First Optical Images of Circumstellar Dust Surrounding the Debris Disk Candidate HD 32297
Near-infrared imaging with the Hubble Space Telescope recently revealeda circumstellar dust disk around the A star HD 32297. Dust-scatteredlight is detected as far as 400 AU radius, and the linear morphology isconsistent with a disk ~10° away from an edge-on orientation. Herewe present the first optical images that show the dust-scattered lightmorphology from 560 to 1680 AU radius. The position angle of theputative disk midplane diverges by ~31°, and the color of dustscattering is most likely blue. We associate HD 32297 with a wall ofinterstellar gas and the enigmatic region south of the Taurus molecularcloud. We propose that the extreme asymmetries and blue disk colororiginate from a collision with a clump of interstellar material as HD32297 moves southward, and discuss evidence consistent with an age of 30Myr or younger.
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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.
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Kinematical Structure of the Local Interstellar Medium: The Galactic Anticenter Hemisphere
A survey of interstellar Na I D1 and D2 absorption features in thespectra of 104 early-type stars in the second and third Galacticquadrants reveals the large-scale kinematics of the interstellar gaswithin the Galactic anticenter hemisphere at distances from the Sunbetween ~70 and ~250 pc. Employing a technique that uses both the radialvelocities and column densities of the Na I absorptions produced by theintervening gas we have identified the velocity vectors and determinedthe spatial distribution of eight interstellar clouds in the volumeexplored. The average internal H I+H2 densities of the cloudsrange between 0.03 and 1.7 cm-3, and their masses between 80and 104 Msolar, although uncertainties in thesizes of the clouds, their possible extension beyond the regionexplored, and the presence of denser gas embedded in the larger cloudsimply that these will tend to be lower limits. We have clearlyidentified clumps of denser gas immersed in the low-density gas in oneof the clouds; these clumps show internal H I+H2 densities oforder 50 cm-3. Although we are not able to detect anyinterstellar Na I within 70 pc, the sizes of some of the clouds implythat their near edges are within that range of distances from the Sun.With respect to the local standard of rest the clouds move withvelocities between 19 and 54 km s-1. Their velocity vectorsdo not support the view of a local interstellar medium uniquelydominated by expansion from centers in the Scorpio-Centaurus OBassociation; our results suggest that this expansion is present in theGalactic center hemisphere but in the Galactic anticenter hemisphere isrestricted to the immediate neighborhood of the Sun.
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Merged catalogue of reflection nebulae
Several catalogues of reflection nebulae are merged to create a uniformcatalogue of 913 objects. It contains revised coordinates,cross-identifications of nebulae and stars, as well as identificationswith IRAS point sources.The catalogue is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/399/141
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New periodic variables from the Hipparcos epoch photometry
Two selection statistics are used to extract new candidate periodicvariables from the epoch photometry of the Hipparcos catalogue. Theprimary selection criterion is a signal-to-noise ratio. The dependenceof this statistic on the number of observations is calibrated usingabout 30000 randomly permuted Hipparcos data sets. A significance levelof 0.1 per cent is used to extract a first batch of candidate variables.The second criterion requires that the optimal frequency be unaffectedif the data are de-trended by low-order polynomials. We find 2675 newcandidate periodic variables, of which the majority (2082) are from theHipparcos`unsolved' variables. Potential problems with theinterpretation of the data (e.g. aliasing) are discussed.
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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.
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Discovery of Reflection Nebulosity around Five Vega-like Stars
Coronagraphic optical observations of six Vega-like stars revealreflection nebulosities, five of which were previously unknown. Thenebulosities illuminated by HD 4881, HD 23362, HD 23680, HD 26676, andHD 49662 resemble that of the Pleiades, indicating an interstellarorigin for dust grains. The reflection nebulosity around HD 123160 has adouble-arm morphology, but no disklike feature is seen as close as 2.5"from the star in K-band adaptive optics data. We demonstrate that auniform density dust cloud surrounding HD 23362, HD 23680, and HD 123160can account for the observed 12-100 μm spectral energy distributions.For HD 4881, HD 26676, and HD 49662, an additional emission source, suchas from a circumstellar disk or nonequilibrium grain heating, isrequired to fit the 12-25 μm data. These results indicate that insome cases, particularly for Vega-like stars located beyond the LocalBubble (>100 pc), the dust responsible for excess thermal emissionmay originate from the interstellar medium rather than from a planetarydebris system.
