Rebrightening of the symbiotic star V919 Sgr

ATel #16326; J. Merc (Charles University), F. Teyssier, C. Eldridge, J. Guarro Flo (ARAS Group), F.-J. Hambsch (Vereniging voor Sterrenkunde, Center for Backyard Astrophysics, AAVSO), T. Kojima (Tsumagoi, Gunma, Japan)
on 7 Nov 2023; 07:27 UT
Credential Certification: Jaroslav Merc (jaroslav.merc@mff.cuni.cz)

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V919 Sgr is a relatively poorly studied symbiotic star despite being known since the seventies (Sanduleak & Stephenson, 1973; ApJ, 185, 899; Allen, 1978; MNRAS, 184, 601). The star has been observed in three active stages so far. The first documented outburst occurred in 1991 and was analyzed by Ivison et al. (1993; A&A, 277, 510). The second active phase commenced in 2007 (Munari et al., 2007; CBET 999) and witnessed several rebrightenings following the initial, most prominent outburst. According to the AAVSO light curve of V919 Sgr, the system returned to its quiescent brightness around 2015.

A new active stage began in 2022 (Munari et al., 2022; ATel #15528), approximately 15 years after the onset of the previous one. Munari et al. classified the 2022 brightening as a 'cool'-type outburst based on spectroscopic data. Notably, highly ionized emission lines, namely He II and [O III], but also He I, disappeared from the spectrum, leaving only H I and Fe II lines observable. Observations available in the ARAS database (Teyssier, 2019; CAOSP, 49, 217), collected mainly in August and September 2022, corroborated these findings. It is worth noting that during the 2007 outburst, weak emission lines of [O III] were still detectable in the spectra.

Here, we report on the rebrightening of V919 Sgr observed in 2023. The ASAS-SN light curve well illustrates the system's brightness evolution. In contrast with the behavior observed during the previous active stage, the rebrightening in 2023 surpassed the 2022 outburst by approximately 0.4 mag in the V filter, possibly marking the star's brightest state since the beginning of observations. Interestingly, the ASAS-SN light curve revealed a minor dip in brightness, around 0.2 mag, at the beginning of June 2023, during the ascent to the current maximum. The peak brightness was reached in mid-October, and our BVRI photometric observations, available in the AAVSO database, show that the brightness is already decreasing. The B-V color of the system remained about the same during the maxima in 2022 and 2023, around 0.55 mag.

Our spectroscopic observations obtained at the current maximum revealed significant differences when compared to the data from the 2022 event. Particularly, the emission lines of H I and Fe II exhibited higher intensity in contrast to the previous outburst, and faint He I lines reappeared in the spectra. Additionally, the emission lines displayed distinct P-Cygni profiles. On the other hand, a majority of absorption lines observed in the spectra from the previous year appeared diminished or were entirely absent. These observations imply that, during the current brightening, nebular emission has intensified significantly compared to the previous year. The data are available in the ARAS database.

Continued observations of V919 Sgr during its ongoing active stage are strongly encouraged. The current observing season is now almost over, and the system will reemerge in the morning sky in February/March 2024.

Spectra of V919 Sgr in the ARAS database