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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 (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/432/657
| 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.
| Sixth Catalogue of Fundamental Stars (FK6). Part III. Additional fundamental stars with direct solutions
The FK6 is a suitable combination of the results of the HIPPARCOSastrometry satellite with ground-based data, measured over a longinterval of time and summarized mainly in the FK5. Part III of the FK6(abbreviated FK6(III)) contains additional fundamental stars with directsolutions. Such direct solutions are appropriate for single stars or forobjects which can be treated like single stars. Part III of the FK6contains in total 3272 stars. Their ground-based data stem from thebright extension of the FK5 (735 stars), from the catalogue of remainingSup stars (RSup, 732 stars), and from the faint extension of the FK5(1805 stars). From the 3272 stars in Part III, we have selected 1928objects as "astrometrically excellent stars", since their instantaneousproper motions and their mean (time-averaged) ones do not differsignificantly. Hence most of the astrometrically excellent stars arewell-behaving "single-star candidates" with good astrometric data. Thesestars are most suited for high-precision astrometry. On the other hand,354 of the stars in Part III are Δμ binaries in the sense ofWielen et al. (1999). Many of them are newly discovered probablebinaries with no other hitherto known indication of binarity. The FK6gives, besides the classical "single-star mode" solutions (SI mode),other solutions which take into account the fact that hidden astrometricbinaries among "apparently single-stars" introduce sizable "cosmicerrors" into the quasi-instantaneously measured HIPPARCOS proper motionsand positions. The FK6 gives, in addition to the SI mode, the "long-termprediction (LTP) mode" and the "short-term prediction (STP) mode". TheseLTP and STP modes are on average the most precise solutions forapparently single stars, depending on the epoch difference with respectto the HIPPARCOS epoch of about 1991. The typical mean error of anFK6(III) proper motion in the single-star mode is 0.59 mas/year. This isa factor of 1.34 better than the typical HIPPARCOS errors for thesestars of 0.79 mas/year. In the long-term prediction mode, in whichcosmic errors are taken into account, the FK6(III) proper motions have atypical mean error of 0.93 mas/year, which is by a factor of about 2better than the corresponding error for the HIPPARCOS values of 1.83mas/year (cosmic errors included).
| UBVRI photometry of the FK5 Extension Catalogue Stars
UBVRI photometry in the Kron-Cousins system for 272 stars of theExtension Catalogue of the Fifth Fundamental Star Catalogue (FK5 stars)in the declination zone +7 deg to -90 deg is presented. Tables 1-2 arealso available in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html Based on observations made atthe European Southern Observatory, La Silla, Chile.
| UBV Observations of AB Dor, 1994-5
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| UBV Observations of AB Dor, 1993
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| The December 1993 Light Curve of AB Dor
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| 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).
| 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.
| Changes in the Light Curve of AB Doradus (HD 36705)
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| December 1988 Photometry on AB Doradus (HD 36705)
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| 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.
| Analyse d'étoiles à raies métalliques. II. Composition chimique de ζ Lyr A. Spectre infrarouge proche de cinq étoiles Am
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