Contents
Images
Upload your image
DSS Images Other Images
Related articles
A chemical analysis of five hot stars towards the Galactic centre
High resolution echelle spectroscopy is presented for thirteen starslying in the direction of the Galactic centre which, on the basis ofphotographic photometry and low dispersion spectroscopy, have beenclassified as early-B-type. Eight of these stars have large rotationalvelocities which preclude a detailed analysis. The five stars withmoderate to low projected rotational velocities have been analysed usingmodel atmosphere techniques to determine atmospheric parameters andchemical compositions. Two of these stars appear to be evolved bluehorizontal branch objects on the basis of their chemical compositionsand small projected rotational velocity. The evolutionary status of athird is ambiguous but it is probably a post-asymptotic-giant branchstar. The remaining two objects are probably young massive stars andshow enhanced abundances of N, C, Mg and Si, consistent with theirformation in the inner part of the Galactic disk. However their Oabundances are normal, confirming results found previously for otherearly-type stars, which would imply a flat abundance gradient for thiselement in the inner region of our Galaxy.
| Early-type stars in the Galactic halo from the Palomar-Green survey-III. Completion of a magnitude range limited sample
High-resolution (R~ 40000) echelle spectroscopic observations of 13high-latitude early-type stars are presented. These stars comprise thefinal part of a complete magnitude range limited sample based onlow-resolution spectroscopy of targets drawn from the Palomar-Greensurvey. The magnitude range under consideration is 13<=BPG<= 14.6, corresponding to an approximate distancelimit for main-sequence B-type objects of 5 <=d<= 40 kpc. Threestars are found to be apparently normal, young stars, based on theirpositions on the (Teff, log g) diagram, normal abundancepatterns and relatively large projected rotational velocities. A furtherstar, PG 1209+263, was found to belong to the chemically peculiar (CP)silicon star class of objects. The remainder are evolved subluminousstars lying on post-horizontal branch (post-HB) tracks, with theexception of PG 2120+062, which appears to be in a post-asymptotic giantbranch evolutionary stage. For the young stars in the sample, we havederived distance and age estimates through comparison of the atmosphericparameters with recent theoretical evolutionary models. We discussformation scenarios by comparing times-of-flight and evolutionarytime-scales. It is found that all stars could have formed in theGalactic disc and been ejected from there soon after their birth, withthe exception of PG 1209+263. The adopted proper motion is found to be acrucial factor in the kinematical analysis. We also present some numberdensities for young B-type halo stars, which indicate that they areextremely scarce objects.
| Rotation Velocities of Red and Blue Field Horizontal-Branch Stars
We present measurements of the projected stellar rotation velocities(vsini) of a sample of 45 candidate field horizontal-branch (HB) starsspanning a wide range of effective temperatures, from red HB stars withTeff~=5000K to blue HB stars with Teff of 17,000K.Among the cooler blue HB stars (Teff=7500-11500 K), weconfirm prior studies showing that, although a majority of stars rotateat vsini<15kms-1, there exists a subset of ``fastrotators'' with vsini as high as 30-35 km s-1. All but one ofthe red HB stars in our sample have vsini<10kms-1, and noanalogous rotation bimodality is evident. We also identify anarrow-lined hot star (Teff~=16,000K) with enhancedphotospheric metal abundances and helium depletion, similar to theabundance patterns found among hot BHB stars in globular clusters, andfour other stars that may also belong in this category. We discussdetails of the spectral line fitting procedure that we use to deducevsini and explore how measurements of field HB star rotation may shedlight on the issue of HB star rotation in globular clusters.
