The dynamical state of the first hydrostatic core candidate Chamaeleon-MMS1

Tsitali, Anastasia; Беллоче, А.; Commerçon, B.; Menten, K. M.

doi:10.1051/0004-6361/201321204

Cited by 26 publications

(46 citation statements)

References 93 publications

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“…All cores but Cha1-C1 are starless. Cha1-C1 corresponds to Cha-MMS1, which is a candidate first hydrostatic core (see Belloche et al 2006;Tsitali et al 2013). (a) 13 CO 2−1 was observed in parallel to C 18 O 2−1.…”

Section: Chamaeleon I Datamentioning

confidence: 99%

“…IRAM 04191+1522 and Oph A SM1N were used as calibration sources. The pointing was checked every ∼1 h. Tsitali et al (2013) calculated a value of 0.34 for the main beam efficiency of the telescope through a detailed calibration analysis. The northern part of Cha I was mapped in CO 3−2 with APEX in 2006 June with the on-the-fly mode (project M-77.C-0016-2006).…”

Section: Chamaeleon I Datamentioning

confidence: 99%

“…The outer (radii ≥20 000 AU) gas kinetic temperature of the densest core in Cha I, Cha1-C1 (Cha-MMS1) was constrained to 9 K through radiative transfer modelling (Tsitali et al 2013). Less dense cores may have a slightly higher kinetic temperature, and we assume T = 10 K as an approximation.…”

Section: Virial Analysismentioning

confidence: 99%

“…3a show that at most five cores are gravitationally bound (Cha1-C1, C2, C3, C4, C5) and one is virialized in Cha I when taking the total dust mass into account. The virialized core is Cha1-C1 (also known as Cha-MMS1), which is a first hydrostatic core candidate (Belloche et al 2006(Belloche et al , 2011aTsitali et al 2013). On the other hand, no single molecular line indicates that any core in Cha III is virialized and we find that only Cha3-C1 is gravitationally bound (see Tables 4 and A .2,and Fig.…”

Section: Virial Analysismentioning

confidence: 99%

“…We used the offline-version of the non-LTE radiative transfer code RADEX (van der Tak et al 2007) to calculate the column densities of C 18 O, C 17 O, CH 3 OH, C 34 S, HC 3 N, and N 2 H + , applying the escape probability method for a uniform sphere. We assumed a kinetic temperature of 10 K for all observed transitions except for C 18 O and C 17 O 2-1 for which we used 12 K. The initial assumption of 10 K for C 18 O and C 17 O 2-1 gave rise to inconsistent (unrealistically high) column densities for a few cores.…”

Section: Observational Molecular Abundancesmentioning

confidence: 99%

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Star formation in Chamaeleon I and III: a molecular line study of the starless core population

Tsitali

Беллоче

Garrod

et al. 2015

A&A

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Context. The Chamaeleon dark molecular clouds are excellent nearby targets for low-mass star formation studies. Even though they belong to the same cloud complex, Cha I and II are actively forming stars while Cha III shows no sign of ongoing star formation. Aims. We aim to determine the driving factors that have led to the very different levels of star formation activity in Cha I and III and examine the dynamical state and possible evolution of the starless cores within them. Methods. Observations were performed in various molecular transitions with the APEX and Mopra telescopes. We examine the kinematics of the starless cores in the clouds through a virial analysis, a search for contraction motions, and velocity gradients. The chemical differences in the two clouds are explored through their fractional molecular abundances, derived from a non-LTE analysis, and comparison to predictions of chemical models.Results. Five cores are gravitationally bound in Cha I and one in Cha III. The so-called infall signature indicating contraction motions is seen toward 8-17 cores in Cha I and 2-5 cores in Cha III, which leads to a range of 13-28% of the cores in Cha I and 10-25% of the cores in Cha III that are contracting and may become prestellar. There is no significant difference in the turbulence level in the two clouds. Future dynamical interactions between the cores will not be dynamically significant in either Cha I or III, but the subregion Cha I North may experience collisions between cores within ∼0.7 Myr. Turbulence dissipation in the cores of both clouds is seen in the high-density tracers N 2 H + 1-0 and HC 3 N 10-9 which have lower non-thermal velocity dispersions compared to C 17 O 2-1, C 18 O 2-1, and C 34 S 2-1. Evidence of depletion in the Cha I core interiors is seen in the abundance distributions of the latter three molecules. The median fractional abundance of C 18 O is lower in Cha III than Cha I by a factor of ∼2. The median abundances of most molecules (except methanol) in the Cha III cores lie at the lower end of the values found in the Cha I cores. A difference in chemistry is thus seen. Chemical models suitable for the Cha I and III cores are used to constrain the effectiveness of the HC 3 N to N 2 H + abundance ratio as an evolutionary indicator. Both contraction and static chemical models indicate that this ratio is a good evolutionary indicator in the prestellar phase for both gravitationally bound and unbound cores. In the framework of these models, we find that the cores in Cha III and the southern part of Cha I are in a similar evolutionary stage and are less chemically evolved than the central region of Cha I. Conclusions. The measured HC 3 N/N 2 H + abundance ratio and the evidence for contraction motions seen towards the Cha III starless cores suggest that Cha III is younger than Cha I Centre and that some of its cores may form stars in the future if contraction does not cease. The cores in Cha I South may on the other hand be transient structures.

