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Evolution of magnetic fields in stars across the upper main sequence: I. Catalogue of magnetic field measurements with FORS 1 at the VLT
To properly understand the physics of Ap and Bp stars it is particularlyimportant to identify the origin of their magnetic fields. For that, anaccurate knowledge of the evolutionary state of stars that have ameasured magnetic field is an important diagnostic. Previous resultsbased on a small and possibly biased sample suggest that thedistribution of magnetic stars with mass below 3 M_ȯ in the H-Rdiagram differs from that of normal stars in the same mass range (Hubriget al. 2000). In contrast, higher mass magnetic Bp stars may well occupythe whole main-sequence width (Hubrig, Schöller & North 2005b).In order to rediscuss the evolutionary state of upper main sequencemagnetic stars, we define a larger and bias-free sample of Ap and Bpstars with accurate Hipparcos parallaxes and reliably determinedlongitudinal magnetic fields. We used FORS 1 at the VLT in itsspectropolarimetric mode to measure the magnetic field in chemicallypeculiar stars where it was unknown or poorly known as yet. In thisfirst paper we present our results of the mean longitudinal magneticfield measurements in 136 stars. Our sample consists of 105 Ap and Bpstars, two PGa stars, 17 HgMn stars, three normal stars, and nine SPBstars. A magnetic field was for the first time detected in 57 Ap and Bpstars, in four HgMn stars, one PGa star, one normal B-type star and fourSPB stars.
| 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.
| A study of bright southern slowly pulsating B stars. III. Mode identification for singly-periodic targets in spectroscopy
We present the results of the mode identification for a sample of 7bright southern slowly pulsating B stars showing one pulsation frequencyin the λλ 413 nm Si II profiles. We combined the resultsfrom (1) the method of photometric amplitudes; (2) the moment method;and (3) the amplitude and phase variation across the profile to searchfor the ℓ and m values of the modes best fitting the data. It is thefirst time that the applicability of these techniques is tested to asample of main-sequence g-mode pulsators. Combining the moment methodwith the amplitude and phase variations across the observed line profilegives an improvement in spectroscopic identification of low degree ℓg-mode pulsations. Using the variations of the higher order even moments< v4> and < v6> of the moment methodsolutions can also help. For HD 181558, HD 24587, HD 140873 and HD177863, the photometric and spectroscopic results are compatible andpoint towards (ℓ,m) = (1, +1) sectoral modes. For HD 215573, HD53921 and HD 92287, the results are inconclusive. Our proposedmethodology for mode identification is also applicable to γDoradus stars.Based on observations collected with the CAT Telescope of the EuropeanSouthern Observatory and with the Swiss Photometric Telescope of theGeneva Observatory, both situated at La Silla in Chile.
| 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
| A study of bright southern slowly pulsating B stars. II. The intrinsic frequencies
We present the results of detailed frequency analyses of a sample ofthirteen confirmed slowly pulsating B stars. Our analysis is based on acombination of elaborate photometric and spectroscopic data-sets. Theoriginal sample consists of a mixture of five confirmed slowly pulsatingB stars and twelve candidate slowly pulsating B stars discovered thanksto the photometric measurements of the HIPPARCOS satellite. HD 55522 andHD 131120 turn out to be chemically peculiar stars. HD 169978 and HD69144 are two ellipsoidal variables for which no intrinsic variabilityis found. At least nine of the thirteen studied slowly pulsating B starsare multi-periodic. For HD 74195, HD 85953, HD 123515 and HD 215573, theobserved frequency spacings suggest that we are dealing with frequencymultiplets. For the apparent mono-periodic binary HD 24587, it is notclear if the observed variations are induced by stellar pulsation and/orby rotation modulation. We highlight the statistical character of theobserved pulsational properties of our sample. Based on observationscollected with the CAT Telescope of the European Southern Observatoryand with the Swiss Photometric Telescope of the Geneva Observatory, bothsituated at La Silla in Chile Full Tables 2-4, 6-15 are only availablein electronic form at the CDS via anounymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/393/965
| Spectroscopy and Time Variability of Absorption Lines in the Direction of the Vela Supernova Remnant
We present high-resolution (R~75,000), high signal-to-noise (S/N~100) CaII λ3933.663 and Na I λλ5889.951, 5895.924 spectraof 68 stars in the direction of the Vela supernova remnant. The spectracomprise the most complete high-resolution, high S/N optical survey ofearly-type stars in this region of the sky. A subset of the sight lineshas been observed at multiple epochs, 1993/1994 and 1996. Of the 13stars observed twice, seven have spectra revealing changes in theequivalent width and/or velocity structure of lines, most of which arisefrom remnant gas. Such time variability has been reported previously forthe sight lines toward HD 72089 and HD 72997 by Danks & Sembach andfor HD 72127 by Hobbs and coworkers. We have confirmed the ongoing timevariability of these spectra and present new evidence of variability inthe spectra of HD 73658, HD 74455, HD 75309, and HD 75821. We havetabulated Na I and Ca II absorption-line information for the sight linesin our sample to serve as a benchmark for further investigations of thedynamics and evolution of the Vela SNR. Based on observations obtainedat the European Southern Observatory, La Silla, Chile.
