Contents
Images
Upload your image
DSS Images Other Images
Related articles
Joint Hα and X-Ray Observations of Massive X-Ray Binaries. II. The Be X-Ray Binary and Microquasar LS I +61 303
We present the results of an Hα monitoring campaign on the BeXRBand microquasar system LS I +61 303. We use radial velocity measurementsof He I lines in our spectra to reevaluate the orbital elements and tobetter establish the time of periastron. We list equivalent widths andother parameters for the Hα emission line and discuss the orbitalphase related variations observed. We call attention to a dramaticepisode of emission weakening that occurred in less than 1 day thatprobably resulted from exposure to a transient source of ionizingradiation. We argue that the increase in Hα and X-ray emissionfollowing periastron probably results from the creation of an extendeddensity wave in the disk created by tidal forces. We also discussestimates of the size of the disk from the Hα equivalent widthmeasurements, and we suggest that the disk radius from the averageequivalent width corresponds to a resonant truncation radius of the diskwhile the maximum equivalent width corresponds to a radius limited bythe separation of the stars at periastron. We note that a nearby faintcompanion is probably an unrelated foreground object.
| INTEGRAL and XMM-Newton observations of LSI +61° 303
LSI +61° 303 is one of the few X-ray binaries with Be star companionfrom which both radio and high-energy γ-ray emission have beenobserved. We present XMM-Newton and INTEGRAL observations which revealvariability of the X-ray spectral index of the system. The X-rayspectrum is hard (photon index Γ ~= 1.5) during the orbital phasesof both high and low X-ray flux. However, the spectrum softens at themoment of transition from high to low X-ray state. The spectrum of thesystem in the hard X-ray band does not reveal the presence of a cut-off(or, at least a spectral break) at 10-60 keV energies, expected if thecompact object is an accreting neutron star. The observed spectrum andspectral variability can be explained if the compact object in thesystem is a rotation-powered pulsar.
| Binary and Multiple O-Type Stars in the Cassiopeia OB6 Association
We present the results of time-resolved spectroscopy of 13 O-type starsin the Cas OB6 stellar association. We conducted a survey for radialvelocity variability in search of binary systems, which are expected tobe plentiful in young OB associations. Here we report the discovery oftwo new single-lined binaries, and we present new orbital elements forthree double-lined binaries (including one in the multiple-star systemHD 17505). One of the double-lined systems is the eclipsing binarysystem DN Cas, and we present a preliminary light-curve analysis thatyields the system inclination, masses, and radii. We compare the spectraof the single stars and the individual components of the binary starswith model synthetic spectra to estimate the stellar effectivetemperatures, gravities, and projected rotational velocities. We alsomake fits of the spectral energy distributions to derive E(B-V),R=AV/E(B-V), and angular diameter. A distance of 1.9 kpcyields radii that are consistent with evolutionary models. We find that7 of 14 systems with spectroscopic data are probable binaries,consistent with the high binary frequency found for other massive starsin clusters and associations.
| Catalog of Galactic β Cephei Stars
We present an extensive and up-to-date catalog of Galactic β Cepheistars. This catalog is intended to give a comprehensive overview ofobservational characteristics of all known β Cephei stars, coveringinformation until 2004 June. Ninety-three stars could be confirmed to beβ Cephei stars. We use data from more than 250 papers publishedover the last nearly 100 years, and we provide over 45 notes onindividual stars. For some stars we reanalyzed published data orconducted our own analyses. Sixty-one stars were rejected from the finalβ Cephei list, and 77 stars are suspected to be β Cepheistars. A list of critically selected pulsation frequencies for confirmedβ Cephei stars is also presented.We analyze the β Cephei stars as a group, such as the distributionsof their spectral types, projected rotational velocities, radialvelocities, pulsation periods, and Galactic coordinates. We confirm thatthe majority of the β Cephei stars are multiperiodic pulsators. Weshow that, besides two exceptions, the β Cephei stars with highpulsation amplitudes are slow rotators. Those higher amplitude starshave angular rotational velocities in the same range as thehigh-amplitude δ Scuti stars (Prot>~3 days).We construct a theoretical HR diagram that suggests that almost all 93β Cephei stars are main-sequence objects. We discuss theobservational boundaries of β Cephei pulsation and the physicalparameters of the stars. We corroborate that the excited pulsation modesare near to the radial fundamental mode in frequency and we show thatthe mass distribution of the stars peaks at 12 Msolar. Wepoint out that the theoretical instability strip of the β Cepheistars is filled neither at the cool nor at the hot end and attempt toexplain this observation.
