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A high-resolution spectroscopy survey of β Cephei pulsations in bright stars
We present a study of absorption line-profile variations in early-B typenear-main-sequence stars without emission lines. We have surveyed atotal of 171 bright stars using the Nordic Optical Telescope (NOTSA),William Herschel Telescope (ING) and Coudé Auxiliary Telescope(ESO). Our sample contains 75% of all O9.5-B2.5 III-V non-emission-linestars brighter than 5.5 mag. We obtained high signal-to-noise,high-resolution spectra of the SiIII λ4560 triplet - for 125stars of our sample we obtained more than one spectrum - and examinedthese for pulsational-like line-profile variations and/or structure. Weconclude that about half of our sample stars show evidence forline-profile variations (LPV). We find evidence for LPV in about 65% ofour sample stars brighter than V=5.5. For stars with rotationalbroadening V sin i 100 km s-1, we find evidence for LPVin about 75% of the cases. We argue that it is likely that these LPV areof pulsational origin, and that hence more than half of thesolar-neighbourhood O9.5-B2.5 III-V stars is pulsating in modes that canbe detected with high-resolution spectroscopy. We detected LPV in 64stars previously unknown to be pulsators, and label these stars as newβ Cep candidates. We conclude that there is no obvious differencein incidence of (pulsational) LPV for early-B type near-main-sequencestars in binaries or in OB associations, with respect to single fieldstars.
| 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.
| CHORIZOS: A χ2 Code for Parameterized Modeling and Characterization of Photometry and Spectrophotometry
We have developed CHi-square cOde for parameterRized modeling andcharacterIZation of phOtometry and Spectrophotmetry (CHORIZOS). CHORIZOScan use up to two intrinsic free parameters (e.g., temperature andgravity for stars, type and redshift for galaxies, or age andmetallicity for stellar clusters) and two extrinsic parameters (amountand type of extinction). The code uses χ2 minimization tofind all models compatible with the observed data in the modelN-dimensional (N=1, 2, 3, 4) parameter space. CHORIZOS can use eithercorrelated or uncorrelated colors as input and is specially designed toidentify possible parameter degeneracies and multiple solutions. Thecode is written in IDL and is available to the astronomical community.Here we present the techniques used, test the code, apply it to a fewwell-known astronomical problems, and suggest possible applications. Asa first scientific result from CHORIZOS, we confirm from photometry theneed for a revised temperature-spectral type scale for OB starspreviously derived from spectroscopy.
| Chandra X-Ray Observations of Young Clusters. II. Orion Flanking Fields Data
We present results of Chandra observations of two flanking fields (FFs)in Orion, outside the Orion Nebula Cluster (ONC). The observations weretaken with the ACIS-I camera with an exposure time of about 48 ks eachfield. We present a catalog of 417 sources, which includes X-rayluminosity, optical and infrared photometry, and X-ray variabilityinformation. We have found 91 variable sources, 33 of which have aflarelike light curve and 11 of which have a pattern of a steadyincrease or decrease over a 10 hr period. The optical and infraredphotometry for the stars identified as X-ray sources are consistent withmost of these objects being pre-main-sequence stars with ages youngerthan 10 Myr. We present evidence for an age difference among theX-ray-selected samples of NGC 2264, Orion FFs, and ONC, with NGC 2264being the oldest and ONC being the youngest.
| 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.
| Testing Models of Low-Excitation Photodissociation Regions with Far-Infrared Observations of Reflection Nebulae
This paper presents Kuiper Airborne Observatory observations of thephotodissociation regions (PDRs) in nine reflection nebulae. Theseobservations include the far-infrared atomic fine-structure lines of [OI] 63 and 145 μm, [C II] 158 μm, and [Si II] 35 μm and theadjacent far-infrared continuum to these lines. Our analysis of thesefar-infrared observations provides estimates of the physical conditionsin each reflection nebula. In our sample of reflection nebulae, thestellar effective temperatures are 10,000-30,000 K, the gas densitiesare 4×102-2×104 cm-3, thegas temperatures are 200-690 K, and the incident far-ultravioletintensities are 300-8100 times the ambient interstellar radiation fieldstrength (1.2×10-4 ergs cm-2 s-1sr-1). Our observations are compared with current theory forlow-excitation PDRs. The [C II] 158 μm to [O I] 63 μm line ratiodecreases with increasing incident far-ultraviolet intensity. This trendis due in part to a positive correlation of gas density with incidentfar-ultraviolet intensity. We show that this correlation arises from abalance of pressure between the H II region and the surrounding PDR. The[O I] 145 to 63 μm line ratio is higher (greater than 0.1) thanpredicted and is insensitive to variations in incident far-ultravioletintensity and gas density. The stellar temperature has little effect onthe heating efficiency that primarily had the value3×10-3, within a factor of 2. This result agrees with amodel that modifies the photoelectric heating theory to account forcolor temperature effects and predicts that the heating efficiencieswould vary by less than a factor of 3 with the color temperature of theilluminating field. In addition to the single-pointing observations, an[O I] 63 μm scan was done across the molecular ridge of one of oursample reflection nebulae, NGC 1977. The result appears to supportprevious suggestions that the ionization front of this well-studied PDRis not purely edge-on.
