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Hubble Space Telescope Measurements of Vacuum Ultraviolet Lines of Interstellar CH
Three interstellar absorption lines near 1370 Å seen toward ζOph have been assigned by Watson to Rydberg transitions in the G-X (or3d-X) band of CH. Our survey of a dozen diffuse interstellar lines ofsight shows that the three absorption lines are consistent with theknown column densities of CH, by deriving the following oscillatorstrengths: f(1368.74)=0.019+/-0.003, f(1369.13)=0.030+/-0.005, andf(1370.87)=0.009+/-0.001. We also determined intrinsic line widths thatcorrespond to decay rates of (1.5+/-0.6)×1011,(3.8+/-0.7)×1011, and (1.1+/-0.6)×1010s-1 for λλ1368, 1369, and 1370, respectively.These rates are significantly higher than those associated withradiative decays and, thus, are readily attributable to predissociationof the Rydberg state. A fourth interstellar line near 1271 Å hasbeen conjectured by Watson to be the strongest transition in the 4d-XRydberg band of CH. We detected this line along four sight lines and ourspectrum syntheses show that with f(1271.02)=0.007+/-0.002, it is alsoconsistent with the known column densities of CH. In addition, weconducted a search for the F-X band of CH near 1549 Å, andsuccessfully discovered two of its absorption features along four sightlines. The astronomical oscillator strengths derived for these featuresare f(1549.05)=0.021+/-0.006 and f(1549.62)=0.013+/-0.003. Finally, theX Per sight line provided us with an astronomical detection of anotherCH band via two D-X features near 1694 Å. Comparisons with resultsof available theoretical calculations for the four CH bands arepresented.
| Observations of Star-Forming Regions with the Midcourse Space Experiment
We have imaged seven nearby star-forming regions, the Rosette Nebula,the Orion Nebula, W3, the Pleiades, G300.2-16.8, S263, and G159.6-18.5,with the Spatial Infrared Imaging Telescope on the Midcourse SpaceExperiment (MSX) satellite at 18" resolution at 8.3, 12.1, 14.7, and21.3 μm. The large angular scale of the regions imaged (~7.2-50deg2) makes these data unique in terms of the combination ofsize and resolution. In addition to the star-forming regions, twocirrus-free fields (MSXBG 160 and MSXBG 161) and a field near the southGalactic pole (MSXBG 239) were also imaged. Point sources have beenextracted from each region, resulting in the identification over 500 newsources (i.e., no identified counterparts at other wavelengths), as wellas over 1300 with prior identifications. The extended emission from thestar-forming regions is described, and prominent structures areidentified, particularly in W3 and Orion. The Rosette Nebula isdiscussed in detail. The bulk of the mid-infrared emission is consistentwith that of photon-dominated regions, including the elephant trunkcomplex. The central clump, however, and a line of site toward thenorthern edge of the cavity show significantly redder colors than therest of the Rosette complex.
| Radial velocities of early-type stars in the Perseus OB2 association
We present radial velocities for 29 B- and A-type stars in the field ofthe nearby association Perseus OB2. The velocities are derived fromspectra obtained with AURELIE, via cross correlation with radialvelocity standards matched as closely as possible in spectral type. Theresulting accuracy is ~ 2-3 km s-1. We use thesemeasurements, together with published values for a few other early-typestars, to study membership of the association. The mean radial velocity(and measured velocity dispersion) of Per OB2 is 23.5 +/- 3.9 kms-1, and lies ~ 15 km s-1 away from the meanvelocity of the local disk field stars. We identify a number ofinterlopers in the list of possible late-B- and A-type members which wasbased on Hipparcos parallaxes and proper motions, and discuss thecolour-magnitude diagram of the association.Based on observations made at the Observatoire de Haute-Provence (CNRS),France.
| Autocorrelation Analysis of Hipparcos Photometry of Short-Period Be Stars
We have used Hipparcos epoch photometry and a form of autocorrelationanalysis to investigate the amplitude and timescale of the short-periodvariability of 82 Be stars, including 46 Be stars that were analyzed byHubert & Floquet using Fourier and CLEAN analysis and 36 other Bestars that were suspected of short-period variability. Our method hasgiven useful information for about 84% of these stars; for the rest, thetime distribution of the Hipparcos epoch photometry limits thecapability of our technique.