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Interstellar Extinction and Polarization in the Taurus Dark Clouds: The Optical Properties of Dust near the Diffuse/Dense Cloud Interface
Observations of interstellar linear polarization in the spectral range0.35-2.2 μm are presented for several stars reddened by dust in theTaurus region. Combined with a previously published study by Whittet etal., these results represent the most comprehensive data set availableon the spectral dependence of interstellar polarization in this nearbydark cloud (a total of 27 sight lines). Extinction data for these andother reddened stars in Taurus are assembled for the same spectralrange, combining published photometry and spectral classifications withphotometry from the Two Micron All Sky Survey. The polarization andextinction curves are characterized in terms of the parametersλmax (the wavelength of maximum polarization) andRV (the ratio of total to selective extinction),respectively. The data are used to investigate in detail the question ofwhether the optical properties of the dust change systematically as afunction of environment, considering stars observed throughprogressively more opaque (and thus progressively denser) regions of thecloud. At low visual extinctions (03, real changes in grainproperties occur, characterized by observed RVvalues in the range 3.5-4.0. A simple model for the development ofRV with AV suggests thatRV may approach values of 4.5 or more in thedensest regions of the cloud. The transition between ``normal''extinction and ``dense cloud'' extinction occurs at AV~3.2, avalue coincident with the threshold extinction above whichH2O-ice is detected on grains within the cloud. Changes inRV are thus either a direct consequence ofmantle growth or occur under closely similar physical conditions. Dustin Taurus appears to be in a different evolutionary state compared withother nearby dark clouds, such as ρ Oph, in which coagulation is thedominant physical process.
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Revisiting Hipparcos data for pre-main sequence stars
We cross-correlate the Herbig & Bell and Hipparcos Catalogues inorder to extract the results for young stellar objects (YSOs). Wecompare the distances of individual young stars and the distance oftheir presumably associated molecular clouds, taking into accountpost-Hipparcos distances to the relevant associations and usingHipparcos intermediate astrometric data to derive new parallaxes of thepre-main sequence stars based on their grouping. We confirm that YSOsare located in their associated clouds, as anticipated by a large bodyof work, and discuss reasons which make the individual parallaxes ofsome YSOs doubtful. We find in particular that the distance of TaurusYSOs as a group is entirely consistent with the molecular clouddistance, although Hipparcos distances of some faint Taurus-Auriga starsmust be viewed with caution. We then improve some of the solutions forthe binary and multiple pre-main sequence stars. In particular, weconfirm three new astrometric young binaries discovered by Hipparcos:RY Tau, UX Ori, and IXOph. Based on observations made with the ESA Hipparcosastrometry satellite
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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
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Photometry from the HIPPARCOS Catalogue: Constant MCP Stars, Comparison and Check Stars
Photometry from the Hipparcos catalogue is used to verify the constancyof four magnetic CP stars, as well as the comparison and the check starsused for variability studies of normal and chemically peculiar B and Astars with the Four College Automated Photoelectric Telescope;variability in these stars can produce spurious results. A few of thecomparison stars are found to be variable and should be replaced forfuture differential photometric studies.
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Spectral energy distributions and physical parameters of the atmospheres of main-sequence A stars with infrared excesses: Comparison with normal stars
For eight stars with infrared excesses greater than 0.5m in the IRASbands, we obtained the energy distribution over the range 3200-7600Angstroms and measured their infrared JHKLM magnitudes. Similarobservations were performed for 21 stars of various subclasses of thespectral type A with excesses no greater than 0.3m. Based on the energydistribution derived from the response curves of the photometric UBV andWBVR systems, we computed the synthetic B-V color indices, which are ingood agreement with the photometric observations. A comparison of thenormalized energy distribution in the spectra of A stars with infraredexcesses greater than 0.5m in the IRAS bands and the mean energydistribution for stars of the corresponding subclasses shows that themaximum difference does not exceed 10% both in the ultraviolet(3200-4000 Angstroms) and in the near infrared (up to 7600 Angstroms) Inall of the stars studied, we detected no excesses in the JHKLM bandsthat were greater than the accuracy of our measurements. Using themethod of infrared fluxes and comparing the observed energy distributionwith theoretical models of Kurucz, we determined the effectivetemperatures and angular diameters of the stars. For three stars, weestimated the parameters of their dust shells.
