Оглавление
Изображения
Загрузить ваше изображение
DSS Images Other Images
Публикации по объекту
The Subdwarf Database: Released
The work on the Subdwarf Database, presented at the previous meeting,has been completed, and the tool is now publicly available. The firstrelease contains data from close to 240 different literature sources,but more still awaits entry. The database interface includes advancedsearch capabilities in coordinate, magnitude and color space. Outputtables can be generated in HTML with hyperlinks to automaticallygenerated finding charts, the Aladin viewer and a detailed data sheetthat displays all registered data for each target, including physicaldata such as temperature, gravity and helium abundance, together with afinding chart. Search results can be visualized automatically asinteractive position, magnitude or color diagrams.
| New Estimates of the Solar-Neighborhood Massive Star Birthrate and the Galactic Supernova Rate
The birthrate of stars of masses >=10 Msolar is estimatedfrom a sample of just over 400 O3-B2 dwarfs within 1.5 kpc of the Sunand the result extrapolated to estimate the Galactic supernova ratecontributed by such stars. The solar-neighborhood Galactic-plane massivestar birthrate is estimated at ~176 stars kpc-3Myr-1. On the basis of a model in which the Galactic stellardensity distribution comprises a ``disk+central hole'' like that of thedust infrared emission (as proposed by Drimmel and Spergel), theGalactic supernova rate is estimated at probably not less than ~1 normore than ~2 per century and the number of O3-B2 dwarfs within the solarcircle at ~200,000.
| Two New Low Galactic D/H Measurements from the Far Ultraviolet Spectroscopic Explorer
We analyze interstellar absorption observed toward two subdwarf O stars,JL 9 and LS 1274, using spectra taken by the Far UltravioletSpectroscopic Explorer (FUSE). Column densities are measured for manyatomic and molecular species (H I, D I, C I, N I, O I, P II, Ar I, FeII, and H2), but our main focus is on measuring the D/Hratios for these extended lines of sight, as D/H is an importantdiagnostic for both cosmology and Galactic chemical evolution. We findD/H=(1.00+/-0.37)×10-5 toward JL 9 andD/H=(0.76+/-0.36)×10-5 toward LS 1274 (2 σuncertainties). With distances of 590+/-160 and 580+/-100 pc,respectively, these two lines of sight are currently among the longestGalactic lines of sight with measured D/H. With the addition of thesemeasurements, we see a significant tendency for longer Galactic lines ofsight to yield low D/H values, consistent with previous inferences aboutthe deuterium abundance from D/O and D/N measurements. Short lines ofsight with H I column densities of logN(HI)<19.2 suggest that thegas-phase D/H value within the Local Bubble is(D/H)LBg=(1.56+/-0.04)×10-5. However, thefour longest Galactic lines of sight with measured D/H, which haved>500 pc and logN(HI)>20.5, suggest a significantly lower valuefor the true local disk gas-phase D/H value,(D/H)LDg=(0.85+/-0.09)×10-5. Oneinterpretation of these results is that D is preferentially depletedonto dust grains relative to H and that longer lines of sight thatextend beyond the Local Bubble sample more depleted material. In thisscenario, the higher Local Bubble D/H ratio is actually a betterestimate than (D/H)LDg for the true local disk D/H,(D/H)LD. However, if (D/H)LDg is different from(D/H)LBg simply because of variable astration and incompleteinterstellar medium mixing, then (D/H)LD=(D/H)LDg.Based on observations made with the NASA-CNES-CSA Far UltravioletSpectroscopic Explorer (FUSE), which is operated for NASA by JohnsHopkins University under NASA contract NAS5-32985.
