High resolution spectroscopy and BVRI photometry of
                Fermi J0639+0548 = Nova Mon 2012

ATel #4320; U. Munari (INAF Astr. Obs. Padova),
            S. Dallaporta, P. Valisa (ANS Collaboration)
on 20 Aug 2012; 21:11 UT Credential Certification: U. Munari (ulisse.munari@oapd.inaf.it)

Subjects: Optical, Gamma Ray, Nova, Transient

The coincidence between the new gamma-ray transient Fermi J0639+0548,
discovered on June 22 by the Fermi Large Area Telescope (Cheung et al. 2012, 
ATel #4224) and Nova Mon 2012 discovered by S.  Fujikawa on Aug. 9.805 UT 
(and announced on Aug 17 via CBET #3202) when it was emerging from
the conjunction with the Sun, has been recently pointed out by Cheung et al. 
(2012, ATel #4310), who also note how this is only the third known case
(after V407 Cyg and Nova Sco 2012) of gamma-ray transient detection from a
nova by Fermi-LAT.

Soon after the announcement of its discovery was posted to the net, we begun
monitoring Nova Mon 2012 with telescopes operated by ANS Collaboration
(described by Munari et al.  2012, BaltA 21, 13).  The following table
summarize the BVRcIc photometry collected so far.  A BVRcIc comparison
sequence was established around Nova Mon 2012 from APASS BVgri Survey data
following the transformation equations given in Munari (2012, JAVSO tmp
206).

 UT date          V      B-V     V-Rc    V-Ic
2012 08 16.141  10.009                  1.758
2012 08 17.143  10.025  0.104   1.603   1.723
2012 08 19.125   9.985  0.078   1.590   1.675
2012 08 20.128  10.037  0.121   1.605   1.659

It is worth noticing that (1) the value of B-V is consistent with a limited
reddening, (2) the 0.05 mag amplitude, day to day fluctuations are larger
than the total error budgets of the individual measurements (<0.01 mag), and
(3) the current decline rate is very slow, consistent with the >50 days
passed since the source was first detected in the gamma-rays.

We have also obtained a high resolution Echelle spectrum of Nova Mon 2012 on
August 20, 03:25 UT, with the Multi-Mode Spectrograph mounted on the 0.6m
telescope of the Schiaparelli Observatory in Varese (Italy), operating in
binned mode at a resolving power of 11,000.  The integrated flux [in
erg/(cm**2 sec Ang)] and the FWHM (in km/sec) of the strongest emission
lines are:

 line             flux          FWHM
Hgamma          3.55e-11        2168
Hbeta           5.78e-11        2195
[OIII] 5007     5.89e-11        3035
NII 5680        1.16e-11        2605
[NII] 5755      2.03e-11        2500
HeI 5876        4.06e-11        2380
[OI] 6300       5.24e-12        2260
Halpha          9.42e-10        2085
HeI 6678        1.39e-11        2200
HeI 7065        4.77e-11        2190
[OII] 7325      9.29e-11        2395
OI 7772         2.90e-11        2150
OI 8446         1.02e-10        2005

The emission lines generally show saddle-like profiles, with noticeable
differences among them. The large OI 8446/7772 ratio indicates pumping by
Ly-beta fluorescence. At the 11,000 resolving power of our spectrum, the
interstellar lines appear as unblended, single-component. The 0.49 Ang
equivalent width of interstellar NaI 5890 corresponds to a reddening of
E(B-V)=0.30 following the calibration by Munari and Zwitter (1997, A&A 318,
269). The heliocentric velocity of interstellar NaI is +25 km/sec,
consistent with the absorption medium being centered at a distance of about
1 kpc from the Sun.