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Observations of Hα, iron, and oxygen lines in B, Be, and shell stars
We carried out a spectroscopic survey of several B, Be, and shell starsin optical and near-infrared regions. Line profiles of the Hα lineand of selected Fe II and O I lines are presented.
| Properties and nature of Be stars Dra. XXIII. Long-term variations and physical properties of κ Dra.
We present an analysis of new spectroscopic observations of the brightBe star κ Dra obtained at the Ondřejovobservatory during 1992-2003 and U BV photometric observations securedat several observatories. General characteristics and a lineidentification of the spectrum of κ Dra areobtained in the regions 3730-5650 Å and 5850-7800 Å by acomparison with the theoretical spectrum. The fundamental stellarparameters have been obtained from a comparison with a grid of NLTEmodel atmospheres. The best fit was found for Teff=14 000 K,log g = 3.5, and v sin i = 170 km s-1. These values togetherwith a Hipparcos parallax lead to a stellar mass M=4.8±0.8Mȯ and radius R=6.4±0.5 Rȯ. It isencouraging to see that these values agree well with the expectedevolutionary mass and radius for the effective temperature we derived.Long-term variations of κ Dra were analysedusing measurements of equivalent widths, central intensities, peakintensities of emission lines and emission peak velocity differences forHα, Hβ, Hγ, Hδ, and some helium, silicon, andiron lines. The previously reported period of 23 years in the variationof the emission strength is probably a cyclic, not a strictly periodicphenomenon. An attempt to find out a period from all available recordsof the Hβ emission strength led to a value of (8044 ± 167)days (22.0 years) but the phase plots show that each cycle has adifferent shape and length. The maximum strength of the emission lagsbehind the brightness maximum. This is a behaviour usually observed forlong-term changes of Be stars with a positive correlation between thebrightness and emission strength. Since there are obviously no publishedspeckle observations of the star, we suggest these should be carriedout. They could help to deny or confirm the possibility that theemission episodes are triggered by a periastron passage of a putativebinary companion moving in an eccentric orbit with a 8044-d period, asit seems to be the case for some Be binaries. For the moment, the natureand origin of the disk around κ Dra remainsunknown. From the comparison of the electronic spectra obtained atdifferent phases of the long-term cycle and synthetic spectra it appearsthat there are no detectable changes in the photospheric part of theBalmer lines related to variations in the Balmer emission strength whichcould be attributed to an extended photosphere corresponding to innerparts of the disk, optically thick in continuum.Tables 2 to 4 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/419/607
| Spectroscopy of the growing circumstellar disk in the delta Scorpii Be binary
We present the results of a spectroscopic monitoring program of thebinary system delta Scorpii, whose primary became a Be star after thelast periastron encounter in the Summer of 2000. The observations covera period of 2 years (March 2001-June 2003) and are a continuation of ourprevious campaign reported in Miroshnichenko et al. (\cite{metal}). Wefound that the emission-line spectrum was gradually strengthening overthe whole monitoring period. Several short-term increases of the lineemission, possibly due to outbursts of matter ejected from the stellarsurface, were detected. The outbursts seem to be responsible for thebrightness fadings, seen afterwards. We attempt to explain the overallobserved line and continuum behaviour in terms of a circumstellar disk,growing in density and size. The disk is most likely Keplerian with anouter radius of ~10 Rstar and a mean expansion speed of ~0.4 km s-1.Tables 1-2 are also available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/408/305}
| Autocorrelation Analysis of Hipparcos Photometry of Short-Period Be Stars
We have used Hipparcos epoch photometry and a form of autocorrelationanalysis to investigate the amplitude and timescale of the short-periodvariability of 82 Be stars, including 46 Be stars that were analyzed byHubert & Floquet using Fourier and CLEAN analysis and 36 other Bestars that were suspected of short-period variability. Our method hasgiven useful information for about 84% of these stars; for the rest, thetime distribution of the Hipparcos epoch photometry limits thecapability of our technique.