| Metallicities of the SPB stars from the IUE ultraviolet spectra
We derived the stellar parameters (angular diameters, effectivetemperatures, metallicities) and interstellar reddenings for 20 SPB and34 reference stars observed during the IUE satellite mission. Theparameters were derived by means of an algorithmic procedure of fittingtheoretical flux distributions to the low-resolution IUE spectra andoptical spectrophotometric observations. Since the metallicity [m/H] hasa special importance for pulsating B type stars, we focused ourattention on that parameter. We found that the mean value of themetallicity of the considered SPB and reference stars amounts to [m/H] ~-0.20. The results only slightly depend on the reduction procedure usedfor the IUE images (NEWSIPS and INES). The metal abundances obtained inthis paper are in accordance with the average value of -0.2 dex forstars in the solar neighborhood recently reported by otherinvestigators.Tables 3-7 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/404/689
| A peculiar metal-rich star, HD 135485
Local thermodynamic equilibrium (LTE) absolute and differentialabundances are presented for a peculiar metal-rich B-type star, HD135485. These suggest that HD 135485 has a general enrichment of ~0.5dexin all the metals observed (C, N, O, Ne, Mg, Al, Si, P, S, Cl, Ar, Sc,Ti, Cr, Mn, Fe and Sr), except for nickel. The helium enhancement andhence hydrogen deficiency can account for <=0.2dex of thisenhancement of metals, with the additional enhancement probably beingrepresentative of the progenitor gas. However, some of the metals appearto have greater enhancements, which may have occurred during the star'sevolution. The significantly larger nitrogen abundance coupled with amodest helium enhancement observed in HD 135485 indicates thatcarbon-nitrogen (CN) processed material has possibly contaminated thestellar surface. Neon and carbon enhancements may indicate that heliumcore flashes have also occurred in HD 135485. Some of the iron-groupelements (viz. Mn and Ni) appear to have similar abundance patterns tothat of silicon Ap stars, but it is uncertain how these abundancepatterns formed if they were not present in the progenitor gas. From akinematical investigation it is unclear whether this star formed in ametal-rich region as implied by its chemical composition. From itsposition in the Hertzsprung-Russell diagram, HD 135485 would appear tobe an evolved star lying close to or on the horizontal branch.
| H I Spectra and Column Densities toward HVC and IVC Probes
We show 21 cm line profiles in the direction of stars and extragalacticobjects, lying projected on high- and intermediate-velocity clouds (HVCsand IVCs). About half of these are from new data obtained with theEffelsberg 100 m telescope, about a quarter are extracted from theLeiden-Dwingeloo Survey (LDS), and the remaining quarter were observedwith other single-dish telescopes. H I column densities were determinedfor each HVC/IVC. Paper I of this series uses these in combination withoptical and ultraviolet high-resolution measurements to deriveabundances. Here an analysis is given of the difference and ratio of N(HI) as observed with a 9' versus a 35' beam. For HVCs and IVCs the ratioN(H I-9')/N(H I-35') lies in the range 0.2-2.5. For low-velocity gasthis ratio ranges from 0.75 to 1.3 (the observed ratio is 0.85-1.4, butit appears that the correction for stray radiation is slightly off). Thesmaller range for the low-velocity gas may be caused by confusion in theline of sight, so that a low ratio in one component can be compensatedby a high ratio in another-for 11 low-velocity clouds fitted by onecomponent the distribution of ratios has a larger dispersion. Comparisonwith higher angular resolution data is possible for 16 sight lines.Eight sight lines with H I data at 1'-2' resolution show a range of0.75-1.25 for N(H I-2')/N(H I-9'), while in eight other sight lines N(HI-Lyα)/N(H I-9') ranges from 0.74 to 0.98.
| Distances and Metallicities of High- and Intermediate-Velocity Clouds
A table is presented that summarizes published absorption linemeasurements for the high- and intermediate-velocity clouds (HVCs andIVCs). New values are derived for N(H I) in the direction of observedprobes, in order to arrive at reliable abundances and abundance limits(the H I data are described in Paper II). Distances to stellar probesare revisited and calculated consistently, in order to derive distancebrackets or limits for many of the clouds, taking care to properlyinterpret nondetections. The main conclusions are the following. (1)Absolute abundances have been measured using lines of S II, N I, and OI, with the following resulting values: ~0.1 solar for one HVC (complexC), ~0.3 solar for the Magellanic Stream, ~0.5 solar for a southern IVC,and ~solar for two northern IVCs (the IV Arch and LLIV Arch). Finally,approximate values in the range 0.5-2 solar are found for three moreIVCs. (2) Depletion patterns in IVCs are like those in warm disk or halogas. (3) Most distance limits are based on strong UV lines of C II, SiII, and Mg II, a few on Ca II. Distance limits for major HVCs aregreater than 5 kpc, while distance brackets for several IVCs are in therange 0.5-2 kpc. (4) Mass limits for major IVCs are0.5-8×105 Msolar, but for major HVCs theyare more than 106 Msolar. (5) The Ca II/H I ratiovaries by up to a factor 2-5 within a single cloud, somewhat morebetween clouds. (6) The Na I/H I ratio varies by a factor of more than10 within a cloud, and even more between clouds. Thus, Ca II can beuseful for determining both lower and upper distance limits, but Na Ionly yields upper limits.
