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|The Magnetic Field Strength in the Wall of the Local Bubble toward l, b ~ 300°, 0°|
We present polarization measurements in the region around l, b =300°, 0°, toward stars with well-determined distances, primarilyin the range 40-200 pc. We argue that these observations tracepolarization caused by dust in the wall of the Local Bubble (LB). Usinga Chandrasekhar-Fermi analysis, we derive a plane-of-the-sky magneticfield strength, in the wall of the LB in this direction, of⊥>=8+5-3 μG, equivalent to a magneticpressure of PB/k~1.8×104 K cm-3.This pressure equals, to within the uncertainties, that in the bubbleinterior, as derived from EUVE observations, assuming collisionalionization equilibrium. Such a magnetic field could help us explain theobserved low O VI column density associated with the LB wall.
|Optical polarimetry of infrared excess stars|
We present UBRVI polarimetry measurements for a group of 38 IRASinfrared excess stars and complement these observations with V-band datataken from the literature for 87 additional objects. After correctingthe observed values by the interstellar contribution, we find that 48%of the analyzed sample has polarization excess. In addition, thepolarization of these stars may correlate with infrared color excesses,particularly at 60 and 100 μm. We caution, however, that poor IRASdata quality at longer wavelengths affects this correlation. We analyzethe wavelength dependence of the linear polarization of 15 polarizedobjects in relation to Serkowski's empirical interstellar law. We findthat for 6 to 7 objects (depending on the interstellar model) themeasured polarization differs significantly from the empiricalinterstellar law, suggesting an intrinsic origin. We analyze thepolarimetry distribution of IRAS infrared excess objects in relation tothe Exoplanet host stars (i.e., stars associated with at least onelikely planetary mass object). The corresponding polarimetrydistributions are different within a high confidence level. Finally, wecompare the metallicity distributions of F and G IRAS infrared excess,Exoplanet host and field main sequence stars, and find that F-G IRASinfrared excess objects have metallicities quite similar (although notidentical) to field main sequence stars and significantly different fromthe Exoplanet host group.
|Limb polarization of Uranus and Neptune. I. Imaging polarimetry and comparison with analytic models|
Imaging polarimetry of Uranus and Neptune in the R, i, and z bands arepresented. In all observations a radial limb polarization on the orderof 1% was detected with a position angle perpendicular to the limb. Thepolarization is higher in both planets for the shorter wavelength bands.As a first approximation, the polarization seems to be equally strongalong the entire limb. This is unlike Jupiter and Saturn, wheresignificant limb polarization is only observed at the poles. Wedetermined flux-weighted averages of the limb polarization and radiallimb polarization profiles, and investigated the degradation andcancellation effects in the polarization signal due to theseeing-limited spatial resolution of our observations. Taking this intoaccount we derived corrected values for the limb polarization in Uranusand Neptune. The results are compared with analytic models for Rayleighscattering atmospheres for the semi-infinite case and finite layers withground albedo. The comparison shows that the detected polarization iscompatible with expectations. This indicates that limb-polarizationmeasurements offer a powerful diagnostic tool for investigating theproperties of scattering particles in the upper atmospheres of Uranusand Neptune, in particular if more sophisticated numerical modeling ofthe limb polarization becomes available. It is also concluded from theoverall strength of the limb polarization that the disk-integratedpolarization of Uranus and Neptune for large phase angles is high(p>20%). This is of interest for future polarimetric detections ofextra-solar planets with atmospheric properties similar to Uranus andNeptune.
|A high sampling-density polarization study of the Southern Coalsack|
We present a densely sampled map of visual polarimetry of stars in thedirection of the Southern Coalsack dark cloud. Our sample consists ofnew polarimetric observations of 225 stars drawn from thespectrophotometric survey of Seidensticker, and an additional 173 stars,covering the surrounding areas of the cloud, taken from the literature.Because all the target stars have at least spectroscopic parallaxes, wecan reliably investigate the spatial origins of the polarization, inthree dimensions. We decompose the polarization into three components,due to (i) the wall of the local hot bubble, (ii) the Coalsack cloud and(iii) material in the Carina spiral arm. The polarization due to theCoalsack varies, both in alignment efficiency (p/AV) and inthe dispersion in polarization angle, across the cloud. Using asimplified radiative transfer treatment we show that the measuredpolarization in background gas is significantly affected by foregroundpolarization, and specifically that the analysis of the Coalsackpolarization must take the effects of the local hot bubble wall intoconsideration. Correcting for this effect as well as for the internalline-of-sight averaging in the Coalsack, we find, based on aChandrasekhar-Fermi analysis, a plane-of-the-sky magnetic field for theCoalsack cloud of = 93 +/- 23 μG. Asystematic error, best described by a multiplicative factor between 0.5and 1.5, additionally arises from radiative transfer effectuncertainties. We propose that this high value for the magnetic field inthe cloud envelope is due to the fact that the Coalsack cloud isembedded in the hot interior of the Upper Centaurus-Lupus superbubble.
