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|Astrometric orbits of SB^9 stars|
Hipparcos Intermediate Astrometric Data (IAD) have been used to deriveastrometric orbital elements for spectroscopic binaries from the newlyreleased Ninth Catalogue of Spectroscopic Binary Orbits(SB^9). This endeavour is justified by the fact that (i) theastrometric orbital motion is often difficult to detect without theprior knowledge of the spectroscopic orbital elements, and (ii) suchknowledge was not available at the time of the construction of theHipparcos Catalogue for the spectroscopic binaries which were recentlyadded to the SB^9 catalogue. Among the 1374 binaries fromSB^9 which have an HIP entry (excluding binaries with visualcompanions, or DMSA/C in the Double and Multiple Stars Annex), 282 havedetectable orbital astrometric motion (at the 5% significance level).Among those, only 70 have astrometric orbital elements that are reliablydetermined (according to specific statistical tests), and for the firsttime for 20 systems. This represents a 8.5% increase of the number ofastrometric systems with known orbital elements (The Double and MultipleSystems Annex contains 235 of those DMSA/O systems). The detection ofthe astrometric orbital motion when the Hipparcos IAD are supplementedby the spectroscopic orbital elements is close to 100% for binaries withonly one visible component, provided that the period is in the 50-1000 drange and the parallax is >5 mas. This result is an interestingtestbed to guide the choice of algorithms and statistical tests to beused in the search for astrometric binaries during the forthcoming ESAGaia mission. Finally, orbital inclinations provided by the presentanalysis have been used to derive several astrophysical quantities. Forinstance, 29 among the 70 systems with reliable astrometric orbitalelements involve main sequence stars for which the companion mass couldbe derived. Some interesting conclusions may be drawn from this new setof stellar masses, like the enigmatic nature of the companion to theHyades F dwarf HIP 20935. This system has a mass ratio of 0.98 but thecompanion remains elusive.
|Magnetic activity in the young solar analog AB Dor. Active longitudes and cycles from long-term photometry.|
We analyse photometric observations of the young active dwarf AB Dor,spanning more than 20 years. Similar to the young solar analog LQ Hya,AB Dor shows long-lived, nonaxisymmetric spot distribution- activelongitudes in opposite hemispheres. The active longitudes migratenonlinearly in the fixed reference frame, because of the differentialrotation and changes of the mean spot latitudes. At least two activitycycles are found in the data. One cycle originates from repeatingswitches of the activity between the two active longitudes in about(2-3)-year intervals. This results in the flip-flop cycle of about 5.5years, which includes two consecutive switches. The 5.5-yr cycle alsomodulates variations of the minimum stellar brightness and thepeak-to-peak amplitude, that suggests a periodic redistribution of thespot area between the opposite longitudes and supports the reality ofthe flip-flop cycle. The other cycle is clearly seen in variations ofthe mean and maximum stellar brightness on the time-scale of 20 yearsand is reminiscent of the 11-year sunspot cycle.Tables 2 and 3 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (126.96.36.199) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/432/657
|Reprocessing the Hipparcos Intermediate Astrometric Data of spectroscopic binaries. II. Systems with a giant component|
By reanalyzing the Hipparcos Intermediate Astrometric Data of a largesample of spectroscopic binaries containing a giant, we obtain a sampleof 29 systems fulfilling a carefully derived set of constraints andhence for which we can derive an accurate orbital solution. Of these,one is a double-lined spectroscopic binary and six were not listed inthe DMSA/O section of the catalogue. Using our solutions, we derive themasses of the components in these systems and statistically analyzethem. We also briefly discuss each system individually.Based on observations from the Hipparcos astrometric satellite operatedby the European Space Agency (ESA 1997) and on data collected with theSimbad database.