| Line identification in the Ca II K spectral region of sharp-lined B-type stars
Previous Ca Ii K observations of the B-type star HD 83206 have revealedputative high-velocity interstellar clouds (HVCs) at Local Standard ofRest (LSR) velocities of -80 and -110 kms-1. Similar resultswere also found for the sightline towards HD 135485. In this article, weshow that these absorption lines are in fact due to stellar S Iifeatures. As the Ca Ii K absorption line in B-type stars is often usedto assess the presence and distance of HVCs, we also present a very highquality spectrum of HD 83206 in the Ca Ii K region ( ~ +/- 4 Å or+/- 300 kms-1), so that in the future confusion betweenstellar lines and HVC features may be avoided.
| Westerbork HI observations of two High-Velocity Clouds
Westerbork HI synthesis observations are presented for the directions ofthe stars 4 Lac and HD 135485. Interstellar absorption lines at highvelocities had been reported in the UV spectrum of 4 Lac, setting anupper limit of 1.2 kpc on the distance of the associated, small HI cloud(Bates et al. 1990, 1991). The Westerbork observations show that thiscloud (l = 100() o, b = - 7() o, v_LSR +100 km s(-1) ), which must havea high velocity relative to the surrounding disk gas, consists of twosmall condensations; the observations provide constraints on their massand density, and indicate that the metallicity of this cloud is close tosolar. For HD 135485, Albert et al. (1993) had found high-velocityabsorption lines in optical spectra, but later reports indicate thatthese lines are probably circumstellar. The Westerbork observationsaround HD 135485 show that the HI found here is part of a larger HVCcomplex, Complex L, described by Wakker & van Woerden (1991). Forboth objects, the Westerbork results are compared with Jodrell Banksingle-dish observations.
| Helium peculiar stars in the red spectral region
Based upon 33 A/mm dispersion spectroscopic material we examine ifequivalent widths of H and He lines can be used for the detection of newhelium-peculiar stars. The answer is affirmative and we present some newcandidates discovered this way. We have also investigated if the use ofdifferent helium lines than those of the (3) D series (4026, 4471)modifies the assignments of helium peculiar stars. This is not the case,since the use of lambda 6678 ((1) D) and lambda 7065 (3S) gives the sameresults. Based on observations obtained at the Haute ProvenceObservatory (CNRS)
| Age variation of helium abundance in He-rich stars.
Not Available
| A catalogue of [Fe/H] determinations: 1996 edition
A fifth Edition of the Catalogue of [Fe/H] determinations is presentedherewith. It contains 5946 determinations for 3247 stars, including 751stars in 84 associations, clusters or galaxies. The literature iscomplete up to December 1995. The 700 bibliographical referencescorrespond to [Fe/H] determinations obtained from high resolutionspectroscopic observations and detailed analyses, most of them carriedout with the help of model-atmospheres. The Catalogue is made up ofthree formatted files: File 1: field stars, File 2: stars in galacticassociations and clusters, and stars in SMC, LMC, M33, File 3: numberedlist of bibliographical references The three files are only available inelectronic form at the Centre de Donnees Stellaires in Strasbourg, viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5), or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| High-Velocity Clouds
High-velocity clouds (HVCs) consist of neutral hydrogen (\HI) atvelocities incompatible with a simple model of differential galacticrotation; in practice one uses {the absolue value of} VLSR {greater orequal to} 90 km/s to define HVCs. This review describes the mainfeatures of the sky and velocity distributions, as well as the availableinformation on cloud properties, small-scale structure, velocitystructure, and observations other than in 21-cm emission. We show thatHVCs contain heavy elements and that the more prominent ones are morethan 2 kpc from the Galactic plane. We evaluate the hypotheses proposedfor their origin and reject those that account for only one or a fewHVCs. At least three different hypotheses are needed: one for theMagellanic Stream and possibly related clouds, one for the Outer ArmExtension, and one (or more) for the other HVCs. We discuss the evidencefor the accretion and the fountain model but cannot rule out either one.
| The Ca+ abundance of HVC complex C
We report the first detection of Ca II H and K absorption in thehigh-velocity cloud complex C, the largest HVC. Absorption is detectedin the spectra of the quasar PG 1351+640 and of the Seyfert galaxy Mark290, at velocities of -163 and -137km/s (see fig.2). The implied Ca+abundances are about 2x10^-8^, or about 0.01 times the total solarCalcium abundance. This values lies near the middle of the range ofvalues found for other HVCs. The measured abundance will allow firmconclusions about the distance of complex C from the presence or absenceof its absoprtion in stellar spectra.
| 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.
