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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.
| CHARM2: An updated Catalog of High Angular Resolution Measurements
We present an update of the Catalog of High Angular ResolutionMeasurements (CHARM, Richichi & Percheron \cite{CHARM}, A&A,386, 492), which includes results available until July 2004. CHARM2 is acompilation of direct measurements by high angular resolution methods,as well as indirect estimates of stellar diameters. Its main goal is toprovide a reference list of sources which can be used for calibrationand verification observations with long-baseline optical and near-IRinterferometers. Single and binary stars are included, as are complexobjects from circumstellar shells to extragalactic sources. The presentupdate provides an increase of almost a factor of two over the previousedition. Additionally, it includes several corrections and improvements,as well as a cross-check with the valuable public release observationsof the ESO Very Large Telescope Interferometer (VLTI). A total of 8231entries for 3238 unique sources are now present in CHARM2. Thisrepresents an increase of a factor of 3.4 and 2.0, respectively, overthe contents of the previous version of CHARM.The catalog is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/431/773
| Classification of Spectra from the Infrared Space Observatory PHT-S Database
We have classified over 1500 infrared spectra obtained with the PHT-Sspectrometer aboard the Infrared Space Observatory according to thesystem developed for the Short Wavelength Spectrometer (SWS) spectra byKraemer et al. The majority of these spectra contribute to subclassesthat are either underrepresented in the SWS spectral database or containsources that are too faint, such as M dwarfs, to have been observed byeither the SWS or the Infrared Astronomical Satellite Low ResolutionSpectrometer. There is strong overall agreement about the chemistry ofobjects observed with both instruments. Discrepancies can usually betraced to the different wavelength ranges and sensitivities of theinstruments. Finally, a large subset of the observations (~=250 spectra)exhibit a featureless, red continuum that is consistent with emissionfrom zodiacal dust and suggest directions for further analysis of thisserendipitous measurement of the zodiacal background.Based on observations with the Infrared Space Observatory (ISO), aEuropean Space Agency (ESA) project with instruments funded by ESAMember States (especially the Principle Investigator countries: France,Germany, Netherlands, and United Kingdom) and with the participation ofthe Institute of Space and Astronautical Science (ISAS) and the NationalAeronautics and Space Administration (NASA).
| Stars with ISM Polarization Observed with HPOL. II
Polarization data are given for stars whose polarizations are mostlyinterstellar which were observed with the University of Wisconsinspectropolarimeter (HPOL) during 1995-2003. Several cases are found forwhich K in the Serkowski Law for ISM polarization is higher than allowedby published formulas.
| J - K DENIS photometry of a VLTI-selected sample of bright southern stars
We present a photometric survey of bright southern stars carried outusing the DENIS instrument equipped with attenuating filters. Theobservations were carried out not using the survey mode of DENIS, butwith individual target pointings. This project was stimulated by theneed to obtain near-infrared photometry of stars to be used in earlycommissioning observations of the ESO Very Large TelescopeInterferometer, and in particular to establish a network of brightcalibrator sources.We stress that near-infrared photometry is peculiarly lacking for manybright stars. These stars are saturated in 2MASS as well as in regularDENIS observations. The only other observations available for brightinfrared stars are those of the Two Micron Sky Survey dating from overthirty years ago. These were restricted to declinations above≈-30°, and thus cover only about half of the sky accessible fromthe VLTI site.We note that the final 2MASS data release includes photometry of brightstars, obtained by means of point-spread function fitting. However, thismethod only achieves about 30% accuracy, which is not sufficient formost applications.In this work, we present photometry for over 600 stars, each with atleast one and up to eight measurements, in the J and K filters. Typicalaccuracy is at the level of 0\fm05 and 0\fm04 in the J and K_s bands,respectively.Based on observations collected at the European Southern Observatory, LaSilla.Tables 1 and 2 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/cgi-bin/qcat?J/A+A/413/1037
| A Multiplicity Survey of the ρ Oph Dark Cloud
Not Available
| Lyngå 1, A Small Open Cluster Containing a Red-Supergiant Member
We present CCD {UBV}RI} (Cousins system) photometric observationscomplemented with spectroscopic and polarimetric observations that werecarried out in the open cluster Lyngå 1. Our data indicate thatthe cluster reddening is E(B-V)= 0.45+/-0.03, the ratio A[V]/E(B-V)= Rsuggests that the extinction law may be slightly anomalous ( R ≈3.5) and that the cluster distance modulus is V0 - M[V] =11.40+/-0.2. The age of Lyngå 1 is between 100 and 125 Myraccording to a fitting of theoretical isochrones, and the slope of itsmass spectrum is x ≈ 1.7. The brightest red star in the field isa cluster member of spectral type K2 II-Ib.