| A study of bright southern slowly pulsating B stars. I. Determination of the orbital parameters and of the main frequency of the spectroscopic binaries
In 1996, we started a long-term spectroscopic and photometric study of17 southern Slowly Pulsating B-stars. In this paper, we report ourfinding that at least 8 of them turn out to be spectroscopic binaries.We present the results of the determination of the orbits from thespectroscopic data. There is a great variety in the derived orbits.HD123515 and HD140873 were known as single-lined spectroscopic binaries,but both turn out to be double-lined. All the others binaries aresingle-lined. For HD140873 and HD177863, we find orbits with a largeeccentricity of respectively e=0.731 +/- 0.006 and e=0.603 +/- 0.007.HD69144, HD92287 and HD169978 are three circular binaries with a veryshort orbital period (a few days). Since their photometric measurementsare dominated by a (close to) sinusoidal variation with twice theorbital frequency, these stars are ellipsoidal variables. Their orbitalperiods are of the same order of magnitude as the periods of pulsation.After removing the orbit, we find the same first frequency in theresidual radial velocities as in the gathered photometric measurementsfor 6 stars. For HD69144 and HD169978 we did not yet succeed in derivingan intrinsic period, although HD69144 has prominent line profilevariations. HD169978 was misclassified as an SPB. Based on observationscollected with the CAT Telescope of the European Southern Observatoryand with the Swiss Photometric Telescope of the Geneva Observatory, bothsituated at La Silla in Chile
| The 74th Special Name-list of Variable Stars
We present the Name-list introducing GCVS names for 3153 variable starsdiscovered by the Hipparcos mission.
| A Second Catalog of Orbiting Astronomical Observatory 2 Filter Photometry: Ultraviolet Photometry of 614 Stars
Ultraviolet photometry from the Wisconsin Experiment Package on theOrbiting Astronomical Observatory 2 (OAO 2) is presented for 614 stars.Previously unpublished magnitudes from 12 filter bandpasses withwavelengths ranging from 1330 to 4250 Å have been placed on thewhite dwarf model atmosphere absolute flux scale. The fluxes wereconverted to magnitudes using V=0 for F(V)=3.46x10^-9 ergs cm^-2 s^-1Å^-1, or m_lambda=-2.5logF_lambda-21.15. This second catalogeffectively doubles the amount of OAO 2 photometry available in theliterature and includes many objects too bright to be observed withmodern space observatories.
