Contenuti
Immagini
Carica la tua immagine
DSS Images Other Images
Articoli relazionati
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.
| Evolution of interacting binaries with a B type primary at birth
We revisited the analytical expression for the mass ratio distributionfor non-evolved binaries with a B type primary. Selection effectsgoverning the observations were taken into account in order to comparetheory with observations. Theory was optimized so as to fit best withthe observed q-distribution of SB1s and SB2s. The accuracy of thistheoretical mass ratio distribution function is severely hindered by theuncertainties on the observations. We present a library of evolutionarycomputations for binaries with a B type primary at birth. Some liberalcomputations including loss of mass and angular momentum during binaryevolution are added to an extensive grid of conservative calculations.Our computations are compared statistically to the observeddistributions of orbital periods and mass ratios of Algols. ConservativeRoche Lobe Over Flow (RLOF) reproduces the observed distribution oforbital periods but fails to explain the observed mass ratios in therange q in [0.4-1]. In order to obtain a better fit the binaries have tolose a significant amount of matter, without losing much angularmomentum.
| Doppler imaging and surface differential rotation of young open cluster stars - I. HD 307938 (R58) in IC 2602
In this paper we present Doppler images of a young active G dwarf (HD307938) in the southern open cluster IC 2602. Spectroscopic data wereobtained over a four-night period in 2000 January at the 3.9-mAnglo-Australian Telescope using the University College London EchelleSpectrograph. Simultaneous photometric observations (in the V and Rbands) were obtained at the 1.0-m Australian National Universitytelescope. By applying least-squares deconvolution (LSD) to the 2500+photospheric lines in each echelle spectrum a single highsignal-to-noise ratio LSD profile was produced for each phase of thespectroscopic observations. Maximum-entropy image reconstruction,incorporating both the LSD profiles and the photometric data, was usedto produce maps of the surface features of the star, with the inclusionof the photometric data producing an increase (compared with the use ofspectroscopic data alone) in the spot occupancy in both low- andmid-latitude regions of the star. The maps show that HD 307938 possessesa large, broken polar spot extending down to ~60° latitude, as wellas lower-latitude spots similar to other rapidly rotating G dwarfs. Byincorporating a solar-like differential rotation law into the imagingprocess the surface differential rotation of HD 307938 was determined.This gave a surface shear of dΩ= 0.025 +/- 0.015 radd-1 (for an inclination angle of 60°). Thus the equatorof HD 307938 laps the poles every ~250 d and has a photospheric sheararound half that of the Sun.
| 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.
| Empirical Absolute Magnitudes, Luminosities and Effective Temperatures of SPB Variables and the Problem of Variability Classification of Monoperiodic Stars
We derive semi--empirical log L/Lodot for 27 stars classifiedas SPB on the basis of Hipparcos photometry and we plot these stars onthe log Teff-log L/Lodot diagram. We confirmpulsations of HIP 63210 and HIP 108348 and show that luminosities andmasses derived from photometry are of limited use for asteroseismology.For HIP 69174 and 77227, two SB2 systems with an SPB primary, we computethe age of the systems, the orbital inclination - i, the large semi-axis- a, and the masses, radii, log Teff, log g and logL/Lodot of the components.We discover five new multiperiodic stars classified in the literature asSPB, namely, HIP 5161, 20963, 26243, 26464 and 44996. One of thesestars, HIP 26243, shows periods on the time-scales of days and hours.Finally, we discuss classification of monoperiodic SPBs and show thatphotometry combined with evolutionary models can be helpful inpreselecting tentative pulsators.