| An Optical, Dual-Beam, Automated Medium Resolution Spectropolarimeter for the Vainu Bappu Telescope
Fabrication of an optical dual-beam spectropolarimeter as an add-onfacility to an existing astronomical spectrograph at the Vainu BappuTelescope is described. The polarimetric optics consists of asuperachromatic Pancharatnam design half-wave plate and a modifiedGlan-Taylor polarizing beam splitter. Instrumental response, calibrationand characterization of the system are presented. Performance of thespectropolarimeter has been assessed based on the results ofobservations of polarized and unpolarized standard stars. The attainableaccuracy of the instrument is found to be dependent on the S/N of thedata. The present data set yields an accuracy of ±0.5% at4000 Å and ±0.3% at 7500 Å, at a spectralresolution of 7.2 Å. Analysis of spectropolarimetric data issystematically covered for removal of instrumental errors. Thespectropolarimetric reduction software (SPRS), extremely versatile, userfriendly and compatible with the IRAF image processing package, wasdeveloped for reducing spectropolarimetric data. The empirical relationby Serkowski (IAU Symposium 52, Interstellar Dust and Related Topics, J.M. Greenberg and H. C. van de Hulst (eds.), Dordrecht, Reidel, 1975, p.145) for wavelength dependence of polarization due to interstellarmedium has been fitted to the data for the star HD 43384 (9 Gem). Ourresult shows a polarization larger by 0.49% from Hsu and Berger (ApJ262, 1982, 732). We attribute this difference to the long term variationin P for this star.
| An Ultra-high-Resolution Survey of the Interstellar 7Li/6Li Isotope Ratio in the Solar Neighborhood
In an effort to probe the extent of variations in the interstellar7Li/6Li ratio seen previously,ultra-high-resolution (R~360,000), high signal-to-noise spectra of starsin the Perseus OB2 and Scorpius OB2 associations were obtained. Thesemeasurements confirm our earlier findings of an interstellar7Li/6Li ratio of about 2 toward ο Per, thevalue predicted from models of Galactic cosmic-ray spallation reactions.Observations of other nearby stars yield limits consistent with theisotopic ratio of ~12 seen in carbonaceous chondrite meteorites. If thisratio originally represented the gas toward ο Per, then todecrease the original isotope ratio to its current value an order ofmagnitude increase in the Li abundance is expected, but it is not seen.The elemental K/Li ratio is not unusual, although Li and K are formedvia different nucleosynthetic pathways. Several proposals to account forthe low 7Li/6Li ratio were considered, but noneseems satisfactory. Analysis of the Li and K abundances from our surveyhighlighted two sight lines where depletion effects are prevalent. Thereis evidence for enhanced depletion toward X Per, since both abundancesare lower by a factor of 4 when compared to other sight lines. Moreover,a smaller Li/H abundance is observed toward 20 Aql, but the K/Habundance is normal, suggesting enhanced Li depletion (relative to K) inthis direction. Our results suggest that the7Li/6Li ratio has not changed significantly duringthe last 4.5 billion years and that a ratio of ~12 represents most gasin the solar neighborhood. In addition, there appears to be a constantstellar contribution of 7Li, indicating that one or twoprocesses dominate its production in the Galaxy.