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Section: Chamaeleon I Datamentioning

confidence: 99%

Section: Chamaeleon I Datamentioning

confidence: 99%

Section: Virial Analysismentioning

confidence: 99%

Section: Virial Analysismentioning

confidence: 99%

Section: Observational Molecular Abundancesmentioning

confidence: 99%

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Star formation in Chamaeleon I and III: a molecular line study of the starless core population

Tsitali

Беллоче

Garrod

et al. 2015

A&A

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High-resolution ammonia mapping of the very young protostellar core Chamaeleon-MMS1

Väisälä

Harju

Mantere

et al. 2014

A&A

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Aims. The aim of this study is to investigate the structure and kinematics of the nearby candidate first hydrostatic core Cha-MMS1. Methods. Cha-MMS1 was mapped in the NH 3 (1, 1) line and the 1.2 cm continuum using the Australia Telescope Compact Array (ATCA). The angular resolution of the ATCA observations is 7 (∼1000 AU), and the velocity resolution is 50 m s −1 . The core was also mapped with the 64 m Parkes Telescope in the NH 3 (1, 1) and (2, 2) lines. Observations from Herschel Space Observatory and Spitzer Space Telescope were used to help interpretation. The ammonia spectra were analysed using Gaussian fits to the hyperfine structure. A two-layer model was applied in the central parts of the core where the ATCA spectra show signs of self-absorption. Results. A compact high column density core with a steep velocity gradient (∼20 km s −1 pc −1 ) is detected in ammonia. We derive a high gas density (∼10 6 cm −3 ) in this region, and a fractional ammonia abundance compatible with determinations towards other dense cores (∼10 −8 ). This suggests that the age of the high density core is comparable to the freeze-out timescale of ammonia in these conditions, on the order of 10 4 years. The direction of the velocity gradient agrees with previous single-dish observations, and the overall velocity distribution can be interpreted as rotation. The rotation axis goes through the position of a compact far-infrared source detected by Spitzer and Herschel. The specific angular momentum of the core, ∼10 −3 km s −1 pc, is typical for protostellar envelopes. A string of 1.2 cm continuum sources is tentatively detected near the rotation axis. The ammonia spectra suggest the presence of warm embedded gas in its vicinity. An hourglass-shaped structure is seen in ammonia at the cloud's average LSR velocity, also aligned with the rotation axis. Although this structure resembles a pair of outflow lobes the ammonia spectra show no indications of shocked gas. Conclusions. The observed ammonia structure mainly delineates the inner envelope around the central source. The velocity gradient is likely to originate in the angular momentum of the contracting core, although influence of the outflow from the neighbouring young star IRS4 is possibly visible on one side of the core. The tentative continuum detection and the indications of a warm background component near the rotation axis suggest that the core contains a deeply embedded outflow which may have been missed in previous single-dish CO surveys owing to beam dilution.

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From forced collapse to H ii region expansion in Mon R2: Envelope density structure and age determination withHerschel

Didelon

Motte

Tremblin

et al. 2015

A&A

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Context. The surroundings of H  regions can have a profound influence on their development, morphology, and evolution. This paper explores the effect of the environment on H  regions in the MonR2 molecular cloud. Aims. We aim to investigate the density structure of envelopes surrounding H  regions and to determine their collapse and ionisation expansion ages. The Mon R2 molecular cloud is an ideal target since it hosts an H  region association, which has been imaged by the Herschel PACS and SPIRE cameras as part of the HOBYS key programme.Methods. Column density and temperature images derived from Herschel data were used together to model the structure of H  bubbles and their surrounding envelopes. The resulting observational constraints were used to follow the development of the Mon R2 ionised regions with analytical calculations and numerical simulations.Results. The four hot bubbles associated with H  regions are surrounded by dense, cold, and neutral gas envelopes, which are partly embedded in filaments. The envelope's radial density profiles are reminiscent of those of low-mass protostellar envelopes. The inner parts of envelopes of all four H  regions could be free-falling because they display shallow density profiles: ρ(r) ∝ r −q with q 1.5. As for their outer parts, the two compact H  regions show a ρ(r) ∝ r −2 profile, which is typical of the equilibrium structure of a singular isothermal sphere. In contrast, the central UCH  region shows a steeper outer profile, ρ(r) ∝ r −2.5 , that could be interpreted as material being forced to collapse, where an external agent overwhelms the internal pressure support. Conclusions. The size of the heated bubbles, the spectral type of the irradiating stars, and the mean initial neutral gas density are used to estimate the ionisation expansion time, t exp ∼ 0.1 Myr, for the dense UCH  and compact H  regions and ∼0.35 Myr for the extended H  region. Numerical simulations with and without gravity show that the so-called lifetime problem of H  regions is an artefact of theories that do not take their surrounding neutral envelopes with slowly decreasing density profiles into account. The envelope transition radii between the shallow and steeper density profiles are used to estimate the time elapsed since the formation of the first protostellar embryo, t inf ∼ 1 Myr, for the ultra-compact, 1.5−3 Myr for the compact, and greater than ∼6 Myr for the extended H  regions. These results suggest that the time needed to form a OB-star embryo and to start ionising the cloud, plus the quenching time due to the large gravitational potential amplified by further in-falling material, dominates the ionisation expansion time by a large factor. Accurate determination of the quenching time of H  regions would require additional small-scale observationnal constraints and numerical simulations including 3D geometry effects.

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The dynamical state of the first hydrostatic core candidate Chamaeleon-MMS1

Cited by 26 publications

References 93 publications

Star formation in Chamaeleon I and III: a molecular line study of the starless core population

Star formation in Chamaeleon I and III: a molecular line study of the starless core population

High-resolution ammonia mapping of the very young protostellar core Chamaeleon-MMS1

From forced collapse to H ii region expansion in Mon R2: Envelope density structure and age determination withHerschel

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