New burst of the symbiotic star V426 Sge (HBHA 1704-05)

ATel #16280; A. Skopal, S. Shugarov, N. Shagatova (ASI SAS, Tatranska Lomnica), F. Teyssier, D. Boyd, F. Sims, J. Guarro Flo, P. Fricker, G. Bertrand, P. Dubreuil, V. Lecocq (ARAS Group)
on 11 Oct 2023; 08:12 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Augustin Skopal (skopal@ta3.sk)

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The star V426 Sge (HBHA 1704-05) started its activity in 1968 when it experienced a symbiotic nova outburst that ceased around 1990. The following quiescent phase was interrupted by a Z And-type outburst that commenced during the first decade of August 2018 (see Munari et al. 2018, ATel #11937; Skopal et al. 2020, A&A, 636, A77).

Based on our UBVRcIc CCD photometry we report on a new burst of V426 Sge that started during September 2023. The following are some of our recent measurements:

Date (UT) U B V Rc Ic Aug. 13, 2023, 13.715 13.600 12.489 11.292 9.743 Aug. 27, 2023, 13.619 13.497 12.387 11.205 9.709 Sep. 17, 2023, 13.159 13.410 12.386 11.231 9.750 Oct. 04, 2023, 11.626 12.435 11.646 10.690 9.471 Oct. 05, 2023, 11.670 12.483 11.702 10.725 9.502 Oct. 06, 2023, 11.653 12.436 11.666 10.684 9.453 Oct. 08, 2023, 11.723 12.490 11.694 10.686 9.451

The measurements suggest a brightening about of 1.5, 0.95, 0.7, 0.5 and 0.25 mag in the U, B, V, Rc and Ic passband, respectively. Photometric observations were obtained at the Stara Lesna Observatory with a 60 cm telescope using the FLI ML3041 CCD camera. Our multicolor photometry covering the period from the 2018 outburst to the present is shown at http://www.ta3.sk/~astrskop/atel_v426sge/hbha-lc.png. In the figure, the gray belt indicates the recent brightening, the vertical dotted lines are the positions of photometric minima separated by 493.4 days, and the arrows indicate the dates of our example spectroscopic observations.

Low-resolution spectra were obtained within the Astronomical Ring for Access to Spectroscopy (ARAS). The spectrum from the quiescent phase was obtained on November 22.729, 2022 UT at the West Challow Observatory (D.B.) and from the recent brightening, we selected the spectrum obtained on October 6.139, 2023 UT at the Desert Celestial Observatory (F.S.) with a similar resolution of R = 1100. A comparison of the HeII 4686 and H-beta line profiles is shown in the figure available at http://www.ta3.sk/~astrskop/atel_v426sge/v426_oq.png. The spectra are roughly calibrated with the aid of our simultaneous photometry. They are not dereddened. Similar to the 2018 outburst, the flux emitted by the HeII 4686 line increased by a factor of ~2 with respect to the quiescence. Also, the flux ratio, F(HeII)/F(H-beta) > 1 during the current burst, signals a significant increase in the temperature of the burning white dwarf. However, more accurate quantitative analysis requires higher resolution spectra.