scholarly journals Molecules in star formation

1997 ◽  
Vol 178 ◽  
pp. 19-30 ◽  
Author(s):  
F.H. Shu
Keyword(s):  
Star Formation ◽  
Molecular Diagnostics ◽  
Accretion Disks ◽  
Central Star ◽  
Flow Dynamics ◽  
Molecular Outflows ◽  
Self Similar ◽  
Cloud Cores ◽  
Cloud Core ◽  
Review Current

We review current ideas and models in the problem of star formation from molecular cloud cores that are relatively isolated from the influences of other forming stars. We discuss the time scales, flow dynamics, and density and temperature structures applicable to each of the four stages of the entire process: (a) formation of a magnetized cloud core by ambipolar diffusion and evolution to a pivotal state of gravomagneto catastrophe; (b) self-similar collapse of the pivotal configuration and the formation of protostars, disks, and pseudo-disks; (c) onset of a magnetocentrifugally driven, lightly ionized wind from the interaction of an accretion disk and the magnetosphere of the central star, and the driving of bipolar molecular outflows; (d) evolution of pre-main-sequnce stars surrounded by dusty accretion disks. For each of these stages and processes, we consider the characteristics of the molecular diagnostics needed to investigate the crucial aspects of the observational problem.

Hydromagnetic winds from accretion disks

1986 ◽  
Vol 64 (4) ◽  
pp. 501-506 ◽  
Author(s):  
Ralph E. Pudritz ◽  
Colin A. Norman
Keyword(s):  
Accretion Disks ◽  
Energy Transport ◽  
Cataclysmic Variables ◽  
Wind Model ◽  
Ionized Gas ◽  
Molecular Outflows ◽  
Self Similar ◽  
Similar Solutions ◽  
Accretion Shock ◽  
Hoop Stresses

We present a hydromagnetic wind model for molecular and ionized gas outflows associated with protostars. If the luminosity of protostars is due to accretion, then centrifugally driven winds that arise from the envelopes of molecular disks explain the observed rates of momentum and energy transport. Ionized outflow originates from disk radii r ≤ 1015 cm inside of which Ly-continuum photons from the protostellar accretion shock are intercepted. Observed molecular outflows arise from the cool disk envelope at radii 1015 ≤ r ≤ 1017 cm. The mass-loss rates of these two component outflows are [Formula: see text] and [Formula: see text]. These winds solve the angular-momentum problem of star formation. We propose that the collimation of such outflows is due to "hoop" stresses generated by the increasingly toroidal magnetic field in the wind and suggest that the structure of the underlying disks makes self-similar solutions for these outflows likely. Finally, we apply this analysis to other accreting systems such as cataclysmic variables.

scholarly journals Star Formation: Can There BE a Break in the IMF Near 0.1Mʘ?

1998 ◽  
Vol 11 (1) ◽  
pp. 425-426
Author(s):  
Takenori Nakano
Keyword(s):  
Star Formation ◽  
Mass Function ◽  
Small Mass ◽  
Initial Mass Function ◽  
Core Mass ◽  
The Core ◽  
Cloud Cores ◽  
Formation Efficiency ◽  
Cloud Core ◽  
The Imf

The initial mass function of stars (IMF) at small masses depends on several factors. First, it depends on the mass function of cloud cores in which stars form. Second, there must be a lower limit to the core mass for contraction; very small mass cores may not contract even if they exist. This must affect greatly the IMF near its lower end. Third, not all core matter may become stars; we must determine the stellar mass M*, or the star formation efficiency M*/Mcc, as a function of the mass of the cloud core, Mcc. In this paper we discuss the second and third points.

Protostellar X-Rays, Jets, and Bipolar Outflows

1997 ◽  
Vol 182 ◽  
pp. 225-239
Author(s):  
Frank H. Shu ◽  
Hsien Shang
Keyword(s):  
Mathematical Formulation ◽  
Central Star ◽  
Young Stellar Objects ◽  
X Rays ◽  
Bipolar Outflows ◽  
Stellar Objects ◽  
Molecular Outflows ◽  
Cloud Cores ◽  
Average State

We review the theory of x-winds in young stellar objects (YSOs). In particular, we consider how a model where the central star does not corotate with the inner edge of the accretion disk may help to explain the enhanced emission of X-rays from embedded protostars. We argue, however, that the departure from corotation is not large, so a mathematical formulation that treats the long-term average state as steady and axisymmetric represents a useful approximation. Magnetocentrifugally driven x-winds of this description collimate into jets, and their interactions with the surrounding molecular cloud cores of YSOs yield bipolar molecular outflows.

scholarly journals Dense cloud cores

1991 ◽  
Vol 147 ◽  
pp. 430-431
Author(s):  
R. Güsten ◽  
A. Schulz ◽  
E. Serabyn
Keyword(s):  
Star Formation ◽  
Molecular Species ◽  
Angular Resolution ◽  
Gas Temperature ◽  
Isotopic Species ◽  
First Results ◽  
Linear Molecules ◽  
Cloud Cores ◽  
Symmetric Top Molecules ◽  
Cloud Core

In order to search for ultra-dense gas condensations as possible sites of future star formation, observations with highest possible angular resolution in high-gas density probing molecular species are required. Here we report first results from two-telescope (IRAM 30-m & CSO 10.4-m) multi-transition excitation studies of the linear molecules CS and HCN, both with critical densities nc∼107 cm−3. We obtained maps towards a number of galactic cloud cores in the CS(J=5−4;7−6) and the HCN(3-2;4-3) mm/submm transitions and those of their optically thin isotopic species (C34S; H13CN) accessible from ground. For a proper excitation analysis, the gas temperature has been determined independently from the symmetric top molecules NH3 or CH3CN. Here we present first results obtained towards the NGC 2024 molecular cloud core (Schulz et al. 1990).

scholarly journals Dense cloud cores

1991 ◽  
Vol 147 ◽  
pp. 430-431
Author(s):  
R. Güsten ◽  
A. Schulz ◽  
E. Serabyn
Keyword(s):  
Star Formation ◽  
Molecular Species ◽  
Angular Resolution ◽  
Gas Temperature ◽  
Isotopic Species ◽  
First Results ◽  
Linear Molecules ◽  
Cloud Cores ◽  
Symmetric Top Molecules ◽  
Cloud Core

In order to search for ultra-dense gas condensations as possible sites of future star formation, observations with highest possible angular resolution in high-gas density probing molecular species are required. Here we report first results from two-telescope (IRAM 30-m & CSO 10.4-m) multi-transition excitation studies of the linear molecules CS and HCN, both with critical densities nc∼107 cm−3. We obtained maps towards a number of galactic cloud cores in the CS(J=5−4;7−6) and the HCN(3-2;4-3) mm/submm transitions and those of their optically thin isotopic species (C34S; H13CN) accessible from ground. For a proper excitation analysis, the gas temperature has been determined independently from the symmetric top molecules NH3 or CH3CN. Here we present first results obtained towards the NGC 2024 molecular cloud core (Schulz et al. 1990).

scholarly journals H_2O Megamasers: Accretion Disks, Jet Interaction, Outflows or Massive Star Formation?

2005 ◽  
Vol 295 (1-2) ◽  
pp. 107-116 ◽  
Author(s):  
C. Henkel ◽  
J. A. Braatz ◽  
A. Tarchi ◽  
A. B. Peck ◽  
N. M. Nagar ◽  
...  
Keyword(s):  
Star Formation ◽  
Accretion Disks ◽  
Massive Star ◽  
Massive Star Formation ◽  
Jet Interaction
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