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Discovery of magnetic fields in the βCephei star ξ1 CMa and in several slowly pulsating B stars*
We present the results of a magnetic survey of a sample of eightβCephei stars and 26 slowly pulsating B (SPBs) stars with the FOcalReducer low dispersion Spectrograph at the Very Large Telescope. A weakmean longitudinal magnetic field of the order of a few hundred Gauss isdetected in the βCephei star ξ1CMa and in 13 SPBstars. The star ξ1CMa becomes the third magnetic staramong the βCephei stars. Before our study, the star ζCas wasthe only known magnetic SPB star. All magnetic SPB stars for which wegathered several magnetic field measurements show a field that varies intime. We do not find a relation between the evolution of the magneticfield with stellar age in our small sample. Our observations imply thatβCephei and SPB stars can no longer be considered as classes ofnon-magnetic pulsators, but the effect of the fields on the oscillationproperties remains to be studied.
| 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.
| B Star Rotational Velocities in h and χ Persei: A Probe of Initial Conditions during the Star Formation Epoch?
Projected rotational velocities (vsini) have been measured for 216 B0-B9stars in the rich, dense h and χ Persei double cluster and comparedwith the distribution of rotational velocities for a sample of fieldstars having comparable ages (t~12-15 Myr) and masses (M~4-15Msolar). For stars that are relatively little evolved fromtheir initial locations on the zero-age main sequence (ZAMS) (those withmasses M~4-5 Msolar), the mean vsini measured for the h andχ Per sample is slightly more than 2 times larger than the meandetermined for field stars of comparable mass, and the cluster and fieldvsini distributions differ with a high degree of significance. Forsomewhat more evolved stars with masses in the range 5-9Msolar, the mean vsini in h and χ Per is 1.5 times thatof the field; the vsini distributions differ as well, but with a lowerdegree of statistical significance. For stars that have evolvedsignificantly from the ZAMS and are approaching the hydrogen exhaustionphase (those with masses in the range 9-15 Msolar), thecluster and field star means and distributions are only slightlydifferent. We argue that both the higher rotation rates and the patternof rotation speeds as a function of mass that differentiatemain-sequence B stars in h and χ Per from their field analogs werelikely imprinted during the star formation process rather than a resultof angular momentum evolution over the 12-15 Myr cluster lifetime. Wespeculate that these differences may reflect the effects of the higheraccretion rates that theory suggests are characteristic of regions thatgive birth to dense clusters, namely, (1) higher initial rotationspeeds; (2) higher initial radii along the stellar birth line, resultingin greater spin-up between the birth line and the ZAMS; and (3) a morepronounced maximum in the birth line radius-mass relationship thatresults in differentially greater spin-up for stars that become mid- tolate-B stars on the ZAMS.
| 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.
| Stars with ISM Polarization Observed with HPOL. II
Polarization data are given for stars whose polarizations are mostlyinterstellar which were observed with the University of Wisconsinspectropolarimeter (HPOL) during 1995-2003. Several cases are found forwhich K in the Serkowski Law for ISM polarization is higher than allowedby published formulas.
| 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.
| Photometric modelling of slowly pulsating B stars
The photometric characteristics of slowly pulsating B stars areinvestigated using a numerical approach. Stability calculations areperformed for a set of stellar models representative of the mid-B type,using a non-radial non-adiabatic pulsation code. The results from thesecalculations are used to synthesize photometry, in several commonsystems, for unstable modes of harmonic degrees l=1...4. Focusing on theGeneva system for illustrative purposes, a variety of techniques areemployed to analyse and visualize the synthetic data, including the useof multicolour-amplitudes and amplitude-phase diagnostic diagrams. Oneoutstanding aspect of the analysis is the discovery, for the l=2...4modes, of `inter-term cancellation' (ITC) - the process of destructiveinterference between the flux variations originating from surfacetemperature perturbations and those arising from radius perturbations.The ITC can be severe enough that a mode may be excited to a significantamplitude, and yet exhibit levels of photometric variability that fallbelow typical observational detection thresholds. Furthermore, it canaffect not only the light variations in a given photometric passband,but also the variations of the bolometric flux. However, thecancellation is dependent on wavelength, and will not occur to the samedegree in more than one passband. Therefore, simultaneous observation ina multitude of passbands represents the best approach to ensuring thatno modes are overlooked during searches for variability in B-type stars.A consequence of ITC is that ratios between the variability amplitude,in differing passbands, become very sensitive towards mode-to-modechanges in the pulsation. This increased sensitivity will tend tocomplicate any attempts at identifying the harmonic degrees of the modesresponsible for observed variability. However, the cancellation alsointroduces significant phase differences between the light variations ineach passband, especially for the l=3 and l=4 modes. On the grounds thatcorrespondingly large phase differences are not seen in observationaldata, it is argued that the variability seen in slowly pulsating B starscan tentatively be attributed to l=1 and l=2 modes.