| 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
| Rotational velocities of A-type stars in the northern hemisphere. II. Measurement of v sin i
This work is the second part of the set of measurements of v sin i forA-type stars, begun by Royer et al. (\cite{Ror_02a}). Spectra of 249 B8to F2-type stars brighter than V=7 have been collected at Observatoirede Haute-Provence (OHP). Fourier transforms of several line profiles inthe range 4200-4600 Å are used to derive v sin i from thefrequency of the first zero. Statistical analysis of the sampleindicates that measurement error mainly depends on v sin i and thisrelative error of the rotational velocity is found to be about 5% onaverage. The systematic shift with respect to standard values fromSlettebak et al. (\cite{Slk_75}), previously found in the first paper,is here confirmed. Comparisons with data from the literature agree withour findings: v sin i values from Slettebak et al. are underestimatedand the relation between both scales follows a linear law ensuremath vsin inew = 1.03 v sin iold+7.7. Finally, thesedata are combined with those from the previous paper (Royer et al.\cite{Ror_02a}), together with the catalogue of Abt & Morrell(\cite{AbtMol95}). The resulting sample includes some 2150 stars withhomogenized rotational velocities. Based on observations made atObservatoire de Haute Provence (CNRS), France. Tables \ref{results} and\ref{merging} are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.125.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/393/897
| CHARM: A Catalog of High Angular Resolution Measurements
The Catalog of High Angular Resolution Measurements (CHARM) includesmost of the measurements obtained by the techniques of lunaroccultations and long-baseline interferometry at visual and infraredwavelengths, which have appeared in the literature or have otherwisebeen made public until mid-2001. A total of 2432 measurements of 1625sources are included, along with extensive auxiliary information. Inparticular, visual and infrared photometry is included for almost allthe sources. This has been partly extracted from currently availablecatalogs, and partly obtained specifically for CHARM. The main aim is toprovide a compilation of sources which could be used as calibrators orfor science verification purposes by the new generation of largeground-based facilities such as the ESO Very Large Interferometer andthe Keck Interferometer. The Catalog is 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/386/492, and from theauthors on CD-Rom.
| CCD UBVI Photometry and Polarimetry in the Open Cluster Trumpler 21
CCD UBVI photometry was carried out in the field of the open clusterTrumpler 21. Our data locate the cluster at a distance of 1380 pc in alow absorption zone with E(B-V) = 0.25. The age of the cluster isestimated to be 25-30 × 106 yr based on thesuperposition of isochrones computed with mass loss and overshooting.The cluster mass spectrum has a slope of 1.44 similar to the typicalvalue 1.35 for field stars. UBVRI polarimetry of its brightest membersled us to the finding that diffuse interstellar material is responsiblefor both polarization percentage and its direction.
