Садржај
Слике
Уплоадјуј своје слике
DSS Images Other Images
Везани чланци
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.
| Chemical composition of the magnetic B star HR 5049
A spectrum synthesis analysis for photospheric lines in the magnetic Bstar HR 5049 is presented, based on a high quality spectrogram obtainedwith the EMMI spectrograph attached to the NTT at ESO. It is found thatlight elements such as He, C and O are under-abundant. One of the mostnotable features is the deficiency of He by more than -2.0 dex. Co andCl are over-abundant by +3.5 dex and +1.9 dex, respectively. Other ironpeak elements are over-abundant ranging from +0.47 dex (Ti II) to +1.94dex (Cr I). For rare earth elements, the lines of once-ionized speciesare generally weak, while the third spectra (especially those of Pr andNd) are very prominent. Although rare earth elements show significantover-abundances ranging from +3.0 dex to as large as +4.0 dex, Ba hasthe solar abundance. The Nd-Pr abundance difference, which shows anapparent decreasing trend with increasing effective temperature among CPstars, is found to be unusually small in HR 5049.Based on observations collected at the La Silla Observatory, ESO (Chile)with the New Technology Telescope (NTT).The full 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/420/673
| The 77th Name-List of Variable Stars
We present the next regular Name-List of variable stars containinginformation on 1152 variable stars recently designated in the system ofthe General Catalogue ofVariable Stars. New designations are alsointroduced for two ``old'' variables whose corrected coordinates bringthem to other constellations.
| Catalogue of averaged stellar effective magnetic fields. I. Chemically peculiar A and B type stars
This paper presents the catalogue and the method of determination ofaveraged quadratic effective magnetic fields < B_e > for 596 mainsequence and giant stars. The catalogue is based on measurements of thestellar effective (or mean longitudinal) magnetic field strengths B_e,which were compiled from the existing literature.We analysed the properties of 352 chemically peculiar A and B stars inthe catalogue, including Am, ApSi, He-weak, He-rich, HgMn, ApSrCrEu, andall ApSr type stars. We have found that the number distribution of allchemically peculiar (CP) stars vs. averaged magnetic field strength isdescribed by a decreasing exponential function. Relations of this typehold also for stars of all the analysed subclasses of chemicalpeculiarity. The exponential form of the above distribution function canbreak down below about 100 G, the latter value representingapproximately the resolution of our analysis for A type stars.Table A.1 and its references are only available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/407/631 and Tables 3 to 9are only available in electronic form at http://www.edpsciences.org
| On the Periods of the Magnetic CP Stars
An HR diagram annotated to show several ranges of photometericallydetermined periods has been constructed for the magnetic CP stars whoseperiods have been determined by the author and his collaborators. Thedistribution of periods reflects both the initial conditions as well asthe subsequent stellar histories. Since the stellar magnetic field doesnot penetrate the convective core, eventually a shear zone near thecore-radiative envelope boundary may develop which produces turbulenceand modifies the field. Many, but not all, of the most rapidly rotatingmCP stars are close to the ZAMS and some of the least rapidly rotatingmCP stars are the furthest from the ZAMS.
| 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.
| Measurements of stellar magnetic fields using synthetic spectrum fitting
A sample of Ap and Bp stars have been investigated with respect to theirsurface magnetic field using synthetic spectrum fitting. The advantageof this technique is the simplicity in determining the surface fieldstrength and the possibility to apply it to objects whose spectrum doesnot display resolved Zeeman components. We show the usefulness of themethod by demonstrations on stellar spectra with resolved Zeemancomponents, where the results have been compared with values based onmeasurements of the Zeeman splitting for the magnetically sensitive FeIi lambda 6149 line. The objects HD 192678 andHD 165474 have been observed over their rotationalperiod to investigate magnetic field variations. The analysis is thenextended to objects where no resolved structure is observed. The rapidlyrotating stars HD 22316 and HD10783 are used as examples where this method is useful toachieve a value of the surface field. The relative intensification ofthe Fe Ii lambda lambda 6147, 6149 lines is investigated in an attemptto understand its relation to the surface magnetic field strength forthe stars HD 22316 and HD 10783. Based on observations obtained with theNordic Optical Telescope, operated on the island of La Palma jointly byDenmark, Finland, Iceland, Norway, and Sweden, in the SpanishObservatorio del Roque de los Muchachos of the Instituto de Astrofisicade Canarias.
| 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
| A spectroscopic study of the magnetic CP-star HR 1094
The chemically peculiar star HR 1094 has beeninvestigated with respect to its chemical composition and the magneticinfluence on its stellar spectrum. By using spectral lines slightlyaffected by the field v sin i was determined to be <= 17 kms-1. The iron-group elements as well as chlorine and theheavy elements platinum, gold and mercury show an overabundance comparedto the sun. The analysis also revealed the rare earth elements to bepresent from lines of their second and third spectrum. Based onobservations obtained with the Nordic Optical Telescope, operated on theisland of La Palma jointly by Denmark, Finland, Iceland, Norway, andSweden, in the Spanish Observatorio del Roque de los Muchachos of theInstituto de Astrofísica de Canarias.
