Contents
Images
Upload your image
DSS Images Other Images
Related articles
The Origins and Evolutionary Status of B Stars Found Far from the Galactic Plane. II. Kinematics and Full Sample Analysis
This paper continues the analysis of faint high-latitude B stars fromMartin. Here we analyze the kinematics of the stars and combine themwith the abundance information from the first paper to classify eachone. The sample contains 31 Population I runaways, 15 old evolved stars(including 5 blue horizontal-branch [BHB] stars, 3 post-HB stars, 1pulsating helium dwarf, and 6 stars of ambiguous classification), 1 Fdwarf, and 2 stars that do not easily fit in one of the othercategories. No star in the sample unambiguously shows thecharacteristics of a young massive star formed in situ in the halo. Thetwo unclassified stars are probably extreme Population I runaways. Thelow binary frequency and rotational velocity distribution of thePopulation I runaways imply that most were ejected from dense starclusters by the dynamic ejection scenario. However, we remain puzzled bythe lack of runaway Be stars. We also confirm that PB 166 and HIP 41979are both nearby solar-metallicity BHB stars.Based on observations made at the 2.1 m Otto Struve Telescope ofMcDonald Observatory, operated by the University of Texas at Austin.
| Improved oscillator strengths and wavelengths in Hf II, with applications to stellar elemental abundances
Aims. We present new and improved radiative lifetimes for eight levelsin Hf I and 18 levels in Hf II, along with oscillator strengths andwavelengths for 195 transitions in Hf II. With these data we determinethe abundance of hafnium in two chemically peculiar stars: the hot-Amstar HR 3383 and the HgMn star χ Lupi, and discuss the implicationsof the new data to the hafnium abundance for the Sun and the metal-poorgalactic halo stars CS 22892-052 and CS 31082-001. Methods: . Theoscillator strengths are derived by combining radiative lifetimesmeasured with the laser induced fluorescence technique and branchingfractions determined from intensity calibrated Fourier transformspectra. The hafnium abundance in the two sharp-lined peculair stars isdetermined by comparison of spectra obtained from instruments onboardthe Hubble Space Telescope with synthetic spectra, while the abundanceof hafnium in the solar photosphere and the metal-poor halo stars isdiscussed in terms of rescaling previous investigations using the new gfvalues. Results: . The abundance enhancement of hafnium has beendetermined in HR 3383 to be +1.7 dex and that for χ Lupi A is +1.3dex. In the course of the analysis we have also determined an abundanceenhancement for molybdenum in HR 3383 to be +1.2 dex, which is similarto that known for χ Lupi A. The abundances in the metal-poor halostars CS 31082-001 and CS 22892-052 were rescaled to log ɛ(Hf) =-0.75 and -0.82 respectively, with smaller 1σ uncertainty. Thishas the effect of improving the theoretical fits of r-processnucleosynthesis to abundance data for heavy elements. The change of gfvalues also implies that the hafnium abundance in the solar photosphereshould be reduced by up to 0.2 dex, thereby inducing a discrepancy withthe meteoritic hafnium abundance.
| New clues on outburst mechanisms and improved spectroscopic elements of the black hole binary V4641 Sagittarii*
We present spectroscopic observations of the black hole binary V4641Sagittarii, obtained between 2004 July 4 and 2005 March 28, which coverthe minor outburst of the star in early 2004 July and quiescencevariations on 19 nights scattered over six months. During the outburst,the star peaked approximately 3 mag brighter than usual, and our spectrawere dominated by broad hydrogen, helium and iron emission lines. Thevery first spectra showed P Cygni profiles, which disappeared within afew hours, indicating rapid changes in matter ejection. The Hαline had multiple components, one being a broad blueshifted wingexceeding 5000 km s-1. During a simultaneously observed10-min photometric flare up, the equivalent width of the Hα linetemporarily decreased, implying that it was a flare of the continuum.The overall spectral appearance was similar to that observed in the 1999September active phase, which suggests that similar mass-ejectionprocesses were associated with both eruptions. In quiescence, thespectra were those of the early-type secondary star showing its orbitalmotion around the primary. By measuring cross-correlation radialvelocities, we give an improved set of spectroscopic elements. Whereaswe measure the same velocity amplitude (K2= 211.3 +/- 1.0 kms-1), within errors, as Orosz et al., our centre-of-massvelocity (γ= 72.7 +/- 3.3 km s-1) differs significantlyfrom the previously published value (107.4 +/- 2.9 km s-1).However, we find evidence that the difference is caused by a systematicerror in data reduction in the previous study, rather than bygravitational effects of an invisible third component.
