REMARKABLE CHANGES IN THE NEAR-INFRARED SPECTRUM OF THE NOVA-LIKE VARIABLE V4332 SAGITTARII

摘要

We report on recent near-IR observations of V4332 Sgr-the nova-like variable that erupted in 1994. Its rapid, post-outburst evolution to a cool M-type giant/supergiant, soon after its outburst, showed that it was an unusual object differing from other eruptive variables, such as classical/symbiotic novae or born-again asymptotic giant branch stars. The present study of V4332 Sgr was motivated by the keen interest in the recent eruption of V838 Mon-an object with a spectacular light echo that, along with V4332 Sgr, is believed to belong to a new class of objects (we propose that they be called "quasi novae"). Our observations show new developments in the evolution of V4332 Sgr. The most striking feature is the detection of several molecular bands of AlO-a rarely seen molecule in astronomical spectra-in the JHK spectra. Many of these bands are being detected for the first time. The only other detection of some of these AlO bands is in V838 Mon, thereby showing further spectral similarities between the two objects. JHK photometry shows the development of a new dust shell around V4332 Sgr with a temperature of ～900 K and a lower limit on the derived mass of M_(dust) = 3.7 x 10~(-12) solar mass. This dust shell does not appear to be associated with ejecta of the 1994 outburst but is due to a second mass-loss episode, which is not expected in a classical nova outburst. The cold molecular environment, suggested by the AlO emission, is also not expected in novae ejecta. We model the AlO bands and also discuss the possible formation mechanism of the AlO. These results show the need to monitor V4332 Sgr regularly for unexpected developments. The results can also be significant in predicting possible changes in the future evolution of V838 Mon.