Detecting Transits of Detecting Transits of Extrasolar Planets and Extrasolar Planets and

their Moonstheir Moons

Alea SmithAlea Smith

Advisor: Dr. Bill RomanishinAdvisor: Dr. Bill Romanishin

OutlineOutlineBackgroundBackground What is an Extrasolar planet?What is an Extrasolar planet?

MotivationMotivation

Detection MethodsDetection Methods

TrES-3bTrES-3b

Detecting MoonsDetecting Moons

ResultsResults

ConclusionConclusion

What is an Extrasolar planet?What is an Extrasolar planet?

Extrasolar planet (Exoplanet)Extrasolar planet (Exoplanet) Planet in orbit around a star other than our sunPlanet in orbit around a star other than our sun

Over 300 discoveredOver 300 discovered

Most much more massiveMost much more massive

than Earth; Jupiter-likethan Earth; Jupiter-like Jupiter is 11 times radius Jupiter is 11 times radius

of Earth & 300 times mass of Earth & 300 times mass

of Earthof Earth

Jupiter ~1/10 size of SunJupiter ~1/10 size of Sun

Relative size of Earth and Jupiter

www.wikipedia.org

Exoplanet DiscoveriesExoplanet Discoveries

MotivationMotivationGather more data on a planet known to transit parent Gather more data on a planet known to transit parent starstar

Show amateur telescopes are capable of observationsShow amateur telescopes are capable of observations Large telescopes expensive to operateLarge telescopes expensive to operate Difficult to get observing timeDifficult to get observing time

Image of Transit

www.transitsearch.org

Extrasolar PlanetsExtrasolar Planets

Estimated that 10% of sun-like stars (main-sequence) Estimated that 10% of sun-like stars (main-sequence) have orbiting planetshave orbiting planets

Jupiter formed far from sunJupiter formed far from sun

Exoplanets orbit close to starsExoplanets orbit close to stars Not necessarily more common than Earth-like planetsNot necessarily more common than Earth-like planets Size and orbital period make them easier to detect?Size and orbital period make them easier to detect?

Direct Detection MethodsDirect Detection MethodsPicturesPictures Can’t get images Can’t get images

around sun-like starsaround sun-like stars Seen around brown Seen around brown

dwarfsdwarfs Only a few observed Only a few observed

using this methodusing this method Not much informationNot much information

First extrasolar planet to have ever been First extrasolar planet to have ever been directly imaged.directly imaged.

http://en.wikipedia.org/wiki/Extrasolar_planethttp://en.wikipedia.org/wiki/Extrasolar_planet

Indirect Detection MethodsIndirect Detection MethodsDoppler TechniqueDoppler Technique Gravitational tug causes Gravitational tug causes

stellar wobblestellar wobble Star not at center of massStar not at center of mass

http://en.wikipedia.org/wiki/Extrasolar_planet

Exoplanet in Orbit

http://obswww.unige.ch/~udry/planet/method.html

Indirect Detection Methods (cont)Indirect Detection Methods (cont)TransitsTransits Planet passes in front of Planet passes in front of

starstar Periodic dimming seen Periodic dimming seen

in light curvesin light curves A few percent dimmingA few percent dimming ~ 30 planets discovered~ 30 planets discovered

www.eso.org

Brightness Variations of Two Stars with Transiting Exoplanets

Phase

Rel

ativ

e F

lux

Limb DarkeningLimb Darkening

Light curve not flat but curvedLight curve not flat but curved

Limb DarkeningLimb Darkening Decrease in intensity from the center of the star to the Decrease in intensity from the center of the star to the

edge (or “limb”)edge (or “limb”)

Caused by decrease in density and temperature as Caused by decrease in density and temperature as distance from center of star increasesdistance from center of star increases

Occurs just after star is fully transiting and right before Occurs just after star is fully transiting and right before it stops transitingit stops transiting Even though completely transiting star, light not as Even though completely transiting star, light not as

intense at edgesintense at edges

Choosing an ObjectChoosing an Object

Our object discovered by (TrES)Our object discovered by (TrES)

Trans-Atlantic Exoplanet SurveyTrans-Atlantic Exoplanet Survey Three 4” telescopesThree 4” telescopes

Low resolution wide-field survey Low resolution wide-field survey

cameras detect decrease in brightness cameras detect decrease in brightness

from small area in sky around starfrom small area in sky around star Brightest star fading a littleBrightest star fading a little Fainter star fading a lotFainter star fading a lot

Telescopes like OU’s able to focus on candidate stars Telescopes like OU’s able to focus on candidate stars and find what is causing the dimmingand find what is causing the dimming

Lowell Observatory

ResearchResearchObserve candidate star when possible transit Observe candidate star when possible transit expected to occurexpected to occur

