Volume 636, April 2020
|Number of page(s)||18|
|Section||Stellar structure and evolution|
|Published online||21 April 2020|
The path to Z And-type outbursts: The case of V426 Sagittae (HBHA 1704-05)⋆
Astronomical Institute, Slovak Academy of Sciences, 059 60
Tatranská Lomnica, Slovakia
2 Sternberg Astronomical Institute, Moscow State University, Universitetskij pr., 13, Moscow 119991, Russia
3 INAF – Osservatorio Astronomico di Padova, 36012 Asiago VI, Italy
4 INAF – Osservatorio di Astrofisica e Scienza dello Spazio, via Gobetti 93/3, 40129 Bologna, Italy
5 Departamento de Ciencias Físicas, Universidad Andrés Bello, Fernández Concha 700, Las Condes, Santiago, Chile
6 Dipartimento di Fisica, Università degli Studi di Torino, via Pietro Giuria 1, 10125 Torino, Italy
7 INFN – Istituto Nazionale di Fisica Nucleare, Sezione di Torino, via Pietro Giuria 1, 10125 Turin, Italy
8 Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata, Paseo del Bosque, B1900FWA La Plata, Argentina
9 Instituto de Astrofísica de La Plata, CONICET-UNLP, CCT La Plata, Paseo del Bosque, B1900FWA La Plata, Argentina
10 Scientific Research Institute, Crimean Astrophysical Observatory, 298409 Nauchny, Crimea
11 Castanet Tolosan Observatory, 6 place Clemence Isaure, 31320 Castanet Tolosan, France
12 Observatoire de l’Eridan et de la Chevelure de Bérénice, 02400 Epaux-Bézu, France
13 ANS Collaboration, c/o Astronomical Observatory, 36012 Asiago VI, Italy
14 Observatoire de la Tourbière, 38690 Chabons, France
15 Institute of Astronomy, Russian Academy of Sciences, Moscow, Russia
16 Vihorlat Astronomical Observatory, Mierová 4, 066 01 Humenné, Slovakia
17 Sonneberg Observatory, Sternwartestr. 32, 96515 Sonneberg, Germany
Accepted: 3 March 2020
Context. The star V426 Sge (HBHA 1704-05), originally classified as an emission-line object and a semi-regular variable, brightened at the beginning of August 2018, showing signatures of a symbiotic star outburst.
Aims. We aim to confirm the nature of V426 Sge as a classical symbiotic star, determine the photometric ephemeris of the light minima, and suggest the path from its 1968 symbiotic nova outburst to the following 2018 Z And-type outburst.
Methods. We re-constructed an historical light curve (LC) of V426 Sge from approximately the year 1900, and used original low- (R ∼ 500–1500; 330–880 nm) and high-resolution (R ∼ 11 000–34 000; 360–760 nm) spectroscopy complemented with Swift-XRT and UVOT, optical UBVRCIC and near-infrared JHKL photometry obtained during the 2018 outburst and the following quiescence.
Results. The historical LC reveals no symbiotic-like activity from ∼1900 to 1967. In 1968, V426 Sge experienced a symbiotic nova outburst that ceased around 1990. From approximately 1972, a wave-like orbitally related variation with a period of 493.4 ± 0.7 days developed in the LC. This was interrupted by a Z And-type outburst from the beginning of August 2018 to the middle of February 2019. At the maximum of the 2018 outburst, the burning white dwarf (WD) increased its temperature to ≳2 × 105 K, generated a luminosity of ∼7 × 1037 (d/3.3 kpc)2 erg s−1 and blew a wind at the rate of ∼3 × 10−6 M⊙ yr−1. Our spectral energy distribution models from the current quiescent phase reveal that the donor is a normal M4-5 III giant characterised with Teff ∼ 3400 K, RG ∼ 106 (d/3.3 kpc) R⊙ and LG ∼ 1350 (d/3.3 kpc)2 L⊙ and the accretor is a low-mass ∼0.5 M⊙ WD.
Conclusions. During the transition from the symbiotic nova outburst to the quiescent phase, a pronounced sinusoidal variation along the orbit develops in the LC of most symbiotic novae. The following eventual outburst is of Z And-type, when the accretion by the WD temporarily exceeds the upper limit of the stable burning. At this point the system becomes a classical symbiotic star.
Key words: binaries: symbiotic / novae / cataclysmic variables / stars: individual: V426 Sagittae (HBHA 1704-05)
Full Table A.1–A.3 are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (22.214.171.124) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/636/A77
© ESO 2020
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