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Публикации по объекту
Variations in D/H and D/O from New Far Ultraviolet Spectroscopic Explorer Observations
We use data obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE) to determine the interstellar abundances of D I, N I, O I, Fe II,and H2 along the sight lines to WD 1034+001, BD +39 3226, andTD1 32709. Our main focus is on determining the D/H, N/H, O/H, and D/Oratios along these sight lines, with logN(H)>20.0, that probe gaswell outside of the Local Bubble. Hubble Space Telescope (HST) andInternational Ultraviolet Explorer (IUE) archival data are used todetermine the H I column densities along the WD 1034+001 and TD1 32709sight lines, respectively. For BD +39 3226, a previously published N(HI) is used. We find(D/H)×105=2.14+0.53-0.45,1.17+0.31-0.25, and1.86+0.53-0.43 and(D/O)×102=6.31+1.79-1.38,5.62+1.61-1.31, and7.59+2.17-1.76 for the WD 1034+001, BD +39 3226,and TD1 32709 sight lines, respectively (all 1 σ). The scatter inthese three D/H ratios exemplifies the scatter that has been found byother authors for sight lines with column densities in the range19.2
| High-precision elements of double-lined spectroscopic binaries from combined interferometry and spectroscopy. Application to the β Cephei star β Centauri
Aims.We present methodology to derive high-precision estimates of thefundamental parameters of double-lined spectroscopic binaries. We applythe methods to the case study of the double-lined β Cephei starβ Centauri. We also present a detailed analysis of βCentauri's line-profile variations caused by its oscillations.Methods: .High-resolution spectral time series and visual orinterferometric data with a good phase distribution along the orbitalperiod are required. We point out that a systematic error in the orbitalamplitudes, and any quantities derived from them, occurs if the radialvelocities of blended component lines are computed without spectraldisentangling. This technique is an essential ingredient in thederivation of the physical parameters if the goal is to obtain aprecision of only a few percent. We have devised iteration schemes toobtain the orbital elements for systems whose lines are blendedthroughout the orbital cycle. Results: .We derive the componentmasses and dynamical parallax of β Centauri with a precision of 6%and 4%, respectively. Modelling allowed us to refine the mass estimatesto 1% precision resulting in M_1=10.7± 0.1 M_ȯ andM_2=10.3± 0.1 M_ȯ, and to derive the age of the system asbeing (14.1± 0.6)× 106 years. We deduce twooscillation frequencies for the broad-lined primary of β Centauri:f_1=7.415 c d-1 and f_2=4.542 c d-1 or one oftheir aliases. The degrees of these oscillation modes are higher than 2for both frequencies, irrespective of the alias problem. No evidence ofoscillations in the narrow-lined secondary was found. Conclusions: .We propose that our iteration schemes be used in anyfuture derivations of the spectroscopic orbital parameters ofdouble-lined binaries with blended component lines to whichdisentangling can be successfully applied. The combination of parametersresulting from the iteration schemes with high-precision estimates ofthe orbital inclination and the angular semi-major axis frominterferometric or visual measurements allows a complete solution of thesystem.
| 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.
| Atlas and Catalog of Dark Clouds Based on Digitized Sky Survey I
We present a quantitative atlas and catalog of dark clouds derived byusing the optical database ``Digitized Sky Survey I''. Applying atraditional star-count technique to 1043 plates contained in thedatabase, we produced an AV map covering the entire region inthe galactic latitude range |b| ≤ 40°. The map was drawn at twodifferent angular resolutions of 6' and 18', and is shown in detail in aseries of figures in this paper. Based on the AV map, weidentified 2448 dark clouds and 2841 clumps located inside them. Somephysical parameters, such as the position, extent, and opticalextinction, were measured for each of the clouds and clumps. We alsosearched for counterparts among already known dark clouds in theliterature. The catalog of dark clouds presented in this paper lists thecloud parameters as well as the counterparts.
