Low-mass stars like our Sun begin their evolution within cold (10 K) and dense ($\sim 10^5$ cm$^{-3}$) cores of gas and dust. The physical structure of starless cores is best probed by thermal emission of dust grains. We present a high resolution dust continuum study of the starless cores in the B10 region of the Taurus Molecular Cloud. New observations at 1.2mm and 2.0mm ($12^{"}$ and $18^{"}$ resolution) with the NIKA2 instrument on the IRAM 30m have probed the inner regions of 14 low-mass starless cores. We perform sophisticated 3D radiative transfer modelling for each of these cores through the radiative transfer framework $\textit{pandora}$, which utilizes RADMC-3D. Model best-fits constrain each cores' central density, density slope, aspect ratio, opacity, and interstellar radiation field strength. These `typical' cores in B10 span central densities from $5 \times 10^4 - 1 \times 10^6$ cm$^{-3}$, with a mean value of $2.6 \times 10^5$ cm$^{-3}$. We find the dust opacity laws assumed in the 3D modelling, as well as the estimates from $\textit{Herschel}$, have dust emissivity indices, $β$'s, on the lower end of the distribution constrained directly from the NIKA2 maps, which averages to $β= 2.01\pm0.48$. From our 3D density structures and archival NH$_3$ data, we perform a self-consistent virial analysis to assess each core's stability. Ignoring magnetic field contributions, we find 9 out of the 14 cores ($64\%$) are either in virial equilibrium or are bound by gravity and external pressure. To push the bounded cores back to equilibrium, an effective magnetic field difference of only $\sim 15 μ$G is needed.
Recent observations indicate that organic molecules are prevalent towards starless and prestellar cores. Deuteration of these molecules has not been well-studied during the starless phase. Published observations of singly-deuterated methanol, CH$_2$DOH, have only been observed in a couple of well-studied, dense and evolved prestellar cores (e.g. L1544, L183). Since the formation of gas-phase methanol during this cold phase is believed to occur via desorption from the icy grain surfaces, observations of CH$_2$DOH may be useful as a probe of the deuterium fraction in the ice mantles of dust grai…
The chemical and physical evolution of starless and pre-stellar cores are of paramount importance to understanding the process of star formation. The Taurus Molecular Cloud cores TMC 1-C and TMC 1-CP share similar initial conditions and provide an excellent opportunity to understand the evolution of the pre-stellar core phase. We investigated the evolutionary stage of starless cores based on observations towards the prototypical dark cores TMC 1-C and TMC 1-CP, mapping them in the CS $3\rightarrow 2$, C$^{34}$S $3\rightarrow 2$, $^{13}$CS $2\rightarrow 1$, DCN $1\rightarrow 0$, DCN $2\rightarr…
The formation scenario of brown dwarfs is still unclear because observational studies to investigate its initial condition are quite limited. Our systematic survey of nearby low-mass star-forming regions using the Atacama Compact Array (aka Morita array) and the IRAM 30 m telescope in 1.2 mm continuum has identified a centrally concentrated starless condensation with a central H$_2$ volume density of $\sim$10$^6$ cm$^{-3}$, MC5-N, connected to a narrow (width $\sim$0.03 pc) filamentary cloud in the Taurus L1495 region. The mass of the core is $\sim$0.2-0.4 $M_{\odot}$, which is an order of mag…
Methanol, one of the simplest complex organic molecules in the Interstellar Medium (ISM), has been shown to be present and extended in cold environments such as starless cores. We aim at studying methanol emission across several starless cores and investigate the physical conditions at which methanol starts to be efficiently formed, as well as how the physical structure of the cores and their surrounding environment affect its distribution. Methanol and C$^{18}$O emission lines at 3 mm have been observed with the IRAM 30m telescope within the large program "Gas phase Elemental abundances in Mo…