Use differential photometry and interpret light curvesUse differential photometry and interpret light curves Differential photometry is measurement of changes in Differential photometry is measurement of changes in

brightness of object compared to other nearby objectsbrightness of object compared to other nearby objects

EquipmentEquipment 16 inch LX-200 16 inch LX-200

telescope telescope AP7p charge-coupled AP7p charge-coupled

device (CCD) cameradevice (CCD) camera

Observatory.ou.edu

OU’s Telescope

TrES-3 bTrES-3 bFirst detected in 2007First detected in 2007

800 light-years away800 light-years away

Located in constellation Located in constellation

HerculesHercules

1.92 M1.92 MJup Jup &1.295 R&1.295 RJupJup

Orbital period of 1.306 daysOrbital period of 1.306 days

Diminishes light from starDiminishes light from star

by 2.98%by 2.98%

Parent star ~0.9 solar massesParent star ~0.9 solar masses Hercules

Star Field of TrES-3 bStar Field of TrES-3 b

TrES-3

Reducing ImagesReducing Images

Use IRAF (Image Reduction and Analysis Facility) Use IRAF (Image Reduction and Analysis Facility) software for image reduction and analysis of datasoftware for image reduction and analysis of data

Flat-fieldingFlat-fielding Take image of uniformly Take image of uniformly

illuminated surfaceilluminated surface Records imperfections Records imperfections

in equipment such as in equipment such as

difference in sensitivitydifference in sensitivity

of pixels or dust on CCDof pixels or dust on CCD

Flat Field Image

Reducing Images (cont.)Reducing Images (cont.)

Dark frameDark frame Image taken with the shutter closedImage taken with the shutter closed Records noise in CCDRecords noise in CCD

To get calibrated image,To get calibrated image,

divide dark subtracted divide dark subtracted

raw image by flat imageraw image by flat image

Dark Image

TrES-3

Data for TrES-3

Detecting Moons Around Transiting Detecting Moons Around Transiting Exoplanets Exoplanets

Moons too small for direct observationMoons too small for direct observation Need another methodNeed another method timing of planet transits timing of planet transits

Use exoplanet transits to determine limiting Use exoplanet transits to determine limiting magnitudes for being able to detect moonsmagnitudes for being able to detect moons

Create star-planet-moon systemCreate star-planet-moon system Vary one parameter at a time Vary one parameter at a time

see how affects limiting see how affects limiting

magnitudemagnitudePeriod of planet, period of moon, Period of planet, period of moon,

mass of planet, mass of moon, mass of planet, mass of moon,

mass of starmass of star

Original SystemOriginal SystemParameters:Parameters: Mass of planet=mass of JupiterMass of planet=mass of Jupiter Mass of moon=mass of Earth’s moonMass of moon=mass of Earth’s moon Mass of star=mass of sunMass of star=mass of sun Period of planet=1 yearPeriod of planet=1 year Period of moon=1 monthPeriod of moon=1 month

Goal: Observe how changing one parameter at a time Goal: Observe how changing one parameter at a time affects types of stars moons can be detected aroundaffects types of stars moons can be detected around

Center of Mass (COM)Center of Mass (COM)Moon changes COM of planetMoon changes COM of planet Produces changing transit times that can be observedProduces changing transit times that can be observed

If planet first, planet transits earlierIf planet first, planet transits earlier

If moon first, planets transits laterIf moon first, planets transits later

Direction of orbit

Direction of orbit

Moon

Star

Exoplanet

XCM

Star

ExoplanetMoon

XCM

Corresponding Light CurvesCorresponding Light Curves

Planet without moon

Planet and moon with planet first in transit transit earlier

Planet and moon with moon first in transit transit later

Transit center for no moon

Can Moons be Detected with Small Can Moons be Detected with Small Telescopes?Telescopes?

Once change in transit time found, need to calculate Once change in transit time found, need to calculate minimum number of photons needed to observe minimum number of photons needed to observe changechange

Need minimum of 2 exposures per change in transit Need minimum of 2 exposures per change in transit timetime

Typical drop in light from transit ~ 1%Typical drop in light from transit ~ 1% Need an error less than ½% to resolveNeed an error less than ½% to resolve Error = 1/(signal-to-noise) Error = 1/(signal-to-noise) S/N=200 S/N=200 (S/N)² is number of photons detected = 40,000(S/N)² is number of photons detected = 40,000

Ex: If 1 exposure is 10 seconds, need to detect Ex: If 1 exposure is 10 seconds, need to detect minimum of 4,000 photons/s minimum of 4,000 photons/s

Limiting MagnitudesLimiting MagnitudesAfter finding minimum number of photons needed to After finding minimum number of photons needed to detect, determine limiting magnitude for systemdetect, determine limiting magnitude for system