| X-Ray Counterparts of Runaway Stars
An X-ray search for possible compact companions of runaway OB stars hasbeen conducted using pointed ROSAT observations. Of a list of 71 runawaystars, ROSAT exposures were available for 24, of which 13 are detected.These numbers are nearly 3 times larger than for a previously studiedEinstein sample, and spectral information is exploited as well.Luminosities, hardness ratios, and long-term variability are as fornormal OB stars and do not suggest the presence of collapsed companions.A result like this is often interpreted as support for dynamicalejection from a dense group rather than a supernova event in a binary asa production process for runaway stars. There are, however, severalcircumstances that may adversely affect the observability of a compactcompanion, or after a supernova explosion systems may be disruptedbecause of the large natal kick velocity imparted to the neutron star asa result of asymmetries in the explosions. It is noted that there isactually evidence for both of these production routes and that they maybe expected to occur sequentially in the evolution of OB associations.
| The Evolution of Massive Stars: The Be Star and Microquasar Phenomena
Not Available
| Total to Selective Extinction Ratios and Visual Extinctions from Ultraviolet Data
We present determinations of the total to selective extinction ratio R_Vand visual extinction A_V values for Milky Way stars using ultravioletcolor excesses. We extend the analysis of Gnacinski and Sikorski (1999)by using non-equal weights derived from observational errors. We presenta detailed discussion of various statistical errors. In addition, weestimate the level of systematic errors by considering differentnormalization of the extinction curve adopted by Wegner (2002). Ourcatalog of 782 R_V and A_V values and their errors is available in theelectronic form on the World Wide Web.
| HD 108: The mystery deepens with XMM-Newton observations
In 2001, using a large spectroscopic dataset from an extensivemonitoring campaign, we discovered that the peculiar Of star HD 108displayed extreme line variations. This strange behaviour could beattributed to a variety of models, and an investigation of the highenergy properties of HD 108 was needed to test the predictions fromthese models. Our dedicated XMM-Newton observation of HD 108 shows thatits spectrum is well represented by a two temperature thermal plasmamodel with kT10.2 keV and kT21.4 keV. Inaddition, we find that the star does not display any significantshort-term changes during the XMM-Newton exposure. Compared to previousEinstein and ROSAT detections, it also appears that HD 108 does notpresent long-term flux variations either. While the line variationscontinue to modify HD 108's spectrum in the optical domain, the X-rayemission of the star appears thus surprisingly stable: no simple modelis for the moment able to explain such an unexpected behaviour. Thanksto its high sensitivity, the XMM-Newton observatory has also enabled theserendipitous discovery of 57 new X-ray sources in the field of HD 108.Their properties are also discussed in this paper.Based on observations collected at the Observatoire de Haute-Provence(France) and with XMM-Newton, an ESA Science Mission with instrumentsand contributions directly funded by ESA Member States and the USA(NASA).
| A Galactic O Star Catalog
We have produced a catalog of 378 Galactic O stars with accuratespectral classifications that is complete for V<8 but includes manyfainter stars. The catalog provides cross-identifications with othersources; coordinates (obtained in most cases from Tycho-2 data);astrometric distances for 24 of the nearest stars; optical (Tycho-2,Johnson, and Strömgren) and NIR photometry; group membership,runaway character, and multiplicity information; and a Web-based versionwith links to on-line services.
