A Survey of Local Group Galaxies Currently Forming Stars. III. A Search for Luminous Blue Variables and Other Hα Emission-Line Stars
A Survey of Local Group Galaxies Currently Forming Stars. III. A Search for Luminous Blue Variables and Other Hα Emission-Line Stars
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DOI：
10.1086/523658
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发表时间：
2007-09
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影响因子：
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通讯作者：
P. Massey;P. Massey;R. McNeill;R. McNeill;R. McNeill;K. Olsen;P. Hodge;C. Blaha;G. Jacoby;R. C. Smith;Shay Strong;Shay Strong;Shay Strong
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作者：
P. Massey;P. Massey;R. McNeill;R. McNeill;R. McNeill;K. Olsen;P. Hodge;C. Blaha;G. Jacoby;R. C. Smith;Shay Strong;Shay Strong;Shay Strong
我们描述了利用KPNO和CTIO 4 m望远镜和马赛克相机的干涉滤光成像，在M31、M33和本星系群或附近的7颗矮星（IC 10、NGC 6822、WLM、六分星B、六分星a、飞马座和凤凰矮星）中搜索Hα发射线恒星。这项调查的主要目的是通过光谱相似性来识别新的发光蓝变量（lbv），避免对光度变化的偏见，如果lbv经历长时间的静止期，这可能需要几个世纪的时间才能显现出来。WIYN的后续光谱学证实，我们的调查发现了大量光谱与已知lbv相似的恒星。我们对已知LBV的光谱进行“分类”，并将其与新的LBV候选者的光谱进行比较。我们展示了几个新的LBV候选者的惊人的光谱变化，比如AM2，以前被归类为Wolf-Rayet星（WR），现在显示出Fe I， Fe II和Balmer发射线，但没有N III λλ4634, 4642和He II λ4686的发射线。对于其他疑似和已知的lbv，也注意到深刻的光谱变化。在过去的10-20年里，一些LBV候选者的V值也出现了0.5 mg的变化。已知或疑似lbv的数量现在是M31中的24个，M33中的37个，ngc6822中的1个，ic10中的3个。我们估计M31和M33中的lbv总数可能有几百个，而历史上通过大规模光度变化已知的lbv只有8个。这对LBV阶段的时间尺度具有重要意义。我们还发现了一些新的wr和特殊的发射天体。
We describe a search for Hα emission-line stars in M31, M33, and seven dwarfs in or near the Local Group (IC 10, NGC 6822, WLM, Sextans B, Sextans A, Pegasus, and the Phoenix dwarf) using interference filter imaging with the KPNO and CTIO 4 m telescopes and Mosaic cameras. The survey is aimed primarily at identifying new luminous blue variables (LBVs) from their spectroscopic similarity to known LBVs, avoiding the bias toward photometric variability, which may require centuries to manifest itself if LBVs go through long quiescent periods. Follow-up spectroscopy with WIYN confirms that our survey detected a wealth of stars whose spectra are similar to the known LBVs. We "classify" the spectra of known LBVs and compare these to the spectra of the new LBV candidates. We demonstrate spectacular spectral variability for several of the new LBV candidates, such as AM2, previously classified as a Wolf-Rayet star (WR), which now shows Fe I, Fe II, and Balmer emission lines but neither the N III λλ4634, 4642 nor the He II λ4686 emission it did in 1982. Profound spectral changes are also noted for other suspected and known LBVs. Several of the LBV candidates also show >0.5 mag changes in V over the past 10-20 years. The number of known or suspected LBVs is now 24 in M31, 37 in M33, 1 in NGC 6822, and 3 in IC 10. We estimate that the total number of LBVs in M31 and M33 may be several hundred, in contrast to the eight known historically through large-scale photometric variability. This has significant implications for the timescale of the LBV phase. We also identify a few new WRs and peculiar emission-line objects.