| Statistical analysis of intrinsic polarization, IR excess and projected rotational velocity distributions of classical Be stars
We present the results of statistical analyses of a sample of 627 Bestars. The parameters of intrinsic polarization (p*),projected rotational velocity (v sin i), and near IR excesses have beeninvestigated. The values of p* have been estimated for a muchlarger and more representative sample of Be stars (~490 objects) thanpreviously. We have confirmed that most Be stars of early spectral typehave statistically larger values of polarization and IR excesses incomparison with the late spectral type stars. It is found that thedistributions of p* diverge considerably for the differentspectral subgroups. In contrast to late spectral types (B5-B9.5), thedistribution of p* for B0-B2 stars does not peak at the valuep*=0%. Statistically significant differences in the meanprojected rotational velocities (/line{vsin i}) are found for differentspectral subgroups of Be stars in the sense that late spectral typestars (V luminosity class) generally rotate faster than early types, inagreement with previously published results. This behaviour is, however,not obvious for the III-IV luminosity class stars. Nevertheless, thecalculated values of the ratio vt/vc of the truerotational velocity, vt, to the critical velocity forbreak-up, vc, is larger for late spectral type stars of allluminosity classes. Thus, late spectral type stars appear to rotatecloser to their break-up rotational velocity. The distribution of nearIR excesses for early spectral subgroups is bi-modal, the position ofthe second peak displaying a maximum value E(V-L)~ 1 . m 3for O-B1.5 stars, decreasing to E(V-L)~0. m8 for intermediatespectral types (B3-B5). It is shown that bi-modality disappears for latespectral types (B6-B9.5). No correlations were found betweenp* and near IR excesses and between E(V-L) and vsin i for thedifferent subgroups of Be stars. In contrast to near IR excesses, arelation between p* and far IR excesses at 12 mu m is clearlyseen. A clear relation between p* and vsin i (as well asbetween p* and /line{vsin i}/vc) is found by thefact that plots of these parameters are bounded by a ``triangular"distribution of p*: vsin i, with a decrease of p*towards very small and very large vsin i (and /line{vsini}/vc) values. The latter behaviour can be understood in thecontext of a larger oblateness of circumstellar disks for the stars witha rapid rotation. From the analysis of correlations between differentobservational parameters we conclude that circumstellar envelopes forthe majority of Be stars are optically thin disks with the range of thehalf-opening angle of 10degr
| Suprathermal rotation of PAHs in the ISM II. Observational evidence for the rotational broadening of lambda 5797 DIB in reflection nebulae - implication for the carrier size
In a previous paper, we described a model which can explain thelambda5797 diffuse interstellar band (DIB) profile as seen in absorptionin the diffuse interstellar medium and in emission in the Red Rectangle(RR), as a rotational envelope of electronic transitions where themolecular carrier is a free PAH of size ~ 40 atoms. One of the strongestpredictions is the behaviour of the rotational temperature of PAH in thecase of regions rich in UV such as Reflection Nebulae: it must besuprathermal with respect to the gas temperature but clamped to ~ 100 Kfor any PAH size. The width of the DIB, in such regions, can then bebroader than in the classical ISM (T_rot ~ 30 K) if the values of themolecular transition are favorable. In order to test this prediction, wehave obtained high resolution spectra of 27 reddened early type stars,mostly in reflection nebulae, in order to compare their lambda 5797 DIBwidth to those of stars in classical diffuse interstellar medium. Thesespectra were made for several DIBs such as lambda 5797, lambda6379 andlambda6613 , with a spectral resolving power of about 60 000. Theanalysis of the results agrees with our predic tion since the width ofthe lambda 5797 DIB is broader in a majority of areas with strong UVradiation. Moreover, the broadening is not observed on DIBs lambda6379and lambda6613 , indicating that the molecular parameters of theelectronic transitions at the origin of the different DIBs are prettyvariable from one DIB to another and confirming that the measuredbroadening on lambda 5797 is not due to an instrumental bias. Thestatistical measurement of the lambda 5797 width in this medium permitsthe derivation of new constraints on the size of the carrier of thisDIB, a molecule that should have 30 to 45 carbon atoms if, as wepropose, it is indeed a PAH. Based on observations made at Observatoirede Haute Provence (CNRS), France.