| High-Mass Triple Systems: The Classical Cepheid Y Carinae
We have obtained a Hubble Space Telescope STIS ultraviolethigh-dispersion echelle-mode spectrum of the binary companion of thedouble-mode classical Cepheid Y Car. The velocity measured for the hotcompanion from this spectrum is very different from reasonablepredictions for binary motion, implying that the companion is itself ashort-period binary. The measured velocity changed by 7 kms-1 during the 4 days between two segments of theobservation, confirming this interpretation. We summarize ``binary''Cepheids that are in fact members of a triple system and find that atleast 44% are triples. The summary of information on Cepheids withorbits makes it likely that the fraction is underestimated.Based on observations made with the NASA/ESA Hubble Space Telescope,obtained at the Space Telescope Science Institute, which is operated bythe Association of Universities for Research in Astronomy, Inc.
| Heavy Element Abundances in Late-B and Early-A Stars. I. Co-Added IUE Spectra of HgMn Stars
Very heavy elements (Pt, Au, Hg, Tl, and Bi) are found to be enhanced inthe atmospheres of the chemically peculiar stars of the upper mainsequence by up to a million times the solar system levels. Suchenhancements are believed to result from atmospheric dynamics (i.e.,diffusion) rather than scenarios that dredge up nuclear-processedmaterial to the surface or transfer processed material between binarycompanions. However, the theoretical framework needs to be furtherconstrained by observations beyond the realm of the spectral types forwhich such abundance enhancements are observed at optical wavelengths.The International Ultraviolet Explorer (IUE) satellite collected spectraof bright stars for which chemical peculiarities have been derived fromground-based data. For several elements the abundance enhancements haveonly been recently measured using Hubble Space Telescope data and havetherefore not yet been exploited in the IUE data. We have initiated aprogram to analyze IUE high-dispersion spectra to more fullycharacterize the pattern of very heavy element enhancement for manymercury-manganese (HgMn) stars and to potentially extend the spectralclass (effective temperature) boundaries over which these abundanceanomalies are known to exist. The abundances of very heavy elements inchemically normal B and A-type stars provide a base level that may becompared with the solar system abundances. These early spectral typestars may therefore reveal clues for galactic chemical evolution studiessince they were formed at a later epoch than the Sun in the history ofthe Galaxy. This first paper presents the motivation for the analyses tofollow, outlines our spectral co-addition technique for IUE spectra, anddiscusses the choice of model atmospheres and the synthetic spectrumprocedures, while initiating the study by highlighting the abundance ofgold in several HgMn stars.
| The Indo-US Library of Coudé Feed Stellar Spectra
We have obtained spectra for 1273 stars using the 0.9 m coudéfeed telescope at Kitt Peak National Observatory. This telescope feedsthe coudé spectrograph of the 2.1 m telescope. The spectra havebeen obtained with the no. 5 camera of the coudé spectrograph anda Loral 3K×1K CCD. Two gratings have been used to provide spectralcoverage from 3460 to 9464 Å, at a resolution of ~1 Å FWHMand at an original dispersion of 0.44 Å pixel-1. For885 stars we have complete spectra over the entire 3460 to 9464 Åwavelength region (neglecting small gaps of less than 50 Å), andpartial spectral coverage for the remaining stars. The 1273 stars havebeen selected to provide broad coverage of the atmospheric parametersTeff, logg, and [Fe/H], as well as spectral type. The goal ofthe project is to provide a comprehensive library of stellar spectra foruse in the automated classification of stellar and galaxy spectra and ingalaxy population synthesis. In this paper we discuss thecharacteristics of the spectral library, viz., details of theobservations, data reduction procedures, and selection of stars. We alsopresent a few illustrations of the quality and information available inthe spectra. The first version of the complete spectral library is nowpublicly available from the National Optical Astronomy Observatory(NOAO) via ftp and http.
| Rotational Velocities of B, A, and Early-F Narrow-lined Stars
Projected rotational velocities for 58 B, A, and early-F stars have beendetermined from high-resolution spectroscopic observations made at KittPeak National Observatory with the coudé feed telescope. All thestars are slowly rotating with vsini<60 km s-1. Because oftheir low rotational velocities, 15 of the stars have been observed asprospective, early-type, radial velocity standards.