| 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
| An extensive Delta a-photometric survey of southern B and A type bright stars
Photoelectric photometry of 803 southern BS objects in the Deltaa-system as detection tool for magnetic chemically peculiar (=CP2) starshas been carried out and compared to published spectral types. Thestatistical yield of such objects detected by both techniques ispractically the same. We show that there are several factors whichcontaminate the search for these stars, but this contamination is onlyof the order of 10% in both techniques. We find a smooth transition fromnormal to peculiar stars. Our sample exhibits the largest fraction ofCP2 stars at their bluest colour interval, i.e. 10% of all stars in thecolour range -0.19 <= B-V < -0.10 or -0.10 <= b-y < -0.05.No peculiar stars based on the Delta a-criterion were found at bluercolours. Towards the red side the fraction of CP2 stars drops to about3% for positive values of B-V or b-y with red limits roughlycorresponding to normal stars of spectral type A5. The photometricbehaviour of other peculiar stars: Am, HgMn, delta Del, lambda Boo, Heabnormal stars, as well as Be/shell stars and supergiants shows someslight, but definite deviations from normal stars. Spectroscopic andvisual binaries are not distinguished from normal stars in their Delta abehaviour. The results of this work justify larger statistical work(e.g. in open clusters) employing more time-saving photometric methods(CCD). \newpage Based on observations obtained at the European SouthernObservatory, La Silla, Chile. This research has made use of the Simbaddatabase, operated at CDS, Strasbourg, France. Table 2 is only availablein electronic form via anonymous ftp 130.79.128.5 orhttp://cdsweb.u-strasbg.fr/Abstract.html
| 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.
| 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.
| The distribution of interstellar dust in the solar neighborhood
We surveyed the IRAS data base at the positions of the 1808 O6-B9.5stars in The Bright Star Catalog for extended objects with excessemission at 60 microns, indicating the presence of interstellar dust atthe location of the star. Within 400 pc the filling factor of theinterstellar medium, for dust clouds with a density greater than 0.5/cucm is 14.6 + or - 2.4%. Above a density of 1.0/cu cm, the densitydistribution function appears to follow a power law index - 1.25. Whenthe dust clouds are mapped onto the galactic plane, the sun appears tobe located in a low-density region of the interstellar medium of widthabout 60 pc extending at least 500 pc in the direction of longitudes 80deg - 260 deg, a feature we call the 'local trough'.
| Atlas of extinction curves derived from ultraviolet spectra of the TD-1 satellite
The collection of 166 extinction curves derived from the publishedlow-resolution spectra acquired with the aid of the spectrometer onboard the TD-1 satellite is presented. The observed variety ofextinction laws is apparently due to the varied physical parameters ofinterstellar clouds; for example, the bright stars, included in thesample of TD-1 material, are very likely to be obscured by single clouds(interstellar or circumstellar). The system of standards constructedwith the aid of a special procedure allowing the possible effects ofspectral mismatch to be avoided and making possible the derivation ofextinction curves even in cases of very small E(B-V)S, was applied. Thecurves are presented in the form of plots, normalized to E(B-V) = 1.
| Empirical temperature calibrations for early-type stars
Three temperature calibrations of suitable photometric quantities havebeen derived for O and B stars. A sample of 120 stars with reliableT(eff.) determinations has been used for establishing each calibration.The different calibrations have been critically discussed and compared.Temperature determinations for 1009 program stars have been obtainedwith an accuracy of the order of 10 percent.
| The VELA star cloud. III - The B8 to A0 stars and interstellar reddening
The present discussion of intermediate band and H-beta observations of360 HD stars B8-A0 in Vela, and all of the CPD stars in a small adjacentregion, notes that the interstellar absorption in both cases can beunderstood as a combination of three absorbing clouds of 1 kpc-A(V) =1.5, 0.5, and 0.17. The major difference in the two environments is thepresence of numerous T Tauri stars in Taurus. Several clusters in theVela region are discussed.
| Binaries among bright stars - Systems with evolved primary components and their relation to the properties of main-sequence binaries
A study on the distribution of Delta m of main-sequence visual binaries(VBs), derived using previously published data, suggests that thesubgiants and early-type giants are one magnitude brighter than whenthey were dwarfs. The progenitors of late-type giants are on average F1dwarfs, while those of VBs with Delta m of less than 8, 5, or 3magnitudes are on average A7, A2, and B9.5 dwarfs, respectively. Theintrinsic logarithmic distribution of the semimajor axis (a) is derivedfrom dwarf, subgiant, and early-type giant VBs considered together, andis found to be constant for a of greater than 30 AU. Takingspectroscopic binaries into account, the proportion of single starsamong all stellar systems is found to be at the most 23 percent.
