Tartalom
Képek
Kép feltöltése
DSS Images Other Images
Kapcsolódó cikkek
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.
| Are Stellar Rotational Axes Distributed Randomly?
Stellar line widths yield values of Vsini, but the equatorial rotationalvelocities, V, cannot be determined for individual stars withoutknowledge of their inclinations, i, relative to the lines of sight. Forlarge numbers of stars we usually assume random orientations ofrotational axes to derive mean values of V, but we wonder whether thatassumption is valid. Individual inclinations can be derived only inspecial cases, such as for eclipsing binaries where they are close to90° or for chromospherically active late-type dwarfs or spotted(e.g., Ap) stars where we have independent information about therotational periods. We consider recent data on 102 Ap stars for whichCatalano & Renson compiled rotational periods from the literatureand Abt & Morrell (primarily) obtained measures of Vsini. We findthat the rotational axes are oriented randomly within the measuringerrors. We searched for possible dependence of the inclinations onGalactic latitude or longitude, and found no dependence.
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
| Research Note Hipparcos photometry: The least variable stars
The data known as the Hipparcos Photometry obtained with the Hipparcossatellite have been investigated to find those stars which are leastvariable. Such stars are excellent candidates to serve as standards forphotometric systems. Their spectral types suggest in which parts of theHR diagrams stars are most constant. In some cases these values stronglyindicate that previous ground based studies claiming photometricvariability are incorrect or that the level of stellar activity haschanged. Table 2 is 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/367/297
| 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.
| Absolute declinations with the photoelectric astrolabe at Calern Observatory (OCA)
A regular observational programme with a photoelectric astrolabe havebeen performed at ``Observatoire du Calern" (Observatoire de laCôte d'Azur, OCA, phi = +43() o44′55.011″; lambda =-0() h27() m42.44() s, Calern, Caussols, France) for the last twentyyears. It has been almost fully automatized between 1984 and 1987. Since1988 the photoelectric astrolabe was used without any modification. Inaddition to determining the daily orientation of the local vertical, theyearly analysis of the residuals permits to derive corrections to theused star catalogue \cite[(Vigouroux et al. 1992)]{vig92}. A globalreduction method was applied for the ASPHO observations. The new form ofthe equations \cite[(Martin & Leister 1997)]{mar97} give us thepossibility of using the entire set of the observing program using datataken at two zenith distances (30() o and 45() o). The program containsabout 41648 stars' transits of 269 different stars taken at``Observatoire du Calern" (OCA). The reduction was based on theHIPPARCOS system. We discuss the possibility of computing absolutedeclinations through stars belonging simultaneously to the 30() o and45() o zenith distances programmes. The absolute declination correctionswere determined for 185 stars with precision of 0.027arcsec and thevalue of the determined equator correction is -0.018arcsec +/-0.005arcsec . The instrumental effects were also determined. The meanepoch is 1995.29. Catalogue only available at CDS in electronic from viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| On the HIPPARCOS photometry of chemically peculiar B, A, and F stars
The Hipparcos photometry of the Chemically Peculiar main sequence B, A,and F stars is examined for variability. Some non-magnetic CP stars,Mercury-Manganese and metallic-line stars, which according to canonicalwisdom should not be variable, may be variable and are identified forfurther study. Some potentially important magnetic CP stars are noted.Tables 1, 2, and 3 are available only in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| The observed periods of AP and BP stars
A catalogue of all the periods up to now proposed for the variations ofCP2, CP3, and CP4 stars is presented. The main identifiers (HD and HR),the proper name, the variable-star name, and the spectral type andpeculiarity are given for each star as far as the coordinates at 2000.0and the visual magnitude. The nature of the observed variations (light,spectrum, magnetic field, etc.) is presented in a codified way. Thecatalogue is arranged in three tables: the bulk of the data, i.e. thosereferring to CP2, CP3, and CP4 stars, are given in Table 1, while thedata concerning He-strong stars are given in Table 2 and those foreclipsing or ellipsoidal variables are collected in Table 3. Notes arealso provided at the end of each table, mainly about duplicities. Thecatalogue contains data on 364 CP stars and is updated to 1996, October31. This research has made use of the SIMBAD database, operated at CDS,Strasbourg, France.
| Do SI stars undergo any rotational braking?