| The Chemical Composition of α Cen A: Strong Lines and the ABO Theory of Collisional Line Broadening
The mean abundances of Mg, Si, Ca, Ti, Cr, and Fe based on both strongand weak lines of α Cen A are determined by matching the observedline profiles with those synthesised from stellar atmospheric models andcomparing these results with a similar analysis for the Sun. There isgood agreement between the abundances from strong and weak lines. Stronglines should generally be an excellent indicator of abundance and fareasier to measure than the weak lines normally used. Until thedevelopment of the Anstee, Barklem, and O'Mara (ABO) theory forcollisional line broadening, the uncertainty in the value of the dampingconstant prevented strong lines being used for abundance determinationsother than in close differential analyses. We found that α Cen Ahas a mean overabundance of 0.12 +/- 0.06 dex compared to solar meanabundances. This result agrees remarkably well with previous studiesthat did not use strong lines or the ABO theory for collisional linebroadening. Our result supports the conclusion that reliable abundancescan be derived from strong lines provided this new theory for linebroadening is used to calculate the van der Waals damping.
| Orbital parameters, masses and distance to β Centauri determined with the Sydney University Stellar Interferometer and high-resolution spectroscopy
The bright southern binary star β Centauri (HR5267) has beenobserved with the Sydney University Stellar Interferometer (SUSI) andspectroscopically with the European Southern Observatory Coude AuxiliaryTelescope and Swiss Euler telescope at La Silla. The interferometricobservations have confirmed the binary nature of the primary componentand have enabled the determination of the orbital parameters of thesystem. At the observing wavelength of 442nm the two components of theprimary system have a magnitude difference of 0.15 +/- 0.02. Thecombination of interferometric and spectroscopic data gives thefollowing results: orbital period 357.00 +/- 0.07d, semimajor axis 25.30+/- 0.19mas, inclination 67.4 +/-0.3, eccentricity0.821 +/- 0.003, distance 102.3 +/- 1.7pc, primary and secondary massesM1=M2= 9.1 +/- 0.3 Msolar and absolutevisual magnitudes of the primary and secondary M1V=-3.85 +/-0.05 and M2V=-3.70 +/- 0.05, respectively. The high degree ofaccuracy of the results offers a fruitful starting point for futureasteroseismic modelling of the pulsating binary components.
| Catalog of Galactic β Cephei Stars
We present an extensive and up-to-date catalog of Galactic β Cepheistars. This catalog is intended to give a comprehensive overview ofobservational characteristics of all known β Cephei stars, coveringinformation until 2004 June. Ninety-three stars could be confirmed to beβ Cephei stars. We use data from more than 250 papers publishedover the last nearly 100 years, and we provide over 45 notes onindividual stars. For some stars we reanalyzed published data orconducted our own analyses. Sixty-one stars were rejected from the finalβ Cephei list, and 77 stars are suspected to be β Cepheistars. A list of critically selected pulsation frequencies for confirmedβ Cephei stars is also presented.We analyze the β Cephei stars as a group, such as the distributionsof their spectral types, projected rotational velocities, radialvelocities, pulsation periods, and Galactic coordinates. We confirm thatthe majority of the β Cephei stars are multiperiodic pulsators. Weshow that, besides two exceptions, the β Cephei stars with highpulsation amplitudes are slow rotators. Those higher amplitude starshave angular rotational velocities in the same range as thehigh-amplitude δ Scuti stars (Prot>~3 days).We construct a theoretical HR diagram that suggests that almost all 93β Cephei stars are main-sequence objects. We discuss theobservational boundaries of β Cephei pulsation and the physicalparameters of the stars. We corroborate that the excited pulsation modesare near to the radial fundamental mode in frequency and we show thatthe mass distribution of the stars peaks at 12 Msolar. Wepoint out that the theoretical instability strip of the β Cepheistars is filled neither at the cool nor at the hot end and attempt toexplain this observation.
| XMM-Newton observations of β Centauri (B1 III): The temperature structure in the hot plasma and the photosphere-wind connection
We present XMM-Newton observations of the B giant β Centauri (B1III). The spectra are rich of spectral lines from a wide range ofionization stages which indicate temperatures in the range ~0.1-0.6 keV.Simultaneous fits to the rgs, epic-mos, and epic-pn spectra yield threeplasma temperatures (0.1, 0.2, and 0.6 keV), emission measures, andelemental abundances which are quite close to solar values. Thesetemperatures are confirmed by DEM modeling. According to the derivedmodels the intrinsic source X-ray luminosity in the energy range 0.3-10keV is Lx = 10 × 1030 erg s-1 ata distance of 161 pc. An analysis of the X-ray light curve suggests thatthe photospheric variability does not have much of an effect on theproperties of the X-ray luminosity. The sensitivity of the He-likeforbidden and intercombination lines to a strong ultraviolet stellarradiation field is used to constrain the radial distances at which thelines of Ne ix, O vii, and N vi originate.
