Velocity Distribution of Collapsing Starless Cores, L694‐2 and L1197

Lee, Seok Ho; Park, Yong-Sun; Sohn, Jungjoo; Lee, Chang Won; Lee, Hyung Mok

doi:10.1086/513682

Cited by 16 publications

(9 citation statements)

References 26 publications

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“…also invoke the possibility of infall from the observations of two other cores, L1498 and L1517B despite the absence of a clear velocity gradient and Williams et al (2006) found that L694-2 has a profile reminiscent of L1544, which is also indicative of probable infall. This was confirmed by Lee et al (2007) who also reported the infall of L1197. Here the amplitude of the inward motion of N 2 H + is not strongly constrained but is clearly necessary to reproduce the velocity-profile plot: no infall at all is clearly the wrong result but the details of the radial velocity profile are uncertain.…”

Section: Discussionmentioning

confidence: 55%

L1506: a prestellar core in the making

Pagani¹,

Ristorcelli

Boudet

et al. 2010

A&A

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Context. Exploring the structure and dynamics of cold starless clouds is necessary to understand the different steps leading to the formation of protostars. Because clouds evolve slowly, many of them must be studied in detail to identify different moments in a cloud's lifetime. Aims. We study a fragment of the long filament L1506 in the Taurus region, which we name L1506C, a core with interesting dust properties observed by the PRONAOS balloon-borne telescope. Methods. To trace the mass content of L1506C and its kinematics, we mapped the dust emission, and the line emission of two key species, C 18 O and N 2 H + . We also observed 13 CO and C 17 O. We model the species emission using 1D Monte Carlo models.Results. This cloud is reminiscent of L1498 but also exhibits peculiar features: i) a large envelope emitting solely in 13 CO that contains a much smaller core with strong C 18 O depletion at its centre despite a low maximum opacity (A V ∼ 20 mag); ii) extremely narrow C 18 O lines indicating a low, non-measurable turbulence; iii) contraction traced by C 18 O itself (plus rotation); iv) unexpectedly, the kinematical signature of the external envelope is opposite to that of the core, the 13 CO and C 18 O velocity gradients having opposite directions and the C 18 O line profile being blue peaked in contrast to the 13 CO one which is red peaked. The core is large (r = 3 × 10 4 AU) and not very dense (n(H 2 ) ≤ 5 × 10 4 cm −3 , possibly less). This core is therefore not yet prestellar. Conclusions. All these properties imply that the core is kinematically detached from its envelope and in the process of forming a prestellar core. This is the first time that the dynamical formation of a prestellar core has been witnessed. The extremely low turbulence could explain the strong depletion of this core despite its relatively low density and opacity in contrast to undepleted cores such as L1521E, which exhibits a turbulence at least 4 times as high.

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Section: Discussionmentioning

confidence: 55%

L1506: a prestellar core in the making

Pagani¹,

Ristorcelli

Boudet

et al. 2010

A&A

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“…Correcting our 24 μm mass by a factor 5, as discussed above, yields a core mass that exceeds the Jeans mass by a factor of ∼4. Like L1544, this source has been studied in some detail (e.g., Lee et al 1999;Harvey et al 2003aHarvey et al , 2003bLee et al 2004;Crapsi et al 2005;Williams et al 2006;Lee et al 2007;Sohn et al 2007;Caselli et al 2008). Crapsi et al (2005) measure the N 2 H + (2-1) and N 2 D + (2-1) line widths to be 0.27 and 0.24 km s −1 , respectively; the N 2 H + (3-2) and N 2 D + (3-2) were 0.31 and 0.24 km s −1 , respectively.…”

Section: Resultsmentioning

confidence: 99%

SPITZERAND HEINRICH HERTZ TELESCOPE OBSERVATIONS OF STARLESS CORES: MASSES AND ENVIRONMENTS

Stutz

Rieke

Bieging

et al. 2009

ApJ

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We present Spitzer observations of a sample of 12 starless cores selected to have prominent 24 μm shadows. The Spitzer images show 8 μm and 24 μm shadows and in some cases 70 μm shadows; these spatially resolved absorption features trace the densest regions of the cores. We have carried out a 12 CO (2-1) and 13 CO (2-1) mapping survey of these cores with the Heinrich Hertz Telescope (HHT). We use the shadow features to derive optical depth maps. We derive molecular masses for the cores and the surrounding environment; we find that the 24 μm shadow masses are always greater than or equal to the molecular masses derived in the same region, a discrepancy likely caused by CO freezeout onto dust grains. We combine this sample with two additional cores that we studied previously to bring the total sample to 14 cores. Using a simple Jeans mass criterion, we find that ∼2/3 of the cores selected to have prominent 24 μm shadows are collapsing or near collapse, a result that is supported by millimeter line observations. Of this subset at least half have indications of 70 μm shadows. All cores observed to produce absorption features at 70 μm are close to collapse. We conclude that 24 μm shadows, and even more so the 70 μm ones, are useful markers of cloud cores that are approaching collapse.

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“…Interestingly, monotonic velocity profiles do not match the data. For both starless cores, Lee et al (2007) found that the inferred contraction speed begins relatively small at the cloud edge, reaches a maximum about halfway inwards in radius and thereafter declines towards the cloud centre. This type of velocity profile emerges naturally from our dynamical model (Paper I, fig.…”

Section: Observations Of the Moleculesmentioning

confidence: 94%

“…Because of the range in optical depths in the three lines, the profiles of HCN are potentially useful for tracing the full velocity structure of a dense core. Lee et al (2007) constructed single‐dish spatial maps of emission for two starless cores, L694‐2 and L1197. To complement their observations, they also performed a radiative transfer calculation in spherical cloud models with adjustable density and velocity profiles.…”

Section: Observations Of the Moleculesmentioning

confidence: 99%

Molecular line profiles from contracting dense cores

Stahler

Yen

2010

Monthly Notices of the Royal Astronomical Society

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We recently proposed that molecular cloud dense cores undergo a prolonged period of quasistatic contraction prior to true collapse. This theory could explain the observation that many starless cores exhibit, through their spectral line profiles, signs of inward motion. We now use our model, together with a publicly available radiative transfer code, to determine the emission from three commonly used species -N 2 H + , CS and HCN. A representative dense core of 3 M that has been contracting for 1 Myr has line profiles that qualitatively match the observed ones. In particular, optically thick lines have about the right degree of blue-red asymmetry, the empirical hallmark of contraction. The J = 2 → 1 rotational transition of CS only attains the correct type of profile if the species is centrally depleted, as has been suggested by previous studies. These results support the idea that a slow, but accelerating, contraction leads to protostellar collapse. In the future, the kind of analysis presented here can be used to assign ages to individual starless cores.

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Velocity Distribution of Collapsing Starless Cores, L694‐2 and L1197

Cited by 16 publications

References 26 publications

L1506: a prestellar core in the making

L1506: a prestellar core in the making

SPITZERAND HEINRICH HERTZ TELESCOPE OBSERVATIONS OF STARLESS CORES: MASSES AND ENVIRONMENTS

Molecular line profiles from contracting dense cores

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