Coronagraphic imaging of pre-main-sequence stars: Remnant evvelopes of star formation seen in reflection

1995 ◽  
Vol 109 ◽  
pp. 1181 ◽  
Author(s):  
Tadashi Nakajima ◽  
David A. Golimowski
Keyword(s):  
Star Formation ◽  
Main Sequence ◽  
Main Sequence Stars

scholarly journals Circumstellar Disks and Star Formation

1992 ◽  
Vol 9 ◽  
pp. 377-380
Author(s):  
L. Hartmann ◽  
M. Gomez ◽  
S.J. Kenyon
Keyword(s):  
Star Formation ◽  
Spectral Region ◽  
Main Sequence ◽  
Circumstellar Disks ◽  
Central Star ◽  
Disk Accretion ◽  
Main Sequence Stars ◽  
Excess Emission ◽  
Infrared Spectral ◽  
The Masses

Results from the IRAS satellite showed that many pre-main sequence stars exhibited unexpectedly large fluxes in the infrared spectral region. Several studies have shown that the simplest and most satisfying explanation of this excess emission is that it arises in optically-thick, dusty, circumstellar disks (Rucinski 1985; Adams, Lada, and Shu 1987, 1988; Kenyon and Hartmann 1987; Bertout, Basri, and Bouvier 1988; Basri and Bertout 1989). The masses of these disks are estimated to range between 10-3M⊙ to 1M⊙ (Beckwith et al. 1990; Adams et al. 1990), large enough that disk accretion may have a significant effect on the evolution of the central star. Indeed, Mercer-Smith, Cameron, and Epstein (1984) suggested that stars are essentially completely accreted from disks, rather than formed from quasi-spherical accretion (Stabler 1983, 1988).

GRAVITATIONAL COLLAPSE AND FRAGMENTATION OF MOLECULAR CLOUD CORES

2001 ◽  
Vol 10 (02) ◽  
pp. 115-211 ◽  
Author(s):  
LEONARDO DI G. SIGALOTTI ◽  
JAIME KLAPP
Keyword(s):  
Star Formation ◽  
Binary Stars ◽  
Molecular Cloud ◽  
Main Sequence ◽  
Numerical Models ◽  
Present Theory ◽  
Main Sequence Stars ◽  
Consistent Manner ◽  
Cloud Cores ◽  
Observational Knowledge

The detected multiplicity of main-sequence and pre-main-sequence stars along with the emerging evidence for binary and multiple protostars, imply that stars may ultimately form by fragmentation of collapsing molecular cloud cores. These discoveries, coupled with recent observational knowledge of the structure of dense cloud cores and of the properties of young binary stars, provide serious constraints to the theory of star formation. Most theoretical progress in the field of star formation is largely based on numerical calculations of the early collapse and fragmentation of protostellar clouds. Although these models have been quite successful at predicting the formation of binary protostars, a direct comparison between theory and observations has not yet been established. The results of recent observations as well as of early and recent analytic and numerical models, on which the present theory of star formation is based, are reviewed here in a self-consistent manner.

scholarly journals Fossil magnetic fields in intermediate-mass and massive stars

2019 ◽  
Vol 82 ◽  
pp. 345-355 ◽  
Author(s):  
E. Alecian ◽  
F. Villebrun ◽  
J. Grunhut ◽  
G. Hussain ◽  
C. Neiner ◽  
...  
Keyword(s):  
Magnetic Properties ◽  
Star Formation ◽  
Magnetic Fields ◽  
Main Sequence ◽  
Massive Stars ◽  
Main Sequence Stars ◽  
Intermediate Mass ◽  
Subsequent Evolution

A small fraction of the population of intermediate-mass and massive stars host strong and stable magnetic fields organised on large scales. These fields are believed to be remnants of star formation. It is however not clear how such fossil fields have been shaped during their formation and subsequent evolution. We report recent and ongoing studies on the magnetic properties of pre-main sequence stars and main sequence binaries, allowing us to make progress in this field.

Fossil magnetic fields and rotation of early-type stars

1994 ◽  
Vol 162 ◽  
pp. 184-185
Author(s):  
A.E. Dudorov
Keyword(s):  
Magnetic Field ◽  
Star Formation ◽  
Magnetic Fields ◽  
Molecular Clouds ◽  
Main Sequence ◽  
Early Type ◽  
Main Sequence Stars ◽  
Early Type Stars ◽  
Quadrupole Magnetic Field ◽  
Interstellar Molecular Clouds

Observational data of the last 10 years allow two main conclusions:a) Main sequence stars can be separated in two classes: - magnetic (Bp) stars with surface strengths of a dipole or quadrupole magnetic field of Bs ≈ n · (102 − 103) G, n = 2,3,4…7, and - normal main sequence stars (F-O) with magnetic fields Bs ≈ 1 − 100 G (< 300 G);b) Typical star formation takes place in interstellar molecular clouds with magnetic field strengths B ≈ 10-5 G (See Dudorov 1990).

