Contenuti
Immagini
Carica la tua immagine
DSS Images Other Images
Articoli relazionati
B Star Rotational Velocities in h and χ Persei: A Probe of Initial Conditions during the Star Formation Epoch?
Projected rotational velocities (vsini) have been measured for 216 B0-B9stars in the rich, dense h and χ Persei double cluster and comparedwith the distribution of rotational velocities for a sample of fieldstars having comparable ages (t~12-15 Myr) and masses (M~4-15Msolar). For stars that are relatively little evolved fromtheir initial locations on the zero-age main sequence (ZAMS) (those withmasses M~4-5 Msolar), the mean vsini measured for the h andχ Per sample is slightly more than 2 times larger than the meandetermined for field stars of comparable mass, and the cluster and fieldvsini distributions differ with a high degree of significance. Forsomewhat more evolved stars with masses in the range 5-9Msolar, the mean vsini in h and χ Per is 1.5 times thatof the field; the vsini distributions differ as well, but with a lowerdegree of statistical significance. For stars that have evolvedsignificantly from the ZAMS and are approaching the hydrogen exhaustionphase (those with masses in the range 9-15 Msolar), thecluster and field star means and distributions are only slightlydifferent. We argue that both the higher rotation rates and the patternof rotation speeds as a function of mass that differentiatemain-sequence B stars in h and χ Per from their field analogs werelikely imprinted during the star formation process rather than a resultof angular momentum evolution over the 12-15 Myr cluster lifetime. Wespeculate that these differences may reflect the effects of the higheraccretion rates that theory suggests are characteristic of regions thatgive birth to dense clusters, namely, (1) higher initial rotationspeeds; (2) higher initial radii along the stellar birth line, resultingin greater spin-up between the birth line and the ZAMS; and (3) a morepronounced maximum in the birth line radius-mass relationship thatresults in differentially greater spin-up for stars that become mid- tolate-B stars on the ZAMS.
| Kinematical Structure of the Local Interstellar Medium: The Galactic Anticenter Hemisphere
A survey of interstellar Na I D1 and D2 absorption features in thespectra of 104 early-type stars in the second and third Galacticquadrants reveals the large-scale kinematics of the interstellar gaswithin the Galactic anticenter hemisphere at distances from the Sunbetween ~70 and ~250 pc. Employing a technique that uses both the radialvelocities and column densities of the Na I absorptions produced by theintervening gas we have identified the velocity vectors and determinedthe spatial distribution of eight interstellar clouds in the volumeexplored. The average internal H I+H2 densities of the cloudsrange between 0.03 and 1.7 cm-3, and their masses between 80and 104 Msolar, although uncertainties in thesizes of the clouds, their possible extension beyond the regionexplored, and the presence of denser gas embedded in the larger cloudsimply that these will tend to be lower limits. We have clearlyidentified clumps of denser gas immersed in the low-density gas in oneof the clouds; these clumps show internal H I+H2 densities oforder 50 cm-3. Although we are not able to detect anyinterstellar Na I within 70 pc, the sizes of some of the clouds implythat their near edges are within that range of distances from the Sun.With respect to the local standard of rest the clouds move withvelocities between 19 and 54 km s-1. Their velocity vectorsdo not support the view of a local interstellar medium uniquelydominated by expansion from centers in the Scorpio-Centaurus OBassociation; our results suggest that this expansion is present in theGalactic center hemisphere but in the Galactic anticenter hemisphere isrestricted to the immediate neighborhood of the Sun.