| 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.
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
| Far-Infrared Study of IRAS 00494+5617 and IRAS 05327-0457
High angular resolution far-infrared observations at 143 and 185 μm,using the Tata Institute of Fundamental Research 1 m balloon-bornetelescope, are presented for two Galactic star-forming complexesassociated with IRAS 00494+5617 and IRAS 05327-0457. The latter map alsoreveals the cold dust in OMC-3. Both these regions are illuminated atthe edges by high-mass stars with substantial UV flux. The HIRES(High-Resolution processing using Maximum Correlation Method) processedIRAS maps at 12, 25, 60, and 100 μm have also been presented forcomparison. The present study is aimed at quantifying the role of thenearby stars vis-à-vis embedded young stellar objects in theoverall heating of these sources. Based on the FIR observations at 143and 185 μm carried out simultaneously with almost identical angularresolution, reliable dust temperature and optical depth maps have beengenerated for the brighter regions of these sources. Radiative transfermodeling in spherical geometry has been carried out to extract physicalparameters of these sources by considering the observationalconstraints, such as spectral energy distribution, angular size atdifferent wavelengths, dust temperature distribution, etc. It isconcluded that for both IRAS 00494+5617 and IRAS 05327-0457, theembedded energy sources play the major role in heating them with finitecontribution from the nearby stars. The best-fit model for IRAS00494+5617 is consistent with a simple two-phase clump-interclumppicture with ~5% volume filling factor (of clumps) and a densitycontrast of ~80.
| B Stars as a Diagnostic of Star Formation at Low and High Redshift
We have extended the evolutionary synthesis models by Leitherer et al.by including a new library of B stars generated from the IUEhigh-dispersion spectra archive. We present the library and show how thestellar spectral properties vary according to luminosity classes andspectral types. We have generated synthetic UV spectra for prototypicalyoung stellar populations varying the IMF and the star formation law.Clear signs of age effects are seen in all models. The contribution of Bstars in the UV line spectrum is clearly detected, in particular forgreater ages when O stars have evolved. With the addition of the newlibrary we are able to investigate the fraction of stellar andinterstellar contributions and the variation in the spectral shapes ofintense lines. We have used our models to date the spectrum of the localsuper-star cluster NGC 1705-1. Photospheric lines of C III λ1247,Si III λ1417, and S V λ1502 were used as diagnostics todate the burst of NGC 1705-1 at 10 Myr. Interstellar lines are clearlyseen in the NGC 1705-1 spectrum. Broadening and blueshifts of severalresonance lines are stronger in the galaxy spectrum than in our modelsand are confirmed to be intrinsic of the galaxy. Si II λ1261 andAl II λ1671 were found to be pure interstellar lines with anaverage blueshift of 78 km s-1 owing to a directed outflow ofthe interstellar medium. We have selected the star-forming galaxy1512-cB58 as a first application of the new models to high-z galaxies.This galaxy is at z=2.723, it is gravitationally lensed, and its highsignal-to-noise ratio Keck spectrum shows features typical of localstarburst galaxies, such as NGC 1705-1. Models with continuous starformation were found to be more adequate for 1512-cB58 since there arespectral features typical of a composite stellar population of O and Bstars. A model with Z=0.4 Zsolar and an IMF with α=2.8reproduces the stellar features of the 1512-cB58 spectrum.
| 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
| Hipparcos astrometry for 257 stars using Tycho-2 data
We present improved Hipparcos astrometry for 257 Hipparcos stars,resolved into 342 components. For 64 of the stars no astrometry wasobtained in the Hipparcos Catalogue, while for the remaining starsadditional components have been added by this solution or the positionshave been revised considerably. We have used the published Hipparcostransit data for the new solutions, together with results from thesecond reduction of the Tycho data for defining better initial values.Based on observations made with the ESA Hipparcos astrometry satellite.Table 3 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| CCD spectra of MK standards and a preliminary extension of the MK classification to the yellow-red region.