| New periodic variables from the Hipparcos epoch photometry
Two selection statistics are used to extract new candidate periodicvariables from the epoch photometry of the Hipparcos catalogue. Theprimary selection criterion is a signal-to-noise ratio. The dependenceof this statistic on the number of observations is calibrated usingabout 30000 randomly permuted Hipparcos data sets. A significance levelof 0.1 per cent is used to extract a first batch of candidate variables.The second criterion requires that the optimal frequency be unaffectedif the data are de-trended by low-order polynomials. We find 2675 newcandidate periodic variables, of which the majority (2082) are from theHipparcos`unsolved' variables. Potential problems with theinterpretation of the data (e.g. aliasing) are discussed.
| Rotational Velocities of B Stars
We measured the projected rotational velocities of 1092 northern B starslisted in the Bright Star Catalogue (BSC) and calibrated them againstthe 1975 Slettebak et al. system. We found that the published values ofB dwarfs in the BSC average 27% higher than those standards. Only 0.3%of the stars have rotational velocities in excess of two-thirds of thebreakup velocities, and the mean velocity is only 25% of breakup,implying that impending breakup is not a significant factor in reducingrotational velocities. For the B8-B9.5 III-V stars the bimodaldistribution in V can be explained by a set of slowly rotating Ap starsand a set of rapidly rotating normal stars. For the B0-B5 III-V starsthat include very few peculiar stars, the distributions in V are notbimodal. Are the low rotational velocities of B stars due to theoccurrence of frequent low-mass companions, planets, or disks? Therotational velocities of giants originating from late B dwarfs areconsistent with their conservation of angular momentum in shells.However, we are puzzled by why the giants that originate from the earlyB dwarfs, despite having 3 times greater radii, have nearly the samerotational velocities. We find that all B-type primaries in binarieswith periods less than 2.4 days have synchronized rotational and orbitalmotions; those with periods between 2.4 and 5.0 days are rotating withina factor 2 of synchronization or are ``nearly synchronized.'' Thecorresponding period ranges for A-type stars are 4.9 and 10.5 days, ortwice as large. We found that the rotational velocities of the primariesare synchronized earlier than their orbits are circularized. The maximumorbital period for circularized B binaries is 1.5 days and for Abinaries is 2.5 days. For stars of various ages from 107.5 to1010.2 yr the maximum circularized periods are a smoothexponential function of age.
| Search for duplicity in periodic variable Be stars
Four Be stars, HR 1960, HR 2968,HR 3237 and HR 3642, selectedaccording to their periodic variations in HIPPARCOS and GENEVAphotometries, were monitored from 1998 until 2001 with the CORALIEspectrograph. Among these stars, two are new spectroscopic binaries andone is a new lambda Eri short period variable. HR 1960 is a lowamplitude (K = 3.4 km s-1) SB1 with a period of 395.48 d inagreement with the photometric prediction. HR 3237 is a short period SB1(P = 5.1526 d). HR 3642 presents some interesting variations inphotometry and spectroscopy: indeed, a mid- and a short-term variationis present with periods of 137.99 d (Hp magnitude) and 1.13028 d (radialvelocity) respectively. The short-term variation, characteristic of thelambda Eri stars, probably implies non-radial pulsations orinhomogeneities in the corotating disc. The last star, HR 2968, is anexcellent photometric binary candidate, but no spectroscopic obviousnessof a companion has been found. Based on observations collected at theSwiss 40 cm, 70 cm and 120 cm telescopes at the European SouthernObservatory (La Silla, Chile) and on data from the ESA HIPPARCOSsatellite. The photometric and radial velocity data are only availablein electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/385/488 Table 3 is onlyavailable in electronic form at http://www.edpsciences.org
| Ultraviolet Spectrophotometry of Variable Early-Type Be and B Stars Derived from High-Resolution IUE Data
High-dispersion IUE data encode significant information about aggregateline absorptions that cannot be conveniently extracted from individualstellar spectra. Here we apply a new technique in which fluxes from eachechelle order of a short-wavelength IUE spectrum are binned together toconstruct low-resolution spectra of a rapidly varying B or Be star. Thedivision of binned spectra obtained during a ``bright-star'' phase byspectra from a ``faint-star'' phase leads to a ratioed spectrum thatcontains information about the mechanism responsible for a star'svariability. The most likely candidate mechanisms are either theperiodic or episodic occultations of the star by ejected matter or achange in photospheric structure, e.g., from pulsation. We model thevariations caused by these mechanism by means of model atmosphere andabsorbing-slab codes. Line absorptions strength changes are rathersensitive to physical conditions in circumstellar shells and ``clouds''at temperatures of 8000-13,000 K, which is the regime expected forcircumstellar structures of early B stars. To demonstrate proofs of thisconcept, we construct spectral ratios for circumstellar structuresassociated with flux variability in various Be stars: (1) Vela X-1 has abow-shock wind trailing its neutron star companion; at successive phasesand hence in different sectors, the wind exhibits spectrophotometricsignatures of a 13,000 or 