Contemporaneous high resolution ultraviolet (HST/STIS) and Nordic Optical Telescope (NOT/FIES) spectroscopy of V339 Del = Nova Del 2013 in the Nebular Stage

ATel #6088; 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), D. van Rossum (Univ. of Chicago), M. Bode ([Liverpool John Moores Univ.), C. E. Woodward (Univ. of Minn.), and R. E. Williams (STScI)
on 22 Apr 2014; 02:24 UT
Credential Certification: S. N. Shore (shore@df.unipi.it)

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In our continuing campaign on V339 Del = Nova Del 2013, we obtained nearly simultaneous spectra with HST/STIS (medium resolution echelle, 1150 - 3000A) (ATel#5409,5624) on 2014 Apr. 19.1 UT and the Nordic Optical Telescope (FIES high resolution echelle, 3800 - 7400A) on 2014 Apr. 15.2 UT. The observations occurred after the end of the bright supersoft source phase (ATel#5967). The source continues to fade steadily in X-rays. The count rate with the Swift XRT (0.3-10 keV) was about 0.028 +/- 0.005 on Apr. 13, and 0.022 +/- 0.003 on Apr. 20. The UV and optical 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], 3727, 4363, 4959, 5007, [N II] 5755 (the 6548,6583 doublet is still blended with Halpha but now discernible), N III 4636, [Ar III] 7135, [O II] 7320/7330. The [O I] lines at 6300, 6364A remain visible while O I 1302 is now absent. 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 3000 km/s. The STIS UV spectra show a broad range of ionization stages. The excited state transitions O V] 1371 and He II 1640 show almost identical profiles, two peaks at around -500 and +600 km/s (the same as for the optical lines) with the blue to red peak flux ratio of about unity but with the blue peak broader (about 520 km/s vs. 250 km/s FWHM ). N IV] 1718 is very weak if present. Some of the strongest UV transitions detected (integrated fluxes in units of 1E-11 erg/s/cm^2 with no correction for reddening): N V 1240 (1.4), C II 1335 (0.5), O IV] 1403 (0.3), N IV] 1486 (1.4), C IV 1550 (3.2), He II 1640 (0.3), O II] 1667 (0.2), N III] 1750 (1.3), C III] 1910 (2.7), N II 2143 (0.2), C III 2297 (0.04), C II 2324 (0.6), O II 2470 (showing the same profile as [O II] 7319/7330), Mg II 2800 (0.08). Most lines are about a factor of 10 weaker now than in late Nov. 2013. The line profiles vary systematically, the neutral lines have a FWZI of about 2500 km/s (e.g. O I] 6300, 6364) with weaker emission at positive radial velocities while the higher ionization lines, and the Balmer lines, show FWZI ~ 3000 km/s (e.g. N IV] 1487, C II] 1910) and more distinct emission peaks. The complex blend at 1400 is O IV 1401. Based on the optical [O III] and [N II] lines, the electron density is about 5E6/cm^3 (Te ~ 1E4 K) and the filling factor of the ejecta appears to be moderately high, between 0.3 and 1, although all strong lines show discrete emission features with widths of ~ 200 km/s. The Lyman alpha profile still shows weak emission at positive radial velocities, the absorption is consistent with only an interstellar contribution. The integrated flux (1150-7400A) ~ 4.6E-10 erg/s/cm^2 corresponds to~1.8E-9 erg/s/cm^2 with E(B-V)=0.2 applied corresponding to a band-limited luminosity of about 950 L_sun for a distance of 4.2 kpc (Atel#5410). 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. We thank Anlaug Amanda Djupvik and the staff of the NOT. 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). This research has made use of data obtained from NASA's Swift satellite. We thank Neil Gehrels and the Swift team for generous allotments of ToO and fill in time. Support for Program number 13388 was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555.