| A Photometric and Spectroscopic Study of 3 Vulpeculae: An Observer's Nightmare
We describe photometry of 3 Vulpeculae obtained with the Four CollegeAutomated Photoelectric Telescope and spectroscopy obtained with the1.22 m telescope of the Dominion Astrophysical Observatory. We haveanalyzed differential uvby photometric observations obtained over 7 yr.Three main frequencies (f1=0.9719, f2=0.7923, andf3=0.8553 cycles day-1) were found, as well as asum frequency (f1+f2=1.76420 cyclesday-1). A study of the photographic region usinghigh-dispersion spectrograms obtained with a Reticon detector at thecoudé spectrograph confirms the variable nature of 3 Vul as a 53Persei star and indicates that the star's abundances are normal formain-sequence band B stars. The new spectra were combined with thosepreviously published to confirm an orbital period very close to 1 yr.Finally, comparison with models yielded both a mass (4.16Msolar) and an age (25 Myr), and a mass range for thecompanion (0.6-1.1 Msolar). With an orbital period of almost1 yr and a pulsation period of almost 1 day, this star is indeed anobserver's nightmare.
| 3D mapping of the dense interstellar gas around the Local Bubble
We present intermediate results from a long-term program of mapping theneutral absorption characteristics of the local interstellar medium,motivated by the availability of accurate and consistent parallaxes fromthe Hipparcos satellite. Equivalent widths of the interstellar NaID-line doublet at 5890 Å are presented for the lines-of-sighttowards some 311 new target stars lying within ~ 350 pc of the Sun.Using these data, together with NaI absorption measurements towards afurther ~ 240 nearby targets published in the literature (for many ofthem, in the directions of molecular clouds), and the ~ 450lines-of-sight already presented by (Sfeir et al. \cite{sfeir99}), weshow 3D absorption maps of the local distribution of neutral gas towards1005 sight-lines with Hipparcos distances as viewed from a variety ofdifferent galactic projections.The data are synthesized by means of two complementary methods, (i) bymapping of iso-equivalent width contours, and (ii) by densitydistribution calculation from the inversion of column-densities, amethod devised by Vergely et al. (\cite{vergely01}). Our present dataconfirms the view that the local cavity is deficient in cold and neutralinterstellar gas. The closest dense and cold gas ``wall'', in the firstquadrant, is at ~ 55-60 pc. There are a few isolated clouds at closerdistance, if the detected absorption is not produced by circumstellarmaterial.The maps reveal narrow or wide ``interstellar tunnels'' which connectthe Local Bubble to surrounding cavities, as predicted by the model ofCox & Smith (1974). In particular, one of these tunnels, defined bystars at 300 to 600 pc from the Sun showing negligible sodiumabsorption, connects the well known CMa void (Gry et al. \cite{gry85}),which is part of the Local Bubble, with the supershell GSH 238+00+09(Heiles \cite{heiles98}). High latitude lines-of-sight with the smallestabsorption are found in two ``chimneys'', whose directions areperpendicular to the Gould belt plane. The maps show that the LocalBubble is ``squeezed'' by surrounding shells in a complicated patternand suggest that its pressure is smaller than in those expandingregions.We discuss the locations of several HI and molecular clouds. Usingcomparisons between NaI and HI or CO velocities, in some cases we areable to improve the constraints on their distances. According to thevelocity criteria, MBM 33-37, MBM 16-18, UT 3-7, and MBM 54-55 arecloser than ~ 100 pc, and MBM 40 is closer than 80 pc. Dense HI cloudsare seen at less than 90 pc and 85 pc in the directions of the MBM 12and MBM 41-43 clouds respectively, but the molecular clouds themselvesmay be far beyond. The above closest molecular clouds are located at theneutral boundary of the Bubble. Only one translucent cloud, G192-67, isclearly embedded within the LB and well isolated.These maps of the distribution of local neutral interstellar NaI gas arealso briefly compared with the distribution of both interstellar dustand neutral HI gas within 300 pc.Tables 1 and 2 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/411/447
| Stellar differential rotation from direct star-spot tracking
On the Sun, the rotation periods of individual sunspots not only tracethe latitude-dependence of the surface rotation rate, but also provideclues as to the amount of subsurface fluid shear. In this paper wepresent the first measurements of stellar differential rotation made bytracking the rotation of individual star-spots with sizes comparable tothe largest sunspots. To achieve this we re-analyse four sequences ofdensely sampled, high signal-to-noise ratio echelle spectra of ABDoradus spanning several stellar rotations in 1996 December. Usingspectral subtraction, least-squares deconvolution and matched-filteranalysis, we demonstrate that it is possible to measure directly thevelocity amplitudes and rotation periods of large numbers of individualstar-spots at low to intermediate latitude. We derive values for theequatorial rotation rate and the magnitude of the surface differentialrotation, both of which are in excellent agreement with those obtainedby Donati & Collier Cameron from cross-correlation of Doppler imagesderived a year earlier in 1995 December, and with a re-analysis of the1996 data by the χ 2 landscape method. The differencesbetween the rotation rates of individual spots and the fitteddifferential rotation law are substantially greater than theobservational errors. The smaller spots show a greater scatter about themean relation than the larger ones, which suggests that buffeting byturbulent supergranular flows could be responsible.
