Astron. Astrophys. 326, 629-631 (1997)

3. Spectra

Spectra of both components were taken on 1995 February 8, beginning at 1:56 and 2:29 UT, with the ISIS spectrograph of the 4.2-m William Herschel Telescope at La Palma. The R158R and R158B gratings were used with TEK CCDs. The slit was 0.73" wide on the sky, and was set to a position angle of 26.0 degrees, perpendicular to the line intersecting the centers of both stars. The parallactic angle at the time varied from 68.5 to 67.5 degrees. Seeing was 0.9 - 1.0", and weather was photometric. The dispersion was 2.9 Å pixel and the exposure times for both sets of red and blue exposures was 1800 s. A standard reduction was carried out, in which the frames were debiased, flat-fielded with exposures of tungsten lamps, wavelength-calibrated using Cu-Ne and Cu-Ar lamps, sky-subtracted, and flux-calibrated with the spectrum of the standard Feige 34 (Stone 1977). The spectrum of a nearby F8 star, SAO 077760, was also taken, to map the telluric absorption bands to allow their removal.

The resulting spectra of both components of Candidate 5 are shown in Fig. 2. The signal-to-noise ratios are about 20 near H in both red spectra and about 5 for star A and 10 for star B near H in the blue spectra. The only features obvious in the red spectra are H in emission, and the TiO absorption bands at 7165 and 7665 Å. The blue spectra show only faint Mg b 5175 Å in star B. By comparison with Vilnius dwarf spectra (Sviderskiene 1988), we estimate spectral types of M0.5 0.5 for star A and K7.5 0.5 for star B. H has equivalent widths of 7.3 0.5 Å and 22.8 0.8 Å and full-widths at half-maxima of   and   in stars A and B, respectively. Since radial velocity standards were not taken, it is impossible to quote reliable absolute values for these stars' radial velocities, but the H lines show a difference of   between stars A and B.

Fig. 2. Spectra of components A and B of Candidate 5. Telluric absorption bands were mapped and removed from these sky-subtracted spectra. The TiO 7165 and 7665 Å bands are evident in both red spectra, as is H in emission.

Despite probable light losses through the slit, we deconvolved Johnson-Kron broad-band magnitudes from the spectra. The only bands completely covered were B and We found for star A and and for star B; low signal-to-noise in the blue prevented such a measurement for A. Assuming that star B is a K7 - M0 dwarf, its colors (Bessell 1991) and the extinction law of Howarth (1983) would imply and a distance between 1.5 and 1.9 kpc. Although star A is brighter, it is redder, although these spectra cannot distinguish its luminosity class.

© European Southern Observatory (ESO) 1997

Online publication: October 15, 1997
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