Gives faintest star that moons can be detected around Gives faintest star that moons can be detected around for given systemfor given system

Gather data for ranges of hypothetical casesGather data for ranges of hypothetical cases Vary period of planet: 1 day to 12 yearsVary period of planet: 1 day to 12 years Vary period of moon: 1 day to 9 yearsVary period of moon: 1 day to 9 years Vary mass of planet: 1/300Vary mass of planet: 1/300thth M MJupJup to10 M to10 MJupJup

Vary mass of moon: 10^21 to 10^24 kgVary mass of moon: 10^21 to 10^24 kg Vary mass of star: 0.1 MVary mass of star: 0.1 MSunSun to 40M to 40MSunSun

4.010

sec/#minlog

4.0

Xkmn

telVega trQAP

photonsofmag

Magnitude SystemMagnitude SystemBrighter stars Brighter stars more negative more negative

Logarithmic systemLogarithmic system One magnitude interval corresponds to factor of One magnitude interval corresponds to factor of

100^(1/5) or 2.512 times the amount of intensity100^(1/5) or 2.512 times the amount of intensity

Apparent magnitude of Vega set to zeroApparent magnitude of Vega set to zero

Sun -26.7Sun -26.7

http://www.astronomynotes.com/starprop/s4.htm

Varying Period of PlanetVarying Period of PlanetRange 1 day to 12 years; original value 1 yearRange 1 day to 12 years; original value 1 year

Fainter stars seen with planets of longer periodsFainter stars seen with planets of longer periods

Range of magnitudes ~8.5 to 11.6 Range of magnitudes ~8.5 to 11.6 Varying Period of Planet

10000

100000

1000000

10000000

100000000

1000000000

8 9 10 11 12Limiting Magnitude

Per

iod o

f P

lanet

(s)

Per

iod

of

Pla

net

(s)

Varying Period of MoonVarying Period of MoonRange 1 day to 9 years; original value 30 daysRange 1 day to 9 years; original value 30 days

Fainter stars seen with moons of longer periodsFainter stars seen with moons of longer periods

Range of Magnitudes ~8.2 to 14Range of Magnitudes ~8.2 to 14Varying Period of Moon

10000

100000

1000000

10000000

100000000

1000000000

8 9 10 11 12 13 14

Limiting Magnitude

Per

iod o

f M

oon (s)

Per

iod

of

Mo

on

(s)

Effect of MassEffect of Mass

Two Objects of Equal Mass

Planet More Massive than Moon

Planet Much More Massive than Moon

moon

planet

planet

planet

moon

moon

Varying Mass of PlanetVarying Mass of PlanetRange 1/300-10 MRange 1/300-10 MJupJup; Original value M; Original value MJupJup

Fainter stars seen with planets of smaller massFainter stars seen with planets of smaller mass

Range of magnitudes ~9 to 14Range of magnitudes ~9 to 14Varying Mass of Planet

1E+24

1E+25

1E+26

1E+27

1E+28

1E+29

9 10 11 12 13 14Limiting Magnitude

Mas

s of P

lanet

(k

Mas

s o

f P

lan

et (

kg)

Varying Mass of MoonVarying Mass of MoonRange 10^21 to 10^24 kg; Original value 7x10^22 kgRange 10^21 to 10^24 kg; Original value 7x10^22 kg

Fainter stars seen with moons of greater massFainter stars seen with moons of greater mass

Range of magnitudes ~6 to 13.5Range of magnitudes ~6 to 13.5

10

Varying Mass of Moon

1E+20

1E+21

1E+22

1E+23

1E+24

6 7 8 9 10 11 12 13 14Limiting Magnitude

Mass o

f M

oon (s)

Mas

s o

f M

oo

n (

kg)

Varying Mass of StarVarying Mass of StarRange 0.1-40 MRange 0.1-40 MSunSun; Original value M; Original value MSunSun

Fainter stars seen with stars of smaller massFainter stars seen with stars of smaller mass

Range of Magnitudes ~ 9.3 to 11.5Range of Magnitudes ~ 9.3 to 11.5Varying Mass of Star

1E+29

1E+30

1E+31

1E+32

9 10 11 12Limiting Magnitude

Mas

s of S

tar

(kM

ass

of

Sta

r (k

g)

ConclusionConclusion

Using OU’s telescope and varying one parameter at a Using OU’s telescope and varying one parameter at a time, faintest star moons can be detected around has time, faintest star moons can be detected around has magnitude 14magnitude 14

If real system, magnitude of star known, observe If real system, magnitude of star known, observe change in transit time and determine information about change in transit time and determine information about moonmoon

Relationship between equations usefulRelationship between equations useful can be used to solve for other variablescan be used to solve for other variables

Questions?Questions?