AAS 207th Meeting, 8-12 January 2006
Session 70 Cataclysmic Variables and Novae
Poster, Tuesday, 9:20am-6:30pm, January 10, 2006, Exhibit Hall

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[70.21] V838 Monocerotis: Still Changing

D. K. Lynch, R. J. Rudy, S. Mazuk, C. C. Venturini (The Aerospace Corp.), L. S. Bernstein (Spectral Scineces, Inc), R. C. Puetter (UCSD/CASS), R. B. Perry (NASA LaRC)

V838 Monocerotis is one of the strangest objects known. It erupted in late 2001 and was initially thought to be a nova. Unlike a nova, however, it quickly cooled and developed molecular absorption lines characteristic of M and L stars (Lynch et al. 2004 ApJ 607, 460-473). Since 2002, the most interesting change in the spectrum is the dramatic weakening and in some cases disappearance of the TiO and VO absorption bands. The AlO bands also weakened, though only slightly. Otherwise, the 2005 spectrum looked superficially similar to 2002 spectra although the J-band continuum switched from being blue-trending upward to red-trending and there was also an over-all lowering of shorter wavelengths relative to the longer ones, perhaps indicating a lower temperature. Water and CO remained the strongest absorption features. As in the infrared, the optical spectrum is dominated by broad absorption features - primarily VO and TiO - and there are only minor changes in the three year period. The object continues to slowly fade, its K magnitude increasing from 4.4 to 5.3 between Dec 2002 and Jan 2005. While V838 Mon is not an L-type star, it has are certain spectral similarities with very cool dwarfs. The CO band structure at 2.3 ┬Ám is similar to those seen in L3-L5 stars in both spectra (Kirkpatrick et al. 1999 ApJ 519, 802). The disappearing TiO and VO bands is suggestive of cooling and a consequent spectral evolution from very late M dwarfs to early-mid L dwarfs.

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