Periodic Variability of Pre-Main-Sequence Stars in the NGC 2264 OB Association
We summarize the results of an observing campaign to identify periodicpre-main-sequence (PMS) variables in the NGC 2264 OB association. Wefind 201 periodic candidates. The mean age of the NGC 2264 periodicvariables is approximately 30% greater than their counterparts in theOrion Nebula Cluster. Given the difference in mean age between NGC 2264and Orion, we expect the typical periodic variable in NGC 2264 to have aperiod shorter by a factor of ~1.6, if the initial distribution ofperiods in the two clusters is identical and if stellar angular momentumis conserved. However, we find a period distribution indistinguishablefrom that found in Orion. This suggests that the angular momenta of asignificant fraction of PMS stars in the age range ~0.4 to ~4 Myr mustbe regulated. To examine the hypothesis that disk locking regulates PMSstar angular momenta, we use four different disk indicators (U-V,IC-Ks, H-Ks, and Hα) to searchfor correlations between period and disk indicator. We find noconclusive evidence that more slowly rotating stars have diskindicators, or that faster rotating stars are less likely to have diskindicators.
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Catalogue of averaged stellar effective magnetic fields. I. Chemically peculiar A and B type stars
This paper presents the catalogue and the method of determination ofaveraged quadratic effective magnetic fields < B_e > for 596 mainsequence and giant stars. The catalogue is based on measurements of thestellar effective (or mean longitudinal) magnetic field strengths B_e,which were compiled from the existing literature.We analysed the properties of 352 chemically peculiar A and B stars inthe catalogue, including Am, ApSi, He-weak, He-rich, HgMn, ApSrCrEu, andall ApSr type stars. We have found that the number distribution of allchemically peculiar (CP) stars vs. averaged magnetic field strength isdescribed by a decreasing exponential function. Relations of this typehold also for stars of all the analysed subclasses of chemicalpeculiarity. The exponential form of the above distribution function canbreak down below about 100 G, the latter value representingapproximately the resolution of our analysis for A type stars.Table A.1 and its references are only available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/407/631 and Tables 3 to 9are only available in electronic form at http://www.edpsciences.org
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Far Ultraviolet Spectroscopic Explorer Snapshot Survey of O VI Variability in the Winds of 66 OB-Type Stars
We have used the Far Ultraviolet Spectroscopic Explorer to conduct asnapshot survey of O VI variability in the winds of 66 OB-type stars inthe Galaxy and the Magellanic Clouds. These time series consist of twoor three observations separated by intervals ranging from a few days toseveral months. Although these time series provide the bare minimum ofinformation required to detect variations, this survey demonstrates thatthe O VI doublet in the winds of OB-type stars is variable on variousscales in both time and velocity. For spectral types from O3 to B1, 64%vary in time. At spectral types later than B1, no wind variability isobserved. In view of the limitations of this survey, this fractionrepresents a lower limit on the true incidence of variability in the OVI wind lines, which is very common and probably ubiquitous. Incontrast, for S IV and P V, only a small percentage of the whole sampleshows wind variations, although this may be principally due to selectioneffects. The observed variations extend over several hundreds ofkilometers per second of the wind profile and can be strong. The widthover which the wind O VI profile varies is only weakly correlated withthe terminal velocity (v&infy;), but a significantcorrelation (close to a 1:1 relationship) is derived between the maximumvelocity of the variation and v&infy;. High-velocity O VIwind absorption features (possibly related to the discrete absorptioncomponents seen in other wind lines) are also observed in 46% of thecases for spectral types from O3 to B0.5. These features are variable,but the nature of their propagation cannot be determined from thissurvey. If X-rays can produce sufficient O VI by Auger ionization of OIV and the X-rays originate from strong shocks in the wind, this studysuggests that stronger shocks occur more frequently nearv&infy;, causing an enhancement of O VI nearv&infy;.
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Absolute proper motions of open clusters. I. Observational data
Mean proper motions and parallaxes of 205 open clusters were determinedfrom their member stars found in the Hipparcos Catalogue. 360 clusterswere searched for possible members, excluding nearby clusters withdistances D < 200 pc. Members were selected using ground basedinformation (photometry, radial velocity, proper motion, distance fromthe cluster centre) and information provided by Hipparcos (propermotion, parallax). Altogether 630 certain and 100 possible members werefound. A comparison of the Hipparcos parallaxes with photometricdistances of open clusters shows good agreement. The Hipparcos dataconfirm or reject the membership of several Cepheids in the studiedclusters. Tables 1 and 2 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
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Spectral classification of O-M stars on the basis of UBV photometry
A new technique allowing the Q-method to be used surely for both thespectral classification of young O-A0 stars and older spectralsubclasses A1-M5 is described. Characteristics of interstellar lightabsorption dependence on distance in the given direction of the sky isused as a main criterion for excluding possible multiplicity of starspectral estimates at some constant values of QUBV.Information on open cluster membership probabilities is also useful asadditional criterion of the spectral classification. The method wastested on stars up to V=14 mag in directions of young open clusters NGC2244 and NGC 2264. The spectral study based on UBV photometry wasextended to faint stars of NGC 2264 in the V magnitude range 17-22 mag.
