From Brown Dwarfs to Giant Planets
PHY 688
Stanimir Metchev
Course Focus
• brown dwarfs and extrasolar planets
– structure
– population
– formation
• observational perspective
– direct imaging and spectroscopy
• context:
– low-mass stars
– solar system planets
Jan 26, 2009
PHY 688, Lecture 1
2
Course Organization
• weekly lectures
– MWF 10:40–11:35am
• lecture notes
– after lectures, on course website
• weekly readings
– “New Light on Dark Stars” (Reid & Hawley 2005, 2nd ed.)
• bookstore ($???)
• amazon.com: $95 new, from $70 used
– select scientific papers
• NASA ADS (http://adsabs.harvard.edu/abstract_service.html)
• bi-weekly problem sets
– from textbook + other sources
• office hours
– MTh 1–2pm, ESS 452
Jan 26, 2009
PHY 688, Lecture 1
3
Evaluation of Coursework
• bi-weekly problem sets (40% of grade)
– collaborative, but shown own work
• mid-term (30%)
– closed book, formula sheet
• oral presentations (20%)
– list of suggested topics from course website
• evaluations of peers’ oral presentations (10%)
– i.e., “an evaluation of your evaluations”
Jan 26, 2009
PHY 688, Lecture 1
4
Course Material
• overview of astronomical concepts
• internal structure of low-mass stars, brown dwarfs, giant
planets
• substellar atmospheres & evolution
• detection and properties of brown dwarfs
• detection and properties of extrasolar planets
• star, planet, and brown dwarf formation
• can expand with suggestions
– or present topic of interest at final oral presentation
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PHY 688, Lecture 1
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Prerequisite Knowledge
• required
– classical mechanics
– thermodynamics
– E&M
• optional
– fundamental astronomy
– stellar structure
– basic computer programming
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Perspective and History
Lecture 1
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Brown Dwarfs:
Link between Stars and Giant Planets
• no H fusion
• <0.07 M ~ 75 MJup
• star-like properties:
stars
brown dwarfs
“planets”
– formation, selfluminous, B fields,
multiplicity
Jan 26, 2009
PHY 688, Lecture 1
Burrows et al. (2001)
8
Brown Dwarfs:
Link between Stars and Giant Planets
• no H fusion
• <0.07 M ~ 75 MJup
• star-like properties:
– formation, selfluminous, B fields,
multiplicity
stars
brown dwarfs
“planets”
Jan 26, 2009
PHY 688, Lecture 1
Burrows et al. (2001)
9
Brown Dwarfs:
Link between Stars and Giant Planets
• no H fusion
• <0.07 M ~ 75 MJup
• star-like properties:
M
13
Ju
p
10
M
Ju
p
• planet-like properties:
Jan 26, 2009
M
– formation, selfluminous, B fields,
multiplicity
– low Teff, mass, clouds
and “weather”, radius
stars
brown dwarfs
“planets”
5M
Jup
stars
brown1 dwarfs
M
“planets”Jup
giant planet formation Burrows et al. (2001)
PHY 688, Lecture 1
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The Stellar/Substellar Continuum
Sun
stars
(G dwarf) M dwarf
5700 K
~3500 K
brown dwarfs
L dwarf
T dwarf
Jupiter
~2000 K
~1000 K
160 K
visible light
Jan 26, 2009
planets
PHY 688, Lecture 1
R. Hurt (Caltech/IPAC)
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Significance of Brown Dwarfs
• important component of galactic population
– as numerous as stars?
• unique probes of Galactic processes
– star formation, metal enrichment, dynamics
• extreme low-temperature environments
– chemistry, clouds, exo-solar climatology
• planetary analogues?
– directly detectable
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Brown Dwarfs as Dark Matter?
NGC 720
Chandra X-ray Observatory
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Extrapolation of IMF to Low Masses
• Salpeter (1955) IMF
– dN*/dM ∝ M–2.35
• Extrapolation to
0.01MSun
– 8x more mass in
brown dwarfs than
stars!
Jan 26, 2009
dN
"(M) =
d log(M / MSun )
PHY 688, Lecture 1
!
15
BDs: a Theoretical Expectation
• Kumar (1963)
– modeling of
<0.1MSun stars
– importance of
electron degeneracy
• minimum mass
below which objects
can not fuse H
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The Long Search for Brown Dwarfs
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1985: van Biesbroeck 8B
• first claim of a detected brown dwarf
– McCarthy et al. (1985, ApJ)
– vB 8A is an M7V member of the Hyades open cluster
• speckle interferometry
– better than seeing limited (~1”) resolution
– vB 8B: ~1” away, 3 mag fainter than primary in NIR
– Kitt Peak 3.8 and 2.3m telescopes; two nights in 1984; H+K
near-IR bands
• impetus for theoretical modeling of brown dwarfs
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PHY 688, Lecture 1
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1985: van Biesbroeck 8B
• first claim of a detected brown dwarf
– McCarthy et al. (1985, ApJ)
– vB 8A is an M7V member of the Hyades open cluster
• speckle interferometry
– better than seeing limited (~1”) resolution
– vB 8B: ~1” away, 3 mag fainter than primary in NIR
– Kitt Peak 3.8 and 2.3m telescopes; two nights in 1984; H+K
near-IR bands
• impetus for theoretical modeling of brown dwarfs
• never confirmed!
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1988: GD 165B
J
H
K
• Zuckerman & Becklin (1988, Nature)
– GD 165A is a white dwarf
• direct imaging
• bizarre spectrum
2MASS
– BD or polluted star?
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1989: HD 114762b
• Latham et al. (1989,
Nature)
• precision radial
velocity
• M sin i = 11 MJup
– a brown dwarf, a
planet, or a star?
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to be continued…
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