Star Formation: Low-Mass:
Low-mass stars like our Sun are formed in dense cores of molecular gas clouds. At optical wavelengths, the star formation process is hidden from view by interstellar dust, and even at infrared wavelengths the most deeply embedded protostars often remain unseen. Since most of the material in dense cores is cold, below 100 K, millimeter wavelengths provide the best probes of the physical conditions and gas motions. Observational diagnostics include thermal dust emission and spectral lines from the rotational transitions of common molecules, which enable detailed study of the key components of protostellar systems: the internal structure of dense cores present before the onset of star formation, the accretion disks that feed the build-up of protostar mass, and the bipolar outflows that remove angular momentum and allow continued accretion. In addition, the influence of magnetic fields is traced through millimeter observations of the polarized emission of spinning dust. Such observations inform us about the conditions under which Sun-like stars and exoplanetary systems form, in regions containing single stars, binaries, and small groups.
Individual Low-mass Protostar Envelopes, Disks and Outflows
The angular resolution of the SMA is sufficient to separate Solar System
scale disks from the dense gas envelopes surrounding embedded protostars,
which has proved to be an important tool to study the physical processes
at work in the complex systems of infall and outflow that accompany the
youngest protostars. The SMA made the first resolved surveys of significant
samples of embedded protostars at different stages of evolution.
Protostellar accretion history traced with chemistry
The luminosities of embedded protostars is much lower than expected from the
energy release due to the steady collapse of dense cores. An appealing
solution to this problem is that accretion is episodic, with protostars
undergoing short periods of high accretion rates that build up their mass.
A clever way to characterise protostellar accretion histories towards
individual sources makes use of the sublimation and freeze-out chemistry of the
CO molecule, which is observed in the gas phase at millimeter wavelengths.
Alignment between Protostellar Outflows and Filaments
Many stars form in filaments, where gas flows suggest embedded dense cores
will rotate primarily parallel or perpendicular to the parent filemant.
If angular momentum at the protostar scale is inherited from this core scale,
then the rotation axes of newly formed prototars and their bipolar ouflows
will share this alignment.
The Influence of Magnetic Fields
Magnetized models of star formation show that magnetic fields have the
potential to strongly effect the the outcome of dense core collapse,
in particular through the process of "magnetic breaking" where a
sufficiently strong field provides a conduit to remove angular momentum from
the system. This process can prevent fragmentation and the develoment of
rotationally supported disks.
References:
T. L. Bourke, A. Crapsi, P. C. Myers, N. J.II Evans, D. J. Wilner, T. L. Huard,
J. K. Jorgensen, C. H. Young,
Discovery of a Low Mass Bipolar Molecular Outflow from L1014-IRS with the Submillimeter Array, 2005, ApJ, 633, L129
C. Brinch, A. Crapsi, J. K. Jorgensen, M. R. Hogerheijde, T. Hill,
A deeply embedded young protoplanetary disk around L1489 IRS observed by the submillimeter array, 2007, A&A, 475, 915
Xuepeng Chen, Tyler L. Bourke, Ralf Launhardt, Thomas Henning,
SMA CO(2-1) Observations of CG30: A Protostellar Binary System with a High-Velocity Quadrupolar Molecular Outflow, 2008, ApJ, 686, L107
Søren Frimann, Jes K. Jørgensen, Michael M. Dunham, Tyler L. Bourke, Lars E. Kristensen, Stella S. R. Offner, Ian W. Stephens, John J. Tobin, Eduard I. Vorobyov,
Protostellar accretion traced with chemistry. High resolution C18O and continuum observations towards deeply embedded protostars in Perseus, 2017, A&A, 602, 120
Galametz, Maud; Maury, Anaelle; Girart, Josep M.; Rao, Ramprasad; Zhang, Qizhou; Gaudel, Mathilde; Valdivia, Valeska; Keto, Eric; Lai, Shih-Ping,
SMA observations of the polarized dust emission in solar-type Class 0 protostars: the magnetic field properties at envelope scales, 2018, accepted to A&A, arXiv:1804.05801
Jes K. Jorgensen, Tyler L. Bourke, Philip C. Myers, James Di Francesco, Ewine F. van Dishoeck, Chin-Fei Lee, Nagayoshi Ohashi, Fredrik L. Schoeier, Shigehisa Takakuwa, David J. Wilner, and Qizhou Zhang,
A Submillimeter Array Survey of Low-Mass Protostars I. Overview of Program: Envelopes, Disks, Outflows and Hot Cores, 2007, ApJ, 659, 479
Jes K. Jorgensen, Ewine F. van Dishoeck, Ruud Visser, Tyler L. Bourke, David J. Wilner, Dave Lommen, Michiel R. Hogerheijde, Philip C. Myers,
PROSAC: A Submillimeter Array survey of low-mass protostars. II. The mass evolution of envelopes, disks, and stars from the Class 0 through I stages, 2009, A&A, 507, 861
Jes K. Jorgensen, Ruud Visser, Jonathan P. Williams, Edwin A. Bergin,
Molecule sublimation as a tracer of protostellar accretion: Evidence for accretion bursts from high angular resolution C18O images, 2015, accepted to A&A, 579, A23
Chin-Fei Lee, Paul T.P. Ho, Aina Palau, Naomi Hirano, Tyler L. Bourke, Hsien Shang, Qizhou Zhang,
Submillimeter arcsecond-resolution mapping of the highly collimated protostellar jet HH 211, 2007, ApJ, 670, 1188
Chin-Fei Lee, Yao-Yuan Mao, Bo Reipurth,
Infall and rotation motions in the HH 111 protostellar system: A flattened envelope in transition to a disk?, 2009, ApJ, 694, 1395
Ngoc Phan-Bao, Basmah Riaz, Chin-Fei Lee, Ya-Wen Tang, Paul T. P. Ho, L. Martin, Eduardo, Jeremy Lim, Nagayoshi Ohashi, Hsien Shang,
First Confirmed Detection of a Bipolar Molecular Outflow from a Young Brown Dwarf, 2008, ApJ, 689, L141
Riwaj Pokhrel, Philip C. Myers, Michael M. Dunham, Ian W. Stephens, Sarah I. Sadavoy, Qizhou Zhang, Tyler L. Bourke, John J. Tobin, Katherine I. Lee, Robert A. Gutermuth, Stella S. R. Offner,
Hierarchical fragmentation in the Perseus molecular cloud: From the cloud scale to protostellar objects, 2018, ApJ, 853, 5
Ian W. Stephens, Michael M. Dunham, Philip C. Myers, Riwaj Pokhrel, Sarah I. Sadavoy, Eduard I. Vorobyov, John J. Tobin, Jaime E. Pineda, Stella S. R. Offner, Katherine I. Lee, Lars E. Kristensen, Jes K. Jørgensen, Alyssa A. Goodman Tyler L. Bourke, Héctor G. Arce, Adele L. Plunkett
Alignment Between Protostellar Outflows and Filamentary Structure, 2017, ApJ, 846, 16
