Gaia18aen: First symbiotic star discovered by Gaia^⋆

¹ Astronomical Institute, Faculty of Mathematics and Physics, Charles University, V Holešovičkách 2, 180 00 Prague, Czech Republic
² Institute of Physics, Faculty of Science, P. J. Šafárik University, Park Angelinum 9, 040 01 Košice, Slovakia
e-mail: jaroslav.merc@student.upjs.sk
³ Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences, Bartycka 18, 00–716 Warsaw, Poland
⁴ Astronomical Observatory, University of Warsaw, Al. Ujazdowskie 4, 00-478 Warszaw, Poland
⁵ Department of Physics and Astronomy, Texas Tech University, Box 41051, Science Building, Lubbock, TX 79409-1051, USA
⁶ Institute of Astronomy, University of Cambridge, Madingley Road, CB3 0HA Cambridge, UK
⁷ ICAMER Observatory of NASU, 27 Acad. Zabolotnoho Str., Kyiv 03143, Ukraine
⁸ Faculty of Physics, Taras Shevchenko National University of Kyiv, 4 Glushkova Ave., Kyiv 03022, Ukraine
⁹ Faulkes Telescope Project, School of Physics, and Astronomy, Cardiff University, The Parade, Cardiff CF24 3AA, UK
¹⁰ Astrophysics Research Institute, Liverpool John Moores University, 146 Brownlow Hill, Liverpool L3 5RF, UK
¹¹ School of Physical Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA, UK
¹² National Astronomical Research Institute of Thailand, 260, Moo 4, T. Donkaew, A. Mae Rim, Chiang Mai 50180, Thailand
¹³ Department of Physics and Astronomy, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
¹⁴ Eastbury Community School, Hulse Avenue, Barking IG11 9UW, UK

Received: 10 August 2020
Accepted: 28 September 2020

Abstract

Context. Besides the astrometric mission of the Gaia satellite, its repeated and high-precision measurements also serve as an all-sky photometric transient survey. The sudden brightenings of the sources are published as Gaia Photometric Science Alerts and are made publicly available, allowing the community to photometrically and spectroscopically follow up on the object.

Aims. The goal of this paper is to analyze the nature and derive the basic parameters of Gaia18aen, a transient detected at the beginning of 2018. This object coincides with the position of the emission-line star WRAY 15-136. The brightening was classified as a “nova?” on the basis of a subsequent spectroscopic observation.

Methods. We analyzed two spectra of Gaia18aen and collected the available photometry of the object covering the brightenings in 2018 and also the preceding and following periods of quiescence. Based on this observational data, we derived the parameters of Gaia18aen and discussed the nature of the object.

Results. Gaia18aen is the first symbiotic star discovered by Gaia satellite. The system is an S-type symbiotic star and consists of an M giant of a slightly super-solar metallicity, where T_eff ∼ 3500 K, a radius of ∼230 R_⊙, and a high luminosity L ∼ 7400 L_⊙. The hot component is a hot white dwarf. We tentatively determined the orbital period of the system ∼487 d. The main outburst of Gaia18aen in 2018 was accompanied by a decrease in the temperature of the hot component. The first phase of the outburst was characterized by the high luminosity L ∼ 27 000 L_⊙, which remained constant for about three weeks after the optical maximum, later followed by the gradual decline of luminosity and increase of temperature. Several re-brightenings have been detected on the timescales of hundreds of days.