Correlating Infall With Deuterium Fractionation in Dense Cores

Schnee, Scott; Brunetti, Nathan; Francesco, James Di; Caselli, P.; Friesen, Rachel; Johnstone, Doug; Pon, Andy

doi:10.1088/0004-637x/777/2/121

Cited by 19 publications

(27 citation statements)

References 49 publications

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“…The fixed and free parameters as well as the results from the fits are summarized in Table 6. The derived infall velocity in the central part of the envelope (∼0.17 km s −1 ) is consistent with observations at 1000 AU scales of the FHSC candidate Cha-MMS1 (Tsitali et al 2013), the young Class 0 source IRAM 04191 (Belloche et al 2002), surveys of Class 0 sources (Schnee et al 2013) as well as simulations of the first core stage (Tomida et al 2015).…”

Section: Infallsupporting

confidence: 85%

Kinematics of a Young Low-mass Star-forming Core: Understanding the Evolutionary State of the First-core Candidate L1451-mm

Maureira

Arce

Dunham

et al. 2017

ApJ

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We use 3mm multi-line and continuum CARMA observations towards the first hydrostatic core (FHSC) candidate L1451-mm to characterize the envelope kinematics at 1000 AU scales and investigate its evolutionary state. We detect evidence of infall and rotation in the NH 2 D(1 1,1 -1 0,1 ), N 2 H + (1-0) and HCN(1-0) molecular lines. We compare the position velocity diagram of the NH 2 D(1 1,1 -1 0,1 ) line with a simple kinematic model and find that it is consistent with an envelope that is both infalling and rotating while conserving angular momentum around a central mass of about 0.06 M . The N 2 H + (1-0) LTE mass of the envelope along with the inferred infall velocity leads to a mass infall rate of approximately 6 × 10 −6 M yr −1 , implying a young age of 10 4 years for this FHSC candidate. Assuming that the accretion onto the central object is the same as the infall rate we obtain that the minimum source size is 1.5-5 AU consistent with the size expected for a first core. We do not see any evidence of outflow motions or signs of outflow-envelope interaction at scales 2000 AU. This is consistent with previous observations that revealed a very compact outflow ( 500 AU). We conclude that L1451-mm is indeed at a very early stage of evolution, either a first core or an extremely young Class 0 protostar. Our results provide strong evidence that L1451-mm is the best candidate for being a bonafide first core.

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Section: Infallsupporting

confidence: 85%

Kinematics of a Young Low-mass Star-forming Core: Understanding the Evolutionary State of the First-core Candidate L1451-mm

Maureira

Arce

Dunham

et al. 2017

ApJ

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“…The fitting process begins using user-defined starting parameters based on the number of free parameters for the input model, which for the HILL5 model are T peak , σ, τ , v LSR , and v in . Estimates for these values were obtained from previous infall speed surveys, such as those conducted by Schnee et al (2013) and Crapsi et al (2005), which found velocity dispersions, peak intensities, local standard of rest velocities, and infall speeds towards the emission peaks of the three cores in this analysis. MPFIT inserts these initial parameters into the equations of the input model and compares the theoretically produced line profile with that of the actual data.…”

Section: Mpfit Line Fittingmentioning

confidence: 83%

“…The distances to each core as listed in Table 1 were used to convert the radial offsets from the dust continuum peak for each pointing into a physical distance in parsecs. (Crapsi et al 2005) b (Schnee et al 2013) c (Kauffmann et al 2008) d (Di Francesco et al 2008) e Although Schnee et al (2013) labeled L492 as a "static core" due to the subtlety of its infall asymmetry in HCO + (3-2), this core has been classified as a "contracting core" by Sohn et al (2007) due to infall asymmetries in all three hyperfine components of HCN(1-0). Lee & Myers (2011) also classify L492 as a "contracting core" based on infall asymmetries determined from CS, HCN, and N 2 H + spectra.…”

Section: Discussionmentioning

confidence: 99%

“…Although L1521F was originally thought to be prestellar, it has recently been found to be protostellar with a confirmed bipolar outflow originating from an embedded VeLLO (Bourke et al 2006;Takahashi et al 2013). All three cores have been found to have signatures of infall asymmetry in previous surveys (e.g., Crapsi et al 2005;Sohn et al 2007;Lee & Myers 2011;Schnee et al 2013). High-resolution spectral line emission maps have also been observed toward L694-2 (Williams et al 2006) which have shown a radial gradient of infall speeds across the core with decreasing speeds as distance from the center increases.…”

