Contents
Images
Upload your image
DSS Images Other Images
Related articles
Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| The Unusual 2001 Periastron Passage in the ``Clockwork'' Colliding-Wind Binary WR 140
We follow, using both optical spectroscopy and photometry, the``textbook'' colliding-wind WR+O binary WR 140 through and between theperiastron passages of 1993 and 2001. An extensive collection ofhigh-quality spectra allows us to derive precise orbital elements forboth components simultaneously. We confirm the extremely higheccentricity of the system, e=0.881+/-0.005, find an excellent match ofthe newly derived period to the previous estimates, P=2899.0+/-1.3 days,and improve the accuracy of the time of periastron passage,T0=HJD2,446,147.4+/-3.7. Around periastron, at orbital phasesφ~0.995-1.015, additional emission components appear on the tops ofthe broad Wolf-Rayet emission lines of relatively low ionizationpotential. The phase-dependent behavior of these excess line emissionspoints to their origin in the wind-wind collision zone, which allows usto place some limits on the orbital inclination of the system,i=50deg+/-15deg, and half-opening angle of the bowshock cone, θ=40deg+/-15deg. The relativelysudden appearance and disappearance of the extra emission componentsprobably signify a rapid switch from an adiabatically to a radiativelydominated regime and back again. Multiyear UBV photometry provides onemore surprise: in 2001 at φ=0.02-0.06, the system went through aseries of rapid, eclipse-like events. Assuming these events to berelated to an episode of enhanced dust formation at periastron, weestimate the characteristic size of the dust grains to be a~0.07 μm.
| Astrometric radial velocities. III. Hipparcos measurements of nearby star clusters and associations
Radial motions of stars in nearby moving clusters are determined fromaccurate proper motions and trigonometric parallaxes, without any use ofspectroscopy. Assuming that cluster members share the same velocityvector (apart from a random dispersion), we apply a maximum-likelihoodmethod on astrometric data from Hipparcos to compute radial and spacevelocities (and their dispersions) in the Ursa Major, Hyades, ComaBerenices, Pleiades, and Praesepe clusters, and for theScorpius-Centaurus, alpha Persei, and ``HIP 98321'' associations. Theradial motion of the Hyades cluster is determined to within 0.4 kms-1 (standard error), and that of its individual stars towithin 0.6 km s-1. For other clusters, Hipparcos data yieldastrometric radial velocities with typical accuracies of a few kms-1. A comparison of these astrometric values withspectroscopic radial velocities in the literature shows a good generalagreement and, in the case of the best-determined Hyades cluster, alsopermits searches for subtle astrophysical differences, such as evidencefor enhanced convective blueshifts of F-dwarf spectra, and decreasedgravitational redshifts in giants. Similar comparisons for the ScorpiusOB2 complex indicate some expansion of its associations, albeit slowerthan expected from their ages. As a by-product from the radial-velocitysolutions, kinematically improved parallaxes for individual stars areobtained, enabling Hertzsprung-Russell diagrams with unprecedentedaccuracy in luminosity. For the Hyades (parallax accuracy 0.3 mas), itsmain sequence resembles a thin line, possibly with wiggles in it.Although this main sequence has underpopulated regions at certaincolours (previously suggested to be ``Böhm-Vitense gaps''), suchare not visible for other clusters, and are probably spurious. Futurespace astrometry missions carry a great potential for absoluteradial-velocity determinations, insensitive to the complexities ofstellar spectra. Based on observations by the ESA Hipparcos satellite.Extended versions of Tables \ref{tab1} and \ref{tab2} are available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.125.8) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/381/446
| WR 140 in ``Eclipse'' Again
Not Available
| A High-Resolution H I Study of the Interstellar Medium Local to HD 193793
A 2° field centered at the optical position of the Wolf-Rayet (WR)star HD 193793 (≡ WR 140) was surveyed in the H I 21 cm line andin the 1420 MHz radio continuum, using the Dominion Radio AstrophysicalObservatory interferometer. The aim of this observations was to look forevidence of an interaction between the WR star and its localinterstellar medium (ISM). Our H I data displays a large oval minimum ata velocity of Vsys~=-12 km s-1, close to theoptical position of HD 193793. We believe this H I void was created byWR 140 and its massive companion (HD 193793 is a member of a well-knownbinary system). The major axis of the H I void is ~11.5 pc and its axialratio, the ratio of major to minor axis, is ~1.4. This structure isobservable over a velocity range of around 11 km s-1. The H Iminimum appears surrounded by a clumpy shell of H I in emission that hasa total mass of neutral hydrogen of MHI~1300 solar masses.The kinematical distance corresponding to a local standard of restvelocity of -12 km s-1 is approximately 5.4 kpc, whichdisagrees with the distance of HD 193793, namely, around 1 kpc.Therefore, it is concluded that the H I bubble was blown in an ISMhaving nonnegligible peculiar motions. Hipparcos proper-motionmeasurements indicate that HD 193793 has a tangential velocity of 28+/-3km s-1 along the major axis of one of the H I minima detectedin the interior of the main H I cavity. To reconcile this motion withthe physical size of the H I structure blown by the winds of the binarysystem, it is concluded that such tangential velocity was acquired bythe system a short while ago, namely, ~1.3×105 yr. Mapsfrom the IRAS database show a large-scale IR feature, with good spatialcorrelation with the H I shell surrounding the main H I void. We believethe emission from the IR shell arises from dust grains heated by theenergetic stellar continuum photons emitted by the stellar objects.
