Tartalom
Képek
Kép feltöltése
DSS Images Other Images
Kapcsolódó cikkek
Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| Anomalous dust-to-gas ratios in the Galaxy
Lines of sight with E(B-V)/N(HI) considerably smaller than the averagevalue for the solar neighbourhood have been selected from the catalogueof Diplas & Savage. In order to develop quantitative considerations,estimates of the molecular hydrogen column density were obtained usingthe relation of Savage et al. extended at E(B-V) > 0.4 with therecent data of Rachford et al. Contrary to the prevailing opinion in theliterature for sightlines with similar behaviour, we found that only 22per cent of our sample was characterized by both an average gas densitylarger than 1 cm-3 and a value of RV larger thanthat in the diffuse interstellar medium. By computing extinction models,we were able to fit the E(B-V)/N(HI) by changing the value ofRV only for some sightlines. For the remaining ones, aρd/ρH ratio different from the averageGalactic value must be invoked. The application of the Kramers-Kronigrelation to the observed extinction curves confirmed this possibility.Moreover, attempts to fit such curves with models having grain volumescorresponding to the standard ρd/ρH ratiofailed.We find a linear relation between ρd/ρHand E(B-V)/N(H) for our sightlines. The average Galactic value marks theseparation into two groups characterized by lower abundances of C and Sitrapped into the grains when E(B-V)/N(H) is smaller than the Galacticvalue, and by larger abundances when E(B-V)/N(H) is greater.
| A HIPPARCOS Census of the Nearby OB Associations
A comprehensive census of the stellar content of the OB associationswithin 1 kpc from the Sun is presented, based on Hipparcos positions,proper motions, and parallaxes. It is a key part of a long-term projectto study the formation, structure, and evolution of nearby young stellargroups and related star-forming regions. OB associations are unbound``moving groups,'' which can be detected kinematically because of theirsmall internal velocity dispersion. The nearby associations have a largeextent on the sky, which traditionally has limited astrometricmembership determination to bright stars (V<~6 mag), with spectraltypes earlier than ~B5. The Hipparcos measurements allow a majorimprovement in this situation. Moving groups are identified in theHipparcos Catalog by combining de Bruijne's refurbished convergent pointmethod with the ``Spaghetti method'' of Hoogerwerf & Aguilar.Astrometric members are listed for 12 young stellar groups, out to adistance of ~650 pc. These are the three subgroups Upper Scorpius, UpperCentaurus Lupus, and Lower Centaurus Crux of Sco OB2, as well as VelOB2, Tr 10, Col 121, Per OB2, alpha Persei (Per OB3), Cas-Tau, Lac OB1,Cep OB2, and a new group in Cepheus, designated as Cep OB6. Theselection procedure corrects the list of previously known astrometricand photometric B- and A-type members in these groups and identifiesmany new members, including a significant number of F stars, as well asevolved stars, e.g., the Wolf-Rayet stars gamma^2 Vel (WR 11) in Vel OB2and EZ CMa (WR 6) in Col 121, and the classical Cepheid delta Cep in CepOB6. Membership probabilities are given for all selected stars. MonteCarlo simulations are used to estimate the expected number of interloperfield stars. In the nearest associations, notably in Sco OB2, thelater-type members include T Tauri objects and other stars in the finalpre-main-sequence phase. This provides a firm link between the classicalhigh-mass stellar content and ongoing low-mass star formation. Detailedstudies of these 12 groups, and their relation to the surroundinginterstellar medium, will be presented elsewhere. Astrometric evidencefor moving groups in the fields of R CrA, CMa OB1, Mon OB1, Ori OB1, CamOB1, Cep OB3, Cep OB4, Cyg OB4, Cyg OB7, and Sct OB2, is inconclusive.OB associations do exist in many of these regions, but they are eitherat distances beyond ~500 pc where the Hipparcos parallaxes are oflimited use, or they have unfavorable kinematics, so that the groupproper motion does not distinguish it from the field stars in theGalactic disk. The mean distances of the well-established groups aresystematically smaller than the pre-Hipparcos photometric estimates.While part of this may be caused by the improved membership lists, arecalibration of the upper main sequence in the Hertzsprung-Russelldiagram may be called for. The mean motions display a systematicpattern, which is discussed in relation to the Gould Belt. Six of the 12detected moving groups do not appear in the classical list of nearby OBassociations. This is sometimes caused by the absence of O stars, but inother cases a previously known open cluster turns out to be (part of) anextended OB association. The number of unbound young stellar groups inthe solar neighborhood may be significantly larger than thoughtpreviously.
| 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
| Equivalent width of NA I and K I lines and reddening.
The profile, radial velocity and equivalent width of the interstellarlines of Na I (5890.0, 5895.9Å) and K I (7699.0Å) have beenobtained from Echelle+CCD observations at resolving powerλ/{DELTA}λ~16,500 for 32 O and early B stars sufferingfrom a reddening between E_B-V_=0.06 and 1.57. The data have been usedto search for and calibrate a relation between equivalent width andreddening. When the interstellar lines show a single and sharpcomponent, useful relations to estimate reddening from equivalent widthshave been derived. The relation for Na I is most sensitive in the range0.0<=E_B-V_<=0.4, and the one for K I takes over at higherreddening. Good quality equivalent width measurements allow E_B-V_ to beestimated with an accuracy of about 0.05 mag. For multi-componentprofiles of Na I and K I lines the estimate of reddening is moreambiguous with a general scatter of 0.15mag. Close blends of multiplecomponents allow only an estimate of an upper limit to E_B-V_.
| 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.
| Intrinsic colour indices of O- and B- type stars in the Vilnius photometric system.
