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R.-D. Scholz 1,
M. Irwin 2,
R. Ibata 3,
H. Jahreiß 4 and
O.Yu. Malkov 5
Received 24 August 1999 / Accepted 12 November 1999
We present the discovery of about 100 new high-proper motion stars in the region between and in right ascension and and in declination, with proper motions between 0.3 and 1.0 arcsec/yr. In addition we have obtained improved coordinates and photographic photometry for another about 100 already known high-proper motion stars in the same region. In this study we have made use of APM measurements of UKST survey plates in 40 survey fields. Using all available information (position, proper motion, photographic R magnitude and colour index), we draw some preliminary conclusions on the nature of the new high-proper motion stars, particularly of extreme cases. In addition, for some of the new high-proper motion stars we carried out low resolution optical spectroscopy with the 1.9m Radcliffe telescope of the South Africa Astronomical Observatory (SAAO). The faintest discovered proper motion stars are a common proper motion pair with arcsec/yr, R magnitudes of 19.7 and 20.9 and magnitudes of 20.6 and 22.9, respectively. A first estimate of the absolute magnitude of this proper motion pair APMPM J0352-4127AB based on estimating the distance from the extant observational data, yields and , respectively for the two components. We conclude that both components are likely to be extremely cool degenerate white dwarfs. The SAAO spectrum of the brighter component is a first confirmation of the cool white dwarf nature, although the signal-to-noise was very low. There are other cool white dwarfs among the stars for which SAAO spectra were obtained. The star with the largest proper motion among the newly detected proper motion stars ( arcsec/yr and ; ) had a spectrum corresponding to a mid-M dwarf. For the extremely red () and blue () stars in our sample, our prior assumptions based on photometry and proper motion of late type M dwarf or normal white dwarf nature respectively, were confirmed by follow-up spectroscopy obtained at the SAAO.
We have also obtained relatively bright stars () with proper motions between 0.3 and 0.8 arcsec/yr, formerly not recognised as high-proper motion stars. The star with the largest proper motion among these new bright high-proper motion stars ( arcsec/yr) was identified with the bright X-ray source 1RXS J023630.5-592827 and classified as a nearby (distance = 12 pc) active M5 dwarf (Scholz et al. 1999).
Key words: astrometry stars: kinematics stars: low-mass, brown dwarfs stars: white dwarfs
* Based on measurements of UKST (United Kingdom Schmidt Telescope) plates with the APM (Automatic Plate Measuring) machine at Cambridge/UK
Send offprint requests to: R.-D. Scholz
Online publication: January 18, 2000