| 3D mapping of the dense interstellar gas around the Local Bubble
We present intermediate results from a long-term program of mapping theneutral absorption characteristics of the local interstellar medium,motivated by the availability of accurate and consistent parallaxes fromthe Hipparcos satellite. Equivalent widths of the interstellar NaID-line doublet at 5890 Å are presented for the lines-of-sighttowards some 311 new target stars lying within ~ 350 pc of the Sun.Using these data, together with NaI absorption measurements towards afurther ~ 240 nearby targets published in the literature (for many ofthem, in the directions of molecular clouds), and the ~ 450lines-of-sight already presented by (Sfeir et al. \cite{sfeir99}), weshow 3D absorption maps of the local distribution of neutral gas towards1005 sight-lines with Hipparcos distances as viewed from a variety ofdifferent galactic projections.The data are synthesized by means of two complementary methods, (i) bymapping of iso-equivalent width contours, and (ii) by densitydistribution calculation from the inversion of column-densities, amethod devised by Vergely et al. (\cite{vergely01}). Our present dataconfirms the view that the local cavity is deficient in cold and neutralinterstellar gas. The closest dense and cold gas ``wall'', in the firstquadrant, is at ~ 55-60 pc. There are a few isolated clouds at closerdistance, if the detected absorption is not produced by circumstellarmaterial.The maps reveal narrow or wide ``interstellar tunnels'' which connectthe Local Bubble to surrounding cavities, as predicted by the model ofCox & Smith (1974). In particular, one of these tunnels, defined bystars at 300 to 600 pc from the Sun showing negligible sodiumabsorption, connects the well known CMa void (Gry et al. \cite{gry85}),which is part of the Local Bubble, with the supershell GSH 238+00+09(Heiles \cite{heiles98}). High latitude lines-of-sight with the smallestabsorption are found in two ``chimneys'', whose directions areperpendicular to the Gould belt plane. The maps show that the LocalBubble is ``squeezed'' by surrounding shells in a complicated patternand suggest that its pressure is smaller than in those expandingregions.We discuss the locations of several HI and molecular clouds. Usingcomparisons between NaI and HI or CO velocities, in some cases we areable to improve the constraints on their distances. According to thevelocity criteria, MBM 33-37, MBM 16-18, UT 3-7, and MBM 54-55 arecloser than ~ 100 pc, and MBM 40 is closer than 80 pc. Dense HI cloudsare seen at less than 90 pc and 85 pc in the directions of the MBM 12and MBM 41-43 clouds respectively, but the molecular clouds themselvesmay be far beyond. The above closest molecular clouds are located at theneutral boundary of the Bubble. Only one translucent cloud, G192-67, isclearly embedded within the LB and well isolated.These maps of the distribution of local neutral interstellar NaI gas arealso briefly compared with the distribution of both interstellar dustand neutral HI gas within 300 pc.Tables 1 and 2 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp:cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/411/447
| Rotational Velocities of B Stars
We measured the projected rotational velocities of 1092 northern B starslisted in the Bright Star Catalogue (BSC) and calibrated them againstthe 1975 Slettebak et al. system. We found that the published values ofB dwarfs in the BSC average 27% higher than those standards. Only 0.3%of the stars have rotational velocities in excess of two-thirds of thebreakup velocities, and the mean velocity is only 25% of breakup,implying that impending breakup is not a significant factor in reducingrotational velocities. For the B8-B9.5 III-V stars the bimodaldistribution in V can be explained by a set of slowly rotating Ap starsand a set of rapidly rotating normal stars. For the B0-B5 III-V starsthat include very few peculiar stars, the distributions in V are notbimodal. Are the low rotational velocities of B stars due to theoccurrence of frequent low-mass companions, planets, or disks? Therotational velocities of giants originating from late B dwarfs areconsistent with their conservation of angular momentum in shells.However, we are puzzled by why the giants that originate from the earlyB dwarfs, despite having 3 times greater radii, have nearly the samerotational velocities. We find that all B-type primaries in binarieswith periods less than 2.4 days have synchronized rotational and orbitalmotions; those with periods between 2.4 and 5.0 days are rotating withina factor 2 of synchronization or are ``nearly synchronized.'' Thecorresponding period ranges for A-type stars are 4.9 and 10.5 days, ortwice as large. We found that the rotational velocities of the primariesare synchronized earlier than their orbits are circularized. The maximumorbital period for circularized B binaries is 1.5 days and for Abinaries is 2.5 days. For stars of various ages from 107.5 to1010.2 yr the maximum circularized periods are a smoothexponential function of age.
| Multiperiodicities from the Hipparcos epoch photometry and possible pulsation in early A-type stars
A selection criterion based on the relative strength of the largestpeaks in the amplitude spectra, and an information criterion are used incombination to search for multiperiodicities in Hipparcos epochphotometry. The method is applied to all stars which have beenclassified as variable in the Hipparcos catalogue: periodic, unsolvedand microvariables. Results are assessed critically: although there aremany problems arising from aliasing, there are also a number ofinteresting frequency combinations which deserve further investigation.One such result is the possible occurrence of multiple periods of theorder of a day in a few early A-type stars. The Hipparcos catalogue alsocontains a number of these stars with single periodicities: such starswith no obvious variability classifications are listed, and informationabout their properties (e.g., radial velocity variations) discussed.These stars may constitute a new class of pulsators.
| On the Variability of Late B III-V Stars
We investigate the Hipparcos Satellite photometry of luminosity classIII-V B6-B9 stars. Most are relatively non-variable. Candidates forwhich further study is desirable are identified.
| Two-colour photometry for 9473 components of close Hipparcos double and multiple stars
Using observations obtained with the Tycho instrument of the ESAHipparcos satellite, a two-colour photometry is produced for componentsof more than 7 000 Hipparcos double and multiple stars with angularseparations 0.1 to 2.5 arcsec. We publish 9473 components of 5173systems with separations above 0.3 arcsec. The majority of them did nothave Tycho photometry in the Hipparcos catalogue. The magnitudes arederived in the Tycho B_T and V_T passbands, similar to the Johnsonpassbands. Photometrically resolved components of the binaries withstatistically significant trigonometric parallaxes can be put on an HRdiagram, the majority of them for the first time. Based on observationsmade with the ESA Hipparcos satellite.
| The 74th Special Name-list of Variable Stars
We present the Name-list introducing GCVS names for 3153 variable starsdiscovered by the Hipparcos mission.
| The ROSAT all-sky survey catalogue of optically bright OB-type stars.
