The path to Z And-type outbursts: The case of V426 Sagittae (HBHA 1704-05)
Authors:
A. Skopal, S. Shugarov, U. Munari, N. Masetti, E. Marchesini, R. Komzik, E. Kundra, N. Shagatova, T. N. Tarasova, C. Buil, C. Boussin, V. I. Shenavrin, F.-J. Hambsh, S. Dallaporta, A. Frigo, O. Garde, A. M. Zubareva, P. Dubovsky, P. Kroll
Image & caption:
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Image caption::
Transition from the symbiotic nova outburst to Z And-type outburst for AG Peg and V426 Sge. The sine curve fits the wave-like orbitally related variation. a: AG Peg - descending part of the historical light curve from its 1850 symbiotic nova outburst to the 2015 Z And-type outburst.
b: V426 Sge – the 1968 symbiotic nova outburst and the 2018 Z And-type outburst (V in red).
Description:
At the beginning of August 2018, a rather unknown star HBHA 1704-05 in the constellation of Sagittae suddenly brightened. We conducted an extensive campaign to measure its radiation from X-rays to the near-infrared. Analysing our observations we revealed that HBHA 1704-05 (now called as V426 Sagittae) went through the so-called Z And-type outburst of a symbiotic binary that is caused by an abrupt increase of the mass-accretion rate onto the white dwarf. The outburst lasted to the middle of February 2019. Re-constructing an historical light curve from the year 1900 we found that V426 Sge experienced also a symbiotic nova outburst in 1968 as a result of a prolonged accretion at a low rate. This event lasted to around 1990. A pronounced sinusoidal variation along the orbit, which developed in the light curve from 1972, was interrupted by the Z And-type outburst in 2018 - exactly as in the case of its sister AG Pegasi and other symbiotic novae. Based on such the common behaviour of this group of objects with very similar physical characteristics we have come to a conclusion that the first Z And-type outburst can occur exclusively after the prior symbiotic nova outburst. In this way, V426 Sagittae (HBHA 1704-05) became a classical symbiotic star.
Reference:
Astronomy & Astrophysics 636, article no. A77, p. 1-18 (2020)
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