The N2D+/N2H+ ratio as an evolutionary tracer of Class 0 protostars

Emprechtinger, M.; Caselli, P.; Volgenau, N. H.; Stützki, J.; Wiedner, Martina C.

doi:10.1051/0004-6361:200810324

Cited by 142 publications

(256 citation statements)

References 76 publications

(157 reference statements)

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“…The N 2 H + column densities are also comparable to those determined towards several other low-mass starless cores and Class 0 protostellar objects (Caselli et al 2002b;Crapsi et al 2005;Roberts & Millar 2007;Daniel et al 2007;Emprechtinger et al 2009;Friesen et al 2010a,b). On the other hand, the N 2 D + column densities we have obtained are generally larger than those derived for other low-mass cores in the studies mentioned above.…”

Section: Molecular Column Densities and Abundancessupporting

confidence: 79%

“…The SABOCA peaks appeared to systematically lie southeast from the LABOCA peak positions. The difference in angular resolution between SABOCA and LABOCA data did not of deuteration, or the N(N 2 D + )/N(N 2 H + ) column density ratio, towards selected positions and found the values in the range 0.03-0.04, comparable to those seen in other low-mass starforming regions (e.g., Crapsi et al 2005;Emprechtinger et al 2009;Friesen et al 2010b). Taking advantage of the H 2 D + data from Harju et al (2006), the ionisation degree and the cosmicray ionisation rate of H 2 towards the same target positions were estimated to be x(e) ∼ 10 −7 and ζ H 2 ∼ 1−2 × 10 −16 s −1 , respectively.…”

Section: Introductionmentioning

confidence: 68%

“…Note that we have employed the DCO + (4−3) transition, which is expected to trace the inner part of the highdensity envelope, where heating by the embedded protostar may affect the deuterium chemistry [by lowering the R D (HCO + ) ratio]. For comparison, Jørgensen et al (2004) Previous studies of low-mass starless and protostellar cores have found correlations between the degree of CO depletion and deuterium fractionation (Bacmann et al 2003;Jørgensen et al 2004;Crapsi et al 2005;Emprechtinger et al 2009) …”

Section: Depletion and Deuterationmentioning

confidence: 99%

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A (sub)millimetre study of dense cores in Orion B9

Miettinen

Harju

Haikala

et al. 2012

A&A

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Context. Studies of dense molecular-cloud cores at (sub)millimetre wavelengths are needed to understand the early stages of star formation. Aims. We aim to further constrain the properties and evolutionary stages of dense cores in Orion B9. The prime objective of this study is to examine the dust emission of the cores near the peak of their spectral energy distributions, and to determine the degrees of CO depletion, deuterium fractionation, and ionisation. Methods. The central part of Orion B9 was mapped at 350 μm with APEX/SABOCA. A sample of nine cores in the region were observed in C 17 O(2−1), H 13 CO + (4−3) (towards 3 sources), DCO + (4−3), N 2 H + (3−2), and N 2 D + (3−2) with APEX/SHFI. These data are used in conjunction with our previous APEX/LABOCA 870-μm dust continuum data. Results. All the LABOCA cores in the region covered by our SABOCA map were detected at 350 μm. The strongest 350 μm emission is seen towards the Class 0 candidate SMM 3. Many of the LABOCA cores show evidence of substructure in the higher-resolution SABOCA image. In particular, we report on the discovery of multiple very low-mass condensations in the prestellar core SMM 6. Based on the 350-to-870 μm flux density ratios, we determine dust temperatures of T dust 7.9−10.8 K, and dust emissivity indices of β ∼ 0.5−1.8. The CO depletion factors are in the range f D ∼ 1.6−10.8. The degree of deuteration in N 2 H + is 0.04−0.99, where the highest value (seen towards the prestellar core SMM 1) is, to our knowledge, the most extreme level of N 2 H + deuteration reported so far. The level of HCO + deuteration is about 1-2%. The fractional ionisation and cosmic-ray ionisation rate of H 2 could be determined only towards two sources with the lower limits of ∼2−6 × 10 −8 and ∼2.6 × 10 −17 −4.8 × 10 −16 s −1 , respectively. We also detected D 2 CO towards two sources. Conclusions. The detected protostellar cores are classified as Class 0 objects, in agreement with our previous SED results. The detection of subcondensations within SMM 6 shows that core fragmentation can already take place during the prestellar phase. The origin of this substructure is likely caused by thermal Jeans fragmentation of the elongated parent core. Varying levels of f D and deuteration among the cores suggest that they are evolving chemically at different rates. A low f D value and the presence of gas-phase D 2 CO in SMM 1 suggest that the core chemistry is affected by the nearby outflow. The very high N 2 H + deuteration in SMM 1 is likely to be remnant of the earlier CO-depleted phase.