| The standard theory of extinction and the spectrum of stars with very little reddening
This paper examines the relationship between spectra of stars of samespectral type with extremely low reddenings. According to the standardtheory, the relationship between the spectrum of stars with samespectral type and small, but different reddenings should be different inthe optical and in the UV. This difference is not observed: the ratio ofthe spectra of two stars in directions where the reddening is largeenough to be detected and low enough not to give a noticeable2200Å bump is an exponential of /1/λ from the near-infraredto the far-UV. This result is in conformity with the ideas introduced inpreceding papers: the exponential optical extinction extends to the UV,and the spectrum of stars with enough reddening is contaminated by lightscattered at close angular distance from the stars. An application willbe the determination of the spectrum of a non-reddened star from thespectrum of a star of same spectral type with little reddening.
| 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
| On the origin of the O and B-type stars with high velocities. II. Runaway stars and pulsars ejected from the nearby young stellar groups
We use milli-arcsecond accuracy astrometry (proper motions andparallaxes) from Hipparcos and from radio observations to retrace theorbits of 56 runaway stars and nine compact objects with distances lessthan 700 pc, to identify the parent stellar group. It is possible todeduce the specific formation scenario with near certainty for twocases. (i) We find that the runaway star zeta Ophiuchi and the pulsarPSR J1932+1059 originated about 1 Myr ago in a supernova explosion in abinary in the Upper Scorpius subgroup of the Sco OB2 association. Thepulsar received a kick velocity of ~ 350 km s-1 in thisevent, which dissociated the binary, and gave zeta Oph its large spacevelocity. (ii) Blaauw & Morgan and Gies & Bolton alreadypostulated a common origin for the runaway-pair AE Aur and mu Col,possibly involving the massive highly-eccentric binary iota Ori, basedon their equal and opposite velocities. We demonstrate that these threeobjects indeed occupied a very small volume ~ 2.5 Myr ago, and show thatthey were ejected from the nascent Trapezium cluster. We identify theparent group for two more pulsars: both likely originate in the ~ 50 Myrold association Per OB3, which contains the open cluster alpha Persei.At least 21 of the 56 runaway stars in our sample can be linked to thenearby associations and young open clusters. These include the classicalrunaways 53 Arietis (Ori OB1), xi Persei (Per OB2), and lambda Cephei(Cep OB3), and fifteen new identifications, amongst which a pair ofstars running away in opposite directions from the region containing thelambda Ori cluster. Other currently nearby runaways and pulsarsoriginated beyond 700 pc, where our knowledge of the parent groups isvery incomplete.
