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Register a new userHigh precision transit observations of the exoplanet WASP-13b with the RISE instrument
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Added by
Susana Cristina Cabral de Barros
Publication date
2011
fields
Physics
and research's language is
English
Authors
S. C. C. Barros
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WASP-13b is a sub-Jupiter mass exoplanet orbiting a G1V type star with a period of 4.35 days. The current uncertainty in its impact parameter (0 < b < 0.46) resulted in poorly defined stellar and planetary radii. To better constrain the impact parameter we have obtained high precision transit observations with the RISE instrument mounted on 2.0 m Liverpool Telescope. We present four new transits which are fitted with an MCMC routine to derive accurate system parameters. We found an orbital inclination of 85.2 pm 0.3 degrees resulting in stellar and planetary radii of 1.56 pm 0.04 Rodot and 1.39 pm 0.05 RJup, respectively. This suggests that the host star has evolved off the main-sequence and is in the shell hydrogen-burning phase. We also discuss how the limb darkening affects the derived system parameters. With a density of 0.17{rho}J, WASP-13b joins the group of low density planets whose radii are too large to be explained by standard irradiation models. We derive a new ephemeris for the system, T0 = 2455575.5136 pm 0.0016 (HJD) and P = 4.353011 pm 0.000013 days. The planet equilibrium temperature (Tequ = 1500 K) and the bright host star (V = 10.4 mag) make it a good candidate for follow-up atmospheric studies.
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We report the discovery of WASP-13b, a low-mass $ M_p = 0.46 ^{+ 0.06}_{- 0.05} M_J$ transiting exoplanet with an orbital period of $4.35298 pm 0.00004$ days. The transit has a depth of 9 mmag, and although our follow-up photometry does not allow us to constrain the impact parameter well ($0 < b < 0.46$), with radius in the range $R_p sim 1.06 - 1.21 R_J$ the location of WASP-13b in the mass-radius plane is nevertheless consistent with H/He-dominated, irradiated, low core mass and core-free theoretical models. The G1V host star is similar to the Sun in mass (M$_{*} = 1.03^{+0.11}_ {- 0.09} M_{odot}$) and metallicity ([M/H]=$0.0pm0.2$), but is possibly older ($8.5^{+ 5.5}_{- 4.9}$ Gyr).
We present Rossiter-McLaughlin observations of WASP-13b and WASP-32b and determine the sky-projected angle between the normal of the planetary orbit and the stellar rotation axis ($lambda$). WASP-13b and WASP-32b both have prograde orbits and are consistent with alignment with measured sky-projected angles of $lambda={8^{circ}}^{+13}_{-12}$ and $lambda={-2^{circ}}^{+17}_{-19}$, respectively. Both WASP-13 and WASP-32 have $T_{mathrm{eff}}<6250$K and therefore these systems support the general trend that aligned planetary systems are preferentially found orbiting cool host stars. A Lomb-Scargle periodogram analysis was carried out on archival SuperWASP data for both systems. A statistically significant stellar rotation period detection (above 99.9% confidence) was identified for the WASP-32 system with $P_{mathrm{rot}}=11.6 pm 1.0 $ days. This rotation period is in agreement with the predicted stellar rotation period calculated from the stellar radius, $R_{star}$, and $v sin i$ if a stellar inclination of $i_{star}=90^{circ}$ is assumed. With the determined rotation period, the true 3D angle between the stellar rotation axis and the planetary orbit, $psi$, was found to be $psi=11^{circ} pm 14$. We conclude with a discussion on the alignment of systems around cool host stars with $T_{mathrm{eff}}<6150$K by calculating the tidal dissipation timescale. We find that systems with short tidal dissipation timescales are preferentially aligned and systems with long tidal dissipation timescales have a broad range of obliquities.
Ultra-hot Jupiters offer interesting prospects for expanding our theories on dynamical evolution and the properties of extremely irradiated atmospheres. In this context, we present the analysis of new optical spectroscopy for the transiting ultra-hot Jupiter WASP-121b. We first refine the orbital properties of WASP-121b, which is on a nearly polar (obliquity $psi^{rm North}$=88.1$pm$0.25$^{circ}$ or $psi^{rm South}$=91.11$pm$0.20$^{circ}$) orbit, and exclude a high differential rotation for its fast-rotating (P$<$1.13 days), highly inclined ($i_mathrm{star}^{rm North}$=8.1$stackrel{+3.0}{_{-2.6}}^{circ}$ or $i_mathrm{star}^{rm South}$=171.9$stackrel{+2.5}{_{-3.4}}^{circ}$) star. We then present a new method that exploits the reloaded Rossiter-McLaughlin technique to separate the contribution of the planetary atmosphere and of the spectrum of the stellar surface along the transit chord. Its application to HARPS transit spectroscopy of WASP-121b reveals the absorption signature from metals, likely atomic iron, in the planet atmospheric limb. The width of the signal (14.3$pm$1.2 km/s) can be explained by the rotation of the tidally locked planet. Its blueshift (-5.2$pm$0.5 km/s) could trace strong winds from the dayside to the nightside, or the anisotropic expansion of the planetary thermosphere.
We report twelve new transit observations of the exoplanet WASP-4b from the Transit Monitoring in the South Project (TraMoS) project. These transits are combined with all previously published transit data for this planet to provide an improved radius measurement of Rp = 1.395 +- 0.022 Rjup and improved transit ephemerides. In a new homogeneous analysis in search for Transit Timing Variations (TTVs) we find no evidence of those with RMS amplitudes larger than 20 seconds over a 4-year time span. This lack of TTVs rules out the presence of additional planets in the system with masses larger than about 2.5 M_earth, 2.0 M_earth, and 1.0 M_earth around the 1:2, 5:3 and 2:1 orbital resonances. Our search for the variation of other parameters, such as orbital inclination and transit depth also yields negative results over the total time span of the transit observations. Finally we perform a simple study of stellar spots configurations of the system and conclude that the star rotational period is about 34 days.
We present 13 high-precision and four additional light curves of four bright southern-hemisphere transiting planetary systems: WASP-22, WASP-41, WASP-42 and WASP-55. In the cases of WASP-42 and WASP-55, these are the first follow-up observations since their discovery papers. We present refined measurements of the physical properties and orbital ephemerides of all four systems. No indications of transit timing variations were seen. All four planets have radii inflated above those expected from theoretical models of gas-giant planets; WASP-55b is the most discrepant with a mass of 0.63 Mjup and a radius of 1.34 Rjup. WASP-41 shows brightness anomalies during transit due to the planet occulting spots on the stellar surface. Two anomalies observed 3.1 d apart are very likely due to the same spot. We measure its change in position and determine a rotation period for the host star of 18.6 +/- 1.5 d, in good agreement with a published measurement from spot-induced brightness modulation, and a sky-projected orbital obliquity of lambda = 6 +/- 11 degrees. We conclude with a compilation of obliquity measurements from spot-tracking analyses and a discussion of this technique in the study of the orbital configurations of hot Jupiters.
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