High-J CO survey of low-mass protostars observed with Herschel-HIFI
High-J CO survey of low-mass protostars observed with Herschel-HIFI
复制标题
用 Herschel-HIFI 观测低质量原恒星的高 J CO 调查
DOI：
10.1051/0004-6361/201220849
复制
发表时间：
2013
影响因子：
6.5
通讯作者：
M. Hogerheijde
中科院分区：
文献类型：
--
作者：
U. Yıldız;L. Kristensen;E. Dishoeck;I. Jose;A. Karska;D. Harsono;M. Tafalla;A. Fuente;R. Visser;J. Jørgensen;M. Hogerheijde
语境。在恒星形成的深埋阶段，原恒星开始加热并驱散周围的云核。传统上，这些源的演化是通过尘埃连续谱能量分布（SED）来追踪的，但由于缺乏高 J CO 观测，尚未探索使用 CO 激发作为演化探针。
目的：目的是使用 CO 的光谱解析赫歇尔数据来约束低质量原恒星包层中温暖气体的物理特征（激发、运动学、柱密度），并将其与由较低激发线追踪的较冷气体进行比较。
方法：对 $^{12}$CO、$^{13}$CO 和 C$^{18}$O 的高 J 线（最高 J$_u$ = 10，E$_u$ 最高 300 K）进行 Herschel-HIFI 观测，针对 26 个深埋的低质量 0 级和 I 级年轻恒星天体，作为赫歇尔 (WISH) 关键计划的恒星形成区水的一部分获得。这是针对此类源进行的首次大型光谱分辨高 J CO 调查。使用地面望远镜（例如 JCMT 和 APEX）观察互补的较低 J CO 地图，并进行卷积以匹配光束尺寸。
结果：所有物体都检测到 $^{12}$CO 10-9 谱线，并且由于静态包络线和夹带的流出材料，通常可以分别分解为窄分量和宽分量。 $^{12}$CO 激发温度随着速度从 ~{}60 K 增加到 ~{}130 K。从单温度拟合 J$_u$ = 2-10 积分强度得出的 $^{12}$CO、$^{13}$CO 和 C$^{18}$O 的中值激发温度分别为 ~{}70 K、48 K 和 37 K，0 类和 Class 之间没有显着差异我使用 M$_{env}$ 或 L$_{bol}$ 获取数据，但没有趋势。因此，与连续 SED 相比，谱线能量分布 (SLED) 在嵌入阶段没有显示任何演变。相比之下，随着包膜的分散，所有CO同位素同位素的积分线强度随着进化阶段明显下降。原恒星包膜的塌缩和演化模型很好地再现了 C$^{18}$O 结果，但由于这些模型中缺乏紫外线加热和流出分量，因此无法产生 $^{13}$CO 和 $^{12}$CO 激发温度。与 H$_{2}$O/CO 3-2 比率相反，H$_{2}$O 1$_{10}$ - 1$_{01}$/CO 10-9 强度比不随速度显着变化，表明 CO 10-9 是线翼探测与 H$_{2}$O 相同的热冲击气体的最低跃迁。全套 C$^{18}$O 线的建模表明 0 类源的丰度概况与低于 25 K 的冻结区和较高温度下的蒸发一致，但部分 CO 在冷阶段转化为其他物质。相比之下，蛇夫座中两个 I 类源的观测结果与恒定的高 CO 丰度特征一致。
结论：速度解析线剖面通过线强度降低、流出翼不那么突出以及平均 CO 丰度增加，追踪了从 0 类到 I 类阶段的演变。然而，CO 激发温度几乎保持恒定。这里发现的多个成分表明，对光谱未解析数据（例如 SPIRE 和 PACS 提供的数据）的分析必须谨慎进行。赫歇尔是 ESA 空间观测站，其科学仪器由欧洲领导的首席研究员联盟提供，并得到 NASA 的重要参与。附录 C 和 D 的电子版本可在 http://www.aanda.org 上获取。
Context. In the deeply embedded stage of star formation, protostars start to heat and disperse their surrounding cloud cores. The evolution of these sources has traditionally been traced through dust continuum spectral energy distributions (SEDs), but the use of CO excitation as an evolutionary probe has not yet been explored due to the lack of high-J CO observations.