26,000 K medium; (2) 88 Her undergoes episodic``outbursts'' during which its UV flux fades, followed a year later by adimming at visible wavelengths as well; the ratioed spectrum indicatesthe ``phase lag'' is a result of a nearly gray opacity that dominatesall wavelengths as the shell expands from the star and cools, permittingthe absorptions in the visible to ``catch up'' to those in the UV; and(3) ζ Tau and 60 Cyg exhibit periodic spectrum and flux changes,which match model absorptions for occulting clouds but are actually mosteasily seen from selective variations of various resonance lines. Inaddition, ratioed UV spectra of radial and large-amplitude nonradialpulsating stars show unique spectrophotometric signatures, which can besimulated with model atmospheres. An analysis of ratioed spectraobtained for a representative sample of 18 classical Be stars known tohave rapid periodic flux variations indicates that 13 of them haveratioed spectra that are relatively featureless or have signatures ofpulsation. Ratioed spectra of three others in the sample exhibitsignatures that are consistent with the presence of corotating clouds.
| A Search for High-Velocity Be Stars
We present an analysis of the kinematics of Be stars based uponHipparcos proper motions and published radial velocities. We findapproximately 23 of the 344 stars in our sample have peculiar spacemotions greater than 40 km s-1 and up to 102 kms-1. We argue that these high-velocity stars are the resultof either a supernova that disrupted a binary or ejection by closeencounters of binaries in young clusters. Be stars spun up by binarymass transfer will appear as high-velocity objects if there wassignificant mass loss during the supernova explosion of the initiallymore massive star, but the generally moderate peculiar velocities of BeX-ray binaries indicate that the progenitors lose most of their massprior to the supernova (in accordance with model predictions). Binaryformation models for Be stars predict that most systems bypass thesupernova stage (and do not receive runaway velocities) to createultimately Be+white dwarf binaries. The fraction of Be stars spun up bybinary mass transfer remains unknown, since the post-mass transfercompanions are difficult to detect.
| Statistical analysis of intrinsic polarization, IR excess and projected rotational velocity distributions of classical Be stars
We present the results of statistical analyses of a sample of 627 Bestars. The parameters of intrinsic polarization (p*),projected rotational velocity (v sin i), and near IR excesses have beeninvestigated. The values of p* have been estimated for a muchlarger and more representative sample of Be stars (~490 objects) thanpreviously. We have confirmed that most Be stars of early spectral typehave statistically larger values of polarization and IR excesses incomparison with the late spectral type stars. It is found that thedistributions of p* diverge considerably for the differentspectral subgroups. In contrast to late spectral types (B5-B9.5), thedistribution of p* for B0-B2 stars does not peak at the valuep*=0%. Statistically significant differences in the meanprojected rotational velocities (/line{vsin i}) are found for differentspectral subgroups of Be stars in the sense that late spectral typestars (V luminosity class) generally rotate faster than early types, inagreement with previously published results. This behaviour is, however,not obvious for the III-IV luminosity class stars. Nevertheless, thecalculated values of the ratio vt/vc of the truerotational velocity, vt, to the critical velocity forbreak-up, vc, is larger for late spectral type stars of allluminosity classes. Thus, late spectral type stars appear to rotatecloser to their break-up rotational velocity. The distribution of nearIR excesses for early spectral subgroups is bi-modal, the position ofthe second peak displaying a maximum value E(V-L)~ 1 . m 3for O-B1.5 stars, decreasing to E(V-L)~0. m8 for intermediatespectral types (B3-B5). It is shown that bi-modality disappears for latespectral types (B6-B9.5). No correlations were found betweenp* and near IR excesses and between E(V-L) and vsin i for thedifferent subgroups of Be stars. In contrast to near IR excesses, arelation between p* and far IR excesses at 12 mu m is clearlyseen. A clear relation between p* and vsin i (as well asbetween p* and /line{vsin i}/vc) is found by thefact that plots of these parameters are bounded by a ``triangular"distribution of p*: vsin i, with a decrease of p*towards very small and very large vsin i (and /line{vsini}/vc) values. The latter behaviour can be understood in thecontext of a larger oblateness of circumstellar disks for the stars witha rapid rotation. From the analysis of correlations between differentobservational parameters we conclude that circumstellar envelopes forthe majority of Be stars are optically thin disks with the range of thehalf-opening angle of 10degr
| 250 GHz observations of Be stars
New 250 GHz flux density measurements with the 30 m telescope at PicoVeleta are presented for 23 Be stars. We suggest that the radio spectralindex is typically close to 1.4 for these stars. We present in adiscusssion of own and literature data some evidence that in few casesslow variations with a time scale of about a year occur. Both evidenceis compatible with the idea that there is no stellar activity type radioemission of Be stars but a maybe slightly modulated quiescent radiationof the outer parts of selfsimilar circumstellar disks. An immediateimprovement of existing models is not possible.
