Spectrum of the Novalike Variable ASASSN-V J205457.73+515731.9

ATel #13923; Howard E. Bond (Penn State U)
on 7 Aug 2020; 22:12 UT
Credential Certification: Howard E. Bond (heb11@astro.psu.edu)

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ASASSN-V J205457.73+515731.9 (hereafter ASASJ2054) is a newly discovered variable star, recently found to be undergoing a dimming episode during the All Sky Automated Survey for SuperNovae. It was announced by Jayasinghe et al. in ATel 13824. An earlier, shallower dip was seen in 2017. Such dips are characteristic of the VY Sculptoris class of cataclysmic variables (CVs).

In ATel 13825, I pointed out that ASASJ2054 appears to be associated with a faint extended nebula, previously uncataloged. The variable lies near the western edge of the nebula, which measures about 3x4 arcmin. The system thus appears to be similar to the novalike stars BZ Cam and V341 Ara, which are also associated with faint nebulae.

In ATel 13829, Denisenko discussed the appearance of the nebula in H-alpha and broadband images obtained in the IPHAS project. He also pointed out a nearby 12th-mag star, TYC 3587-837-1, whose proper motion would place it near ASASJ2054 and the center of the nebula some 6450 years ago.

Spectrograms of both stars were obtained on 2020 August 6 UT with the low-resolution spectrograph, LRS2-B, on the Hobby-Eberly Telescope (HET) at McDonald Observatory (Resident Astronomer S. Rostopchin; Telescope Operator J. Pautzke). The ASAS-SN light curve (https://asas-sn.osu.edu) shows that ASASJ2054 was at about g=14.2 at the time of the HET observation, which is some 0.4 mag fainter than its normal brightness level of g=13.8 (Jayasinghe et al.).

The spectrum of ASASJ2054 shows strong Balmer emission lines, superposed on shallow, broad absorption features at H-beta and shortward. Typical full widths at half maximum for the Balmer emission lines are about 8.4 A (600 km/s). Several sharper emission lines of He I are present. The spectrum is somewhat similar to that of V341 Ara, but the emission lines are considerably stronger. This is consistent with the spectroscopic behavior of dwarf-nova-type CVs at a brightness level intermediate between maximum and quiescence.

The neighboring star TYC 3587-837-1 shows a spectral type of about F8 IV, with no obvious peculiarities.

In summary, the HET spectrum confirms that ASASJ2054 is a novalike variable, which is normally in a high-luminosity state, but currently about 0.4 mag fainter. It is remarkably similar to V341 Ara in being a novalike variable lying well off-center in a faint extended nebula.

Based on observations obtained with the Hobby-Eberly Telescope, which is a joint project of the University of Texas at Austin, the Pennsylvania State University, Ludwig-Maximilians-Universitat Munchen, and Georg-August-Universitat Gottingen. The HET is named in honor of its principal benefactors, William P. Hobby and Robert E. Eberly.