The Strömgren uvby photometric observations were carried out on 9 nights in June, 1999, using the 0.9 m telescope at Sierra Nevada Observatory (Spain) equipped with a six-channel (uvby+) spectrograph photometer (Nielsen 1983). Earlier, UBV measurements were obtained on one single night in March, 1999, using the 0.4 m Cassegrain-type telescope of Szeged Observatory equipped with a single-channel Optec SSP-5A photometer. These observations covered only 5 hours and revealed a 0.2 mag variation between two consecutive minima. We carried out differential photometry with respect to HD 103150 (V=8.45, =0.54, =0.335, =0.149, =0.381 mag). The overall accuracy of the standard transformation is about mag for V, and and mag for . The light and colour curves were phased using the corrected ephemeris (see below) and are plotted in Fig. 1.
Table 1. The journal of observations
The spectroscopic observations were carried out at David Dunlap Observatory with the Cassegrain spectrograph attached to the 74" telescope on two nights in May, 1999. The detector and the spectrograph setup were the same as used by Vinkó et al. (1998). The resolving power () was 11,000 and the signal-to-noise ratio reached 30-50, depending on the weather conditions. The spectra were centered on 6600 Å and reduced with standard IRAF tasks, including bias removal, flat-fielding, cosmic ray elimination, aperture extraction (with the task doslit) and wavelength calibration. For the latter, two FeAr spectral lamp exposures were used, which were obtained before and after every three stellar exposures. The sequence of observations FeAr-var-var-var-FeAr was chosen because of the short period of HV UMa. Careful linear interpolation between the two comparison spectra was applied in order to take into account the sub-pixel shifts of the three stellar spectra caused by the movement of the telescope. We chose an exposure time of 10 minutes, which corresponds to 0.01 in binary orbital phase, avoiding phase smearing of the radial velocity curve. The spectra were normalized to the continuum by fitting a cubic spline, omitting the region of H.
Besides a few telluric features, only the H line could be detected with acceptable S/N ratio in our 200 Å-wide spectra. At the phases of maximum light the line exhibited significant broadening and an excess bump appeared on the wings alternating between the blue and the red side (see Fig. 2). It can be interpreted most easily as the effect of a close companion star, therefore HV UMa is most probably a spectroscopic binary. Fig. 2 shows a few sample spectra with the calculated orbital phase indicated on the right side of every spectrum.
© European Southern Observatory (ESO) 2000
Online publication: April 10, 2000