Section: Observationsmentioning

confidence: 92%

“…Since CO is depleted towards the central regions, however, deuterated molecules with easily detectable rotational lines, such as N 2 D + , can be formed (Crapsi et al 2005). Studies have also linked deuterium enrichment to physical evolution, with a higher fraction of deuterated molecules corresponding to a more dynamically evolved core (Crapsi et al 2005;Schnee et al 2013). …”

Section: Introductionmentioning

confidence: 99%

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Infall/Expansion Velocities in the Low-Mass Dense Cores L492, L694-2, and L1521f: Dependence on Position and Molecular Tracer

Keown¹,

Schnee²,

Bourke³

et al. 2016

ApJ

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Although surveys of infall motions in dense cores have been carried out for years, few surveys have focused on mapping infall across cores using multiple spectral line observations. To fill this gap, we present IRAM 30-m Telescope maps of N 2 H + (1-0), DCO + (2-1), DCO + (3-2), and HCO + (3-2) emission towards two prestellar cores (L492 and L694-2) and one protostellar core (L1521F). We find that the measured infall velocity varies with position across each core and choice of molecular line, likely as a result of radial variations in core chemistry and dynamics. Line-of-sight infall speeds estimated from DCO + (2-1) line profiles can decrease by 40-50 m s −1 when observing at a radial offset ≥0.04 pc from the core's dust continuum emission peak. Median infall speeds calculated from all observed positions across a core can also vary by as much as 65 m s −1 depending on the transition. These results show that while single-pointing, single-transition surveys of core infall velocities may be good indicators of whether a core is either contracting or expanding, the magnitude of the velocities they measure are significantly impacted by the choice of molecular line, proximity to the core center, and core evolutionary state.

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Why Do Some Cores Remain Starless?

Anathpindika

2016

Publ. Astron. Soc. Aust.

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Prestellar cores, by definition, are gravitationally bound but starless pockets of dense gas. Physical conditions that could render a core starless(in the local Universe) is the subject of investigation in this work. To this end we studied the evolution of four starless cores, B68, L694-2, L1517B, L1689, and L1521F, a VeLLO. The density profile of a typical core extracted from an earlier simulation developed to study core-formation in a molecular cloud was used for the purpose. We demonstrate -(i) cores contracted in quasistatic manner over a timescale on the order of ∼ 10 5 years. Those that remained starless did briefly acquire a centrally concentrated density configuration that mimicked the density profile of a unstable Bonnor Ebert sphere before rebounding, (ii) three of our test cores viz. L694-2, L1689-SMM16 and L1521F remained starless despite becoming thermally super-critical. On the contrary B68 and L1517B remained sub-critical; L1521F collapsed to become a VeLLO only when gas-cooling was enhanced by increasing the size of dust-grains. This result is robust, for other cores viz. B68, L694-2, L1517B and L1689 that previously remained starless could also be similarly induced to collapse. Our principle conclusions are : (a) acquiring the thermally supercritical state does not ensure that a core will necessarily become protostellar, (b) potentially star-forming cores (the VeLLO L1521F here), could be experiencing coagulation of dust-grains that must enhance the gasdust coupling and in turn lower the gas temperature, thereby assisting collapse. This hypothesis appears to have some observational support, and (c) depending on its dynamic state at any given epoch, a core could appear to be pressure-confined, gravitationally/virially bound, suggesting that gravitational/virial boundedness of a core is insufficient to ensure it will form stars, though it is crucial for gas in a contracting core to cool efficiently so it can collapse further to become protostellar. Gas temperature in these purely hydrodynamic calculations was calculated by explicitly solving the respective equations of thermal-balance for gas and dust; the attenuation factor for the interstellar radiation-field, χ, which in literature has been well constrained to ∼ 10 −4 for putative star-forming clumps and cores was adopted in these calculations.

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Correlating Infall With Deuterium Fractionation in Dense Cores

Cited by 19 publications

References 49 publications

Kinematics of a Young Low-mass Star-forming Core: Understanding the Evolutionary State of the First-core Candidate L1451-mm

Kinematics of a Young Low-mass Star-forming Core: Understanding the Evolutionary State of the First-core Candidate L1451-mm

Infall/Expansion Velocities in the Low-Mass Dense Cores L492, L694-2, and L1521f: Dependence on Position and Molecular Tracer

Why Do Some Cores Remain Starless?

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