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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.
| Open clusters or their remnants: B and V photometry of NGC 1901 and NGC 1252
Photometry in the B and V bands is presented for the southern stellargroups NGC 1901 and NGC 1252. NGC 1901 is often described as an opencluster while NGC 1252 consists of a concentration of about 20 starscentered ~20' north of the original New General Cataloguecoordinates, and at the southwest edge of the large region previouslyassigned to this object in the literature. NGC 1901 has a clear mainsequence and shares similarities with the Hyades. We derive a reddeningvalue E(B-V) = 0.04, a distance from the Sun dsun = 0.45 kpc(Z = -0.23 kpc) and an age 0.6 +/- 0.1 Gyr. NGC 1901 is conclusively aphysical system, dynamically comparable to or more evolved than theHyades. The colour-magnitude diagram of NGC 1252 suggests a turnoff andmain sequence, and a total of 12 probable members. We simulated theGalactic field colour-magnitude diagram in the same direction and foundit to be a poor match to NGC 1252, suggesting that NGC 1252 is not afield fluctuation. Isochrone fitting to the probable members isconsistent with E(B-V) = 0.02, dsun = 0.64 kpc (Z = -0.46kpc) and an age 3 +/- 1 Gyr. NGC 1252 cannot be ruled out as a physicalgroup with the available data. If so, evidence is found that it is not aclassical open cluster, but rather an open cluster remnant.
| Long-term monitoring of active stars. IX. Photometry collected in 1993
As a part of an extensive program focused on the global properties andevolution of active stars, high-precision UBV(RI)_c and UBV photometryof 31 selected stars is presented. The UBV(RI)_c observations werecollected at the European Southern Observatory over the 31 December1992-18 January 1993 and the 20 November-3 December 1993 intervals.Additional UBV photometry obtained by the ``Phoenix" and by the CataniaAstrophysical Observatory Automatic Photoelectric Telescopes from 1990to 1993 is also presented for some of the program stars. Significantevolution of the light curves, period variations and evidence forlong-term variability of the global degree of spottedness are found.Some spectral classifications are revised and the inferred photometricparallaxes are compared, whenever possible, with the values measured bythe Hipparcos satellite. These observations are finalized to theconstruction of an extended photometric database, which can giveimportant clues on topics such as the stability of spotted areas,differential rotation, solar-like cycles and the correlation betweeninhomogeneities at different atmospheric levels. Based on data collectedat the European Southern Observatory, La Silla, Chile. Tables and thecomplete data set are also 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/367/910
| Two-colour photometry for 9473 components of close Hipparcos double and multiple stars
Using observations obtained with the Tycho instrument of the ESAHipparcos satellite, a two-colour photometry is produced for componentsof more than 7 000 Hipparcos double and multiple stars with angularseparations 0.1 to 2.5 arcsec. We publish 9473 components of 5173systems with separations above 0.3 arcsec. The majority of them did nothave Tycho photometry in the Hipparcos catalogue. The magnitudes arederived in the Tycho B_T and V_T passbands, similar to the Johnsonpassbands. Photometrically resolved components of the binaries withstatistically significant trigonometric parallaxes can be put on an HRdiagram, the majority of them for the first time. Based on observationsmade with the ESA Hipparcos satellite.
| Long-term monitoring of active stars. VIII. UBV(RI)_(c) photometry collected in February 1992
As a part of an extensive program focusing on the global properties andevolution of active stars, high-precision UBV(RI)_c photometry of 31selected stars, collected at the European Southern Observatory over the14-29 February 1992 interval, is presented. Significant evolution of thelight curves, period variations and evidence for long-term variabilityof the global degree of spottedness are found. Some spectralclassifications are revised and the inferred photometric parallaxes arecompared, whenever possible, with the values measured by the Hipparcossatellite. Flare events were detected for the star HD16157 = CC Eri, EXO 055609-3804.4 TY Coland HD 119285 = V851 Cen. Optical variability wasdiscovered for the Pop II binary HD 89499. Theseobservations contribute to the establishment of a time-extendedphotometric database which can give important clues on topics such asthe stability of spotted areas, differential rotation, solar-like cyclesand the correlation between inhomogeneities at different atmosphericlevels. based on data collected at the European Southern Observatory, LaSilla, Chile.
