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Radial Velocities of Population II Stars. II.
A program for radial velocity measurements of Population II stars wasstarted in 1988 and was carried out during six observing runs. Theprogram includes metal-deficient stars, components of Population IIvisual binaries or common proper motion stars, suspected radial velocityvariables and the Population II stars from the Hipparcos program. Themeasurements were made with the 1 meter reflector at the MaidanakObservatory in Uzbekistan. The average error of a single measurement isabout 0.6 km/s, but for stars at 13 mag or for extremely metal-deficientstars the error is about 2.5 km/s. The catalog contains 621 measurementsfor 164 stars.
| Radial velocities of Population II stars. I
Radial velocity measurements are presented for 81 Population II stars.The sample comprises components of metal-poor binary stars,spectroscopic binary candidates, high latitude supergiants,metal-deficient stars with spectroscopic determinations of Fe/H,HIPPARCOS program stars, and some other stars of metal-poor population.The radial velocity measurements were made in February 1988 with aphotoelectric stellar velocimeter.
| A medium sensitivity X-ray survey using the Einstein Observatory - The log N-log S relation for extragalactic X-ray sources
The paper presents results of an X-ray survey of about 50 sq deg of thehigh galactic latitude sky at sensitivities in the range of 7 x 10 tothe -14 to 5 x 10 to the -12 ergs/sq cm/s. The number-flux relation isderived for the extragalactic population to yield a best-fit power-lawslope of 1.53 + or - 0.16, and the content of the sample is analyzed interms of types of sources, appearing to be significantly different fromthe content of similar samples selected at higher fluxes. The mediumsensitivity sample of extragalactic sources is dominated by activegalactic nuclei, while samples selected at higher fluxes and higherenergies are dominated by clusters of galaxies. Thus, the number-fluxrelation for extragalactic sources may be interpreted to a firstapproximation as the sum of the two different distributions with flatterand steeper slopes describing clusters and AGNs, respectively.
| Results from an extensive Einstein stellar survey
The preliminary results of the Einstein Observatory stellar X-ray surveyare presented. To date, 143 soft X-ray sources have been identified withstellar counterparts, leaving no doubt that stars in general constitutea pervasive class of low-luminosity galactic X-ray sources. Stars alongthe entire main sequence, of all luminosity classes, pre-main sequencestars as well as very evolved stars have been detected. Early type OBstars have X-ray luminosities in the range 10 to the 31st to 10 to the34th ergs/s; late type stars show a somewhat lower range of X-rayemission levels, from 10 to the 26th to 10 to the 31st ergs/s. Late typemain-sequence stars show little dependence of X-ray emission levels uponstellar effective temperature; similarly, the observations suggest weak,if any, dependence of X-ray luminosity upon effective gravity. Instead,the data show a broad range of emission levels (about three orders ofmagnitude) throughout the main sequence later than F0.
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| Takýmyýldýz: | Yilan |
| Sað Açýklýk: | 15h52m03.88s |
| Yükselim: | +20°14'53.0" |
| Görünürdeki Parlaklýk: | 8.953 |
| Uzaklýk: | 89.366 parsek |
| özdevim Sað Açýklýk: | 92.7 |
| özdevim Yükselim: | -59.5 |
| B-T magnitude: | 9.676 |
| V-T magnitude: | 9.013 |
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