| The Local Interstellar Medium in Puppis-Vela
The first study of the local interstellar medium (LISM) towardPuppis-Vela (l=245deg to 275°, b=-15deg to+5°, d<200 pc) is presented in this paper. A study of thelocations, sizes, and physical characteristics of local interstellargas, i.e.``astronephography,'' is included, and relies upon the improveddistance measurements provided by Hipparcos parallax measurements. Allspectra of more distant sight lines contain absorption features due tointervening local gas, and more distant structures can only be studiedaccurately if components due to the LISM have been isolated. Towardsthis end, high-resolution (R~95,000), high signal-to-noise (S/N ~ 110 to250) Na I λλ5889.951, 5895.924 spectra of 11 nearby starsin the direction of Puppis-Vela have been obtained with the CoudéEchelle Spectrograph on the 1.4 m Coudé Auxiliary Telescope atthe European Southern Observatory. Toward Puppis-Vela, absorption due tothe Local Interstellar Cloud (LIC) was not observed, but components atthree distinct velocities were found, and the extent of the local gasproducing the features was estimated. The three components have thefollowing locations and velocities: component A-(l~276° to 298°,b~-5degto +4°), Vhelio=+6 to +9 kms-1, and d~104 pc; component B-(l~264deg to276°, b~-7deg to +3°), Vhelio=+12 to +15km s-1, and d~115 pc; component C-(l~252deg to271°, b~-8deg to -6°), Vhelio=+21 to +23km s-1, and d~131 pc. The conclusions regarding theultraviolet spectrum of γ2 Vel (l=263deg,b=-8deg, d=258+/-35 pc) presented by Fitzpatrick &Spitzer were reexamined in light of this new LISM data, and theambiguity in their conclusions about several absorption components isresolved. The stars in Puppis-Vela flank the region of the apparentextension of the Local Bubble (or Cavity) known as the β CMatunnel, and measurements of the Na I column density towards the samplestars have been used to modify existing estimates of the extent of thetunnel. A compilation of all existing Na I observations of less than 200pc sight lines around the tunnel reveal that low column densities havebeen exclusively detected within l~210deg to 250°, andb~-21deg to -9°. Near the Galactic plane, at latitudes-10deg
| The eclipsing binary V578 Mon in the Rosette nebula: age and distance to NGC 2244 using Fourier disentangled component spectra
V578 Mon is a member of the young stellar cluster NGC 2244 which isembedded in the Rosette nebula. It is a double-lined binary, consistingof two early-B type components which eclipse each other partially duringtheir 2.40848-day orbit. A novel technique of Fourier disentangling isapplied to disentangle the spectrum of the binary into the spectra ofits components, allowing a direct spectroscopic temperaturedetermination for each component. Together with an analysis of the lightcurve, the spectral disentangling process allows us to derive theorbital and fundamental stellar parameters. The hotter star (T_eff = 30000 K) has a mass of 14.5 Msun and a radius of 5.2 Rsun. The cooler one (T_eff = 26 400 K) has a mass of 10.3 Msun and a radius of 4.3 Rsun . Both stars are well insidetheir critical Roche lobe and move in an eccentric orbit (e=0.087) whichhas a semi-major axis of 22 Rsun and is seen at aninclination of 72.6degr . The rotation of both stars is synchronizedwith the orbital motion. The systemic velocity of 34.9 km s-1,confirms that the binary belongs to NGC 2244. The age of the binary,and hence of NGC 2244, is (2.3±0.2) 106 years. Fromthe fundamental stellar parameters and the interstellar absorption, thedistance to the cluster is derived to be 1.39 ±0.1 kpc, i.e.slightly lower than that found from photometric studies. Its age andspace velocity indicate that NGC 2244 is formed in the galactic plane.The high accuracy obtained (e.g. probable errors of 0.5% for the masses,1m -1.5% for the radii, despite the lack of total eclipses,and 1.5% for the temperatures) is a direct consequence of the spectraldisentangling technique, which as a by-product delivers very accurateradial velocities for all orbital phases. Based on observations obtainedat the European Southern Observatory (ESO), La Silla, Chile Table 5 isonly available in electronic form at the CDS via anonymous ftp to130.79.128.5 or at http://cdsweb.u-strasbg.fr
| Spectroscopic binary orbits from photoelectric radial velocities. Paper 148: HR 7955
Not Available
| Multisite observations of surface structures on AB Doradus in 1994 November