| A High-Resolution Survey of Interstellar K I Absorption
We present high-resolution (FWHM ~0.4-1.8 km s-1) spectra,obtained with the AAT UHRF, the McDonald Observatory 2.7 m coudéspectrograph, and/or the KPNO coudé feed, of interstellar K Iabsorption toward 54 Galactic stars. These new K I spectra revealcomplex structure and narrow, closely blended components in many linesof sight. Multicomponent fits to the line profiles yield estimates forthe column densities, line widths, and velocities for 319 individualinterstellar cloud components. The median component width (FWHM) and thetrue median separation between adjacent components are both <~1.2 kms-1. The median and maximum individual component K I columndensities, about 4×1010 and 1012cm-2, correspond to individual component hydrogen columndensities of about 2×1020 and 1021cm-2 and E(B-V)~0.03 and 0.17, respectively. If T istypically ~100 K, then at least half the individual components havesubsonic internal turbulent velocities. We also reexamine therelationships between the column densities of K I, Na I, C I, Li I,Htot, H2, and CH. The four trace neutral speciesexhibit essentially linear relationships with each other over wideranges in overall column density. If C is uniformly depleted by 0.4 dex,then Li, Na, and K are each typically depleted by 0.6-0.7 dex. The totalline of sight values for N(K I) and N(Na I) show roughly quadraticdependences on N(Htot), but the relationships for theensemble of individual clouds could be significantly steeper. Thesequadratic (or steeper) dependences appear to rule out significantcontributions to the ionization from cosmic rays, X-rays, and/or chargeexchange with C II in most cases. Charge exchange with negativelycharged large molecules may often be more important than radiativerecombination in neutralizing most singly ionized atomic species in coolH I clouds, however-suggesting that the true ne,nH, and thermal pressures may be significantly smaller thanthe values estimated by considering only radiative recombination. BothN(CH) and N(H2) are nearly linearly proportional to N(K I)and N(Na I) [except for 1015cm-2<~N(H2)<~1019cm-2, over which H2 makes the transition to theself-shielded regime]. Those relationships appear also to hold for manyindividual components and component groups, suggesting thathigh-resolution spectra of K I and Na I can be very useful forinterpreting lower resolution molecular data. The scatter about allthese mean relationships is generally small (<~0.1-0.2 dex), ifcertain consistently ``discrepant'' sight lines are excluded-suggestingthat both the relative depletions and the relative ionization of Li, C,Na, and K are generally within factors of 2 of their mean values.Differences noted for sight lines in Sco-Oph, in the Pleiades, near theOrion Trapezium, and in the LMC and SMC may be due to differences in thestrength and/or shape of the ambient radiation fields, perhaps amplifiedby the effects of charge transfer with large molecules.
| The Physical Basis of Luminosity Classification in the Late A-, F-, and Early G-Type Stars. II. Basic Parameters of Program Stars and the Role of Microturbulence
Paper I of this series presented precise MK spectral types for 372 lateA-, F-, and early G-type stars with the aim of understanding the natureof luminosity classification on the MK spectral classification systemfor this range of spectral types. In this paper, a multidimensionaldownhill simplex technique is introduced to determine the basicparameters of the program stars from fits of synthetic spectra andfluxes with observed spectra and fluxes from Strömgren uvbyphotometry. This exercise yields useful calibrations of the MK spectralclassification system but, most importantly, gives insight into thephysical nature of luminosity classification on the MK spectralclassification system. In particular, we find that in this range ofspectral types, microturbulence appears to be at least as important asgravity in determining the MK luminosity type.
| The Physical Basis of Luminosity Classification in the Late A-, F-, and Early G-Type Stars. I. Precise Spectral Types for 372 Stars
This is the first in a series of two papers that address the problem ofthe physical nature of luminosity classification in the late A-, F-, andearly G-type stars. In this paper, we present precise spectralclassifications of 372 stars on the MK system. For those stars in theset with Strömgren uvbyβ photometry, we derive reddenings andpresent a calibration of MK temperature types in terms of the intrinsicStrömgren (b-y)0 index. We also examine the relationshipbetween the luminosity class and the Strömgren c1 index,which measures the Balmer jump. The second paper will address thederivation of the physical parameters of these stars, and therelationships between these physical parameters and the luminosityclass. Stars classified in this paper include one new λ Bootisstar and 10 of the F- and G-type dwarfs with recently discoveredplanets.
