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The 2MASS Wide-Field T Dwarf Search. II. Discovery of Three T Dwarfs in the Southern Hemisphere
We present the discovery of three new southern hemisphere T dwarfsidentified in the Two Micron All Sky Survey. These objects, 2MASS0348-6022, 2MASS 0516-0445, and 2MASS 2228-4310, have classificationsT7, T5.5, and T6.5, respectively. Using linear absolutemagnitude/spectral type relations derived from T dwarfs with measuredparallaxes, we estimate spectrophotometric distances for thesediscoveries; the closest, 2MASS 0348-6022, is likely within 10 pc of theSun. Proper motions and estimated tangential velocities are consistentwith membership in the Galactic disk population. We also list southernhemisphere T dwarf candidates that were either not found in subsequentnear-infrared imaging observations and are most likely uncataloged minorplanets, or have near-infrared spectra consistent with background stars.
| Outbursts in the Be star HR 2501
The Be star HR 2501 was monitored in photometry, from1978 to 1998 in the GENEVA system and from 1990 to 1992 by the HIPPARCOSsatellite, and in spectroscopy from 1998 to 2001 by using the CORALIEspectrograph. Several mostly unrelated periods or time scalescharacterize the variability of HR 2501. First, theradial velocity data reveals that this is a new lambda Eri star, with aperiod of 0.79187 d due to non-radial pulsations or clouds close to thestellar photosphere. Second, both GENEVA and HIPPARCOS photometriesexhibit a mid- to long-term variability of characteristic time ~ 500 dand peak-to-peak amplitude ~ 0.4 mag, most probably a consequence ofthe recurrent outbursts of matter from the rapidly rotating Be startowards its disk. Third, a characteristic time of ~ 300 d between theoutbursts is shown by spectroscopy by looking at the variations of theequivalent width of Hα , Hβ and HeI (5875.6 Å)emission lines (the outbursts studied in photometry and spectroscopy areunfortunately not the same due to the non-simultaneity of themonitorings). Fourth, the V/R ratio of the double peaks in Hα andHβ show a periodic-type variation during the second of thespectroscopic outbursts, with periods of respectively 16.7 and 15.1 d,in agreement with the prediction of the dynamical evolution of a blob ofmaterial ejected from the equator of the star into the Keplerian disk.Fifth, a short-term photometric period of 0.46 d is detected during anepoch of intensive monitoring; however, it must be noted that if thisvariability is confirmed, the value of this short-term period is unsure.The other main results are: i) During the 27 months of the spectroscopicsurvey, in addition to the mentioned outbursts, the emission in Hαand Hβ lines decreased progressively until it almost completelyvanishes at the end. ii) The estimated radius of the circumstellar diskvaries and reaches 5.5, 4 and 2 stellar radii at maximum for theHα , Hβ and HeI emission regions respectively; iii) Thespectroscopic monitoring was particularly successful, and the series ofobservation of the line profiles, with the variation of the emissionfrom day to day, is quite exceptional in the studies of Be stars.Based on observations collected at the Swiss 40 cm, 70 cm and 120 cmtelescopes at the European Southern Observatory (La Silla, Chile) and ondata from the ESA HIPPARCOS satellite.The photometric and radial velocity data are only available inelectronic form at the 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/401/271
| Search for duplicity in periodic variable Be stars
Four Be stars, HR 1960, HR 2968,HR 3237 and HR 3642, selectedaccording to their periodic variations in HIPPARCOS and GENEVAphotometries, were monitored from 1998 until 2001 with the CORALIEspectrograph. Among these stars, two are new spectroscopic binaries andone is a new lambda Eri short period variable. HR 1960 is a lowamplitude (K = 3.4 km s-1) SB1 with a period of 395.48 d inagreement with the photometric prediction. HR 3237 is a short period SB1(P = 5.1526 d). HR 3642 presents some interesting variations inphotometry and spectroscopy: indeed, a mid- and a short-term variationis present with periods of 137.99 d (Hp magnitude) and 1.13028 d (radialvelocity) respectively. The short-term variation, characteristic of thelambda Eri stars, probably implies non-radial pulsations orinhomogeneities in the corotating disc. The last star, HR 2968, is anexcellent photometric binary candidate, but no spectroscopic obviousnessof a companion has been found. Based on observations collected at theSwiss 40 cm, 70 cm and 120 cm telescopes at the European SouthernObservatory (La Silla, Chile) and on data from the ESA HIPPARCOSsatellite. The photometric and radial velocity data are only availablein electronic form at the 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/385/488 Table 3 is onlyavailable in electronic form at http://www.edpsciences.org
| The 76th Name-List of Variable Stars
We present the next regular Name-List of variable stars containinginformation on 1406 variable stars recently designated in the system ofthe General Catalogue of Variable Stars.