The first hydrostatic core, the first quasi-hydrostatic object formed during the star formation process, is still the observational missing link between the prestellar and protostellar phases, mainly due to its short lifetime. Although we have not established a clear method to identify this rare object, recent theoretical studies predict that the first core has millimeter continuum emission and low-velocity outflow with a wide opening angle. An extensive continuum/outflow survey toward a large number of $"$starless$"$ cores in nearby star-forming regions works as a pathfinder. We observed 32 p…
L1521E is a dense starless core in Taurus that was found to have relatively low molecular depletion by earlier studies, thus suggesting a recent formation. We aim to characterize the chemical structure of L1521E and compare it to the more evolved L1544 pre-stellar core. We have obtained $\sim$2.5$\times$2.5 arcminute maps toward L1521E using the IRAM-30m telescope in transitions of various species. We derived abundances for the species and compared them to those obtained toward L1544. We estimated CO depletion factors. Similarly to L1544, $c$-C$_3$H$_2$ and CH$_3$OH peak at different positions…
We present the results of mapping observations toward a nearby starless filamentary cloud, the Taurus Molecular Cloud 1 (TMC-1), in the CCS(JN=43-32, 45.379033 GHz) emission line, using the Nobeyama 45-m telescope. The map shows that the TMC-1 filament has a diameter of ~0.1 pc and a length of ~0.5 pc at a distance of 140 pc. The position-velocity diagrams of CCS clearly indicate the existence of velocity-coherent substructures in the filament. We identify 21 substructures that are coherent in the position-position-velocity space by eye. Most of the substructures are elongated along the major …
c-C3H2 deuteration towards prestellar and starless cores in the Perseus Molecular Cloud
RIKEN Cluster for Pioneering Research（理化学研究所前沿研究集群）；National Radio Astronomy Observatory（国家射电天文台）；University of Virginia（弗吉尼亚大学）；University of California, Berkeley（加州大学伯克利分校）；University of Arizona（亚利桑那大学）；Centro de Astrobiología (CAB), CSIC-INTA（天体生物学中心（CAB），西班牙高等科学研究委员会-国家航空航天技术研究所）
Detection of a turbulent gas component associated with a starless core with subthermal turbulence in the Orion A cloud
我们报告了在猎户座A云中对无星核心TUKH 122的NH $_3$发射中的机翼组件的检测。这个NH $_3$核心被认为是在恒星形成的边缘，因为NH $_3$核心内部的湍流几乎完全消散，也因为它被CCS包围，这类似于金牛座的星前核心L1544，显示出坠落运动。观测是用Nobeyama 45米望远镜以0.05公里/秒的$^{-1}$速度分辨率进行的。我们发现，NH $_3$线配置文件由两个组件。静止的主分量具有0.3 km s $^{-1}$的小线宽，主要由热运动控制，而红移的翼分量具有1.36 km s $^{-1}$的大线宽，代表湍流运动。这些组分的动力学温度分别为11 K和$<$ 30 K。此外，NH $_3$静止气体（$VLSR=3.7$ km s $^{-1}$）和湍流气体（$VLSR=4.4$ km s $^{-1}$）之间存在明显的速度偏移。湍流气体的质心速度对应于由$^{13}$ CO（$J=1-0$）和CS（$J=2-1$）线追踪的周围气体的质心速度。对CS和CO的LVG模型计算表明，湍流气体的温度为$8-13$ K，H $_2$密度为~ $10^4$ cm $^{-3}$，表明湍流组分的温度也为~ 10 K。NH $_3$静止和机翼成分的检测可能表明从湍流母云到静止致密核心的急剧转变。
In the context of the IRAM 30m Large Program GEMS, we present a study of thioformaldehyde in several starless cores located in star-forming filaments of Taurus, Perseus, and Orion. We investigate the influence of the environmental conditions on the abundances of these molecules in the cores, and the effect of time evolution. We have modelled the observed lines of H2CS, HDCS, and D2CS using the radiative transfer code RADEX. We have also used the chemical code Nautilus to model the evolution of these species depending on the characteristics of the starless cores. We derive column densities and …
We use 3mm continuum NOEMA and NH$_3$ VLA observations towards the First Hydrostatic Core (FHSC) candidate CB 17 MMS to reveal the dust structure and gas properties down to 600-1,100 au scales and constrain its evolutionary stage. We do not detect any compact source at the previously identified 1.3 mm point source, despite expecting a minimum signal-to-noise of 9. The gas traced by NH$_3$ exhibits subsonic motions, with an average temperature of 10.4 K. A fit of the radial column density profile derived from the ammonia emission finds a flat inner region of radius $\sim$1,800 au and a central …
Measurement of chemical and kinematic structures in prestellar cores is essential for better understanding the star formation process. Here, we study the three prestellar cores (TMC-1C, L1544, and TMC-1) of the Taurus molecular cloud by means of the thioxoethenylidene (CCS) radical and ammonia (NH3) molecule observed with Karl G. Jansky Very Large Array telescope in D, C, and CNB configurations. Our main results are based on the CCS observation of the TMC-1C core, showing complex structures are present. Spatial offset relative to dust emission is observed in the CCS radical. Across a wide regi…