| The open cluster Havlen-Moffat No. 1 revisited
A deep CCD UBVRI photometric survey combined with UBVRI polarimetricobservations of 21 bright stars was carried out in the region of theopen cluster Havlen-Moffat No. 1. Our data reveal that the extinctionlaw in this cluster is variable and that six cluster stars show veryhigh polarisation values (>4%), probably because of the presence of anearby small dust cloud. The cluster is at a distance of d = 3300 pc, itis 2-4 Myr old and the initial mass function of its most massive stars(M > 3 Msun ) has a flat slope of x~ 0.7. As an additionalresult, it was possible to reconcile the absolute magnitudes of the twoWN7-type members using the R-values valid in the regions where they arelocated. Based on observations collected at the University of TorontoSouthern Observatory, Las Campanas, Chile, and the ComplejoAstronómico El Leoncito, (CASLEO), Argentina, operated underagreement between the Consejo Nacional de InvestigacionesCientíficas y Técnicas de la República Argentinaand the National Universities of La Plata, Córdoba and San Juan.Table 1 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/cgi-bin/qcat?J/A+A/371/908.
| 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
| OB association members in the ACT and TRC catalogues
The Hipparcos Catalogue contains members of nearby OB associationsbrighter than 12th magnitude in V. However, membership lists arecomplete only to magnitude V=7.3. In this paper we discuss whetherproper motions listed in the `Astrographic Catalogue+Tycho' referencecatalogue (ACT) and the Tycho Reference Catalogue (TRC), which arecomplete to V~10.5mag, can be used to find additional associationmembers. Proper motions in the ACT/TRC have an average accuracy of~3masyr-1. We search for ACT/TRC stars which have propermotions consistent with the spatial velocity of the Hipparcos members ofthe nearby OB associations already identified by de Zeeuw et al. Thesestars are first selected using a convergent-point method, and thensubjected to further constraints on the proper-motion distribution,magnitude and colour to narrow down the final number of candidatemembers. Monte Carlo simulations show that the proper-motiondistribution, magnitude, and colour constraints remove ~97per cent ofthe field stars, while at the same time retain more than 90per cent ofthe cluster stars. The procedure has been applied to five nearbyassociations: the three subgroups of Sco OB2, plus Per OB3 and Cep OB6.In all cases except Cep OB6, we find evidence for new associationmembers fainter than the completeness limit of the Hipparcos Catalogue.However, narrow-band photometry and/or radial velocities are needed topinpoint the cluster members, and to study their physicalcharacteristics.
| Multicolor Polarimetry of Selected BE Stars: 1995-1998
A new polarimeter called AnyPol has been used at Limber Observatory for4 yr to monitor annually the broadband linear polarization of a sampleof bright northern Be stars. This is the fourth report on a programstarted in 1985 at McDonald Observatory and the first one to comeentirely from the new installation. Although no variability was detectedat the 3 sigma level during the current reporting period, analysis ofthe full 13 yr data set is beginning to reveal hints of long-termvariability that may provide clues for understanding the Be phenomenon.
| Ultraviolet Interstellar Linear Polarization. V. Analysis of the Final Data Set
Using recent measurements of ultraviolet interstellar polarization, wehave examined its relationship to ultraviolet extinction and topolarization and extinction measurements in the visible and infrared.The relationship between the relative amount of ultraviolet polarizationand the parameter lambda_max, determined using only visible data, isconfirmed and strengthened, for example, by a tight correlation betweenp(6 mum^-1)/p_max and lambda^-1_max. A good fit to the wavelengthdependence of the polarization from the infrared to the ultraviolet canbe achieved with a five-parameter function combining a power law in theinfrared and a Serkowski-like function in the ultraviolet. Thepolarization efficiency (ratio of polarization to extinction) is less inthe ultraviolet than in the visual, and the ratio of these efficienciesincreases systematically with lambda^-1_max. We relate these effects tosystematic changes in the underlying aligned grain size distribution.The polarization efficiency of the grains causing the 2175 Åextinction bump along most sight lines is so (unusually) small that nostatistically significant polarization feature is detectable in thatwavelength region. Only two of 28 sight lines show a definitepolarization feature. The environments of the two bump sight lines aresimilar but not unique, and the mechanism for producing the polarizationfeature along only these two sight lines is still not known.
| 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.