| Metallicity of mono- and multiperiodic β Cephei stars
Analyzing IUE ultraviolet spectra of β Cep pulsating stars wenoticed that multiperiodic variables have a larger mean metal abundancein the photosphere, [ m/H] , than monoperiodic ones. We applystatistical tests to verify this dichotomy. We obtain that, with a largeprobability, the multiperiodic β Cep stars have greater values of [m/H] . This result is consistent with the linear non-adiabatic theory ofpulsation of early B-type stars.
| Metallicities of the β Cephei stars from low-resolution ultraviolet spectra
We derive basic stellar parameters (angular diameters, effectivetemperatures, metallicities) and interstellar reddening for all βCephei stars observed during the IUE satellite mission, including thosebelonging to three open clusters. The parameters are derived by means ofan algorithmic procedure of fitting theoretical flux distributions tothe low-resolution IUE spectra and ground-based spectrophotometricobservations. Since the metallicity has a special importance forpulsating B-type stars, we focus our attention in particular on thisparameter.Tables 1, 2, 4 and 5 are only available in electronic form athttp://www.edpsciences.org
| CHARM2: An updated Catalog of High Angular Resolution Measurements
We present an update of the Catalog of High Angular ResolutionMeasurements (CHARM, Richichi & Percheron \cite{CHARM}, A&A,386, 492), which includes results available until July 2004. CHARM2 is acompilation of direct measurements by high angular resolution methods,as well as indirect estimates of stellar diameters. Its main goal is toprovide a reference list of sources which can be used for calibrationand verification observations with long-baseline optical and near-IRinterferometers. Single and binary stars are included, as are complexobjects from circumstellar shells to extragalactic sources. The presentupdate provides an increase of almost a factor of two over the previousedition. Additionally, it includes several corrections and improvements,as well as a cross-check with the valuable public release observationsof the ESO Very Large Telescope Interferometer (VLTI). A total of 8231entries for 3238 unique sources are now present in CHARM2. Thisrepresents an increase of a factor of 3.4 and 2.0, respectively, overthe contents of the previous version of CHARM.The catalog is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/431/773
| Modelling of dust scattering toward the Coalsack
Murthy, Henry & Holberg discovered intense far-ultraviolet (FUV)(λλ912-1600) emission from the direction of the Coalsackmolecular cloud 10 years ago. We have used their results in conjunctionwith a Monte Carlo model for the scattering in the region to show thatthe scattering is from dust in the foreground of the Coalsack. Thealbedo of the grains is 0.4 +/- 0.2. This is one of the fewdeterminations of the albedo of dust in the diffuse interstellar mediumin the FUV.
| Classification of Spectra from the Infrared Space Observatory PHT-S Database
We have classified over 1500 infrared spectra obtained with the PHT-Sspectrometer aboard the Infrared Space Observatory according to thesystem developed for the Short Wavelength Spectrometer (SWS) spectra byKraemer et al. The majority of these spectra contribute to subclassesthat are either underrepresented in the SWS spectral database or containsources that are too faint, such as M dwarfs, to have been observed byeither the SWS or the Infrared Astronomical Satellite Low ResolutionSpectrometer. There is strong overall agreement about the chemistry ofobjects observed with both instruments. Discrepancies can usually betraced to the different wavelength ranges and sensitivities of theinstruments. Finally, a large subset of the observations (~=250 spectra)exhibit a featureless, red continuum that is consistent with emissionfrom zodiacal dust and suggest directions for further analysis of thisserendipitous measurement of the zodiacal background.Based on observations with the Infrared Space Observatory (ISO), aEuropean Space Agency (ESA) project with instruments funded by ESAMember States (especially the Principle Investigator countries: France,Germany, Netherlands, and United Kingdom) and with the participation ofthe Institute of Space and Astronautical Science (ISAS) and the NationalAeronautics and Space Administration (NASA).
