Contents
Images
Upload your image
DSS Images Other Images
Related articles
The SPEAR Instrument and On-Orbit Performance
The SPEAR (or ``FIMS'') instrumentation has been used to conduct thefirst large-scale spectral mapping of diffuse cosmic far-ultraviolet(FUV; 900-1750 Å) emission, including important diagnostics ofinterstellar hot (104-106 K) and photoionizedplasmas, H2, and dust-scattered starlight. Theinstrumentation's performance has allowed for the unprecedenteddetection of astrophysical diffuse FUV emission lines. A spectralresolution of λ/Δλ~550 and an imaging resolution of5' is achieved on-orbit in the Short (900-1150 Å) and Long(1350-1750 Å) bandpass channels within their respective4.0d×4.6 arcmin and 7.4d×4.3 arcmin fields of view. Wedescribe the SPEAR imaging spectrographs, their performance, and thenature and handling of their data.
| A high-resolution spectroscopy survey of β Cephei pulsations in bright stars
We present a study of absorption line-profile variations in early-B typenear-main-sequence stars without emission lines. We have surveyed atotal of 171 bright stars using the Nordic Optical Telescope (NOTSA),William Herschel Telescope (ING) and Coudé Auxiliary Telescope(ESO). Our sample contains 75% of all O9.5-B2.5 III-V non-emission-linestars brighter than 5.5 mag. We obtained high signal-to-noise,high-resolution spectra of the SiIII λ4560 triplet - for 125stars of our sample we obtained more than one spectrum - and examinedthese for pulsational-like line-profile variations and/or structure. Weconclude that about half of our sample stars show evidence forline-profile variations (LPV). We find evidence for LPV in about 65% ofour sample stars brighter than V=5.5. For stars with rotationalbroadening V sin i 100 km s-1, we find evidence for LPVin about 75% of the cases. We argue that it is likely that these LPV areof pulsational origin, and that hence more than half of thesolar-neighbourhood O9.5-B2.5 III-V stars is pulsating in modes that canbe detected with high-resolution spectroscopy. We detected LPV in 64stars previously unknown to be pulsators, and label these stars as newβ Cep candidates. We conclude that there is no obvious differencein incidence of (pulsational) LPV for early-B type near-main-sequencestars in binaries or in OB associations, with respect to single fieldstars.
| Some implications of the introduction of scattered starlight in the spectrum of reddened stars
This paper presents new investigations on coherent scattering in theforward direction (orders of magnitude; conservation of energy;dependence of scattered light on geometry and wavelength), and on howscattered light contamination in the spectrum of reddened stars ispossibly related to as yet unexplained observations (the diminution ofthe 2200 Å bump when the obscuring material is close to the star,the difference between Hipparcos and photometric distances). This paperthen goes on to discuss the fit of the extinction curve, a possible roleof extinction by the gas in the far-UV, and the reasons of theinadequacy of the Fitzpatrick and Massa [ApJSS, 72 (1990) 163] fit.
| Shocked Clouds in the Vela Supernova Remnant
Unusually strong high-excitation C I has been detected in 11 lines ofsight through the Vela supernova remnant (SNR) by means of UV absorptionline studies of IUE data. Most of these lines of sight lie near thewestern edge of the bright X-ray region of the SNR in a spatiallydistinct band approximately 1° by 4° oriented approximatelynorth-south. The high-excitation C I (denoted C I* and C I**) isinterpreted as evidence of a complex of shocked dense clouds interactingwith the SNR, because of the high pressures indicated in this region. Tofurther analyze the properties of this region of enhanced C I* and CI**, we present new HIRES-processed IRAS data of the entire Vela SNR. Atemperature map calculated from the HIRES IRAS data, based on atwo-component dust model, reveals the signature of hot dust at severallocations in the SNR. The hot dust is anticorrelated spatially withX-ray emission, as would be expected for a dusty medium interacting witha shock wave. The regions of hot dust are strongly correlated withoptical filaments, supporting a scenario of dense clouds interior to theSNR that have been shocked and are now cooling behind the supernovablast wave. With few exceptions, the lines of sight to the stronghigh-excitation C I pass through regions of hot dust and opticalfilaments. Possible mechanisms for the production of the unexpectedlylarge columns of high-excitation C I are discussed. Dense clouds on theback western hemisphere of the remnant may explain the relatively lowX-ray emission in the western portion of the Vela SNR due to the slowerforward shock velocity in regions where the shock has encountered thedense clouds. An alternate explanation for the presence of ground-stateand excited-state neutrals, as well as ionized species, along the sameline of sight is a magnetic precursor that heats and compresses the gasahead of the shock.