Aims: The aim is to constrain the physical characteristics (excitation, kinematics, column density) of the warm gas in low-mass protostellar envelopes using spectrally resolved Herschel data of CO and compare those with the colder gas traced by lower excitation lines.
Methods: Herschel-HIFI observations of high-J lines of $^{12}$CO, $^{13}$CO, and C$^{18}$O (up to J$_u$ = 10, E$_u$ up to 300 K) are presented toward 26 deeply embedded low-mass Class 0 and Class I young stellar objects, obtained as part of the Water In Star-forming regions with Herschel (WISH) key program. This is the first large spectrally resolved high-J CO survey conducted for these types of sources. Complementary lower J CO maps were observed using ground-based telescopes, such as the JCMT and APEX and convolved to matching beam sizes.
Results: The $^{12}$CO 10-9 line is detected for all objects and can generally be decomposed into a narrow and a broad component owing to the quiescent envelope and entrained outflow material, respectively. The $^{12}$CO excitation temperature increases with velocity from ~{}60 K up to ~{}130 K. The median excitation temperatures for $^{12}$CO, $^{13}$CO, and C$^{18}$O derived from single-temperature fits to the J$_u$ = 2-10 integrated intensities are ~{}70 K, 48 K and 37 K, respectively, with no significant difference between Class 0 and Class I sources and no trend with M$_{env}$ or L$_{bol}$. Thus, in contrast to the continuum SEDs, the spectral line energy distributions (SLEDs) do not show any evolution during the embedded stage. In contrast, the integrated line intensities of all CO isotopologs show a clear decrease with evolutionary stage as the envelope is dispersed. Models of the collapse and evolution of protostellar envelopes reproduce the C$^{18}$O results well, but underproduce the $^{13}$CO and $^{12}$CO excitation temperatures, due to lack of UV heating and outflow components in those models. The H$_{2}$O 1$_{10}$ - 1$_{01}$/CO 10-9 intensity ratio does not change significantly with velocity, in contrast to the H$_{2}$O/CO 3-2 ratio, indicating that CO 10-9 is the lowest transition for which the line wings probe the same warm shocked gas as H$_{2}$O. Modeling of the full suite of C$^{18}$O lines indicates an abundance profile for Class 0 sources that is consistent with a freeze-out zone below 25 K and evaporation at higher temperatures, but with some fraction of the CO transformed into other species in the cold phase. In contrast, the observations for two Class I sources in Ophiuchus are consistent with a constant high CO abundance profile.
Conclusions: The velocity resolved line profiles trace the evolution from the Class 0 to the Class I phase through decreasing line intensities, less prominent outflow wings, and increasing average CO abundances. However, the CO excitation temperature stays nearly constant. The multiple components found here indicate that the analysis of spectrally unresolved data, such as provided by SPIRE and PACS, must be done with caution. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Appendices C and D are available in electronic form at http://www.aanda.org
DOI：
10.1111/j.1365-2966.2009.15347.x
发表时间：
2009-07
影响因子：
4.8
作者：
J. Buckle;R. Hills;Henry Smith;W. R. F. Dent;Graham S. Bell;E. Curtis;Roger Dace;Hugh Gibson;S. Graves;J. Leech;J. Richer;R. Williamson;S. Withington;G. Yassin;Richard J. Bennett;P. Hastings;I. Laidlaw;J. Lightfoot;T. Burgess;P. Dewdney;G. Hovey;A. Willis;R. O. Redman;B. Wooff;D. Berry;B. Cavanagh;Gary R. Davis;J. Dempsey;P. Friberg;T. Jenness;R. Kackley;N. Rees;R. Tilanus;C. Walther;W. Zwart;T. Klapwijk;M. Kroug;T. Zijlstra
通讯作者：
J. Buckle;R. Hills;Henry Smith;W. R. F. Dent;Graham S. Bell;E. Curtis;Roger Dace;Hugh Gibson;S. Graves;J. Leech;J. Richer;R. Williamson;S. Withington;G. Yassin;Richard J. Bennett;P. Hastings;I. Laidlaw;J. Lightfoot;T. Burgess;P. Dewdney;G. Hovey;A. Willis;R. O. Redman;B. Wooff;D. Berry;B. Cavanagh;Gary R. Davis;J. Dempsey;P. Friberg;T. Jenness;R. Kackley;N. Rees;R. Tilanus;C. Walther;W. Zwart;T. Klapwijk;M. Kroug;T. Zijlstra