1.E+00

1.E+02

1.E+04

1.E+06

1.E+08

1.E+10

1970 1980 1990 2000 2010

Year

Number of transistors in new microprocessors doubles every 24 months

Number of extrasolar planets doubles every 29 months

With Kepler planet candidates

6 December 2011 Astronomy 111, Fall 2011 1

Today in Astronomy 111: exoplanet detection

The successful search for extrasolar planets around ordinary stars

Radial-velocity planet detection

Exoplanetary transits and eclipses

Measurement of mass, radius and surface temperature of exoplanets

Exoplanetary atmospheres

Exponential progress: Moore’s law compared to exoplanet discovery. (Data from Intel, AMD, IBM, Zilog, Motorola, Sun Microsystems, Kepler and exoplanet.eu.)

http://en.wikipedia.org/wiki/Transistor_count�http://kepler.nasa.gov/Mission/discoveries/candidates/�http://exoplanet.eu/�

The bad news

Exam #2 takes place here next Tuesday. To the test bring only a writing instrument, a calculator,

and one 8.5”×11” sheet on which you have written all the formulas and constants that you want to have at hand. • No computers, no access to internet or to electronic

notes or stored constants in calculator. The best way to study is to work problems like those in

homework and recitation, understand the solutions and reviews we distributed, refer to the lecture notes when you get stuck, and make up your cheat sheet as you go along.

Try the Practice Exam on the web site. Under realistic conditions, of course.

6 December 2011 Astronomy 111, Fall 2011 2

6 December 2011 Astronomy 111, Fall 2011 3

The successful search for extrasolar planets

By which we mean, mature planets around normal stars. The first four extrasolar planets were observed around neutron stars (Wolszczan & Frail 1992, Backer et al. 1993.) In the early 1990s, groups in San Francisco and Geneva were gearing up for long searches for giant planets around normal stars by Doppler-velocity techniques. The idea: detect the relatively small, but periodic, Dopper

shift in the spectrum of a star due to its orbital motion around the center of mass of a star-planet system.

The new part of the idea: simultaneously to use thousands of stellar spectral lines in a broad wavelength range, always viewed through a cell filled with a gas (iodine) which has many spectral lines but which is rare in stars.

http://adsabs.harvard.edu/abs/1992Natur.355..145W�http://adsabs.harvard.edu/abs/1992Natur.355..145W�http://adsabs.harvard.edu/abs/1992Natur.355..145W�http://adsabs.harvard.edu/abs/1993Natur.365..817B�

6 December 2011 Astronomy 111, Fall 2011 4

Example: orbital speeds of Sun and Jupiter

Recall, from our discussion of the two-body system on 29 September 2011, applied to Jupiter and the Sun:

The best planet-search spectrometers can measure stellar Doppler velocities as small as

( )30

-1

-1

Reduced mass: 1.897 10 gm

Orbital speeds, dictated by momentum conservation:

13.044 km sec

0.012 km sec

JJ

J

JJ

JJ

M MM

M M

GMv

M r

MGMv v

M r M

µ

µ

µ

= = × ≅+

= =

= = =

-1 10.0002 km sec 20 cm sec .−=

http://www.pas.rochester.edu/~dmw/ast111/Lectures/Lect_9b.pdf�http://www.pas.rochester.edu/~dmw/ast111/Lectures/Lect_9b.pdf�

6 December 2011 Astronomy 111, Fall 2011 5

The successful search for extrasolar planets (continued)

The observers thought they were going to detect Jupiters like this, so they were prepared to do observations over the course of many years. (Recall that Jupiter’s orbital period is 11.9 years.)

So it was much to their surprise that they detected their first planets in a matter of days: • 51 Peg b: msini = 0.46MJ, P = 4.2 days (Mayor & Queloz

1995, Marcy & Butler 1995) • 70 Virginis b: msini = 6.5MJ, P = 117 days (Marcy &

Butler 1996) • 47 Ursae Majoris b: msini = 2.5MJ, P = 1100 days

(Butler & Marcy 1996) Jupiter-size planets, in terrestrial-planet-size orbits (or smaller)?

http://adsabs.harvard.edu/abs/1995Natur.378..355M�http://adsabs.harvard.edu/abs/1995Natur.378..355M�http://adsabs.harvard.edu/abs/1995Natur.378..355M�http://adsabs.harvard.edu/abs/1995AAS...187.7004M�http://adsabs.harvard.edu/abs/1996ApJ...464L.147M�http://adsabs.harvard.edu/abs/1996ApJ...464L.147M�http://adsabs.harvard.edu/abs/1996ApJ...464L.153B�

6 December 2011 Astronomy 111, Fall 2011 6

The successful search for extrasolar planets (continued)

In 1999, after several more exoplanets had been detected, two more milestones in the search were reached: One planet detected

by radial velocity, HD 209458 b, was seen to transit: to eclipse a tiny portion of the star (Henry et al. 2000). • Thus its orbit is

viewed close to edge on and its mass can be determined precisely:

( )90i ≈ °

Deeg and Garrido 2000 0.69 0.05 .Jm M= ±

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6 December 2011 Astronomy 111, Fall 2011 7

The successful search for extrasolar planets (continued)

Also in 1999, the first multiple exoplanetary system was detected: υ Andromedae c and υ Andromedae d (periods 242 and 1275 days), to go with the previously-detected υ Andromedae b (4.6 days).