| Hipparcos astrometry for 257 stars using Tycho-2 data
We present improved Hipparcos astrometry for 257 Hipparcos stars,resolved into 342 components. For 64 of the stars no astrometry wasobtained in the Hipparcos Catalogue, while for the remaining starsadditional components have been added by this solution or the positionshave been revised considerably. We have used the published Hipparcostransit data for the new solutions, together with results from thesecond reduction of the Tycho data for defining better initial values.Based on observations made with the ESA Hipparcos astrometry satellite.Table 3 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
| A Search for Star Clusters from the HIPPARCOS Data
We present results of a search for nearby star clusters and associationsusing Hipparcos Catalogue data, restricting the sample to stars withparallaxes above 2 mas (d <~ 500 pc). Two new OB associations havebeen identified in the Carina-Vela and Cepheus-Cygnus-Lyra-Vulpecularegions. A very probable new open cluster has been discovered in Carina.The cluster, a Car, named after its brightest member, is young (60 Myr)and nearby (d = 132 pc). However, only seven bona fide members can bedrawn from the Hipparcos data. We report a detection of nine opencluster candidates in the distance range of 150 to 400 pc, and sixpossible associations almost all located within the Gould belt, althoughslightly older than the known nearby associations. In all cases, wepresent Yale theoretical isochrone fits to the color-magnitude diagrams,which indicate a moderate spread of ages between 60 to 200 Myr.Evidently, these young open cluster and association candidates arerelated to the overall distribution of young OB and A-type stars in thesolar neighborhood.
| The Tokyo PMC catalog 90-93: Catalog of positions of 6649 stars observed in 1990 through 1993 with Tokyo photoelectric meridian circle
The sixth annual catalog of the Tokyo Photoelectric Meridian Circle(PMC) is presented for 6649 stars which were observed at least two timesin January 1990 through March 1993. The mean positions of the starsobserved are given in the catalog at the corresponding mean epochs ofobservations of individual stars. The coordinates of the catalog arebased on the FK5 system, and referred to the equinox and equator ofJ2000.0. The mean local deviations of the observed positions from theFK5 catalog positions are constructed for the basic FK5 stars to comparewith those of the Tokyo PMC Catalog 89 and preliminary Hipparcos resultsof H30.
| UvbyHbeta_ photometry of main sequence A type stars.
We present Stroemgren uvby and Hbeta_ photometry for a set of575 northern main sequence A type stars, most of them belonging to theHipparcos Input Catalogue, with V from 5mag to 10mag and with knownradial velocities. These observations enlarge the catalogue we began tocompile some years ago to more than 1500 stars. Our catalogue includeskinematic and astrophysical data for each star. Our future goal is toperform an accurate analysis of the kinematical behaviour of these starsin the solar neighbourhood.
| Interstellar extinction in the vicinity of the North America and Pelican Nebulae. II
The results of photoelectric photometry of 564 stars in the Vilniusseven-color system in three areas near the North America and PelicanNebulae are given. Photometric spectral types, absolute magnitudes,color excesses, interstellar extinction,s and distances to the stars aredetermined. We find that the dark cloud separating both nebulae is at580 pc distance. A number of stars immersed in the dark cloud have beenfound. It seems that the dark cloud extends south down to 40 degdeclination. The area southwest of alpha Cygni in the declination zones42 deg and 43 deg is comparatively transparent at least up to 1 kpc.
| Radial velocity measurements. IV - Ground-based accompaniment to the HIPPARCOS observation program
The paper presents 396 radial velocities of stars distributed in 19fields of 4 x 4 degrees. The study employs the Fehrenbach objectiveprism method and the same measuring technique used in a previous paper(Fehrenbach et al., 1987).
| Visual multiples. VIII - 1000 MK types
A total of 1000 new classifications are given for stars brighter than B= 8.0 mag in the Aitken double star catalog. The classificationssupplement 865 classifications obtained in 1981 and 1984. Among thenewly discovered stars are 12 new Ap stars, eight Lambda Bootis stars,one Ba II star, and 60 Am stars. A detailed list of the newclassifications is given.
| The spectra, magnitudes and colours of O-A type stars in an area of the Milky Way, with the Center alpha = 20h16m, delta = +42 D 30'.
Not Available
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
| Constellation: | はくちょう座 |
| Right ascension: | 20h21m14.02s |
| Declination: | +43°35'21.2" |
| Apparent magnitude: | 7.83 |
| Distance: | 218.818 parsecs |
| Proper motion RA: | 4.9 |
| Proper motion Dec: | 0 |
| B-T magnitude: | 7.836 |
| V-T magnitude: | 7.831 |
Catalogs and designations:
|