For the detailed statistical analysis of the X-ray emission of hot starswe selected all stars of spectral type O and B listed in the Yale BrightStar Catalogue and searched for them in the ROSAT All-Sky Survey. Inthis paper we describe the selection and preparation of the data andpresent a compilation of the derived X-ray data for a complete sample ofbright OB stars.
| 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.
| An Einstein Observatory SAO-based catalog of B-type stars
About 4000 X-ray images obtained with the Einstein Observatory are usedto measure the 0.16-4.0 keV emission from 1545 B-type SAO stars fallingin the about 10 percent of the sky surveyed with the IPC. Seventy-fourdetected X-ray sources with B-type stars are identified, and it isestimated that no more than 15 can be misidentified. Upper limits to theX-ray emission of the remaining stars are presented. In addition tosummarizing the X-ray measurements and giving other relevant opticaldata, the present extensive catalog discusses the reduction process andanalyzes selection effects associated with both SAO catalog completenessand IPC target selection procedures. It is concluded that X-rayemission, at the level of Lx not less than 10 exp 30 ergs/s, is quitecommon in B stars of early spectral types (B0-B3), regardless ofluminosity class, but that emission, at the same level, becomes lesscommon, or nonexistent, in later B-type stars.
| The determination of the parameters of binary star components from data on their UV spectra
A quantitative method for determining the main parameters of binarysystem components, such as their effective temperature and radius ratio,is described. The method is based on the analysis of the total observedspectrum in the UV and visible ranges. The results of the application ofthis method to 14 double systems are presented.
| Micrometer observations of double stars and new pairs. XIII
From a program of double star observations which emphasizes orbital,neglected, and newly discovered pairs, results obtained from October1984 to January 1987 are presented. A total of 3030 visual and 550photographic measures are listed. The positions in WDS format andDurchmusterung numbers are shown for 117 pairs for which firstobservations appear in this paper. Magnitudes are estimated for some ofthe objects.
| The local system of early type stars - Spatial extent and kinematics
Published uvby and H-beta photometric data and proper motions arecompiled and analyzed to characterize the structure and kinematics ofthe bright early-type O-A0 stars in the solar vicinity, with a focus onthe Gould belt. The selection and calibration techniques are explained,and the data are presented in extensive tables and graphs and discussedin detail. The Gould belt stars of age less than 20 Myr are shown togive belt inclination 19 deg to the Galactic plane and node-lineorientation in the direction of Galactic rotation, while the symmetricaldistribution about the Galactic plane and kinematic properties (purecircular differential rotation) of the belt stars over 60 Myr oldresemble those of fainter nonbelt stars of all ages. The unresolveddiscrepancy between the expansion observed in the youngest nearby starsand the predictions of simple models of expansion from a point isattributed to the inhomogeneous distribution of interstellar matter.
| Measurements of binary stars performed at Nice (Second series)
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1984A&AS...57..467M&db_key=AST
| On the behaviour of the lines 2905 SI II and 2932 MG II in the spectra of B-A stars
Using Orion-2 observational data, it is shown that the ratio of theintensities of absorption lines 2905 (2904+2906) Si II and 2932(2928+2936) Mg II varies strongly when moving from B0 stars to A0 stars.It is shown that this phenomenon may be used as a sensitive indicatorfor determining the effective temperature of hot stars.
| Mesures d'etoiles doubles faites a Nice.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1978A&AS...33..275M&db_key=AST
| Is star formation bimodal ? II. The nearest early-type stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1977PASP...89..187E&db_key=AST
| Micrometer observations of double stars.8.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1975ApJS...29..315H&db_key=AST
| Four-color and H beta photometry for the bright B8 and B9 type stars north of declination -10 degre.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1973AJ.....78..738C&db_key=AST
| Absorption, structure et rotation de la Galaxie dans une région de Cassiopée
Not Available
| U, b, v, and Hβ Photometry for the Bright B8- and B9-TYPE Stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1963ApJ...137..530C&db_key=AST
| Étude spectrophotométrique et statistique d'une région obscure dans Cassiopée
Not Available
|
Sottometti un nuovo articolo
Link relazionati
Sottometti un nuovo link
Membro dei seguenti gruppi:
|
Osservazione e dati astrometrici
| Costellazione: | Cassiopea |
| Ascensione retta: | 01h13m09.90s |
| Declinazione: | +61°42'21.0" |
| Magnitudine apparente: | 6.41 |
| Distanza: | 200 parsec |
| Moto proprio RA: | 33.7 |
| Moto proprio Dec: | -1.1 |
| B-T magnitude: | 6.46 |
| V-T magnitude: | 6.496 |
Cataloghi e designazioni:
|
INHABITED SKY
