Star Formation

Main Content

Questions

Do stellar clusters form rapidly during a single collapse event or slowly over many crossing times?
What is the initial mass function (IMF) of stars and brown dwarfs? Is it universal, or does it vary with environment? Can we use the IMF to test models of star formation?
Why are massive stars rare, and do they form via accretion disks or stellar mergers?
How does the feedback from OB stars both promote and inhibit further star formation?
When and why does primordial mass segregation occur (i.e. concentration of the OB stars into the core)?
What is the smallest mass of brown dwarfs? How do brown dwarfs form? What makes it possible for such small objects to fragment and collapse?
What is the frequency of circumstellar disks as a function of stellar mass, age, and environment? What does this frequency tell us about the formation of stars and planets? How do disks compare between stars and brown dwarfs? Can planets form around brown dwarfs?
What is the frequency of binaries among stars and brown dwarfs as a function of primary mass, secondary mass, separation, and environment? What does this tell us about star formation?
What effect do shocked OB winds have on the physics of the HII region and the confining molecular cloud?
What fraction of stars in the Galaxy form from triggered processes?
What determines whether a young stellar cluster survives the dispersal of its parental molecular gas and becomes a bound open or globular cluster?

Discoveries and Milestones

Kevin Luhman has measured the IMF of stars and brown dwarfs in several nearby star-forming regions, showing that 1) stars outnumber brown dwarfs by a factor of ~6, 2) the IMF extends down to at least ~0.005-10 M_Sun (5-10 M_Jup) in Taurus and Chamaeleon, and 3) the IMF differs significantly in Taurus relative to other regions.
Leisa Townsley discovered a 10-million-degree X-ray "champagne flow" in the nearby massive star-forming region M17; this hot plasma outflow is caused by the powerful winds of an embedded cluster of massive stars.
Kevin Luhman has performed a complete census of disks in Taurus, Chamaeleon, IC 348, and sigma Ori, showing that 1) disks exist around brown dwarfs with masses as low as ~5 M_Jup, 2) disks are as common around brown dwarfs as around stars, and 3) the timescale for clearing of optically thick inner disks around stars is short compared to the lifetimes of those disks.
Leisa Townsley discovered a third massive cluster in the star-forming complex NGC 6357, making this neglected southern HII region complex one of the few very young "clusters of clusters" known in the Galaxy.
Kevin Luhman discovered the first known wide binary brown dwarf, demonstrating that brown dwarfs can form without the involvement of ejection or other dynamical processes. He also discovered the first known brown dwarfs that have been born in isolation rather than in a stellar cluster, providing additional evidence that dynamical interactions among stars are not required for the formation of brown dwarfs.

Current Projects

Kevin Luhman is continuing to measure the IMF of low-mas stars and brown dwarfs in the nearest star forming regions.
The MYSTIX team (Townsley, Feigelson, Kuhn, Getman, Povich, Luhman, et al.) is comparing and contrasting 20 nearby massive star-forming complexes in X-ray and infrared light using the Chandra X-ray Observatory, the Spitzer Space Telescope, 2MASS, UKIDSS, and data from the WHIRC camera on WIYN.
Leisa Townsley is leading a group of 57 investigators studying the Great Nebula in Carina through its X-ray and infrared emission. This effort has yielded >14,000 X-ray point sources (mostly young stars in Carina) and detailed maps of the diffuse X-ray emission that pervades the complex. Sixteen papers on this project are published in a Special Issue of the Astrophysical Journal. At least 4 more papers are underway.
John Bochanski, Kevin Luhman, and Sonali Shukla are using images from the Hubble Space Telescope to search for young brown dwarfs down to ~3 M_Jup, providing a better constraint on the minimum mass at which free-floating bodies can form.

Student Highlights

Kamen Todorov discovered a planetary-mass companion to a young brown dwarf using high-resolution images from the Hubble Space Telescope.
Amanda Morrow used spectra from the Spitzer Space Telescope to show that grain growth in disks -- one of first steps in planet formation -- may occur faster for brown dwarfs than for stars.

Participants