| Distribution of gas, dust and the lambda 6613 Å DIB carrier in the Perseus OB2 association
We present a study of the spatial distribution of the lambda 6613 ÄDIB carrier in the Perseus OB2 association based on high resolutionobservations toward lines of sight representing different interstellarenvironments. We determined that in the studied region, the lambda 6613Ä DIB carrier is concentrated in two distinct clouds withvelocities of 1.4 (+/- 0.4) and 12.0 (+/- 0.9) km s(-1) . We comparedthe lambda 6613 Ä DIB carrier's velocity with the Na I velocitydistribution derived from our survey measurements, as well as with CO,OH, H I and Ca Ii measurements from the literature. We conclude that thebehaviour of the carrier of the lambda 6613 Ä DIB follows theoverall expansion motion of the gas in the association. The DIB velocityis directly linked to that of Ca Ii and H I. The DIB total columndensity is proportional to the total column density of Ca Ii and H Imaking those atoms good tracers of the lambda 6613 Ä DIB carrier.Those new results support the assumption that the lambda 6613 Ä DIBwould arise from a gas phase molecule, possibly single-ionized(Sonnentrucker et al. 1997). We also conclude that the DIB carrier isdistributed in shell structures over the whole association. We finallyshow from the DIB velocity structure that the DIB carrier, gas and dustare well mixed toward the association but that the DIB shells have anangular extent twice larger than that of the dust. Based on observationswith OHP 1.52m Telescope and Aurelie spectrograph.
| A HIPPARCOS Census of the Nearby OB Associations
A comprehensive census of the stellar content of the OB associationswithin 1 kpc from the Sun is presented, based on Hipparcos positions,proper motions, and parallaxes. It is a key part of a long-term projectto study the formation, structure, and evolution of nearby young stellargroups and related star-forming regions. OB associations are unbound``moving groups,'' which can be detected kinematically because of theirsmall internal velocity dispersion. The nearby associations have a largeextent on the sky, which traditionally has limited astrometricmembership determination to bright stars (V<~6 mag), with spectraltypes earlier than ~B5. The Hipparcos measurements allow a majorimprovement in this situation. Moving groups are identified in theHipparcos Catalog by combining de Bruijne's refurbished convergent pointmethod with the ``Spaghetti method'' of Hoogerwerf & Aguilar.Astrometric members are listed for 12 young stellar groups, out to adistance of ~650 pc. These are the three subgroups Upper Scorpius, UpperCentaurus Lupus, and Lower Centaurus Crux of Sco OB2, as well as VelOB2, Tr 10, Col 121, Per OB2, alpha Persei (Per OB3), Cas-Tau, Lac OB1,Cep OB2, and a new group in Cepheus, designated as Cep OB6. Theselection procedure corrects the list of previously known astrometricand photometric B- and A-type members in these groups and identifiesmany new members, including a significant number of F stars, as well asevolved stars, e.g., the Wolf-Rayet stars gamma^2 Vel (WR 11) in Vel OB2and EZ CMa (WR 6) in Col 121, and the classical Cepheid delta Cep in CepOB6. Membership probabilities are given for all selected stars. MonteCarlo simulations are used to estimate the expected number of interloperfield stars. In the nearest associations, notably in Sco OB2, thelater-type members include T Tauri objects and other stars in the finalpre-main-sequence phase. This provides a firm link between the classicalhigh-mass stellar content and ongoing low-mass star formation. Detailedstudies of these 12 groups, and their relation to the surroundinginterstellar medium, will be presented elsewhere. Astrometric evidencefor moving groups in the fields of R CrA, CMa OB1, Mon OB1, Ori OB1, CamOB1, Cep OB3, Cep OB4, Cyg OB4, Cyg OB7, and Sct OB2, is inconclusive.OB associations do exist in many of these regions, but they are eitherat distances beyond ~500 pc where the Hipparcos parallaxes are oflimited use, or they have unfavorable kinematics, so that the groupproper motion does not distinguish it from the field stars in theGalactic disk. The mean distances of the well-established groups aresystematically smaller than the pre-Hipparcos photometric estimates.While part of this may be caused by the improved membership lists, arecalibration of the upper main sequence in the Hertzsprung-Russelldiagram may be called for. The mean motions display a systematicpattern, which is discussed in relation to the Gould Belt. Six of the 12detected moving groups do not appear in the classical list of nearby OBassociations. This is sometimes caused by the absence of O stars, but inother cases a previously known open cluster turns out to be (part of) anextended OB association. The number of unbound young stellar groups inthe solar neighborhood may be significantly larger than thoughtpreviously.