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The O-type Binary 15 Monocerotis Nears Periastron
We present new radial velocity measurements for the massive binary 15Monocerotis which indicate that the system is now very close toperiastron (1996.9) in its 24 yr orbit. The velocity separation in thecoming year may be large enough to permit an accurate estimate of massratio. We also present our first astrometric measurement of 15 Mon madewith the Hubble Space Telescope Fine Guidance Sensors (FGS). The FGStransfer functions are consistent with an advanced orbital positionclose to periastron, and we present preliminary orbital elements for thecombined spectroscopic and astrometric orbit.
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On the normal energy distribution in stellar spectra: Main-sequence B stars
Not Available
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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
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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.
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The photoelectric astrolabe catalogue of Yunnan Observatory (YPAC).
The positions of 53 FK5, 70 FK5 Extension and 486 GC stars are given forthe equator and equinox J2000.0 and for the mean observation epoch ofeach star. They are determined with the photoelectric astrolabe ofYunnan Observatory. The internal mean errors in right ascension anddeclination are +/- 0.046" and +/- 0.059", respectively. The meanobservation epoch is 1989.51.
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IRAS-selected Galactic star-forming regions - II. Water maser detections in the extended sample
The results of the analysis of the occurrence of 22.2-GHz H_2O maseremission in a sample of 1409 IRAS sources north of declination -30 degassociated with star-forming regions are presented. Our sample containsall the IRAS sources that satisfy Emerson criteria for selectingmolecular cores associated with the earliest evolutionary stages of thestar-forming process. In a previous paper, we have reported the resultsof the observations of about one third of the sample. In the presentpaper the observations of the remaining IRAS sources are presented: 18of them are newly detected maser sources. The results show that 20 percent of all IRAS sources that satisfy the Wood & Churchwell criteriahave H_2O water masers. This is in agreement with the assumption thatthese criteria select objects that are connected with the early phasesof the evolution of high-mass star-forming regions. Moreover, about onethird of the whole sample selected according to Emerson criteriacontains IRAS sources that are not associated with massive star-formingprocesses, but probably with molecular cores in low-mass star-formingregions.
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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 optical extinction law and distance estimate for the Taurus-Auriga molecular cloud
This paper presents optical spectrophotometry of field stars projectedon the Taurus-Auriga molecular cloud. We derive extinction laws forheavily reddened stars in this sample and show that the reddening lawthrough the dark cloud is nearly identical to the standard law forlambda-lambda(3600-6100) and AV approximately less than 3mag. Our spectroscopic parallaxes suggest a distance of 140 +/- 10 pcfor the northern portion of the cloud and show no compelling evidencefor a substantial variation in distance across the leading edge of thecloud.
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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'.
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IRAS sources beyond the solar circle. III - Observations of H2O, OH, CH3OH and CO
We have used the 100-m Effelsberg and 32-m Medicina radiotelescopes tosearch for H2O maser emission (22.235 GHz) towards 1143 IRAS sources,for OH (1665/67 MHz) towards 303 IRAS sources, and for CH3OH (12.179GHz) towards 19 IRAS sources. The IRAS sources have been selected tohave colors of premain sequence objects. To obtain an estimate of thekinematic distance, we observed (C-12)O (J = 2 to 1) and (C-12)O (J = 3to 2) with the KOSMA 3-m telescope towards 25 sources showing H2Oemission and not yet observed in CO. This paper presents theobservational results in form of tables with line parameters or upperlimits and spectra of detected sources.