| 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.
| A three-year Strömgren photometric survey of suspected beta Pictoris-like stars
We carried out a Strömgren photometric survey of thirteen southernbright stars, including beta Pictoris itself, during three years,d'Astrophysique de Paris, in order to detect possible weak photometricvariations. beta Pictoris presents a small long-term variation with achange of brightness by -2.1 10-3 mag per year, over abouttwo years from beginning of 1996, a situation relatively similar to theone about 18 years ago. Among the other stars, only HD 38392 presentsweak photometric variations with a period of 21.4 days, probably relatedto the star rotation period. The negative result concerning photometricvariations of all other stars suggests that those stars are actuallyreally stable and strengthens the reality of the variations discoveredin the case of beta Pictoris and HD 38392. Based on observationsobtained at the Danish 50 cm telescope (SAT) at ESO, La Silla, Chile.
| 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.
| Geneva photometry of the Be star HR 1960: periodicity and extremely small amplitude
The Be star HR 1960 has been monitored from 1982 to 1998 in Genevaphotometry and from November 1989 to March 1993 by the Hipparcossatellite. This star shows two kinds of luminosity variation: i) Themean luminosity in V has slightly increased, by 5 millimags, during thesurvey (long-term variation); ii) A periodic light variation with aperiod of 395 d has been observed, in both Geneva and Hipparcosphotometries (mid-term variation). The periodic variation ischaracterized by extremely small semi-amplitudes, 3 millimags in V and 2millimags in [B-V]. This is most probably the long-period variable starwith the smallest amplitude yet known. The V and [B-V] curves areanti-correlated, i.e. the star is found to be redder when brighter inthe Paschen continuum. Both types of variability are attributed to theBe characteristics of the star. A model similar to that of Carrier etal. ( te{carrier}) for HR 2968 is proposed: the Be star could be themain component of a binary system having an orbit of period 395 d; itwould be surrounded by matter expelled in its equatorial plane and thevariability would results from the gravitational and/or radiativeinteraction of its companion star with this disk. The physicalparameters of HR 1960 are determined by using Geneva photometriccalibrations and the Hipparcos parallax. Based on observations collectedat the Swiss 40$\,$cm and 70$\,$cm telescopes at the European SouthernObservatory (La Silla, Chile) and on data from the ESA Hipparcossatellite.