| Properties and nature of Be stars. XIX. Spectral and light variability of 60 Cygni
An analysis of electronic spectra secured between 1992 and 1999 at theHaute Provence, Ondřejov and Dominion Astrophysical Observatoriesand of differential UBV measurements of 60 Cyg obtained between 1984 and1999 at Hvar, San Pedro Mártir, Toronto and XinglongObservatories, the all-sky Hipparcos satellite H_p photometrytransformed to Johnson V and B magnitudes, and all-sky UBV observationspublished by several authors and dating back to fifties, led to thefollowing findings: 1. 60 Cyg exhibits pronounced long-term spectralvariations characterized by the B -> Be -> B phase transitions.These long-term spectral changes of 60 Cyg are also accompanied bycorresponding, though rather mild, secular light and colour variations.The character of these variations is indicative of a positivecorrelation between the brightness and emission-line strength. 2. NLTEmodel atmosphere analysis of spectra secured during the quiescence state(B phase) of 60 Cyg shows that the star has overabundance of helium.Best results were obtained for N_He/N_H= 0.2. 3. The presence ofperiodic medium-term changes, with a period of 146.6 d +/- 0.6 d wasfound in the radial-velocity of the Hα He I 4471 Å lines. Ifconfirmed by future observations, these variations could indicate that60 Cyg is a spectroscopic binary. 4. There are clear rapid periodicline-profile changes of (a) overall line asymmetry, and (b) weaksub-features passing across the line profiles every about 0.1 d. Theradial velocity and asymmetry of He I lines vary with a period of 1.0647d and a double-wave curve. There is no evidence of this period inphotometry, however. 5. The rapid light variations of 60 Cyg aredominated by rapid changes with a full amplitude of almost 0.1 m. Aperiod analysis of V magnitude data prewhitened for the long-termchanges indicates a period of 0.2997029 d, reported earlier. The mostinteresting finding is that also all recorded series of movingsub-features in the line profiles can be reconciled with this period:the sub-features reappear at the same phase intervals of the 0.2997 dperiod in the line profiles over an interval of several years.Considering the acceleration of these sub-features, 1900 km s^{-1}d^{-1}, it is conceivable that the true physical (super) period of thesechanges is either 0.8991 d or 1.1988 d. 6. The findings mentioned inpoints 4 and 5 represent a challenge for the NRP scenario since thelight changes would be dominated by a high-order mode instead of alow-order one.
| Catalogue of H-alpha emission stars in the Northern Milky Way
The ``Catalogue of Stars in the Northern Milky Way Having H-alpha inEmission" appears in Abhandlungen aus der Hamburger Sternwarte, Band XIin the year 1997. It contains 4174 stars, range {32degr <= l() II< 214degr , -10degr < b() II < +10degr } having the Hαline in emission. HBH stars and stars of further 99 lists taken from theliterature till the end of 1994 were included in the catalogue. We givethe cross-identification of stars from all lists used. The catalogue isalso available in the Centre de Données, Strasbourg ftp130.79.128.5 or http://cdsweb.u-strasbg.fr and at the HamburgObservatory via internet.