|The tidal effects on the lithium abundance of binary systems with giant component|
We analyse the behavior of lithium abundance as a function of effectivetemperature, projected rotational velocity, orbital period andeccentricity for a sample of 68 binary systems with giant component andorbital period ranging from about 10 to 6400 days. For these binarysystems the Li abundances show a gradual decrease with temperature,paralleling the well established result for single giants. We have alsoobserved a dependence of lithium content on rotation. Binary systemswith moderate to high rotation present also moderate to high Li content.This study shows also that synchronized binary systems with giantcomponent seem to retain more of their original lithium than theunsynchronized systems. For orbital periods lower than 100 to 250 days,typically the period of synchronization for this kind of binary systems,lithium depleted stars seems to be unusual. The suggestion is made thatthere is an ``inhibited zone" in which synchronized binary systems withgiant component having lithium abundance lower than a threshold levelshould be unusual. Based on observations collected at ESO, La Silla.
|MSX, 2MASS, and the LARGE MAGELLANIC CLOUD: A Combined Near- and Mid-Infrared View|
The Large Magellanic Cloud (LMC) has been observed by the MidcourseSpace Experiment (MSX) in the mid-infrared and the Two Micron All SkySurvey (2MASS) in the near-infrared. We have performed across-correlation of the 1806 MSX catalog sources and nearly 1.4 million2MASS cataloged point and extended sources and find 1664 matches. Usingthe available color information, we identify a number of stellarpopulations and nebulae, including main-sequence stars, giant stars, redsupergiants, carbon- and oxygen-rich asymptotic giant branch (AGB)stars, planetary nebulae, H II regions, and other dusty objects likelyassociated with early-type stars. A total of 731 of these sources haveno previous identification. We compile a listing of all objects, whichincludes photometry and astrometry. The 8.3 μm MSX sensitivity is thelimiting factor for object detection: only the brighter red objects,specifically the red supergiants, AGB stars, planetary nebulae, and H IIregions, are detected in the LMC. The remaining objects are likely inthe Galactic foreground. The spatial distribution of the infrared LMCsources may contribute to understanding stellar formation and evolutionand the overall galactic evolution. We demonstrate that a combined mid-and near-infrared photometric baseline provides a powerful means ofidentifying new objects in the LMC for future ground-based andspace-based follow-up observations.
|Speckle Interferometry of New and Problem HIPPARCOS Binaries|
The ESA Hipparcos satellite made measurements of over 12,000 doublestars and discovered 3406 new systems. In addition to these, 4706entries in the Hipparcos Catalogue correspond to double star solutionsthat did not provide the classical parameters of separation and positionangle (rho,theta) but were the so-called problem stars, flagged ``G,''``O,'' ``V,'' or ``X'' (field H59 of the main catalog). An additionalsubset of 6981 entries were treated as single objects but classified byHipparcos as ``suspected nonsingle'' (flag ``S'' in field H61), thusyielding a total of 11,687 ``problem stars.'' Of the many ground-basedtechniques for the study of double stars, probably the one with thegreatest potential for exploration of these new and problem Hipparcosbinaries is speckle interferometry. Results are presented from aninspection of 848 new and problem Hipparcos binaries, using botharchival and new speckle observations obtained with the USNO and CHARAspeckle cameras.
|UBV Observations of AB Dor, Late 1995|
|UBV Observations of AB Dor, 1994-5|
|U-Filter Photometry of AB Doradus|
|Photoelectric Observations of \theta Tucanae and AB Doradus|
|Observations of AB Doradus in 1986|
The results of photometric and spectroscopic observations of AB Dor inNovember 1986 confirm presence of a rapid (on a scale of a fewrotational periods) variability of light curve of the variable. Minimaof light curves in different colors are shifted in phase relative toeach other. All photometric observations available in literature can bephased with a single period without necessity of invoking any systematicspot migration. The value of the surface flux of the line core emissionin H and K lines places AB Dor among the most chromospherically activestars known at present.
|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.