Evolution of starless cores in massive clumps seen by the ALMA ASHES and QUARKS surveys
Yunnan University（云南大学）；Shanghai Astronomical Observatory, Chinese Academy of Sciences（中国科学院上海天文台）；Universidad de Chile（智利大学）；Chinese Academy of Sciences South America Center for Astronomy, National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台南美天文中心）；Department of Astronomy, School of Science, The University of Tokyo（东京大学理学部天文学科）；Max Planck Institute for Astronomy（马克斯·普朗克天文学研究所）；Xinjiang Astronomical Observatory, Chinese（中国科学院新疆天文台）
We have performed survey-type observations in 1 mm continuum and molecular lines toward dense cores (32 prestellar + 7 protostellar) with an average density of $\gtrsim$10$^5$ cm$^{-3}$ in the Taurus molecular clouds using the Atacama Large Millimeter/submillimeter Array-Atacama Compact Array (ALMA-ACA) stand-alone mode with an angular resolution of 6.$''$5 ($\sim$900 au). The primary purpose of this study is to investigate the innermost part of dense cores toward understanding the initial condition of star formation. In the protostellar cores, contributions from protostellar disks dominate th…
Chemical study of two starless cores in the B213/L1495 filament
Centro de Astrobiología (CSIC-INTA)（天体生物学中心）；European Space Agency (ESA)（欧洲航天局）；European Space Astronomy Centre (ESAC)（欧洲航天天文中心）；Observatorio Astronómico Nacional (OAN)（国家天文台）；Observatorio de Yebes (IGN)（耶韦斯天文台）；Instituto de Astrofísica de Canarias (IAC)（加那利群岛天体物理研究所）；Departamento de Astrofísica, Universidad de La Laguna（拉帕尔马大学天体物理学系）
我们提出了我们的研究结果的八个致密的核心，以前被归类为无星，红外（3-160 { \micron }）成像观测与\textit{AKARI}望远镜和分子线（HCN和N $_2$ H $^+$）映射观测与\textit{KVN}望远镜。结合我们的研究结果与档案IR毫米连续数据，我们研究了这八个核心的无星性质。八个核心中的两个被发现有亮度为$\sim0.3-4.4$ L $_{\odot}$的微弱原恒星。其他六个核心被发现仍然作为无星，可能是在一个动态的过渡状态。使用多波长图像生成的温度图显示，这些核心的外边界增强了约3-6 K，这表明它们很可能是由附近的恒星和/或星际辐射场外部加热的。大维里参数和核心上红色不对称线轮廓的过度主导可能表明核心被设置为膨胀或振荡运动，可能是由于外部加热。大多数无星核都表现出由于微米级尘埃颗粒对光的光的散射而产生的核芯效应。这可能意味着核心的年龄是$\sim10^{5}$年的顺序，与核心演变成振荡阶段所需的时间尺度一致，由于外部扰动。我们的观测结果支持了这样一种观点，即来自邻近恒星和/或星际辐射场的外部反馈可能在核的动力学演化中起重要作用。
We have carried out observations of CCH and its two $^{13}$C isotopologues, $^{13}$CCH and C$^{13}$CH, in the 84 - 88 GHz band toward two starless cores, L1521B and L134N (L183), using the Nobeyama 45 m radio telescope. We have detected C$^{13}$CH with a signal-to-noise (S/N) ratio of 4, whereas no line of $^{13}$CCH was detected in either the dark clouds. The column densities of the normal species were derived to be ($1.66 \pm 0.18$)$\times 10^{14}$ cm$^{-2}$ and ($7.3 \pm 0.9$)$\times 10^{13}$ cm$^{-2}$ ($1 σ$) in L1521B and L134N, respectively. The column density ratios of $N$(C$^{13}$CH)/$…
We perform a virial analysis of starless dense cores in three nearby star-forming regions : L1688 in Ophiuchus, NGC 1333 in Perseus, and B18 in Taurus. Our analysis takes advantage of comprehensive kinematic information for the dense gas in all of these regions made publicly available through the Green Bank Ammonia Survey Data Release 1, which used to estimate internal support against collapse. We combine this information with ancillary data used to estimate other important properties of the cores, including continuum data from the James Clerk Maxwell Telescope Gould Belt Survey for core ident…
The JCMT Gould Belt Survey: First results from the SCUBA-2 observations of the Ophiuchus molecular cloud and a virial analysis of its prestellar core population
在本文中，我们提出了第一次观测的蛇夫座分子云的詹姆斯克拉克麦克斯韦望远镜（JCMT）古尔德带调查（GBS）的一部分，与SCUBA-2仪器。我们展示了将这些数据与以前的HARP CO，Herschel和IRAM N $_{2}$ H $^{+}$观测相结合的方法，以准确地量化蛇夫座SCUBA-2源的特性。我们制作了一份SCUBA-2发现的所有来源的目录。我们把它们分成原恒星和无恒星的核心。我们列出了所有的无星核心，并进行了全面的维里分析，包括外部压力。这是第一次将外部压力包括在这一详细程度中。我们发现我们的大多数核心要么是束缚的，要么是男性化的。引力能和外压的平均值在数量级上是相似的，但各区域之间有一些差异。我们发现，在OPH A区域的核心是重力约束的星前核心，而在OPH C和E区域的核心是压力限制。我们确定，N $_{2}$ H $^{+}$是一个很好的示踪剂的结合材料的星前核心，虽然我们发现了一些证据N $_{2}$ H $^{+}$冻结在非常高的核心密度。我们发现，非热线宽之间的跟踪由C $^{18}$ O和跟踪由N $_{2}$ H $^{+}$，表明在较高的密度湍流耗散的气体大幅减少。我们发现，临界Bonnor-Ebert稳定性准则是不是一个很好的指标，我们的核心的有界性。我们探测到前褐矮星候选者Oph B-11，并发现与以前的工作一致的通量密度和质量。我们讨论的核心的性质…
