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

Ted MaxwellTed MaxwellIndiana University AstronomyIndiana University AstronomyA540: Stellar AtmospheresA540: Stellar Atmospheres April 1, 2005April 1, 2005

OutlineOutline

HistoryHistory CharacteristicsCharacteristics DistributionsDistributions Current UnderstandingCurrent Understanding Future questions/goalsFuture questions/goals

HistoryHistory

Harvard Harvard Morgan and Keenan (MK) Morgan and Keenan (MK) Only class M2 and earlierOnly class M2 and earlier Before 1940s, observations mostly in Blue-Green Before 1940s, observations mostly in Blue-Green

Spectral Feature saturate quickly with decrease in Spectral Feature saturate quickly with decrease in TempTemp

Yerkes (Morgan and Kuiper) vs Mount Wilson Yerkes (Morgan and Kuiper) vs Mount Wilson (Joy) system(Joy) system TiO band strength in green vs. blue regimeTiO band strength in green vs. blue regime Diverge for later-type M dwarfsDiverge for later-type M dwarfs

Wolf 359 (Gl 406) was M8 vs. dM6eWolf 359 (Gl 406) was M8 vs. dM6e

HistoryHistory

Keenan and MacNeil Keenan and MacNeil add wavelength add wavelength coverage (1976)coverage (1976)

Boeshaar Boeshaar 6800 A 6800 A KIRKPATRICK et al. (KHM system) (1991)KIRKPATRICK et al. (KHM system) (1991)

6300-9000 A features + Overall slope6300-9000 A features + Overall slope Finally a standard set for late M DwarfsFinally a standard set for late M Dwarfs

Bessell has competing system, close to KHM, Bessell has competing system, close to KHM, but less widely usedbut less widely used

Tinney and Reid (1999) expand atlas for later Tinney and Reid (1999) expand atlas for later spectral typesspectral types

HistoryHistory In 1988 – GD 165B discovered In 1988 – GD 165B discovered Clearly different Clearly different 2MASS + Keck follow up spectroscopy = GD165B no 2MASS + Keck follow up spectroscopy = GD165B no

longer so odd!longer so odd! 1999 Kirkpatrick et al. 1999 Kirkpatrick et al. New spectral type is codified, New spectral type is codified,

called L and defined to L8, later expanded to L9.5called L and defined to L8, later expanded to L9.5 T is suggested for Gl 229B-like methane dwarfs.T is suggested for Gl 229B-like methane dwarfs. Burgasser et al. and Geballe et al. Provided first Burgasser et al. and Geballe et al. Provided first

schemes for T dwarfs (2002) in near-IR, Burgasser et al. schemes for T dwarfs (2002) in near-IR, Burgasser et al. 2003 in the visible.2003 in the visible.

Currently ~400 L dwarfs, ~50 T dwarfs are knownCurrently ~400 L dwarfs, ~50 T dwarfs are known http://spider.ipac.caltech.edu/staff/davy/ARCHIVE/http://spider.ipac.caltech.edu/staff/davy/ARCHIVE/ http://research.amnh.org/~adam/tdwarf/http://research.amnh.org/~adam/tdwarf/

M DwarfsM Dwarfs

TiO bands to ~ M6, VO dominate after thatTiO bands to ~ M6, VO dominate after that Become fully convective at 0.3 MBecome fully convective at 0.3 Mּסּס, Mbol 8.5, , Mbol 8.5,

~M4~M4 Chromospheric activity remains constant down Chromospheric activity remains constant down

to ultra cool M Dwarfs where Hto ultra cool M Dwarfs where Hαα emission emission drops rapidly.drops rapidly.

Magnetic fields from turbulent dynamo?Magnetic fields from turbulent dynamo? Flares still common, but not coupled to rotation!Flares still common, but not coupled to rotation!

L DwarfsL Dwarfs

TiO and VO bands TiO and VO bands disappeardisappear

Hydride bands become Hydride bands become apparentapparent

HH-- opacity drops opacity drops red red spectrum clears up!spectrum clears up!

