EDP Sciences
Free Access
Issue
A&A
Volume 543, July 2012
Article Number A63
Number of page(s) 12
Section Planets and planetary systems
DOI https://doi.org/10.1051/0004-6361/201118140
Published online 27 June 2012

Online material

Appendix A: Comments on individual sources

In this Appendix we discuss in detail the sample of ten remaining CoRoT candidates, that were selected using the cut in impact parameter and were presented in Sect. 4 and Table 1. In Figs. A.1, we show for each candidate the blended light fraction k versus reduced χ2, and the best fitting blended light models for k = 0.2, 0.5, 0.9, and 0.95. In Table A.1, we show best-matching system parameters for the full CoRoT IRa01, assuming no blended light.

A.1. Selected planet candidates from the lightcurves alone

E2-1126-0102890318

We find a 2σ upper limit for blended light contribution of k < 0.14, therefore a blend scenario can be excluded for this source at high confidence using the lightcurve alone. In addition, by assuming that the host star is on the main sequence, its mean density points to a  ~ 1.5 RJup radius, well in the range of known hot Jupiters. Of course, this source is exoplanet CoRoT-1b (Barge et al. 2008).

E1-0330-0102912369

We find a 2σ upper limit for blended light contribution of k < 0.31 from its lightcurve, meaning that only a small contribution of blended light is tollerated. Assuming the host star is on the main sequence, its mean density points to a  ~ 1.2 RJup radius for the secondary. This object is identified as exoplanet CoRoT-4b (Aigrain et al. 2008). Eventhough the CoRoT-4b host star is of similar brightness as CoRoT-1b, the significantly longer orbital period, the residual variability (caused by a spotted rotating stellar photosphere) and the 1.8 times smaller transit depth are the causes of the lower confidence on blended light.

E2-0203-0102825481

The 2σ upper limit for blended light is k < 0.3 from its lightcurve. Radial velocity follow-up by the CoRoT team showed this to be an eclipsing binary of a low-mass M dwarf and a G-type primary (Morales et al., in prep). Assuming the host star is on the main sequence, its mean density points to a  ~1.7   RJup radius. Although not a planet, it is consistent with a non-blended system as found from our lightcurve fitting. Such systems always require RV follow-up since late M dwarfs and Jupiter-mass planets can have similar radii.

E2-1712-0102826302

We find a 2σ upper limit for blended light contribution of k < 0.93. We can therefore only exclude a high contribution of blended light for this shallow (2.4 mmag) transit. This means that at 2σ confidence the true eclipse depth is less than 2.4% in the presence of blended light. The fitted host star mean density points to an early type or evolved system. HARPS radial velocity follow-up has confirmed that the host star is an evolved fast rotator and Moutou et al. (2009) conclude that a triple system is the most probable scenario.

E1-4108-0102779966

Because of the poor signal-to-noise of this transit and the relatively high impact parameter b = 0.8, the 2σ upper limit for blended light is k < 0.95, therefore only a very high contribution of blended light can be excluded for this candidate. Assuming the host star is on the main sequence, its density is slightly lower compared to the solar value, indicating a stellar radius of R1 ~ 1.2   R. However, spectroscopic follow-up with HARPS suggested that the host is a low mass (~0.8   M) star. No additional follow-up has thusfar been obtained by the CoRoT team.

A.2. Candidates rejected due to their large size

E1-4617-0102753331

The 2σ upper limit for blended light is k < 0.20, therefore a blend scenario can be excluded at high confidence for this source. Assuming the host star is on the main sequence, its very low density points to an early B-type primary with a K dwarf secondary. The planet hypothesis is rejected and no additional follow-up is therefore required judging from the lightcurve alone. Note that an orbit with an eccentricity of e = 0.5, orientated in the right way, could increase the estimated stellar density to that of the Sun, and decrease R2 to 2 RJup. This ambiguity can be easily removed by taking a single spectrum of the star, resolving its spectral type.

E2-2430-0102815260

We find a 2σ upper limit for blended light contribution of k < 0.44. Again, only a small contribution of blended light is tollerated. Assuming the host star is on the main sequence, its mean density, consistent with an A type or evolved star, points to a radius R2 > 2.5   RJup. Radial velocity follow-up by the CoRoT team showed this to be a single lined eclipsing binary of a fast rotating host star and an early type M dwarf (Moutou et al. 2009).

E2-4073-0102863810

For this source, we find a 2σ upper limit for blended light of k < 0.67. This object shows  ~ 4% deep eclipses around a host star that is  ~ 20% less dense than the sun. This candidate was introduced in the original list of Carpano et al. (2009), but is not mentioned in the follow-up paper of Moutou et al. (2009). With an anticipated secondary radius of  ~ 2.1   RJup this object could still belong to the rare group of low mass stars or brown dwarfs. In the case of a stellar M5 secondary, the secondary eclipse would be detectable at  ~ 3.5 mmag in depth.

E2-1736-0102855534

The 2σ upper limit for blended light is k < 0.62. The low mean density of the host star, consistent with a very early main sequence or evolved star, points to a  > 2.0   RJup radius. Analysis of the lightcurve reveals a secondary eclipse at the 9σ level, which indicates the secondary is in fact a low mass star. CoRoT radial velocity follow-up has confirmed that the host star is a fast rotating early type star and the system is a single lined eclipsing binary.

E2-3724-0102759638

For this source, we find a 2σ upper limit for blended light of k < 0.78. Assuming the host star is on the main sequence, its very low density points to an A type primary, therefore R2 > 2.0   RJup. This object is listed both as a planet candidate and a binary by Carpano et al. (2009).

thumbnail Fig. A.1

For each CoRoT IRa01 candidate: the blended light fraction k versus reduced χ2 (left panels) and the best fitting blended light models for k = 0.2, 0.5, 0.9, and 0.95.

Open with DEXTER

Table A.1

Fitting parameters for our blend models when applied to the CoRoT IRa01 sample, assuming k = 0.


© ESO, 2012

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