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A ROSAT medium-sensitivity Galactic plane survey at 180°< l < 280°
We have performed a moderately deep soft X-ray (0.1-2keV) survey of theGalactic plane using pointed observations with the ROSAT PositionSensitive Proportional Counter (PSPC). The survey is more than an orderof magnitude more sensitive than previous X-ray surveys near theGalactic plane. The data consist of nine fields each of ~10ks exposure,pointed at positions on or very close to the Galactic plane(|b|<0°.3) in the longitude range 180°<~l<~280°.This region has relatively low X-ray absorbing material out to distancesof several hundred pc and presents fewer source-confusion problems thanat other longitudes. The total sky area surveyed was 2.5deg2this yielded 93 sources, 89 of which were detected in the `hard'(0.4-2.0keV) band. Nine sources were detected in both `soft'(0.1-0.4keV) and hard bands. In the hard band, the survey coverage is>~90 per cent for sources brighter than 0.002counts-1(~2×10-14ergcm-2s-1), but fallssteeply below this value, with the weakest sources being~0.001counts-1. The median limiting flux is~0.0013counts-1(~1.3×10-14ergcm-2s-1). There are64 sources with hard-band count rates >0.002counts-1. Wepresent the catalogue of X-ray sources and the number-flux relations(logN-logS). Eighteen sources have possible identifications from theSIMBAD data base. We have searched the Tycho-2 and USNO-A2.0 cataloguesto find all possible optical counterparts brighter than ~19th magnitude,and attempt to classify these on the basis oflog(fX/fopt) versus optical colour diagrams andnear-infrared photometry from the 2MASS Second Incremental Data Release.Hence, we have found the majority of these sources to be consistent withbeing late-type main-sequence stars, as previous studies have proposedfrom incompletely identified surveys. Comparison of the measurednumber-flux relations with predictions of Galactic (stellar) andextragalactic populations supports the view that the population of youngstars in the plane is denser than previously thought.
| The Tokyo PMC catalog 90-93: Catalog of positions of 6649 stars observed in 1990 through 1993 with Tokyo photoelectric meridian circle
The sixth annual catalog of the Tokyo Photoelectric Meridian Circle(PMC) is presented for 6649 stars which were observed at least two timesin January 1990 through March 1993. The mean positions of the starsobserved are given in the catalog at the corresponding mean epochs ofobservations of individual stars. The coordinates of the catalog arebased on the FK5 system, and referred to the equinox and equator ofJ2000.0. The mean local deviations of the observed positions from theFK5 catalog positions are constructed for the basic FK5 stars to comparewith those of the Tokyo PMC Catalog 89 and preliminary Hipparcos resultsof H30.
| U, V, W velocity components for the old disk using radial velocities of 1295 stars in the three cardinal Galactic directions
New radial velocities are presented for 1295 stars chosen at random nearthe three cardinal Galactic directions of l = 180 deg, b = 0; l = 90deg, b = 0 deg; and b = 90 deg, giving the distribution in U, V, and W,respectively, from the radial velocities alone. The measurements weremade with the coude spectrograph of the Mount Wilson 100 in. Hookerreflector. The purpose of the program is to set limits on the densitynormalization in the solar neighborhood of the old thin disk, the oldthick disk, and the halo. Many more high-velocity stars are present inthe unbiased sample than expected from previous estimates of thenormalization. The data suggest the density ratios in the solarneighborhood to be about 90 percent, 10 percent, and about 0.5 percentfor the thin disk, thick disk, and halo populations, respectively.
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