How to Find Brown Dwarfs andExtrasolar Planets?

PHY 688, Lecture 2Stanimir Metchev

Jan 28, 2009 PHY 688, Lecture 2 2

Previously in PHY 688…

Jan 28, 2009 PHY 688, Lecture 2 3

Brown Dwarfs:Link between Stars and Giant Planets

Burrows et al. (2001)

starsbrown dwarfs“planets”

giant planet formationgiant planet formation

13 MJup10 M

Jup

5 MJup

1 MJup

starsbrown dwarfs“planets”M

• no H fusion• <0.08 M ~ 80 MJup

• star-like properties:– formation, self-

luminous, B fields,multiplicity

• planet-like properties:– low Teff, mass, clouds

and “weather”, radius

Jan 28, 2009 PHY 688, Lecture 2 4

The Stellar/Substellar Continuum

Sun

M dwarf T dwarfL dwarf Jupiter

brown dwarfs planetsstars

5700 K ~3500 K ~2000 K ~1000 K 160 K

(G dwarf)

R. Hurt (Caltech/IPAC)visible light

Jan 28, 2009 PHY 688, Lecture 2 5

Hertzsprung-Russel Diagram

Jan 28, 2009 PHY 688, Lecture 2 6

1963–1995:The Search for Substellar Objects

• 1985: the disappearingcompanion vB 8”B”– speckle interferometry

• 1988: the unusuallycool GD 165B– resolved imaging

• 1989: HD 114762b, thefirst r.v. brown dwarf /planet?– radial velocity

J H K

2MASS

1.2, 1.6, 2.2 µmcolor composite

(Zuckerman & Becklin 1988)

(Latham et al. 1989)

Jan 28, 2009 PHY 688, Lecture 2 7

1987: G 29–38B?• Zuckerman & Becklin

(1987, Nature)• primary is a white dwarf• suspicious infrared excess

– unresolved brown dwarfcompanion?

– dust shell?

• expect periodic modulationof white dwarf pulsationfrom companion– not seen, so dust

Jan 28, 2009 PHY 688, Lecture 2 8

1987: G 29–38B?• Zuckerman & Becklin

(1987, Nature)• primary is a white dwarf• suspicious infrared excess

– unresolved brown dwarfcompanion?

– dust shell?

• expect periodic modulationof white dwarf pulsationfrom companion– not seen, so dust

Jan 28, 2009 PHY 688, Lecture 2 9

1992: Pulsar Planets!

• Wolsczczan & Frail (1992,Nature)

• pulsar rot. period (~0.006 s)known to 10–14 s accuracy

• PSR 1257+12bc– ~ 4 MEarth

– planets a+d reported later– 0.020, 0.0004 MEarth

Jan 28, 2009 PHY 688, Lecture 2 10

1992: Pulsar Planets!

• Wolsczczan & Frail (1992,Nature)

• pulsar rot. period (~0.006 s)known to 10–14 s accuracy

• PSR 1257+12bc– ~ 4 MEarth

– planets a+d reported later– 0.020, 0.0004 MEarth

Jan 28, 2009 PHY 688, Lecture 2 11

1995: Teide 1• Rebolo et al. (1995, Nature)• spectroscopic signature oflithium in absorption– destroyed in the convective

interiors of low-mass stars

• candidate member of 100Myr-old Pleiades opencluster

• but skepticism about age

Jan 28, 2009 PHY 688, Lecture 2 12

1995: Gliese 229B!

• Nakajima et al. (1995,Nature)

• Gl 229A is a nearbylow-mass M star

• unambiguously cooland substellar

• direct imaging +adaptive optics– contrast enhancement

Palomar 1.5 mdiscovery

Hubble Telescopeconfirmation

Jan 28, 2009 PHY 688, Lecture 2 13

Gl 229B:More Like a Planet Than a Star

Geballe et al. (1996)

Jan 28, 2009 PHY 688, Lecture 2 14

1995: 51 Pegb!

• first planet detectedaround a normal star– Mayor & Queloz

(1995, Nature)• M sin i = 0.47 MJup

• primary is a sun-likeG2 V star

Jan 28, 2009 PHY 688, Lecture 2 15

1995: SubstellarAstrophysics

Begins

Jan 28, 2009 PHY 688, Lecture 2 16

1996–Present:100’s of Brown Dwarfs and Planets

• brown dwarfsfound mostly inlarge-area skysurveys– 0.8–2.5µm– DENIS,

2MASS, SDSS

• planets foundmostly throughradial velocitymonitoring ofstars

0.6 µm, year 1951 0.6 µm, year 1989

1.2 µmyear 1999

1.6 µmyear 1999

2.1 µmyear 1999

Jan 28, 2009 PHY 688, Lecture 2 17

Summary of Substellar ObjectDetection Techniques

• precision radial velocity monitoring– periodic Doppler shift of host star

spectrum due to planet’sgravitational pull

• resolved imaging of binary systems– seeing-limited, speckle

interferometry, adaptive optics• unresolved photometry of hot stars

– e.g., cool infrared excess in anotherwise much hotter white dwarf

• large-area sky surveys– extremely red objects

• precision radial velocity monitoring• pulsar timing

– apparent periodicity in pulsarrotation period due to planet’sgravitational pull

• transit photometry– ~1% dimming of star due to planet

passing in front• microlensing

– gravitational lensing of light frombackground stars

• resolved imaging!– extremely high-contrast adaptive

optics

brown dwarfs exoplanets

Jan 28, 2009 PHY 688, Lecture 2 18

First Brown Dwarfs Discovered asCompanions to Stars

Gl 229 B: first T dwarf

Latham et al. (1987); Becklin & Zuckerman (1988); Nakajima et al. (1995)

1.2 µm 1.6 µm 2.2 µm

GD 165 B: first L dwarf

HD 114762b: first brown dwarf?

Jan 28, 2009 PHY 688, Lecture 2 19

…But Most L’s and T’s Now Foundfrom Large-Area Imaging Surveys

>500>500

~100~100

DwarfArchives.org

Jan 28, 2009 PHY 688, Lecture 2 20

Brown Dwarfs by the NumbersMass of a brown dwarf in solar massesMass of a brown dwarf in Jupiter massesRadius of an evolved brown dwarf in solar radiiRadius of an evolved brown dwarf in Jupiter radiiLowest measured brown dwarf luminosity (solar units)Lowest surface temperature of a brown dwarf in °KPressure at the center of a brown dwarf in barNumber of “spectral classes” of brown dwarfsNumber of brown dwarfs known todayRatio of brown dwarfs to stars in GalaxyPercentage of dark matter

< 0.07< 750.1110–6

6001011

3> 1000< 1:1< 2