Internal structure of a cold dark molecular cloud inferred from the extinction of background starlight

Alves, J.; Lada, Charles J.; Lada, Elizabeth A.

doi:10.1038/35051509

Cited by 430 publications

(527 citation statements)

References 15 publications

Supporting

Mentioning

497

Contrasting

Order By: Relevance

“…However, the oversimplified approach of uniform density initial conditions (widely employed for several decades) should be questioned, because this object, if gravitationally unstable, can never exist in equilibrium. In contrast, we know from observations that there are real objects (such as Barnard 68) for which there is a striking agreement with uniformly rotating Bonnor-Ebert spheres (BES) (see, e.g., Alves et al 2001or Lada et al 2003.…”

Section: Initial Conditionsmentioning

confidence: 85%

Protostellar collapse of rotating cloud cores

Schönke

Tscharnuter

2011

A&A

View full text Add to dashboard Cite

Aims. We investigate the influence of turbulent viscosity on the collapse of a rotating molecular cloud core with axial symmetry, in particular, on the first and second collapse phase, as well as the evolution of the second (protostellar) core during its first accretion period. By using extensive numerical calculations, we monitor the intricate interactions between the newly formed protostar and the surrounding accretion disk (the first core) in which the star is embedded. Methods. We use a grid-based radiation-hydrodynamics code with a spatial grid designed to meet the high resolution required to study the second core. The radiative transfer is treated in the flux-limited diffusion approximation. A slightly supercritical Bonnor-Ebert sphere of 1 M and uniform rotation according to a fixed centrifugal radius of 100 AU serves as the initial condition without exception. In a parameter study, we vary the β-viscosity driving the angular momentum transport. Results. Without viscosity (β = 0), a highly flattened accretion disk forms that fragments into several "cold" rings. For β = 10 −4 , a single "warm" ring forms that undergoes collapse due to hydrogen dissociation. For β = 10 −3 , ring formation is suppressed completely. The second collapse proceeds on the local thermal timescale, which is in contrast to the current view of a generally dynamical second collapse. During the first accretion period of the second core, the first core heats up globally and, as a consequence, a nearly spherical outflow occurs, destroying the structure of the former accretion disk completely. Finally, for β = 10 −2 , we see the classical dynamical second collapse and a shorter but more rapid accretion phase. The impact on the surrounding accretion disk is even more pronounced. We follow the resulting massive outflow up to several kyr after the second collapse, where the central parts (R < 0.7 AU) are now cut out and replaced with an appropriate inner boundary condition. Matter is found to turn back to the center at a radius of 500 AU after about 4 kyr and to reach the protostar again after approximately 7 kyr. The results suggest that the star formation process consists of short and rapid accretion phases (lasting on the order of 100 yr) between long and quiet outflow periods (lasting several kyr).

show abstract

Section: Initial Conditionsmentioning

confidence: 85%

Protostellar collapse of rotating cloud cores

Schönke

Tscharnuter

2011

A&A

View full text Add to dashboard Cite

show abstract

“…Alves, Lada & Lada 2001). The BE model treats a core as an isothermal, self-gravitating, polytropic sphere bounded by external pressure.…”

Section: Bonnor-ebert Critical Massmentioning

confidence: 99%

The JCMT Gould Belt Survey: first results from the SCUBA-2 observations of the Ophiuchus molecular cloud and a virial analysis of its prestellar core population

Pattle¹,

Ward-Thompson²,

Kirk³

et al. 2015

Monthly Notices of the Royal Astronomical Society

139

146

View full text Add to dashboard Cite

In this paper we present the first observations of the Ophiuchus molecular cloud performed as part of the James Clerk Maxwell Telescope (JCMT) Gould Belt Survey (GBS) with the SCUBA-2 instrument. We demonstrate methods for combining these data with previous HARP CO, Herschel, and IRAM N 2 H + observations in order to accurately quantify the properties of the SCUBA-2 sources in Ophiuchus. We produce a catalogue of all of the sources found by SCUBA-2. We separate these into protostars and starless cores. We list all of the starless cores and perform a full virial analysis, including external pressure. This is the first time that external pressure has been included in this level of detail. We find that the majority of our cores are either bound or virialised. Gravitational energy and external pressure are on average of a similar order of magnitude, but with some variation from region to region. We find that cores in the Oph A region are gravitationally bound prestellar cores, while cores in the Oph C and E regions are pressure-confined. We determine that N 2 H + is a good tracer of the bound material of prestellar cores, although we find some evidence for N 2 H + freezeout at the very highest core densities. We find that non-thermal linewidths decrease substantially between the gas traced by C 18 O and that traced by N 2 H + , indicating the dissipation of turbulence at higher densities. We find that the critical Bonnor-Ebert stability criterion is not a good indicator of the boundedness of our cores. We detect the pre-brown dwarf candidate Oph B-11 and find a flux density and mass consistent with previous work. We discuss regional variations in the nature of the cores and find further support for our previous hypothesis of a global evolutionary gradient across the cloud from southwest to northeast, indicating sequential star formation across the region.

show abstract

“…Alves, Lada & Lada 2001). The BE model treats a core as an isothermal, selfgravitating, polytropic sphere bounded by external pressure.…”

Section: Bonnor-ebert Stability Analysismentioning

confidence: 99%

The JCMT Gould Belt Survey: first results from SCUBA-2 observations of the Cepheus Flare region

Pattle

Ward-Thompson

Kirk

et al. 2016

Mon. Not. R. Astron. Soc.

View full text Add to dashboard Cite

We present observations of the Cepheus Flare obtained as part of the James Clerk Maxwell Telescope (JCMT) Gould Belt Legacy Survey (GBLS) with the SCUBA-2 instrument. We produce a catalogue of sources found by SCUBA-2, and separate these into starless cores and protostars. We determine masses and densities for each of our sources, using source temperatures determined by the Herschel Gould Belt Survey. We compare the properties of starless cores in four different molecular clouds: L1147/58, L1172/74, L1251 and L1228. We find that the core mass functions for each region typically show shallower-than-Salpeter behaviour. We find that L1147/58 and L1228 have a high ratio of starless cores to Class II protostars, while L1251 and L1174 have a low ratio, consistent with the latter regions being more active sites of current star formation, while the former are forming stars less actively. We determine that, if modelled as thermally-supported Bonnor-Ebert spheres, most of our cores have stable configurations accessible to them. We estimate the external pressures on our cores using archival 13 CO velocity dispersion measurements and find that our cores are typically pressure-confined, rather than gravitationally bound. We perform a virial analysis on our cores, and find that they typically cannot be supported against collapse by internal thermal energy alone, due primarily to the measured external pressures. This suggests that the dominant mode of internal support in starless cores in the Cepheus Flare is either non-thermal motions or internal magnetic fields.

show abstract

Internal structure of a cold dark molecular cloud inferred from the extinction of background starlight

Cited by 430 publications

References 15 publications

Protostellar collapse of rotating cloud cores

Protostellar collapse of rotating cloud cores

The JCMT Gould Belt Survey: first results from the SCUBA-2 observations of the Ophiuchus molecular cloud and a virial analysis of its prestellar core population

The JCMT Gould Belt Survey: first results from SCUBA-2 observations of the Cepheus Flare region

Contact Info

Product

Resources

About