| An extensive Delta a-photometric survey of southern B and A type bright stars
Photoelectric photometry of 803 southern BS objects in the Deltaa-system as detection tool for magnetic chemically peculiar (=CP2) starshas been carried out and compared to published spectral types. Thestatistical yield of such objects detected by both techniques ispractically the same. We show that there are several factors whichcontaminate the search for these stars, but this contamination is onlyof the order of 10% in both techniques. We find a smooth transition fromnormal to peculiar stars. Our sample exhibits the largest fraction ofCP2 stars at their bluest colour interval, i.e. 10% of all stars in thecolour range -0.19 <= B-V < -0.10 or -0.10 <= b-y < -0.05.No peculiar stars based on the Delta a-criterion were found at bluercolours. Towards the red side the fraction of CP2 stars drops to about3% for positive values of B-V or b-y with red limits roughlycorresponding to normal stars of spectral type A5. The photometricbehaviour of other peculiar stars: Am, HgMn, delta Del, lambda Boo, Heabnormal stars, as well as Be/shell stars and supergiants shows someslight, but definite deviations from normal stars. Spectroscopic andvisual binaries are not distinguished from normal stars in their Delta abehaviour. The results of this work justify larger statistical work(e.g. in open clusters) employing more time-saving photometric methods(CCD). \newpage Based on observations obtained at the European SouthernObservatory, La Silla, Chile. This research has made use of the Simbaddatabase, operated at CDS, Strasbourg, France. Table 2 is only availablein electronic form via anonymous ftp 130.79.128.5 orhttp://cdsweb.u-strasbg.fr/Abstract.html
| Obscured AGB stars in the Magellanic Clouds. I. IRAS candidates
We have selected 198 IRAS sources in the Large Magellanic Cloud, and 11in the Small Magellanic Cloud, which are the best candidates to bemass--loosing AGB stars (or possibly post--AGB stars). We used thecatalogues of \cite[Schwering \& Israel (1990)]{ref42} and\cite[Reid et al. (1990)]{ref36}. They are based on the IRAS pointedobservations and have lower detection limits than the Point SourceCatalogue. We also made cross-identifications between IRAS sources andoptical catalogues. Our resulting catalogue is divided in 7 tables.Table \ref{tab1} lists optically known red supergiants and AGB stars forwhich we found an IRAS counterpart (7 and 52 stars in the SMC and LMC,respectively). Table \ref{tab2} lists ``obscured'' (or ``cocoon'') AGBstars or late-type supergiants which have been identified as such inprevious works through their IRAS counterpart and JHKLM photometry (2SMC and 34 LMC sources; no optical counterparts). Table \ref{tab3} listsknown planetary nebulae with an IRAS counterpart (4 SMC and 19 LMC PNe).Table \ref{tab4} lists unidentified IRAS sources that we believe to begood AGB or post--AGB or PNe candidates (11 SMC and 198 LMC sources).Table~\ref{tab5} lists unidentified IRAS sources which could be any typeof object (23 SMC and 121 LMC sources). Table \ref{tab6} lists IRASsources associated with foreground stars (29 SMC and 135 LMC stars).Table \ref{tab7} lists ruled out IRAS sources associated with HIIregions, hot stars, etc... We show that the sample of IRAS AGB stars inthe Magellanic Clouds is very incomplete. Only AGB stars more luminousthan typically 10^4 L_\odot and with a mass-loss rate larger thantypically 5 10^{-6} M_\odot/yr could be detected by the IRAS satellite.As a consequence, one expects to find very few carbon stars in the IRASsample. We also expect that most AGB stars with intermediate mass--lossrates have not been discovered yet, neither in optical surveys, nor inthe IRAS survey. Tables 1 to 8 are also available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| 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.
| Stroemgren photometry of F- and G-type stars brighter than V = 9.6. I. UVBY photometry
Within the framework of a large photometric observing program, designedto investigate the Galaxy's structure and evolution, Hβ photometryis being made for about 9000 stars. As a by-product, supplementary uvbyphotometry has been made. The results are presented in a cataloguecontaining 6924 uvby observations of 6190 stars, all south ofδ=+38deg. The overall internal rms errors of one observation(transformed to the standard system) of a program star in the interval6.5
| Supernova 1987A - Photometry of the discovery and pre-discovery plates
An analysis of the discovery and prediscovery plates for SN 1987A ispresented. The second earliest reliable photometric measurements for theSN have found to have a B magnitude of 5.00 (+/- 0.15) on Feb.24.12 UT1987, while for Sanduleak -69 deg 202 was found to have a B magnitude of12.12 (+/- 0.15) on Feb 23.08 UT 1987. These discovery and pre-discoveryplates represent, respectively, the second earliest reliable photometricmeasure for the SN and the last known observation of its precursor. TheB magnitude reported here for SN 1987A is about 0.2 mag fainter thanfound by Shelton and Lapasset (1993) five hours later, indicating thatthe supernova was still rising to 'first maximum light' in the Bbandpass 19 hours after the IMB/Kamiokande-II neutrino detection. Dataobtained subsequent to this observation through to the third dayindicates a nearly constant B magnitude.