| The Quadruple System μ Orionis: Three-dimensional Orbit and Physical Parameters
The star μ Orionis is a spectroscopic visual quadruple system inwhich each visual component is a short-period spectroscopic binary. Thevisual orbit has a period of 18.644 yr, a high eccentricity of 0.7426,and a high inclination of 96.2d. The visual primary consists of an Amstar and probably a G or early K dwarf that orbit each other in a nearlycircular orbit with a period of 4.4475858 days. The visual secondaryconsists of a pair of F5: V stars in a circular orbit with a period of4.7835361 days. While the masses of the two stars are nearly identicaland the magnitude difference between the pair is close to zero, theprojected rotational velocities differ by almost a factor of 2. Theorbit for the B subsystem is not coplanar with the visual orbit, whilethat for the A subsystem is probably not coplanar as well. The orbitalparallax of 0.02107"+/-0.00018" is more accurate than that obtained fromthe Hipparcos observations and corresponds to a distance of 47.5+/-0.4pc. A comparison with evolutionary tracks indicates that the Am star isnear the end of its main-sequence evolution.
| Rotational velocities of A-type stars in the northern hemisphere. II. Measurement of v sin i
This work is the second part of the set of measurements of v sin i forA-type stars, begun by Royer et al. (\cite{Ror_02a}). Spectra of 249 B8to F2-type stars brighter than V=7 have been collected at Observatoirede Haute-Provence (OHP). Fourier transforms of several line profiles inthe range 4200-4600 Å are used to derive v sin i from thefrequency of the first zero. Statistical analysis of the sampleindicates that measurement error mainly depends on v sin i and thisrelative error of the rotational velocity is found to be about 5% onaverage. The systematic shift with respect to standard values fromSlettebak et al. (\cite{Slk_75}), previously found in the first paper,is here confirmed. Comparisons with data from the literature agree withour findings: v sin i values from Slettebak et al. are underestimatedand the relation between both scales follows a linear law ensuremath vsin inew = 1.03 v sin iold+7.7. Finally, thesedata are combined with those from the previous paper (Royer et al.\cite{Ror_02a}), together with the catalogue of Abt & Morrell(\cite{AbtMol95}). The resulting sample includes some 2150 stars withhomogenized rotational velocities. Based on observations made atObservatoire de Haute Provence (CNRS), France. Tables \ref{results} and\ref{merging} are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.125.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/393/897
| The presence of Nd and Pr in HgMn stars
Optical region spectra for a number of upper main sequence chemicallypeculiar (CP) stars have been observed to study singly and doublyionized praseodymium and neodymium lines. In order to improve existingatomic data of these elements, laboratory measurements have been carriedout with the Lund VUV Fourier Transform Spectrometer (FTS). From thesemeasurements wavelengths and hyperfine structure (hfs) have been studiedfor selected Pr Ii, Pr Iii and Nd Iii lines of astrophysical interest.Radiative lifetimes for some excited states of Pr Ii have beendetermined with the aid of laser spectroscopy at the Lund Laser Center(LLC) and have been combined with branching fractions measured in thelaboratory to calculate gf values for some of the stronger optical linesof Pr Ii. With the aid of the derived gf values and laboratorymeasurements of the hfs, a praseodymium abundance was derived fromselected Pr Ii lines in the spectrum of the Am star 32 Aqr. Thisabundance was used to derive astrophysical gf values for selected Pr Iiilines in 32 Aqr, and these gf values were used to get a praseodymiumabundance for the HgMn star HR 7775. The praseodymium abundance in HR7775 was then utilized to derive astrophysical gf values for allobservable Pr Iii lines in this star. The neodymium abundance, derivedfrom unblended lines of Nd Ii in HR 7775, has been utilized to establishastrophysical gf values for observed Nd Iii lines in the optical regionof this star. Selected Pr Iii and Nd Iii lines have been identified andstudied in a number of HgMn stars and three hot Am stars. Thepraseodymium and neodymium abundance change rapidly from an approximate1-1.2 dex enhancement for the hot Am stars to 1.5-3 dex enhancement forthe cool HgMn stars, indicating a well-defined boundary between the hotAm and HgMn stars in the vicinity of 10 500 K. The enhancement ofpraseodymium and neodymium in Am and HgMn stars may be explained bydiffusive processes active in the stellar atmosphere, while the observeddiscontinuity might be explained by a thin hydrogen convection zonethought to be present for the Am stars, but absent in the HgMn stars.The absence of a convection zone would cause the diffused elements togather higher in the atmosphere of HgMn stars compared to Am stars, andexplain the observed increase in abundance.
