Ten protostellar outflows in the Orion molecular clouds were mapped in the
$^{12}$CO/$^{13}$CO ${J=6\rightarrow5}$ and $^{12}$CO ${J=7\rightarrow6}$
lines. The maps of these mid-$J$ CO lines have an ...angular resolution of about
10$''$ and a typical field size of about 100$''$. Physical parameters of the
molecular outflows were derived, including mass transfer rates, kinetic
luminosities, and outflow forces. The outflow sample was expanded by
re-analyzing archival data of nearby low-luminosity protostars, to cover a wide
range of bolometric luminosities. Outflow parameters derived from other
transitions of CO were compared. The mid-$J$ ($J_{\rm up} \approx 6$) and
low-$J$ ($J_{\rm up} \leq 3$) CO line wings trace essentially the same outflow
component. By contrast, the high-$J$ (up to $J_{\rm up} \approx 50$)
line-emission luminosity of CO shows little correlation with the kinetic
luminosity from the ${J=6\rightarrow5}$ line, which suggests that they trace
distinct components. The low/mid-$J$ CO line wings trace long-term outflow
behaviors while the high-$J$ CO lines are sensitive to short-term activities.
The correlations between the outflow parameters and protostellar properties are
presented, which shows that the strengths of molecular outflows increase with
bolometric luminosity and envelope mass.
CS Depletion in Prestellar Cores Kim, Shinyoung; Chang Won Lee; Gopinathan, Maheswar ...
arXiv.org,
02/2020
Paper, Journal Article
Odprti dostop
The CS molecule is known to be absorbed onto dust in the cold and dense conditions, causing it to get significantly depleted in the central region of cores. This study is aimed to investigate the ...depletion of the CS molecule using the optically thin C\(^{34}\)S molecular line observations. We mapped five prestellar cores, L1544, L1552, L1689B, L694-2, and L1197 using two molecular lines, C\(^{34}\)S \((J=2-1)\) and N\(_2\)H\(^+\) \((J=1-0)\) with the NRO 45-m telescope, doubling the number of cores where the CS depletion was probed using C\(^{34}\)S. In most of our targets, the distribution of C\(^{34}\)S emission shows features that suggest that the CS molecule is generally depleted in the center of the prestellar cores. The radial profile of the CS abundance with respect to H\(_2\) directly measured from the CS emission and the Herschel dust emission indicates that the CS molecule is depleted by a factor of \(\sim\)3 toward the central regions of the cores with respect to their outer regions. The degree of the depletion is found to be even more enhanced by an order of magnitude when the contaminating effect introduced by the presence of CS molecules in the surrounding envelope that lie along the line-of-sight is removed. Except for L1197 which is classified as relatively the least evolved core in our targets based on its observed physical parameters, we found that the remaining four prestellar cores are suffering from significant CS depletion at their central region regardless of the relative difference in their evolutionary status.
Prestellar cores are self-gravitating dense and cold structures within molecular clouds where future stars are born. They are expected, at the stage of transitioning to the protostellar phase, to ...harbor centrally concentrated dense (sub)structures that will seed the formation of a new star or the binary/multiple stellar systems. Characterizing this critical stage of evolution is key to our understanding of star formation. In this work, we report the detection of high density (sub)structures on the thousand-au scale in a sample of dense prestellar cores. Through our recent ALMA observations towards the Orion molecular cloud, we have found five extremely dense prestellar cores, which have centrally concentrated regions \(\sim\) 2000 au in size, and several \(10^7\) \(cm^{-3}\) in average density. Masses of these centrally dense regions are in the range of 0.30 to 6.89 M\(_\odot\). {\it For the first time}, our higher resolution observations (0.8\('' \sim \) 320 au) further reveal that one of the cores shows clear signatures of fragmentation; such individual substructures/fragments have sizes of 800 -1700 au, masses of 0.08 to 0.84 M\(_\odot\), densities of \(2 - 8\times 10^7\) \(cm^{-3}\) and separations of \(\sim 1200\) au. The substructures are massive enough (\(\gtrsim 0.1~M_\odot\)) to form young stellar objects and are likely examples of the earliest stage of stellar embryos which can lead to widely (\(\sim\) 1200 au) separated multiple systems.