| On the cobalt abundances of early-type stars
Photographic region high-dispersion high signal-to-noise spectra of Aand F main sequence band stars which exhibit modest rotation show Co Ilines. In the hottest of these stars, we also found weak Co II lineswhose abundances are consistent with those from Co I lines. As a classthe Am stars have cobalt abundances which are greater than solar whilethe normal stars have solar values.
| UVBY photometry of the chemically peculiar stars HD 15980, HR 1094, 33 Gem, and HD 115708
Differential Strömgren uvby photometry obtained with the FourCollege Automated Photoelectric Telescope shows that the hot HgMn star33 Gem is photometrically constant. The Si star HD 15980 is found to bea variable whose period is significantly greater than 2 years. Theunusual magnetic chemically peculiar Co star HR 1094 is discovered to bea low amplitude photometric variable with the magnetic field period ofHill & Blake, 2.9761 days. The ephemeris for the magnetic chemicallypeculiar star HD 115708 of Wade et al. is confirmed with the error inits period of 5.07622 days being greatly reduced. The {u}, {v}, {b}, and{y} light curves for both HR 1094 and HD 115708 exhibit differenceswhich indicate complex elemental photospheric abundance distributions.Tables 3-6 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/Abstract.html
| Spectroscopic Analysis of the Cobalt Peculiar Star HR 5049 in the Red Spectral Region
A detailed LTE analysis of metallic lines in the red spectral region(between lambda 5700 Angstroms and lambda 6700 Angstroms) was carriedout for the B-type peculiar star HR 5049. The abundances of 5 elementsfrom 8 ions were determined. This star exhibits unusually strong linesof Co I and Co II, and this element is found to be overabundant by asmuch as 4.0 dex compared to the solar abundance. Weak Cl I lines havebeen detected in the observed region, and Cl was estimated to beoverabundant by 3.0 dex. The abundances of Si, Cr, and Fe are alsostrongly enhanced. Although lines of Pr III were found to vary with thephase in the rotation period of the star, other elements were found notto vary. From its observed abundance-pattern, HR 5049 is suggested to bea member of a rare group of CP stars which are characterized byenhancements of chlorine and cobalt, as in HR 1094.
| 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.
| Abundance analysis of roAp stars. II. HD 203932
A new tool to simplify abundance analyses which is based on stand-aloneprograms has been applied to the rapidly oscillating Ap star HD 203932(BI Mic, CD -30 18600, SAO 212996; Ap(SrEu), V=8.82mag). Thespectroscopically determined T_eff_=7450+/-100K and logg=4.3+/-0.15 putthis star close to the ZAMS. Other fundamental atmospheric parametersare v_micro_<0.6km/s and the total abundance of all iron peakelements [M/H]=0.0+/-0.1. The fundamental parameters put HD 203932 in aregion of the HR-diagram where convection starts becoming efficient andthe standard mixing length theory models lead to severe problems in thedetermination of the atmospheric parameters. The difference between theupper limit for logg obtained from several variants of the mixing lengththeory and the Canuto-Mazzitelli model indicates that the choice of aparticular convection model can influence the determination of basicstellar parameters. For the first time abundances were determined for HD203932 showing a pattern for the 35 investigated elements which issimilar to α Cir (Kupka et al. 1996A&A...308..886K, Paper I).Fe and Ni have about solar abundance, Cr and especially Co are clearlyoverabundant as well as rare earth elements. The most underabundantelement is Sc, followed by C, N, and O, which is a common property ofCP2 stars. The lack of a correlation in our data between individual lineabundances and their effective Lande factors implies a mean magneticfield modulus not exceeding few kG. Compared to the last homogeneousspectroscopic investigation of a large sample of chemically peculiarstars (21 cool Ap stars, Adelman 1973ApJ...183...95A), our analysis isbased on data with higher spectral resolution and signal-to-noise ratio.Even more important, we are using a much larger atomic line data basewith more precise atomic parameters than available more than twentyyears ago.
| Is HR 1094 an AP star?
Photoelectric magnetic field measurements of the star HR 1094 revealthat it possesses a fairly strong magnetic field. The effectivelongitudinal field varies between -2200 and 600 gauss. Until now, it wasnot known whether this star was an Ap star that possessed some HgMn-likeabundance anomalies or vice versa. The presence of a magnetic fieldclearly indicates that it is a magnetic Ap star.
| Interstellar Extinction in the Camelopardalis Dark Clouds
An area of about 3times 3 deg in the direction of the Camelopardalisdark clouds is investigated using the Vilnius photometric system.Magnitudes V, color indices, spectral classes, absolute magnitudes,color excesses, interstellar extinctions and distances are determinedfor 126 stars. The interstellar extinction begins at 100 pc distance. Itgrows monotonically and reaches about 2 mag at 300 pc.
