Download Search for Planetary Candidates within the OGLE Stars

Search for planetary
candidates within
the OGLE stars
Adriana V. R. Silva & Patrícia C. Cruz
CRAAM/Mackenzie
COROT 2005 - 05/11/2005
Summary
 Method to distinguish between planetary and
stellar companions;
 Observed transits in OGLE data:
– 177 stars;
 Model:
– Orbital parameters: P; r/Rs, a/Rs, i
– Kepler’s 3rd law + mass-radius relation for MS stars
 Results tested on 7 known bonafide planets;
 28 proposed planetary candidates for
spectroscopic follow up
 Silva & Cruz – Astrophysical Journal Letters,
637, 2006 (astro-ph/0505281)
Planet definition
 Based on the object’s mass
According to the IAU WORKING GROUP
ON EXTRASOLAR PLANETS (WGESP):
 stars: objects capable of thermonuclear
fusion of hydrogen (>0.075 Msun);
 Brown dwarf: capable of deuterium burning
(0.013<M<0.075 Msun);
 Planets: objects with masses below the
deuterium fusion limit (M<13 MJup), that orbit
stars or stellar remains (independently of the
way in which they formed).
Newton’s gravitation law
F
GM *m plan
r
2
Both planet and star orbit their common
center-of-mass.
Planet’s gravitational attraction causes a
small variation in the star’s light.
The effect will be greater for close in
massive planets.
Extra-solar Planets Encyclopedia
 www.obspm.fr/encycl/encycl.html
 169 planets (until 24/10/2005):
– 145 planetary systems
– 18 multiple planetary systems
 9 transiting: HD 209458, TrES-1, OGLE 10,
56, 111, 113, 132, HD 189733, HD 149026.
Radial velocity shifts
Planetary mass
determined:
 2G 
K 

 P 
1/ 3
M p sen i
1
(M *  M p )2 / 3 1  e2
Venus transit – 8 June 2004
Transits
HD209458
In 2000, confirmation that the radial velocity measurements
were indeed due to an orbiting planet.
Planetary detection by transits
 Only 9 confirmed planets.
 Orbits practically perpendicular to the plane
of the sky (i=90o).
 Radial velocity: planet mass;
 Transit: planet radius and orbit inclination
angle;
 Ground based telescopes able to detect giant
planets only. Satellite based observations
needed for detection of Earth like planets.
OGLE project
 177 planets with “transits”;
 Only 5 confirmed as planets by radial velocity
measurements (10, 56, 111, 113, 132).
 OGLE data (Udalski 2002,
2003, 2004)
 Published orbital period
 Model the data to obtain:
– r/Rs (planet radius);
– aorb/Rs (orbital radius –
assumed circular orbit);
– i (inclination angle).
Transit simulation
Model
 Star  white light image of
the sun;
 Planet  dark disk of
radius r/Rs;
 Transit: at each time
interval, the planet is
centered at a given
position in its orbit (with
aorb/Rs and i) and the total
flux is calculated;
Transit Simulation
Lightcurve
 I/I=(r/Rs)2, larger planets
cause bigger dimming in
brightness.
 For Jupiter  1% decrease
 Larger orbital radius (planet
further from the star) yield
shorter phase interval.
 Inclination angle close to 90o
(a transit is observed).
 Smaller angles, shorter
phase interval;
 Grazing transits for i<80o.
r
aorb
i
Orbit
aorb
 Circular orbits;
 Period from OGLE project;
 Perform a search in parameter space for the best
values of r/Rs, aorb/Rs, and i (minimum 2).
 Error estimate of the model parameters from
1000 Monte Carlo simulation, taken from only
those within 1 sigma uncertainty of the data;
Test of the model
7 known planets: HD 209458, TrES-1,
OGLE-TR-10, 56, 111, 113, and 132
OGLE-TR-122 which companion is a
brown dwarf with M=0.092 Msun and
R=0.12 Rsun (Pont et al. 2005)
 Synthetic lightcurve with random noise
added.
M1 (Msun) M2 (Msun)
R2 (RJ) Semi-axis AU) angle
Input
4.00
0.32
3.9
0.075
84
Output
3.75
0.29
3.6
0.074
85.3
OGLE 132
OGLE 122
OGLE 56
OGLE 111
HD209458
TrES-1
test
OGLE 113
OGLE 10
Model test results
Fit Parameters
M 1  M 2 4 2  a 
 


3
2 
R1
GP  Rs 
3
Equations
 4 unknowns: M1, R1, M2, and R2
3
 Kepler’s 3rd law:
 a  GP 2 ( M
  
 Rs 
 Transit depth I/I:
 M2)
4 R13
1
2
Rp
R2

Rs R1
 Mass-radius relationship for MS stars (Allen
Astrophysical Quantities, Cox 2000) for both
primary and secondary:
R1  M 1 

 
RSun  M Sun 
0 .8
R2  M 2 

 
RSun  M Sun 
0 .8
Model parameters
Planetary candidates selection
 Density:
M 1  M 2 4 2  a 
 


R13
GP 2  Rs 
3
– Densities < 0.7 to rule out big stars (O, B, A): 1-2%
dimming due to 0.3-0.5 Msun companions:
0.7    2.3 sun
– Densities > 2.3 maybe due to M dwarfs or binary
systems.
 Radius of the secondary:
 28 candidates
R2  1.5 RJ
Model parameters
0.7<<2.3
R2<1.5 RJ
Comparison with other results
100% agreement with:
– Elipsoidal variation: periodic modulation in
brightness due to tidal effects between the two
stars (Drake 2003, Sirko & Paczynski 2003)
– Low resolution radial velocity obs. (Dreizler et
al. 2002, Konacki et al. 2003)
– Giants: espectroscopic study in IR (Gallardo et
al. (2005)
6 stars (OGLE-49, 151, 159, 165, 169, 170)
failed the criterion of Tingley & Sackett
(2005) of >1.
Conclusions
 From the transit observation of a dim object in front
of the main star, one obtains:
– Ratio of the companion to the main star radii: r/Rs;
– Orbital radius (circular) in units of stellar radius: aorb/Rs;
– Orbital inclination angle, i, and period, P.
 Combining Kepler’s 3rd law, a mass-radius relation
(RM0.8), and the transit depth  infer the mass
and radius of the primary and secondary objects.
 Model was tested successfully on 7 known planets.
 28 planetary candidates: density between 0.7 and
2.3 solar density and secondary radius < 1.5 RJ.
 Method does not work for brown dwarfs with M0.1
Msun and sizes similar to Jupiter’s.
CoRoT
 Method can be easily applied to CoRoT
observations of transits.