Not Available
| Photoelectric photometry of OB stars in the Vilnius system
Not Available
| Empirical temperature calibrations for early-type stars
Three temperature calibrations of suitable photometric quantities havebeen derived for O and B stars. A sample of 120 stars with reliableT(eff.) determinations has been used for establishing each calibration.The different calibrations have been critically discussed and compared.Temperature determinations for 1009 program stars have been obtainedwith an accuracy of the order of 10 percent.
| Observations of interstellar diffuse absorption band at 4430 A
Observations of the interstellar diffuse absorption band at 4430 A for800 O and B stars in Neckel's (1967) catalog are being carried out, and482 spectra obtained up to September 1983 have been reduced. It isconfirmed that the strength of the interstellar diffuse absorption bandat 4430 A does not simply relate to the abundance of interstellar grainson the line of sight. The relation between the color excess E(B-V) andthe equivalent width of the band to the direction of l = 130-140 deg andb = -5 to +5 deg shows that some parameter(s) other than E(B-V) is (are)needed to understand the cause of this band.
| Catalog of O-B stars observed with Tokyo Meridian Circle
A catalog of the O-B stars, selected from 'Blaauw-Parenago' list andRubin's catalog, has been compiled on the FK4 system by the observationsmade with Gautier 8-inch Meridian Circle at the Tokyo AstronomicalObservatory during the period, 1971 to 1979. It contains 1059 stars andwas compiled for the future establishment of high precision propermotions of O-B stars.
| A catalog of ultraviolet interstellar extinction excesses for 1415 stars
Ultraviolet interstellar extinction excesses are presented for 1415stars with spectral types B7 and earlier. The excesses with respect to Vare derived from Astronomical Netherlands Satellite (ANS) 5-channel UVphotometry at central wavelengths of approximately 1550, 1800, 2500, and3300 A. A measure of the excess extinction in the 2200-A extinction bumpis also given. The data are valuable for investigating the systematicsof peculiar interstellar extinction and for studying the character of UVinterstellar extinction in the general direction of stars for which theextinction-curve shape is unknown.
| The S201 far-ultraviolet imaging survey. II - A field in Cygnus
Far-ultraviolet imagery of a region in Cygnus, a 20 deg diameter fieldcentered near (1950) R. A. 21 h 31.2 m decl. +37 deg 25 arcmin, wasobtained by the S201 far-ultraviolet camera during the Apollo 16mission. In a 10 minute exposure covering the 1250-1600 A wavelengthrange (effective wavelength 1400 A), 730 star images can be detected,corresponding to a limiting ultraviolet magnitude of about m (1400) =10. Assuming nominal interstellar extinction values in this region nearthe galactic plane, this result corresponds to the detection of A0 Vstars to a distance of 300 pc and of B0 V stars to 1500 pc.Uncertainties in spectral classification and interstellar extinction forindividual objects are probably more significant than calibration ormeasurement errors. Most of the objects detected are identified withstars in the Smithsonian Astrophysical Observatory Star Catalog (1966),or the Catalog of Stellar Identifications (1979) or both, but 87 objectsremain unidentified (or are identified with late-type stars).
| Exciting stars and the distances of the diffuse nebulae
Not Available
| A survey of ultraviolet objects
An all-sky survey of ultraviolet objects is presented together with astatistical analysis that leads to the conclusion that there is asignificantly higher population of hot subdwarfs lying below themain-sequence than hitherto thought. The distribution of all ultravioletobjects, main sequence ultraviolet objects, and MK unclassifiedultraviolet objects are shown in galactic coordinates, and the absolutemagnitudes and color-color diagrams for these groups are presented.Scale heights are derived, giving values similar to planetary nebulaefor the hottest groups.
| The interstellar 2200 A band - A catalogue of equivalent widths
Not Available
| Radial velocities of 65 early-type stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972AJ.....77..138A&db_key=AST
| Structure in the Interstellar-Extinction Curve
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1971ApJ...166...65Y&db_key=AST
| Troisième catalogue de l'Observatoire de Besançon comprenant 764 étoiles réduites à 1950, 0 sans mouvement propre et 326 étoiles FK3 pour l'époque moyenne d'observation
Not Available
| Vergleich der Spiralstruktur bei frühen galaktischen Sternhaufen H II-Regionen, H I-Regionen und auβergalaktischen Sternsystemen. Mit 4 Textabbildungen
Not Available
| Photoelectric distances of 461 Northern OB-stars and galactic structure from Hγ- luminosities Author: Beer, A.
Abstract image available at:http://adsabs.harvard.edu/abs/1964MNRAS.128..261B
| Studies in Galactic STRUCTURE.II.LUMINOSITY Classification for 1270 Blue Giant Stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1955ApJS....2...41M&db_key=AST
| Studies in Galactic Structure. I. a Preliminary Determination of the Space Distribution of the Blue Giants.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1953ApJ...118..318M&db_key=AST
|
Új cikk hozzáadása
Kapcsolódó hivatkozások
- - (nincs kapcsolódó hivatkozás) -
Új link hozzáadása
Besorolás csoportokba:
|
Pozíciós és asztrometriai adatok
| Csillagkép: | Hattyú |
| Rektaszcenzió: | 21h14m05.46s |
| Deklináció: | +37°46'53.8" |
| Vizuális fényesség: | 7.343 |
| Távolság: | 813.008 parszek |
| RA sajátmozgás: | -1.8 |
| Dec sajátmozgás: | -5.2 |
| B-T magnitude: | 7.123 |
| V-T magnitude: | 7.325 |
Katalógusok és elnevezések:
|
