Nova Cephei 2013 has emerged from dust obscuration
ATel #5389; U. Munari, P. Ochner (INAF Padova-Asiago), A. Siviero (Univ. Padova, Asiago), M. Graziani, S. Dallaporta, G. L. Righetti, G. Cherini, F. Castellani (ANS Collaboration)
on 12 Sep 2013; 17:07 UT
Credential Certification: U. Munari (ulisse.munari@oapd.inaf.it)
Nova Cep 2013 was discovered by K. Nishiyama and F. Kabashima on Feb 2.4
UT at 10.3 unfiltered magnitude (CBET #3397). After maximum brightness was
reached around Feb 4.2 UT at B=13.15, V=11.23, Rc=9.94 and Ic=8.81, the nova
begun a normal decline that was interrupted by dust forming in the ejecta
when the nova was 3.4 mag below maximum in V band (cf. Munari et al. ATel
#4893). The formation of dust was later confirmed by infrared observations
(Raj et al. ATel #5026; Ninan et al. ATel #5269). Attempts to detect the
nova at radio wavelengths and in the X-rays have been reported by Chomiuk et
al. (ATel #4950) and Dutta et al. (ATel #5375).
We have followed the BVRcIc photometric evolution of the nova during the
dust formation with various ANS Collaboration telescopes. In a matter of only
a few days after the onset of dust formation, the nova dropped
below optical detection. Our last attempt on Apr 12.3 UT to detect it
provided an upper brightness limit of V>19.5. In the following months
sparse revisits were paid to the nova field looking for its emergence from
dust obscuration.
The first positive detection of the nova occoured on Aug 17, after which
the photometric observations were conducted also with the Asiago 67/92cm
Schmidt telescope in addition to the ANS Collaboration telescopes. The last set
of observations collected between Sep 4 and 7 allow measure the nova at average
B=20.0, V=18.25, Rc=17.22, Ic=16.68. The red colors seem primarily a
consequence of the large interstellar reddening affecting the nova.
Preliminary low resolution spectra (2.3 Ang/pix, range 3200-7700 Ang) of
the nova after the emergence from dust obscuration were obtained with the
Asiago 1.22m + B&C spectrograph on Sept 7 and 11. Given the faintness of
the nova, its red color and the short exposure times (30 min), the spectrum
of the nova is recorded only longword of 4700 Ang. It is of the nebular
type, dominated by the emission lines of Hbeta, Halpha, [OIII] 4959 and 5007
Ang, [NII] 5755, and [OII] 7325. The emission line profiles are all similar
and double peaked. The velocity separation of the two peaks ranges from the
1000 km/s of Halpha to 1210 km/s for [OIII], and the width at half
maximum from 1670 km/s of Halpha to 1880 km/s for [OIII]. The full
width at zero intensity of emission lines is about 3400 km/s.
