B[e] star CI Cam is pulsing in a single mode nowстатья

Дата последнего поиска статьи во внешних источниках: 14 февраля 2019 г.

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[1] Goranskij V. P., Barsukova E. A. B[e] star ci cam is pulsing in a single mode now // The Astronomer’s Telegram. — 2018. — no. 12097. — P. 1–1. CI Cam is a transient, which had a strong outburst in the wide range of electromagnetic waves in April 1998. We have found previously that the system consists of a B4 III-V star displaying B[e] phenomenon, and a white dwarf on an eccentric orbit with the period of 19.407 days (ATel #416). Additionally, it was shown that wind emission lines of Fe II and [N II] 5754 Å shifted slowly in the spectra, and this shift reversed its direction in 2007. A treatment with the Doppler effect implies the presence of a third companion in the system which passed the periastron in a close approach that time (ATel #9663). Just after this event, the brightness of the star increased gradually by 0.4 mag in the V band and reached maximum in 2013. The star stays in the active state so far. Before the 2007 event, CI Cam exhibited double-mode pulsations with the periods of 0.4152 and 0.2667 days with the full amplitudes of 0.019 and 0.017 mag in the V band, correspondingly (ATel #1381). The ratio of periods of these waves was close to 3:2, and their interaction had signs of resonance (CoAst #159, 71, 2009): the amplitude of the light change increases several times when phases of the waves coincide. To verify the presence of pulsations in active state, we performed photometric monitoring of CI Cam at the Crimean Astronomical Station of the Moscow University. The observations were carried out with the 50 cm Maksutov meniscus telescope and CCD Apogee Alta U8300 in the prime focus with the V filter four nights in row from 4 to 7 October, 2018 (JD 2458396.43 - 2458399.62). The interval of observations corresponds to the orbital phase range 0.44 - 0.61, around the white dwarf elliptical orbit apastron, when the orbital light variations are minimum. An accuracy of the observations is 0.006 mag. We found regular pulsations only in a single mode with the period of 0.4062 ± 0.0015, the moment of maximum brightness is JD 2458398.5245. The light curve is slightly asymmetric. Amplitude of pulsations is 0.030 mag. So, in the active state with the brightness increase by 0.3 mag between 2006 and 2018, the pulsation period in this mode decreased by 2.5 %, and amplitude increased by 60 %. The pulsations in the secondary mode disappeared. This phenomenon suggests that pulsations are radial, and the secondary mode was excited earlier due to a resonance. The CI Cam pulsation is a unique phenomenon among B[e] stars. It rejects the classification of this star as a sgB[e].

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