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C.C. Venturini, D.K. Lynch, R.J. Rudy, R.W. Russell, S. Mazuk, W. Dimpfl (The Aerospace Corporation), M. Sitko (Univ. of Cincinnati), R.C. Puetter (Univ. of Ca San Diego), L.S. Bernstein (Spectral Sciences, Inc.), R.B. Perry (NASA Langley Research Center)
Multiple spectrum of V838 Mon have been obtained from two different instruments providing data with combined wavelength coverage between 0.8 to 14 microns. The first measurements were taken in January 2002 followed by another set of measurements about a year later. Initially, the 3-14 micron spectrum showed a source with a smooth continuum consistent with a black body at about 2350 K and roughly 50 percent excess above the black body fit between the 8 to 10 micron region. Data between 0.8-2.5 microns exhibited a continuum that peaked near one micron (implying a temperature of roughly 3000 K) with a slightly elevated continuum near 1.6 microns suggestive of the H-opacity minimum. The continuum also showed significant broad structure between 0.8 and 1.2 microns. Emission lines present included HI Paschen and weak Bracket lines, many with strong P-Cygni profiles indicating an expansion velocity of around 500 km/sec. Also present were the Ca II IR triplet with strong absorption and weak emission, and deep CO first overtone band absorption near 2.3 microns.
The second set of measurements, taken approximately a year later, revealed a spectrum that had changed dramatically. The hydrogen emission lines had disappeared and the continuum shape indicted that the source had cooled by roughly one-two thousand degrees. Between the two epochs, the K brightness increased by about a factor of three while the N brightness increased by roughly a factor a 20. The source now showed deep molecular absorption bands of H2O, CO, TiO, AlO, VO and probably OH. The AlO bands were particularly prominent: the A-X (4,0) doublet with peak absorptions at 1.225 and 1.244 microns, and the A-X (2,0) doublet at 1.650 and 1.687 microns. CrH and FeH may have been present but methane was not seen. In a years time, V838 Mon went from looking like late type star around 3000 K with weak hydrogen emission from a small expanding shell to an object that was cool enough to show no atomic lines but only a wide range of molecules.
The authors acknowledge the assistance of NASA origins grant NAG 5-9475, the Aerospace Corporation Independent Research and Development program, and the US Air Force Space and Missile Systems Center through the Mission Oriented Investigation and Experimentation program, under contract F4701-00-C-0009.
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Bulletin of the American Astronomical Society, 35 #3
© 2003. The American Astronomical Soceity.