| A study of visual double stars with early type primaries. IV Astrophysical data
Astrophysical parameters (MK class, color excess, absolute magnitude,distance, effective temperature, mass, and age) are derived fromcalibrations of the uvby-beta indices for the members of 253 doublestars with O or B type primaries and faint secondaries. The photometricspectral classification is compared to the MK classes, and the agreementis very good. The derived data together with spectroscopic and JHKL dataare used for deciding which pairs are likely to be physical and whichare optical, and it is shown that 98 (34 percent) of the secondaries arelikely to be members of physical systems. For 90 percent of the physicalpairs the projected separation between the components is less than25,000 AU. A majority of the physical secondaries are late-type stars,and 50 percent of them are contracting towards the zero-agemain-sequence. Also presented are new uvby-beta data for 43 secondariesand a computer program for determining astrophysical parameters fromuvby-beta data.
| The local system of early type stars - Spatial extent and kinematics
Published uvby and H-beta photometric data and proper motions arecompiled and analyzed to characterize the structure and kinematics ofthe bright early-type O-A0 stars in the solar vicinity, with a focus onthe Gould belt. The selection and calibration techniques are explained,and the data are presented in extensive tables and graphs and discussedin detail. The Gould belt stars of age less than 20 Myr are shown togive belt inclination 19 deg to the Galactic plane and node-lineorientation in the direction of Galactic rotation, while the symmetricaldistribution about the Galactic plane and kinematic properties (purecircular differential rotation) of the belt stars over 60 Myr oldresemble those of fainter nonbelt stars of all ages. The unresolveddiscrepancy between the expansion observed in the youngest nearby starsand the predictions of simple models of expansion from a point isattributed to the inhomogeneous distribution of interstellar matter.
| Erratum - Distant Blue Stars in the Southern Milky-Way
Not Available
| UBV photometry for southern OB stars
New UBV photometry of 1227 OB stars in the southern Milky Way ispresented. For 1113 of these stars, MK spectral types have been reportedpreviously in a comprehensive survey to B = 10.0 mag.
| A study of visual double stars with early type primaries. II - Photometric results
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1983A&AS...51..161L&db_key=AST
| A study of visual double stars with early type primaries. I - Spectroscopic results
Attention is given to spectral peculiarities found in data on thespectral classes of 486 stars in 254 visual doublet or multiplet systemswith O or B type primaries, in order to isolate a group of very youngstars that may serve for the study of early stellar evolutioncharacteristics. It is noted that the material contains a substantialfraction of secondaries that are likely to be physical, and that severalof these may be in the premain-sequence phase of stellar evolution, orhave reached the zero-age main sequence.
| The F0 IA stars in NGC 457 and IC 2581
H-beta and intermediate band observations of stars in NGC 457 and IC2581 are used to derive mean modulus and mean reddening values. Theformer cluster is found to be similar to h and Chi Per, although on areduced scale, while the latter is very similar to CMa OB I. The brightstars in the vicinity of IC 2581, which have been suggested by Turner(1973, 1978) to be associated with the cluster, may form an association,but not one which contains IC 2581. The reddening of IC 2581 is found tobe largely uniform, with the exception of the south-proceeding quadrantof the cluster.
| The interstellar 2200 A band - A catalogue of equivalent widths
Not Available
| The VELA star cloud. I - NGC 2547, TR 10, the Gamma Velorum system, and bright stars
The first results of an intermediate-band, large-scale photometricsurvey of the Vela star cloud are discussed. Attention is given to theluminosity and reddening, as well as the apparent or proper motions ofall the CPD stars near NGC 2547, the brightest stars in Trumpler 10, arandom selection of stars in the region of Gamma Velorum, and the HRstars. The similarity of the Alpha Persei cluster with the clusters inthe Vela sheet is shown, and it is found that the Vela sheet, at leastover the region surveyed, is nearly perpendicular to the line of sight.The probability is demonstrated that a thin sheet of coeval (2.5 x 10 tothe 7th yr) stars, some 425 pc distant and with a similar metalabundance, lies in front of a dense dark cloud.
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