| On the Expansion of Stellar Association Per OB2
Not Available
| Investigation of the variability of bright Be stars using HIPPARCOS photometry
The high accuracy and the homogeneity of Hipparcos data for bright starshave allowed us to quantify the degree of variability of Be stars. Thisdegree has been found to be highly dependent on the temperature of thestar. Rapid variability is the main feature of the 86% of early Be andless than 20% of late Be stars taking into account the limit ofdetection considered. In addition to Be stars reported in the Hipparcoscatalogue (ESA 1997) as short-period variables, we have been able toenlarge the number of detections as well as to confirm periodspreviously determined. Be stars that show larger amplitude rapidvariations are proposed as candidates for a search of multiperiodicityi.e. as non-radial pulsators. We have also searched for the presence ofoutbursts and fading events in the Hipparcos data. Outbursts have beenfrequently and preferentially detected in early Be stars with rather lowto moderate v sini while fading events seem to be more conspicuous instars with higher v sini. Mid-term and long-term variations have alsobeen investigated. Several stars have shown some evidence of temporaryquasi-periodic oscillations ranging between 10 and 200 days. Finallyinformation concerning long-term variations is reported. Cycles shorterthan or equal to the Hipparcos mission have mainly been detected instars earlier than B6. Long-term time scales of late Be stars areconfirmed to be longer by far. Tables 1 and 2 are only available inelectronic form at CDS via ftp to cdsarc.u-strasbg.fr (130.79.128.5) orvia http://cdsweb.u-strasbg.fr/Abstract.html
| The NRAO VLA Sky Survey
The NRAO VLA Sky Survey (NVSS) covers the sky north of J2000.0 delta =-40 deg (82% of the celestial sphere) at 1.4 GHz. The principal dataproducts are (1) a set of 2326 4 deg x 4 deg continuum ``cubes'' withthree planes containing Stokes I, Q, and U images plus (2) a catalog ofalmost 2 x 10^6 discrete sources stronger than S ~ 2.5 mJy. The imagesall have theta = 45" FWHM resolution and nearly uniform sensitivity.Their rms brightness fluctuations are sigma ~ 0.45 mJy beam^-1 ~ 0.14 K(Stokes I) and sigma ~ 0.29 mJy beam^-1 ~ 0.09 K (Stokes Q and U). Therms uncertainties in right ascension and declination vary from <~1"for the N ~ 4 x 10^5 sources stronger than 15 mJy to 7" at the surveylimit. The NVSS was made as a service to the astronomical community. Alldata products, user software, and updates are being released via theWorld Wide Web as soon as they are produced and verified.
| Multi-color Polarimetry of the Dust Disk Candidate BD+31 degrees 643
The tentative detection of a dust disk around the main-sequence star BD+31 deg643 was recently announced by Kalas & Jewitt and representsonly the second such object ever to be imaged. Here, we presentmultiband visual polarimetry of this object. Our single-aperturepolarimetry also strongly suggests the presence of a disk. We find thatthe poles of the disk are oriented parallel to the polarization of themajority of background sources in the region and, hence, probably to themagnetic field in the cloud, as would be expected from star formationtheory. The polarization observed toward BD +31 deg643 can be modeled asa combination of Rayleigh scattering from material in the polar regionsof the disk and a term due to the disk itself.
| Two partially overlapping clouds of different optical properties in the Perseus OB2 association.
