The bright star Scorpii (HD 143275, HR 5953, V = 2.32, MK B0.3IV, v sin i = 145 km/s) is a member of the Upper Scorpius region of the Sco-Cen association. It is a visual and spectroscopic binary, with P = 10.583 years, e = 0.92 and T₀ = 1979.41 (Hartkopf et al. 1996). These parameters imply that a periastron passage is occurring at July 2000. It is also known to be a non-radial pulsator (Smith 1986, Telting & Schrijvers 1998).

 Sco is currently undergoing a bright optical and H outburst. The optical brightening was first detected by the visual observer Sebastián Otero (Liga Ibero-Americana de Astronomía), who, at the end of June 2000, noticed the star 0.1 mag brighter than its quiescient V = 2.32 magnitude. Ever since the brightening has continued, reaching V = 1.9 mag by the end of July. The light curve displaying Otero's visual estimates during the period 30 June - 2 August is presented in Figure 1.

Follow-up spectroscopic observations were obtained with the 1.3 m telescope at Skinakas Observatory (Crete, Greece), with spectral resolution of 0.3  in the range 580-760 nm. The spectra reveal the H line clearly in emission, confirming the Be star nature of Sco. Two spectra obtained on July 19 and 20 are presented in Figure 2. Measured equivalent widths are -0.34±0.02 nm and -0.33±0.02 nm (FWHM 0.69±0.01 nm) respectively.

Figure 2: H line low resolution spectra. The bottom spectrum was obtained on July 19, and the top one on July 20, 2000.

A further high-resolution spectrum is presented in Figure 3. It was obtained on July 28 with the 2.6 m Shain Telescope at the Crimean Astrophysical Observatory, Ukraine. The H emission line shows a double peaked structure with a peak separation of about 150 km/s.

Figure 3: H line high resolution spectrum, obtained on 28 July 2000.

Emission features in  Sco were first detected in 1990 by Coté & van Kerkwijk (1993), who observed weak emission on the flanks of the H line core in absorption, and proposed its classification as a Be star. During the last five years emission lines have been frequently observed, although the spectra showing them are not yet published (Harmanec et al., in preparation). Hence, the observations of Coté & van Kerkwijk might represent the onset of the current Be phase, which would have been active during the last ten years.

The optical outburst starts around the end of June 2000. Surprisingly, there is not apparent line variability associated to the optical brightening. The three H lines presented in this paper, obtained about 9 days apart, show similar shape and equivalent width. Spectra obtained within the Be Star Spectrographic Survey Project by the Aude Association (Buil 2000) cover a longer baseline. Their first spectrum was obtained on June 3, prior to the beginning of the optical outburst, when the star was at its quiescent V = 2.3 magnitude. The last one corresponds to July 30, when  Sco had brightened more than 0.4 mag. With the exception of the different resolution, both H lines appear identical. These spectra can be found at http://astroccd.com/terre/buil/us/catalog/7sco.htm.

Since its announcement in IAU Circ. 7461, the outburst of  Sco is attracting the interest of many observers and researchers. There are currently several open discussion forums in Internet. Interested readers can find some of them at the Be-Stars Mailing List (Townsend 2000, http://www.mailbase.ac.uk/lists/be-stars/), and the VSNET (international mailing list on variable stars, http://www.kusastro.kyoto-u.ac.jp/vsnet).

References

Buil, C. 2000, Be Star News, 34, 42
Coté, J. & van Kerkwijk, M. H. 1993, A&A, 274, 870
Hartkopf, W. I., Mason, B. D., & McAlister, H. A. 1996, AJ, 111, 370
Smith, M. A. 1986, ApJ, 304, 728
Telting, J. & Schrijvers, C. 1998, ASP-CS, 135, 149
Townsend, R. 2000, Be Star News, 34, 43