Simultaneous high resolution ultraviolet (HST/STIS) and Nordic Optical Telescope spectroscopy of V339 Del = Nova Del 2013

ATel #5624; S. N. Shore (Univ. of Pisa and INFN-Pisa), G. J. Schwarz (AAS), S. Starrfield (Arizona State Univ.), F. M. Walter (SUNY-Stony Brook), K. L. Page and J. P. Osborne (Univ. of Leicester), J-U. Ness (ESA), E. Mason (INAF-Trieste), D. van Rossum (Univ. of Chicago), M. Bode ([Liverpool John Moores Univ.), and C. E. Woodward (Univ. of Minn.)
on 4 Dec 2013; 01:55 UT
Distributed as an Instant Email Notice Novae
Credential Certification: S. N. Shore (shore@df.unipi.it)

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In our continuing campaign of observations of V339 Del = Nova Del 2013, we have obtained simultaneous spectroscopy with HST/STIS (medium resolution echelle, 1150 - 3000A) (ATel#5409) and the Nordic Optical Telescope (FIES high resolution echelle, 3800 - 7400A) on 2013 Nov. 21. The nova was well into the supersoft phase at the time of the observations (ATel#5573), and showed a countrate with the Swift XRT of about 32 c/s at the time of the HST observation. The spectra show that the nova is now in the nebular stage with the dominant optical lines being hydrogen Balmer, He I, He II, O III] 4363, 4959, 5007, [N II] 5755 (the 6548,6583 doublet is still severely blended with Halpha), and N III 4636. The rich emission line spectrum also includes the [O I] lines at 6300, 6364. The Balmer profiles are similar to those of He I: asymmetric with the blue side of the line being about a factor of two stronger than the red and FWZI of about 4000 km/s. The STIS UV spectra show a broad range of ionization stages. The excited state transitions O V] 1371, N IV] 1718, and He II 1640 show almost identical profiles, two peaks at around -600 and +600 km/s (as for the optical lines) with the blue to red peak ratio of about 3. Some of the strongest UV transitions detected (with uncorrected integrated fluxes in units of 1E-11 erg/s/cm^2): N V 1240 (22), O I 1302 (0.8), C II 1335 (4.8), N IV] 1486 (16.3), C IV 1550 (32.0), He II 1640 (2.4), O II] 1667 (2.9), N III] 1750 (17.0), C III] 1910 (28.0), N II 2143 (2.3), C III 2297, C II 2324 (5.5), O II 2470, O IV 2510/2517, He II 2733, Mg II 2800 (1.3), C II 2837, F III 2932. The line profiles vary systematically, the neutral lines have a FWZI of about 2500 km/s (e.g. O I] 6300, 6364) while the higher ionization lines, and the Balmer lines, show FWZI ~ 4000 km/s (e.g. N IV] 1487, C II] 1910). The complex blend at 1400 is primarily O IV 1401 but possibly has a contribution from S IV; the Si IV doublet is absent. The stronger peak on the blue side of the line, at around -600 km/s, is at about half the radial velocity of the H and He-like ions reported in absorption from the Chandra observations (ATel#5593). If this is absorption from the ejecta instead of from the white dwarf photosphere, it would explain the systematic asymmetries in the higher ion profiles (the neutral and low ionization potential species are more symmetric and narrower in velocity). The filling factor of the ejecta appears to be moderately high, around 0.1 to 0.5, even though all strong profiles show discrete emission features with FWHM ~ 200 km/s. These are consistent across all of the permitted and intercombination transitions; the forbidden lines (e.g. [O III] 4959, 5007) show far lower contrast between the discrete features and the broader profile and a greater ratio of the blue to red emission peak at +/-600 km/s. The Lyman alpha profile is consistent with only interstellar absorption with N_H ~ 1E21/cm^2. Based on observations made with the Nordic Optical Telescope, operated by the Nordic Optical Telescope Scientific Association at the Observatorio del Roque de los Muchachos, La Palma, Spain, of the Instituto de Astrofisica de Canarias. The research leading to these results has received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement No. 312430 (OPTICON).