Optical Spectroscopy of GK Per (Nova Per 1901) during the 2015 Outburst
ATel #7217; A. Wilber (ASU), M. Neric (ASU), S. Starrfield (ASU), R. M. Wagner (LBTO/OSU), C. E. Woodward (Minnesota)
on 13 Mar 2015; 04:32 UT
Credential Certification: R. Mark Wagner (rmw@as.arizona.edu)
Subjects: Optical, Cataclysmic Variable, Nova
On 2015 March 6.84 UT, Dubovsky (VSNET-ALERT 18388) and Schmeer (VSNET-ALERT 18389) discovered that the old nova and intermediate polar cataclysmic variable GK Per (Nova Per 1901) was in outburst at a magnitude of 12.8. GK Per undergoes dwarf nova outbursts on time scales of 1-2 years with optical amplitudes of 2-3 magnitudes that last several months. Previous outbursts were recorded in 2006 (ATEL #965) and 2010 (ATEL #2466) as well as a weak outburst in 2013. An analysis of the optical and X-ray outbursts of GK Per was recently presented by Šimon (2015, A&A, 575, A65).
We obtained an optical spectrum (range: 398-685 nm; resolution 0.3 nm) of GK Per during the current outburst on 2015 March 10.326 UT with the 2.4 m Hiltner Telescope (+OSMOS) of the MDM Observatory on Kitt Peak. Our spectrum shows strong, single-peaked emission lines of the Balmer series of hydrogen; He I 447.1, 471.3, 492.1, 501.5, 587.5, and 667.8 nm; He II 468.6 and 541.1 nm; and N III 464.0 nm. In addition, the absorption lines of Na I D are prominent. He II 468.6 nm emission is quite strong with an equivalent width of 1.2 nm and with an intensity ratio with respect to Hβ of about 1.8. The resolution-corrected FWHM of He II 468.6 nm and Hα are about 650 km/s and 507 km/s respectively.
A comparison of our spectrum of GK Per with the spectra presented by Reinsch (1994, A&A, 281, 108) as well as a spectrum (range: 320-670 nm; resolution 0.5 nm) obtained in quiescence by some of us in October 1995 at the 4.5 m MMT typically show that the intensity ratio of He II 468.6 nm to Hβ is about 0.4-0.5. These spectra also exhibit absorption lines arising from the K2-type secondary star which contributes about 1/3 of the total light of the system at optical wavelengths (see Reinsch 1994 and references therein). Our spectrum obtained during the outburst shows no evidence of the secondary star since the system is brighter at the present time. Additional photometric, spectroscopic, and X-ray observations are encouraged during the current outburst.