Not Available
| On the normal spectral energy distribution of stars: Spectral types O9-B5
The normal energy distributions for fifteen spectral subtypes from O9 toB5 for luminosity classes V, IV, and III are derived. Threephotometrically uniform catalogs served as the source of thespectrophotometric data used. Synthetic color indices for all spectraltypes are calculated using the energy distribution curves obtained.Comparison of these indices with the expected normal color indicessuggests that the energy distributions derived are reliable.
| Measurements of double stars 1993.67 - 1998.13
624 Micrometer Measurements of 224 pairs with a 32.5 cm Cassegrain, 719Measurements of 310 double stars with a 360 mm Newtonian are given.Tables 1 to 4 are available in electronic form only at the CDS130.79.128.5 or via http://cdsweb.u-strasbg.fr/Abstract.html
| 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
| HD 37017 = V 1046 ORI A double-lined spectroscopic binary with a B2e He-strong magnetic primary
We report on a detailed spectroscopic and photometric study of V1046Orionis undertaken to resolve uncertainties about the period(s) andcauses of the spectroscopic and photometric variations of thishelium-strong star. We have detected the lines of the secondary star inan extensive series of photographic and electronic spectra. Thiseliminates any doubt about the duplicity of this star. The orbitalelements we derive from our measures of these spectra confirm theunusually large orbital eccentricity, e = 0.433, for the short, P =18.65612d, orbital period. The line profiles, V/R ratio of the double\ha emission, residuals of the primary radial velocities from theorbital velocity curve, brightness and colour of the object, magneticfield, and radio emission of this system all vary with a period of0.9011836d. We tentatively follow earlier investigators in interpretingthis as the rotational period of the primary and summarize the evidenceof the phase shifts among the different phenomena, using the accuratevalue of the 0.9d period, to put tight constraints on any future modelof these changes. We postpone our own attempt at a quantitativemodelling of the variations with the 0.9d period for a separate study.Tables~3 and 5 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/Abstract.html
| Spectroscopic observations of some Be/B stars at high galactic latitudes
Spectral types, rotational velocities, and radial velocities wereestimated for eight Be and two non-emission B stars at high galacticlatitudes from CCD spectra, and their distances from the galactic planecalculated. All of the objects appear to be spectroscopically normal;for the Be stars, at least, there is no reason to evoke an unusualorigin for this sample of stars. (SECTION: Stars)
| Classification and Identification of IRAS Sources with Low-Resolution Spectra
IRAS low-resolution spectra were extracted for 11,224 IRAS sources.These spectra were classified into astrophysical classes, based on thepresence of emission and absorption features and on the shape of thecontinuum. Counterparts of these IRAS sources in existing optical andinfrared catalogs are identified, and their optical spectral types arelisted if they are known. The correlations between thephotospheric/optical and circumstellar/infrared classification arediscussed.
| X-ray properties of bright OB-type stars detected in the ROSAT all-sky survey.
The ROSAT all-sky survey has been used to study the X-ray properties forall OB-type stars listed in the Yale Bright Star Catalogue. Here wepresent a detailed astrophysical discussion of our analysis of the X-rayproperties of our complete sample of OB-type stars; a compilation of theX-ray data is provided in an accompanying paper (Berghoefer, Schmitt& Cassinelli 1996A&AS..118..481B). We demonstrate that the``canonical'' relation between X-ray and total luminosity ofL_x_/L_Bol_=~10^-7^ valid for O-type stars extends among the earlyB-type stars down to a spectral type B1-B1.5; for stars of luminosityclasses I and II the spectral type B1 defines a dividing line forearly-type star X-ray emission. We discuss the X-ray properties of X-raydetected B2-B9 stars (LC III-V) in the context of possible companions.We also compare our results to the results obtained from EinsteinObservatory data and ROSAT pointed observations. We show for our sampleof stars that X-ray variability is generally not common for O-type starsas well as early B-type stars.
| Wind variability of B supergiants. II. The two-component stellar wind of γ Arae.
