2 Observation and data reduction

The spectroscopic observations of UX Ari were carried out with the 2.16 m telescope at the Xinglong station of the National Astronomical Observatories, China during three observing seasons: February 19-24, September 15-17, and November 11 2000. The Coude echelle spectrograph with a spectral resolution about 34 000 and a 1024$\times$1024 pixel CCD detector was used during the observations. The reciprocal dispersions are 0.082 Å/pixel for the He I D₃ and Na I D₁, D₂ line spectral region, 0.091 Å/pixel for the H$\alpha$ line spectral region, 0.119 Å/pixel for the Ca II IRT (8498.06 Å, 8542.14 Å) line spectral region, and 0.120 Å/pixel for the Ca II IRT (8662.17 Å) line spectral region. Correspondingly, the spectral resolution determined as the FWHM of the arc comparison lines is 0.151, 0.167, 0.212, 0.215 Å, respectively. The signal to noise ratio (S/N) is more than 100 for all observations. The observing log is listed in Table 1. For each observation, the observing date, UT, orbital phase, and exposure time are given.

 

 

Table 1: The observational log of UX Ari.

Date	UT	Phase	Exposure time (s)
2000.02.19	13:10:06	0.132	1200
2000.02.19	13:32:19	0.135	1200
2000.02.20	14:13:40	0.295	1200
2000.02.20	14:34:50	0.297	1200
2000.02.21	14:41:11	0.453	3600
2000.02.22	13:20:54	0.600	1200
2000.02.22	13:41:31	0.602	1200
2000.02.23	13:21:30	0.755	1800
2000.02.23	13:52:19	0.758	1800
2000.02.24	13:07:26	0.909	1200
2000.02.24	13:28:20	0.911	1200
2000.09.15	19:23:13	0.625	1800
2000.09.16	17:28:18	0.781	1800
2000.09.17	17:32:30	0.933	1800
2000.11.11	17:01:55	0.492	1200

The spectral images are reduced by means of the IRAF package. The standard procedures are used, which include image trimming, bias subtraction, flat-field division, and 1-D spectrum extraction. The wavelength calibration was obtained by taking the spectrum of a Th-Ar lamp. Finally, all spectra have been normalized by a spline3 fitting to the continuum of the observed spectra.

On some nights of our observing seasons when the telluric lines were heavy, two rapidly rotating early-type stars HR8858 (B5V, $v\sin{i}=332$ km s^-1) and HR7894 (B5IV, $v\sin{i}=330$ km s^-1) were observed. Their observed spectra are fitted by using high order spline3 function to derive the telluric line templates. The telluric lines in the spectra of UX Ari are removed by means of these templates. Figure 1 shows examples of such a procedure in different spectral regions.

Figure 1: The illustrations for removing telluric lines from the observed spectra in He I D3, Na I D1, D2, H$_\alpha$, and Ca II IRT wavelength bands.