| 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.
| Interpretation of the variability of the β Cephei star λ Scorpii. I. The multiple character
We derive accurate values of the orbital parameters of the close binaryβ Cephei star λ Scorpii. Moreover, we present the firstdetermination of the properties of the triple system to which λScorpii belongs. Our analysis is based on a time series of 815high-resolution spectra, covering a timespan of 14 years. We find aclose orbit of 5.9525 d days (e=0.26) and a wide orbit of approximately1082d days (e=0.23). The orbital parameters of the triplestar and a spectrum synthesis lead us to conclude that the system iscomposed of two early-type B stars and a low-mass pre-main-sequence starrather than containing an ultra-massive white dwarf as claimed before.Our proposed configuration is compatible with population synthesis. Theradial velocity variations of the primary allow us to confirm thepresence of at least one pulsation mode with frequency 4.679410 cd-1 which is subject to the light-time effect in the triplesystem. A detailed analysis of the complex line-profile variations isdescribed in a subsequent paper.Based on observations obtained with the Coudé EchelleSpectrograph on the ESO CAT telescope and with the CORALIE EchelleSpectrograph on the 1.2-m Euler Swiss telescope, both situated at LaSilla, ChileTable \ref{observations} is only available in electronic form athttp://www.edpsciences.org
| Coronal versus photospheric abundances of stars with different activity levels
We report a detailed analysis of the coronal abundance of 4 stars withvarying levels of activity and with accurately known photosphericabundances. The coronal abundance is determined here using a line fluxanalysis and a full determination of the differential emission measure.Photospheric abundance values are taken from the literature. Previouscoronal abundance determinations have generally been compared to solarphotospheric abundances; from this a number of general properties havebeen inferred, such as the presence of a coronal metal depletion with aninverse First Ionization Potential correlated with activity level. Herewe show that, when coronal abundances are compared with realphotospheric values for the individual stars, the resulting pattern canbe very different. Also, we present evidence that, in some cases, thecoronal metal abundance may not be uniform in the corona; in particularit can vary with the temperature of the emitting plasma.Tables 4-7 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/416/281
| β Cep stars from a spectroscopic point of view
In this review we present the current status of line-profile-variationstudies of β Cep stars. Such studies have been performed for 26bright members of this class of pulsating stars in the past 25 years. Wedescribe all these currently available data and summarize theinterpretations based on them in terms of the excited pulsation modes.We emphasize that line-profile variations offer a much more detailedpicture of the pulsational behaviour of pulsating stars compared toground-based photometric data. The latter, however, remain necessary tounravel the often complex frequency pattern and to achieve unambiguousmode identification for multiperiodic β Cep stars and also toderive the pulsational properties of the faint members of the class. Wehighlight the statistical properties of the sample of 26 stars for whichaccurate spectroscopic studies are available and point out some futureprospects.
| Statistics of the Instability Strip of β Cephei Stars
We present a study of the β Cephei instability strip based on asample of 49 stars of this type. After deriving their effectivetemperatures and luminosities from their observed (B-V), (U-B) colorsand parallaxes we find their positions in the HR diagram to be mostlyconfined to the main sequence, and their masses to lie between 7Mȯ and 30 Mȯ. Their distribution on theHR diagram matches well with our previous theoretical instability stripwhich has an upper bound in the luminosity and rather tight boundariesin the effective temperature.
| Spectroscopic mode identification for the beta Cephei star EN (16) Lacertae
We perform for the first time spectroscopic mode identification in theeclipsing binary beta Cephei star EN (16) Lac. This mode identificationis based upon a time series of 942 line profiles of the He I lambdalambda 6678 Åline in its spectrum. All three known frequenciesf1, f,SUB>2,/SUB>, f3 of the star arepresent in the line-profile variations, but we failed to find additionalmodes. Using different identification methods we find conclusiveevidence for the radial nature of the main mode and for the l=2, m=0identification of the mode with frequency f2. A uniqueidentification of the third mode is not possible from the spectra, butwe do derive that l3<3. Fits to the amplitude and phasevariability of the modes imply a rotation frequency between 0.1 and 0.4c d-1. The star's rotation axis is not aligned with theorbital axis.Based on observations gathered with the coudé spectrographattached to the 2.0 m reflector telescope at Tautenburg Observatory.