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The low filling factor of dust in the Galaxy
The neighborhood of 745 luminous stars in the IRAS Skyflux plates wasexamined for the presence of dust heated by the nearby star. One-hundredtwenty-three dust clouds were found around only 106 of the stars with avolume filling factor of 0.006 and an intercloud separation of 46 pc.Nowhere was a region found where the dust is smoothly distributedthrough the volume of space heated by the star; hence an upper limit of0.06/cu cm is placed on the equivalent gas density in the intercloudregions. Due to the lack of IR emission near the star, it is found thatless than 1 percent of the stellar luminosity is reprocessed within 10pc of the star. The clouds have an average density of 0.22/cu cm and aradius of 1.9 pc, albeit with wide variations in their properties. Twodifferent scale heights of 140 and 540 pc were found for the number ofclouds around different groups of stars, which are interpreted asevidence for different distributions of dust in and out of the Galacticdisk.
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Spectroscopic binaries in the Alpha Persei cluster
An average of 16 radial velocity measures for each of the 28 brightest(B3-A2) cluster members and found four binaries was obtained. Theresulting binary frequency of 14 percent is, like the previous 20percent for the B6-A1 stars in the Pleiades, unusually low compared witha typical 30 percent for early-type field stars or with 30 percent ormore in other open clusters. These two clusters are the only known oneswith unusually high mean rotational velocities. It is suspected that themean rotational velocities are high either because these clusters lackshort-period binaries or are not old enough for synchronization ofrotational and orbital velocities to have occurred. The four AlphaPersei binaries are all relatively wide ones (greater than 20 d) andwith small mass ratios (0.1-0.5). The same results apply to the youngOrion Nebula cluster. These results can be explained in terms of theformation of binaries by capture in that during the first free-falltime, capture will produce wide binaries with small mass ratios, as inthe Orion Nebula and Alpha Persei clusters, but repeated captures anddisruptions will produce more closely spaced binaries with many massratios near 1.0, as in IC 4665.
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Star formation in Taurus-Auriga - The high-mass stars
The question of whether the star formation in the Tau-Aur cloudsproduces low-mass stars exclusively is considered. The paper identifies29 B stars as possible kinematic members of the T association, and it isargued that the data are consistent with the existence of a singleinitial mass function (IMF) generating the low and high-mass stars. Itis concluded that the Tau-Aur T association is related to the Cas-Tau OBassociation, and there is no evidence that the association IMF differsfrom the field star IMF.
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Third preliminary catalogue of stars observed with the photoelectric astrolabe of the Beijing Astronomical Observatory.
Not Available
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Lunar occultations of IRAS point sources, 1991-2000
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1989ApJS...69..651C&db_key=AST
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Interstellar extinction curves originated in single clouds
This paper reports great differences between extinction curves derivedfrom spectra of bright nearby stars, likely to be obscured by onlysingle clouds. The differences concern the shapes of the curves as wellas the total-to-selective ratios which, in some cases, reach the valueof about 15. The changes of extinction laws coincide with those ofintensity ratios of two prominent diffuse bands at 578 nm and 579.7 nm.It is concluded that physical (optical) parameters of singleinterstellar clouds differ seriously; interstellar absorption featuresobserved in the spectra of heavily reddened stars are usuallyill-defined averages over many different clouds. The lack of reasonableidentification of structural details of interstellar grains follows thisfact. The derived individual extinction curves are proposed forcomparison with theoretical or laboratory results.
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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.
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A survey of IRAS point sources in Taurus for high-velocity molecular gas
A sample of young stellar objects selected from the IRAS Point SourceCatalog (1985) has been surveyed for the presence of high-velocity(C-12)O J = 1-0 emission with the Five College Radio AstronomyObservatory 14-m telescope. Three new molecular outflows have beendetected from this survey. The high-velocity emission from these regionsis dominated by redshifted material indicative of monopolar outflow. Theenergy injection rate from all stellar winds within the Taurus cloudcomplex is compared to the energy dissipation rate due to radiativecollisions of clumps. It is uncertain, based on these observations, thatthe stellar winds can provide the energy necessary to sustain thesupersonic turbulent motions which characterize molecular clouds. From amap of (C-13)O J = 1-0 emission of the B18 cloud, the ring of enhancedline widths detected from an earlier study of (C-12)O J = 1-0 emissionis confirmed. This ring may be due to the cumulative interaction ofaccelerated shells driven by stellar winds from several T Tauri starsassociated with the cloud.
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INHABITED SKY
