미국 Lick 천문대에서 위상이 다른 세 시기에 공생별 AG Peg을 분광 관측하고 방출선 H I, He II, O III를 조 사하였다. 6개의 O III Bowen 선의 FWHM과 선세기를 측정하고 형광 기작 효율을 연구하였다. 세 시기의 O III 일반 선과 Bowen 선의 평균 FWHM은 큰 차이가 없었으나 선세기 비는 약 4.0 배 정도로 O III Bowen 선이 높았다. O III Bowen 선의 이론적 세기 비와 관측 세기 비를 비교한 결과, O III λ 3759.87만 제외하고 관측한 세기가 이론적 세기보 다 크다는 사실을 알았다. O III λ 3791.26과 3754.67의 선세기 비는 세 시기 중에서 2001년도만이 Saraph and Seaton (1980)의 모델과 잘 일치하였다. 다른 두 시기는 AG Peg의 효율(R)을 구할 수 없었으나 2002년은 R=0.47을 얻었다. 이 때문에, 2002년 효율 결과를 기초로 He II λ 4685.68에 대한 O III 일반선과 Bowen 선의 세기 비를 구하여 시기에 따른 효율 변화를 알아보았다. 그 결과 AG Peg의 효율은 1998년이 가장 높았고 2001년이 가장 낮았다. 결론적으로, 위상에 따른 효율 변화는 이온화된 가스의 전자 온도 변화에 기인하는데, AG Peg의 효율은 전자 온도가 증가함에 따라 증가하고 있다. 우리 연구 결과는 선세기 비 및 효율의 경향성 파악과 공생별에서 이온화된 껍질의 물리적 조건을 이해하는데 사용될 수 있다.

There is much observational evidence that active star formation is taking place in the Hii regions Sh 2-255 – 257. We present a photometric study of this star forming region (SFR) using imaging data obtained in passbands from the optical to the mid-infrared, in order to study the star formation process. A total of 218 members were identified using various selection criteria based on their observational properties. The SFR is reddened by at least E(B −V ) = 0.8 mag, and the reddening law toward the region is normal (RV = 3.1). From the zero-age main sequence fitting method it is confirmed that the SFR is 2.1 ± 0.3 kpc from the Sun. The median age of the identified members is estimated to be about 1.3 Myr from a comparison of the Hertzsprung-Russell diagram (HRD) with stellar evolutionary models. The initial mass function (IMF) is derived from the HRD and the near-infrared (J, J −H) color-magnitude diagram. The slope of the IMF is about 􀀀 = −1.6 ± 0.1, which is slightly steeper than that of the Salpeter/Kroupa IMF. It implies that low-mass star formation is dominant in the SFR. The sum of the masses of all the identified members provides the lower limit of the cluster mass (169M⊙). We also analyzed the spectral energy distribution (SED) of pre-main sequence stars using the SED fitting tool of Robitaille et al., and confirm that there is a significant discrepancy between stellar mass and age obtained from two different methods based on the SED fitting tool and the HRD.

We have investigated the intensities and full width at half maximum (FWHM) of the high dispersion spectroscopic N III emission lines of AG Peg, observed with the Hamilton Echelle Spectrograph (HES) in three different epochs at Mt. Hamilton’s Lick Observatory. The earlier theoretical Bowen line study assumed the continuum fluorescence effect, presenting a large discrepancy with the present data. Hence, we analyzed the observed N III lines assuming line fluorescence as the only suitable source: (1) The O III and N III resonance line profiles near λ 374 were decomposed, using the Gaussian function, and the contributions from various O III line components were determined. (2) Based on the theoretical resonant N III intensities, the expected N III Bowen intensities were obtained to fit the observed values. Our study shows that the incoming line photon number ratio must be considered to balance at each N III Bowen line level in the ultraviolet radiation according to the observed lines in the optical zone. We also found that the average FWHM of the N III Bowen lines was about 5 km·s-1 greater than that of the O III Bowen lines, perhaps due to the inherently different kinematic characteristics of their emission zones.