In this study, 36 cores (30 starless and 6 protostellar) identified in Orion were surveyed to search for inward motions. We used the Nobeyama 45 m radio telescope, and mapped the cores in the \(J = ...1\rightarrow0\) transitions of HCO\(^+\), H\(^{13}\)CO\(^+\), N\(_2\)H\(^+\), HNC, and HN\(^{13}\)C. The asymmetry parameter \(\delta V\), which was the ratio of the difference between the HCO\(^+\) and H\(^{13}\)CO\(^+\) peak velocities to the H\(^{13}\)CO\(^+\) line width, was biased toward negative values, suggesting that inward motions were more dominant than outward motions. Three starless cores (10% of all starless cores surveyed) were identified as cores with blue-skewed line profiles (asymmetric profiles with more intense blue-shifted emission), and another two starless cores (7%) were identified as candidate blue-skewed line profiles. The peak velocity difference between HCO\(^+\) and H\(^{13}\)CO\(^+\) of them was up to 0.9 km s\(^{-1}\), suggesting that some inward motions exceeded the speed of sound for the quiescent gas (\(\sim10-17\) K). The mean of \(\delta V\) of the five aforementioned starless cores was derived to be \(-\)0.5\(\pm\)0.3. One core, G211.16\(-\)19.33North3, observed using the ALMA ACA in DCO\(^+\) \(J = 3\rightarrow2\) exhibited blue-skewed features. Velocity offset in the blue-skewed line profile with a dip in the DCO\(^+\) \(J = 3\rightarrow2\) line was larger (\(\sim 0.5\) km s\(^{-1}\)) than that in HCO\(^+\) \(J = 1\rightarrow0\) (\(\sim 0.2\) km s\(^{-1}\)), which may represent gravitational acceleration of inward motions. It seems that this core is at the last stage in the starless phase, judging from the chemical evolution factor version 2.0 (CEF2.0).
We study the HII regions associated with the NGC 6334 molecular cloud observed in the sub-millimeter and taken as part of the B-fields In STar-forming Region Observations (BISTRO) Survey. In ...particular, we investigate the polarization patterns and magnetic field morphologies associated with these HII regions. Through polarization pattern and pressure calculation analyses, several of these bubbles indicate that the gas and magnetic field lines have been pushed away from the bubble, toward an almost tangential (to the bubble) magnetic field morphology. In the densest part of NGC 6334, where the magnetic field morphology is similar to an hourglass, the polarization observations do not exhibit observable impact from HII regions. We detect two nested radial polarization patterns in a bubble to the south of NGC 6334 that correspond to the previously observed bipolar structure in this bubble. Finally, using the results of this study, we present steps (incorporating computer vision; circular Hough Transform) that can be used in future studies to identify bubbles that have physically impacted magnetic field lines.
We present the results of a systematic search for molecular outflows in 68 Very Low Luminosity Objects (VeLLOs) from single-dish observations in CO isotopologues which find 16 VeLLOs showing clear ...outflow signatures in the CO maps. With additional three VeLLOs from the literature, we analyzed the outflow properties for 19 VeLLOs, identifying 15 VeLLOs as proto-Brown Dwarf (BD) candidates and four VeLLOs as likely faint protostar candidates. The proto-BD candidates are found to have a mass accretion rate (\(\sim 10^{-8} - 10^{-7}\) \(\rm M_{\odot}\) yr\(^{-1}\)) lower than that of the protostar candidates (\(\gtrsim 10^{-6}\) \(\rm M_{\odot}\) yr\(^{-1}\)). Their accretion luminosities are similar to or smaller than their internal luminosities, implying that many proto-BD candidates might have had either small accretion activity in a quiescent manner throughout their lifetime, or be currently exhibiting a relatively higher (or episodic) mass accretion than the past. There are strong trends that outflows of many proto-BDs are less active if they are fainter or have less massive envelopes. The outflow forces and internal luminosities for more than half of the proto-BD candidates seem to follow an evolutionary track of a protostar with its initial envelope mass of \(\sim\)0.08 \(\rm M_{\odot}\), indicating that some BDs may form in less massive dense cores in a way similar to normal stars. But, because there also exists a significant fraction (about 40%) of proto-BDs with much weaker outflow force than expected by the relations for protostars, we should not rule out the possibility of other formation mechanism for the BDs.