The stellar wind of the rapidly rotating early-B supergiant, γAra, is studied using time series, high-resolution IUE spectroscopysecured over ~6 days in 1993 March. Results are presented based on ananalysis of several line species, including N V, C IV, Si IV, Si III, CII, and Al III. Comparisons of the time-averaged wind line morphology ofγ Ara to the UV spectra of other OB stars, and to profiles fromspherically symmetric wind models, suggest that the wind of γ Arais equatorially enhanced. Co-existing time variable features areidentified at low-velocity (redward of ~750km/s) and at higher-speedsextending to ~-1500km/s. The observed interface between these structuresis `defined' by the appearance of a discrete absorption component whichis extremely sharp (in velocity space). The central velocity of this`Super DAC' changes only gradually, over several days, between ~-400 and-750km/s in most of the ions. However, its location is shifted redwardby almost 400km/s in Al III and C II, indicating that the physicalstructure giving rise to this feature has a substantial velocity andionization jump. Constraints on the relative ionization properties ofthe wind structures are discussed. The overall wind activity in γAra exhibits a clear ion dependence, such that low-speed features arepromoted in low-ionization species, including Al III, C II, and Si III.We also highlight that - in contrast to most OB stars - there aresubstantial differences in the epoch-to-epoch time-averaged windprofiles of γ Ara and that the high-speed component observedduring our 1993 time series is normally not present. We discuss thepotential roles of the radiative bi-stability mechanism and windcompressed regions due to rapid stellar rotation for providing grosswind distortions in γ Ara.
| The Pulkovo Spectrophotometric Catalog of Bright Stars in the Range from 320 TO 1080 NM
A spectrophotometric catalog is presented, combining results of numerousobservations made by Pulkovo astronomers at different observing sites.The catalog consists of three parts: the first contains the data for 602stars in the spectral range of 320--735 nm with a resolution of 5 nm,the second one contains 285 stars in the spectral range of 500--1080 nmwith a resolution of 10 nm and the third one contains 278 stars combinedfrom the preceding catalogs in the spectral range of 320--1080 nm with aresolution of 10 nm. The data are presented in absolute energy unitsW/m(2) m, with a step of 2.5 nm and with an accuracy not lower than1.5--2.0%.
| Proper motions of stars in the region of the Orion Nebula cluster (C 0532-054).
Relative proper motions and membership probabilities for 333 starswithin an area of 1.6deg by 1.8deg centred on the Orion Nebula M 42 aredetermined using plates taken over a period of 83 years with the doubleastrograph of Shanghai Observatory (scale of 30"/mm). The plates weremeasured with the ASTROSCAN automatic plate-measuring machine of LeidenObservatory. The average proper motion accuracy obtained for stars inthe photographic magnitude range 7 to 14 is 0.3mas/yr. Errors aresomewhat larger towards fainter and brighter magnitude, but the majoritylie well below 1mas/yr. 64% of the stars have been measured successfullyon at least 13 out of 18 plates. The number of stars with membershipprobabilities higher than 0.7 is 184. It is shown by a detaileddiscussion that the proper motions and membership probabilities of thestars determined in this paper are in good agreement with the resultspresented recently by other authors. Although there is a clearconcentration in the proper motion diagram, both the remainingdispersion of the internal motions and the distribution of "members" asprojected on the sky indicate that the stars in this region are notbound as one system, but do have a common origin. A similar conclusioncan be drawn from a comparison with spectroscopic and radial velocitydata.
| 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.
| Mesures et decouvertes d'etoiles doubles effectuees a la lunette de 50cm de l'Observatoire de Nice. Measures and discoveries of visual double stars made with the 50cm refractor at the Nice Observatory.