| Photometric Separation of Stellar Properties Using SDSS Filters
Using synthetic photometry of Kurucz model spectra, we explore thecolors of stars as a function of temperature, metallicity, and surfacegravity with Sloan Digital Sky Survey (SDSS) filters, u'g'r'i'z'. Thesynthetic colors show qualitative agreement with the few publishedobservations in these filters. We find that the locus of synthetic starsis basically two-dimensional for 4500 < T < 8000 K, whichprecludes simultaneous color separation of the three basic stellarcharacteristics we consider. Colors including u' contain the mostinformation about normal stellar properties; measurements in this filterare also important for selecting white dwarfs. We identify two differentsubsets of the locus in which the loci separate by either metallicity orsurface gravity. For 0.5 < g' - r' < 0.8 (corresponding roughly toG stars), the locus separates by metallicity; for photometric error of afew percent, we estimate metallicity to within ~0.5 dex in this range.In the range -0.15 < g' - r' < 0.00 (corresponding roughly to Astars), the locus shows separation by surface gravity. In both cases, weshow that it is advantageous to use more than two colors whendetermining stellar properties by color. Strategic observations in SDSSfilters are required to resolve the source of a ~5% discrepancy betweensynthetic colors of Gunn-Stryker stars, Kurucz models, and externaldeterminations of the metallicities and surface gravities. The syntheticstar colors can be used to investigate the properties of any normal starand to construct analytic expressions for the photometric prediction ofstellar properties in special cases.
| UBV beta Database for Case-Hamburg Northern and Southern Luminous Stars
A database of photoelectric UBV beta photometry for stars listed in theCase-Hamburg northern and southern Milky Way luminous stars surveys hasbeen compiled from the original research literature. Consisting of over16,000 observations of some 7300 stars from over 500 sources, thisdatabase constitutes the most complete compilation of such photometryavailable for intrinsically luminous stars around the Galactic plane.Over 5000 stars listed in the Case-Hamburg surveys still lackfundamental photometric data.
| Investigation of the variability of bright Be stars using HIPPARCOS photometry
The high accuracy and the homogeneity of Hipparcos data for bright starshave allowed us to quantify the degree of variability of Be stars. Thisdegree has been found to be highly dependent on the temperature of thestar. Rapid variability is the main feature of the 86% of early Be andless than 20% of late Be stars taking into account the limit ofdetection considered. In addition to Be stars reported in the Hipparcoscatalogue (ESA 1997) as short-period variables, we have been able toenlarge the number of detections as well as to confirm periodspreviously determined. Be stars that show larger amplitude rapidvariations are proposed as candidates for a search of multiperiodicityi.e. as non-radial pulsators. We have also searched for the presence ofoutbursts and fading events in the Hipparcos data. Outbursts have beenfrequently and preferentially detected in early Be stars with rather lowto moderate v sini while fading events seem to be more conspicuous instars with higher v sini. Mid-term and long-term variations have alsobeen investigated. Several stars have shown some evidence of temporaryquasi-periodic oscillations ranging between 10 and 200 days. Finallyinformation concerning long-term variations is reported. Cycles shorterthan or equal to the Hipparcos mission have mainly been detected instars earlier than B6. Long-term time scales of late Be stars areconfirmed to be longer by far. Tables 1 and 2 are only available inelectronic form at CDS via ftp to cdsarc.u-strasbg.fr (130.79.128.5) orvia http://cdsweb.u-strasbg.fr/Abstract.html
| Photometric Monitoring of Bright Be Stars. III. 1988-89 and 1992-95
We report long-term photometric (BV) observations of 23 bright, activeBe stars made in 1988 and 1989 and 1992 and 1995 with the 0.4m telescopeat the University of Toronto. Cumulative light curves, includingobservations made earlier at the University of Toronto, and with theAutomatic Photometric Telescope Service in Arizona, are presented forseveral of the stars. Many of the stars show cyclic variations of up to0.2 in V and B on time scales of a few years, as well as variations ontime scales of about a day. (SECTION: Stars)
| Catalogue of stars in the northern Milky Way having H-alpha in emission
Not Available
| UBV photometry of Be stars at Hvar: 1972--1990
A summary of results of the systematic UBV photoelectric monitoring ofbright northern Be stars carried out at the Hvar Observatory between1972 and 1990 is presented. Altogether, 76 Be stars of all luminosityclasses were observed and 13,848 UBV measurements secured.Simultaneously, 9,648 UBV measurements of 48 check stars (most of themof early spectral types) were obtained. A careful transformation of allobservations into the standard Johnson system allowed detection andmonitoring of even very mild long-term light and colour variations ofthese objects. Almost all early-type Be stars in the sample turned outto be variable. For several stars phase-locked light variations relatedto their binary nature were established. Sudden brightenings, on a timescale of a few days, were detected for o Cas and QR Vul. Tables 2 and 3are only available in electronic form at CDS via ftp tocdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html
