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Spectroscopy of the novae M31N_2008-08a and M31N_2008-08b

ATEL # 1703; F. Di Mille , S. Ciroi (Univ. of Padova), M. Orio (INAF Padova and UW Madison),P. Rafanelli, A. Bianchini (Univ. of Padova),T.Nelson(INAF-Padova and UW Madison), G. Andreuzzi (Fundacion Galileo Galilei - INAF)
on 8 Sep 2008; 9:12 UT
Password Certification: Stefano Ciroi (stefano.ciroi@unipd.it)

Subjects: Optical, Nova

We obtained low resolution spectra of the two optical nova candidates in M31 (see ATEL #1654). The spectra were obtained with the 3.5-m Telescopio Nazionale Galileo of INAF equipped with the DOLORES spectrograph and camera (spectral range 330-790 nm, resolution 1.2 nm) on Aug 17.13 for 2008-08a and on Aug 17.17 for 2008-08b (8 days after the discovery of both novae, which were below the detection limits 2 days earlier).

M31N_2008-08a shows the typical spectrum of a nova in the early decline stage. The lines of the Balmer series and the OI (777.3 nm ) emission line are the strongest features in the spectrum. These lines show a double profile with the blue component brighter than the red one. Gaussian decomposition of the profile of H_alpha gives a FWHM of 1200 km/s and 1350 km/s respectively for the blue and the red component. The presence of the FeII (42) (492.4,501.8, 516.9 nm ) emission lines allows to classify this object as a FeII nova in the Tololo scheme (Williams 1992,AJ,104,725).

The recurrent nova candidate M31N_2008-08b spectrum shows a fairly blue continuum and strong Balmer emission lines up to H_delta. The brightest non-Balmer lines are HeII (468.6 nm)+ C III/N III in blend (464 nm). He I (587.6; 667.5; 706.5) lines are also detectable. The FWHM of H_alpha is 850 km/s while H_beta and the HeII (468.6 nm) lines are narrower, FWHM 400 km/s . The presence of the HeI and HeII lines suggests that the object is quite likely a helium nova. The values of the FWHM of the lines are peculiarly low. The spectrum is similar to the spectra of the recurrent nova V3890 Sgr, taken 10-11 days after maximum by Buckley et al. (1990, IAUC # 5019 ).


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