|UBV Observations of AB Dor, 1993|
|The December 1993 Light Curve of AB Dor|
|Evolved GK stars near the Sun. 2: The young disk population|
From a sample of nearly 2000 GK giants a group of young disk stars withwell determined space motions has been selected. The zero point of theluminosity calibrations, both from the ultraviolet flux (modifiedStroemgren system) and that in the region of 4200 to 4900 A (DDOsystem), show a discontinuity of about a half magnitude at the border ofthe young disk and old disk domains. The population separation is basedon the space velocity components, which are also an age discriminant,with the population interface near 2 x 109 yr, based onmodels with convective overshoot at the core. This age corresponds togiant masses near 1.7 solar mass, near the critical mass separating theyoung stars that do not burn helium in degenerate cores from older starsthat do. Ten percent of both populations show CN anomalies in that thederived value of P(Fe/H) from CN (Cm) and fromFe(M1) differ by more than 0.1 dex and the weak and strong CNstars occur equally in the old disk but the weak CN stars predominate inthe young disk. Peculiar stars, where flux distortions affect theluminosity calibrations, are of the CH+(Ba II) and CH-(weak G band)variety and represent less than 1% of the stars in both populations. Theyoung disk giants are restricted to ages greater than about109 yr, because younger stars are bright giants orsupergiants (luminosity class 2 or 1), and younger than about 2 x109 yr, because the old disk-young disk boundary occurs near1.7 solar mass. The distribution of heavy element abundances, P(Fe/H),for young disk giants is both more limited in range (+/- 0.4 dex) and isskewed toward higher abundances, compared with the nearly normaldistribution for old disk giants. The distribution of (U,V) velocityvectors gives (U,V,W) and their dispersions = (+17.6 +/- 18.4, -14.8 +/-8.4, -6.9 +/- 13.0) and (+3.6 +/- 38.4, -20.7 +/- 27.5, -6.7 +/-17.3)km/s for young and old disk giants, respectively.
|Longterm Photometry of Variables at ESO - Part Two - the Second Data Catalogue 1986-1990|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&AS..102...79S&db_key=AST
|Statistical Analysis of a Sample of Spectroscopic Binaries Containing Late Type Giants|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&A...271..125B&db_key=AST
|UBV(RI)c observations for 13 bright Cepheids|
Photometry in the UBV(RI)c system has been obtained for 13 of thebrightest Cepheids in the southern sky available to the new SydneyUniversity Stellar Interferometer. The stars observed were Eta Aq1, 1Car, U Car, AX Cir, Beta Dor, Zeta Gem, T Mon, Kappa Pav, U Sgr, W Sgr,X Sgr, Y Sgr, and AH Vel. The main purpose of the photometry is toprovide current epoch data for the phases of the variables, although forseveral of the stars these data are also the first in the (RI)c system.
|Earliest photometry of SN 1987A|
Seven wide-field photographic exposures, obtained of the LMC field on1987 Feb. 22 - 24 in Australia, and including the earliest recordedimages of SN 1987A, have been scanned and photometrically calibrated bymeans of bright field stars. Accurate V-magnitudes of SN 1987A arederived by means of fixed-diaphragm, color adjusted, integrated fluxes;on Feb. 23 it is found to be 0.2 - 0.8 mag brighter than indicated byearlier estimates, based on image diameters alone. The measurements nowagree rather better with the theoretical light curves, e.g. those byWoosley (1988).
|Fifth fundamental catalogue. Part 2: The FK5 extension - new fundamental stars|
The mean positions and proper motions for 3117 new fundamental starsessentially in the magnitude range about 4.5 to 9.5 are given in thisFK5 extension. Mean apparent visual magnitude is 7.2 and is on average2.5 magnitudes fainter then the basic FK5 which has a mean magnitude of4.7. (The basic FK5 gives the mean positions and proper motions for theclassical 1535 fundamental stars). The following are discussed: theobservational material, reduction of observations, star selection, andthe system for the FK5 extension. An explanation and description of thecatalog are given. The catalog of 3117 fundamental stars for the equinoxand epoch J2000.0 and B1950.0 is presented. The parallaxes and radialvelocities for 22 extension stars with large forecasting effects aregiven. Catalogs used in the compilation of the FK5 fundamental catalogare listed.