We present time-resolved optical spectroscopy and broad-band photometryof the rapidly rotating southern K0 dwarf star AB Doradus, obtainedduring 1994 November. The data were obtained as part of a collaborationdedicated to MUlti-SIte COntinuous Spectroscopy (MUSICOS), and entailedcoordinated observations on three continents to obtain the fullest phasecoverage possible subject to limitations of local weather conditions.The Doppler images from the three consecutive nights of the run showexcellent mutual agreement, with a dark polar cap and numerousintermediate- and low-latitude features. Simultaneous optical photometryshowed numerous short-duration U-band flares, and two longer durationoptical flares with durations of the order of hours. The latter producedbroad-band continuum enhancements throughout the optical spectrum. Wheresimultaneous spectroscopy was available, both types of flare were seento have counterparts in Hα and the Caii H line. Simultaneoustime-resolved ultraviolet spectroscopy from the Goddard High ResolutionSpectrograph (GHRS) aboard the Hubble Space Telescope, reportedelsewhere, shows that at least one of the short-duration U-band flareswas also observed in Civ with the GHRS. Time-series Hα spectrashowed significant evolution of the circumstellar prominence system overfive consecutive stellar rotations. One prominence underwent a dramaticincrease in distance from the stellar rotation axis. We speculate thatthis event may have been associated with one of the long-durationflares.
| Selection of a sample of bright southern Slowly Pulsating B Stars for long-term photometric and spectroscopic monitoring
The photometric experiment on Hipparcos has led to the discovery of,among other types of variables, a large amount of new Slowly Pulsating BStars. We have selected twelve bright southern stars of this sample,together with five previously known Slowly Pulsating B Stars, forspectroscopic and photometric monitoring. These seventeen stars havespectral types ranging from B 2 up to B 9 and thus fully cover theinstability strip. We here present the results of a preliminary analysisof our data and show that our sample is an extremely important one toperform seismology of intermediate-massive stars. In particular, we findthat all but one of the selected stars exhibit clear line-profilevariability. The broader-lined Slowly Pulsating B Stars tend to havemore complex line-profile variations. One of the previously known SlowlyPulsating B stars was known to be a binary. Besides this star, anothersix of the selected Slowly Pulsating B stars turn out to be multiplesystems. Five of these seven binaries have large rotational velocitiesand complicated line-profile variations with moving subfeatures. It isnot yet clear whether or not the binarity results in a particularspectrum of excited modes. Based on observations collected with the CATTelescope of the European Southern Observatory and with the SwissPhotometric Telescope of the Geneva Observatory, both situated at LaSilla in Chile
| Study of an unbiased sample of B stars observed with Hipparcos: the discovery of a large amount of new slowly pulsating B stars
We present a classification of 267 new variable B-type stars discoveredby Hipparcos. We have used two different classification schemes and theyboth result in only a few new beta Cephei stars, a huge number of newslowly pulsating B stars, quite some supergiants with alpha Cyg-typevariations and variable CP stars, and further some new periodic Be starsand eclipsing binaries. Our results clearly point out the biased naturetowards short-period variables of earlier, ground-based surveys ofvariable stars. The position of the new beta Cephei stars and slowlypulsating B stars in the HR diagram is determined by means of Genevaphotometry and is confronted with the most recent calculations of theinstability strips for both groups of variables. We find that the newbeta Cephei stars are situated in the blue part of the instability stripand that the new slowly pulsating B stars almost fully cover thetheoretical instability domain determined for such stars. Thesupergiants with alpha Cyg-type variations are situated between theinstability strips of the beta Cephei and the slowly pulsating B starson the one hand and previously known supergiants that exhibitmicrovariations on the other hand. This suggests some connection betweenthe variability caused by the kappa mechanism acting in a zone ofpartially ionised metals and the unknown cause of the variations insupergiants.
