论文标题
高质量原恒星中的甲醇侵占
Methanol deuteration in high-mass protostars
论文作者
论文摘要
在甲醇（Ch $ _3 $ OH）中形成的分子形成的分子的剥离对它们在密集的冷云中形成过程中的物理条件很敏感，并且可以通过观察到热核中的氘代甲醇来探测。与Alma的观察，包含CH $ _3 $ oh，ch $ _2 $ doh，CHD $ _2 $ oh，$^{13} $ ch $ _3 $ oh和ch $ _3^{18} $ OH的观察结果。 CH $ _2 $ DOH，CHD $ _2 $ oh和Ch $ _3 $ oh的列密度均针对所有来源确定，其中Ch $ _3 $ OH的列密度源自光学上的薄$^{13} $ C和$^{18} $ o Isotopologues。因此，考虑到统计效应的甲醇的D/H比。在我们的高质量原恒星样本中，发现了单独剥离的甲醇（Ch $ _2 $ doh），其中25个来源中有25个来源。包括上限，$ \ rm（d/h）_ {ch_3oh} $比率从$ n_ \ mathrm {ch_2doh}/n_ \ mathrm {ch_3oh} $衍生为99个来源中的38个，在$ \ \ sim10^{ - sim10^{ - 3} -10} -10} -2.2^$之间。包括文献中的其他高质量热核，平均甲醇D/H比为$ 1.1 \ pm0.7 \ times10^{ - 3} $。这比低质量原始系统（$ 2.2 \ pm1.2 \ times10^{ - 2} $）低一个数量级。在99个来源中，检测到了倍增的脱耐酸甲醇（CHD $ _2 $ OH）。包括15个来源的上限，$ \ rm（d/h）_ {ch_2doh} $比率衍生自$ n_ \ mathrm {chd_2oh}/n_ \ mathrm {ch_2doh} $均高于$ \ \ rm（d/h h）_ ch_3oh， $ 2.0 \ pm0.8 \ times10^{ - 1} $，类似于低质量来源的$。与文献晶粒模型的比较表明，高质量的prestell阶段要么是温暖（$> 20 $ k），要么比自由下落的时间表短。相比之下，对于低质量原始恒定体，$ <15 $ k的低温和prestell阶段时间尺度都比自由下落时间尺度更长。
The deuteration of molecules forming in the ices such as methanol (CH$_3$OH) is sensitive to the physical conditions during their formation in dense cold clouds and can be probed through observations of deuterated methanol in hot cores. Observations with ALMA containing transitions of CH$_3$OH, CH$_2$DOH, CHD$_2$OH, $^{13}$CH$_3$OH, and CH$_3^{18}$OH are investigated. The column densities of CH$_2$DOH, CHD$_2$OH, and CH$_3$OH are determined for all sources, where the column density of CH$_3$OH is derived from optically thin $^{13}$C and $^{18}$O isotopologues. Consequently, the D/H ratio of methanol is derived taking statistical effects into account. Singly deuterated methanol (CH$_2$DOH) is detected toward 25 of the 99 sources in our sample of the high-mass protostars. Including upper limits, the $\rm (D/H)_{CH_3OH}$ ratio inferred from $N_\mathrm{CH_2DOH}/N_\mathrm{CH_3OH}$ was derived for 38 of the 99 sources and varies between $\sim10^{-3}-10^{-2}$. Including other high-mass hot cores from the literature, the mean methanol D/H ratio is $1.1\pm0.7\times10^{-3}$. This is more than one order of magnitude lower than what is seen for low-mass protostellar systems ($2.2\pm1.2\times10^{-2}$). Doubly deuterated methanol (CHD$_2$OH) is detected toward 11 of the 99 sources. Including upper limits for 15 sources, the $\rm (D/H)_{CH_2DOH}$ ratios derived from $N_\mathrm{CHD_2OH}/N_\mathrm{CH_2DOH}$ are more than two orders of magnitude higher than $\rm (D/H)_{CH_3OH}$ with an average of $2.0\pm0.8\times10^{-1}$ which is similar to what is found for low-mass sources. Comparison with literature GRAINOBLE models suggests that the high-mass prestellar phases are either warm ($>20$ K) or live shorter than the free-fall timescale. In contrast, for low-mass protostars, both a low temperature of $<15$ K and a prestellar phase timescale longer than the free-fall timescale are necessary.