| The ROSAT Galactic Plane Survey: Analysis of a low latitude sample area in Cygnus
The analysis of the part of the ROSAT all-sky survey covering thegalactic plane is the scope of a dedicated project called the ROSATGalactic Plane Survey. In order to statistically understand the natureof the ~14,000 sources discovered by ROSAT at |b| <= 20 degrees, anumber of sample areas have been chosen for follow-up opticalidentification. In this paper we present the X-ray and optical materialgathered in a region located in the Cygnus constellation, centered at l= 90 degrees, b = 0 degrees and covering an area of 64.5deg2. A total of 95 and 128 sources are detected with amaximum likelihood larger than 10 and 8 respectively. With a typicalsurvey exposure time of the order of 700 to 900 s the flux completenesslevel is ~0.02 cnts s^{-1} corresponding to ~2 10^{-13} erg cm^{-2}s^{-1}. The position of the sample area allows to investigate the softX-ray content of a rather typical region of the galactic plane. In thispaper we describe the details of the observational procedures and datareduction. For each ROSAT source we list the main X-ray characteristicstogether with those of the proposed optical identification. Whenappropriate, we also show optical spectra and finding charts. The fullanalysis and discussion of these data are presented in a companion paper(\cite[Motch et al. 1997]{ref13}). Tables 2 to 6 are also available inelectronic form at the CDS via anonymous ftp cdsarc.u-strasbg.fr.Figures are only published electronically and are made available athttp://www.ed-phys.fr/Abstract.html.
| The ROSAT galactic plane survey: analysis of a low latitude sample area in Cygnus.
We present the analysis of the point source content of a low galacticlatitude region selected from the ROSAT all-sky survey. The test fieldis centered at l=90deg, b=0deg and has an area of 64.5deg^2^. A total of128 soft X-ray sources are detected above a maximum likelihood of 8.Catalogue searches and optical follow-up observations show that in thisdirection of the galactic plane, 85% of the sources brighter than 0.03PSPC cts/s are identified with active coronae. F-K type stars represent67%(+/-13%) of the stellar identifications and M type stars account for19%(+/-6%). A small but significant number of X-ray sources areassociated with A type stars on the basis of positional coincidence.These results together with those of similar optical campaignsdemonstrate that the soft X-ray population of the Milky Way is largelydominated by active stars. We show that the density and distribution influx and spectral type of the active coronae detected in X-rays areconsistent with the picture drawn from current stellar population modelsand age dependent X-ray luminosity functions. The modelling of thispopulation suggests that most of the stars detected by ROSAT in thisdirection are younger than 1Gyr. This opens the possibility to extractin a novel way large samples of young stars from the ROSAT all-skysurvey. The small number of unidentified sources at low X-ray flux putrather strong constraints on the hypothetical X-ray emission from oldneutron stars accreting from the interstellar medium. Our observationsclearly rule out models which assume no dynamical heating for thispopulation and a total number of N_ns_=10^9^ neutron stars in theGalaxy. If accretion on polar caps is the dominant mode then our upperlimit may imply N_ns_=~10^8^. Among the non coronal identifications arethree white dwarfs, a Seyfert 1 active nucleus, two early type stars andone cataclysmic variable. We also report the discovery of a Me + WDclose binary system with P_orb_=~12h.
| A Catalogue of Correlations Between Eclipsing Binaries and Other Categories of Double Stars
Among the 9110 stars in The Bright Star Catalogue, there are 225eclipsing or ellipsoidal variables. A search has been made for these incatalogues of spectroscopic binaries, visual double or multiple stars,speckle interferometry, occulation binaries, and galatic clusters. Themajority of the photometric binaries are also members of groups ofhigher multiplicity. The variables are in systems ranging from one to 91stars, five on the average. 199 are either spectroscopic binaries (SB)or stars with variable radial velocity, with orbital periods known for160. Photometric periods are lacking for 48 while SB periods areavailable for 23 of these. Observers with photoelectric equipment areencouraged to plan observations to test if the SB periods are consistentwith photometric data. Observers are likewise encouraged to examinethose stars for which the photometric and SB periods appear to beinconsistent. Parallaxes are available for 86 of the stars, 41 of themindicating distances nearer than 50 parsecs.
| The ROSAT all-sky survey catalogue of optically bright OB-type stars.
