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Near infrared intraday variability of Mrk 421
We report results from our monitoring of the BL Lac object Mrk 421 inthe near-IR J band. The observations, aimed at studying the intradayvariability (IDV) of the object, were carried out systematically over anextended (and near-continuous) period of eight nights from the 1.2 mMount Abu Infrared Telescope, India. There are limited studies for Mrk421 in the J band for such an extended period. The observation epoch forthis study (25 February-5 March 2003) was chosen to significantlyoverlap other concurrent studies of Mrk 421 in the X-ray/γ-rayregions being conducted using the Rossi X-ray timing explorer (RXTE) andthe solar tower atmospheric Cherenkov effect experiment (STACEE). Hencethese results could be useful for a multi-wavelength analysis of thevariability behavior of Mrk 421. We find that Mrk 421 was quite activeduring the observed period and showed significant IDV and short termvariability. A maximum variation of 0.89 mag is seen over the entiretyof the observed period. Flaring activity, with typical brightnessvariations of ˜0.4, are also seen on several occasions. The extentof the variability observed by us is compared with the results of othersimilar studies of Mrk 421 in the J band.Table \ref{tab1} is only available in electronic form athttp://www.edpsciences.org
| Interstellar polarization toward MKN421
Interstellar polarization in the direction of MKN421 reaches a valuebetween .1% and .2% at a distance of 600 pc.
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
| Photometric and spectroscopic studies of cool stars discovered in EXOSAT X-ray images. IV. The northern hemisphere sample
We present high-precision photometry, high- and medium-resolutionspectroscopy for a sample of 32 stars likely to be the opticalcounterparts of X-ray sources serendipitously detected by the EXOSATsatellite. Using also recent results from the Hipparcos satellite, weinfer spectral types, compute X-ray luminosities and Li abundances andinvestigate the single or binary nature of the sample stars. We foundeleven new variable stars, whose photometric periods fall in the1.2-27.5 day range, for most of which the optical variability isconsistent with the presence of photospheric cool spots. For our sampleof X-ray selected stars we confirm the existence of a strong correlationbetween the stellar rotation rate and the level of activity, and alsobetween the X-ray and bolometric luminosities. Two stars in our sampleare likely to be pre-main sequence objects, one is likely to be apreviously unknown M-type star within 25 pc. Based on data collected atCatania Astrophysical Observatory (Mt. Etna, Italy), at ObservatorioAstronomico Nacional (UNAM, S. Pedro Martir, BC, Mexico) and at KittPeak National Observatory (Kitt Peak, AZ, USA) Table 1 is available inthe on-line version; Table 3 and the complete data set are available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr orvia http://cdsweb.u-strasbg.fr/Abstract.html}
| Radial velocities. Measurements of 2800 B2-F5 stars for HIPPARCOS
Radial velocities have been determined for a sample of 2930 B2-F5 stars,95% observed by the Hipparcos satellite in the north hemisphere and 80%without reliable radial velocity up to now. Observations were obtainedat the Observatoire de Haute Provence with a dispersion of 80Ä,mm(-1) with the aim of studying stellar and galactic dynamics.Radial velocities have been measured by correlation with templates ofthe same spectral class. The mean obtained precision is 3.0 km s(-1)with three observations. A new MK spectral classification is estimatedfor all stars. Based on observations made at the Haute ProvenceObservatory, France and on data from The Hipparcos Catalogue, ESA.Tables 4, 5 and 6 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr or viahttp://cdsweb.u-strasbg.fr/Abstract.htm
| Ultraviolet photometry of A-type stars at high galactic latitudes
Ultraviolet photometry on the International Ultraviolet Explorer (IUE)was used to study four stars located in one target of an earlier diffusebackground sounding-rocket experiment. The resulting stellar correctionis much smaller than that previously estimated, giving a higher diffusebackground at this target. Visible photometry appears to be a betterindicator of ultraviolet flux than spectral type. The discrepancybetween previous predictions and the present observations is explainedin terms of: (1) misclassification of two stars; (2) use of a spectraltype/effective temperature calibration hotter than more recentdeterminations; and (3) inadequacy of the Kurucz models, in the farultraviolet, for A-type stars.
| Apparent radii and other parameters for 416 B5 V-F5 V stars of the catalogue of the Geneva Observatory
Apparent radius, visual brightness, effective temperature and absoluteradius for 416 B5 v-F5 v stars of the catalogue of the GenevaObservatory (Rufener, 1976) have been determined. Twenty-eight stars,anomalous in log a" versus (m~)o diagrams, have been singled out. A goodcorrelation for seven stars, in common with the list of Hanbury Brown etal. (1974), has been found. Similar parameters determined for 279 B5v-F5 v stars of two preceding papers (Fracassini et al., 1973, 1975)have allowed us to determine the averaged diagrams , and versus (B -V)0 for 695 B5 v-F5 v stars. Moreover, in the present paper a goodcorrelation versus and carefulrelation = -7.40 + 3.31 for B5v-F5 V stars have been determined. Plain correlations between log R/R0and blanketing parameter m2 for some spectral types seem to point outthat there are real differences in the absolute radii of stars of thesame spectral type, in agreement with recent researches on the HRdiagram (Houck and Fesen, 1978). Systematic differences between double(spectroscopic and visual) and single stars are found. In particular,the averaged relation versus shows that A2v-F5 v double stars may have a higher metallicity index m2 and smallerabsolute radii than single stars. Finally, the diagram log v sin iversus log R/R0 confirms some properties of binary systems found byother researchers (Huang, 1966; Plavec, 1970; Levato, 1974; Kitamura andKondo, 1978)
| UBV Photoelectric Photometry of 259 PZT Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1980PASP...92..215G&db_key=AST
| Spectra and colors of A-type stars in a north galactic pole region.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1968AJ.....73..152S&db_key=AST
| A finding-list of stars of spectral type F2 and earlier in a north galactic pole region.
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Osservazione e dati astrometrici
| Costellazione: | Orsa Maggiore |
| Ascensione retta: | 11h04m18.19s |
| Declinazione: | +38°52'05.7" |
| Magnitudine apparente: | 7.143 |
| Distanza: | 114.025 parsec |
| Moto proprio RA: | -37.8 |
| Moto proprio Dec: | -1.4 |
| B-T magnitude: | 7.404 |
| V-T magnitude: | 7.165 |
Cataloghi e designazioni:
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