The paper considers the properties of H I clouds seen in front of thetwo "arms" of the giant CO complex observed in Perseus (Per OB2association - see Fig. 1). The clouds observed towards both "arms" showstriking differences in the pattern of interstellar absorptions: theshapes of the extinction curves derived from vacuum-UV photometric andspectroscopic data, the strength ratio of the two major diffuseinterstellar bands: 5780 and 5797 and, probably in the strengths ofmolecular features. The diffuse band ratio which varies across the PerOB2 association suggests, together with the varying widths of sodiumlines, that two, partially overlapping clouds, differing strongly in theoptical properties, are situated towards the aggregate. Only towards oneof the "arms" we observe the absorption features of simple, interstellarmolecules such as CN or CH. The results suggest that at least theperipheral layers of giant molecular clouds, giving birth to OBassociations, are not well-mixed, containing thus H I clouds ofdifferent provenience. The hypothesis that giant clouds are formed bygathering diffuse interstellar clouds gets support.
| 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.
| AG Persei: Absolute dimensions and membership of Perseus OB2
Accurate physical parameters for the B-type eclipsing binary AG Per (HD25833; B4 V, V = 6.7, P = 2.03 days) have been determined for a completere-analysis of available light curves and recent spectrscopic elements(Popper & Hill 1991). The components have masses of 5.36 +/- 0.16and 4.90 +/- 0.13 solar mass and radii of 2.99 +/- 0.07 and 2.60 +/-0.07 solar radii, respectively, and they are among the least evolved Bstars with well-determined dimensions. Effective temperatures of 18 200+/- 800 K and 17b 400 +/- 800 K are derived. The orbit is slightlyeccentric (e = 0.0710 +/- 0.0010) and shows apsidal motion with awell-established period of U = 75.6 +/- 0.6 yr. Comparison with stellarevolution models based on the latest opacity library by Rogers &Iglesias (1992) and including a moderate amount of convectiveovershooting (Claret & Gimenez 1992) shows AG Per to be young; anage of about 4-6 107 yr is derived from the scale independentmasses and radii. AG Per is too little evolved to provide anyconstraints on the amount of convective overshooting. The mean densityconcentration coefficient determined from the apsidal motion parameters,log k2 = -2.14 +/- 0.04, agrees well with that computed forthe models, provided a relativistic correction based on the generalrelativity theory is included. In its present formulation andcalibration the alternative non-symmetric gravitational theory proposedby Moffat (1989) is not supported. AG Per is generally accepted as amember of Per OB2. We find a distance of 355 +/- 30 pc for the binary,compared to 330-420 pc given by various authors for the association. Newstellar models and calibrations indicate a photometric age of about1-1.5 107 yr for Per OB2, larger than previously obtained butstill well below that of AG Per (4-6 107 yr. This weakens thestatus of AG as a member. New observations of (potential Per OB2members, including fainter stars, are clearly needed.
| Polarization of starlight by dust in the BOK globule B 5.
Not Available
| Interstellar extinction in the direction of the open cluster IC 348 and the Per OB2 association
The relationship between interstellar extinction and distance in thedirection of dark clouds in the areas around the open cluster IC 348 andthe association Per OB2 is determined using the results of photoelectricphotometry of 189 stars in the Vilnius photometric system. Two absorbinglayers are found. The nearest layer, covering the whole area around IC348, shows the mean extinction A(V) of about 0.7 mag. It begins at thedistance of 160 pc and probably is an extension of the Taurus darkclouds to the northwest. The second absorbing layer has the form of achain of dark condensations named L1468, L1470, and L1471 and is at 260pc distance. This layer has a higher density, its mean extinction beingabout 2.0 mag. The cluster IC 348 is at about the same distance and isphysically related to the dark cloud L1470. The distance of the Per OB2association is found to be 340 pc and the mean extinction of its membersis 0.95 mag. A model of the spatial distribution of the Perseus andTaurus dark clouds based on photometric distance determinations in thisand previous papers is proposed. Six stars in the IC 348 area aresuspected to have emission in the H-alpha line.
