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Recent Optical Spectroscopy of V339 Del 2013

ATel #5493; C. E. Woodward (U. Minnesota), R. M. Wagner (Ohio State U.), R. A. Hounsell (STScI), S. Starrfield (Arizona State U.)
on 21 Oct 2013; 07:19 UT
Credential Certification: R. Mark Wagner (rmw@as.arizona.edu)

Subjects: Optical, Cataclysmic Variable, Nova

Referred to by ATel #: 5546

C. E. Woodward (U. Minnesota), R. M. Wagner (Ohio State U.), R. A. Hounsell (STScI), S. Starrfield (Arizona State U.) report optical spectroscopy of V339 Del obtained on on 2013 October 20.14 UT using the Steward Observatory 2.3 m Bok telescope on Kitt Peak with the B&C spectrograph covering the spectral range 325.0 to 925.0 nm at a spectral resolution of ~0.63 nm. In addition, we obtained an earlier spectrum of V339 Del on 2013 September 5.14 UT with the 2.4 m Hiltner telescope of the MDM Observatory on Kitt Peak using the OSU CCD spectrograph (CCDS) and covering the spectral range 320.0 to 965.0 nm at a spectral resolution of 0.9 nm.

Comparing the spectra between these two epochs, we find that the entire optical spectral energy distribution has faded. V339 Del is evolving towards the nebular stage. The 2013 September 5.14 UT spectrum is qualitatively similar to that described by Shore et al. (ATEL #5378) but at lower resolution and exhibits strong permitted emission lines of H, Fe II, O I 844.6 and 777.4 nm as well as many weaker features. The Hα profile is nearly Gaussian in shape with a FWHM of about 1300 km s-1 while the higher order Balmer and Fe II emission lines exhibit a weak P-Cygni profile. No castellated structure is apparent at this spectral resolution. In addition, weak forbidden lines of [O I] 630.0 and 636.3 nm may also be present.

In the 2013 October 20.14 UT spectrum, the strongest observed emission line is Hα with a peak flux of nearly 8 × 10-12 erg cm-2 s-1 Å-1 followed by Hβ at ~2 × 10-12 erg cm-2 s-1 Å-1. O I 844.6 nm is present indicating that Lyβ must still be strong. O I 777.4 nm is weak or absent. We also see higher order Paschen series emission lines in the October spectrum. Over the last month since our MDM spectroscopy, the [O III] lines at 495.9 and 500.7 nm have appeared and are likely strengthening as the density in the ejected gases declines. The tops of the emission lines profiles show castellated structure suggestive of asymmetric ejection. Finally, the complex of lines at around 464.0 nm which are typical of a classical nova in the nebular stage are present. However, He II 468.6 nm is not present, commensurate with recent Swift observations of weak emission at both hard and soft X-rays reported by Page et al. (ATEL #5470). The continued fading and interesting evolution of V339 Del's spectrum suggests that further observations are warranted.