The old question of rotational braking of Ap Si stars is revisited onthe empirical side, taking advantage of the recent Hipparcos results.Field stars with various evolutionary states are considered, and it isshown that the loose correlation between their rotational period andtheir surface gravity is entirely compatible with conservation ofangular momentum. No evidence is found for any loss of angular momentumon the Main Sequence, which confirms earlier results based on lessreliable estimates of surface gravity. The importance of reliable,fundamental T_eff determinations of Bp and Ap stars is emphasized. Basedon data from the ESA Hipparcos satellite
| 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.
| A new list of effective temperatures of chemically peculiar stars. II.
Not Available
| Catalogue of CP stars with references to short time scale variability
A catalogue was compiled which contains all references in the literaturesince 1962 related to variations of CP stars on time scales shorter thanthe rotation period. The role of this catalogue lies in the unbiasedlisting of all available references, and not in a critical evaluation.
| Third supplement to the catalogue of observed periods of AP stars
New data on the periods of Ap stars with references are presented.Twelve further stars are introduced for which a periodic variability hasrecently been discovered or not reported in previous issues of thiscatalog. For many stars also present in previous issues of the catalognew determinations of the periods are given. Recently attributedvariable star names are also quoted.
| The correction in right ascension of 508 stars determinated with PMO photoelectric transit instrument.
Not Available
| On the origin of the statistical correlation between rotation periods and apparent radii for CP 2 stars
Apparent rotational velocities and rotation periods for CP 2 stars areused to study the 'apparent' radius distribution of R sin i. It impliesa distribution for the radii of CP 2 stars which is almost normal fortheir temperatures when compared to main sequence stars. However, astatistical correlation exists between rotation period P and R sin i. Itis argued that, at least in the case of silicon stars, neitherconservation of angular momentum on the main sequence, nor bias in themeasured v sin i values are able to induce a correlation of the observedstrength. Thus, one has to postulate either additional rotationalbraking depending statistically on R, or a detection bias dependingstatistically on i. It is shown that the correlation might be explainedin both ways and the implications of each possibility are discussed.
| The new helium-weak star HR 446
The CP star HR 446 (HD 9531, B8p V, m = 5.69) is one of the CP starswith no definitely assigned peculiarity type. It is shown by applicationof synthetic spectra that the star in a helium-weak type of thetitanium-strontium subgroup. Photometric observations confirmed therotational period of 0.6684 d discovered earlier. The presentphotometric observations do not indicate rapid variability exceeding0.005 mag within the limits of 5-300 min.
| 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.
| The Chemically Peculiar Star W-Ursae - Part One - Identification of Spectral Lines
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1985CoSka..13....9H&db_key=AST
| 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.
| Evidence of decay of the magnetic fields of AP stars
Data obtained in the Geneva photometric system (Rufener, 1981) andappropriate calibrations of this system in terms of surface magneticfield and gravity are used to provide, on the basis of 708 field andcluster Ap stars, observational evidence that these stars undergo decayof their magnetic field on an evolutionary timescale. Justifications aregiven for the application of a photometric gravity calibration topeculiar stars. The dependence of the photometrically estimated surfacemagnetic field on gravity is found to differ markedly from availabletheoretical calculations. HgMn stars are found to show the same trend,strengthening the impression that they might be slightly magnetic.He-weak stars do not.
| The rotation of AP stars
Photometric periods of silicon stars belonging to clusters andassociations as well as to the field are discussed in relation withtheories of magnetic braking taking place on the main sequence. It isshown that Si stars do not lose the bulk of their angular momentumduring their main-sequence lifetime, but must have lost it before. Anybraking mechanism which predicts an e-folding time of the order of, orshorter than, the star's lifetime seems ruled out. The theory of purelyhydromagnetic rotational braking is much too efficient to fit theobservations (unless under its earlier form proposed by Kulsrud, 1971),while the accretion theory does not fit them either, although it seemsmore realistic. Preinjection of cosmic rays by means of Ap stars appearsdoubtful.