Top: from Butler et al. 1999 Bottom: animation by Sylvain Korzennik (CfA)

http://adsabs.harvard.edu/abs/1999ApJ...526..916B�http://cfa-www.harvard.edu/afoe/simulation.html�http://cfa-www.harvard.edu/afoe/simulation.html�http://www.journals.uchicago.edu/action/showFullPopup?doi=10.1086/308035&id=_e8�

6 December 2011 Astronomy 111, Fall 2011 8

The successful search for extrasolar planets (continued)

Later (in 2005) the Spitzer Space Telescope detected the eclipse of HD 209458b (the planet) by HD 209458 (the star) – meaning that the light from the planet is directly detected at mid-infrared wavelengths when not in eclipse (Deming et al. 2005).

Animation by Robert Hurt, SSC

http://adsabs.harvard.edu/abs/2005Natur.434..740D�http://www.spitzer.caltech.edu/video-audio/746-ssc2005-09v3-How-to-Measure-a-Planetary-Eclipse�

The successful search for extrasolar planets (continued)

2008 saw two historic firsts: an image of a planet orbiting the bright, nearby star

Fomalhaut, which truncates the remains of the disk from which it formed. This planet’s orbit was correctly predicted two years earlier (by Alice Quillen, on the basis of the disk truncation) – the first time since Le Verrier and Galle (1846, Neptune) that anyone has accomplished such a feat.

6 December 2011 Astronomy 111, Fall 2011 9

Paul Kalas, UC Berkeley/STScI/NASA

http://adsabs.harvard.edu/abs/2006MNRAS.372L..14Q�http://hubblesite.org/newscenter/archive/releases/2008/39/�http://hubblesite.org/newscenter/archive/releases/2008/39/�http://hubblesite.org/newscenter/archive/releases/2008/39/�http://hubblesite.org/newscenter/archive/releases/2008/39/�http://hubblesite.org/newscenter/archive/releases/2008/39/�

The successful search for extrasolar planets (continued)

and an image of three planets in orbit around another bright nearby star, HR 8799. Another reported in 2010.

HR 8799 was previously known to have two debris belts (Chen et al. 2006), which turn out to lie inside and outside the orbits of the planets. The resemblance to our Solar system’s giant planets, asteroid belt and Kuiper belt is striking.

6 December 2011 Astronomy 111, Fall 2011 10

-0.01

0.09

0.19

0.29

0.39

0.49

5 15 25 35 45 55 65Ph

otos

pher

e-su

btra

cted

flux

den

sity (

Jy)

Wavelength (μm)

152 K

35 K

Spitzer-IRS

IRASHR 8799

Total

C. Marois and B. Macintosh, Keck Observatory

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The successful search for extrasolar planets (continued)

And this year, 2011, has seen, among many other results, the first detection of a planet in orbit around a binary star, Kepler 16AB b… The stars are K and M type in a 41-day period; the planet

is Saturn-like in a 229-day period (Doyle et al. 2011).

6 December 2011 Astronomy 111, Fall 2011 11

So the stars and the planet’s orbital distance are about right for Tatooine, but the planet’s mass is way too large. (Lucasfilm )

http://adsabs.harvard.edu/abs/2011Sci...333.1602D�http://adsabs.harvard.edu/abs/2011Sci...333.1602D�http://www.starwars.com/explore/the-movies/episode-iv/�http://www.starwars.com/explore/the-movies/episode-iv/�

Kraus & Ireland 2011

The successful search for extrasolar planets (continued)

…and the first detection – via imaging – of an infant giant planet orbiting in the gap of a transitional disk, LkCa 15. Planet (blue) seems to be accompanied by a streamer of

material (red) which shows up at longer wavelengths.

6 December 2011 Astronomy 111, Fall 2011 12

Andrews et al. 2011

Kraus & Ireland 2011

http://adsabs.harvard.edu/abs/2011arXiv1110.3808K�http://adsabs.harvard.edu/abs/2011ApJ...742L...5A�http://adsabs.harvard.edu/abs/2011ApJ...742L...5A�

6 December 2011 Astronomy 111, Fall 2011 13

Today’s exoplanets

Today there are 708 objects listed as exoplanets: 181 by radial velocity and transits.