| Rotational velocities of A-type stars. I. Measurement of v sin i in the southern hemisphere
Within the scope of a Key Programme determining fundamental parametersof stars observed by HIPPARCOS, spectra of 525 B8 to F2-type starsbrighter than V=8 have been collected at ESO. Fourier transforms ofseveral line profiles in the range 4200-4500 Å are used to derivev sin i from the frequency of the first zero. Statistical analysis ofthe sample indicates that measurement error is a function of v sin i andthis relative error of the rotational velocity is found to be about 6%on average. The results obtained are compared with data from theliterature. There is a systematic shift from standard values from\citet{Slk_75}, which are 10 to 12% lower than our findings. Comparisonswith other independent v sin i values tend to prove that those fromSlettebak et al. are underestimated. This effect is attributed to thepresence of binaries in the standard sample of Slettebak et al., and tothe model atmosphere they used. Based on observations made at theEuropean Southern Observatory (ESO), La Silla, Chile, in the frameworkof the Key Programme 5-004-43K. Table 4 is only available in electronicform at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.125.5)or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/381/105
| Stellar populations in Seyfert 2 galaxies. I. Atlas of near-UV spectra
We have carried out a uniform spectroscopic survey of Seyfert 2 galaxiesto study the stellar populations of the host galaxies. New spectra havebeen obtained for 79 Southern galaxies classified as Seyfert 2 galaxies,7 normal galaxies, and 73 stars at a resolution of 2.2 Å over thewavelength region 3500-5300 Å. Cross-correlation between thestellar spectra is performed to group the individual observations into44 synthesis standard spectra. The standard groups include a solarabundance sequence of spectral types from O5 to M3 for dwarfs, giants,and supergiants. Metal-rich and metal-weak F-K giants and dwarfs arealso included. A comparison of the stellar data with previouslypublished spectra is performed both with the individual spectra and thestandard groups. For each galaxy, two distinct spatial regions areconsidered: the nucleus and the external bulge. Spectroscopic variationsfrom one galaxy to another and from the central to the external regionare briefly discussed. It is found that the central region of a Seyfert2 galaxy, after subtracting the bulge stellar population, always shows anear-UV spectrum similar to one of three representative categories: a)many strong emission lines and only two visible absorption lines (Ca IiK and G band) (Sey2e); b) few emission lines, many absorption lines, anda redder continuum than the previous category (Sey2a); c) an almost flatcontinuum and high-order Balmer lines seen in absorption (Sey2b). Theproportion of Seyfert 2 galaxies belonging to each class is found to be22%, 28%, and 50% respectively. We find no significative differencesbetween morphology distributions of Seyfert 2 galaxies with Balmer linesdetected in absorption and the rest of the sample. This quick lookthrough the atlas indicates that half of Seyfert 2 galaxies harbour ayoung stellar population (about or less than 100 Myr) in their centralregion, clearly unveiled by the high order Balmer series seen inabsorption. Based on observations collected at the European SouthernObservatory, Chile (ESO 65.P-0014(A)). Tables 1-3 and 8 and Fig. A.1(Appendix A) are only available in electronic form athttp://www.edpsciences.org
| 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
| Research Note Hipparcos photometry: The least variable stars
The data known as the Hipparcos Photometry obtained with the Hipparcossatellite have been investigated to find those stars which are leastvariable. Such stars are excellent candidates to serve as standards forphotometric systems. Their spectral types suggest in which parts of theHR diagrams stars are most constant. In some cases these values stronglyindicate that previous ground based studies claiming photometricvariability are incorrect or that the level of stellar activity haschanged. Table 2 is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/367/297
| Sixth Catalogue of Fundamental Stars (FK6). Part III. Additional fundamental stars with direct solutions
The FK6 is a suitable combination of the results of the HIPPARCOSastrometry satellite with ground-based data, measured over a longinterval of time and summarized mainly in the FK5. Part III of the FK6(abbreviated FK6(III)) contains additional fundamental stars with directsolutions. Such direct solutions are appropriate for single stars or forobjects which can be treated like single stars. Part III of the FK6contains in total 3272 stars. Their ground-based data stem from thebright extension of the FK5 (735 stars), from the catalogue of remainingSup stars (RSup, 732 stars), and from the faint extension of the FK5(1805 stars). From the 3272 stars in Part III, we have selected 1928objects as "astrometrically excellent stars", since their instantaneousproper motions and their mean (time-averaged) ones do not differsignificantly. Hence most of the astrometrically excellent stars arewell-behaving "single-star candidates" with good astrometric data. Thesestars are most suited for high-precision astrometry. On the other hand,354 of the stars in Part III are Δμ binaries in the sense ofWielen et al. (1999). Many of them are newly discovered probablebinaries with no other hitherto known indication of binarity. The FK6gives, besides the classical "single-star mode" solutions (SI mode),other solutions which take into account the fact that hidden astrometricbinaries among "apparently single-stars" introduce sizable "cosmicerrors" into the quasi-instantaneously measured HIPPARCOS proper motionsand positions. The FK6 gives, in addition to the SI mode, the "long-termprediction (LTP) mode" and the "short-term prediction (STP) mode". TheseLTP and STP modes are on average the most precise solutions forapparently single stars, depending on the epoch difference with respectto the HIPPARCOS epoch of about 1991. The typical mean error of anFK6(III) proper motion in the single-star mode is 0.59 mas/year. This isa factor of 1.34 better than the typical HIPPARCOS errors for thesestars of 0.79 mas/year. In the long-term prediction mode, in whichcosmic errors are taken into account, the FK6(III) proper motions have atypical mean error of 0.93 mas/year, which is by a factor of about 2better than the corresponding error for the HIPPARCOS values of 1.83mas/year (cosmic errors included).