scholarly journals On the nature of variations in the measured star formation efficiency of molecular clouds

2019 ◽  
Vol 488 (2) ◽  
pp. 1501-1518 ◽  
Author(s):  
Michael Y Grudić ◽  
Philip F Hopkins ◽  
Eve J Lee ◽  
Norman Murray ◽  
Claude-André Faucher-Giguère ◽  
...  
Keyword(s):  
Star Formation ◽  
Molecular Clouds ◽  
Main Sequence ◽  
Giant Molecular Clouds ◽  
Main Sequence Stars ◽  
Stellar Feedback ◽  
Magnetohydrodynamic Simulations ◽  
Formation Efficiency ◽  
The Relationship ◽  
Very High

Abstract Measurements of the star formation efficiency (SFE) of giant molecular clouds (GMCs) in the Milky Way generally show a large scatter, which could be intrinsic or observational. We use magnetohydrodynamic simulations of GMCs (including feedback) to forward-model the relationship between the true GMC SFE and observational proxies. We show that individual GMCs trace broad ranges of observed SFE throughout collapse, star formation, and disruption. Low measured SFEs (${\ll} 1\hbox{ per cent}$) are ‘real’ but correspond to early stages; the true ‘per-freefall’ SFE where most stars actually form can be much larger. Very high (${\gg} 10\hbox{ per cent}$) values are often artificially enhanced by rapid gas dispersal. Simulations including stellar feedback reproduce observed GMC-scale SFEs, but simulations without feedback produce 20× larger SFEs. Radiative feedback dominates among mechanisms simulated. An anticorrelation of SFE with cloud mass is shown to be an observational artefact. We also explore individual dense ‘clumps’ within GMCs and show that (with feedback) their bulk properties agree well with observations. Predicted SFEs within the dense clumps are ∼2× larger than observed, possibly indicating physics other than feedback from massive (main-sequence) stars is needed to regulate their collapse.

Structure and Appearance of Envelopes around Protostars

1977 ◽  
Vol 42 ◽  
pp. 38-64
Author(s):  
Harold W. Yorke
Keyword(s):  
Star Formation ◽  
Main Sequence ◽  
Interstellar Matter ◽  
Main Sequence Stars ◽  
Hydrogen Burning ◽  
Final Answer

The existence of material in the immediate vicinity of young main sequence stars or even younger objects, protostars, still contracting and evolving towards the main sequence, is related closely to the details of star formation. Although a number of individual idealized problems related to star formation have been well studied, our overall understanding of how interstellar matter evolves into full fledged hydrogen-burning stars can be deemed qualitative at best. The emerging picture is neither complete nor should it be considered the final answer as to how stars form. Let us summarize this picture by a list of “axioms”, valid for star formation (SF) in the plane of our Galaxy.

scholarly journals Expanding associations in the Vela-Puppis region

2019 ◽  
Vol 626 ◽  
pp. A17 ◽  
Author(s):  
T. Cantat-Gaudin ◽  
C. Jordi ◽  
N. J. Wright ◽  
J. J. Armstrong ◽  
A. Vallenari ◽  
...  
Keyword(s):  
Star Formation ◽  
Main Sequence ◽  
Unsupervised Classification ◽  
Young Stars ◽  
Proper Motions ◽  
Main Sequence Stars ◽  
Stellar Formation ◽  
Anisotropic Expansion ◽  
History Of ◽  
Kinematic Distribution

Context. The Vela-Puppis region is known to host the Vela OB2 association as well as several young clusters featuring OB and pre-main-sequence stars. Several spatial and kinematic subgroups have been identified in recent years. Aims. By grouping stars based on their positions and velocity, we can address the question of the dynamical history of the region and the mechanisms that drove stellar formation. The Gaia DR2 astrometry and photometry enables us to characterise the 3D spatial and 3D kinematic distribution of young stars and to estimate the ages of the identified components. Methods. We used an unsupervised classification method to group stars based on their proper motions and parallax. We studied the expansion rates of the different identified groups based on 3D velocities and on corrected tangential velocities. We used theoretical isochrones to estimate ages. Results. The young stars can be separated into seven main groups of different ages and kinematical distribution. All groups are found to be expanding, although the expansion is mostly not isotropic. Conclusions. The size of the region, the age substructure, and the anisotropic expansion rates are compatible with a prolonged period of star formation in a turbulent molecular cloud. The current kinematics of the stars cannot be explained by internal processes alone (such as gas expulsion).

Sign in / Sign up

Export Citation Format

Share Document