|The total-to-selective extinction ratio determined from near IR photometry of OB stars|
The paper presents an extensive list of the total to selectiveextinction ratios R calculated from the infrared magnitudes of 597 O andB stars using the extrapolation method. The IR magnitudes of these starswere taken from the literature. The IR colour excesses are determinedwith the aid of "artificial standards" - Wegner (1994). The individualand mean values of total to selective extinction ratios R differ in mostcases from the average value R=3.10 +/-0.05 - Wegner (1993) in differentOB associations. The relation between total to selective extinctionratios R determined in this paper and those calculated using the "methodof variable extinction" and the Cardelli et al. (1989) formulae isdiscussed. The R values presented in this paper can be used to determineindividual absolute magnitudes of reddened OB stars with knowntrigonometric parallaxes.
|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.
|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 (220.127.116.11) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
|The distribution of bright OB stars in the Canis Major-Puppis-Vela region of the Milky Way|
The picture of the young stellar groups in the Canis Major-Puppis-Vela(215 deg
|Vela OB1: Probable New Members and Hertzsprung-Russell Diagram|
Several dozen stars are identified as probable previously unrecognizedmembers of the association Vel OB1, including the Vela X-1 binary pulsarsystem. Based on a variable extinction analysis of 70 stars, thedistance and ratio of total to selective absorption of the associationare determined to be 1750 pc and 3.70, respectively. Vel OB1 may besignificantly larger than previously appreciated, perhaps up to 600 by300 pc in the sense of longitude by latitude. This physical extent, andthe fact that the H-R diagram includes both low-mass evolved yellowsupergiants and massive, early-type supergiants, indicates that Vel OB1is probably not coeval.
|A Second Catalog of Orbiting Astronomical Observatory 2 Filter Photometry: Ultraviolet Photometry of 614 Stars|
Ultraviolet photometry from the Wisconsin Experiment Package on theOrbiting Astronomical Observatory 2 (OAO 2) is presented for 614 stars.Previously unpublished magnitudes from 12 filter bandpasses withwavelengths ranging from 1330 to 4250 Å have been placed on thewhite dwarf model atmosphere absolute flux scale. The fluxes wereconverted to magnitudes using V=0 for F(V)=3.46x10^-9 ergs cm^-2 s^-1Å^-1, or m_lambda=-2.5logF_lambda-21.15. This second catalogeffectively doubles the amount of OAO 2 photometry available in theliterature and includes many objects too bright to be observed withmodern space observatories.
|Polarimetry of the LMC X-Ray Binary A0538-66 during an ``On/Off'' Transition in 1991|
We present polarimetric and spectroscopic observations of the X-raybinary A0538-66 obtained in 1991 near periastron passage during cycles291, 294, and 310. The system was in an active phase during cycle 291(phi=0.98), with X-ray outbursts being observed in the previous twocycles. By cycle 294 (phi=0.00-0.12) the system had entered alow-activity phase, and by cycle 310 (phi=0.06) the system appears to befully ``off.'' We address the implications of these new observations andinterpret them within the context of the model put forward by Clayton etal. in which the polarization arises from scattering of the B2 IIIestar's light from circumstellar disk material as well as additionalmaterial in the orbital plane. The rapid change in position angle nearperiastron passage, observed in the previous polarimetric studies andascribed to additional scattering material in the Clayton et al. model,is not seen in our postoutburst observation. We suggest that the absenceof additional scatterers may be associated with the transition from the``on'' to the ``off'' state that took place in 1991.
|UBV beta Database for Case-Hamburg Northern and Southern Luminous Stars|
A database of photoelectric UBV beta photometry for stars listed in theCase-Hamburg northern and southern Milky Way luminous stars surveys hasbeen compiled from the original research literature. Consisting of over16,000 observations of some 7300 stars from over 500 sources, thisdatabase constitutes the most complete compilation of such photometryavailable for intrinsically luminous stars around the Galactic plane.Over 5000 stars listed in the Case-Hamburg surveys still lackfundamental photometric data.
|UBV polarimetry of 361 A- and F-type stars in selected areas|
We present simultaneous UBV linear polarization measurements for 361 A-and F-type stars with accurate colour excess and distance determination.These stars are distributed in 35 Kapteyn's Selected Areas, covering thethird and fourth quadrants of the galactic plane (|b| <= 30degr ).The obtained polarization and the known colour excess are compared. Ananalysis of the polarization distribution as a function of the stellardistance is also performed. Based on observations collected at theEuropean Southern Observatory (ESO), La Silla, Chile.