| 64 Orionis: Three-Dimensional Orbit and Physical Parameters
We have obtained radial velocities of the components of the short-periodsubsystem of the B-type triple star 64 Orionis, covering a full cycle ofthe long-period orbit since the date of our earlier paper by Fekel &Scarfe. We use all of our radial velocities, together with availablespeckle interferometry, to derive a three-dimensional orbit for thelong-period system. The system has orbital periods of 14.57213 days and12.98 yr. We also determine spectroscopically a magnitude difference at4500 Å of 1.0+/-0.1 between the components of the close pair.Although radial velocities of the third component continue to elude us,we are able to derive masses and luminosities for all three componentsby requiring that they lie within the populated band of the observedmass-luminosity relationship. With this constraint, the orbital parallaxis 0.00374"+/-0.00017". Our results are consistent with the spectraltypes and colors derived previously and with the b magnitude differencedetermined by earlier lunar occultation observations, within theuncertainties of those parameters.
| A spectroscopic study of the magnetic CP-star HR 1094
The chemically peculiar star HR 1094 has beeninvestigated with respect to its chemical composition and the magneticinfluence on its stellar spectrum. By using spectral lines slightlyaffected by the field v sin i was determined to be <= 17 kms-1. The iron-group elements as well as chlorine and theheavy elements platinum, gold and mercury show an overabundance comparedto the sun. The analysis also revealed the rare earth elements to bepresent from lines of their second and third spectrum. Based onobservations obtained with the Nordic Optical Telescope, operated on theisland of La Palma jointly by Denmark, Finland, Iceland, Norway, andSweden, in the Spanish Observatorio del Roque de los Muchachos of theInstituto de Astrofísica de Canarias.
| Determining the Physical Properties of the B Stars. I. Methodology and First Results
We describe a new approach to fitting the UV-to-optical spectra of Bstars to model atmospheres and present initial results. Using a sampleof lightly reddened stars, we demonstrate that the Kurucz modelatmospheres can produce excellent fits to either combined low-dispersionIUE and optical photometry or HST FOS spectrophotometry, as long as thefollowing conditions are fulfilled: (1) an extended grid of Kuruczmodels is employed; (2) the IUE NEWSIPS data are placed on the FOSabsolute flux system using the Massa & Fitzpatrick transformation;(3) and all of the model parameters and the effects of interstellarextinction are solved for simultaneously. When these steps are taken,the temperatures, gravities, abundances, and microturbulence velocitiesof lightly reddened B0-A0 V stars are determined to high precision. Wealso demonstrate that the same procedure can be used to fit the energydistributions of stars that are reddened by any UV extinction curve thatcan be expressed by the Fitzpatrick & Massa parameterization scheme.We present an initial set of results and verify our approach throughcomparisons with angular diameter measurements and the parametersderived for an eclipsing B-star binary. We demonstrate that themetallicity derived from the ATLAS9 fits to main-sequence B stars isessentially the Fe abundance. We find that a near zero microturbulencevelocity provides the best fit to all but the hottest or most luminousstars (where it may become a surrogate for atmospheric expansion) andthat the use of white dwarfs to calibrate UV spectrophotometry is valid.
