Gaia18aen: First symbiotic star discovered by Gaia

Abstract

Context. Besides the astrometric mission of the Gaia satellite, its repeated and high-precision measurements serve also 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 the object. Aims. The goal of this paper was to analyze the nature and derive the basic parameters of Gaia18aen, transient detected at the beginning of 2018. It coincides with the position of the emission line star WRAY 15-136. The brightening was classified as a "nova?" on the basis of subsequent spectroscopic observation. Methods. We have 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 have 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, with T eff ∼ 3 500 K, a radius of ∼ 230 R , and a high luminosity L ∼ 7 400 L . The hot component is a hot white dwarf. We tentatively determined the orbital period of the system ∼ 487 days. 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.

Discovery of five new Galactic symbiotic stars in the VPHAS+ survey

“…Finally, Merc et al (2020) have recently presented the discovery of a new SySt (Gaia18aen) in the GAIA catalog. This third Galactic SySt also satisfies both selection criteria (ii & iii) providing an additional validation.…”

“…The recently updated catalogues of SySts (Akras et al 2019a;Merc et al 2019) lists only 257 Galactic and 66 extragalactic members. Since the publication of these two catalogues, three more Galactic SySts were discovered: Hen 3-1678 (Lucy et al 2018), HBHa 1704-05 (Munari & et al 2018;Skopal et al 2019) and Gaia18aen (Merc et al 2020). Yet, the overall population of Galactic SySts is still incompatible with the theoretical predictions (3,000 to 400,000 SySts; Kenyon 1986;Munari & Renzini 1992;Kenyon et al 1993;Magrini et al 2003;Lü et al 2006).…”