For the detailed statistical analysis of the X-ray emission of hot starswe selected all stars of spectral type O and B listed in the Yale BrightStar Catalogue and searched for them in the ROSAT All-Sky Survey. Inthis paper we describe the selection and preparation of the data andpresent a compilation of the derived X-ray data for a complete sample ofbright OB stars.
| The photoelectric astrolabe catalogue of Yunnan Observatory (YPAC).
The positions of 53 FK5, 70 FK5 Extension and 486 GC stars are given forthe equator and equinox J2000.0 and for the mean observation epoch ofeach star. They are determined with the photoelectric astrolabe ofYunnan Observatory. The internal mean errors in right ascension anddeclination are +/- 0.046" and +/- 0.059", respectively. The meanobservation epoch is 1989.51.
| Monitoring MWC 560 = V694 Monocerotis in 1990-1995. I. Conventional and high-speed UBV photometry.
We present results of an extensive photometric monitoring campaign ofthe peculiar emission star MWC 560 that covers the range 1990-1995. Thetime interval corresponds to the length of the proposed orbital periodof this highly peculiar binary, which attracted considerable interest inJanuary-April 1990, when absorption components, shifted by -6000km/sfrom corresponding emission lines, were observed. Here we presentphotometric data secured during: 113 nights of conventional UBVphotoelectric photometry, 45 nights of high speed UBV photoelectricphotometry to study the flickering activity, and 682 visual photometricestimates. MWC 560 has experienced a decrease in magnitude since thebright (V=9.2mag) phase in 1990. After the minimum reached in May 1994(V=10.7mag), the star is currently increasing slowly in brightness. Thedecrease has been accompanied in all bands by large fluctuationssuperimposed on the mean trend. The B-V colour has shown a steadyincrease by 0.0.33mag/yr. U-B has remained stable at -0.07mag since late1990. In all the observing nights devoted to high speed photometry weobserved flickering activity in MWC 560. The data show that theflickering amplitude {DELTA}U increases with the decrease of the Umagnitude. Quasi-periodic variations have always been detected. A periodof ~70min has been observed in ~13 nights which is close to the ~60minquasi-period reported by Michalitsianos et al. (1993). However, nocoherent variability is traceable throughout the whole set of flickeringdata.
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| Near-infrared photometric observations of Be stars.
Not Available
| Spectroscopic Observations of Pu-Vulpeculae in the 3210 TO 10950A Range during the Nebular Phase
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1994MNRAS.271..875A&db_key=AST
| An IUE survey of interstellar H I LY alpha absorption. 1: Column densities
We measure Galactic interstellar neutral hydrogen column densities byanalyzing archival interstellar Ly alpha absorption line data toward 554B2 and hotter stars observed at high resolution with the IUE satellite.This study more than doubles the number of lines of sight with measuresof N(H I) based on Ly alpha. We have included the scattered lightbackground correction algorithm of Bianchi and Bohlin in our datareduction. We use the correlation between the Balmer discontinuity(c1) index and the stellar Ly alpha absorption in order toassess the effects of stellar Ly alpha contamination. Approximately 40%of the B stars with measured (c1) index, exhibit seriousstellar Ly alpha contamination. One table contains the derived values ofthe interstellar N(H I) for 393 stars with at most small amounts ofstellar contamination. Another lists the observed values of total N(H I)for 161 stars with suspected stellar Ly alpha contamination and/oruncertain stellar parameters.
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| Csillagkép: | Hattyú |
| Rektaszcenzió: | 21h01m10.90s |
| Deklináció: | +46°09'21.0" |
| Vizuális fényesség: | 5.37 |
| Távolság: | 418.41 parszek |
| RA sajátmozgás: | 3.6 |
| Dec sajátmozgás: | 3.5 |
| B-T magnitude: | 5.163 |
| V-T magnitude: | 5.397 |
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