| Studying the populations of our Galaxy using the kinematics of sdB stars
We have analysed the kinematics of a sample of 114 hot subdwarf stars.For 2/3 of the stars, new proper motions, spectroscopic and photometricdata are presented. The vast majority of the stars show a kinematicbehaviour that is similar to that of Thick Disk stars. Some stars havevelocities rather fitting to solar, i.e. Thin Disk, kinematics. About˜15 objects have orbital velocities which differ considerably fromthose of Disk stars. These are members of the Galactic Halo. Weinvestigated the velocity dispersions and calculated the orbits. Moststars feature orbits with disk character (eccentricity of less than0.5), a few reach far above the Galactic plane and have very eccentricorbits (eccentricity of more than 0.7). The intermediate eccentricityrange is poorly populated. This seems to indicate that the (Thick) Diskand the Halo are kinematically disjunct. Plotting a histogram of theorbit data points along z leads to the z-distance probabilitydistribution of the star; doing this for the whole sample leads to thez-distance probability distribution of the sample. The logarithmichistogram shows two slopes, each representing the scale height of apopulation. The disk component has a scale height of 0.9 (±0.1)kpc, which is consistent with earlier results and is similar to that ofthe Thick Disk. The other slope represents a component with a scaleheight ˜7 kpc, a much flatter gradient than for the diskcomponent. This shows that the vast majority of the sdBs are disk stars,but a Halo minority is present, too. The kinematic history andpopulation membership of the sdB stars on the whole is different fromthat of the cooler HBA stars, which are predominantly or evenexclusively Halo objects. This leads to the question, whether the HalosdB stars are of similar origin as the HBA stars, or whether theirkinematical behaviour possibly represents another origin, such asinfalling stellar aggregates or inner disk events.Based on data obtained at the 1.54 m telescope of the European SouthernObservatory, runs 58.D-0478, 60.D-0306, 62.L-0220, 64.L-0077,64.H-0023(A), 65.H-0250, 65.H-0341(A) and 68.D-0192(A).
| Optical spectroscopy of GX 339-4 - I. Orbital modulation
Optical spectroscopic observations of GX 339-4 were carried out between1998 May (X-ray high state) and 1999 May (X-ray low state) over sevenepochs. The equivalent width of H? increased during the high stateand then decreased during the low state. The equivalent width ofHeII?4686 decreased over both states. The full-width athalf-maximum of H?, H?, HeII?4686 and the Bowen blendincreased from 1998 to 1999, indicating that the emission-line regionsmoved closer to the compact object. H? shows a redshiftedabsorption feature at ?4880 at all epochs. This line remainsunidentified. Analysis of individual spectra from 1998 May 28-31 showsmodulation of the radial velocities, equivalent width and V/R ratios ofH? on the 14.86-h orbital period. The equivalent width ofHeII?4686 also varies on the orbital period. The semi-amplitudeof the H? radial velocities is K1= 14 kms-1. Hence the mass function = 2 × 10-4Msolar.
| Catalog of Galactic OB Stars
An all-sky catalog of Galactic OB stars has been created by extendingthe Case-Hamburg Galactic plane luminous-stars surveys to include 5500additional objects drawn from the literature. This work brings the totalnumber of known or reasonably suspected OB stars to over 16,000.Companion databases of UBVβ photometry and MK classifications forthese objects include nearly 30,000 and 20,000 entries, respectively.
| Kinematical trends among the field horizontal branch stars
Horizontal branch (HB) stars in the field of the Milky Way can be usedas tracers for the study of early stages of the evolution of our galaxy.Since the age of individual HB stars is not known a priori, we havestudied the kinematics of a sample of field HB stars measured withHipparcos to look for signs of age and population nature. Our samplecomprises 14 HBA, 2 HBB and 5 sdB/O stars. We found that the kinematicsof the HBA stars is very different from that of the sdB/O stars(including those from an earlier study). The HBA stars have low orbitalvelocities, some are even on retrograde orbits. Their orbits have largeeccentricities and in many cases reach large distances above thegalactic plane. In contrast, the sdB/O stars show disk-like orbitalcharacteristics. The few HBB stars (with T_eff> 10,000 K) in oursample seem to have kinematics similar to that of the sdB/O stars. Inorder to see if there is a trend among the HB stars in their kinematics,we investigated also RR Lyrae stars measured with Hipparcos. Here wefound a mixed kinematical behaviour, which was already known fromprevious studies. Some RR Lyrae stars have disk-like orbits (most ofthese being metal rich) but the majority has halo-like orbits, verysimilar to those of our HBA stars. Since the atmospheres of most typesof HB stars do not reflect original metallicities any more thekinematics is the only aspect left to study the origin and populationmembership of these stars. Thus, the clear trend found in kinematics ofstars along the HB, which is also a sequence in stellar mass, shows thatthe different kinds of field HB stars arose from stars having differentorigins in age and, e.g., metallicity or mass loss rate. Based in parton HIPPARCOS data
| Spectrophotometry: Revised Standards and Techniques
The telluric features redward of 6700 Å have been removed from theaccurate spectrophotometric standards of Hamuy et al. to permit morereliable relative and absolute spectrophotometry to be obtained from CCDspectra. Smooth fluxes from 3300 to 10500 Å are best determined bydividing the raw spectra of all objects taken in a night by the rawspectrum of a ``smooth'' spectrum star before deriving the instrumentalresponse function using the revised standard star fluxes. In this waythe telluric features and any large instrumental variation withwavelength are removed from the raw data, leaving smooth spectra thatneed only small corrections to place them on an absolute flux scale.These small corrections with wavelength are well described by alow-order polynomial and result in very smooth flux-calibrated spectra.
