Search for planetary candidates within the OGLE stars

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Search for planetary candidates within the OGLE
stars

• Adriana V. R. Silva Patrícia C. Cruz
• CRAAM/Mackenzie

COROT 2005 - 05/11/2005
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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
• Keplers 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)

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Planet definition

• Based on the objects mass
• According to the IAU WORKING GROUP ON EXTRASOLAR
  PLANETS (WGESP)
• stars objects capable of thermonuclear fusion of
  hydrogen (gt0.075 Msun)
• Brown dwarf capable of deuterium burning
  (0.013ltMlt0.075 Msun)
• Planets objects with masses below the deuterium
  fusion limit (Mlt13 MJup), that orbit stars or
  stellar remains (independently of the way in
  which they formed).

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Newtons gravitation law

• Both planet and star orbit their common
  center-of-mass.
• Planets gravitational attraction causes a small
  variation in the stars light.
• The effect will be greater for close in massive
  planets.

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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.

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Radial velocity shifts
Planetary mass determined
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Venus transit 8 June 2004
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Transits
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HD209458
In 2000, confirmation that the radial velocity
measurements were indeed due to an orbiting
planet.
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Planetary detection by transits

• Only 9 confirmed planets.
• Orbits practically perpendicular to the plane of
  the sky (i90o).
• 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.

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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).

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Transit simulation
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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

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Transit Simulation
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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 ilt80o.

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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

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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
  M0.092 Msun and R0.12 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
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OGLE 132
OGLE 122
test
OGLE 56
OGLE 111
OGLE 113
OGLE 10
HD209458
TrES-1
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Model test results
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Fit Parameters
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Equations

• 4 unknowns M1, R1, M2, and R2
• Keplers 3rd law
• Transit depth ?I/I
• Mass-radius relationship for MS stars (Allen
  Astrophysical Quantities, Cox 2000) for both
  primary and secondary

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Model parameters
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Planetary candidates selection

• Density
• Densities lt 0.7 to rule out big stars (O, B, A)
  1-2 dimming due to 0.3-0.5 Msun companions
• Densities gt 2.3 maybe due to M dwarfs or binary
  systems.
• Radius of the secondary
• 28 candidates

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Model parameters
0.7lt?lt2.3 R2lt1.5 RJ
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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 ?gt1.

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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 Keplers 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 lt 1.5 RJ.
• Method does not work for brown dwarfs with M?0.1
  Msun and sizes similar to Jupiters.

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CoRoT

• Method can be easily applied to CoRoT
  observations of transits.