| 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
| A chlorine-cobalt peculiar star HR 1094
The abundances of 11 elements and the upper limits of three otherelements in a peculiar B-type star, HR 1094, have been determined. Thisstar exhibits unusually strong lines of Cl II and Co II. These elementswere found to be overabundant by 3.8 dex and 3.3 dex, respectively. Theabundances of Ti, Cr, Fe, Sr, Pt, and Hg are enhanced while those of Scand Ni are not. Several light metals, Mg, Si, and Ca, were found to beunderabundant. The abundance pattern found in HR 1094 is quite uniqueamong B-type CP stars, showing the composite abundance characteristicsof both Hg-Mn stars and magnetic stars.
| An analysis of the ultraviolet spectrum of HD 101065 by line coincidence statistics
Element identifications in the long wavelength IUE spectrum of HD 101065(Przybylski's star) using wavelength coincidence statistics arereported. The definite presence of the common iron-peak elements, inaddition to numerous doubly ionized rare-earth species, is confirmed.Radial velocity sweeps yield no strong evidence of segregation betweenthe iron-peak and lanthanide rare-earth elements. Evidence to supportthe identification of Co I and Co II is also presented. The similaritybetween HD 101065 and several hot, magnetic Ap stars which also exhibitan unusually strong presence of cobalt relative to iron is noted.
| 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.
| Radial velocities of northern Mercury stars
About 200 radial velocities of 96 bright northern Hg-Mn or candidateHg-Mn stars are presented. Past and present data have been reexaminedfor periodic variability in cases that were neither previously known tobe binaries with well determined orbits nor were considered to haveconstant velocity. One definite new orbit was found (that of HR 3361)and several possible orbital solutions are given.
| Photometric properties of AP stars in the Geneva system
An examination of the properties in some photometric diagrams of morethan 600 Ap stars measured in the Geneva photometric system confirm thatthe Balmer discontinuity is smaller than for normal stars, along withthe link between a proposed peculiarity parameter and both rotationalvelocity and effective magnetic field. It is shown that the peculiarityparameter is sensitive to interstellar reddening, and it is foundthrough examination of the standard deviations for visual magnitudesthat cool CP 2 stars without Eu peculiarity have the greatestamplitudes. Rapid rotators have a mild peculiarity, while positivecorrelation exists for Si and SrCr stars.
| Stellar abundances from line statistics
The method of linear statistical modeling has been combined with arudimentary model of stellar photospheres to obtain abundance estimatesfor a large member of normal and peculiar upper-main-sequence stars. Theadopted standard abundances, obtained from published fine analyses, canbe fitted by the algorithms with about 0.5 dex as the standarddeviation. A major advantage of the technique introduced here, based onwavelength coincidences, is that the statistical presence ofintrinsically faint stellar lines plays a key role. This can minimizesystematic errors due to curve-of-growth-saturation effects. Errors dueto misidentified features are also minimized. In spite of theseadvantages, the present method is advocated as an ancillary tool foruse, ultimately, in the improvement of results obtained by moretraditional methods. Abundances, rounded to the nearest 0.5 dex, arereported for Cr, Mn, Fe, and Y. The largest ranges of abundances arefound for chromium and yttrium. A remarkable constancy has been foundfor iron.
| Cobalt in the southern magnetic AP star HR 5049
The spectrum of the bright southern magnetic Ap star HR 5049 from 3300 Ato 4800 A is dominated by strong lines of the singly ionized metals TiII, Cr II, Fe II, and extraordinarily strong Co II. Both Si II and Sr IIare rather weak, and rare earths are not definitely identified. Theestimated stellar abundance of cobalt is of the order of 1000 times thesolar value. Many strong unidentified lines may be Co II lines not yetobserved in the laboratory. Previous classifications disagree with oneanother, which suggests the possibility of spectrum variability.
| A spectrophotometric survey of stars along the Milky Way. IV
In the present paper a catalogue of spectrophotometric quantities,spectral types, monochromatic magnitudes and colour equivalents is givenfor all stars brighter than the magnitude m4400 = 10.5 in aregion of the Milky Way in Perseus. No absorption is found for starscloser than about r = 100 pc. The absorbing clouds are situated atdistances closer than 1 kpc and at about 2.5 kpc in the local arm andthe Perseus arm, respectively. The space between the two arms is freefrom absorption. It is also concluded that the Perseus arm continuesbeyond l = 140 deg, containing not only hydrogen gas but also dust to atleast l = 150 deg), while the content of OB stars decreases abruptly atl = 140 deg.
| Photometric parameters for AM and AP stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1978A&A....69..285H&db_key=AST
|
Додај нови чланак
Линкови у сродству са темом
Додај нови линк
Чланови следећих група \:
|
Посматрања и Астрометриски подаци
| Сазвежђа: | Жирафа |
| Ректацензија: | 03h38m19.70s |
| Deклинација: | +56°55'58.0" |
| Apparent магнитуда: | 6.3 |
| Даљина: | 170.94 parsecs |
| Proper motion RA: | 26.7 |
| Proper motion Dec: | -34.2 |
| B-T magnitude: | 6.153 |
| V-T magnitude: | 6.265 |
Каталог и designations:
|