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HRI observations of PMS stars in NGC 2264
We analyze six ROSAT HRI observations pointed toward the Star FormingRegion (SFR) NGC 2264. Three are pointed to the southern star formationcore, the other three about 20' to the north. We detect 169 X-raysources, ~ 95% of which are likely to be Pre Main Sequence (PMS) stars,significantly enlarging the known population of the SFR in the areacovered by the observations. Using published BVRI photometry we placethe X-ray sources with well defined optical counterparts on the HRIdiagram and estimate their masses and ages. Our comparison of the massfunction and age distribution of the X-ray sources with resultspreviously obtained for NGC 2264, demonstrates that deep X-rayobservations provide, at least in this case, a very efficient method ofselecting SFR members and does not introduce stronger biases than othermethods. Since the observation cover a time span of ~ 5 years, we areable to study in detail the X-ray variability of our sample of PMSstars. We find that: 1) a large fraction of our sources are variable onseveral time scales and 2) Classical T Tauri Systems (i.e. starssurrounded by disks) are significantly more variable than the rest ofour sample, suggesting a role of accretion disks in the emission and/orin the absorption of the X-ray radiation.
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Derivation of the Galactic rotation curve using space velocities
We present rotation curves of the Galaxy based on the space-velocitiesof 197 OB stars and 144 classical cepheids, respectively, which rangeover a galactocentric distance interval of about 6 to 12kpc. Nosignificant differences between these rotation curves and rotationcurves based solely on radial velocities assuming circular rotation arefound. We derive an angular velocity of the LSR of{OMEGA}_0_=5.5+/-0.4mas/a (OB stars) and {OMEGA}_0_=5.4+/-0.5mas/a(cepheids), which is in agreement with the IAU 1985 value of{OMEGA}_0_=5.5mas/a. If we correct for probable rotations of the FK5system, the corresponding angular velocities are {OMEGA}_0_=6.0mas/a (OBstars) and {OMEGA}_0_=6.2mas/a (cepheids). These values agree betterwith the value of {OMEGA}_0_=6.4mas/a derived from the VLA measurementof the proper motion of SgrA^*^.
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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.
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A new list of effective temperatures of chemically peculiar stars. II.
Not Available
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Uvby-Beta and JHKLM Photometry of Peculiar Stars in the Galactic Cluster NGC2264
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&AS..102..201N&db_key=AST
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An Einstein Observatory SAO-based catalog of B-type stars
About 4000 X-ray images obtained with the Einstein Observatory are usedto measure the 0.16-4.0 keV emission from 1545 B-type SAO stars fallingin the about 10 percent of the sky surveyed with the IPC. Seventy-fourdetected X-ray sources with B-type stars are identified, and it isestimated that no more than 15 can be misidentified. Upper limits to theX-ray emission of the remaining stars are presented. In addition tosummarizing the X-ray measurements and giving other relevant opticaldata, the present extensive catalog discusses the reduction process andanalyzes selection effects associated with both SAO catalog completenessand IPC target selection procedures. It is concluded that X-rayemission, at the level of Lx not less than 10 exp 30 ergs/s, is quitecommon in B stars of early spectral types (B0-B3), regardless ofluminosity class, but that emission, at the same level, becomes lesscommon, or nonexistent, in later B-type stars.
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VBLUW photometry of the very young open cluster NGC 2264
This study presents and discusses VBLUW photometry of 112 stars with Vless than 13 in the area of the very young cluster NGC 2264.Temperatures, gravities, and reddening for stars hotter than 8400 K aredetermined. The reddening and the distance are found to be in goodagreement with the results of other references; to the existing list ofpresumable nonmembers, six stars are tentatively added as possiblenonmembers.
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More radial-velocity measurements in young open clusters
Further high resolution radial-velocity measurements are reported in 23young open clusters using the Kitt Peak CCD coude spectrograph on the0.9-m feed telescope. The radial velocities for the cluster stars arederived with the technique of cross correlation. The internal precisionof the velocity measurements is typically 2 km/s for early type stars.From these new data and previously published velocities, the observedstars in two clusters, NGC 663 and NGC 2287, were found to show arelatively small dispersion in the measured mean velocities. Furtherobservations of stars in young clusters will be useful in helping toestablish an early-type-star-velocity standard system.
