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M. Ishii, M. Tamura (National Astronomical Observatory of Japan), T. Nagata, S. Sato (Nagoya University), Y. Yao, Z. Jiang (Purple Mountain Observatory), K. Yanagisawa (Okayama Astrophysical Observatory)
Herbig Ae/Be stars (HAeBes) are intermediate-mass pre-mainsequence stars, many of which show the infrared spectral energy distributions (SEDs) similar to those of low-mass Class II sources. We observed the near-infrared K band spectra of 55 HAeBes to examine their general properties depending on the spectral types, or SEDs.
The 2.02 to 2.35 \mum spectra were obtained with resolution R~500 using Super-OASIS mounted on the 1.88-m telescope at Okayama Astrophysical Observatory. We detected Br\gamma emission, He~I emission (2.05 \mum), CO (2-0) emission and H2 [1-0 S(1)] emission in 87%, 15%, 7%, and 2% of the 55 objects, respectively. The detection rates are similar between Herbig Ae and Herbig Be stars, except for higher rate of He~I in HBes. Neither found we the dependence of the detection rates on the infrared spectral indices [d\log(\lambda F\lambda)/d\log(\lambda) from 2 to 25 \mum] in the HAeBe sample. On the other hand, we found that the detection rate of the H2 emission in the HAeBe sample is much lower than that found in luminous Class I YSOs that are considered to be the precursor of HAeBes (Ishii et al. 2001, AJ, 121, 3191). This indicates that the detection of H2 emission is related to the degree of the dispersal of circumstellar envelopes, where H2 molecules are probably excited by shocks from outflows.
The author(s) of this abstract have provided an email address for comments about the abstract: ishii@optik.mtk.nao.ac.jp
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Bulletin of the American Astronomical Society, 35 #3
© 2003. The American Astronomical Soceity.