| 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.
| The Evolution of Surface Structures on Ab-Doradus
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995MNRAS.277.1145U&db_key=AST
| New limits on starspot lifetimes for AB Doradus
I present a set of maximum entropy reconstructions of the starspotdistribution on the surface of the rapidly rotating K0 dwarf AB Doradus,obtained on the night of 1992 December 14. The Doppler imaging code usedin the reconstructions has been modified to incorporate a newdata-weighting scheme that allows us to reconstruct stellar surfaceimages from the profiles of several photospheric lines observedsimultaneously. Comparison of the 1992 December image with thepreviously published images of the star in 1992 January shows verylittle change in the low- to intermediate-latitude spot configurationover the intervening eleven months. This is consistent with earlierreports of the long-term stability of the rotational phases oflight-curve minima and maxima on this star. The structure in thehigh-latitude `polar crown' is not so repeatable, and it appears that anew spot emerged between 1992 January and December. It is not yet clearwhether the short-term variations in the star's light-curve morphologymay be linked to either high-latitude rotational shear or rapidevolution of the high-latitude magnetic structures.
| 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.
| Four-colour photometry of eclipsing binaries. XXXB. The early B-type near-contact binary LZ Centauri.
LZ Cen is a double-lined, near-contact but detached eclipsing binaryconsisting of two evolved early B stars (B0.5-B1). This paper presentsthe first photoelectric and spectroscopic analysis of the system, basedon new light curves and spectroscopic data. uvby light curves wereobtained with the Danish 50 cm telescope at ESO, La Silla (916 points ineach colour). They were analysed with both the WINK model (Wood 1971,1972) and the Wilson-Devinney (1971) program in its extended versions(Wilson 1979, 1993), adopting a circular orbit. The codes of both modelswere improved with modifications in the numerical solution procedure,and the Wilson-Devinney model has been implemented with the possibilityof using tables of model atmosphere calculations, following the samephilosophy as the WINK model. These modifications are documented here insome detail for future reference. The mass and luminosity ratios androtations in the system are determined from a few photographic and CCDspectra. They show that the hotter component, eclipsed at primaryeclipse, is also the smaller, less massive, and less luminous of the twostars. It was found difficult to obtain light curve solutions which wereconsistent with both the observed mass and luminosity ratios, but withthe small number of spectra available, our best compromise solutionyields M_A_=12.5Msun_, M_B_=13.5Msun_(+/-10%),R_A_=8.4Rsun_, and R_B_=9.1Rsun_(+/-3-4%). Bothstars have temperatures close to 26500K and luminositiesL_A_=3.1x10^4^Lsun_ and L_B_=3.6x10^4^Lsun_. Withlog g values as low as 3.66, the stars are obviously quite evolved andnear the end of their life on the main sequence. We have explored thelikely evolutionary state of LZ Cen in more detail by comparing itsobserved properties with the standard and overshooting models of Claret& Gimenez (1989, 1992). The analysis shows that both stars in LZ Cenhave evolved to the very point of central hydrogen exhaustion or beyondif standard models are assumed, while LZ Cen is still well within themain-sequence band of the overshooting models, a rather more plausiblescenario. In the latter case, models with Z=~0.01 fit the observedtemperatures best for an age of some 12x10^6^yr, consistent with otherrecent results on young B stars.
