Gaia18aen: First symbiotic star discovered by Gaia

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 Teff ∼ 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.

Hen 3-860: New southern eclipsing symbiotic star observed in the outburst

“…6). One pair has supposedly the interstellar origin and its velocity is used to put the lower limit on the distance to some symbiotic stars (see e.g., Merc et al 2020;Mikołajewska et al 2021). Our preliminary analysis of the spectroscopic data of AX Per confirmed that the other pair arises in the symbiotic system.…”

“…The values from the 2MASS catalogue were converted to the standard system of Bessell & Brett (1988) using the transformations of Carpenter (2001). Note that in the case of the S-type symbiotic star Gaia18aen, the extinction value based on the comparison of synthetic and observed NIR spectra of the cool giant was larger than the one from the dust maps (by about 0.2 mag, similar to Hen 3-860; Merc et al 2020).…”

The symbiotic binary St 2-22: Orbital and stellar parameters and jet evolution following its 2019 outburst

“…Assuming a blackbody spectrum and case B recombination, the fluxes of Hβ, He i 5876, and He ii 4686 lines require T h ∼ 100 kK (also indicated by the presence of weak [Fe vii] emission lines in the best-exposed spectra), and luminosity (within a factor of 2), L h ∼ 200 L (see, e.g. Merc et al 2020). The estimated luminosity is similar to the quiescent L h ≈ 220 L resulting from the emission line fluxes published by Mikołajewska et al (1997) corrected for the reddening and distance adopted in this study (Sect.…”

The symbiotic binary St 2-22: Orbital and stellar parameters and jet evolution following its 2019 outburst

“…Assuming a blackbody spectrum and case B recombination, the fluxes of Hβ, He i 5876, and He ii 4686 lines require T h ∼ 100 kK (also indicated by the presence of weak [Fe vii] emission lines in the best-exposed spectra), and luminosity (within a factor of 2), L h ∼ 200 L (see, e.g. Merc et al 2020). The estimated luminosity is similar to the quiescent L h ≈ 220 L resulting from the emission line fluxes published by Mikołajewska et al (1997) corrected for the reddening and distance adopted in this study (Sec.…”