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Toshihiko TanabÉ, Kentaro Motohara, Ken Tateuchi, Noriyuki Matsunaga, Yoshifusa Ita, Koji Toshikawa, Masahiro Konishi, Natsuko Kato, Yuzuru Yoshii, Paschen α Observations of Be Stars Toward the SMC Cluster NGC 330, Publications of the Astronomical Society of Japan, Volume 65, Issue 3, 25 June 2013, 55, https://doi.org/10.1093/pasj/65.3.55
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We made imaging observations of the young SMC cluster NGC 330 in the near-infrared |$ J$|, |$ H$|, |$ K_{\rm s}$| as well as two narrow-band Pa|$ \alpha $| and Pa|$ \alpha $|-off filters. The observations were carried out at a high-altitude site, 5640 m, where the atmospheric extinction is small enough to make the spectral range around Pa|$ \alpha $| transparent. We present the calibration of specially designed narrow-band filters, and the method used to identify Pa|$ \alpha $| emission using photometric colors. We have successfully detected Pa|$ \alpha $| emission from almost all Be stars within the detection limit of the small telescope and the narrow-band filters. The strength of Pa|$ \alpha $| emission well correlates with that of H|$ \alpha $|, which also confirms the proper detection of Pa|$ \alpha $| emission. This was the first systematic detection of the Pa|$ \alpha $| emission line from Be stars. We also found new candidates of Pa|$ \alpha $| emission-line objects. This work demonstrates that the photometric colors, including the Pa|$ \alpha $| band, can be used to detect the Pa|$ \alpha $| line when observed from high-altitude sites.
