arXiv 2401.069502024-01-13astro-ph.SRastro-ph.GA

基于Spitzer/IRS恒星光谱的硅酸盐消光轮廓

Silicate Extinction Profile Based on the Stellar Spectrum by Spitzer/IRS

Zhenzhen Shao, Biwei Jiang

AI总结：

本文利用Spitzer/IRS光谱和配对法测定49颗恒星的9.7μm及18μm硅酸盐消光轮廓，揭示其峰值波长、光学深度与色余的关系，并验证了方法与大气模型SED替代参考星的一致性。

摘要：

9.7μm和18μm星际光谱特征源自非晶硅酸盐尘埃的Si--O伸缩振动和O--Si--O弯曲振动模式，是红外波段最强的消光特征。本文使用“配对法”，通过比较49颗具有明显消光的目标星的Spitzer/IRS光谱与相同光谱型且未红化的恒星光谱，来确定硅酸盐消光轮廓。9.7μm消光轮廓由全部49颗恒星确定，18μm轮廓由6颗恒星确定。研究发现，该轮廓的峰值波长分别位于约9.2--9.8μm和约18--22μm。9.7μm特征的峰值波长似乎随晚型光谱型恒星而变短，同时半高全宽（FWHM）似乎与光谱型无关，这可能与星周硅酸盐发射有关。9.7μm处的硅酸盐光学深度Δτ_{9.7}大多随J-K_S色余（E_{JK_S}）的增加而增大。可见消光与9.7μm硅酸盐吸收光学深度的平均比值为A_V/Δτ_{9.7}≈17.8，与太阳邻域弥散星际介质的比值高度一致。当E_{JK_S} > 4时，这一比例关系发生变化。9.7μm特征的峰值波长与FWHM之间的相关系数为0.4，考虑到参数的不确定性，这表明二者存在正相关。将该方法与用大气模型光谱能量分布（SED）替代参考星的方法进行了比较，未发现显著差异。

英文摘要：

The 9.7$μm$ and 18$μm$ interstellar spectral features, arising from the Si--O stretching and O--Si--O bending mode of amorphous silicate dust, are the strongest extinction feature in the infrared. Here we use the "pair method" to determine the silicate extinction profile by comparing the \emph{Spitzer}/IRS spectra of 49 target stars with obvious extinction with that of un-reddened star of the same spectral type. The 9.7$μm$ extinction profile is determined from all the 49 stars and the 18$μm$ profile is determined from six stars. It is found that the profile has the peak wavelength around $\sim$9.2- 9.8$μm$ and $\sim$18-22$μm$ respectively. The peak wavelength of the 9.7$μm$ feature seems to become shorter from the stars of late spectral type, meanwhile the FWHM seems irrelevant to the spectral type, which may be related to circumstellar silicate emission. The silicate optical depth at 9.7$μm$, $Δτ_{9.7}$, mostly increases with the color excess in $J-K_S$ ($E_{\rm JK_S}$). The mean ratio of the visual extinction to the 9.7$μm$ silicate absorption optical depth is $A_{\rm V}/Δτ_{9.7}\approx 17.8$, in close agreement with that of the solar neighborhood diffuse ISM. When $E_{\rm JK_S}$ > 4, this proportionality changes. The correlation coefficient between the peak wavelength and FWHM of the 9.7$μm$ feature is 0.4, which indicates a positive correlation considering the uncertainties of the parameters. The method is compared with replacing the reference star by an atmospheric model SED and no significant difference is present.

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