| Toward an Orbit for the High-Luminosity Cepheid T Monocerotis
We have obtained new velocities of the long-period Cepheid T Mon fromthe ground and velocities of its hot companion with the Hubble SpaceTelescope (HST) and the International Ultraviolet Explorer (IUE).Although observations do not cover a full orbit, both the maximum andminimum orbital velocities have now been obtained. We present apreliminary orbit and discuss the uncertainties in the orbitalparameters. The velocities for the companion appear to be inconsistentwith binary orbital motion, and it is likely that the companion isitself a binary in a short-period orbit. The HST spectrum of thecompanion shows that it is a chemically peculiar star, probablymagnetic. Because it is coupled with the more massive Cepheid, it mustbe very close to the zero-age main sequence. The well-determined massfunction from the preliminary orbit implies that the inclination of thelong-period system is close to 90 deg.
| Radial velocities of HIPPARCOS southern B8-F2 type stars
Radial velocities have been determined for a sample of B8-F2 type starsobserved by the Hipparcos satellite. Observations were obtained withinthe framework of an ESO key-program. Radial velocities have beenmeasured using a cross-correlation method, the templates being a grid ofsynthetic spectra. The obtained precision depends on effectivetemperature and projected rotational velocity of the star as well as ona possible asymmetry of the correlation peak generally due to secondarycomponents. New spectroscopic binaries have been detected from theseasymmetries and the variability of the measured radial velocity.Simulations of binary and triple systems have been performed. Forbinaries our results have been compared with Hipparcos binary data.Adding the variable radial velocities, the minimum binary fraction hasbeen found 60% for physical systems. Radial velocities have beendetermined for 581 B8-F2 stars, 159 being new. Taking into accountpublished radial velocities, 39% south A-type stars with V magnitudelower than 7.5 have a radial velocity. Based on observations obtained atthe European Southern Observatory (ESO, La Silla, Chile) and on datafrom the ESA Hipparcos astrometry satellite.}\fnmsep \thanks{Tables 7, 8and 9 are only available in electronic form at the CDS via anonymous ftpto cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| The nature of the sharp-lined A1V star HD 72660
In order to specify the nature of the sharp-lined A1V star HD 72660, itseffective temperature and surface gravity have been determined using twodifferent methods. First, the ultraviolet energy distribution of HD72660 has been compared with that of the normal A0 star HD 10939 andwith the predictions of two model atmospheres. Secondly, the parametershave been derived from Moon & Dworetsky's (1985) calibration of uvbycolors. Both methods yield consistent values Teff = 9750 +/-\200 K, logg = 4.00 +/-\ 0.20 dex. In a second part, high resolution highsignal to noise optical spectra centered on <~mbda4500 Angstroms,<~mbda5080 Angstroms and <~mbda6160 Angstroms have beensynthesized using Gray's (1995) and Takeda's (1995) LTE codes. Theabundances of 13 elements were derived. C and O are found to beunderabundant with respect to the solar value (-0.60 and -0.52 dexrespectively) whereas Ti, Cr, Fe, Ni are overabundant (between +0.37 and+0.72 dex). Ca appears to be moderately overabundant (+0.16 dex). Theseresults suggest that HD 72660 is a hot Am star. Based on observationscollected at Observatoire de Haute Provence (France)
| Hot-Am stars as intermediary objects to the HgMn and AM stars
We describe the early results of an investigation into the spectralcharacteristics of the hottest Am stars (A0 - A2) in an attempt to linkthe HgMn and Am classes of chemical peculiarity. A limited sample ofhot-Am stars was searched for the presence of lines from the very heavyelements platinum and mercury, as well as a search for lines from therare-earth elements in HgMn stars. Our analysis of the strong opticalplatinum and mercury lines in the spectrum of the HgMn star HR 7775 hasdetected isotopic shifts that are different from those found atultraviolet wavelengths and, in the case of mercury, vary withionization stage.