| 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
| Intensive photometry of southern Be variables. II - Summer objects
Results are presented of photometric campaign on some bright southern Bestars to search for periodic light variations. In order to obtain goodphase coverage, many observations were conducted from two sites withdifferent longitudes: ESO and SAAO. A large fraction of early-Be starsare found to be variable with periods close to or equal to theirrotational periods. Particular attention is devoted to the late-Bestars. Unlike the hotter members of this class, the late-Be stars do notseem to have detectable periodic light variations except for one or twostars of very small amplitude.
| 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).
| 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).
| Detection of the unusually blue Of flare star HD 269665
The observation of the very blue star HD 269665 in the LMC is reported.At 1640 A the star has m(1640) = 5.0 m + or - 0.1 m, m(1640) - V = - 6.2m. The color may be due to a variability of the star which ischaracteristic of stars of the Of or Be type. It is also possible thatthe star was detected in the act of flaring.
| Photometry of SN 1987A
Photometric observations of SN 1987A have been carried out at La Sillain the UBVRI, Geneva, H-beta, Stromgren and Walraven systems. Luminosityvariations on short timescales have also been investigated. The resultsfor the period from February 24 to March 22 are reported.
| The local system of early type stars - Spatial extent and kinematics
Published uvby and H-beta photometric data and proper motions arecompiled and analyzed to characterize the structure and kinematics ofthe bright early-type O-A0 stars in the solar vicinity, with a focus onthe Gould belt. The selection and calibration techniques are explained,and the data are presented in extensive tables and graphs and discussedin detail. The Gould belt stars of age less than 20 Myr are shown togive belt inclination 19 deg to the Galactic plane and node-lineorientation in the direction of Galactic rotation, while the symmetricaldistribution about the Galactic plane and kinematic properties (purecircular differential rotation) of the belt stars over 60 Myr oldresemble those of fainter nonbelt stars of all ages. The unresolveddiscrepancy between the expansion observed in the youngest nearby starsand the predictions of simple models of expansion from a point isattributed to the inhomogeneous distribution of interstellar matter.
| Radial velocities of bright southern stars. I - 139 B-type HR and FK stars
Radial velocity determinations for 139 southern B stars in the BrightStar, FK4, and FK4 Supplement catalogues and for 53 bright southernlate-type stars are presented, based on coudespectrograms taken with theESO 1.5 m telescope at La Silla. The programs, observations,measurements, and reductions are described. Among the data presented arethe visual magnitude, spectral class, mean error, E/T variabilityparameter, velocity of interstellar lines, and rotation class.
| Intermediate band photometry of early-type stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1977PASP...89..205E&db_key=AST
| Is star formation bimodal ? II. The nearest early-type stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1977PASP...89..187E&db_key=AST
| Polarization measurements and magnetic field structure within the magellanic clouds.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1970A&A.....6..294S&db_key=AST
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Pozíciós és asztrometriai adatok
| Csillagkép: | Aranyhal |
| Rektaszcenzió: | 05h36m54.70s |
| Deklináció: | -66°33'37.0" |
| Vizuális fényesség: | 6.31 |
| Távolság: | 262.467 parszek |
| RA sajátmozgás: | -5 |
| Dec sajátmozgás: | 11.9 |
| B-T magnitude: | 6.21 |
| V-T magnitude: | 6.265 |
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