• You can take 177 of them to the bank, as we’re 100% sure they’re of planetary mass.

471 others by radial velocity alone. Something like 5-10% of these may prove to be brown dwarfs eventually. • e.g. the earliest discovery on the list, HD 114762 b.

These 652 planets live in 534 planetary systems: there are 78 multiple-planet RV or RV+T systems so far. • 24 have three or more planets. • The most populous systems have six confirmed

planets each: HD 10180, Kepler 11.

http://exoplanet.eu/catalog-all.php�http://adsabs.harvard.edu/abs/1989Natur.339...38L�

Exosolar systems with three or more planets

6 December 2011 Astronomy 111, Fall 2011 14

0.01 0.1 1 10 100Orbital semimajor axis (AU)

47 UMa55 Cnc61 VirGJ 581GJ 876HD 10180HD 125612HD 136352HD 181433HD 20794HD 31527HD 37124HD 39194HD 40307HD 69830HIP 14810HIP 57274HR 8799Kepler-11Kepler-18Kepler-9KOI-730µ Araυ AndSun

Today’s exoplanets (continued)

14 others, in 9 systems, have been discovered by timing pulsars (neutron stars) or pulsating giant stars.

42 more have been found by direct imaging (29) or gravitational micro-lensing (13). Many of those imaged might be brown dwarfs.

The official list currently includes only transit events which have been confirmed by RV measurements to be planets. But the planetary-transit satellites, COROT (ESA) and

Kepler (NASA), have produced a huge number of candidates for RV followup, the vast majority of which are expected to turn out to be planets.

Kepler’s current list of 2326 candidates includes candidate planets as small as

6 December 2011 Astronomy 111, Fall 2011 15

0.6 . (!!)R R⊕=

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6 December 2011 Astronomy 111, Fall 2011 16

Radial-velocity planet detection and msini measurement

…in which one makes a series of accurate measurements of tiny periodic variations in the Doppler shift of the host star. For help in visualizing how this works, click here. Steps: measure P and K. Measure the period P of the

Doppler shift’s variation. This determines the length of the semimajor axis of the planet- star separation via Kepler’s third law:

( )3 2 22 24 4

G M m GMa P Pπ π

+= ≅

From exoplanets.org

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6 December 2011 Astronomy 111, Fall 2011 17

Radial-velocity planet detection and msini measurement (continued)

Measure also the amplitude K (maximum Doppler shift with respect to the average) of the star’s radial velocity:

sinK V i=

Observer’s view Side view

Orbit Orbit

m

tV tV

rV K=

V

i

90 − i

Orbital axis

Line of sight

6 December 2011 Astronomy 111, Fall 2011 18

Radial-velocity planet detection and msini measurement (continued)

If the orbital eccentricity is close to zero, the radial velocity varies sinusoidally with time.

If the orbital eccentricity is not close to zero, the radial- velocity curve looks lopsided compared to a sine wave. In this case, fitting the velocities of an elliptical orbit to the radial-velocity curve allows one to determine the eccentricity and the position of periastron, as well as as a function of time.

Either way, this allows a determination of the planet mass m. For low eccentricity,

sinV i

sinV a aM aMm M MV V m i Kv GM G G

= = = ⇒ =

6 December 2011 Astronomy 111, Fall 2011 19

Radial-velocity planet detection and msini measurement (continued)

The mass of the star is usually known, from its age and spectral type.

The orientation usually is not known, unless: • the star and planet are both seen in images, and the

transverse component of motion is seen too; or • the star has a debris disk that is resolved in images: the

planet will usually be in the same plane; or • the star and planet eclipse each other ( 90 ).i ≈ °

6 December 2011 Astronomy 111, Fall 2011 20

Exoplanetary transits: sini and R measurements

During a transit, the planet passes in front of the star, dimming the system at visible wavelengths. Because i must be very close to 90 degrees (i.e.

for this to happen, observation of transits and radial velocities allow unambiguous determination of the planetary mass m, not just the lower limit

The duration of the transit enables a measurement of the diameter of the star and /or the precise orbit inclination.

The depth of the flux “dip,” and time it takes the it to turn off or on, offer a measurement of the diameter of the planet.

sin 1)i →

sin .m i

Time

Flux

ta tb tc td

Exoplanetary transits: sini and R measurements (continued)

Much can be made of the details of the shapes of the light curve at the onset (ingress) and end (egress) of the transit, to make out details in the atmosphere of star and planet, such as the uniformity of the brightness of each. • This will be one of the

first subjects taken up in AST 142, in the context of binary stars.