| A HIPPARCOS Census of the Nearby OB Associations
A comprehensive census of the stellar content of the OB associationswithin 1 kpc from the Sun is presented, based on Hipparcos positions,proper motions, and parallaxes. It is a key part of a long-term projectto study the formation, structure, and evolution of nearby young stellargroups and related star-forming regions. OB associations are unbound``moving groups,'' which can be detected kinematically because of theirsmall internal velocity dispersion. The nearby associations have a largeextent on the sky, which traditionally has limited astrometricmembership determination to bright stars (V<~6 mag), with spectraltypes earlier than ~B5. The Hipparcos measurements allow a majorimprovement in this situation. Moving groups are identified in theHipparcos Catalog by combining de Bruijne's refurbished convergent pointmethod with the ``Spaghetti method'' of Hoogerwerf & Aguilar.Astrometric members are listed for 12 young stellar groups, out to adistance of ~650 pc. These are the three subgroups Upper Scorpius, UpperCentaurus Lupus, and Lower Centaurus Crux of Sco OB2, as well as VelOB2, Tr 10, Col 121, Per OB2, alpha Persei (Per OB3), Cas-Tau, Lac OB1,Cep OB2, and a new group in Cepheus, designated as Cep OB6. Theselection procedure corrects the list of previously known astrometricand photometric B- and A-type members in these groups and identifiesmany new members, including a significant number of F stars, as well asevolved stars, e.g., the Wolf-Rayet stars gamma^2 Vel (WR 11) in Vel OB2and EZ CMa (WR 6) in Col 121, and the classical Cepheid delta Cep in CepOB6. Membership probabilities are given for all selected stars. MonteCarlo simulations are used to estimate the expected number of interloperfield stars. In the nearest associations, notably in Sco OB2, thelater-type members include T Tauri objects and other stars in the finalpre-main-sequence phase. This provides a firm link between the classicalhigh-mass stellar content and ongoing low-mass star formation. Detailedstudies of these 12 groups, and their relation to the surroundinginterstellar medium, will be presented elsewhere. Astrometric evidencefor moving groups in the fields of R CrA, CMa OB1, Mon OB1, Ori OB1, CamOB1, Cep OB3, Cep OB4, Cyg OB4, Cyg OB7, and Sct OB2, is inconclusive.OB associations do exist in many of these regions, but they are eitherat distances beyond ~500 pc where the Hipparcos parallaxes are oflimited use, or they have unfavorable kinematics, so that the groupproper motion does not distinguish it from the field stars in theGalactic disk. The mean distances of the well-established groups aresystematically smaller than the pre-Hipparcos photometric estimates.While part of this may be caused by the improved membership lists, arecalibration of the upper main sequence in the Hertzsprung-Russelldiagram may be called for. The mean motions display a systematicpattern, which is discussed in relation to the Gould Belt. Six of the 12detected moving groups do not appear in the classical list of nearby OBassociations. This is sometimes caused by the absence of O stars, but inother cases a previously known open cluster turns out to be (part of) anextended OB association. The number of unbound young stellar groups inthe solar neighborhood may be significantly larger than thoughtpreviously.
