We present medium resolution (1000) K-band spectra of 12 post-AGB candidates and related stars. For several objects in our sample, these spectra were obtained for the first time. The Br$\gamma$ line in emission is detected in seven objects indicating the onset of photo-ionization in these objects. Four objects show the presence of He i line. We detect H2 emission line in the spectra of IRAS 06556+1623, IRAS 22023+5249, IRAS 18062+2410 and IRAS 20462+3416. H2 emission line ratio 1-0 S(1)/2-1 S(1) indicate that H2 is radiatively excited due to the UV radiation of hot post-AGB central stars. When compared with the recent observations by other investigators, the Br$\gamma$ and H2 emission fluxes varied in some of the objects. The hot post-AGB stars IRAS 22495+5134, IRAS 22023+5249, IRAS 18062+2410 and IRAS 20462+3416 seem to be evolving rapidly to young low excitation planetary nebula phase. The spectra of the objects presented in this paper may be useful for future observers as some of these stars show spectral variation and since the post-AGB evolution of some of these stars is relatively rapid.

中文翻译：

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选定的 AGB 后候选者的 K 波段光谱

我们展示了 12 颗 AGB 后候选恒星和相关恒星的中等分辨率 (1000) K 波段光谱。对于我们样本中的几个物体，这些光谱是第一次获得。在七个物体中检测到发射中的 Br$\gamma$ 线，表明这些物体中光电离的开始。四个物体显示了 He i 线的存在。我们在 IRAS 06556+1623、IRAS 22023+5249、IRAS 18062+2410 和 IRAS 20462+3416 的光谱中检测到 H2 发射谱线。H2 发射线比率 1-0 S(1)/2-1 S(1) 表明 H2 因 AGB 后中心恒星的紫外线辐射而被辐射激发。与其他研究人员最近的观察相比，一些物体的Br$\gamma$和H2排放通量不同。AGB 后的热门恒星 IRAS 22495+5134、IRAS 22023+5249、IRAS 18062+2410 和 IRAS 20462+3416 似乎正在迅速演化到年轻的低激发行星状星云阶段。本文中提出的天体的光谱可能对未来的观察者有用，因为其中一些恒星显示光谱变化，并且其中一些恒星的后 AGB 演化相对较快。