| Doppler Images of Ab-Doradus in 1992JAN
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1994MNRAS.269..814C&db_key=AST
| An IUE survey of interstellar H I LY alpha absorption. 1: Column densities
We measure Galactic interstellar neutral hydrogen column densities byanalyzing archival interstellar Ly alpha absorption line data toward 554B2 and hotter stars observed at high resolution with the IUE satellite.This study more than doubles the number of lines of sight with measuresof N(H I) based on Ly alpha. We have included the scattered lightbackground correction algorithm of Bianchi and Bohlin in our datareduction. We use the correlation between the Balmer discontinuity(c1) index and the stellar Ly alpha absorption in order toassess the effects of stellar Ly alpha contamination. Approximately 40%of the B stars with measured (c1) index, exhibit seriousstellar Ly alpha contamination. One table contains the derived values ofthe interstellar N(H I) for 393 stars with at most small amounts ofstellar contamination. Another lists the observed values of total N(H I)for 161 stars with suspected stellar Ly alpha contamination and/oruncertain stellar parameters.
| Dense clumps of ionized gas near Pi Scorpii, as revealed by the fine-structure excitation of N II
The column density and the emission of the ionized gas along the line ofsight toward the B1 V + B2 V binary star Pi Sco are measured on thebasis of the fine-structure absorption lines of the ground state N II.It is found that the bulk of this ionized gas must be clumped on alength scale of 0.025 pc, which is far smaller than the observed size ofthe diffuse H II region surrounding Pi Sco of about 6 pc. The observedcolumn density of S III toward Pi Sco yields an upper limit on thedistance of the absorbing, clumped gas from the star of less than about0.02 pc, assuming that both the N II and S III absorption arise from thesame gas. The possibility that the ionized gas originates from aphotoevaporating circumstellar disk directly surrounding Pi Sco isexcluded, since such a disk would have an unusual size of order 0.025 pcand would have had to survive for the estimated age of Pi Sco of 5-8Myr. The derived mean density of the clumped gas is of order 40/cu cm,so that the gas is at a pressure that far exceeds the mean pressure inthe H II region. It is concluded that the ionized gas could originatefrom evaporation flows off a cluster of compact neutral objects thatevaporate due to the ionizing radiation of Pi Sco.
| Effective temperature of B-type stars from the SI II lines of the UV multiplet 13.04 at 130.5-130.9 NM
An analysis was performed for the 129.3-132.0 nm region of ten normaland two helium-weak peculiar B-type stars of spectral types ranging fromB2 to B9 and luminosity classes IV-V. Computations of spectra made itpossible to determine the Si abundance from the Si III lines and toestimate the effective temperature from the Si III profiles. Therotational velocities of all the stars were also investigated.
| Interstellar reddening in the Southern Hemisphere. I - The UVBY beta observations
The uvby-beta photometric data obtained from a Southern Hemisphereobservational project is presented. A uvby-beta photometric network ofnearly 3900 A and early F stars has been established with the intentthat the stars serve as 'space probes' for measurements of interstellarreddening.
| Criteria for the spectral classification of B stars in the ultraviolet
A set of criteria for the classification of G stars from UV spectraalone, using standards drawn form the optical region, is developed.About 100 stars having normal MK spectral types in the range B0-B8,III-V, have been classified. The UV spectral types are found to be veryconsistent with the optical MK types, implying that it is possible to dotwo-dimensional spectral classification in the UV without any knowledgeof the optical spectrum.
| Catalogue of i and w/w crit values for rotating early type stars
Not Available
| Secondary standards for H-beta photometry in the E regions.
Not Available
|
Sottometti un nuovo articolo
Link relazionati
Sottometti un nuovo link
Membro dei seguenti gruppi:
|
Osservazione e dati astrometrici
| Costellazione: | Poppa |
| Ascensione retta: | 07h52m38.70s |
| Declinazione: | -38°51'47.0" |
| Magnitudine apparente: | 4.49 |
| Distanza: | 196.464 parsec |
| Moto proprio RA: | -9.7 |
| Moto proprio Dec: | 2.9 |
| B-T magnitude: | 4.253 |
| V-T magnitude: | 4.445 |
Cataloghi e designazioni:
|
INHABITED SKY
