1 / 17

Today Only, A New Exhibit: M,L, and T Dwarfs!

Today Only, A New Exhibit: M,L, and T Dwarfs!. Ted Maxwell Indiana University Astronomy A540: Stellar Atmospheres April 1, 2005. Outline. History Characteristics Distributions Current Understanding Future questions/goals. History. Harvard  Morgan and Keenan (MK)

deiter
Download Presentation

Today Only, A New Exhibit: M,L, and T Dwarfs!

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Today Only, A New Exhibit:M,L, and T Dwarfs! Ted Maxwell Indiana University Astronomy A540: Stellar Atmospheres April 1, 2005

  2. Outline • History • Characteristics • Distributions • Current Understanding • Future questions/goals

  3. History • Harvard  Morgan and Keenan (MK) • Only class M2 and earlier • Before 1940s, observations mostly in Blue-Green  Spectral Feature saturate quickly with decrease in Temp • Yerkes (Morgan and Kuiper) vs Mount Wilson (Joy) system • TiO band strength in green vs. blue regime • Diverge for later-type M dwarfs • Wolf 359 (Gl 406) was M8 vs. dM6e

  4. History • Keenan and MacNeil  add wavelength coverage (1976) • Boeshaar  6800 A • KIRKPATRICK et al. (KHM system) (1991) • 6300-9000 A features + Overall slope • Finally a standard set for late M Dwarfs • Bessell has competing system, close to KHM, but less widely used • Tinney and Reid (1999) expand atlas for later spectral types

  5. History • In 1988 – GD 165B discovered  Clearly different • 2MASS + Keck follow up spectroscopy = GD165B no longer so odd! • 1999 Kirkpatrick et al.  New spectral type is codified, called L and defined to L8, later expanded to L9.5 • T is suggested for Gl 229B-like methane dwarfs. • Burgasser et al. and Geballe et al. Provided first schemes for T dwarfs (2002) in near-IR, Burgasser et al. 2003 in the visible. • Currently ~400 L dwarfs, ~50 T dwarfs are known • http://spider.ipac.caltech.edu/staff/davy/ARCHIVE/ • http://research.amnh.org/~adam/tdwarf/

  6. M Dwarfs • TiO bands to ~ M6, VO dominate after that • Become fully convective at 0.3 Mסּ, Mbol 8.5, ~M4 • Chromospheric activity remains constant down to ultra cool M Dwarfs where Hα emission drops rapidly. • Magnetic fields from turbulent dynamo? • Flares still common, but not coupled to rotation!

  7. L Dwarfs • TiO and VO bands disappear • Hydride bands become apparent • H- opacity drops  red spectrum clears up! • Na I, K I, Rb I, and Cs I doublets appear more strongly • K I resonance doublet VERY broad (100s of Å) • Lots of dust grains, even clouds

  8. L Dwarfs

  9. T Dwarfs • CH4 and H20 • Surface temp as low as 700 K • Color? Magenta due to huge Na absorption. • Li lines get very small as Li  molecules • Clouds dissipate • Radii are the same as for L dwarfs. • These guys are brown dwarfs!

  10. Compare sizes/ colors Sun, M dwarf, hot L dwarf, T Dwarf, visible http://spider.ipac.caltech.edu/staff/davy/2mass/science/comparison.html

  11. Evolution of Atmosphere Black spots are M dwarfs Red are L dwarfs Blue are T dwarfs. Purple line is normal, mixed stellar atmosphere Right hand black line is cloudy atmosphere Left hand black line is cleared up atomophere Dark line traces possible evolution path. Burgasser, A.J., et al. 2002, ApJ 571, L151

  12. What is a Brown Dwarf? • Central temp < 3 Million K • Mass <~ 75 Jupiter Masses which is 8 percent of our Sun's mass • Burns Deuterium at >~ 13 Jupiter Masses for ~ 10’s of Myrs  heating from contraction • Highly convective • Hot Corona may disappear around 2770 K i.e. LP 944-20

  13. Photometry • Need a good distinguisher of temperature from colors • Special narrow band filters can be used to measure band strength and tus give spectral types • I-J is a good bet!

  14. Answered Questions • Are they the missing mass? • Nope, There may be one for each other star, but they just don’t have enough mass • Are their field brown dwarves? • Yep, plenty! • Do they have strong magnetic fields? • Actually yes, but that leads us to..

  15. Unanswered Questions • Where do the magnetic fields and activity come from in late dwarfs? • What exactly is the difference between how a planet vs. a brown dwarf forms…. • Can we get an even more complete survey of the local population? • Can we get better models of these objects?

  16. Odd assortment of References • http://hubblesite.org/newscenter/newsdesk/archive/releases/1995/03/text/ • http://www.solstation.com/stars/pc10bd.htm • http://www.solstation.com/stars/lp944-20.htm • http://www.ipac.caltech.edu/2mass/overview/dwarfs.html • http://spider.ipac.caltech.edu/staff/davy/PAPERS/kirkpatrick_iaupap.ps • http://www.ipac.caltech.edu/2mass/publications/proceedings.html • http://www.mpia-hd.mpg.de/homes/calj/tdwarfs_parallax_venus2004.pdf • http://xxx.lanl.gov/PS_cache/astro-ph/pdf/0207/0207672.pdf • Reid, I. N. et al., 1999, ApJ, 527, 105 • Kirkpatrick, J. D. et al., 1999, ApJ, 519, 802 • Reid and Hawley, New Light on Dark Stars, Springer, 2000

More Related