Measurement of magnetic field strengths in a molecular cloud is essential for determining the criticality of magnetic support against gravitational collapse. In this paper, as part of the JCMT BISTRO ...survey, we suggest a new application of the Davis-Chandrasekhar-Fermi (DCF) method to estimate the distribution of magnetic field strengths in the OMC-1 region. We use observations of dust polarization emission at 450 \(\mu\)m and 850 \(\mu\)m, and C\(^{18}\)O (3-2) spectral line data obtained with the JCMT. We estimate the volume density, the velocity dispersion and the polarization angle dispersion in a box, 40\(''\) \(\times\) 40\(''\) (5\(\times\)5 pixels), which moves over the OMC-1 region. By substituting three quantities in each box to the DCF method, we get magnetic field strengths over the OMC-1 region. We note that there are very large uncertainties in inferred field strengths, as discussed in detail in this paper. The field strengths vary from 0.8 to 26.4 mG and their mean value is about 6 mG. Additionally, we obtain maps of the mass-to-flux ratio in units of a critical value and the Alfv\(\acute{e}\)n mach number. The central parts of the BN-KL and South (S) clumps in the OMC-1 region are magnetically supercritical, so the magnetic field cannot support the clumps against gravitational collapse. However, the outer parts of the region are magnetically subcritical. The mean Alfv\(\acute{e}\)n mach number is about 0.4 over the region, which implies that the magnetic pressure exceeds the turbulent pressure in the OMC 1 region.
"TRAO FUNS" is a project to survey Gould Belt's clouds in molecular lines. This paper presents its first results on the central region of the California molecular cloud, L1478. We performed ...On-The-Fly mapping observations using the Taedeok Radio Astronomy Observatory (TRAO) 14m single dish telescope equipped with a 16 multi-beam array covering \(\sim\)1.0 square degree area of this region using C\(^{18}\)O (1-0) mainly tracing low density cloud and about 460 square arcminute area using N\(_{2}\)H\(^{+}\) (1-0) mainly tracing dense cores. CS (2-1) and SO \((3_{2}-2_{1})\) were also used simultaneously to map \(\sim\)440 square arcminute area of this region. We identified 10 filaments by applying the dendrogram technique to the C\(^{18}\)O data-cube and 8 dense N\(_{2}\)H\(^{+}\) cores by using {\sc FellWalker}. Basic physical properties of filaments such as mass, length, width, velocity field, and velocity dispersion are derived. It is found that L1478 consists of several filaments with slightly different velocities. Especially the filaments which are supercritical are found to contain dense cores detected in N\(_{2}\)H\(^{+}\). Comparison of non-thermal velocity dispersions derived from C\(^{18}\)O and N\(_{2}\)H\(^{+}\) for the filaments and dense cores indicates that some of dense cores share similar kinematics with those of the surrounding filaments while several dense cores have different kinematics with those of their filaments. This suggests that the formation mechanism of dense cores and filaments can be different in individual filaments depending on their morphologies and environments.
L1521F is found to be forming multiple cores and it is cited as an example of the densest core with an embedded VeLLO in a highly dynamical environment. We present the core-scale magnetic fields ...(B-fields) in the near vicinity of the VeLLO L1521F-IRS using submm polarization measurements at 850\(~\mu\)m using JCMT POL-2. This is the first attempt to use high-sensitivity observations to map the sub-parsec scale B-fields in a core with a VeLLO. The B-fields are ordered and very well connected to the parsec-scale field geometry seen in our earlier optical polarization observations and the large-scale structure seen in Planck dust polarization. The core scale B-field strength estimated using Davis-Chandrasekhar-Fermi relation is \(\rm 330\pm100~\mu\)G which is more than ten times of the value we obtained in the envelope (envelope in this paper is "core envelope"). This indicates that B-fields are getting stronger on smaller scales. The magnetic energies are found to be 1 to 2 orders of magnitude higher than non-thermal kinetic energies in the envelope and core. This suggests that magnetic fields are more important than turbulence in the energy budget of L1521F. The mass-to-flux ratio of 2.3\(\pm\)0.7 suggests that the core is magnetically-supercritical. The degree of polarization is steadily decreasing towards the denser part of the core with a power law slope of -0.86.
We present the results of on-the-fly mapping observations of 44 fields containing 107 SCUBA-2 cores in the emission lines of molecules, N\(_2\)H\(^+\), HC\(_3\)N, and CCS at 82\(-\)94 GHz using the ...Nobeyama 45-m telescope. This study aimed at investigating the physical properties of cores that show high deuterium fractions and might be close to the onset of star formation. We found that the distributions of the N\(_2\)H\(^+\) and HC\(_3\)N line emissions are approximately similar to that of 850-\(\mu\)m dust continuum emission, whereas the CCS line emission is often undetected or is distributed in a clumpy structure surrounding the peak position of the 850-\(\mu\)m dust continuum emission. Occasionally (12%), we observe the CCS emission which is an early-type gas tracer toward the young stellar object, probably due to local high excitation. Evolution toward star formation does not immediately affect nonthermal velocity dispersion.