| The Mass of the Cepheid Binary V636 Scorpii
The mass-luminosity relation for Cepheids depends on the degree ofmixing in their main-sequence progenitors. Masses of Cepheids can beinferred by using different aspects of pulsation theory. These methodshave in the past led to diverging results, showing that something waswrong in either evolution theory or pulsation theory or both. For somebinary Cepheids dynamical masses, which are independent of pulsation andevolution theories, can be determined. V636 Sco is one of a handful ofCepheid binaries whose companions are bright enough in the ultravioletthat orbital radial velocities can be measured. We have here attemptedto determine the radial velocity of the companion V636 Sco B to theCepheid V636 Sco A by means of two Hubble Space Telescope (HST) spectrataken at phases of minimum and maximum Cepheid orbital velocities. Theratio of the orbital velocity of the companion and the Cepheid (which isthe inverse of their mass ratio) came out to be 1.25 +/- 0.17. V636 ScoB has a spectral type B9.5 V, for which we expect a stellar mass of 2.5M_ȯ. For the Cepheid we thus determine a mass of 3.1 +/- 0.4M_ȯ, which is surprisingly low. If true, such a low mass wouldindicate an extremely large amount of excess mixing, which is veryunlikely. We discuss the likely possibility that V636 Sco B may itselfbe a binary with an unseen secondary, in which case the mass derivedfrom the two measurements discussed above is not correct. Although theerror limits for the mass of each Cepheid are rather large, the combinedmass-luminosity relation for all Cepheids studied by us so far by meansof HST spectra indicates excess mixing corresponding to core convectiveovershoot by 0.25 to about 0.5 pressure scale height in themain-sequence progenitors of the Cepheids. Based on observations madewith the NASA/ESA Hubble Space Telescope, obtained at the SpaceTelescope Science Institute, which is operated by the Association ofUniversities for Research in Astronomy, Inc., under NASA contractNASS-26555.
| Classical Cepheid Masses: U Aquilae
We have obtained medium-resolution spectra ( lambda / Delta lambda ~20,000) of the hot binary companion to the classical Cepheid U Aql withthe Goddard High Resolution Spectrograph on the Hubble Space Telescope(HST). These have been used to determine the orbital velocity amplitude.Combining this with the orbital velocity amplitude of the Cepheid fromthe ground-based orbit and the mass of the companion inferred from itsspectral type, we measure a mass of the Cepheid of 5.1 +/- 0.7 Mȯ.We discuss the full sample of Cepheids for which we have determinedmasses with HST (S Mus, V350 Sgr, Y Car, and U Aql) and also SU Cyg(mass from IUE). The HST masses are in agreement with the luminositiespredicted by recent evolutionary tracks with moderate overshoot. Thiscomparison, however, may be altered by reassessment of Cepheid distancesbased on Hipparcos parallaxes.
| Detection of atmospheric velocity fields in A-type stars
High signal-to-noise spectra with spectral resolution of more than 10(5)have been obtained of one normal B9.5V, one normal A1V, two Am stars,and two HgMn B stars having v sin i less than 6 km s(-1) . These spectraare modeled with LTE line profile synthesis to test the extent to whichthe spectrum of each star can be modeled correctly with a single set ofparameters T_e, log g, chemical abundances, v sin i, and(depth-independent) microturbulent velocity xi . The answer to thisquestion is important for abundance analysis of A and B stars; ifconventional line synthesis does not reproduce the line profilesobserved in stars of small v sin i, results obtained from such analysisare not likely to be very precise. The comparison of models withobservations is then used to search for direct evidence of atmosphericmotions, including line-strength dependent broadening, line core shape,and line asymmetries, in order to study how the microturbulence derivedfrom abundance analysis is related to more direct evidence ofatmospheric velocity fields. It is found for the three stars with 12,000>= T_e >= 10,200 K (the normal star 21 Peg and the two HgMn stars53 Tau and HD 193452) that xi is less than 1 km s(-1) , and lineprofiles are reproduced accurately by the synthesis with a single set ofparameters. The slightly cooler (T_e ~ 9800 K) star HD 72660 has only aslightly stronger surface convective layer than the hotter stars, butfor this star xi ~ 2.2 km s(-1) . Strong spectral lines all showsignificant asymmetry, with the blue line wing deeper than the red wing,and have line bisectors which have curvature towards the blue with aspan of about 0.5 to 1.0 km s(-1) . A single model fits all linessatisfactorily. The two Am stars (HD 108642 and 32 Aqr), with T_e ~ 8000K, are found to have much larger values of xi (4 to 5 km s(-1) ). Thestrong spectral lines of these two stars are extremely asymmetric, withdepressed blue wings, and the bisectors have spans of order 3 km s(-1) .No consistent fit to all lines can be found with a single model of thetype used here. It is concluded (a) that classical LTE line synthesis isable to reproduce with considerable accuracy the line profiles of late Band early A stars with T_e above about 9500 K, but that the LTE modelwith depth-independent microturbulence provides a very poorapproximation for cooler A stars, (b) that curve-of-growthmicroturbulent velocities in A stars are related to directly detectableatmospheric velocity fields, and (c) that the discrepancies betweencalculated and observed line profiles in stars with temperatures in thevicinity of 8000 K are so large that abundances derived mainly fromsaturated lines may well contain significant errors. As a by-product,laboratory gf values for Fe II between 3800 and 5300 Angstroms have beencombined to form a set of data optimized for internal consistency of thegf values. Based on observations obtained with the Canada-France-Hawaiitelescope, operated by the National Research Council of Canada, theCentre National de Recherche Scientifique of France, and the Universityof Hawaii, and with the 1.52-m telescope of the Observatoire de HauteProvence, operated by the Centre National de Recherche Scientifique ofFrance.
