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Optical Spectroscopy of V959 Mon (2012) in the Nebular Stage

ATel #5499; C. E. Woodward (U. Minnesota), R. M. Wagner (Ohio State U.), R. A. Hounsell (STScI), S. Starrfield (Arizona State U.)
on 22 Oct 2013; 10:09 UT
Credential Certification: R. Mark Wagner (rmw@as.arizona.edu)

Subjects: Optical, Cataclysmic Variable, Nova

Referred to by ATel #: 5500

C. E. Woodward (U. Minnesota), R. M. Wagner (Ohio State U.), R. A. Hounsell (STScI), and S. Starrfield (Arizona State U.) report optical spectroscopy of V959 Mon (Nova Mon 2012) obtained on 2013 September 4.503 UT and 2013 October 21.451 UT using the MDM Observatory 2.4 m Hiltner and the Steward Observatory 2.3 m Bok telescopes respectively on Kitt Peak, Arizona. The MDM spectra (range: 363.5 to 726.0 nm; resolution: 0.9 nm) were obtained using the OSU CCD spectrograph (CCDS) while the Bok spectra (range: 420.0 to 745.0 nm; resolution: 0.63 nm) were obtained using the B&C spectrograph.

V959 Mon was first detected as a γ-ray source by the Fermi/LAT detector on 22 June 2012 (ATEL #4224). Later optical observations (9 August 2012: CBET #3202) reported the discovery of a classical nova past maximum and, subsequently, the realization that the γ-ray source was the nova (ATEL #4310). Continuing observations over the next few months revealed a 7.1 hr X-ray and optical period (ATEL #4727; #4737; #4803; Page et al. 2013, ApJL, 768, L26; Munari et al. 2013, MNRAS, 435, 771) that could be associated with the orbital period of the system. V959 Mon was also identified as an ONe nova by Munari (ATEL #4709) based on the presence of strong [Ne III], [Ne IV], and [Ne V] emission lines. A more complete analysis of early ground based and HST/STIS spectra of V959 Mon was reported by Shore et al. (2013, A&A, 553, A123) who also confirmed the ONe nature.

Our spectra obtained about 1 year later are similar to those reported by Shore et al. (2013) and exhibit broad (FWHM ~2300 km s-1) permitted emission lines of Hα, Hβ, Hγ, and higher order Balmer lines; He II 468.6 and 541.1 nm; He I 706.5, 667.8, 587.5, 471.3, and 447.1 nm; and the C III/N III blend at 464.0-465.0 nm. Broad forbidden emission lines present include [Ne III] 386.9 and 3968 nm; [O III] 495.9 and 500.7 nm; [Fe VII] 515.9 and 608.7 nm; [O I] 630.0 and 636.3 nm; and [Ar III] 713.5 nm.

Based on the MDM spectrum, we find the following integrated intensity ratios relative to Hβ: Hα: 7.7, [OIII] 495.9 nm + 500.7 nm: 28.7, [Ne III] 386.8 nm + 396.5 nm: 4.3, and [Fe VII] 608.7 nm: 0.14. Shore et al. (2013) obtained spectra on 2012 November 20-21 and reported the following intensity ratios with respect to Hβ: Hα: 6.5, [OIII] 495.9 nm + 500.7 nm: 3.8, [Ne III] 386.8 nm + 396.5 nm: 3.6, and [Fe VII] 608.7 nm: 0.11. Therefore, the major change in the spectrum over nearly the past year is the growth in emission of [O III] with respect to Hβ. Its discovery as a γ-ray emitting nova, without a giant secondary (as in V407 Cyg), suggests that this nova is sufficiently interesting for continued monitoring at a broad range of wavelengths as it returns to quiescence.