| The relation between far-UV and visible extinctions
For directions of sufficient reddening (/E(B-V)>~0.25), there is asimple relation between the slope of the extinction curve in the far-UVand /E(B-V). Regardless of direction, the far-UV extinction curve isproportional to 1/λn e-2E(B-V)/λ(/λ in μm, /n=4), in accordance with the idea that reddenedstars spectra are contaminated by scattered light (Zagury, 2001b). Thisrelation is not compatible with the standard theory of extinction whichstates that far-UV and visible extinctions are due to different classesof particle. In that model the two (far-UV and visible) extinctions varythus independently according to the proportion of each type of particle.In preceding papers I have shown that the standard theory cannot explainUV observations of nebulae, and is contradicted by the UV spectra ofstars with very low reddening: for how long shall the standard theory beconsidered as the interpretation of the extinction curve?
| 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
| Interpretation of the UV spectrum of some stars with little reddening
The UV spectrum of a few reddened stars will be decomposed into twoterms. One is the direct starlight, F_*,lambda^0 e^ - tau_lambda, whichis the product of the flux of the star corrected for interstellarextinction, F_*,lambda^0, and of the extinction e^ - tau_lambda. Thesecond is starlight scattered by interstellar dust into the beam of theobservation. This excess of scattered starlight affects the FUV part ofthe spectrum (lambda < 2200 A). The combination of both terms givesthe shape of the UV spectrum of a reddened star, with its characteristicdepression at 2200 A.
| Spectroscopy and Time Variability of Absorption Lines in the Direction of the Vela Supernova Remnant
We present high-resolution (R~75,000), high signal-to-noise (S/N~100) CaII λ3933.663 and Na I λλ5889.951, 5895.924 spectraof 68 stars in the direction of the Vela supernova remnant. The spectracomprise the most complete high-resolution, high S/N optical survey ofearly-type stars in this region of the sky. A subset of the sight lineshas been observed at multiple epochs, 1993/1994 and 1996. Of the 13stars observed twice, seven have spectra revealing changes in theequivalent width and/or velocity structure of lines, most of which arisefrom remnant gas. Such time variability has been reported previously forthe sight lines toward HD 72089 and HD 72997 by Danks & Sembach andfor HD 72127 by Hobbs and coworkers. We have confirmed the ongoing timevariability of these spectra and present new evidence of variability inthe spectra of HD 73658, HD 74455, HD 75309, and HD 75821. We havetabulated Na I and Ca II absorption-line information for the sight linesin our sample to serve as a benchmark for further investigations of thedynamics and evolution of the Vela SNR. Based on observations obtainedat the European Southern Observatory, La Silla, Chile.
