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Star Formation

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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?
  • How does the feedback from massive OB stars, particularly their powerful winds, affect their environment.  Does it promote or inhibit further star formation?
  • 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 fraction of stars in the Galaxy form from triggered processes?


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 MSun (5-10 MJup) 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 and other star forming regions using the Chandra X-ray Observatory.  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 MJup, 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 led an international collaboration in the Chandra Carina Complex Project, published as a Special Issue of ApJ Supplements in 2011.  Earlier, Eric Feigelson led a similar collaboration in the Chandra Orion Ultradeep Project published as a Special Issue in 2005 with ~22 papers garnering ~1600 citations.
  • 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.
  • Kosta Getman has used the Chandra X-ray Observatory to find several cases of progressive star formation triggered by an expanding HII region including IC 1396N, Cepheus B, CG 12 and IC 1396A.

Current Projects

  • Kevin Luhman is continuing to measure the IMF of low-mas stars and brown dwarfs in the nearest star forming regions.
  • Eric Feigelson and Leisa Townsley are leading the MYSTIX project to compare the young stellar populations and diffuse gas in 20 nearby massive star-forming complexes.  MYStIX combined in X-ray and infrared light using Chandra X-ray Observatory, Spitzer Space Telescope and UKIRT. Michael Kuhn is completing a dissertation on the spatial structure and origins of star clusters.  Kosta Getman finds spatial gradients in star formation with a new stellar age estimator.
  • 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 MJup, 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.

Participants

  • Faculty
  • Postdocs and Research Associates

Pat Broos


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