OGLE-BLG504.12.201843: a possible extreme dwarf nova. Issue 2 (7th October 2022)

• Record Type: Journal Article
• Authors: Landri, Camille; Pejcha, Ondrej; Pawlak, Michał; Udalski, Andrzej; Prieto, Jose L; Barrientos, Manuel; Strader, Jay; Dong, Subo
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 517:Issue 2(2022)
• Page Start: 2746
• Page End: 2756
• Publication Date: 2022-10-07
• Subjects: accretion, accretion discs -- (stars:) binaries (including multiple): close -- stars: dwarf novae -- (stars:) novae, cataclysmic variables; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stac2864
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: We present the analysis of existing optical photometry and new optical spectroscopy of the candidate cataclysmic variable star OGLE-BLG504.12.201843. As was shown previously, this object has an orbital period of 0.523419 d and exhibits year-long outbursts with a mean period of 973 d. Using digitized photographic archives, we show that the earliest recorded outburst occurred in 1910. We propose that this object is a U Gem-type dwarf nova (DN) with extreme properties. The orbital variability of the system in outburst shows clear signs of an accretion disc, from which the outburst likely originates. During quiescence, the object slowly brightens by up to 0.75 mag in the I band over 600 d before the outburst and exhibits small flares with amplitude ≲0.2 mag in the I band. We interpret the gradual brightening as an increase in the luminosity and temperature of the accretion disc, which is theoretically predicted but only rarely seen in DNe. The origin of small flares remains unexplained. The spectra show Balmer absorption lines both in quiescence and outburst, which can be associated with a bright secondary star or a cold accretion disc. During outbursts, emission lines with full width at half-maximum of about 450 km s −1 appear; however, they lack typical double-peaked profiles. We suggest that either these lines originate in the disc winds or the orbital inclination is low, the latter being consistent with constrains obtained from the orbital variability of the system. Due to its extreme properties and peculiarities, OGLE-BLG504.12.201843 is an excellent object for further follow-up studies.