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Average Profiles and Equivalent Widths of Hydrogen Lines of 76 Normal and Peculiar Stars - Masses and Radii of Studied Stars
Not Available
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Catalogue of Hydrogen Line Spectral Profiles of 236 B-Stars A-Stars and F-Stars
Not Available
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On dependence of helium abundance upon magnetic field in He-r stars.
Not Available
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Remarks to Lapicz positions of stars in NGC 2264.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1990RMxAA..20..113L&db_key=AST
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Walraven photometry of nearby southern OB associations
Homogeneous Walraven (VBLUW) photometry is presented for 5260 stars inthe regions of five nearby southern OB associations: Scorpio Centaurus(Sco OB2), Orion OB1, Canis Major OB1, Monoceros OB1, and Scutum OB2.Derived V and (B - V) in the Johnson system are included.
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Magnetic Fields and Other Parameters of Chemically Peculiar Stars - Part Two
Not Available
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The Relation Between Magnetic Field Strength and Helium Abundance in Helium Rich Stars
Not Available
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UVBY beta photometry of stars in the field of NGC 2244 and NGC 2264
Results are presented from uvby beta photometric observations of 34stars in the fields of NGC 2244 and NGC 2264. Photometric andastrometric indicators suggest that about a third of the sample arenonmembers of the clusters. Cluster color excesses are determined forthe two clusters. For the stars examined, log g and effectivetemperature are estimated. Also, stellar radii, masses, and positions inthe H-R diagram are calculated. The cluster ages and the main-sequencelifetime for massive stars show that star formation in the region hasnot been restricted to a single epoch.
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On the distances to the young open clusters NGC 2244 and NGC 2264
A new determination of the distances of the young open clusters NGC 2244and NGC 2264 is presented. It is based on distance moduli for individualOB-type stars in which the influence of the anomalous ratio of total toselective extinction, if any, is taken into account. A discussion isincluded, first, of the accuracy of the color-difference method comparedto that of other current methods for determining R and, second, of theerrors in the determination of the distances for clusters embedded innonuniform H II regions. New photoelectric measurements (UBVRI andJHKLM), and new spectrophotometric data (IDS spectra) are presented forOB-type stars in these clusters as well as summaries of publishedphotometric data. The locations in the H-R diagram of the program starsseem to suggest that these massive stars are on the main sequence,supporting the idea of continuous star formation.
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The helium abundance in the atmospheres of the stars in the clusters NGC 869, 884 and 2264
The effective temperature, acceleration due to gravity, atmospherichelium abundance, and rotational velocity of 23 B-stars are determinedusing the model atmosphere method. Photographic spectra in the 3900-4900A range obtained on the main stellar spectrograph of the 6-m telescopewere used. It is concluded that significant differences in the meanhelium abundance do not exist from cluster to cluster.
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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.
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On the Effective Temperatures of Chemically Peculiar Stars
Not Available
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A catalog of ultraviolet interstellar extinction excesses for 1415 stars
Ultraviolet interstellar extinction excesses are presented for 1415stars with spectral types B7 and earlier. The excesses with respect to Vare derived from Astronomical Netherlands Satellite (ANS) 5-channel UVphotometry at central wavelengths of approximately 1550, 1800, 2500, and3300 A. A measure of the excess extinction in the 2200-A extinction bumpis also given. The data are valuable for investigating the systematicsof peculiar interstellar extinction and for studying the character of UVinterstellar extinction in the general direction of stars for which theextinction-curve shape is unknown.
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Catalog of BV magnitudes and spectral classes of 6000 stars
The present catalog, compiled at the Abastumani Observatory, contains BVmagnitudes and spectral classes of about 6000 stars up to V(lim) = 13.0min five circular areas of 18 sq deg located near the salactic-equatorplane. The catalog is intended for star-statistics studies ofstar-formation regions.
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Observational problems of investigation of stars with anomalous helium lines.
Not Available
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Positions of stars in NGC 2264
Positions in the region of NGC 2264, obtained using the Lick CarnegieAstrograph are presented. The methods used to obtain the positions arebriefly discussed.
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Study of the open cluster NGC 2264
Photoelectric UBV magnitudes and colors have been determined for 138stars in NGC 2264, having a membership probability greater than 50percent on the basis of proper motion studies. The reddening across thecluster is variable. The distance modulus to the cluster is estimated at9.5 + or - 0.2 mag.
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INHABITED SKY