| The Tokyo PMC catalog 90-93: Catalog of positions of 6649 stars observed in 1990 through 1993 with Tokyo photoelectric meridian circle
The sixth annual catalog of the Tokyo Photoelectric Meridian Circle(PMC) is presented for 6649 stars which were observed at least two timesin January 1990 through March 1993. The mean positions of the starsobserved are given in the catalog at the corresponding mean epochs ofobservations of individual stars. The coordinates of the catalog arebased on the FK5 system, and referred to the equinox and equator ofJ2000.0. The mean local deviations of the observed positions from theFK5 catalog positions are constructed for the basic FK5 stars to comparewith those of the Tokyo PMC Catalog 89 and preliminary Hipparcos resultsof H30.
| The Mass of the Classical Cepheid V350 SGR
Two medium resolution spectra of the hot companion of the Cepheid V350Sgr have been obtained with the Goddard High Resolution Spectrographaboard the Hubble Space Telescope. Comparison of these spectra (in thewavelength range 1840 to 1880 \AA) with the spectrum of $\alpha$ Lyrshows that V350 Sgr B has a projected rotation velocity which may be ashigh as 150 km sec$^{-1}$. The velocity difference between the spectraof V350 Sgr B at two orbital phases is measured to be -23.1 $\pm$ 3.8 kmsec$^{-1}$. The error is dominated by the aperture centering. Whencombined with the orbital velocity variation of the Cepheid derived fromthe ground-based orbit and the mass of the companion deduced from IUEspectra, the mass of the Cepheid is found to be 5.2 $\pm$ 0.9 M$\sun$.The observed mass--luminosity combination of V350 Sgr A is a good matchto recent evolutionary calculations which use moderate convectiveovershoot near the main sequence, however, the blue loops do not extendto temperatures as hot as the Cepheid. (SECTION: Stars)
| The dynamical mass of the beat cepheid Y carinae and stellar opacities.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....114.1176B&db_key=AST
| 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 S/N Echelle spectroscopy in young stellar groups. II. Rotational velocities of early-type stars in SCO OB2.
We investigate the rotational velocities of early-type stars in the ScoOB2 association. We measure v.sin(i) for 156 established and probablemembers of the association. The measurements are performed with threedifferent techniques, which are in increasing order of expectedv.sin(i): 1) converting the widths of spectral lines directly tov.sin(i), 2) comparing artificially broadened spectra of low v.sin(i)stars to the target spectrum, 3) comparing the HeI λ4026 lineprofile to theoretical models. The sample is extended with literaturedata for 47 established members of Sco OB2. Analysis of the v.sin(i)distributions shows that there are no significant differences betweenthe subgroups of Sco OB2. We find that members of the binary populationof Sco OB2 on the whole rotate more slowly than the single stars. Inaddition, we find that the B7-B9 single star members rotatesignificantly faster than their B0-B6 counterparts. We test varioushypotheses for the distribution of v.sin(i) in the association. Theresults show that we cannot clearly exclude any form of randomdistribution of the direction and/or magnitude of the intrinsicrotational velocity vector. We also investigate the effects of rotationon colours in the Walraven photometric system. We show that positions ofB7-B9 single dwarfs above the main sequence are a consequence ofrotation. This establishes the influence of rotation on the Walravencolours, due primarily to surface gravity effects.
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
| Constellation: | Ύδρα |
| Right ascension: | 08h34m01.60s |
| Declination: | -02°09'06.0" |
| Apparent magnitude: | 5.81 |
| Distance: | 100 parsecs |
| Proper motion RA: | -33.3 |
| Proper motion Dec: | 20.1 |
| B-T magnitude: | 5.804 |
| V-T magnitude: | 5.792 |
Catalogs and designations:
|