| Bright OB stars in the Galaxy. I. Mass-loss and wind-momentum rates of O-type stars: A pure H\alpha analysis accounting for line-blanketing
We study mass-loss and wind momentum rates of 29 Galactic O-type starswith luminosity classes I, III and V by means of a pure H\alpha profileanalysis and investigate to what extent the results compare to thoseoriginating from a state-of-the-art, complete spectral analysis. Ourinvestigation relies on the approximate method developed by\citet{Puls96} which we have modified to account for the effects ofline-blanketing. Effective temperatures and gravities needed to obtainquantitative results from such a simplified approach have been derivedby means of calibrations based on most recent spectroscopic NLTEanalyses and models of Galactic stars by \citet{Repo03} and\citet{Martins02}. Comparing (i) the derived wind-densities to thosedetermined by \citet{Repo03} for eleven stars in common and (ii) theWind-momentum Luminosity Relationship (WLR) for our sample stars tothose derived by other investigations, we conclude that our approximateapproach is actually able to provide consistent results. Additionally,we studied the consequences of ``fine tuning'' some of the direct andindirect parameters entering the WLR, especially by accounting fordifferent possible values of stellar reddening and distances. Combiningour data set with the corresponding data provided by \citet{Herrero02}and \citet{Repo03} we finally study the WLR for the largest sample ofGalactic O-type stars gathered so far, including an elaborate errortreatment. The established disagreement between the theoreticalpredictions and the ``observed'' WLRs being a function of luminosityclass is suggested to be a result of wind clumping. Different strategiesto check this hypothesis are discussed, particularly by comparing theH\alpha mass-loss rates with the ones derived from radio observations.
| The Massive Triple Star System HD 16429 A
HD 16429 A is a triple star system consisting of a single-linedspectroscopic binary and a widely separated third component, previouslyidentified via speckle interferometry. Here I present the first orbitalelements for the unblended spectroscopic binary as well as estimates ofthe spectral types and relative flux contributions for each visiblecomponent based on a Doppler tomographic reconstruction of theirspectra. There are several stars around HD 16429 A, including the nearbyBe X-ray binary and microquasar LS I +61deg303, which allprobably belong to a subcluster within the Cas OB6 association.
| The total-to-selective extinction ratio determined from near IR photometry of OB stars
The paper presents an extensive list of the total to selectiveextinction ratios R calculated from the infrared magnitudes of 597 O andB stars using the extrapolation method. The IR magnitudes of these starswere taken from the literature. The IR colour excesses are determinedwith the aid of "artificial standards" - Wegner (1994). The individualand mean values of total to selective extinction ratios R differ in mostcases from the average value R=3.10 +/-0.05 - Wegner (1993) in differentOB associations. The relation between total to selective extinctionratios R determined in this paper and those calculated using the "methodof variable extinction" and the Cardelli et al. (1989) formulae isdiscussed. The R values presented in this paper can be used to determineindividual absolute magnitudes of reddened OB stars with knowntrigonometric parallaxes.
| On the Absolute Magnitudes of the O Stars
The conclusion published in 1992 by Garmany & Stencel from a studyof northern OB associations, that the absolute magnitudes of the O starsshow ``a large scatter ... intrinsic to the classification system,'' iscritically examined. It is found that the differences between theirderived absolute magnitudes of O stars and this author's 1973calibration exhibit large systematic effects in several associations,ranging from -0.74 to +1.02 mag with substantially smaller dispersions.Of course, when these results are combined, the scatter equals the fullrange of the systematic effects. To investigate the possibility ofdistance errors, the Garmany & Stencel B0-B2.5 stars in the sameassociations are subjected to the same analysis. The results for the Bstars show no significant systematic differences, eliminating errors inthe association distances derived by Garmany & Stencel from the Bstars as the source of the differences found for the O stars. It isnoteworthy that the dispersions in the absolute magnitudes of the Bstars within a given association are similar to or larger than those ofthe O stars. An examination of the distribution on the sky of the starsshows that the O and B stars in the discrepant associations aregenerally not colocated; such was already known to be the case for theimportant Perseus OB1 association. It is suggested that despite theirefforts to improve them, significant problems remain with theassociation memberships adopted by Garmany & Stencel; the relativelysmall dispersions of the O star absolute magnitudes even in thediscrepant cases indicate that they belong to different, usually moredistant associations near the lines of sight to the B associations withwhich they have been mistakenly connected. Several individual cases ofunrecognized multiple systems and classification errors are also foundin the Garmany & Stencel sample. It is concluded that the scatter inthe absolute magnitudes of the O stars is not as large as found byGarmany & Stencel, and not larger than that of the B stars.