| Supplementary southern standards for UBV(RI)c photometry
We present UBV(RI)c photometry for 80 southern red and blue stars foruse as additional standards. The data are tied to the Johnson UBV andCousins (RI)c systems and extend the range of the available stars forcolor equation determination, especially in (U-B) for blue stars and(V-R) and (V-I) for red stars. Comparisons with published data are madeand particularly good agreement is found with Bessell for the red(Gliese) stars.
| The Edinburgh-Cape Blue Object Survey - II. Zone 1 - the North Galactic CAP
Results for Zone 1 of the Edinburgh-Cape (EC) Blue Object Survey arepresented. This zone covers that part of the North Galactic Cap morethan ~30 deg from the Galactic plane and south of about -12^ deg_.3declination (although a few fields north of this declination areincluded). The zone effectively complements the Palomar-Green Survey inthe North Galactic Cap, although the EC Survey should be more completeto a fainter limit (B=16.5 mag) and to somewhat redder stars (U-B bluerthan about -0.4). Zone 1 covers approximately 1560 deg^2 and contains675 blue objects for which we list equatorial coordinates accurate to ~1arcsec, UBV photoelectric photometry, and spectral types determined frommoderate-dispersion (100 A mm^-1) spectrograms.
| 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.
| Metal abundances in subdwarf O stars.
We describe a non-LTE analysis of seven subdwarf O stars and fourcentral stars of planetary nebulae. The analysis yields metal abundances(or upper limits to these) of C, N, O, Mg, Al, and Si for most of thesestars. Also effective temperature, surface gravity and helium abundancewere determined for those programme stars for which no reliableestimates of these parameters were available. The derived abundancepatterns prove to be disparate. We also compare the sdO stars in oursample with other sdO analyses (18 object in total) and find that thisstellar class is not homogeneous with respect to metal abundances. Atentative subclassification according to helium content andluminosity-to-mass ratio indicates that the compact, high-gravity sdOstars have similar metal abundances with a strong signature of hydrogenburning in the CNO cycle. They only differ in the amounts of helium andcarbon present in the photosphere, probably caused by varyingefficiencies of mixing or surface erosion. Luminous sdOs, on the otherhand, show markedly different metallicities, suggesting differentorigins. The star CPD-31 1701 is identified as a peculiar object. Ascompared with other O subdwarfs with nearly identical parameters, itsHe^44^Sc II line profiles appear shallow and rounded, lacking a welldefined core. They can also not be fitted by theoretical profiles. Noexplanation for this discrepancy could be found yet. Our analysis yieldsmicroturbulence velocities in the range 0-10km/s for all stars with asufficient number of metal lines. No indication was found for highervalues like the 20km/s reported by Hubeny et al. (1991) for the sdO starBD+75 325.
| The Spacelab-1 Very Wide Field Survey of UV-excess objects. IV. The performance of the instrument in combination with optical photometry as a means of identifying stars with peculiar properties.