| Rotational Velocities of B Stars
We measured the projected rotational velocities of 1092 northern B starslisted in the Bright Star Catalogue (BSC) and calibrated them againstthe 1975 Slettebak et al. system. We found that the published values ofB dwarfs in the BSC average 27% higher than those standards. Only 0.3%of the stars have rotational velocities in excess of two-thirds of thebreakup velocities, and the mean velocity is only 25% of breakup,implying that impending breakup is not a significant factor in reducingrotational velocities. For the B8-B9.5 III-V stars the bimodaldistribution in V can be explained by a set of slowly rotating Ap starsand a set of rapidly rotating normal stars. For the B0-B5 III-V starsthat include very few peculiar stars, the distributions in V are notbimodal. Are the low rotational velocities of B stars due to theoccurrence of frequent low-mass companions, planets, or disks? Therotational velocities of giants originating from late B dwarfs areconsistent with their conservation of angular momentum in shells.However, we are puzzled by why the giants that originate from the earlyB dwarfs, despite having 3 times greater radii, have nearly the samerotational velocities. We find that all B-type primaries in binarieswith periods less than 2.4 days have synchronized rotational and orbitalmotions; those with periods between 2.4 and 5.0 days are rotating withina factor 2 of synchronization or are ``nearly synchronized.'' Thecorresponding period ranges for A-type stars are 4.9 and 10.5 days, ortwice as large. We found that the rotational velocities of the primariesare synchronized earlier than their orbits are circularized. The maximumorbital period for circularized B binaries is 1.5 days and for Abinaries is 2.5 days. For stars of various ages from 107.5 to1010.2 yr the maximum circularized periods are a smoothexponential function of age.
| 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
| Spectroscopic monitoring of 10 new northern slowly pulsating B star candidates discovered from the HIPPARCOS mission
A one-year follow-up campaign of high-resolution, high-signal-to-noisespectroscopy for 10 candidate slowly pulsating B stars, which werediscovered from the HIPPARCOS astrometric mission, shows that all starsexhibit line-profile variability. From our data, and from the HIPPARCOSphotometry, we conclude that all but one of the targets provide evidenceof multiperiodicity, with periods of the order of days, confirming theirpulsational nature. Thus they are confirmed slowly pulsating B stars. Wesummarize the pulsation periods and Q-values and select the mostinteresting targets for very-long-term follow-up observations with thegoal of performing asteroseismology. Based on observations obtained atthe Observatoire de Haute-Provence.
| Observations of OB-stars at the former Leiden Southern Station
About 700 stars, mostly OB-stars, were observed by the author at theformer Leiden Southern Station at Hartebeespoortdam, South Africa, inthe observing seasons 1965, 1968, 1969, 1974, 1977, 1978. Observationswere made in the five channels of the Walraven photometric system. Dueto weathering of the telescope mirror the W channel gave no reliableresults for the faintest stars (m = 11 mag); in these cases the U-Wcolour index is not given. The change in sensitivity in the V channel,supposedly having occurred in 1968, was not recognised. Table~5 is onlyavailable 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/qcat?J/A+A/369/527
| On the Variability of Late B III-V Stars
We investigate the Hipparcos Satellite photometry of luminosity classIII-V B6-B9 stars. Most are relatively non-variable. Candidates forwhich further study is desirable are identified.
| 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.
| Mapping the contours of the Local bubble: preliminary results
We present preliminary results from a long-term program of mapping theneutral absorption characteristics of the local interstellar medium,taking advantage of Hipparcos stellar distances. Equivalent widths ofthe NaI D-line doublet at 5890 Å are presented for thelines-of-sight towards some 143 new target stars lying within 300 pc ofthe Sun. Using these data which were obtained at the Observatoire deHaute Provence, together with previously published NaI absorptionmeasurements towards a further 313 nearby targets, we present absorptionmaps of the distribution of neutral gas in the local interstellar mediumas viewed from 3 different galactic projections. In particular, thesemaps reveal the Local Bubble region as a low neutral densityinterstellar cavity in the galactic plane with radii between 65-250 pcthat is surrounded by a (dense) neutral gas boundary (or ``wall''). Wehave compared our iso-column contours with the contours derived bySnowden et al. (\cite{snowden98}) using ROSAT soft X-ray emission data.Consistency in the global dimensions derived for both sets of contoursis found for the case of a million degree hot LB plasma of emissivity0.0023 cm(-6) pc with an electron density of 0.005 cm(-2) . We havedetected only one relatively dense accumulation of cold, neutral gaswithin 60 pc of the Sun that surrounds the star delta Cyg, and note thatthe nearest molecular cloud complex of MBM 12 probably resides at thevery edge of the Local Bubble at a distance of ~ 90 pc. Our observationsmay also explain the very different physical properties of the columnsof interstellar gas in the line-of-sight to the two hot stars epsilonCMa and beta CMa as being due to their locations with respect to theBubble contours. Finally, in the meridian plane the LB cavity is foundto be elongated perpendicularly to the Gould's Belt plane, possiblybeing ``squeezed'' by the expanding shells of the Sco-Cen andPerseus-Taurus OB associations. Tables 1 and 2 are also available inelectronic form at the CDS (Strasbourg) via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Polarimetry of the young Herbig AE star HD 139614. Differences of polarimetric behaviour of Vega-type stars
We present optical polarimetric data of the Herbig Ae star HD 139614 anddiscuss its behaviour relative to similar stars. In spite of a low levelof polarization (~ 0.05-0.2%), polarimetric variability on a time-scaleof days was detected during a four night synoptic study. The differencein the level of the polarization for HD 139614 relative to other HerbigAe/Be stars such as HD 141569, HD 142666 and HD 169142 might be due tothe inclinations and viewing aspects of their circumstellar disks and totheir different evolutionary stages. This hypothesis is consistent withthe photometric behaviour of these stars, their v sin i values andspectral energy distribution in the near and far IR.