| Three known and twenty-two new variable stars of early spectral type
Photoelectric photometry is reported of three known and 22 newvariables, all brighter than V = 7.5 mag. The three known ones are: theellipsoidal variable 42 (V467) Per, the Beta Cep-type star HR 6684 =V2052 Oph, and the eclipsing variable HR 8854 = V649 Cas. The newvariable stars are listed. They include two Beta Cep candidates, oneeclipsing and three ellipsoidal variables, a 'mid-B' variable, anAlpha(2) CVn variable, and two Lambda Eri stars. The twelve remainingnew variables could not be classified because of insufficient data. TheLambda Eri variables found in the present investigation, together withsome examples from the literature, indicate that rotational modulationoccurs not only in Be, but also in normal B stars.
| 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.
| Catalogue of Hydrogen Line Spectral Profiles of 236 B-Stars A-Stars and F-Stars
Not Available
| 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.
| Catalogue of i and w/w crit values for rotating early type stars
Not Available
| The vicinity of Omicron Per
The region around the B1 III star Omicron Per (HD 23180) in the emissionof the J = 1-0 and J = 2-1 lines of C-12O and C-13O with about 1 arcminresolution. The molecular cloud morphology suggests the presence of awarm hole near the position of the star. It is tempting to think thatOmicron Per is the cause of this molecular gap. However, the observedheating of the cloud edge, as well as optical, infrared (IRAS) andcarbon recombination line data, all suggest that the local ultravioletfield is enhanced only by a factor 10-100. Therefore Omicron Per must belocated at least a few parsecs away from the cloud, and the precisealignment of the observed hole with the star is probably mainly due tochance. Furthermore, other neighboring OB stars could contributeappreciably (even more than Omicron Per) to the ultraviolet enhancementwhich seems to extend over several degrees on the north-east edge of thePerseus local molecular cloud.
| Helium abundance in the atmospheres of B stars in open clusters
The model-atmosphere method is applied to 6-m telescope spectrograms of46 B stars in the Per OB2 and Sco-Cen associations and in the alpha Percluster and the Pleiades to determine effective temperatures, surfacegravities, and helium abundances log epsilon(He). To within the erorrs,each cluster has the same mean epsilon(He).
| Catalog of O-B stars observed with Tokyo Meridian Circle
A catalog of the O-B stars, selected from 'Blaauw-Parenago' list andRubin's catalog, has been compiled on the FK4 system by the observationsmade with Gautier 8-inch Meridian Circle at the Tokyo AstronomicalObservatory during the period, 1971 to 1979. It contains 1059 stars andwas compiled for the future establishment of high precision propermotions of O-B stars.
| 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.
| Peculiar stars in the association Per OB2.
Not Available
| Radial velocities for early type stars in six galactic regions
Coudespectroscopy has been carried out for 353 stars of spectral typesB0-A0 and V magnitudes between 6.5 and 10.8 m, selected in six regions(three northern and three southern) close to the galactic plane at thegalactic longitudes 135, 175, 315 and 350 deg. The radial velocitieswere obtained by cross-correlating each spectrogram with a referencespectrogram giving an internal error of 1.4 km/s.
| X Persei - Optical polarization variation on the 580 day binary-like period
Observations of periodicities in the optical polarization of the weakX-ray source X Persei are reported. Polarization was measured in the Vband 400 times over the course of 356 nights during 1977-1982. The Q andU Stokes parameters derived from the measurements show a definitevariability with a typical amplitude of 0.1%, which is strongest atperiods greater than 100 days. In particular, a strong peak is observedwith a period of 297 days, consistent with the second-harmonic componentof the known 580-day radial velocity cycle. A component with 590-dayperiodicity is not ruled out by the observations, although it was notdetected. Observations imply the 580-day period to be an effect oforbital or rotational processes, with the corotating scattering bodyeither close to the light source or very large in extent, and a systeminclination close to 80 deg.
| Four-color and H-beta photometry for O-A0 type stars in three regions near the galactic equator
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1982A&AS...49..561W&db_key=AST
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