|Positional reference stars in the Magellanic Clouds|
The equatorial coordinates are determined of 926 stars (mainly ofgalactic origin) in the direction of the Magellanic Clouds at the meanepoch T = 1978.4 with an overall accuracy characterized by the meanvalues of the O-C coordinates, Sa = 0.35 arcsec and Sd = 0.38 arcsec,calculated from the coordinates of the Perth reference stars. Thesevalues are larger than the accuracy expected for primary standard stars.They allow the new positions to be considered as those of reliablesecondary standard stars. The published positions correspond to anunquestionable improvement of the quality of the coordinates provided inthe current catalogs. This study represents an 'astrometric step' in thestarting of a 'Durchmusterung' of the Magellanic Clouds organized by deBoer (1988, 1989).
|Uvby-photometry of AB Doradus|
Four-channel uvby photometry of AB Doradus was made during seven nightsbetween December 8 and 21, 1984, at the European Southern Observatory.The light curves show rapid changes during a few stellar rotations. Twodark spot regions were visible in the observations. The photometrycontains a flare that was simultaneous to an H-alpha flare. Theobservations suggest that some X-ray flares of AB Dor may not bedetectable in the visual. The comparison with partly simultaneous broadband observations indicates that narrow band photometry does not haveany excess sensitivity to spot-activity.
|UBVRI observations of southern hemisphere active stars|
A program of high-precision UBVRI photometry of selected southernhemisphere active stars has been carried out at the European SouthernObservatory (La Silla, Chile) from November 1985 to February 1987. Oneresult of such monitoring has been the acquisition of the complete orpartially complete light curves for 11 stars. Significant changes oftheir wavelike light curves, both in amplitude and shape, are found.These observations are important to produce a homogeneous and extendeddatabase, which is necessary to track the formation and evolution ofphotospheric active regions.
|Large and Kinematically Unbiased Samples of G- and K-Type Stars. III. Evolved Young Disk Stars in the Bright Star Sample|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1989PASP..101...54E&db_key=AST
|Large and kinematically unbiased samples of G- and K-type stars. II - Observations of evolved stars in the Bright Star sample. III - Evolved young disk stars in the Bright Star sample|
Four color and RI observations were obtained for a large sample ofG-type and K-type stars in the Bright Star Catalogue. Data are firstpresented for 110 evolved stars. Photometry of evolved young diskpopulation stars have then been calibrated for luminosity, reddening,and metallicity on the basis of results for members of the Hyades andSirius superclusters. New DDO results are given for 120 stars.
|UBV(RI)c Photometry of AB Dor|
|UBV(RI)c Observations of SN 1987A|
|A study of the rapidly rotating variable star HD 36705 (AB Doradus)|
Photoelectric B and V light curves and high disperssion spectroscopicobservations were obtained in 1985 February for the rapidly rotatingspotted star HD 36705. The visual light range was about 0.09 magnitude,with a well correlated B-V change of approximately 0.04 magnitude, thestar being redded when faintest. There is evidence for a broadband flareof about 0.05 magnitude in V and 0.07 magnitude in B. This occurred nearmaximum light. Spectroscopic observations show a variation in theequivalent width of the Ca K emission by a factor of about two inantiphase with the photometric variations, maximum emissioncorresponding to minimum brightness. This is probably due to brightplages and enhanced chromospheric heating associated with thephotospheric starspots. High dispersion, high signal-to-noisespectroscopic observations confirm the presence of lithium 6708 A asreported by Rucinski (1982, 1985). Several interpretations of the natureof HD 36705 are discussed; however, at present, none is completelysatisfactory and further observations are required. As the star isprobably at less than 100 pc, a parallax determination may be possible,and could help answer many of the questions concerning HD 36705.
|Light variations in HD 36705 in October 1982|
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