| High resolution spectroscopy over lambda lambda 8500-8750 Å for GAIA. I. Mapping the MKK classification system
We present an Echelle+CCD high resolution spectroscopic atlas (0.25Ä/pix dispersion, 0.43 Ä FWHM resolution and 20 000 resolvingpower) mapping the MKK classification system over the interval lambdalambda 8500-8750 Ä. The wavelength interval is remarkably free fromtelluric lines and it is centered on the near-IR triplet of Ca II, thehead of hydrogen Paschen series and several strong metallic lines. Thespectra of 131 stars of types between O4 and M8 and luminosity classes Ithrough V are included in the atlas. Special care was put in maintainingthe highest instrumental homogeneity over the whole set of data. Thecapability to derive accurate MKK spectral types from high resolutionobservations over the interval lambda lambda 8500-8750 Ä isdiscussed. The observations have been performed as part of an evaluationstudy of possible spectroscopic performances for the astrometric missionGAIA planned by ESA. Tables~3 and 4 are only available in electronicform at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)or via http://cdsweb.u-strasbg.fr/ Abstract.html}\fnmsep\thanks{ Thespectra of the stars listed in Table~2 are also available in electronicform at the CDS or via the personal HomePagehttp://ulisse.pd.astro.it/Astro/Atlases/}\fnmsep\thanks{ Figures 3--28are only available in electronic form at http://www.edpsciences.com
| 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.
| Wolf-Rayet stars and O-star runaways with HIPPARCOS. II. Photometry
Abundant {HIPPARCOS photometry over 3 years of 141 O and Wolf-Rayetstars, including 8 massive X-ray binaries, provides a magnificentvariety of light curves at the sigma ~ 1-5% level. Among the mostinteresting results, we mention: optical outbursts in HD 102567 (MXRB),coinciding with periastron passages; drastic changes in the light curveshape of HD 153919 (MXRB); previously unknown long-term variability ofHD 39680 (O6V:[n]pe var) and WR 46 (WN3p); unusual flaring of HDE 308399(O9V); ellipsoidal variations of HD 64315, HD 115071 and HD 160641;rotationally modulated variations in HD 66811=zeta Pup (O4Inf) and HD210839=lambda Cep (O6I(n)fp); dust formation episode in WR 121 (WC9). Ina statistical sense, the incidence of variability is slightly higheramong the WR stars, which might be explained by the higher percentage ofknown binary systems. Among the presumably single WR stars, thecandidate runaways appear to be more variable then the rest. Based ondata from the ESA Hipparcos astrometry satellite
| Wolf-Rayet stars and O-star runaways with HIPPARCOS. I. Kinematics
Reliable systemic radial velocities are almost impossible to secure forWolf-Rayet stars, difficult for O stars. Therefore, to study the motions- both systematic in the Galaxy and peculiar - of these two relatedtypes of hot, luminous star, we have examined the Hipparcos propermotions of some 70 stars of each type. We find that (a) both groupsfollow Galactic rotation in the same way, (b) both have a similarfraction of ``runaways'', (c) mean kinetic ages based on displacementand motion away from the Galactic plane tend to slightly favour thecluster ejection over the the binary supernova hypothesis for theirformation, and (d) those with significant peculiar supersonic motionrelative to the ambient ISM, tend to form bow shocks in the direction ofthe motion. Based on data from the ESA Hipparcos astrometry satellite.Table~1 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| ICCD speckle observations of binary stars. XIX - an astrometric/spectroscopic survey of O stars
