Detection of period variations in extrasolar transiting planet OGLE-TR-111b
Summary (2 min read)
- The observations of transiting extrasolar planets have produced some of the most in- teresting results in the study of other planetary systems.
- 3Department of Astronomy, Pontificia Universidad Católica, Casilla 306, Santiago 22, Chile.
- 4Specola Vaticana, V-00120 Citta del Vaticano, Italy.
- It has been further realized that the presence of variations in the timing of transits can be attributed to otherwise undetectable planets in the system (see, for example, Miralda-Escudé 2002; Holman & Murray 2005; Agol et al.
- This last case has been recently argued against by Alonso et al. (2008).
2. OBSERVATIONS AND DATA REDUCTION
- The authors observed two consecutive transits of planetary companion OGLE-TR-111b in the I band with the FORS1 instrument at the European Southern Observatory (ESO) Very Large Telescope (VLT).
- For the observations, a nearby bright star was moved outside the field of view, leaving OGLE-TR-111 near the center of the north-eastern quadrant.
- Aperture photometry was performed on the difference images using IRAF DAOPHOT package (Stetson 1987), which was found to give better results than the ISIS photometry routine phot.csh (for a detailed description of the ISIS routines see Hartman et al. 2004).
- In the same paper Kovács et al. (2005) present an iterative method to reconstruct signals affected by systematics effects, based on the TFA method.
- 1. The standard deviation before the transit of the second night is 2.65 mmag, almost reaching the photon noise limit of 2.55 mmag.
- Planetary and orbital parameters, including the central times of transits, were fitted to the OGLE-TR-111 light curve.
- The uncertainties in the parameters were estimated using the Markov Chain Monte Carlo method, which is described in detail by Tegmark et al. (2004), Ford (2005) and Holman et al. (2006).
- Possible systematic errors may be introduced by the choice of the stellar mass, the orbital period — which affects the determination of the orbital radius—, the model for the limb darkening, and the flux in the reference image.
- The coefficients for the quadratic limb-darkenning model were adjusted from the data instead of fixed to the values of Claret (2000) and, additionally, a linear limb darkenning model was considered, both fixing the linear coefficient to the value computed by Claret (2000) and adjusting it as part of the fit.
- The authors therefore conclude that the values obtained for the central transit times are robust.
4. RESULTS AND DISCUSSION
- In Fig. 3 the authors present the observed-minus-computed (O-C) times for the two transits together with those from W07 and Minniti et al. (2007).
- The central time of this last transit has been remeasured using the procedure described above, which is different from the one employed in the original paper, to reduce any effects produced by differing techniques.
- The authors have been able to discard a few possibilities and study some others.
- On the other hand, the mass of the perturber planet must be around 5 MJup if the orbit of the interior planet is nearly circular.
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