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)

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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).

date and UT	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.