6 December 2011 Astronomy 111, Fall 2011 21

2− 1− 0 1 2

0

0.5

1

Uniform brightness star (this calculation)Realistic (limb-darkened) starStraight line

Time, in units of Rs/vBr

ight

ess

of s

tar,

in u

nits

of i

ts to

tal f

lux

Exoplanetary transits: sini and R measurements (continued)

The “corners” are usually labelled as indicated at right.

During transit, the star and planet move at speeds v1 and v2 in opposite directions perpendicular to the line of sight, where v1 and v2 are the two speeds measured from the orbital periods and radial- velocity amplitudes. Thus

6 December 2011 Astronomy 111, Fall 2011 22

Time

Flux

1t 2t 3t 4t

( )( )( )( )

planet 1 2 2 1

star 1 2 3 1

2

2

R v v t t

R v v t t

= + −

= + −

Ingress Egress

6 December 2011 Astronomy 111, Fall 2011 23

Exoplanetary eclipses and the temperatures of exoplanets

At mid-infrared wavelengths, the difference between transit, eclipse and points in between enables one to isolate flux from the planet, and even to “map” the emission from the planet’s surface. Example: HD 189733b is

brightest near, but not exactly at, eclipse.

That’s planetary blackbody emission, at mid-infrared wavelengths.

HD 189733 at λ = 8μm; Knutson et al. 2007.

Eclipse

Transit

Flux of star alone

http://adsabs.harvard.edu/abs/2007Natur.447..183K�http://adsabs.harvard.edu/abs/2007Natur.447..183K�

6 December 2011 Astronomy 111, Fall 2011 24

Exoplanetary eclipses and T (continued)

Thus the temperature over the planet’s surface can be worked out from the planet brightness through the orbit. Example: in HD

189733b, the warmest spot is offset from the substellar point, in the direction of the planet’s synchronous rotation.

Animations by Tim Pyle (SSC)

T = 1212 K T = 973 K

http://www.spitzer.caltech.edu/video-audio/1025-ssc2007-09v2-Mapping-Exotic-Worlds�

Transits, eclipses and exoplanetary atmospheres

Near-infrared spectra of transits and eclipses with the Hubble Space Telescope’s late, lamented NICMOS instrument have revealed molecular species familiar from the atmospheres of Jupiter and Saturn. Here, the example of HD 189733b: Transit: The difference of spectra in

and out of minimum reveals absorption by water and methane in the starlight transmitted by the planet’s atmosphere (Swain, Vasisht & Tinetti 2008).

6 December 2011 Astronomy 111, Fall 2011 25

A B C D

(A+C+D)/3 – B:

H2O CH4

http://adsabs.harvard.edu/abs/2008Natur.452..329S�http://adsabs.harvard.edu/abs/2008Natur.452..329S�

Transits, eclipses and exoplanetary

atmospheres (continued)

Eclipse: This time the difference reveals the day-side emission spectrum by the planet, again revealing water which this time is joined by CO and CO2, components not prominent in the Solar system’s giant planets (Swain et al. 2009).

6 December 2011 Astronomy 111, Fall 2011 26

A B C D

(A+C+D)/3 – B:

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6 December 2011 Astronomy 111, Fall 2011 27

Exoplanet detection

By any method, the detection of exoplanets is challenging. One must observe each system frequently for at least an

orbital period to be sure of periodicity. For either the radial-velocity or transit method to work,

one needs a spectrometer or camera for which the calibration is extremely steady for longer than the orbital period one is trying to determine. The planetary “signal” is a tiny fraction of the star’s signal.

For eclipse detection to work, one needs a sensitive mid-infrared observatory for which the calibration is extremely steady over orbital periods.

The star needs to cooperate: it can’t be too active or too heavily spotted. RV&T thus very difficult in young stars.

Today in Astronomy 111: exoplanet detectionThe bad newsThe successful search for extrasolar planetsExample: orbital speeds of Sun and JupiterThe successful search for extrasolar planets (continued)The successful search for extrasolar planets (continued)The successful search for extrasolar planets (continued)The successful search for extrasolar planets (continued)The successful search for extrasolar planets (continued)The successful search for extrasolar planets (continued)The successful search for extrasolar planets (continued)The successful search for extrasolar planets (continued)Today’s exoplanetsExosolar systems with three or more planetsToday’s exoplanets (continued)Radial-velocity planet detection and msini measurementRadial-velocity planet detection and msini measurement (continued)Radial-velocity planet detection and msini measurement (continued)Radial-velocity planet detection and msini measurement (continued)Exoplanetary transits: sini and R measurementsExoplanetary transits: sini and R measurements (continued)Exoplanetary transits: sini and R measurements (continued)Exoplanetary eclipses and the temperatures of exoplanetsExoplanetary eclipses and T (continued)Transits, eclipses and exoplanetary atmospheresTransits, eclipses and exoplanetary atmospheres (continued)Exoplanet detection