Na I, K I, Rb I, and Cs I Na I, K I, Rb I, and Cs I doublets appear more doublets appear more stronglystrongly

K I resonance doublet K I resonance doublet VERY broad (100s of VERY broad (100s of Å)Å)

Lots of dust grains, even Lots of dust grains, even cloudsclouds

L DwarfsL Dwarfs

T DwarfsT Dwarfs

CHCH44 and H and H2200 Surface temp as low as Surface temp as low as

700 K700 K Color? Magenta due to Color? Magenta due to

huge Na absorption.huge Na absorption. Li lines get very small as Li lines get very small as

Li Li molecules molecules Clouds dissipateClouds dissipate Radii are the same as Radii are the same as

for L dwarfs.for L dwarfs. These guys are brown These guys are brown

dwarfs!dwarfs!

Compare sizes/ colorsCompare sizes/ colors

Sun, M dwarf, hot L dwarf, T Dwarf, visiblehttp://spider.ipac.caltech.edu/staff/davy/2mass/science/comparison.html

Evolution of AtmosphereEvolution 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

What is a Brown Dwarf?What is a Brown Dwarf?

Central temp < 3 Million KCentral temp < 3 Million K Mass <~ 75 Jupiter Masses which is 8 percent Mass <~ 75 Jupiter Masses which is 8 percent

of our Sun's mass of our Sun's mass Burns Deuterium at >~ 13 Jupiter Masses for ~ Burns Deuterium at >~ 13 Jupiter Masses for ~

10’s of Myrs 10’s of Myrs heating from contraction heating from contraction Highly convectiveHighly convective Hot Corona may disappear around 2770 K i.e. Hot Corona may disappear around 2770 K i.e.

LP 944-20LP 944-20

PhotometryPhotometry

Need a good Need a good distinguisher of distinguisher of temperature from temperature from colorscolors

Special narrow band Special narrow band filters can be used to filters can be used to measure band measure band strength and tus give strength and tus give spectral typesspectral types

I-J is a good bet!I-J is a good bet!

Answered QuestionsAnswered Questions

Are they the missing mass?Are they the missing mass? Nope, There may be one for each other star, Nope, There may be one for each other star,

but they just don’t have enough massbut they just don’t have enough mass

Are their field brown dwarves?Are their field brown dwarves? Yep, plenty!Yep, plenty!

Do they have strong magnetic fields?Do they have strong magnetic fields? Actually yes, but that leads us to..Actually yes, but that leads us to..

Unanswered QuestionsUnanswered Questions

Where do the magnetic fields and activity Where do the magnetic fields and activity come from in late dwarfs?come from in late dwarfs?

What exactly is the difference between What exactly is the difference between how a planet vs. a brown dwarf forms….how a planet vs. a brown dwarf forms….

Can we get an even more complete Can we get an even more complete survey of the local population?survey of the local population?

Can we get better models of these Can we get better models of these objects?objects?

Odd assortment of Odd assortment of ReferencesReferences

http://hubblesite.org/newscenter/newsdesk/archive/releases/1995/http://hubblesite.org/newscenter/newsdesk/archive/releases/1995/03/text/03/text/

http://www.solstation.com/stars/pc10bd.htmhttp://www.solstation.com/stars/pc10bd.htm http://www.solstation.com/stars/lp944-20.htmhttp://www.solstation.com/stars/lp944-20.htm http://www.ipac.caltech.edu/2mass/overview/dwarfs.htmlhttp://www.ipac.caltech.edu/2mass/overview/dwarfs.html http://spider.ipac.caltech.edu/staff/davy/PAPERS/http://spider.ipac.caltech.edu/staff/davy/PAPERS/

kirkpatrick_iaupap.pskirkpatrick_iaupap.ps http://www.ipac.caltech.edu/2mass/publications/proceedings.htmlhttp://www.ipac.caltech.edu/2mass/publications/proceedings.html http://www.mpia-hd.mpg.de/homes/calj/http://www.mpia-hd.mpg.de/homes/calj/

tdwarfs_parallax_venus2004.pdftdwarfs_parallax_venus2004.pdf http://xxx.lanl.gov/PS_cache/astro-ph/pdf/0207/0207672.pdfhttp://xxx.lanl.gov/PS_cache/astro-ph/pdf/0207/0207672.pdf Reid, I. N. et al., 1999, ApJ, Reid, I. N. et al., 1999, ApJ, 527, 527, 105105 Kirkpatrick, J. D. et al., 1999, ApJ, Kirkpatrick, J. D. et al., 1999, ApJ, 519519, 802, 802 Reid and Hawley, Reid and Hawley, New Light on Dark StarsNew Light on Dark Stars, Springer, 2000, Springer, 2000