| The UCSD HIRES/Keck I Damped Lyα Abundance Database. III. An Empirical Study of Photoionization in the Damped Lyα System toward GB 1759+7539
We investigate the ionization state of the damped Lyα system atz=2.62 toward GB 1759+7539 through an analysis of ionic ratios sensitiveto photoionization: Ar0/S+,Fe++/Fe+, N+/N0, andAl++/Al+. Approximately half of the metals arisein a mostly neutral velocity component with H I/H>0.9, based onFe++/Fe+<0.013. In contrast, the remaining halfexhibit Fe++/Fe+~0.3, indicative of a partiallyionized medium with H I/H~0.5. These conclusions are supported by theobserved N+/N0, Al++/Al+,and Ar0/Si+ ratios. We assess ionizationcorrections for the observed column densities through photoionizationmodels derived from the CLOUDY software package. In the neutral gas, theionization corrections are negligible, except for Ar0.However, for the partially ionized gas, element abundance ratios differfrom the ionic ratios by 0.1-0.3 dex for (Si+, S+,Ni+, Al+)/Fe+ ratios and more for(N0, Ar0)/Fe+. Independent of the shapeof the photoionizing spectrum and assumptions of the number ofionization phases, these ionization corrections have minimal impact(<~0.1 dex) on the total metallicity inferred for this dampedLyα system. Measurements of the relative elemental abundances ofthe partially ionized gas, however, have a greater than ~0.15 dexuncertainty, which hides the effects of nucleosynthesis and differentialdust depletion. We caution the reader that this damped system is unusualfor a number of reasons (e.g., a very low Ar0/S+ratio), and we believe its ionization properties are special but notunique. Nevertheless, it clearly shows the value of examiningphotoionization diagnostics such as Fe++/Fe+ in alarger sample of damped systems. Visiting Astronomer, W. M. KeckTelescope. The Keck Observatory is a joint facility of the University ofCalifornia and the California Institute of Technology.
| The Local Interstellar Ultraviolet Radiation Field
I have used the Hipparcos Input Catalogue, together with Kurucz modelstellar atmospheres and information on the strength of the interstellarextinction, to create a model of the expected intensity and spectraldistribution of the local interstellar ultraviolet radiation field,under various assumptions concerning the albedo a of the interstellargrains. (This ultraviolet radiation field is of particular interestbecause of the fact that ultraviolet radiation is capable of profoundlyaffecting the chemistry of the interstellar medium.) By comparing mymodels with the observations, I am able to conclude that the albedo a ofthe interstellar grains in the far-ultraviolet is very low, perhapsa=0.1. I also advance arguments that my present determination of thisalbedo is much more reliable than any of the many previous (andconflicting) ultraviolet interstellar grain albedo determinations.Beyond this, I show that the ultraviolet background radiation that isobserved at high Galactic latitudes must be extragalactic in origin, asit cannot be backscatter of the interstellar radiation field.
| A Search for Fine Structure within the 4430 Å Diffuse Interstellar Band
The dependence of the 4430 Å diffuse interstellar band (DIB) ondust extinction or total gas column density indicates that this DIB,like the narrower features seen in the yellow-red portion of thespectrum, does not continue to grow in strength beyond a certainthreshold. One possible interpretation is that the 4430 Å DIBsaturates at high column densities, suggesting that this band mightconsist of unresolved narrow features (such as molecular rotationallines), individually saturated, that are blended at the resolving powerof previous observations. In this study we use the Ultra High ResolutionFacility on the Anglo-Australian Telescope to assess that question byseeking evidence for fine structure within the 4430 Å DIB at thevery high spectral resolving power ofΔλ/λ~106. Our target stars include linesof sight where apparent rotational line structure has been observed inother DIBs. We find no evidence of fine structure within the 4430Å DIB, suggesting that the broadening of this band is intrinsic.If so, the lack of fine structure may indicate a molecular transitionfollowed by very rapid internal conversion or a molecular transitionconsisting of overlapping rotational lines. In either case, our resultssupport the hypothesis that the apparent saturation of the band as afunction of extinction is a result of the ``skin effect,'' in which thestrength of DIBs stops increasing with extinction because the DIBs formprimarily in the outer boundaries of interstellar clouds.
