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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
| 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.
| UBV Photoelectric Photometry Catalogue (1986). III Errors and Problems on DM and HD Stars
Not Available
| UBV photoelectric catalogue (1986). II - Analysis
The UBV photoelectric data of the stars presenting several entries inthe 1986 edition of the UBV catalog have been systematicallyintercompared, and this paper presents a discussion of the stars forwhich discrepancies larger than 0.2 mag were found. Thirty-six probablyvariable stars have been detected, among which 18 are Be stars. Sixtyfurther stars present differences in the V magnitude larger than 0.2mag. Sixteen stars already appear in the NSV catalog. Although manyproblems are probably due to poor observations, new (eclipsing) variablestars may be found in this sample. Complete disagreement is foundbetween the values published from two independent sources in 34 cases. Afirst analysis of the quality of the UBV data shows that 65 percent ofthe differences in the V magnitude and in U-B color, for respectively11,500 and 7200 stars with two sources of data, are smaller than 0.04.The scatter on the B-V index appears to be smaller, since the samepercentage reaches 79 percent.
| Local photometric standards for CaII emission stars
UBV data are given for 108 stars which are suitable local standards for52 stars with strong Ca2 emissions. An additional eight stars wererejected as possible standards because of suspected variability.
| Spectroscopic studies of stars in ORI OB1 /Belt/
MK spectral classifications are presented for 120 B- and A-type stars inthe Belt subgroup of the Ori OB1 association. Combined with otherpublished spectroscopic data, and the assumed absolute magnitudes givenby Schmidt-Kaler (1965) and Lesh (1979), a mean corrected distancemodulus of 8.56 + or - 0.11 is computed for the eastern region, whilefor the remainder of the Belt a modulus of 8.20 + or - 0.05 is derived.Several B9-A2 subgiants and A7-F0 main-sequence stars were observed inthe western and central regions of the Belt. The ages of these starsimply a spread in formation ages for these subgroups from about 1million yr to at least 10 million yr.
| Photometric studies of stars in ORI OB1 /belt/
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1979AJ.....84.1846G&db_key=AST
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Osservazione e dati astrometrici
| Costellazione: | Orione |
| Ascensione retta: | 05h30m34.67s |
| Declinazione: | +00°21'56.0" |
| Magnitudine apparente: | 7.548 |
| Distanza: | 251.889 parsec |
| Moto proprio RA: | -7.2 |
| Moto proprio Dec: | -3.2 |
| B-T magnitude: | 7.828 |
| V-T magnitude: | 7.572 |
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