| Variable stars in the General Catalogue of Trigonometric Parallaxes
Not Available
| Refined Data for Parallax Stars
Not Available
| Apparent radii and other parameters for 416 B5 V-F5 V stars of the catalogue of the Geneva Observatory
Apparent radius, visual brightness, effective temperature and absoluteradius for 416 B5 v-F5 v stars of the catalogue of the GenevaObservatory (Rufener, 1976) have been determined. Twenty-eight stars,anomalous in log a" versus (m~)o diagrams, have been singled out. A goodcorrelation for seven stars, in common with the list of Hanbury Brown etal. (1974), has been found. Similar parameters determined for 279 B5v-F5 v stars of two preceding papers (Fracassini et al., 1973, 1975)have allowed us to determine the averaged diagrams , and versus (B -V)0 for 695 B5 v-F5 v stars. Moreover, in the present paper a goodcorrelation versus and carefulrelation = -7.40 + 3.31 for B5v-F5 V stars have been determined. Plain correlations between log R/R0and blanketing parameter m2 for some spectral types seem to point outthat there are real differences in the absolute radii of stars of thesame spectral type, in agreement with recent researches on the HRdiagram (Houck and Fesen, 1978). Systematic differences between double(spectroscopic and visual) and single stars are found. In particular,the averaged relation versus shows that A2v-F5 v double stars may have a higher metallicity index m2 and smallerabsolute radii than single stars. Finally, the diagram log v sin iversus log R/R0 confirms some properties of binary systems found byother researchers (Huang, 1966; Plavec, 1970; Levato, 1974; Kitamura andKondo, 1978)
| Spectral classification from the ultraviolet line features of S2/68 spectra. V - Supplement series
The paper presents the ultraviolet classification of more than 450 B-Aand F spectra obtained with the sky survey telescope mounted on the TD1satellite. Concerning abnormal objects, attention is given to the Bestars, the binary stars, the helium weak stars, and the lambda Booobjects. With regard to Be stars, it is concluded that the 1930 Awavelength feature is linked to the existence of either shell structuresor Fe II emission lines in the visual spectral range. In addition, it issuggested that stellar spectra at wavelengths of 1410, 1610-20 and 2400A are equivalent to the He-weak group in the classical range.
| Late B-type stars - Rotation and the incidence of HgMn stars
High-dispersion spectrograms for an unbiased sample of 256 late B-typestars are examined in an attempt to determine whether slow rotation isnecessary and sufficient for the appearance of HgMn anomalies innonmagnetic stars. The peculiar stars in the sample are identified,values of v sin i are derived for all the stars observed, and theradial-velocity variations of the identified HgMn stars are analyzed.The distribution of rotational velocities for late B-type stars isobtained, and the role of rotation in producing extended envelopes isevaluated. The binary frequency and mass-ratio distribution are derivedfor systems containing HgMn components, the effect of duplicity on thedistribution of rotational velocities is estimated, and the role of suchfactors as rotation, age, and binary characteristics in determiningwhether HgMn anomalies are present is investigated. The results clearlyshow that HgMn stars occur only within a limited temperature range, thatall such stars rotate slowly, but that rotation, effective temperature,age, surface gravity, and binary properties do not serve to determinewhether a star will exhibit abundance anomalies.
| Duplicity of late B-type stars
High-dispersion spectroscopic observations of 83 stars are used todetermine the binary characteristics of late B-type stars. For a randomsample of such objects, including peculiar as well as normal stars, thefrequency of binaries with mass ratios m2/m sub 1 greaterthan 0.1 and orbital periods less than 100 days is estimated to be about24%, and the frequency of binaries decreases with decreasingm2/m sub 1. In both respects, the late B-type stars aresimilar to early B-, late A-, and solar-type stars. For the majority ofstars with an orbital period greater than 4 days, the observedrotational velocity exceeds the value that corresponds to synchronism ofrotation and revolution, but the ratio of the observed to thesynchronous rotational velocity seldom exceeds a factor of 2 even forperiods as long as 15 days. An additional 20% of the stars surveyedexhibit low amplitude-velocity variations that, if due to orbitalmotion, correspond to m2 m1 less than 0.1. Themost likely explanation is that these systems are close binary remnantsthat have already passed through the mass-transfer phase, with thepresent secondary being a white dwarf.
|
Új cikk hozzáadása
Kapcsolódó hivatkozások
- - (nincs kapcsolódó hivatkozás) -
Új link hozzáadása
Besorolás csoportokba:
|
Pozíciós és asztrometriai adatok
| Csillagkép: | Androméda |
| Rektaszcenzió: | 01h34m16.60s |
| Deklináció: | +37°14'14.0" |
| Vizuális fényesség: | 5.88 |
| Távolság: | 120.192 parszek |
| RA sajátmozgás: | 14 |
| Dec sajátmozgás: | -17.3 |
| B-T magnitude: | 5.807 |
| V-T magnitude: | 5.881 |
Katalógusok és elnevezések:
|
