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Astron. Astrophys. 347, L39-L42 (1999)

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2. Observations

A journal of the spectroscopic observations is given in Table 1. In this paper the dates are counted from the outburst maximum brightness [FORMULA] mag occurred on JD=2451235.062 (cf. IAU Circ. 7113).


Table 1. Journal of the spectroscopic observations. [FORMULA] = days since maximum brightness (see text); [FORMULA] = [FORMULA] - 2451200; [FORMULA] = orbital phase from SR95; Tel. = telescope code (a = Asiago 1.22m + B&C +CCD; b = Asiago 1.82m + Echelle +CCD; c = ESO NTT + EMMI); disp. = dispersion (in Å/pixel) around H[FORMULA]; FWZI = full width at zero intensity for the H[FORMULA] profile (H[FORMULA] for the first spectrum).

High resolution spectra have been obtained with the Echelle spectrograph mounted at the Cassegrain focus of the 1.82 m telescope which is operated by Astronomical Observatory of Padova on top of Mt. Ekar, Asiago (Italy). The detector was a Thomson THX31156 CCD with 1024[FORMULA]1024 pixels, 19 µm each, and the slit width was set to [FORMULA]. The multi-order Echelle spectra have been successfully processed into single dispersion ones by using spectra of some unreddened A0 V stars close to U Sco and observed under identical conditions (inter-comparison of the similarly processed A0 V star spectra shows the rectification and joining technique to be accurate to better than [FORMULA]3%). The gaps in the red/near-IR visible in the spectra of Fig. 2 are caused by non overlapping Echelle orders.

Medium dispersion spectra were secured with the B&C+CCD spectrograph at the 1.22 m telescope of the Astronomy Dept., Univ. of Padova, located in Asiago too. The detector was a Wright Instr. CCD camera with a 512x512 pixel, 23 µm size, UV-coated chip. The slit width was set to [FORMULA].

On March 16th and 17th U Sco was observed with the ESO NTT and the EMMI instrument. The dispersing element was grism #5 on the 16th, and grisms #5 and #2 the following night. A [FORMULA] slit was used on both nights. The seeing was [FORMULA] the first night and [FORMULA] the second. The DA white dwarf HIP 80300 was observed as flux standard on March 17.

Visual estimates of U Sco brightness have been obtained by one of us (AP) with a private 16" f/4 reflector using the A.Henden (USNO) comparison sequence as distributed by VSNET. The visual estimates are listed in Table 2 and the photometric evolution of the 1999 outburst is compared with those of 1979 and 1987 events in Fig. 1.


Table 2. Visual magnitudes of U Sco during the 1999 outburst. [FORMULA] = [FORMULA] - 2451200; [FORMULA] = pre-outburst observations from VSNET archives; [FORMULA] = data from IAU Circ. 7113.

[FIGURE] Fig. 1. Comparison of the light curves of the last three outbursts of U Sco (data from Table 2, B81 and S88). The thick line is the average brightness in quiescence. Negative detections for 1999 are given as fainter-than symbols.

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© European Southern Observatory (ESO) 1999

Online publication: June 6, 1999