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Absolute proper motions for the calibration of the HIPPARCOS proper motion system
Absolute proper motions of 48 Hipparcos stars in nine fields distributedover the northern hemisphere are presented. The proper motions have beenrecently used as part of the Bonn program for the extragalactic link ofthe Hipparcos proper motion system. We describe methods which have ledto the absolute proper motions of the major part of the Bonn fields forthe link. For six fields the extragalactic calibration was achievedusing the bright quasar in the centre of the field. In addition, data ofthree fields of globular clusters were included. For these fields thelink to an extragalactic reference system was performed by stars, whoseabsolute proper motions with respect to galaxies were determined onplates of the Lick astrograph. In addition, we used for the link in onefield plates from the ESO Schmidt telescope in combination withmeasurements from glass copies of the Palomar Sky Survey. The accuracyof a single proper motion is of the order of 2 to 3 mas/a for eachcoordinate. Table 2 is 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/Abstract.html}
| An exceptional X-ray flare on the dMe star EQ1839.6+8002
A large impulsive flare was detected serendipitously during observationsof the radio galaxy 3C390.3 made with the Ginga satellite on 1991February 14, between 22:30 and 23:00 (UT). The dMe star EQ1839.6+8002 isthe most likely source of this flare. The rise of the flare was observedand the spectra obtained are of sufficient quality to determine thetemperature and emission measure as a function of time. The flare isexceptional in its high peak temperature (T_e~10^8K) and emissionmeasure (~9x10^53 cm^-3), the largest recorded for a flare on a dMestar, and comparable with those for flares in RS CVn systems. Thenormalized X-ray luminosity is also very large (L_X/L_bol~0.25). Theflare geometry and plasma parameters are derived by making variousassumptions concerning the dominant terms in the internal energyequation, which takes account of a varying mass and volume. The initialheating appears to be proportional to the gas pressure. At the peak T_ethe electron density is ~1.7x10^12 cm^-3, and the hot plasma has alength ~10^10 cm. The flare plasma then cools initially by `evaporativeconduction'. Two alternative simple models are made of the flare decaybeyond this time (cooling with constant mass or constant volume). Bothrequire continued heating, and the latter gives results similar to thoseexpected in quasi-static conditions. The evolution of the flaretemperature and density broadly resembles that predicted by numericalsimulations. Observations with the Einstein IPC, the EXOSAT LE and theROSAT PSPC instruments show flaring and quiescent properties similar tothose of the flare stars discussed by Pallavicini et al.
| Stromgren Four-Colour UVBY Photometry of G5-TYPE Hd-Stars Brighter than MV=8.6
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&AS..102...89O&db_key=AST
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משמש של הקבוצה הבאה
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | דרקון |
| התרוממות ימנית: | 18h47m32.88s |
| סירוב: | +80°09'37.9" |
| גודל גלוי: | 8.457 |
| מרחק: | 95.42 פארסק |
| תנועה נכונה: | 20.3 |
| תנועה נכונה: | 71.7 |
| B-T magnitude: | 9.312 |
| V-T magnitude: | 8.528 |
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