The spectroscopic evolution of the symbiotic-like recurrent nova V407 Cygni during its 2010 outburst
II. The circumstellar environment and the aftermath⋆
S. N. Shore1,2, G. M. Wahlgren3,4, T. Augusteijn5, T. Liimets5,6, P. Koubsky7, M. Šlechta7 and V. Votruba7
1 Dipartimento di Fisica “Enrico Fermi”Università di Pisa, largo B. Pontecorvo 3, 56127 Pisa, Italy
2 INFN – Sezione di Pisa, Italy
3 The Catholic University of America, Dept. of Physics, 620 Michigan Ave NE, Washington DC, 20064, USA
4 NASA-GSFC, Code 667, Greenbelt, MD, 20771, USA
5 Nordic Optical Telescope, Apartado 474, 38700 Santa Cruz de La Palma, Santa Cruz de Tenerife, Spain
6 Tartu Observatory, 61602 Tõravere, Estonia
7 Astronomical Institute, Academy of Sciences of the Czech Republic, 251 65 Ondřejov, Czech Republic
Received: 9 September 2011
Accepted: 5 December 2011
Context. The nova outburst of V407 Cyg in 2010 Mar. 10 was the first observed for this star but its close resemblance to the well known symbiotic-like recurrent nova RS Oph suggests that it is also a member of this rare type of Galactic novae. The nova was the first detected at γ-ray energies and is the first known nova explosion for this system. The extensive multiwavelength coverage of this outburst makes it an ideal comparison with the few other outbursts known for similar systems.
Aims. We extend our previous analysis of the Mira and the expanding shock from the explosion to detail the time development of the photoionized Mira wind, circumstellar medium, and shocked circumstellar environment to derive their physical parameters and how they relate to large scale structure of the environment, extending the previous coverage to more than 500 days after outburst.
Methods. We use optical spectra obtained at high resolution with the Nordic Optical Telescope (NOT) (R ≈ 45 000 to 65 000) and medium resolution Ondřejov Observatory (R ≈ 12 000) data and compare the line variations with publicly available archival measurements at 30 GHz OVNR and at X-rays with Swift during the first four months of the outburst, through the end of the epoch of strong XR emission. We use nebular diagnostics and high resolution profile variations to derive the densities and locations of the extended emission.
Results. We find that the higher the ionization and/or the higher the excitation energy, the more closely the profiles resemble the He II/Ca V-type high velocity shock profile discussed in Paper I. This also accounts for the comparative development of the [N II] and [O III] isoelectronic transitions: the [O III] 4363 Å profile does not show the low velocity peaks while the excited [N II] 5754 Å does. If nitrogen is mainly N+3 or higher in the shock, the upper state of the [N II] nebular lines will contribute but if the oxygen is O+2 then this line is formed by recombination, masking the nebular contributor, and the lower states are collisionally quenched but emit from the low density surroundings. Absorption lines of Fe-peak ions formed in the Mira wind were visible as P Cyg profiles at low velocity before Day 69, around the time of the X-ray peak and we identified many absorption transitions without accompanying emission for metal lines. The H Balmer lines showed strong P Cyg absorption troughs that weakened during the 2010 observing period, through Day 128. The Fe-peak line profiles and flux variations were different for permitted and forbidden transitions: the E1 transitions were not visible after Day 128 but had shown a narrow peak superimposed on an extended (200 km s-1) blue wing, while the M1 and E2 transitions persisted to Day 529, the last observation, and showed extended redshifted wings up of the same velocity. We distinguish the components from the shock, the photoionized environment, and the chromosphere and inner Mira wind using spectra taken more than one year after outburst. The multiple shells and radiative excitation phenomenology are similar to those recently cited for GRBs and SNIa.
Key words: binaries: symbiotic / gamma-ray burst: general / novae, cataclysmic variables / stars: individual: V407 Cygni
© ESO, 2012