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Apsidal motion in southern eccentric eclipsing binaries: V539 Ara, GG Lup, V526 Sgr and AO Vel
Several new times of minimum light have been observed photoelectricalyfor the early-type double-lined eccentric eclipsing binaries V539 Ara (P= 3.2 deg, e = 0.05), GG Lup (1.9 deg, 0.15), V526 Sgr (1.9 deg, 0.22)and AO Vel (1.6 deg, 0.07). The O{-}C diagrams are analysed using allreliable timings found in the literature and improved values for theelements of the apsidal motion are computed. We find more precise,relatively short periods of apsidal motion of about 162, 102, 155 and 54years for V539 Ara, GG Lup, V526 Sgr and AO Vel, respectively. Thecorresponding internal structure constants, log k_2, are then found tobe 2.33, 2.16, 2.36 and 2.24 under the assumption that the componentstars rotate pseudosynchronously. The relativistic effects arenegligible, being about 6 7% of the total apsidal motion rate in allsystems. Using the light-time effect solution, for V539 Ara we havefound a third component orbiting with a period of about 42 years, for AOVel we confirmed the third body with an orbital period of 33 years.
| Formation scenarios for the young stellar associations between galactic longitudes l = 280degr - 360degr
We investigate the spatial distribution, the space velocities and agedistribution of the pre-main sequence (PMS) stars belonging toOphiuchus, Lupus and Chamaeleon star-forming regions (SFRs), and of theyoung early-type star members of the Scorpius-Centaurus OB association.These young stellar associations extend over the galactic longituderange from 280degr to 360degr , and are at a distance interval ofaround 100 and 200 pc. This study is based on a compilation ofdistances, proper motions and radial velocities from the literature forthe kinematic properties, and of basic stellar data for the constructionof Hertzsprung-Russel diagrams. Although there was no well-known OBassociation in Chamaeleon, the distances and the proper motions of agroup of 21 B- and A-type stars, taken from the Hipparcos Catalogue,lead us to propose that they form a young association. We show that theyoung early-type stars of the OB associations and the PMS stars of theSFRs follow a similar spatial distribution, i.e., there is no separationbetween the low and the high-mass young stars. We find no difference inthe kinematics nor in the ages of these two populations studied.Considering not only the stars selected by kinematic criteria but thewhole sample of young early-type stars, the scattering of their propermotions is similar to that of the PMS stars and all the young starsexhibit a common direction of motion. The space velocities of theHipparcos PMS stars of each SFR are compatible with the mean values ofthe OB associations. The PMS stars in each SFR span a wide range of ages(from 1 to 20 Myr). The ages of the OB subgroups are 8-10 Myr for UpperScorpius (US), and 16-20 Myr for Upper Centaurus Lupus (UCL) and forLower Centaurus Crux (LCC). Thus, our results do not confirm that UCL isolder than the LCC association. Based on these results and theuncertainties associated with the age determination, we cannot say thatthere is indeed a difference in the age of the two populations. Weanalyze the different scenarios for the triggering of large-scalestar-formation that have been proposed up to now, and argue that mostprobably we are observing a spiral arm that passes close to the Sun. Thealignment of young stars and molecular clouds and the average velocityof the stars in the opposite direction to the Galactic rotation agreewith the expected behavior of star formation in nearby spiral arms.Tables 1 to 4 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/404/913
| A spectroscopic survey for lambda Bootis stars. II. The observational data
lambda Bootis stars comprise only a small number of all A-type stars andare characterized as nonmagnetic, Population i, late B to early F-typedwarfs which show significant underabundances of metals whereas thelight elements (C, N, O and S) are almost normal abundant compared tothe Sun. In the second paper on a spectroscopic survey for lambda Bootisstars, we present the spectral classifications of all program starsobserved. These stars were selected on the basis of their Strömgrenuvbybeta colors as lambda Bootis candidates. In total, 708 objects insix open clusters, the Orion OB1 association and the Galactic field wereclassified. In addition, 9 serendipity non-candidates in the vicinity ofour program stars as well as 15 Guide Star Catalogue stars were observedresulting in a total of 732 classified stars. The 15 objects from theGuide Star Catalogue are part of a program for the classification ofapparent variable stars from the Fine Guidance Sensors of the HubbleSpace Telescope. A grid of 105 MK standard as well as ``pathological''stars guarantees a precise classification. A comparison of our spectralclassification with the extensive work of Abt & Morrell(\cite{Abt95}) shows no significant differences. The derived types are0.23 +/- 0.09 (rms error per measurement) subclasses later and 0.30 +/-0.08 luminosity classes more luminous than those of Abt & Morrell(\cite{Abt95}) based on a sample of 160 objects in common. The estimatederrors of the means are +/- 0.1 subclasses. The characteristics of oursample are discussed in respect to the distribution on the sky, apparentvisual magnitudes and Strömgren uvbybeta colors. Based onobservations from the Observatoire de Haute-Provence, OsservatorioAstronomico di Padova-Asiago, Observatório do Pico dosDias-LNA/CNPq/MCT, Chews Ridge Observatory (MIRA) and University ofToronto Southern Observatory (Las Campanas).
