search for planetary candidates within the ogle stars adriana v. r. silva & patrícia c. cruz...
TRANSCRIPT
Search for planetary candidates within
the OGLE stars
Adriana V. R. Silva & Patrícia C. CruzCRAAM/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 upSilva & Cruz – Astrophysical Journal Letters,
637, 2006 (astro-ph/0505281)
Planet definition
Based on the object’s massAccording 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
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.
2
*
r
mGMF plan
Extra-solar Planets Encyclopedia
www.obspm.fr/encycl/encycl.html169 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.
23/2
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3/1
1
1
)(
sen2
eMM
iM
P
GK
p
p
Planetary massdetermined:
Radial velocity shifts
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
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;
aorb
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 10
OGLE 56 OGLE 111 OGLE 113
OGLE 132
HD209458
OGLE 122 test
TrES-1
Model test results
Fit
Para
mete
rs
3
2
2
31
21 4
sR
a
GPR
MM
Equations4 unknowns: M1, R1, M2, and R2
Kepler’s 3rd law:
Transit depth I/I:
Mass-radius relationship for MS stars (Allen Astrophysical Quantities, Cox 2000) for both primary and secondary:
31
221
23
4
)(
R
MMGP
R
a
s
8.0
11
SunSun M
M
R
R
1
2
R
R
R
R
s
p
8.0
22
SunSun M
M
R
R
Model para
mete
rs
Planetary candidates selection
Density: – Densities < 0.7 to rule out big stars (O, B, A): 1-
2% dimming due to 0.3-0.5 Msun companions:
– Densities > 2.3 maybe due to M dwarfs or binary systems.
Radius of the secondary:
28 candidates
sun 3.27.0
JRR 5.12
3
2
2
31
21 4
sR
a
GPR
MM
Model para
mete
rs
0.7<<2.3R2<1.5 RJ
Comparison with other results100% 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 (RM0.8), 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 M0.1 Msun and sizes similar to Jupiter’s.
CoRoT
Method can be easily applied to CoRoT observations of transits.