2 Observations

The CCD photometric and spectral observations of the 1WGAJ1958.2+3232 were carried out on 2-5 August 2000 at the 1.5 m and 2.12 m telescopes of the Observatorio Astronomico Nacional, San Pedro Martir of the Institute of Astronomy of UNAM, Mexico. The observations log is presented in Table 1.

   

Table 1: Observations log

HJD start	Duration	Time	Band	Telescope
day		of exposure
2541000+	min	s
759.429a	380	120	$R_{\rm c}$	1.5 m
760.383	435	120	$R_{\rm c}$	1.5 m
761.855	173	700	4025-5600 Å	2.12 m
762.649	461	700	4025-5600 Å	2.12 m
763.678	319	700/350	4025-5600 Å	2.12 m

a 2 August.

Figure 1: 1WGAJ1958.2+3232 light curves in $R_{\rm c}$ band are presented. Binning time is 120 s

Figure 2: The CLEANed power spectrum of $R_{\rm c}$ light curve is given. The orbital period $\Omega _{\rm orb}$ and $\omega _{\rm rot}$ spin period frequencies are marked. In the inset part of the cleaned power spectrum with a smaller number of iterations is shown. The beat frequencies $\omega _{\rm rot}-\Omega _{\rm orb}$, $\omega _{\rm rot}+\Omega _{\rm orb}$ and $\omega=1/(727.78~ {\rm s})$ are shown

2.1 Optical photometry

We obtained $R_{\rm c}$-band time-resolved photometry of the optical counterpart of 1WGAJ1958.2+3232 during two nights in August 2000 at the 1.5 m telescope. The telescope was equipped with a $1024\times 1024$ pixel SITE CCD. The frame was reduced in size to $450 \times 450$ pix for faster read-out. It accommodated the object and at least two comparison stars in the field of view. The exposure times were 120 s, which leads to a time resolution of 169 s, taking into account dead time between readouts. In total the object was monitored during $\sim$13.55 h (6.3 h the first night and 7.25 h the second). The data reduction was performed by using ESO-MIDAS and IRAF software. The images were corrected for bias and flatfield before aperture photometry was carried out. An estimate of the uncertainty of the CCD photometry of the optical counterpart of 1WGAJ1958.2+3232 was obtained from the dispersion of magnitudes in the differential photometry of comparison stars with similar brightness. The dispersion ranged from 0.005 to 0.01 mag. We did not obtain an absolute calibration for our photometric data.

2.2 Optical spectroscopy

Time-resolved spectroscopy of the optical counterpart of 1WGAJ1958.2+3232 was obtained on 4-6 Aug., 2000 using the Boller & Chivens spectrograph installed in the Cassegrain focus of the 2.12 m telescope. We used the 400 l/ mm grating with a $13^{\rm o}54$ blaze in the second order, combined with the blue BG39 filter and CCD TEK $1024\times 1024$pix with a $0.24\mu$ pixel size. The slit width was 1.5 arcsec projected on the sky. This combination yielded a spectral resolution of 2.7 Å FWHM and provided a wavelength coverage of $\lambda 4050{-}5600$ Å. Of three nights of spectral observations, the second and third nights were disrupted by passing clouds. However the seeing was satisfactory with images $\leq$1.2 arcsec. The slit was oriented with position angle of $306^\circ$ to accommodate a nearby star for the flux level control. The exposure time in the first two nights was 700 s, while on the third night, 700 and 350 s. The He-Ar comparison spectra were taken every $\sim$120 min. A total of 68 spectra was obtained. The IRAF long slit spectroscopic reduction package was used for extraction of spectra, wavelength and flux calibrations. Beforehand the images were reduced for bias and cosmic rays.