ARAS Optical spectroscopy of GK Per in its current dwarf nova-like outburst

ATel #15858; S. N. Shore (Univ. of Pisa), F. Teyssier, J. Guarro Flo, F. Sims, V. Bouttard (ARAS Eruptive Stars group)
on 14 Jan 2023; 16:41 UT
Distributed as an Instant Email Notice Novae
Credential Certification: S. N. Shore (shore@df.unipi.it)

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The intermediate polar cataclysmic variable GK Per (Nova Per 1901) is currently undergoing a dwarf nova-like outburst, detected on 2022 Dec. 12 (JD JD 2459926) in the AAVSO lightcurve. The latest photometry shows this event has not yet ended (V = 11 on 2023 Jan. 11). This outburst occurred 1520 days after the last one in 2018 (Atel #11995 ). Observations have been obtained at resolutions between 1000 and 9000 (echelle) covering the wavelength interval between 3800 and 9200 A with a variety of telescopes. The spectra show strong emission lines of the Balmer series, He I, He II, a strong CIII/NIII 4639-40 blend and a blue continuum. An unidentified feature at 5687A, perhaps C III 5686.6A, shows a flux of 5.7e-14 erg/s/cm^2. A flux calibrated low resolution spectrum (spectrograph LISA R = 1000) yields continuum fluxes of 1.6, 1.47, 1.1 (in units of 1E-13 erg/s/cm^2 at 4440, 5550, 6800 A. The Balmer lines show equivalent widths and fluxes of (17.6 A 1.6e-12 erg/s/cm^2), ( 4.1, 7.9-E13), (2.6, 5.5E-13), (2.5 5.1E-13) for Halpha - Hdelta. He II 4686 is very strong (2.0 E-13) with a ratio HeII/Hbeta = 2.32, compared to HeII/Hb = 0.44 in our last spectrum secured in quiescent state on MJD 2459841; He II 4542 and 5411 are also present. The HeI 5876 A (1.4E-13 erg/s/cm^2) and 6678 A (2.5E-13) lines are the strongest in the series but the full complement are detected. The He I 6678, which is especially strong, shows a variable profile with two peaks at phase 0.75 and a shift consistent with a velocity amplitude of about 50 km/s, about what is expected with the mass ratio of the WD to the companion; the echelle spectra were secured with the NOU-T spectrograph (R = 9000), the phases use the Alvarez-Hernandez+ (2021, MNRAS, 507, 5805) ephemeris. We will continue monitoring the outburst at the highest cadence possible. The spectra are publicly available in ARAS database (see Teyssier, 2019, CoSka, 49, 217), including spectra secured during quiescent state.

ARAS Dwarf Novae: GK Per