| Ultraviolet Observations toward HD 135485: Searching for Evidence of a Proposed High Velocity Cloud
Optical absorption line studies of the star HD 135485 (Albert et al.1993) revealed several distinct absorption components at Ca II (lambda3933 Angstroms) at high velocities (|v|>100 km/s). If these featuresarise from interstellar clouds, similar features should be observable inother species commonly found in the interstellar medium. Ultravioletspectra toward HD 135485 were obtained to confirm the presence of theseabsorption features in other spectral lines. Interestingly, the strongresonance lines of C II (lambda 1335 Angstroms), Si II (lambda 1526Angstroms, lambda 1260 Angstroms), O I (lambda 1302 Angstroms) and Mg II(lambda lambda 2796,2802 Angstroms) do not show evidence for absorptionat the high velocities indicated by the optical data. We conclude thatthe features observed near Ca II (lambda 3933 Angstroms) are notinterstellar. Indeed, the IUE ultraviolet spectra of HD 135485 reveal acomplex pattern of stellar absorption, in keeping with itsclassification as a B5IIp star.
| On the Distance Determination and Ionization of the High-Velocity Clouds
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1994ApJ...423..665F&db_key=AST
| A new list of effective temperatures of chemically peculiar stars. II.
Not Available
| A high-resolution optical and radio study of Milky Way halo gas
Optical interstellar absorption lines of Ti II and Ca II and the 21 cmemission line of H I were observed at high-resolution (6 and 1 km/s,respectively) and high detection sensitivity along 25 lines of sight inthe Galactic halo. The sample includes 16 distant halo stars matchedwith one or more nearly aligned foreground stars as well as local starsalong five extragalactic sight lines. The data show substantialinterstellar material, at both low and intermediate velocities, between250 and 1000 pc beyond the Galactic plane. As much as one-third of thetotal gas observed in Ca II absorption may be beyond 1 kpc, and thegaseous Ti II may lie in an even thicker layer. The directly determinedgaseous Ti abundance above the Galactic plane exceeds that in the disk,on the average, by a factor of 4 to 6 and, for individual cloudcomponents, is further enhanced at higher LSR velocity. Thirty threediscrete high-latitude clouds are detected in Ca II absorption, and 17discrete clouds, including three high-velocity clouds, are identified inH I emission. The kinematics of the high-latitude gas observed in Ti IIand Ca II absorption is characterized by significant peculiar velocitieswith respect to a model corotating halo.
| Photometric and spectroscopic analysis of high Galactic latitude molecular clouds. I - Distances and extinctions of stars toward 25 selected regions
The paper presents new photoelectric photometry in the UBV, uvby, andH-beta systems for 320 stars at high Galactic latitudes, selected fortheir proximity to the densest portions of a variety of high Galacticlatitude atomic and molecular clouds. Low-resolution digital spectra areemployed to classify 115 of the stars. Several novel techniques aredeveloped for automatic digital spectral classification, and fordereddening Stromgren uvby-beta and Johnson UBV,H-beta photometry. Anempirical determination of the errors in the derived dereddened colors,and techniques for converting between the two photometric systems arepresented on the basis of the analysis of a statistically significantsample of 1480 stars with complete data sets in both photometric systemsand with an accurate MK spectral type. New constraints on the distancesto several clouds are presented.
| A catalogue of Fe/H determinations - 1991 edition
A revised version of the catalog of Fe/H determinations published by G.Cayrel et al. (1985) is presented. The catalog contains 3252 Fe/Hdeterminations for 1676 stars. The literature is complete up to December1990. The catalog includes only Fe/H determinations obtained from highresolution spectroscopic observations based on detailed spectroscopicanalyses, most of them carried out with model atmospheres. The catalogcontains a good number of Fe/H determinations for stars from open andglobular clusters and for some supergiants in the Magellanic Clouds.
| Mid-ultraviolet and optical photometry of helium stars
Mid-ultraviolet and optical photometric analysis of helium stars arepresented. A linear relation exists between the effective temperaturederived from model atmospheres and (1965-V)0 index. The effectivetemperatures derived from (1965-V)0 index are somewhat higher than thatof MK spectral type estimates especially for late B-type helium objects.