We present the results of a speckle interferometric survey made with theCHARA speckle camera and 4 m class telescopes of Galactic O-type starswith V less than 8. We can detect with the speckle camera binaries inthe angular separation range 0.035-1.5 arcsec with delta M less than 3,and we have discovered 15 binaries among 227 O-type systems. We combinedour results on visual binaries with measurements of wider pairs from theWashington Double Star Catalog and fainter pairs from the HipparcosCatalog, and we made a literature survey of the spectroscopic binariesamong the sample. We then investigated the overall binary frequency ofthe sample and the orbital characteristics of the known binaries.Binaries are common among O stars in clusters and associations but lessso among field and especially runaway stars. There are many triplesystems among the speckle binaries, and we discuss their possible rolein the ejection of stars from clusters. The period distribution of thebinaries is bimodal in log P, but we suggest that binaries with periodsof years and decades may eventually be found to fill the gap. The massratio distribution of the visual binaries increases toward lower massratios, but low mass ratio companions are rare among close,spectroscopic binaries. We present distributions of the eccentricity andlongitude of periastron for spectroscopic binaries with ellipticalorbits, and we find strong evidence of a bias in the longitude ofperiastron distribution.
| Deep VLA images of LS I +61(deg) 303: a search for associated extended radio emission
Deep VLA observations at 6 cm of the field around the radio emittingX-ray binary LS I +61(deg) 303 have been carried out in an attempt tosearch for associated extended radio emission. The angular scalesexplored go from the arcsecond to the arcminute range. Only clumps ofextended radio emission within a few arcminutes of the source aredetected. However, in contrast with other X-ray binaries with associatedextended radio emission, all these clumps seem to be unrelated to LS I+61(deg) 303 itself. The fact that some of them are positionallycoincident with optical nebulosities in the field strongly suggests aninterpretation based on free-free radio emitting material from thenearby HII region W4. The possibility that an undetected radio jet ispresent in LS I +61(deg) 303 is also discussed.
| On Space Velocities of Binary Stars in Which One Component Has Experienced a Supernova Explosion
When one component of an evolved binary loses a significant fraction ofits initial mass in a symmetric supernova explosion but remains bound toits companion, the remnant binary recoils with a velocity that can becomparable to the orbital velocity of the supernova precursor. Thisvelocity is enough to explain the observed peculiar space velocitiesand/or distances from the Galactic plane of most X-ray binaries andbinary OB runaway stars. Some exceptions certainly occur, butuncertainties in estimates of velocities and distances, as well asmechanisms other than a popular asymmetric kick, may be responsible formost of the exceptions.
| A Survey for H alpha Emission in Massive Binaries: The Search for Colliding Wind Candidates
I report the results of the first all-sky survey of H alpha emission inthe spectra of O-type binaries. The survey includes 26 systems, of which10 have emission that extends clearly above the continuum. This is thefirst report of emission for four of these. An additional three systemsshow small distortions in the H alpha profile that may result from weakemission. I compare the distribution of emission systems in H-R diagramsfor both binary and single stars, using a survey of single O-type starsdone by Conti (1974). Emission in main-sequence systems is extremelyrare and is completely absent in my sample of binary stars. Among binarystars, 78% of the systems containing giants show some emission, while nosingle giants in Conti's sample do. In the case of supergiants, 78% ofsingle stars show emission, while all supergiant binaries show strongemission. H alpha emission may come from a variety sources, but the factthat binaries have a higher incidence and strength of emission inpost--main-sequence stages may indicate that wind interactions are acommon source of emission in massive binaries. To ascertain whether ornot colliding winds have been observed, it will be necessary to studythe H alpha line profile throughout several orbits of each candidatecolliding wind system and look for recurring orbital-phase--relatedvariations. Such a study is underway.
| The Lyman-Continuum Fluxes and Stellar Parameters of O and Early B-Type Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJ...460..914V&db_key=AST
| DO OB Runaway Stars Have Pulsar Companions?
