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Astron. Astrophys. 345, L55-L57 (1999)

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3. The observed spectrum

Spectroscopic observations of high proper motion stars were obtained at Sutherland on the 1.9m Radcliffe Telescope of the SAAO during the nights of 10th-16th November 1998. The spectrum of APMPM J0237-5928 (Fig. 1) was observed on UT 1998 November 10. A 300 line/mm grating was used in the "grating" spectrograph with a SITe 1.8kx1k CCD as the detector. With this combination each CCD pixel covered 2.28Å per pixel, with an effective spectral resolution of 5Å. The spatial resolution was 0.3" per pixel. The central wavelength for the observations was chosen such that the final wavelength coverage was in the range 3850Å-7700Å. The lower limit includes the useful diagnostic Ca H,K lines in addition to the higher order member of the Balmer series, while the upper limit covers sufficient TiO and VO molecular bands to spectral type late M stars.

[FIGURE] Fig. 1. The spectrum of APMPM J0237-5928. The spectrum is typical of an M5 star and shows the Balmer lines from [FORMULA] to [FORMULA] clearly in emission.

A series of spectrophotometric standard stars were observed each night to provide flux calibration information, although we note that the slit position angle for this instrument is fixed E-W leading to problems accurately flux calibrating data taken over a wide range of airmass. CuAr arcs were taken periodically each night to monitor spectrograph flexure and hence provide an accurate wavelength calibration. Two to three radial velocity standards were also observed each night, since for some objects we wanted to derive reasonably accurate (10-20 km s-1) radial velocities. In these cases CuAr arcs were taken after each target or radial velocity standard observation on sky. Further checks on the wavelength calibration were done by cross-correlating the derived sky spectra, since, at least, at the red end of the spectrum, there are sufficient sky emission lines to provide a diagnostic at the 1/10th pixel level. Standard IRAF tasks were used to bias-correct, flat-field and extract the spectra in pseudo-real time at the telescope.

The radial velocity obtained for APMPM J0237-5928 is [FORMULA] km s-1.

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© European Southern Observatory (ESO) 1999

Online publication: April 28, 1999