| Phase-resolved Simultaneous ORFEUS Far-Ultraviolet and ROSAT X-Ray Observations of the Active Star AB Doradus
We report phase-resolved simultaneous ORFEUS far-ultraviolet (FUV) andROSAT soft X-ray observations of the rapidly rotating young star ABDoradus (HD 36705), obtained with the FUV spectrometer flown on boardORFEUS II and the High Resolution Imager (HRI) on board ROSAT. The linesof C III at 977 and 1176 A , O V at 1218 A, and O VI at 1032 and 1038 A,as well as N II at 1085 A and Si III at 1206 A, are clearly detected inthe ORFEUS spectra. The X-ray flux intrinsically varied during theobservation and FUV and X-ray fluxes are found to correlate. No changesin the line profiles are detectable, but the line profiles of C IIIlambda 977 and O VI lambda 1032 are definitely broadened with respect tothe instrumental line profile. The observed broadening does not exceedthe photospheric v sin i value, suggesting that the observed C III and OVI emission, formed at a characteristic temperature of ~80,000-300,000K, is produced close to the star's surface. The C III lambda 1176/lambda 977 line ratio is found to be larger than that in the Sun,indicating electron densities (at ~80,000 K) of ne ~ 1011 cm ^{-3} orhigher.
| Long-term monitoring of active stars. VII. UBV(RI)_c photometry collected in March 1991
In the framework of an extensive program focusing on the globalproperties and evolution of active stars, high-precision UBV(RI)_cphotometry of 19 selected stars, collected at the European SouthernObservatory over the 15-31 March 1991 interval is presented. Significantevolution of the light curves, period variations and evidence forlong-term variability of the global degree of spottedness are found.Most of the spectral classifications are discussed. A flare event wasdetected for the star HD 127535 = V 841 Cen. These observationscontribute to the establishment of a time-extended photometric databasewhich can give important clues on topics such as the stability ofspotted areas, differential rotation, solar-like cycles and thecorrelation between inhomogeneities at different atmospheric levelsFigure 1 to 24 are only available on the on-line version of A&A athttp://www.ed-phys.fr}. based on data collected at the European SouthernObservatory, La Silla, Chile. Tables and the complete data set are alsoavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr or via http://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 Evolution of Surface Structures on Ab-Doradus
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995MNRAS.277.1145U&db_key=AST
| 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).
| 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.
| SN 1987A in the LMC. III - UBVRI photometry at Cerro Tololo
UBVRI photometry of supernova 1987A in the Large Magellanic Cloud for813 days since outburst is presented. This photometry is based on animproved calibration of the photometry of the local standard stars and acareful analysis of the transformation from the natural system to thestandard photometric system. Compared to the uniform exponential declineseen in UBVRI between days 125 and 400, SN 1987A began to fade morerapidly in all colors starting around day 500, at the time a strongthermal component appeared. Comparison with photometry of SN 1987A takenat other observatories shows that while the internal accuracy of anymeasurement approaches 0.01 mag, the systematic differences betweenUBVRI photometry obtained at different sites can be as large as 0.4 mag,due to the nonstellar nature of the spectral energy distribution of SN1987A.
| UBV (RI)c standard stars in the E- and F-regions and in the Magellanic Clouds - a revised catalogue.
Not Available
| UBV(RI)c Photometry of AB Dor
Not Available
| UBV(RI)c photometry of some standard sequences in the Harvard F regions and in the Magellanic Clouds
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1988MNRAS.231.1047M&db_key=AST
| Zero-Point Checks of Magellanic Cloud Sequences
Not Available
| Revised UBV photometry of Magellanic Cloud sequences
The old photometry of UBV secondary standards in the Magellanic Clouds(Cousins 1970) has been revised. New measurements made at Sutherland arepresented and analyzed.
| Photoelectric (B, V) magnitude sequences in the Magellanic Clouds
Not Available
| Standard Stars for VRI Photometry with S25 Response Photocathodes
Not Available
| Polarization measurements of stars in the Magellanic Clouds.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1970AJ.....75..778M&db_key=AST
| Interstellar polarization in the Large Magellanic Cloud
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1966MNRAS.132..423V&db_key=AST
| U, B, V, photometry in and near the Magellanic Clouds
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1962MNRAS.124..359W&db_key=AST
| Photoelectric Magnitude Sequences for the Magellanic Clouds.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1953ApJ...118..314C&db_key=AST
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