Contingut
Imatges
Carregar la teva Imatge
DSS Images Other Images
Articles Relacionats
New runaway OB stars with HIPPARCOS
A Monte Carlo method for detection of runaway OB stars fromobservational data is proposed. 61 runaway OB star candidates have beendetected by an analysis of Hipparcos proper motions. The peculiartangential and total transverse velocities have been determined forthese stars. A list of the detected runaway star candidates ispresented. The evidence of a discrepancy between photometric andparallactic distances of runaway OB star candidates is presented.
| 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
| 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.
| Kinematic signatures of violent formation of galactic OB associations from HIPPARCOS measurements
Proper motions measured by Hipparcos confirm the large anomalousvelocities of the OB associations located around the Cygnus Superbubble(Cygnus OB1, OB3, OB7, and OB9), and reveal a clearly organizedexpanding pattern in Canis Major OB1. At the distances of theseassociations, the organized velocity patterns imply LSR velocities of upto ~ 60 km s(-1) for the associations in Cygnus, and about ~ 15 km s(-1)in Canis Major OB1. The magnitude and spatial arrangement of theexpanding motions suggests that very energetic phenomena are responsiblefor the formation of the present OB associations. This is independentlysupported by observations of the associated interstellar medium carriedout in other wavelengths. The gravitational instability scenarioproposed by Comeron & Torra 1994 (ApJ 423, 652) to account for theformation of the stars in the Cygnus Superbubble region is reviewed inthe light of the new kinematic data. It is found that the energeticrequirements set by the highest velocities on the OB associationpowering the Superbubble, Cygnus OB2, are too large by orders ofmagnitude. However, the scenario can still account for the formation ofmost of the stars if, as can be reasonably expected, the stars with thehighest measured velocities are actually runaways from Cygnus OB2itself. As for Canis Major OB1, we consider their formation in asupernova remnant, as suggested by Herbst & Assousa 1977 (ApJ, 217,473). The detection of a new runaway star, HIC 35707 (=HD 57682), whosemotion is directed away from the derived center of expansion, supportsthis scenario and provides an independent age for the supernova remnant,assuming that the runaway star was the binary companion of thesupernova. Based on a number of arguments, however, we find it unlikelythat the stars are a direct consequence of instabilities in theexpanding shell. We propose instead that their formation was triggeredin preexisting clouds, accelerated and compressed by the supernovaexplosion.
| Catalogue of stars in the northern Milky Way having H-alpha in emission
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.
| A Catalogue of Be-Stars
Not Available
| V1500 Cygni Nova 1975
Not Available
| Light curve of Nova V1500 CYG 1975.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1976ApJ...209..882Y&db_key=AST
| Observations spectroscopiques d'etoiles Be.
Not Available
| Catalogue d'etoiles O et B.
Not Available
| Stelle con forte moto proprio della zona astrografica di Catania
Not Available
| Etude pour chaque champ de l'absorption et de la repartition des vitesses radiales EN fonction de la distance.
Not Available
| A Spectroscopic and Photometric Study of the be Stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1958ApJ...128..207M&db_key=AST
| Clusters in the Region of the North America Nebula.
Not Available
| Catalogue and Bibliography of Stars of Classes B and a whose Spectra have Bright Hydrogen Lines
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1933ApJ....78...87M&db_key=AST
|
Enviar un nou article
Enllaços Relacionats
- - No s'ha trobat enllaços -
Enviar un nou enllaç
Membre dels grups següents:
|
Dades d'Observació i Astrometria
| Constel·lació: | Cygnus |
| Ascensió Recta: | 21h08m29.63s |
| Declinació: | +47°15'25.4" |
| Magnitud Aparent: | 7.882 |
| Distancia: | 418.41 parsecs |
| Moviment propi RA: | 0.6 |
| Moviment propi Dec: | -1.8 |
| B-T magnitude: | 7.815 |
| V-T magnitude: | 7.877 |
Catàlegs i designacions:
|
