Extrasolar Planets and Brown Dwarfs

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Extrasolar Planets and Brown Dwarfs James
Liebert Steward Observatory University of Arizona
Tucson, AZ
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Extrasolar Planets Planets found around other
stars usually similar to our Sun
and Brown
dwarfs entities between the size (mass) of many
Jupiters and low mass stars Definition of a
star a gravitationally-bound sphere of gas
massive enough to fuse hydrogen into helium,
thereby providing the energy to shine In
units of the mass of the Sun 2 x 1033 gm 2
x 1030 kg 1M? Jupiter is very close to 0.001
M? Jovian planets defined to be up to 13 MJ
(0.013 M?) Brown dwarfs 0.013 - 0.075 M?
Hydrogen fusion requires a mass of 0.075M?
(75MJ)
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Brown is not a color
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Binary stars Each orbits the common center of
mass
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LHS 4033 Most Massive Well Measured White Dwarf
1.31-1.335M?
10,900 K
0.0037R?
Dahn, Bergeron, Liebert, Harris, Canzian,
Leggett, And Boudreault 2004 ApJ, 605, 400
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J. Davy Kirkpatrick -- Annual Reviews of
Astronomy and Astrophysics
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J. Davy Kirkpatrick -- Inventor of the L Dwarf
Classification System
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Adam Burgasser Definer of T Dwarfs and National
Collegiate Diving Champion (U. California, San
Diego)
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Modelling a T6.5 emission Dwarf Infrared Spectrum
(Liebert and Burgasser 2007 ApJ,655,522)
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Dispersion in infrared colors At a given
spectral type Variable dust layers in L s Open
circles subdwarfs (lower Fe/H) also higher
gravity Open triangles young and low gravity
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Temperatures from Luminosities (via trig
parallaxes) and Radii Teff (L / 4pR2)1/4
?1/4 R constant Rjup
Declining Teff as brown dwarf cools with
time Small temperature change from L6 -- T5
means Rapid evolution through these Spectral
types
Infrared types not as cleanly Monotonic with
Teff as are Optical types
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At this time.. the latest T8 dwarfs are believed
to be about Teff 700-750 K The synthetic
spectra from Burrows models shown here suggest
what cooler objects discovered by deeper
surveys will look like Kirkpatrick (2006 PPl V
review) suggests 3 possible qualitative changes
in the spectra that might trigger A new
spectral type Y
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The J Band Bump at early-mid T types CO gt CH4
(and H2) Absorption switches from J to K
band More flux gets out at J Band despite Lower
Teff
Open circles apparently Single stars Filled
circles inside a circle Resolved binaries
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LHS 2534
Rediscovered in SDSS
P. Zeeman 1897, ApJ, 5, 332
First found the Z effect in a Flame of Sodium
Gas Na I 5889,5895A Mg I 5175A triplet Shows
five components Ca II 3933,3968A Should split
into 5 lines
Reid, Liebert, and Schmidt 2001. ApJ, 550, 61