| Some Non-Variable Stars
Not Available
| IUE-IRAS studies of the infrared cirrus
The 60 and 100 micron cirrus emission around 256 lines of sight in theIRAS all-sky survey was measured, and the flux averages were used tostudy the distribution, variations, and correlations of the IRASinfrared cirrus fluxes with various interstellar parameters. It wasfound that the 60 and 100 micron fluxes correlate with the depletion ofSi and show a trend with the depletion of Fe for 51 lines of sighttoward the Galactic halo. No correlation was found with the abundancesof Si, Mn, Fe, S, or Zn or with abundance ratios for the full sample of256 stars. An abundance ratio of about 3 x 10 to the 7th by numberrelative to H was derived from 60 and 100 micron flux ratios and the Hcolumn along the line of sight; this ratio appears to decrease by afactor of 10 into the halo.
| Beta Cephei pulsation and the helium-strong stars
Six He-strong stars are identified which may be good candidates insearches for Beta Cephei pulsation based on their location in a plot ofbeta vs (u-b). The significance of detection of pulsational variabilityamong the He-peculiar stars in the study of excitation mechanisms forBeta Cephei stars is discussed.
| Galactic interstellar abundance surveys with IUE. III - Silicon, manganese, iron, sulfur, and zinc
This paper continues a survey of intestellar densities, abundances, andcloud structure in the Galaxy using the IUE satellite. A statisticaldata set of 223 O3-B2.5 stars is constructed, including 53 stars in theGalactic halo. It is found that S II lines in B stars, of luminosityclasses IV and V, have possible contamination from stellar S II,particular for stars with v sin i less than 200 km/s. The meanlogarithmic depletions are -1.00, -1.19. -0.63, and -0.23 (Si, Mn,Fe,S,Zn). Depletions of Si, Mn, and Fe correlate with the mean hydrogendensity n-bar along the line of sight, with a turnover for n-bar greaterthan 1/cm. Sulfur depletions correlate with n-bar along the line ofsight. The slight Zn depletion correlation also appears to bestatistically insignificant. No correlation of depletion is found withthe physical density derived from H2 rotational states in 21 lines ofsight. Depletion variations in the disk are consistent with a Galacticabundance gradient or with enhanced mean depletions in the anticenterregion.
| Galactic interstellar abundance surveys with IUE. II - The equivalent widths and column densities
This paper continues a survey of interstellar densities, abundances, andcloud structure in the Galaxy, using the International UltravioletExplorer (IUE) satellite. Equivalent widths of 18 ultraviolet resonancetransitions are presented and column densities for Si II, Mn II, Fe II,S II, and Zn II toward 261 early-type stars are derived. Theseequivalent widths and column densities agree within the stated errors ofearlier Copernicus, BUSS, or IUE surveys of Mn II, Fe II, S II, and ZnII for 45 stars in common. The column densities are derived fromsingle-component curves of growth with a common b-value based on that ofFe II and Si II.
| The ultraviolet gallium stars
On the basis of IUE low dispersion spectra, a group of UV peculiar starsin the range of middle and late B-type stars, characterized by strong GaII 1414 A line is defined. This group has no counterpart in the optical3600-4800 A range.
| The extent of the local H I halo
Forty-five high-latitude, OB stars have been observed in the Ly alphaand 21 cm lines of HI in an effort to map out the vertical distributionand extent of the local HI halo. The 25 stars for which a reliable HIcolumn density can be obtained from Ly alpha lie between 60 and 3100 pcfrom the plane. The principal result is that the total column density ofHI at an absolute value of z greater than 1 kpc is, on the average, 5 +or - 3 x 10 to the 19th power/sq cm, or 15 percent of thetotalHI. At relatively low z the data toward some starssuggest a low effective scale height and fairly high average foregrounddensity, while toward others the effective scale height is large and theaverage density is low. This can be understood as the result ofirregularities in the interstellar medium. A model with half of the HImass in clouds having radii of a few pc and a Gaussian verticaldistribution with sigma2 = 135 pc, and half of the mass in anexponential component with a scale height of 500 pc, gives asatisfactory fit to the data. The technique of comparing Ly alpha and 21cm column densities is also used to discuss the problem of estimatingthe distance to several possibly subluminous stars.
| On optical studies of high-velocity clouds
Lists of distant objects that can be used to study physical conditionsin, and distances of, 21 cm (Oort) high-velocity clouds are presented.Recent published observations are used to compile positions, velocities,and distances of the clouds.
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
| Constellation: | Ζυγός |
| Right ascension: | 15h15m45.26s |
| Declination: | -14°41'34.5" |
| Apparent magnitude: | 8.139 |
| Distance: | 181.159 parsecs |
| Proper motion RA: | -1.6 |
| Proper motion Dec: | -35.1 |
| B-T magnitude: | 8.047 |
| V-T magnitude: | 8.132 |
Catalogs and designations:
|