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Section: Molecular Column Densities and Abundancessupporting

confidence: 79%

Section: Introductionmentioning

confidence: 68%

Section: Depletion and Deuterationmentioning

confidence: 99%

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A (sub)millimetre study of dense cores in Orion B9

Miettinen

Harju

Haikala

et al. 2012

A&A

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“…5;Fontani et al 2006;Emprechtinger et al 2009; but see Roberts & Millar 2007). This can be understood as the abundances of H + 3 , and its deuterated forms, which transfer deuterium to other molecules, increase with increasing density because of molecular depletion and a lower degree of ionization.…”

Section: Deuterium Fractionation and Depletion In The Iras 05405-0117mentioning

confidence: 99%

Prestellar and protostellar cores in Orion B9

Miettinen

Harju

Haikala

et al. 2009

A&A

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Context. Dense molecular cores are studied to gain insight into the processes causing clouds to fragment and form stars. In this study, we concentrate on a region that is assumed to represent an early stage of clustered star-formation in a giant molecular cloud. Aims. We aim to determine the properties and spatial distribution of dense cores in the relatively quiescent Ori B9 cloud, and to estimate their ages and dynamical timescales. Methods. The cloud was mapped in the 870 μm continuum with APEX/LABOCA, and selected positions were observed in the lines of N 2 H + and N 2 D + using IRAM-30 m. These were used together with our previous H 2 D + observations to derive the degree of deuteration and some other chemical characteristics. Archival far-infrared Spitzer/MIPS maps were combined with the LABOCA map to distinguish between prestellar and protostellar cores, and to estimate the evolutionary stages of protostars. Results. Twelve dense cores were detected at 870 μm continuum in the Ori B9 cloud. The submm cores constitute ∼4% of the total mass of the Ori B9 region. There is an equal number of prestellar and protostellar cores. Two of the submm sources, which we call SMM 3 and SMM 4, are previously unknown Class 0 candidates. There is a high likelihood of the core masses and mutual separations representing the same distributions as observed in other parts of Orion. We found a moderate degree of deuteration in N 2 H + (0.03-0.04). There is, furthermore, evidence of N 2 H + depletion in the core SMM 4. These features suggest that the cores have reached chemical maturity. We derive a relatively high degree of ionization (∼10 −7 ) in the clump associated with IRAS 05405-0117. The ambipolar diffusion timescales for two of the cores are ∼70-100 times longer than the free-fall time.Conclusions. The distribution and masses of dense cores in Ori B9 are similar to those observed in more active regions of Orion, where the statistical core properties have been explained by turbulent fragmentation. The 50/50 proportions of prestellar and protostellar cores imply that the duration of the prestellar phase is comparable to the free-fall time. However, on the basis of chemical data of the IRAS 05405-0117 region, this timescale could be questioned. A possible explanation is that this survey samples only the densest, i.e., dynamically most advanced cores.

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“…The heating of material by a protostar should rapidly reduce any enhancement in the deuterium species as the CO unfreezes in the inner parts (Emprechtinger et al 2009). Friesen et al (2010) sees an anti-correlation between DR and the distance to heating sources such as embedded protostars.…”

Section: µM Contentmentioning

confidence: 99%

Deuteration in infrared dark clouds

Lackington

Fuller

Pineda

et al. 2015

Monthly Notices of the Royal Astronomical Society

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Much of the dense gas in molecular clouds has a filamentary structure but the detailed structure and evolution of this gas is poorly known. We have observed 54 cores in infrared dark clouds (IRDCs) using N 2 H + (1-0) and (3-2) to determine the kinematics of the densest material, where stars will form. We also observed N 2 D + (3-2) towards 29 of the brightest peaks to analyse the level of deuteration which is an excellent probe of the quiescent of the early stages of star formation. There were 13 detections of N 2 D + (3-2). This is one of the largest samples of IRDCs yet observed in these species. The deuteration ratio in these sources ranges between 0.003 and 0.14. For most of the sources the material traced by N 2 D + and N 2 H + (3-2) still has significant turbulent motions, however three objects show subthermal N 2 D + velocity dispersion. Surprisingly the presence or absence of an embedded 70µm source shows no correlation with the detection of N 2 D + (3-2), nor does it correlate with any change in velocity dispersion or excitation temperature. Comparison with recent models of deuteration suggest evolutionary time-scales of these regions of several freefall times or less.

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The N₂D⁺/N₂H⁺ ratio as an evolutionary tracer of Class 0 protostars

Cited by 142 publications

References 76 publications

A (sub)millimetre study of dense cores in Orion B9

A (sub)millimetre study of dense cores in Orion B9

Prestellar and protostellar cores in Orion B9

Deuteration in infrared dark clouds

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