Prestellar and protostellar cores in Orion B9

Miettinen, O.; Harju, J.; Haikala, L. K.; Kainulainen, J.; Johansson, Lars

doi:10.1051/0004-6361/200811534

Cited by 21 publications

(30 citation statements)

References 109 publications

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“…As discussed in Section 4. Miettinen et al (2009) find R D ≈ (r + 2r 2 )/(3 + 2r + r 2 ). Using the Miettinen et al relation, we then find a mean r = 0.07 across Oph B2 and a lower limit x e > 1.5 × 10 −8 through Equation (9).…”

Section: Ionization Fraction and Electron Abundance X Ementioning

confidence: 83%

The Initial Conditions of Clustered Star Formation. Iii. The Deuterium Fractionation of the Ophiuchus B2 Core

Friesen

Francesco

Myers

et al. 2010

ApJ

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We present N 2 D + 3-2 (IRAM), and H 2 D + 1 11 -1 10 and N 2 H + 4-3 (JCMT) maps of the small cluster-forming Ophiuchus B2 core in the nearby Ophiuchus molecular cloud. In conjunction with previously published N 2 H + 1-0 observations, the N 2 D + data reveal the deuterium fractionation in the high-density gas across Oph B2. The average deuterium fractionation R D = N (N 2 D + )/N(N 2 H + ) ∼ 0.03 over Oph B2, with several small scale R D peaks and a maximum R D = 0.1. The mean R D is consistent with previous results in isolated starless and protostellar cores. The column density distributions of both H 2 D + and N 2 D + show no correlation with total H 2 column density. We find, however, an anticorrelation in deuterium fractionation with proximity to the embedded protostars in Oph B2 to distances 0.04 pc. Destruction mechanisms for deuterated molecules require gas temperatures greater than those previously determined through NH 3 observations of Oph B2 to proceed. We present temperatures calculated for the dense core gas through the equating of non-thermal line widths for molecules (i.e., N 2 D + and H 2 D + ) expected to trace the same core regions, but the observed complex line structures in B2 preclude finding a reasonable result in many locations. This method may, however, work well in isolated cores with less complicated velocity structures. Finally, we use R D and the H 2 D + column density across Oph B2 to set a lower limit on the ionization fraction across the core, finding a mean x e,lim few × 10 −8 . Our results show that care must be taken when using deuterated species as a probe of the physical conditions of dense gas in star-forming regions.

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Section: Ionization Fraction and Electron Abundance X Ementioning

confidence: 83%

The Initial Conditions of Clustered Star Formation. Iii. The Deuterium Fractionation of the Ophiuchus B2 Core

Friesen

Francesco

Myers

et al. 2010

ApJ

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“…The data were used to determine the physical characteristics of dense cores in this region. We mainly investigated the temperatures and kinematics of the cores, and recalculated the temperature-dependent quantities presented in Paper I (Miettinen et al 2009). Our main results and conclusions are as follows:…”

Section: Discussionmentioning

confidence: 99%

“…• 8), at 870 μm dust continuum using LABOCA on APEX, and discovered 12 dense submm cores (Miettinen et al 2009; hereafter Paper I). The cores were classified into starless and protostellar ones by using the Spitzer data, yielding the result that half the cores have embedded drawn from the submm peak positions in the LABOCA 870 μm dust continuum map of the region.…”

Section: Introductionmentioning

confidence: 99%

Physical properties of dense cores in Orion B9

Miettinen

Harju

Haikala

et al. 2010

A&A

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Aims. We aim to determine the physical and chemical properties of the starless and protostellar cores in Orion B9, which represents a relatively quiescent star-forming region in Orion B. Methods. We observed the NH 3 (J, K) = (1, 1) and (2, 2) inversion lines and the N 2 H + (3−2) rotational lines, with the Effelsberg 100-m and APEX telescopes, respectively, towards the submillimetre peak positions in Orion B9. These data are used in conjunction with our APEX/LABOCA 870 μm dust continuum data of the region. Results. The gas kinetic temperature in the cores derived from the NH 3 data is between ∼9.4−13.9 K. The non-thermal velocity dispersion is subsonic in most of the cores. The non-thermal linewidth in protostellar cores appears to increase with increasing bolometric luminosity. The core masses, ∼2−8 M , are very likely drawn from the same parent distribution as the core masses in Orion B North. Based on the virial parameter analysis, starless cores in the region are likely to be gravitationally bound, and thus prestellar. Some of the cores have a lower radial velocity than the systemic velocity of the region, suggesting that they are members of the "low-velocity part" of Orion B. The observed core-separation distances deviate from the corresponding random-like model distributions. The distances between the nearest neighbours are comparable to the thermal Jeans length. The fractional abundances of NH 3 and N 2 H + in the cores are ∼1.5−9.8 × 10 −8 and ∼0.2−5.9 × 10 −10 , respectively. The NH 3 abundance appears to decrease with increasing H 2 column and number densities. The NH 3 /N 2 H + column density ratio is larger in starless cores than in cores with embedded protostars. Conclusions. The core population in Orion B9 is comparable in physical properties to those in nearby low-mass star-forming regions. The Orion B9 cores also seem to resemble cores found in isolation rather than those associated with clusters. Moreover, because the cores may not be randomly distributed within the region (contrary to what was suggested in our Paper I), it is unclear whether the origin of cores could be explained by turbulent fragmentation. On the other hand, many of the core properties conform to the picture of dynamic core evolution. The Orion B9 region has probably been influenced by the feedback from the nearby Ori OB 1b group, and the fragmentation of the parental cloud into cores could be caused by gravitational instability.

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“…Using the LABOCA bolometer array on APEX (Atacama Pathfinder EXperiment), we mapped that region at 870 μm (Miettinen et al 2009, hereafter Paper I). The dust continuum mapping resulted in the discovery of twelve dense cores of which four were found to be associated with IRAS point sources, and eight of them appeared previously unknown sources.…”

Section: Introductionmentioning

confidence: 99%

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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Prestellar and protostellar cores in Orion B9

Cited by 21 publications

References 109 publications

The Initial Conditions of Clustered Star Formation. Iii. The Deuterium Fractionation of the Ophiuchus B2 Core

The Initial Conditions of Clustered Star Formation. Iii. The Deuterium Fractionation of the Ophiuchus B2 Core

Physical properties of dense cores in Orion B9

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

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