| An extensive Delta a-photometric survey of southern B and A type bright stars
Photoelectric photometry of 803 southern BS objects in the Deltaa-system as detection tool for magnetic chemically peculiar (=CP2) starshas been carried out and compared to published spectral types. Thestatistical yield of such objects detected by both techniques ispractically the same. We show that there are several factors whichcontaminate the search for these stars, but this contamination is onlyof the order of 10% in both techniques. We find a smooth transition fromnormal to peculiar stars. Our sample exhibits the largest fraction ofCP2 stars at their bluest colour interval, i.e. 10% of all stars in thecolour range -0.19 <= B-V < -0.10 or -0.10 <= b-y < -0.05.No peculiar stars based on the Delta a-criterion were found at bluercolours. Towards the red side the fraction of CP2 stars drops to about3% for positive values of B-V or b-y with red limits roughlycorresponding to normal stars of spectral type A5. The photometricbehaviour of other peculiar stars: Am, HgMn, delta Del, lambda Boo, Heabnormal stars, as well as Be/shell stars and supergiants shows someslight, but definite deviations from normal stars. Spectroscopic andvisual binaries are not distinguished from normal stars in their Delta abehaviour. The results of this work justify larger statistical work(e.g. in open clusters) employing more time-saving photometric methods(CCD). \newpage Based on observations obtained at the European SouthernObservatory, La Silla, Chile. This research has made use of the Simbaddatabase, operated at CDS, Strasbourg, France. Table 2 is only availablein electronic form via anonymous ftp 130.79.128.5 orhttp://cdsweb.u-strasbg.fr/Abstract.html
| UV Spectral Classification of O and B Stars in the Small Magellanic =
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....114.1951N&db_key=AST
| Red and infrared colours of B stars and the reddening law in the Galaxy
The red and infrared intrinsic colours of B stars are derived fromphotometric observations through the UBV(RI)_CJHK and Hβ filters of257 early-type stars. Those stars for which the UBV and Hβmeasurements match the published spectral class, and which show no othersigns of peculiarity, are used to determine the intrinsic photometriccolours of B stars in the red and infrared. From these intrinsic coloursthe interstellar reddening relationships for the red and infraredcolours are evaluated, and the results are compared with previousestimates of these quantities. The values of R, E(B-V) and the distanceare then determined for the individual stars. R is confirmed to be closeto 3.1 in most cases, but was found to be much larger in somedirections. The relationship between R and the location of a star in theGalaxy is investigated. Usually the abnormally reddened stars seemed tobe associated with known regions of star formation. The paper alsoidentifies seven likely variable stars and a number of stars withpossible dust shells.
| 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.
| Far-Ultraviolet (912--1900 Angstrom ) Energy Distribution in Early-Type Main-Sequence Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...449..280C&db_key=AST
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| An atlas of ultraviolet P Cygni profiles
We have selected spectra of 232 stars from the International UltravioletExplorer (IUE) archives for inclusion in an atlas intended for varioususes but tailored especially for the study of stellar winds. The atlascovers the range in spectral types from O3 to F8. The full atlas coversthe reduced and normalized high resolution spectra from the IUE long-and short-wavelength spectrographs. Here we discuss the selection of thestars and the data reduction, and we present in velocity units theprofiles of lines formed in the stellar winds. The selected lines covera wide range of ionizations, allowing a comparison of the profiles fromdifferent ions in the wind of each star and a comparison of thedifferent wind lines as a function spectral type and luminosity. We alsopresent the basic data on the program stars to facilitate study of thedependence of wind features on stellar parameters such as luminosity,temperature, escape velocity, and v sin i. We provide an overview of thecharacteristic behavior of the wind lines in the H-R diagram. Thecomplete spectra are available in digital form through the NASAAstrophysics Data System (ADS). We offer a description of the electronicdatabase that is available through the ADS and guidelines for obtainingaccess to that database.
| Rnu-dependent optical and near-ultraviolet extinction
We have derived extinctions A(lambda)/A(V) at the wavelengths of theuvby filters for 22 stars, with a range of values of Rnu,from the sample of Cardelli, Clayton, & Mathis (1989, hereafterCCM). We have fit these extinctions, and also UBVRIJHKL, IUE and ANSextinction measurements, with linear relations A(lambda)/A/(V) =a+b/Rnu and fit a and b as a function of x(=1/lambda) withpolynomials to obtain an Rnu-dependent mean extinction law(A(x)/A(V) = a(x) + b(x)/Rnu)in the optical andnear-ultraviolet (1.1/micrometer less than or equal to 3.3/micrometer).This law is virtually identical to the CCM extinction law for largevalues of Rnu(Rnu approximately 5) but is slightlylower in the near-ultraviolet for smaller Rnu (Rnuapproximately 3). The extinction law presented here agrees much betterwith a high-resolution extinction curve for the diffuse interstellarmedium (Rnu approximately 3.1), presented by Bastiaansen(1992), than CCM. The deviations of individual extinction curves fromthe mean are dominated by observational errors. The wavelengthresolution of this work is not high enough to show evidence for oragainst the existence of very broad structure in optical extinctioncurves.