Measures and discoveries of visual double stars made at the Observatoirede la Cote d'Azur at Nice, between 1988 and 1994, with the 50cmrefractor equipped with a filar micrometer and electronic recordingdevice. The programs proposed by J. Dommanget involve the complement ofthe C.C.D.M. (resolving problems of identification of double stars andof coherency in the Index) and the INput CAtalog Hipparcos (resolutionof ambiguities on the binarity and on the position of certain doublestars which have seldom or never been observed again from the epoch ortheir discovery). The author has discovered three new binaries: JCT1,JCT2 and JCT3.
| 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^*^.
| Stars and Seasons in Southern Africa
Although the indigenous people of Southern Africa traditionally viewedthe sky as a place quite apart from the Earth, they believed celestialphenomena to be natural signs united with those of the Earth in aharmonious synchronicity. There is no substantial evidence that thepre-colonial Africans imagined a casual relationship between celestialbodies and the seasonal patterns of life on Earth. They did, however,recognize a coincidental relationship. The traditional African cosmos,then, worked as a noetic principle unifying the observed motions ofcelestial bodies, the sequence of seasons, and the behavior of plantsand animals. Such a cosmos, with local peculiarities, was widelyunderstood in Southern Africa before the end of the last century. By theearly 20th century European colonial paradigms had largely obliteratedthis African worldview. This paper will offer a partial reconstruction.Pre-colonial South African people viewed time as a sequence of discretenatural events; through annual repetition these events served as a guidefor proper human action. The South Africans analyzed the passage of timein terms of the motions of celestial bodies, the maturation ofbeneficial plants, and the mating patterns of animals. The rightfulcourse of human life was seen to fit within the seasonal context ofthese natural phenomena. The visibility of conspicuous stars andasterisms marked significant times of year. For instance, the Lovedupeople greeted the dawn rising of Canopus with joy: "The boy has comeout." The star was a signal for rainmaking and boys' initiationceremonies to proceed. The Venda constellation Thutlwa , the giraffes,comprises and Crucis and and Centauri. In October Thutlwa skimsthe trees of the evening horizon. The Venda Thutlwa literally means&;rising above the trees,' an allusion to the majestic vegetariancreatures and the stars advising the people to be done with their springplanting. This paper will describe stellar associations with othercreatures: wild dogs, warthogs, wildebeests, swallows, cuckoos andcicadas. In each case the visibility of a star will synchronize with abehavior of the associated species. Together, stars and species informedman of the order and unity of an African cosmos -- a worldview that musthave been as satisfying as it was beautiful.
| IRAS LRS Spectra of the Sharpless H II Regions
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJS..100..389C&db_key=AST
| Deep ROSAT HRI observations of the Orion nebula region
We present results from three deep ROSAT high-resolution imagerobservations of the Orion Nebula star-forming region. The X-ray imagescontain over 1500 cataloged stars in a roughly 0.8 sq deg regioncentered on the Trapezium. In all, 389 distinct X-ray sources have beendetected, at least two-thirds of which are associated with a singleproper-motion cluster member. X-ray emission is detected from stars ofall spectral types, from massive O- and B-type components of theTrapezium to the coolest, low-mass pre-main-sequence (PMS) stars. Inthis paper we focus primarily on X-ray emission from the late-type PMSstars. Of the approximately 100 late-type cluster members with measuredspectral types, approximately three-fourths have been detected; we havederived X-ray luminosity upper limits for the remaining stars. We foundcoronal X-ray emission turns on around spectral type F6, with the upperenvelope of activity increasing with deceasing effective temperature.When plotted in an X-ray luminosity versus bolometric luminositydiagram, late-type PMS stars lie below a 'saturation' line correspondingto Lx/Lbol approximately 10-3. Forapproximately solar-mass PMS stars, we find a median X-ray luminosityapproximately 1 x 1030 ergs/s. The late G, K, and M starsexhibit nearly a two order of magnitude spread in X-ray luminosity andin Lx/Lbol at a given effective temperature. Plotsof X-ray activity versus v sin i rotational velocity and rotationalperiod appear to show no clear dependence of activity on rotation.However, because only a small fraction of late-type PMS stars in theOrion Nebula have measured v sin i or Prot and because ofuncertainties in Lx and Lx/Lbol, webelieve the data are not conclusive on this point. Light curves of thedetected X-ray sources have revealed at least 10 strong X-ray flareswith characteristic rise times greater than or approximately equal to 1hr and decay times ranging from approximately 2 to 12 hr. All the flareshave X-ray energies in excess of 3 x 1035 ergs. Many of theX-ray sources associated with late-type cluster members have beenobserved in more than one ROSAT HRI exposure, allowing us to look forvariability on the approximately 1 yr timescale between HRIobservations. A statistical analysis of the resulting count rate ratiossuggests that at least one-fourth of the late-type cluster stars aresignificantly variable on this timescale.
| 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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