UV (195 nm) and Stroemgren uvby photometry of a 110 square degree fieldat high southern galactic latitudes are analyzed through a comparison ofi) UV magnitudes for 57 stars of various types common to the publishedTD1 catalogue and the Very Wide Field Camera (VWFC); and ii) observedand theoretical two-colour diagrams. The higher sensitivity of the VWFC(=~0.5magnitude) and its more complete survey are exemplified by thedetection and UV measurement of a series of objects with moderateUV-excess in addition to detection of some very blue objects of variousnature down to fainter than 12th magnitude in the optical domain. Adeeper survey with a VWFC-type instrument could provide a completesample for studies of the group properties of faint blue stars. Duringthe uvby reductions it was found that the usual procedure of plottingresiduals as functions of declination, hour angle and airmass can be apowerful and diagnostic test of photometer rigidity.
| An IUE survey of interstellar H I LY alpha absorption. 1: Column densities
We measure Galactic interstellar neutral hydrogen column densities byanalyzing archival interstellar Ly alpha absorption line data toward 554B2 and hotter stars observed at high resolution with the IUE satellite.This study more than doubles the number of lines of sight with measuresof N(H I) based on Ly alpha. We have included the scattered lightbackground correction algorithm of Bianchi and Bohlin in our datareduction. We use the correlation between the Balmer discontinuity(c1) index and the stellar Ly alpha absorption in order toassess the effects of stellar Ly alpha contamination. Approximately 40%of the B stars with measured (c1) index, exhibit seriousstellar Ly alpha contamination. One table contains the derived values ofthe interstellar N(H I) for 393 stars with at most small amounts ofstellar contamination. Another lists the observed values of total N(H I)for 161 stars with suspected stellar Ly alpha contamination and/oruncertain stellar parameters.
| Incidence of X-ray sources among magnetic chemically peculiar stars
Cash & Snow (1982) and Golub et al. (1983) have detected X-rayemission from 3 out of 7 observed magnetic chemically peculiar (CP)stars. Although the incidence of X-ray sources apparently is very high,these authors concluded that such emission is not unquestionable becauseof the presence of a companion. To determine the incidence of X-raysources among hot CP stars, I have checked the list of B-type starsmeasured by Grillo et al. (1992) selecting 90 stars. Of the 4 magneticCP stars showing X-ray emission 3 are members of a binary system. Thusit appears that detectable X-ray emission from magnetic CP stars is notvery common and still questionable. To find out whether HD 37017presents X-ray emission (Drake et al. 1987) or not (Grillo et al. 1992),I have analyzed an HRI frame from the ROSAT satellite finding noevidence for X-ray emission at this star's position.
| The Diffuse Ionized Interstellar Medium: Structures Resulting from Ionization by O Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993ApJ...417..579M&db_key=AST
| 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.
| Selection of standard stars for photometric observations with the 91-cm reflector at Okayama
Not Available
| Broad-band photometry of selected southern ultraviolet-bright stars.
Not Available
| Radial velocities and spectral types for a sample of faint blue stars.
Not Available
| IUE studies of mass loss phenomena in hot stars
The determination of mass loss rates and wind velocities in a largesample of hot stars with IUE; the discovery of mass loss and winds inSdO stars; UV studies of mass loss in OB stars in the Magellanic Cloudsand beyond; stimuli to the development of improved radiation pressurewind models; and the discovery of substantial stellar wind variability,epitomized by the occurrence and variation of wind discrete absorptioncomponents in a wide range of stellar types are discussed. This progressresults from the combination of high spectral sensitivity, wavelengthmultiplexing, observatory nature, and longevity of IUE, important infacilitating detailed variability studies of individual sources over awide range of timescales.
| High-velocity ultraviolet iron, silicon, oxygen, and sulfur absorption features associated with the remnant of SN 1006
New low-dispersion IUE spectra of a faint sdOb star located in adirection near the center of the SN 1006 remnant are presented. The UVspectrum of the star exhibits several strong absorption features whichare uncharacteristic of its optical sdOB star classification. Theidentification by Wu et al. (1983) of very broad absorption features at1610, 2370, 2600 A as Fe II gas associated with the SN 1006 remnant issupported. The observed Fe II line profiles indicate a concentration ofFe(+) toward the remnant's center with a radial velocity range on theorder of + or - 5000 km/s. Strong absorption lines at 1281, 1331, and1420 A are interpreted as originating from clumps of O-, Si- and S-richejecta with central radial velocities in the range 5000-6500 km/s. Thepresence in the SN 1006 remnant of an expanding sphere of iron-richejecta interior to O-, Si-, and S-rich clumps of ejecta havingvelocities over the maximum seen for the Fe II absorbing gas isconsistent with type Ia Sn observations and carbon deflagration models.
| A catalogue of spectroscopically identified hot subdwarf stars.
