spans a wavelength range 0.4-10{mu}m, and in many cases spans 0.15-22{mu}m. The resulting SED fits, which have only extinction as a free parameter, provide a virtually model-independent measure of the bolometric flux at Earth. The SED fits are satisfactory for 156 of the EBs, for which we achieve typical precisions in the bolometric flux of {\simeq}3%. Combined with the accurately known bolometric luminosity, the result for each EB is a predicted parallax that is typically precise to <~5%. These predicted parallaxes-with typical uncertainties of 200{mu}as-are 4-5 times more precise than those determined by Hipparcos for 99 of the EBs in our sample, with which we find excellent agreement. There is no evidence among this sample for significant systematics in the Hipparcos parallaxes of the sort that notoriously afflicted the Pleiades measurement. The EBs are distributed over the entire sky, span more than 10mag in brightness, reach distances of more than 5kpc, and in many cases our predicted parallaxes should also be more precise than those expected from the Gaia first data release. The EBs studied here can thus serve as empirical, independent benchmarks for these upcoming fundamental parallax measurements.
- ID:
- ivo://CDS.VizieR/J/AJ/152/16
- Title:
- Bolometric flux estimation for cool evolved stars
- Short Name:
- J/AJ/152/16
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Estimation of bolometric fluxes (F_BOL_) is an essential component of stellar effective temperature determination with optical and near-infrared interferometry. Reliable estimation of F_BOL_ simply from broadband K-band photometry data is a useful tool in those cases were contemporaneous and/or wide-range photometry is unavailable for a detailed spectral energy distribution (SED) fit, as was demonstrated in Dyck et al. Recalibrating the intrinsic F_BOL_ versus observed F_2.2{mu}m_ relationship of that study with modern SED fitting routines, which incorporate the significantly non-blackbody, empirical spectral templates of the INGS spectral library (an update of the library in Pickles) and estimation of reddening, serves to greatly improve the accuracy and observational utility of this relationship. We find that F_BOL_ values predicted are roughly 11% less than the corresponding values predicted in Dyck et al., indicating the effects of SED absorption features across bolometric flux curves.