|Study of an unbiased sample of B stars observed with Hipparcos: the discovery of a large amount of new slowly pulsating B stars|
We present a classification of 267 new variable B-type stars discoveredby Hipparcos. We have used two different classification schemes and theyboth result in only a few new beta Cephei stars, a huge number of newslowly pulsating B stars, quite some supergiants with alpha Cyg-typevariations and variable CP stars, and further some new periodic Be starsand eclipsing binaries. Our results clearly point out the biased naturetowards short-period variables of earlier, ground-based surveys ofvariable stars. The position of the new beta Cephei stars and slowlypulsating B stars in the HR diagram is determined by means of Genevaphotometry and is confronted with the most recent calculations of theinstability strips for both groups of variables. We find that the newbeta Cephei stars are situated in the blue part of the instability stripand that the new slowly pulsating B stars almost fully cover thetheoretical instability domain determined for such stars. Thesupergiants with alpha Cyg-type variations are situated between theinstability strips of the beta Cephei and the slowly pulsating B starson the one hand and previously known supergiants that exhibitmicrovariations on the other hand. This suggests some connection betweenthe variability caused by the kappa mechanism acting in a zone ofpartially ionised metals and the unknown cause of the variations insupergiants.
|A Radial Velocity Database for Stephenson-Sanduleak Southern Luminous Stars|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....113..823R&db_key=AST
|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.
|Polarimetry of the exceptionally long-period eclipsing polar RX J0515.6+0105|
Photopolarimetric observations of RX J0515.6+0105 confirm that thissystem is a polar (i.e. an AM Herculis system). Circular polarization,varying from -2 to 2 per cent, was measured over an interval of sevennights. Furthermore, a periodogram analysis of the data reveals a 7.99-hperiod, consistent with the photometrically determined orbital period.This makes RX J0515.6+0105 the longest period polar, exceeding theerstwhile longest period system by ~3.3h. Although the degree of linearpolarization is low, there is some evidence for a linear polarization`spike' near orbital phase 0.5, corresponding to when the circularpolarization changes sign. Also, the maximum and minimum values of thecircular polarization are seen to coincide with the intensity maxima.These characteristics are evidence for two regions of cyclotron emissionof differing polarity, and argue in favour of cyclotron beaming as thelikely explanation for the prominent humps in the light curves. Thenear-zero circular polarization at eclipse implies that the cyclotronemitting region is offset from the line of centres of the stars by ~90deg. The presence of likely cyclotron spectral features implies amagnetic field strength of <~61 MG, which is well below the valueinferred from Patterson's synchrontron criterion. This is taken asevidence for a much lower accretion rate than the empirical M_solar(P)relation would imply.
|A spectroscopic database for Stephenson-Sanduleak Southern Luminous Stars|
A database of published spectral classifications for objects in theStepenson-Sanduleak Luminous Stars in the Southern Milky Way catalog hasbeen compiled from the literature. A total of 6182 classifications for2562 stars from 139 sources are incorporated.
|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.
|Infrared Polarimetry in the Chamaeleon-I Dark Cloud|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1994MNRAS.267..755M&db_key=AST
|A reassessment of some polarization standard stars|
There have been recent reports suggesting that several polarizedstandard stars exhibit variability. In the investigation here, weconcentrate on the work of Bastien et al. (AJ, 495, 900 (1988)) whoclaim that the majority of their measurements reveal instability of thecataloged standards (11 stars out of 13). We criticize their statisticalassessments and comment on the shortcomings in their data and analyses.Firstly, it is demonstrated that their test based on comparisons ofinternal and external variances does not give rise to criteria forassessing variability. Secondly, their normality tests based on kurtosisand skewness are also shown to be fallacious and that in any case theylack rigor. Problems with the homogeneity of the observations arediscussed with respect to dead-time corrections, instrumentalpolarization and modulation efficiency, all of which may give rise tovariable systematic errors within the pooled data. For four stars whichhave sufficient homogeneous measurements, tests previously used oncatalogs of unpolarized stars have been adopted to investigate the dataand only one star (HD 111613) provides firm evidence for variability.
