ATel #5297


        "Spectroscopy of the very fast Nova Del 2013, already declining past
        maximum brightness"

ATel #5297; U. Munari (INAF Padova), P. Valisa, A. Milani, G. Cetrulo
            (ANS Collaboration) on 17 Aug 2013; 16:07 UT
Credential Certification: U. Munari (ulisse.munari@oapd.inaf.it)

Subjects: Optical, Nova

Nova Del 2013 seems to have reached maximum brightness on August 16.45 UT 
at V=4.3 mag. It immediately entered the decline phase and it is declining 
pretty fast, of the order of 1 mag in a day, qualifying it as a very fast 
nova if the pace will be maintained on the coming days. Also the rise 
toward maximum has been real fast, 2 mag in about 1.5 days according to 
our photometry and AAVSO database. The total outburst amplitude is 12.6 mag 
in V, adopting V=16.9 mag for the progenitor as given by GSC 2.3.2. We are 
monitoring the nova in high resolution with the Echelle spectrographs on 
the Varese 0.61m (res.pow. 18000, range 3900-8600 Ang) and Asiago 1.82m 
(res.pow. 22000, range 3400-7300 Ang) telescopes, and in low resolution 
mode with the Asiago 1.22m (2.3 Ang dispersion, range 3200-7700 Ang) and 
the Polse di Cougnes 0.70cm (1.1 Ang/pix, range 6550-9700 Ang) telescopes. 
The strong CaII (3934, 3968) and NaI (5890, 5896) interstellar lines appear 
single component and have an heliocentric radial velocity of -2.6 +/- 0.2 km/s. 
The equivalent width of NaI 5890 is 0.3945 +/- 0.003 Ang, which corresponds 
to a reddening of E(B-V)=0.182 following the calibration by Munari and Zwitter 
(1997, A&A 318, 269). All strongest diffuse interstellar bands are readily 
visible: 5780 (equivalent width 0.136 Ang), 5797 (e.w. 0.014 Ang), 6196 
(e.w. 0.010 Ang), 6203 (e.w. 0.048 Ang), 6614 (e.w. 0.024). Their low 
intensities confirm the modest reddening affecting the nova, as also 
indicated by the blue energy distribution of the fluxed spectra and the 
low B-V color from photometry. The high Galactic latitude of the nova, 
-9.4 deg, means that the line-of-sight exits the dust layer on the Galactic 
equator well before reaching the nova, which is the main reason for the low 
observed reddening. Extrapolating the rate of decline observed during the 
first 24 hours, the decline time could be as short as t(2)=2 days, which 
would indicate a distance of 5.5 kpc according to the calibration by Cohen 
(1988, ASPC 4, 114) or 3.5 kpc following Della Valle (1991, A&A 252, L9). 
In addition to the description of earlier spectroscopic reports (cf. CBET 
3628, ATel #5279, #5282, #5288, #5291, #5294, #5295), we may note here that: 
(1) line profiles are rapidly and profoundly changing, on time scales of hours, 
both in their absorption and emission components; (2) Tarasova et al. (ATel #5291) 
reported a double peaked Halpha emission for Aug 15.8 UT. Our Echelle spectrum for 
Aug 15.83 shows a flat topped Halpha emission profile (confirming Tomov et 
al. ATel #5288), with - at best - only a feeble trace of a double peak; on Aug 14 
the emission was trapezoidal in shape, on Aug 16 it turned into Gaussian profile; 
(3) HeI lines has weakened during the rise toward maximum: on Aug 14 they displayed 
a marked P-Cyg profile, on Aug 15 the emission component disappeared, and on Aug 16 
also the absorption component vanished; (4) while the equivalent width of the 
absorption component of the P-Cyg profile of Balmer lines have remained essentially 
constant during the rise to maximum, that of emission component has steadily declined: 
for Hbeta it was -24.3 Ang on Aug 14.84, -14.6 Ang on Aug 15.83, -9.1 Ang on Aug 16.85 UT.