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....111.1220P&db_key=AST
| 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.
| X-ray observations of the peculiar Be star LSI +61 303.
We present the results of a ROSAT Position Sensitive ProportionalCounter observation of the variable radio star LS I +61 303. The sourcehas a power law spectrum with photon index 1.1+/-0.3 and a luminosity of5.9x10^33^erg/s in the 0.1-2.4keV range. Variability on a timescale ofdays is clearly visible in the ROSAT data, but no periodic pulsationshave been detected. The low X-ray luminosity is difficult to explain inthe context of the models involving super Eddington accretion which havebeen proposed to account for the non thermal radio outbursts. Though theweak X-ray flux is marginally compatible with the levels expected fromnormal B and Be star winds, the variability and the rather hard spectrumare more suggestive of non thermal emission. This might originate in ashocked region produced by a young pulsar in orbit around the Be star.
| A search for near-infrared variability in LSI+61 303.
We present new near-infrared (NIR) broadband photometry of LSI+61 303centered around two predicted radio maxima and minima in order to searchfor NIR variability that may or may not be correlated with the periodicradio variations in this object. To improve the significance of anyupper limit on variability, we adopted a differential measurementtechnique to minimize the photometric uncertainties. We have combinedour data with those in the literature and calculated the dereddened NIRexcess for the combined data set. Although the excess variesstochastically by more than a factor of two, a search for periodicitiesin the NIR excess with the phase dispersion minimization method gives nostatistically significant periodic variation. Moreover, we find nohour-timescale fluctuations in the NIR of the sort detected at opticalwavebands. The J-H and H-K colors of the dereddened NIR excess are blue,and roughly consistent with those expected from isothermal circumstellardisks or 4000-5000K blackbodies.
| Intrinsic colour indices of O- and B- type stars in the Vilnius photometric system.
Not Available
| An Atlas of Balmer Lines - H-Delta and H-Gamma
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&AS..101..599C&db_key=AST
| A preliminary compilation of DS-programme star positions
A catalog is presented of the double-star-program (DS-program) starpositions, listing right ascensions for 930 DSs and declinations for1225 DSs of the program. The positions were compiled from the observedvalues obtained between 1980 and 1987 with the meridian circles of sixUSSR observatories (the Moscow, Kazan', Kiev, Khar'kov, Odessa, andTashkent Observatories) and the Belgrade Observatory. The measurementsand the treatment of the observational material were performed using therelative method, and the FK-4 system stars were used as reference stars.
| A new library of stellar optical spectra
Attention is given to a new digital optical stellar library consistingof spectra covering 3510-8930 R at 11-A resolution for 72 differentstellar types. These types extend over the spectral classes O-M andluminosity classes I-V. Most spectra are of solar metallicity stars butsome metal-rich and metal-poor spectra are included. This new library isquantitatively compared to two previously published libraries. It offersseveral advantages over them: it is photometrically well-calibratedindividually and consistently from star to star. Good temperature andluminosity coverage has been achieved. The incorporation of stars withwell-determined temperature, metallicity, and surface gravity parametersincreases the accuracy of the spectral type assigned to each compositelibrary star.
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
| Constellation: | Cassiopeia |
| Right ascension: | 02h40m44.95s |
| Declination: | +61°16'56.0" |
| Apparent magnitude: | 7.863 |
| Distance: | 10000000 parsecs |
| Proper motion RA: | 1.3 |
| Proper motion Dec: | -1.2 |
| B-T magnitude: | 8.5 |
| V-T magnitude: | 7.916 |
Catalogs and designations:
|