| 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.
| Kinematical Structure of the Local Interstellar Medium: The Galactic Center Hemisphere
A survey of interstellar Na I D1 and D2 absorption features found in thespectra of 31 early-type stars in the first and fourth Galacticquadrants reveals a new picture of the large-scale kinematics ofinterstellar gas in the vicinity of the Sun. While absorption featuresfound in the spectra of stars in the fourth Galactic quadrant show thegas expanding from stars in the Scorpio-Centaurus OB association, starsin the first Galactic quadrant, in the range of distances covered bythis survey (74--312 pc from the Sun), show interstellar gas fallingtoward the Galactic plane with a bulk motion whose component parallel tothat plane is directed toward the Scorpio-Centaurus association. Thispicture differs completely from generally accepted models in which thenearby interstellar gas flows away from the Scorpio-Centaurusassociation toward the Galactic anticenter. Evidence for the presence ofan expanding shell-like feature that is reaching the solar system ispresented.
| Nonvariability among lambda Bootis stars
With asteroseismic techniques it is possible to investigate the interiorand the evolutionary status of stars via their frequency spectrum. Bothinformation would be very much needed for lambda Bootis stars, a groupof metal-poor Population I, A-type stars, since no conclusive theoryexists explaining the observed abundance anomalies. Geneva and Stromgrenphotometry place these stars inside the classical instability strip orat least very close to it. We therefore have started an extensivephotometric survey for pulsation in lambda Bootis stars and havediscovered so far 13 new variables. In this paper we present results forstars which presumably are constant, because we are able to establishonly an upper level for possible variability. A typical noise level of 3mmag for Stromgren b was achieved in the relevant frequency domain up to100 d^{-1}. Considering the given noise level of our survey, we concludethat at least 50% of all investigated lambda Bootis stars inside theinstability strip are pulsating, making this group remarkable comparedto stars with similar spectral types. This may suggest that a low(surface) metallicity has an influence on the pulsation Based onobservations obtained at ESO-La Silla, CTIO, SAAO, McDonald Observatory,Instituto Astrofisica Andalucia Observatory.
| Rotational Velocity Determinations for 164 Be and B Stars
Rotational velocities, v sin i, have been obtained for 96 Be and 68normal B stars by measurements of the FWHM of the He I lambda-4471 line(for spectral types B0-B4.5) and Mg II lambda-4481 (for types B5-B9.5).The consistency of various published sources is examined. (SECTION:Stars)
| The Distribution of Dust Clouds in the Interstellar Medium
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJ...457..764D&db_key=AST
| The λ 3984 feature in late-B spectroscopic binaries.
We report about a spectroscopic study aimed at searching the line Hg IIλ 3984 in a sample of 28 spectroscopic binaries with primaries inthe same temperature range as HgMn stars. One system, HD 75642, showsthis line very prominently. In another system, HD 41040, Hg may besomewhat overabundant, while HD 87751 shows marginal Mn and Penhancement. The present study does not bring a definitive answer to thequestion of the relation between binarity, slow rotation, and theappearance of HgMn anomalies in late B stars, possibly because othereffects (like the influence of a magnetic field), which could not betaken into consideration, are important too. In the course of thisstudy, 11 new double-lined spectroscopic binaries were discovered, 10 ofwhich were previously known as single-lined systems. Of particularinterest among them are 4 stars that may have the Si or He weakpeculiarities.
| 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.
| Speckle observations of visual and spectroscopic binaries. VI.
Not Available
| 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.
| Physical characteristics of close binary system components
An approximate approach for evaluating the mass of invisible satellitesof close binary systems with the mass-function f(M) much less than 1 issuggested. A possibility of using it is shown for 62 close binarysystems.
| 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'.
| Speckle observations of visual and spectroscopic binaries. III
This is the third paper of this series giving results of speckleobservations carried out for seven visual and 119 spectroscopic binariesat seven nights from May 20 to May 27, 1989, and for 30 visual and 272spectroscopic binaries at 12 nights from June 11 to June 15, and fromAugust 28 to September 3, 1990, using the 212-cm telescope at San PedroMartir Observatory in Mexico. Fringes in the lower spectrum of 31 visualand spectroscopic binaries with angular separation larger than 21 arcsecare obtained. Additionally to two spectroscopic binaries, HD41116 andHD206901, named in the second paper of this series, six spectroscopicbinaries are found each of which has the third component starsurrounding two stars of spectroscopic binary having periodic variationof radial velocity.
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