| beta Centauri: An eccentric binary with two beta Cep-type components
We introduce our observational study of the orbital motion and theintrinsic variability of the double-lined spectroscopic binary beta Cen.Using 463 high signal-to-noise, high-resolution spectra obtained over atimespan of 12 years it is shown that the radial velocity of beta Cenvaries with an orbital period of 357.0 days. We derive for the firsttime the orbital parameters of beta Cen and find a very eccentric orbit(e=0.81) and similar component masses with a mass ratioM1/M2=1.02. beta Cen forms a challenge for currentevolution scenarios in close binaries and it is also a puzzle how amassive binary with such a large eccentricity could have formed in thefirst place. Both the primary and the secondary exhibit line-profilevariations. A period analysis performed on the radial velocityvariations of the primary after prewhitening the orbital motion leads tothe detection of at least 3 pulsation frequencies while the star doesnot show any periodic photometric variability. Based on observationsobtained with the ESO CAT/CES telescope and the Swiss Euler/CORALIEtelescope, both situated at La Silla, Chile.
| 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
| Infrared spectral classification of OB stars with ISO-SWS
We present observations of the Bralpha , Brbeta and Pfalpha lines of 16dwarf and (sub)giant stars in the spectral range O9-B3. The observationswere done using the Short Wavelength Spectrometer on board the InfraredSpace Observatory, and have a signal-to-noise of ~ 20 to > 150 and aresolving power varying from ~ 1400 to 2100. We compare the equivalentwidths of these lines with predictions using non-LTE model atmospheresto investigate to what extent these infrared lines can be used to deriveeffective temperatures. We find that Pfalpha is a sensitive T_effdiagnostic for the range of spectral types investigated, and Bralpha fortypes O9-B2, yielding agreement with optical results to within 1-4 kK orone-three spectral sub-types. We find evidence for a gradient in theturbulent velocity, increasing from la 5 km s-1 for theatmospheric region in which Bralpha is formed to ~ 15 km s-1for the regime where Pfalpha originates. When this gradient in turbulentvelocity is taken into account, the accuracy of the spectral typecalibration is improved to ~ 1 kK or one spectral sub-type. The gravitydependence of the strengths of the investigated infrared lines isrelatively weak, and could not be used to constrain luminosity class.This failure is in part a result of the modest S/N and resolution and inpart a result of a cancelation of gravity effects in the line core andline wing. Our line predictions show that Hei lambda 2.058 is relativelyunsuited for spectral classification of O9-B3 stars. Hualpha , however,is expected to be an even better diagnostic as are Pfalpha and Bralpha .This line may be observed with the VLT Imager and Spectrometer for midInfraRed when it is installed on the Very Large Telescope.
| The proper motions of fundamental stars. I. 1535 stars from the Basic FK5
A direct combination of the positions given in the HIPPARCOS cataloguewith astrometric ground-based catalogues having epochs later than 1939allows us to obtain new proper motions for the 1535 stars of the BasicFK5. The results are presented as the catalogue Proper Motions ofFundamental Stars (PMFS), Part I. The median precision of the propermotions is 0.5 mas/year for mu alpha cos delta and 0.7mas/year for mu delta . The non-linear motions of thephotocentres of a few hundred astrometric binaries are separated intotheir linear and elliptic motions. Since the PMFS proper motions do notinclude the information given by the proper motions from othercatalogues (HIPPARCOS, FK5, FK6, etc.) this catalogue can be used as anindependent source of the proper motions of the fundamental stars.Catalogue (Table 3) is only available at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strastg.fr/cgi-bin/qcat?J/A+A/365/222
| Astrophysics in 1999
The year 1999 saw the arrival of a star with three planets, a universewith three parameters, and a solar corona that could be heated at leastthree ways. In addition, there were at least three papers on everyquestion that has ever been asked in astrophysics, from ``Will theUniverse expand forever?'' to ``Does mantle convection occur in one ortwo layers?'' The answers generally were, ``Yes,'' ``No,'' and ``None ofthe above,'' to each of the questions. The authors have done their bestto organize the richness around centers defined by objects, methods, andmadnesses.
| Dating Ptolemy's star catalogue through proper motions : the Hipparchan epoch.