| Ultraviolet and optical studies of binaries with luminous cool primaries and hot companions. IV - Further IUE detections
We have obtained IUE spectra for 31 middle and late-type giant andsupergiant stars whose TD-1 fluxes or ground-based spectra indicate thepresence of a hot component, or whose radial velocities indicate anunseen component. Stellar components earlier than type F1 were detectedin 22 cases. While 20 of the hot secondaries are seen weakly in opticalspectra, two are UV discoveries: HD 58134 and HD 183864. The hotcompanions are classified accurately by temperature class from theirfar-UV spectra. The interstellar extinction of each system and therelative luminosities of the components are derived from the UV andoptical fluxes, using a new grid of UV intrinsic colors for hot dwarfs.We find that many giant stars apparently have companions which are toohot and hence too luminous for consistency with the primary's spectralclassification.
| Evolution of Supernova 1987A in the Ultraviolet
Two observational aspects of the evolution of SN 1987A in the UV arepresented, based on IUE data. First, the spectral evolution of the NV,NIV], HeII, OIII], NIII] and CIII] emission lines in the period fromMarch 13, 1987 to March 12, 1990. And secondly, the evolution of the SN1987A continuum fluxes in various UV bands using SWP and LWP spectrafrom February 25, 1987 to March 12, 1990. These results are brieflydiscussed.
| Spectral synthesis in the ultraviolet. IV - A library of mean stellar groups
A library of mean UV stellar energy distributions is derived from IUEspectrophotometry of 218 stars. The spectra cover 1230-3200 A with aspectral resolution of about 6 A. They have been corrected forinterstellar extinction and converted to a common flux and wavelengthscale. Individual stars were combined into standard groups according totheir continuum colors, observed UV spectral morphology, MK luminosityclass, and metal abundance. The library consists of 56 groups: 21dwarf(V), 8 subgiant(IV), 16 giant(III), and supergiant(I + II) groups,covering O3-M4 spectral types. A metal-poor sequence is included,containing four dwarf and two giant groups, as is a metal-enhancedsequence with a single dwarf, subgiant, and giant group. Spectralindices characterizing the continuum and several strong absorptionfeatures are examined as temperature, luminosity, and abundancediagnostics. The library is intended to serve as a basis forinterpreting the composite UV spectra of a wide variety of stellarsystems, e.g., elliptical galaxies, starburst systems, and high-redshiftgalaxies.
| The quantitative assessment of UV extinction derived from IUE data of giants and supergiants
It is shown here that the UV interstellar extinction towards hotluminous stars can be determined as accurately as for hot main-sequencestars. An atlas of IUE dereddened fluxes is presented for 13 lightlyreddened stars within the 1160-3125 A range. The fluxes of these starshow absorption line strengths that allow a rather accurate determinationof relative temperatures and luminosities which is more suitable for thedetermination of UV extinction via the pair method than choosing acomparison star based on quoted optical MK classifications.
| Absolute extinction and the influence of environment - Dark cloud sight lines toward VCT 10, 30, and Walker 67
The range of validity of the average absolute extinction law (AAEL)proposed by Cardelli et al. (1988 and 1989) is investigated, combiningpublished visible and NIR data with IUE UV observations for three linesof sight through dense dark cloud environments with high values oftotal-to-selective extinction. The characteristics of the data sets andthe reduction and parameterization methods applied are described indetail, and the results are presented in extensive tables and graphs.Good agreement with the AAEL is demonstrated for wavelengths from 3.4microns to 250 nm, but significant deviations are found at shorterwavelengths (where previous studies of lines of sight through brightnebulosity found good agreement with the AAEL). These differences areattributed to the effects of coatings on small-bump and FUV grains.
| Broad-band photometry of selected southern ultraviolet-bright stars.
Not Available
| Long Slit Observations of Emitting Gas in the VELA Supernova Remnant
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1990MNRAS.245..701W&db_key=AST
| An ultraviolet spectral atlas of interstellar lines toward SN 1987A
An UV spectral atlas of the interstellar spectrum toward SN 1987A in theLMC is presented, based on data obtained with the IUE satellite. Theatlas extends from 1250 to 3200 A and includes 200 lines from 12interstellar species. The results are interpreted in the context ofexisting optical and UV studies of interstellar gas toward the LMC.
