Contingut
Imatges
| - No s'ha trobat Imatges - |
Carregar la teva Imatge
DSS Images Other Images
Articles Relacionats
A systematic study of variability among OB-stars based on HIPPARCOS photometry
Context: Variability is a key factor for understanding the nature of themost massive stars, the OB stars. Such stars lie closest to the unstableupper limit of star formation. Aims: In terms of statistics, thedata from the HIPPARCOS satellite are unique because of time coverageand uniformity. They are ideal to study variability in this large,uniform sample of OB stars. Methods: We used statisticaltechniques to determine an independant threshold of variabilitycorresponding to our sample of OB stars, and then applied an automaticalgorithm to search for periods in the data of stars that are locatedabove this threshold. We separated the sample stars into 4 maincategories of variability: 3 intrinsic and 1 extrinsic. The intrinsiccategories are: OB main sequence stars (~2/3 of the sample), OBe stars(~10%) and OB Supergiant stars (~1/4).The extrinsic category refers toeclipsing binaries. Results: We classified about 30% of the wholesample as variable, although the fraction depends on magnitude level dueto instrumental limitations. OBe stars tend to be much more variable(≈80%) than the average sample star, while OBMS stars are belowaverage and OBSG stars are average. Types of variables include αCyg, β Cep, slowly pulsating stars and other types from the generalcatalog of variable stars. As for eclipsing binaries, there arerelatively more contact than detached systems among the OBMS and OBestars, and about equal numbers among OBSG stars.
| The Stellar Population and Origin of the Mysterious High-Latitude Star-forming Cloud CG 12
The mysterious high Galactic latitude cometary globule CG 12 has beenobserved with the ACIS detector on board the Chandra X-Ray Observatory.We detect 128 X-ray sources, of which half are likely young stars formedwithin the globule's head. This new population of >~50 T Tauri starsand one new embedded protostar is far larger than the previouslyreported few intermediate-mass and two protostellar members of thecloud. Most of the newly discovered stars have masses 0.2-0.7Msolar, and 9%-15% have K-band excesses from innerprotoplanetary disks. X-ray properties provide an independent distanceestimate consistent with CG 12's unusual location >~200 pc above theGalactic plane. The star formation efficiency in CG 12 appears to be15%-35%, far above that seen in other triggered molecular globules. Themedian photometric age found for the T Tauri population assuming Siesset al. (2000) isochrones is ~4 Myr with a large spread of <1-20 Myrand ongoing star formation in the molecular cores. The stellar age andspatial distributions are inconsistent with a simple radiation-drivenimplosion (RDI) model and suggest either that CG 12 is an atypicallylarge shocked globule or that it has been subject to several distinctepisodes of triggering and ablation. We report a previously unnoticedgroup of B-type stars northwest of CG 12 that may be the remnants of anOB association that produced multiple supernova explosions that couldhave shocked and ablated the cloud over a 15-30 Myr period. HD 120958(B3e), the most luminous member of the group, may be currently drivingan RDI shock into the CG 12 cloud.
| New Estimates of the Solar-Neighborhood Massive Star Birthrate and the Galactic Supernova Rate
The birthrate of stars of masses >=10 Msolar is estimatedfrom a sample of just over 400 O3-B2 dwarfs within 1.5 kpc of the Sunand the result extrapolated to estimate the Galactic supernova ratecontributed by such stars. The solar-neighborhood Galactic-plane massivestar birthrate is estimated at ~176 stars kpc-3Myr-1. On the basis of a model in which the Galactic stellardensity distribution comprises a ``disk+central hole'' like that of thedust infrared emission (as proposed by Drimmel and Spergel), theGalactic supernova rate is estimated at probably not less than ~1 normore than ~2 per century and the number of O3-B2 dwarfs within the solarcircle at ~200,000.
| Catalog of Galactic OB Stars
An all-sky catalog of Galactic OB stars has been created by extendingthe Case-Hamburg Galactic plane luminous-stars surveys to include 5500additional objects drawn from the literature. This work brings the totalnumber of known or reasonably suspected OB stars to over 16,000.Companion databases of UBVβ photometry and MK classifications forthese objects include nearly 30,000 and 20,000 entries, respectively.
| 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.
| 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.
| The outer atmospheres of cool M giants: High-dispersion ultraviolet spectra of Rho Per, 2 Cen, and G HER
Long duration IUE spectra were obtained to extend coverage of coolgiants studied in the ultraviolet at high dispersion to M6. Thechromospheric spectra of the three stars, which consist of a profusionof Fe II lines and a few lines of Mg II, Mg I, Al II, C II, C I, Cr II,and Fe I, are remarkably similar, both among themselves and with respectto stars of earlier spectral type. These lines present a picture of awarm chromosphere that is static in the average but may be far fromuniform in density and ionization. The Mg II emission lines of 2 Censhow 2 unresolved absorption components, the shorter at the velocity ofthe local interstellar medium. The longer is blueshifted from the starby 12 to 18 km/sec and must be one of very few observed shell linesuncontaminated by interstellar absorption.
| A Catalogue of Be-Stars
Not Available
| Observations of southern emission-line stars
A catalog of 1929 stars showing H-alpha emission on photographic platesis presented which covers the entire southern sky south of declination-25 deg to a red limiting magnitude of about 11.0. The catalog providesprevious designations of known emission-line stars equatorial (1900) andgalactic coordinates, visual and photographic magnitudes, H-alphaemission parameters, spectral types, and notes on unusual spectralfeatures. The objects listed include 16 M stars, 25 S stars, 37 carbonstars, 20 symbiotic stars, 40 confirmed or suspected T Tauri stars, 16novae, 14 planetary nebulae, 11 P Cygni stars, 9 Bep stars, 87 confirmedor suspected Wolf-Rayet stars, and 26 'peculiar' stars. Two new Tassociations are discovered, one in Lupus and one in Chamaeleon. Objectswith variations in continuum or H-alpha intensity are noted, and thedistribution by spectral type is analyzed. It is found that the skydistribution of these emission-line stars shows significantconcentrations in the region of the small Sagittarius cloud and in theCarina region.
| 60th Name-List of Variable Stars
Not Available
| UBV photometry of southern early-type stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1974MNRAS.168..451H&db_key=AST
| Photometry and spectral classification of early-type stars away from the galactic plane.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1970MNRAS.150...23H&db_key=AST
| Mesures d'étoiles doubles faites au réfracteur de 38 cm de l'Observatoire de Nice
Not Available
|
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: | Centaurus |
| Ascensió Recta: | 13h53m28.23s |
| Declinació: | -39°03'25.9" |
| Magnitud Aparent: | 7.598 |
| Distancia: | 454.545 parsecs |
| Moviment propi RA: | -8.6 |
| Moviment propi Dec: | 1 |
| B-T magnitude: | 7.47 |
| V-T magnitude: | 7.588 |
Catàlegs i designacions:
|
INHABITED SKY
