2006CBET..780....1M

U. Munari, Istituto Nazionale di Astrofisica, Padova Astronomical Observatory; R. L. M. Corradi, Isaac Newton Group (ING), La Palma; A. Henden, AAVSO; and I. G. de la Rosa and A. Vazdekis, Instituto de Astrofisica de Canarias, report that two high-S/N spectra of V838 Mon were obtained on Dec. 18.09 UT with the 4.2-m William Herschel Telescope of the ING at the Observatorio del Roque de los Muchachos, La Palma, using the ISIS spectrograph. A 600-lines/mm grating was used to cover the spectral range from 386 to 554 nm at a resolution of 0.16 nm. The spectrophotometric standard G191-B2B was also observed to flux-calibrate the spectra of V838 Mon. For the first time since the eruption in January 2002, the spectra now display a forest of very strong Fe II and [Fe II] emission lines (far stronger than Balmer lines) on top of the cool continuum of the L-type supergiant dominated by molecular absorptions. Fully developed Fe II multiplets 27, 28, 37, 38, 42, 48, and 49 are observed at heliocentric radial velocity +30.8 (± 1.1) km/s, and [Fe II] multiplets 4, 6, 7, 18, 19, 20, and 21 are observed at +30.3 (± 0.7) km/s. The emission lines are intrinsically sharp enough to be not resolved. The integrated flux of the H_beta emission line is 1.6 x 10**(-15) erg/cm2/s. The integrated flux of [Fe II] 428.740-nm (multiplet 7) is 5.3 times that of H_beta, and for Fe II 531.661-nm (multiplet 49) is 5.5 times that of H_beta. Compared to the situation in December 2005, as described by Barsukova et al. (http://www.astronomerstelegram.org/?read=803), now [Fe II] multiplet 21 emission lines are 9.5 times stronger. The spectrum of the B3 V companion has weakened sensibly, being now just slightly perceptible. Magnitudes obtained with the Sonoita Research Observatory 0.35-m robotic telescope (errors not exceeding 0.02 mag): Oct. 26.409, V = 15.207, B-V = +0.918, V-R_c = +2.111, R_c–Ic = +2.767; Nov. 23.337, 15.560, +1.363, +2.408, +2.869; Dec. 19.276, 15.742, +1.608, +2.568, +2.882; Dec. 20.297, 15.786, +1.852, +2.595, +2.886. The sudden fading and reddening at blue wavelengths announced by Goranskij (http://www.astronomerstelegram.org/?read=964) and Bond (http://www.astronomerstelegram.org/?read=966) is confirmed. The average fading in B since Oct. 26 is 0.025 mag/day, and reddening in B-V is 0.015 mag/day. The decline in the B band is clearly associated with the disappearance of the B3 V spectrum at shorter wavelengths, while the L-type supergiant has remained stable in brightness at R_c within 0.03 magnitude of around 13.15.