|The 70th Name-List of Variable Stars|
|A multiwavelength study of the Carlson-Henize sample of early-type Galactic extreme emission-line stars|
A UV, optical, and radio study of nine early spectral type extremeemission-line Galactic stars from the Carlson and Henize (1979) sampleis presented. He 3-407 and He 3-1482 appear to be analogs of the massiveevolved B(e) and luminous blue variable stars of the Magellanic Clouds.The sample appears to be confined to a narrow range in spectral typefrom about B0 to B6. Most of the observed stars do not show strong Nemission, with the striking exception of He 3-1482, and these Galacticstars may not have mixed significant quantities of nitrogen into theirenvelopes, unlike many of the LMC supergiants, Most of the Galacticstars are considerably fainter than those in the Magellanic Clouds,although their spectral properties are quite similar.
|Interstellar C2, CH, and CN in translucent molecular clouds|
Optical absorption-line techniques have been applied to the study of anumber of translucent molecular clouds in which the total columndensities are large enough that substantial molecular abundances can bemaintained. Results are presented for a survey of absorption lines ofinterstellar C2, CH, and CN. Detections of CN through the A 2Pi-X2Sigma(+) (1,O) and (2,O) bands of the red system are reported andcompared with observations of the violet system for one line of sight.The population distributions in C2 provide diagnostic information ontemperature and density. The measured column densities of the threespecies can be used to test details of the theory of molecule formationin clouds where photoprocesses still play a significant role. The C2 andCH column densities are strongly correlated with each other and probablyalso with the H2 column density. In contrast, the CN column densitiesare found to vary greatly from cloud to cloud. The observations arediscussed with reference to detailed theoretical models.
|Light variations of massive stars (Alpha Cygni variables). IX|
High-precision VBLUW photometry of 22 highly luminous OBA-type stars, 13of which are Alpha Cygni variables and two of which are variable only incolor, is presented. It is suggested that sigma (V-B) increases fasterthan sigma (B-L) with later spectral types due to the absence ofstochastic metal line strength variations in the V band. It is assumedthat short-time-scale stellar spot activity is present, or thattemperature and density waves move through the atmospheres with the sametime scales, producing these line strength variations independent of thecontinuum variations. The possibility of differentiating stars which lieclose to each other in the HR diagram but have different evolutionaryhistories (and thus different metal abundances) with the aid of themaximum light amplitude/sigma (V-B) diagram is considered.
|The maximum amplitude of the optical micro-variations of massive O-F type stars (or Alpha Cygni variables, including LBV's or S DOR variables) across the HR diagram|
The maximum light amplitude (MLA) of the microvariations of nearly 100massive stars with spectral type O 3-F8 are collected from theliterature and unpublished material. These variables, called the AlphaCygni variables, also include the LBVs or S Dor type variables. The SDor type variables must be in a quiescent stage to detect theirintrinsic variations properly. The log T(eff)/MLA diagram exhibits aclear separation between S Dor type variables and the normal Alpha Cygnivariables (the majority). The results suggest that the outer layers ofboth types of stars where gravity waves presumably occur, differphysically from each other.
|The variability of polarized standard stars|
The linear polarization of 11 out of a total of 13 standard polarizedstars has been found to be variable. This implies that these 11 stars,mostly giants and supergiants but also four early-type main-sequencestars, exhibit some level of small, variable, intrinsic polarization.Therefore, they are not suitable as polarized standards for accuratepolarimetry. The problem of finding suitable candidates for standardpolarized stars is therefore nontrivial and basically still unsolved.The general increase in the level of polarization variability with meanpolarization may be partly interstellar in origin, analogous toradio-flux scintillations seen in extragalactic radio sources.
|UBV Photoelectric Photometry Catalogue (1986). III Errors and Problems on DM and HD Stars|
|UBV photoelectric catalogue (1986). II - Analysis|
The UBV photoelectric data of the stars presenting several entries inthe 1986 edition of the UBV catalog have been systematicallyintercompared, and this paper presents a discussion of the stars forwhich discrepancies larger than 0.2 mag were found. Thirty-six probablyvariable stars have been detected, among which 18 are Be stars. Sixtyfurther stars present differences in the V magnitude larger than 0.2mag. Sixteen stars already appear in the NSV catalog. Although manyproblems are probably due to poor observations, new (eclipsing) variablestars may be found in this sample. Complete disagreement is foundbetween the values published from two independent sources in 34 cases. Afirst analysis of the quality of the UBV data shows that 65 percent ofthe differences in the V magnitude and in U-B color, for respectively11,500 and 7200 stars with two sources of data, are smaller than 0.04.The scatter on the B-V index appears to be smaller, since the samepercentage reaches 79 percent.
|Small Magellanic Cloud: H-gamma-line equivalent widths and luminosity classes of the brightest blue star members|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1987A&AS...69..421A&db_key=AST
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|Proper motion RA:||-5.8|
|Proper motion Dec:||4.2|
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