Not Available
| Non-radial pulsations in the extreme helium star HD 160641
Mean periods of 0.35 + or - 0.01, 0.71 + or - 0.05, 1.12 + or - 0.13 and1.77 + or - 0.34 day are identified from separately analyzed photometricobservations of the extreme helium star HD 160641. Radial velocitieswere obtained simultaneously with photometry on three nights in 1982.Optical variations are not accompanied by detectable color changes, andradial velocities are not characteristic of radial pulsation. HD 160641is therefore regarded as a nonradial pulsator. Radial velocity and lightvariations are tentatively interpreted as l = 4 mode pulsation,corresponding to a Wesselink radius of 7.9 + or - 1.0 solar radii. Theconsequent luminosity of log (L/L-solar) = 4.7 + or - 0.3 would beconsistent with Schoenberner's (1977) evolution model for a 1 solar massextreme helium star.
| Confirmation of High-Velocity UV Fe and Si Absorption Lines from the Remnant of SN 1006
Not Available
| CD-24 deg 9052 - A new bright and helium-rich subdwarf O star
CD -24°9052 has been discovered to be a bright subdwarf O star(mv ? 9.6). A spectral analysis based on SAAO Reticonspectra and on a grid of NLTE model atmospheres yields the followingparameters: Teff = 42500K, log g = 5.0, and the helium tohydrogen ratio of 0.5 by numbers. Accordingly, CD -24°9052 belongsto the subclass of helium rich sdO's.
| Southern Hemisphere Spectrophotometric Standards
Not Available
| Analysis of high-depression IUE spectra of subdwarf B stars
High-dispersion IUE spectra of the subdwarf B stars UV 1758+36 and TonS-227 are presented. These spectra are characterized by the presence ofa large number of photospheric low- and medium-excitation lines fromnumerous ions. The lines of C, N, and Si are used in conjunction withlocal thermodynamic equilibrium (LTE) metal line calculations to derivepreliminary abundances for these elements. These results are comparedand contrasted with those obtained or the hotter OB and O subdwarfs.
| P Cygni and related profiles in the ultraviolet spectra of O-stars
P Cygni and related profiles of the resonance lines of N V, Si IV and CIV ions are studied over a sample of 40 O-stars observed with IUE in thehigh resolution mode. The sample includes subdwarf stars, highluminosity population II objects, stars which are not recognized membersof open clusters and/or associations, and stars which are members. Theprofiles give information on the ionization structure of the expandingstellar atmosphere and on the velocity fields. The large variety ofthese profiles and the wide range of observed velocities allow a look tobe taken at the largely unexplored field of stellar individuality.
| Non-LTE analysis of subluminous O-stars. VI - Feige 110
An analysis of the ultraviolet (1150-2000 A) and the blue 4000-5100 A)spectra of the subdwarf O-star Feige 110 is presented. Effectivetemperature, gravity and helium abundance of Feige 110 are determined onthe basis of NLTE model atmospheres. The effective temperature of Feige110 is found to be 40,000 K (+5000 or -3000 K). Helium abundances in thestar were deficient, between 1 and 6 percent. The abundances of carbonand nitrogen were obtained from the ultraviolet resonance lines C IV andN V. The nitrogen abundance was found to be close to that of the sun butcarbon was extremely deficient. Si IV resonance lines were absent in theUV spectrum of Feige 110. It is suggested that the abundance pattern ofFeige 110 may have been affected by diffusion, and that, therefore, thephotospheric abundance of helium, carbon, and silicon may have beenlarger before the onset of diffusion.
|
Добавить новую статью
Внешние ссылки
- - Внешних ссылок не найдено -
Добавить внешнюю ссылку
Группы:
|
Наблюдательные данные и астрометрия
| Созвездие: | Весы |
| Прямое восхождение: | 14h32m21.49s |
| Склонение: | -22°39'25.6" |
| Видимая звёздная величина: | 10.054 |
| Собственное движение RA: | -31.6 |
| Собственное движение Dec: | -13.6 |
| B-T magnitude: | 9.684 |
| V-T magnitude: | 10.024 |
Каталоги и обозначения:
|
