2. The observations
During the night of 7 June 1996 (UT), HD 76534 was observed in service time, employing the UCLES spectrograph mounted on the 3.9 m Anglo-Australian Telescope. The observational set-up included the 31 grooves/mm echelle and a 10241024 Tektronix CCD detector. The resulting spectrum contains 44 orders covering the spectral coverage of 4650 to 7240 Å, including both H and H. The observing strategy was fairly straightforward, we aimed to obtain spectra every few minutes, and employed different exposure times in order to compromise between time-resolution and signal-to-noise. Within a time span of two hours, we obtained 30 spectra with signal-to-noise ratios (SNR) in the H setting ranging from 60 in the shortest (60 s) exposures to 140 in the longest (240 s) exposures. The observing conditions were not ideal, so the total count-rates and SNR are slightly variable.
Data reduction was performed in IRAF (Tody, 1993), and included the procedures of bias-subtraction, flatfielding and wavelength calibration. An observation of a Th-Ar arc lamp was used to provide the wavelength calibration of each spectrum. The resulting spectral resolution was determined to be 10 km s-1 from Gaussian fits through telluric absorption lines.
In total 30 spectra with different exposure times were taken. The summed total spectrum, with a total exposure time of 4500 s has a SNR of 200 in the H order and 300 in the H order. The log of the observations and the SNR in the H order are provided in Table 1.
© European Southern Observatory (ESO) 1999
Online publication: October 4, 1999