| 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.
| Discovery of a Brown Dwarf Companion to Gliese 570ABC: A 2MASS T Dwarf Significantly Cooler than Gliese 229B
We report the discovery of a widely separated (258.3"+/-0.4") T dwarfcompanion to the Gl 570ABC system. This new component, Gl 570D, wasinitially identified from the Two Micron All-Sky Survey. Itsnear-infrared spectrum shows the 1.6 and 2.2 μm CH4absorption bands characteristic of T dwarfs, while its common propermotion with the Gl 570ABC system confirms companionship. Gl 570D(MJ=16.47+/-0.07) is nearly a full magnitude dimmer than theonly other known T dwarf companion, Gl 229B, and estimates ofL=(2.8+/-0.3)x10-6 Lsolar andTeff=750+/-50 K make it significantly cooler and lessluminous than any other known brown dwarf companion. Using evolutionarymodels by Burrows et al. and an adopted age of 2-10 Gyr, we derive amass estimate of 50+/-20 MJup for this object.
| Ca II H and K Filter Photometry on the UVBY System. II. The Catalog of Observations
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....109.2828T&db_key=AST
| Four Colour Photometry of Eclipsing Binaries - Part Thirty-Five - Lightcurves of Gg-Lupi - Young Metal-Deficient B-Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&AS..101..563C&db_key=AST
| Absolute Dimensions of Eclipsing Binaries - Part Twenty - Gg-Lupi - Young Metal Deficient B-Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&A...277..439A&db_key=AST
| A homogeneous catalog of new UBV and H-beta photometry of B- and A-type stars in and around the Scorpius-Centaurus OB association
B- and A-type stars in and near the Sco-Cen OB association areinvestigated with UBV and H-beta photometry to acquire data relevant tothe luminosity function of Sco-Cen. The measurements generally consistof two 10-s integrations of U, B, V, (W, N) filters, and theobservations are corrected iteratively for atmospheric extinction andinstrumental response. The data presented give the mean V magnitude,mean B-V, mean U-B, and the estimated uncertainties for these values.The catalog provides a homogeneous catalog of data for a large fieldwith stellar objects delineating membership to the association Sco-Cenand that affect the luminosity function of the aggregate.
| Walraven photometry of nearby southern OB associations
Homogeneous Walraven (VBLUW) photometry is presented for 5260 stars inthe regions of five nearby southern OB associations: Scorpio Centaurus(Sco OB2), Orion OB1, Canis Major OB1, Monoceros OB1, and Scutum OB2.Derived V and (B - V) in the Johnson system are included.
| Physical parameters of stars in the Scorpio-Centaurus OB association
Walraven photometry is presented of established and probable members ofthe Scorpio-Centaurus OB association. For each star, effectivetemperature and surface gravity are derived using Kurucz (1979)atmosphere models. From the Straizys and Kuriliene (1981) tables,absolute magnitudes are calculated. Distance moduli and visualextinctions are determined for all stars. From a comparison of theHR-diagrams of the stars in each subgroup with theoretical isochrones,the ages of the three subgroups are derived. The distances to the threesubgroups are shown to be different; there is a general trend (alsowithin each subgroup) for the distances to be larger at higher galacticlongitudes. The visual extinction in the youngest subgroupUpper-Scorpius, is well correlated with the IRAS 100-micron map. Thedistance toward the Ophiuchus dark clouds is found to be 125 pc, basedon the photometric distances to the stars. Most of the early-type starsin Upper-Scorpius are located at the far side of the dark clouds.
| Variable and Potential Variable Stars in the Bright Star Catalogue
Not Available
| Photometry of AM stars
Not Available
| Possible new members of a subgroup of the Scorpio-Centaurus association.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972AJ.....77..474G&db_key=AST
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| Takýmyýldýz: | Kurt |
| Sað Açýklýk: | 15h21m35.30s |
| Yükselim: | -40°44'59.0" |
| Görünürdeki Parlaklýk: | 6.2 |
| Uzaklýk: | 97.752 parsek |
| özdevim Sað Açýklýk: | -16.2 |
| özdevim Yükselim: | -27.5 |
| B-T magnitude: | 6.286 |
| V-T magnitude: | 6.194 |
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