| High resolution spectroscopy over lambda lambda 8500-8750 Å for GAIA. I. Mapping the MKK classification system
We present an Echelle+CCD high resolution spectroscopic atlas (0.25Ä/pix dispersion, 0.43 Ä FWHM resolution and 20 000 resolvingpower) mapping the MKK classification system over the interval lambdalambda 8500-8750 Ä. The wavelength interval is remarkably free fromtelluric lines and it is centered on the near-IR triplet of Ca II, thehead of hydrogen Paschen series and several strong metallic lines. Thespectra of 131 stars of types between O4 and M8 and luminosity classes Ithrough V are included in the atlas. Special care was put in maintainingthe highest instrumental homogeneity over the whole set of data. Thecapability to derive accurate MKK spectral types from high resolutionobservations over the interval lambda lambda 8500-8750 Ä isdiscussed. The observations have been performed as part of an evaluationstudy of possible spectroscopic performances for the astrometric missionGAIA planned by ESA. Tables~3 and 4 are only available in electronicform at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)or via http://cdsweb.u-strasbg.fr/ Abstract.html}\fnmsep\thanks{ Thespectra of the stars listed in Table~2 are also available in electronicform at the CDS or via the personal HomePagehttp://ulisse.pd.astro.it/Astro/Atlases/}\fnmsep\thanks{ Figures 3--28are only available in electronic form at http://www.edpsciences.com
| Five-colour photometry of OB-stars in the Southern Hemisphere
Observations of OB-stars, made in 1959 and 1960 at the Leiden SouthernStation near Hartebeespoortdam, South Africa, with the VBLUW photometerattached to the 90 cm light-collector, are given in this paper. They arecompared with photometry obtained by \cite[Graham (1968),]{gra68}\cite[Walraven & Walraven (1977),]{wal77} \cite[Lub & Pel(1977)]{lub77} and \cite[Van Genderen et al. (1984).]{gen84} Formulaefor the transformation of the present observations to those of\cite[Walraven & Walraven (1977)]{wal77} and \cite[Lub & Pel(1977)]{lub77} are given. Table 4 is only available in electronic format the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) orvia http://cdsweb.u-strasbg.fr/Abstract.html
| On correlations between diffuse interstellar bands
One way to better apprehend the problem of diffuse interstellar bands(DIBs) is to search for correlations between the bands in a large sampleof spectra towards various lines of sight: a strict correlation mayimply that a common carrier is at the origin of the bands, whereas anon-correlation means that different species are involved. We proposethis observational test for 10 DIBs collected in up to 62 Galactic linesof sight. Strong DIBs do not strictly correlate, and sometimes thecorrelation is very poor. Only one example of a strict correlation hasbeen found in our sample between the DIBs at 6614 and 6196 Ä, thatcould signify a single carrier for those two bands. The general absenceof strict correlations is discussed in the context of molecular carriersfor the DIBs.
| The Scorpius OB2 Complex
The Sco OB2 complex is a member of the Local Association. Theassociation contains pre-main-sequence stars in addition to objects some3 x 10^7 yr old. If it is assumed that stars in wide binaries arecoeval, then the He-weak variables in the supercluster arepre-main-sequence, elevated above that sequence by an amount similar tothat of the 3 x 10^7 yr old, normal stars but contracting toward thesequence, not evolving from it. The apparent great depth of theassociation is probably a result of some foreground superclustermembers, superposed on Sco OB2, and a rift in the absorption cloudbetween Scorpius and Ophiuchus. The adjoining Chamaeleon complex alsoappears to be a member of the supercluster.
| 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.
| Polarimetric observations of southern hemisphere young solar-type stars
{A report is given on some linear and circular polarimetric observationsof young solar-type stars. Despite a somewhat high level of instrumentalpolarization, the measurements were able to detect polarizations ~0.0001 or\ 0.01%. Temporal variability has been discovered for 59 Virwith an indication that circular polarization is also present. Apolarization at a level of p ~ 1% was found associated with the star SAO251015. Marginal polarizations are also suspected for the stars HD155555 and HD 1835. For SAO 154972 (TU Pyx), a sudden change inpolarization ~ 2% occurred over some tens of minutes and an associatedcircular polarization was also detected.}
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Pozíciós és asztrometriai adatok
| Csillagkép: | Skorpió |
| Rektaszcenzió: | 16h20m38.20s |
| Deklináció: | -24°10'10.0" |
| Vizuális fényesség: | 4.55 |
| Távolság: | 361.011 parszek |
| RA sajátmozgás: | -6.3 |
| Dec sajátmozgás: | -16.8 |
| B-T magnitude: | 5.486 |
| V-T magnitude: | 4.665 |
Katalógusok és elnevezések:
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