Astronomy and Astrophysics – Astronomy
Scientific paper
Mar 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000astl...26..162e&link_type=abstract
Astronomy Letters, vol. 26, p. 162-176 (2000)
Astronomy and Astrophysics
Astronomy
4
Scientific paper
The photometric UBV observations of AS338 that we began after its outburst in 1983 are presented. They were accompanied by yearly spectroscopic observations and by occasional estimations of the star's infrared JHKL magnitudes. In June 1993, the star's optical spectrum was extended to the ultraviolet via IUE observations of AS338. Collectively, the above observations make it possible to trace the evolution of stellar activity over a period of 15 years in various spectral ranges. In particular, a short-time return of the hot component of AS338 to the state when HeII lines reappeared in the star's spectrum was noted in 1993. At this time, a blend of the CIV lambda 5802 and 5812 A lines, which is typical of Wolf-Rayet spectra, was detected in it. In June 1993, the temperature of the hot component was T_h = 8.8 x 10^4 K, and the ratio of its bolometric flux to that of the red giant was F_{h,bol}/F_{g,bol} = 1.0. In August, its temperature increased to about 1.0 x 10^5 K, while the bolometric flux dropped by a factor of 1.5 (F_{h,bol}/F_{g,bol} = 0.7). In the B-V, U diagram, the points referring to this so-called quiescent state form a separate group shifted in B-V from all the remaining ones located in a horizontal strip with delta U =3.5 mag and delta (B-V) = 0.4 mag. This allows us to diagnose the state of the hot component without spectroscopic observations of the star. In October 1993, the hot component flared up again. The main brightness rise took no more than 19 days. The outburst occurred shortly before eclipse egress of the hot component, whose duration was 0.01 P_orb. In December 1993, F_{h,bol}/F_{g,bol} was less than 1.5 at maximum light. During the recurrent, even stronger outburst in April 1995, F_{h,bol}/F_{g,bol} was less than 3.4. The H_alpha line during outbursts has a P Cyg profile and broad wings stretching to velocities of +/- 1500 km/s. The color temperature of the active hot component at short optical wavelengths and in the ultraviolet lies in the range of effective temperatures for hot supergiants. Nevertheless, it always produces an HII region in the circumstellar envelope that is larger in size than this binary system.
Esipov Valentine F.
Kolotilov Eugenii A.
Mikolajewska Joanna
Munari Ulisse
Tatarnikov A. M.
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