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Rapid re-brightening of the red nova V4332 Sgr remnant

ATel #11733; V. P. Goranskij, A. V. Zharova (SAI, Moscow University), E. A. Barsukova, A. F. Valeev (Special Astrophysical Observatory, Russia)
on 19 Jun 2018; 09:52 UT
Credential Certification: Vitaly Goranskij (goray@sai.msu.ru)

Subjects: Optical, Nova

V4332 Sgr is a luminous red nova exploded in 1994. We perform CCD BVRcIc photometry of its remnant since 2003, and medium resolution spectroscopy since 2005 using Russian 6 m telescope BTA, SAO 1 m Zeiss telescope and smaller telescopes of SAI Crimean Station. Between 2006 and 2008, the observations reveal the abrupt drop of flux by 4 times in the blue range, and reddening of stellar continuum, whereas emission line fluxes decreased by 30 times. Since 2012, the star brightness was grown up gradually. However, the rate of brightening accelerated since the last year. The following Table gives magnitudes taken with the BTA 6 m telescope and SCORPIO focal reducer, and with SAO 1 m telescope and UBVRI photometer based on CCD EEV 42-40 chip during the last seven years.

Date, UT B V Rc Ic Telescope

2011 Jun 05.98 21.43 19.90 17.76 15.08 6m

2012 Aug 17.76 21.40 19.61 17.45 - 6m

2014 Jul 16.85 21.24 19.02 17.16 14.79 1m

2016 May 30.95 21.23 18.77 16.86 14.48 6m

2017 Jun 21.96 21.22 18.82 16.85 14.39 6m

2017 Jul 25.86 21.04 18.89 16.79 14.35 1m

2018 May 02.04 - - 16.60 14.13 1m

2018 Jun 11.93 20.56 18.49 16.46 14.04 1m

2018 Jun 12.93 20.69 18.51 16.44 14.03 1m

Note, that magnitudes raised by 0.15 in the Rc band, and by 0.10 in the Ic band during the last month. The contemporary level of brightness has reached the 2002 level in the Rc filter, and has exceeded the 2002 level in Ic filter. Besides, color indices stay essentially red comparatively with the 2002 levels. The last spectrum has been taken with the BTA/SCORPIO on 2017 Jul 21.92 UT. It was flux calibrated using the magnitudes obtained from our photometry. The spectral range was 4048 -- 5842 Å, spectral resolution was 5.3 Å. The fluxes of the strongest emission lines of Ca I, Cr I, AlO look weaker only by 2-3 times comparatively with those in 2005, but Mg I 4571 Å and Sr I 4607 Å emission disappeared. Barsukova et al. (2017, ASPC, 510, 401) suggest that the 1994 event was the merger in a contact system with a 3-rd companion, an M-type giant, and the cool supergiant remnant of the merger was destroyed dynamically under influence of the 3-rd companion. The recent re-brightening was explained by authors as a result of the new approach of remnant debris moving on an elliptical orbit with the M-type star, and the accretion of them onto this star.
Light curves of V4332 Sgr in the Cousins R and I bands