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Cyclicities in the light variations of Luminous Blue Variables. II. R40 developing an S Doradus phase
Stroemgren differential photometry of R40 collected during the timeinterval 1986-1996 is analysed together with Walraven photometry. Thegradual brightening of the star over the last 10 years can be describedby a linear trend with superimposed oscillations (in v, b and y) withfrequency 0.0008cd(-1) ( ~ 1300 d cycle). We interpret theseoscillations as ``normal S Dor'' phases, and suggest that thequasi-linear brightening of the star is the ascending branch of agrowing very-long-term S Dor phase (VLT-SD), as found by van Genderen etal. (1997a) in AG Car and S Dor itself. As R40 is now becoming fainterand bluer, the length of the VLT-SD cycle is about 20 years. Based onobservations obtained at the European Southern Observatory at La Silla,Chile (applications ESO 56D-0249 and 58D-0118)
| A large, complete, volume-limited sample of G-type dwarfs. I. Completion of Stroemgren UVBY photometry
Four-colour photometry of potential dwarf stars of types G0 to K2,selected from the Michigan Spectral Catalogues (Vol. 1-3), has beencarried out. The results are presented in a catalogue containing 4247uvby observations of 3900 stars, all south of δ = -26deg. Theoverall internal rms errors of one observation (transformed to thestandard system) of a program star in the interval 8.5 < V < 10.5are 0.0044, 0.0021, 0.0039, and 0.0059, respectively, in V, b-y, m_1_ ,and c_1_. The purpose of the catalogue, combined with earliercatalogues, is to allow selection of a large, complete, volume-limitedsample of G- and K-type dwarfs, investigate their metallicitydistribution, and compare it to predictions of various models ofgalactic chemical evolution. Future papers in this series will discussthese subjects.
| R 40: The first luminous blue variable in the Small Magellanic Cloud
During the past decade R 40 in the Small Magellanic Cloud (SMC) hasbrightened in the visual range by about 0.5 magnitudes. Correlated withthe brightening the spectral type has changed from B8Ia to A3Ia-O. Thisbehavior shows R 40 to be a luminous blue variable (LBV) the first onediscovered in the SMC. During the past eight years we obtained extensiveStroemgren photometry. R 40 was also observed in the IR range in theJHKL filter system. High resolution spectra were observed in Dec. 1991and Jan. 1993 in the optical range at European Southern Observatory(ESO) with CASPEC at the 3.6 m telescope and with our fiber-linkedechelle spectrograph at the 2.2 m telescope. In addition one highresolution LWP-IUE spectrum and one SWP and LWP low resolution spectrumwere secured during the present outburst phase of R 40. For comparisonIUE archive data were consulted; R 40 had been exposed in the lowresolution SWP and LWP mode in 1987. Apart from the secular brighteningat a timescale of years R 40 exhibits photometric pulsation-likemicrovariations with a quasi-period of 120 days which is also typicalfor LBVs. From the continuum energy distribution (from the satellite UVto the IR range) and from the CASPEC spectrum we derived stellarparameters of R 40 during the outburst phase in 1991 by making use ofKurucz model atmospheres: Teff = 8700 K, log g = 0.75 andwith a distance module of 18.85 for the SMC Mbol = -9.4 and R= 280 solar radii and M = 16 solar mass. The mass-loss rate was derivedfrom the P Cygni type H-alpha profile to 8 x 10-6 solarmass/yr which is small but not exceptional for an LBV (cf. e.g. R110 ofthe Large Magellanic Cloud (LMC)). Comparison of the present spectralenergy distribution with the one of 1987 shows that the brightening inthe visual is accompanied by a corresponding decrease of the satelliteUV continuum; i.e. as expected for LBVs the outburst occurs under thecondition of Mbol = const. Since the metallicity is down by0.6 dex in the SMC, R 40 demonstrates that low metallicity does notpreclude LBV outbursts.
| 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
| 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).
| Long-term photometry of variables at ESO. I - The first data catalogue (1982-1986)
This paper presents the catalog of photometric data in the Stromgrensystem obtained during the first four years (October 1982 - September1986) of the Long-Term Photometry of Variables (LTPV) program at ESO.The data are available in computer-readable form.
| Catalogue of Metal-Deficient F-Stars to M-Stars - Part One - Stars Classified Spectroscopically - Supplement One
Not Available
| Metal-Deficient Giants in the Galactic Field - Catalogue and Some Physical Parameters
Not Available
| Sir John Herschel's Observations of Stars in the Small Magellanic Cloud
Not Available
| Radial velocities of supergiants in the Small Magellanic Cloud
This paper presents the kinematic results of a study, comparing SmallMagellanic Cloud supergiants to galactic supergiants. The stars werechosen from the lists of Florsch (1972a) and Sanduleak (1968). A roughcorrelation is found between the radial velocities of the supergiantsand the radial velocities of neutral hydrogen. In some cases a betterrelation exists with the radial velocities of the H II regions.
| Etude DU Petit Nuage de Magellan par la technique DU prisme-objectif de Fehrenbach.
Not Available
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Membro dei seguenti gruppi:
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Osservazione e dati astrometrici
| Costellazione: | Tucano |
| Ascensione retta: | 01h08m38.57s |
| Declinazione: | -71°50'07.0" |
| Magnitudine apparente: | 8.582 |
| Distanza: | 775.194 parsec |
| Moto proprio RA: | 2.2 |
| Moto proprio Dec: | 12.3 |
| B-T magnitude: | 9.563 |
| V-T magnitude: | 8.663 |
Cataloghi e designazioni:
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INHABITED SKY