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| Spatial Variability in the Ratio of Interstellar Atomic Deuterium to Hydrogen. II. Observations toward γ2 Velorum and ζ Puppis by the Interstellar Medium Absorption Profile Spectrograph
High-resolution far-ultraviolet spectra of the early-type starsγ2 Vel and ζ Pup were obtained to measure theinterstellar deuterium abundances in these directions. The observationswere made with the Interstellar Medium Absorption Profile Spectrograph(IMAPS) during the ORFEUS-SPAS II mission in 1996. IMAPS spectra coverthe wavelength range 930-1150 Å withλ/Δλ~80,000. The interstellar D I features areresolved and cleanly separated from interstellar H I in the Lyδand Lyɛ profiles of both sight lines and also in the Lyγprofile of ζ Pup. The D I profiles were modeled using a velocitytemplate derived from several N I lines in the IMAPS spectra recorded athigher signal-to-noise ratio. To find the best D I column density, weminimized χ2 for model D I profiles that included notonly the N(D I) as a free parameter, but also the effects of severalpotential sources of systematic error, which were allowed to vary asfree parameters. H I column densities were measured by analyzingLyα absorption profiles in a large number of IUE high-dispersionspectra for each of these stars and applying this sameχ2-minimization technique. Ultimately we found thatD/H=2.18+0.36-0.31×10-5 forγ2 Vel and1.42+0.25-0.23×10-5 for ζPup, values that contrast markedly with D/H derived in Paper I forδ Ori A (the stated errors are 90% confidence limits). Evidently,the atomic D/H ratio in the ISM, averaged over path lengths of 250-500pc, exhibits significant spatial variability. Furthermore, the observedspatial variations in D/H do not appear to be anticorrelated with N/H,one measure of heavy-element abundances. We briefly discuss somehypotheses to explain the D/H spatial variability. Within the frameworkof standard big bang nucleosynthesis, the large value of D/H foundtoward γ2 Vel is equivalent to a cosmic baryon densityof ΩBh2=0.023+/-0.002, which we regard as anupper limit since there is no correction for the destruction ofdeuterium in stars. This paper is dedicated in memory of Judith L.Tokel, wife of the first author, who passed away on 2000 June 10. Herenthusiastic support and encouragement were essential to its successfulcompletion.
| What Is the Nature of the Spectroscopic Companion of the Early B Star λ Scorpii?
The B star λ Sco is known to be a spectroscopic binary system.The companion, which is in a short periodic orbit with the B star, is sofar unknown. X-ray observations with ROSAT by Berghöfer et al. in1997 have shown a super-soft X-ray excess, which is unusual for B starsof spectral type B1.5 IV. Here we present an analysis of our longExtreme Ultraviolet Explorer (EUVE) observation of λ Sco. Basedon these data and all available X-ray observations of this star, weconstrain the physical parameters of the companion. As long as no otherexplanation is available for the EUV/soft X-ray excess, thespectroscopic companion of λ Sco is most likely an ultramassivewhite dwarf. The primary B star is thus the most massive star known tohave a white dwarf companion. Such a stellar system can have evolvedonly by mass transfer. Stellar evolution scenarios predict the existenceof such binary systems, which are expected to be precursors of theultrasoft X-ray sources and which finally explode in a supernova TypeIa. The EUV light curve of λ Sco shows significant short-termvariations on a 20% level. A period-folding search carried out tofurther investigate the EUV light curve of λ Sco does not provideclear evidence for any periodicity present in the data. It is worthwhileto mention that the analysis of variance periodogram shows a 2 σfeature at 4.7 cycles days-1, which is close to the mainpulsation frequency of the β Cep-type B star. Further observationshave to confirm the existence of such a periodicity in the EUV lightcurve. Furthermore, when folded with the orbital period, the EUV lightcurve of λ Sco shows two broader dips of 30% intensity loss atphases φ=0.56 and 0.11. At these two phases, the stars pass eachother in the line of sight. We discuss these features in the EUV lightcurve of λ Sco in terms of orbital dependent changes in theabsorption column of the primary's wind along the line of sight towardthe white dwarf companion.
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