| The progenitor of SN1987A
Spatial and spectroscopic information from IUE spectra in the range1150-1950 A is used here to demonstrate that SK-69 202, the starcoinciding positionally with the LMC supernova, has disappeared fromsight. Two weaker sources, named star 2 and star 3 in the astrometricanalysis of the image of SK-69 202 before the supernova outburst, arestill present in the ultraviolet spectra. Their spectra are isolated anda spectral classification is given. It is concluded that Sk-69 202 isthe progenitor for the LMC supernova.
| Ultraviolet interstellar extinction toward NGC 6530 and the intrinsic energy distribution of 9 Sagittarii and HD 165052
The ultraviolet interstellar extinction curve is determined toward 12early B main-sequence stars and one O8 V star in NGC 6530. Theextinction is found to be uniform across the cluster. At shortwavelengths, the extinction curve of NGC 6530 falls below the averageGalactic curve by a full magnitude, indicating that the population ofsmall grains relative to larger grains is lower than normal. Longward of2830 A the curve is almost coincident with the mean Galactic curve. The2175 A feature is narrower than the average. The derived extinctioncurve is used to deredden the observed fluxes of two early O-type starsin NGC 6530:9 Sgr and HD 165052. The intrinsic continua are compared tomodel atmospheres in the region 1200-8200 A. The LTE, line-blanketedmodels of Kurucz (1979) fit the observations better than the non-LTE,unblanketed models of Mihalas (1972) suggesting that line-blanketingeffects are more important than the non-LTE effects in the atmospheresof these stars. The temperatures of the models that best fit theobservations are lower than the Zanstra temperatures and thetemperatures estimated from the strengths of the He I and He II lines,by 10,000 to 20,000 K.
| Mass to line-strength relations from IUE spectra of early-type stars
An extensive survey of the 1200-1900 A region in OB type stellar spectraobtained from the IUE archives has been used to establish line-strengthversus spectral-type relationships. One hundred and sixty-threelow-resolution IUE spectra of 124 well-classified O3 to B5 stars wereexamined. Earlier results that the equivalent width of Si IV (1400 A)and C IV (1550 A) features are well correlated with optical spectraltype are confirmed. The equivalent width/spectral type/luminosity classrelations for these features are then established.
| IUE observations of the broad continuum feature at 1400 A in the silicon and related stars
The upper main sequence chemically peculiar stars have previously beenstudied spectrophotometrically using low-resolution TD-1 spectra. Theseshow that the broad continuum feature at 1400 A is a useful indicator ofSi anomaly. In this paper the observations are extended to IUElow-resolution spectra and it is shown that this feature is indeed wellcorrelated with Si and also with optical chemical peculiarity indices.Its utility in selecting silicon stars is further demonstrated. Thisfeature is likely due to autoionization of Si II and is the bestavailable discriminator of the overabundance of a key element in the Apstars.
| The extinction law in the open cluster NGC 457 and the intrinsic energy distribution of Phi Cassiopeiae (F0 Ia)
Five early B-type stars near the main-sequence turnoff in NGC 457 havebeen observed at low dispersion with the short-wavelength prime and thelong-wavelength redundant cameras of the IUE satellite. The equivalentwidths of spectral features that are particularly strong and sensitiveto temperature and luminosity were computed in the cluster stars and in20 lightly reddened stars of types O9-B3 and luminosity classes III-V.The comparison of the equivalent widths provides a reliable method forfinding matching pairs. Having identified the best comparison star foreach program star, binned fluxes were used to determine the meanextinction curve. In order to cover the visible region, monochromaticfluxes of Phi Cas were derived from observations with the intensifiedReticon scanner mounted on the No. 2 0.9 m telescope of KPNO, and theywere dereddened with the mean extinction curve of Savage and Mathis.Thus, the intrinsic energy distribution of Phi Cas were determined from1500 to 5800 A for use in a detailed model-atmosphere analysis.
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
| Constellation: | Segel des Schiffs |
| Right ascension: | 08h41m05.30s |
| Declination: | -48°55'21.0" |
| Apparent magnitude: | 5.9 |
| Distance: | 492.611 parsecs |
| Proper motion RA: | -5.3 |
| Proper motion Dec: | 3 |
| B-T magnitude: | 5.641 |
| V-T magnitude: | 5.848 |
Catalogs and designations:
|
INHABITED SKY
