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  • 11
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    Kozai-Lidov cycles towards the limit of circumbinary planets (2015)
    Oxford University Press
    Details
    Publication Date: 2015-10-29
    Description: In this Letter, we answer a simple question: Can a misaligned circumbinary planet induce Kozai–Lidov cycles on an inner stellar binary? We use known analytic equations to analyse the behaviour of the Kozai–Lidov effect as the outer mass is made small. We demonstrate a significant departure from the traditional symmetry, critical angles and amplitude of the effect. Aside from massive planets on near-polar orbits, circumbinary planetary systems are devoid of Kozai–Lidov cycles. This has positive implications for the existence of highly misaligned circumbinary planets: an observationally unexplored and theoretically important parameter space.
    Print ISSN: 1745-3925
    Electronic ISSN: 1745-3933
    Topics: Physics
    Published by Oxford University Press
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  • 12
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    Colour-magnitude diagrams of transiting Exoplanets - I. Systems with parallaxes (2014)
    Oxford University Press
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    Publication Date: 2014-03-02
    Description: Broad-band flux measurements centred around [3.6 μm] and [4.5 μm] obtained with Spitzer during the occultation of seven extrasolar planets by their host stars have been combined with parallax measurements to compute the absolute magnitudes of these planets. Those measurements are arranged in two colour–magnitude diagrams. Because most of the targets have sizes and temperatures similar to brown dwarfs, they can be compared to one another. In principle, this should permit inferences about exoatmospheres based on knowledge acquired by decades of observations of field brown dwarfs and ultracool stars’ atmospheres. Such diagrams can assemble all measurements gathered so far and will provide help in the preparation of new observational programmes. In most cases, planets and brown dwarfs follow similar sequences. HD 2094589b and GJ 436b are found to be outliers, so is the night side of HD 189733b. The photometric variability associated with the orbital phase of HD 189733b is particularly revealing. The planet exhibits what appears like a spectral type and chemical transition between its day and night sides: HD 189733b straddles the L–T spectral class transition, which would imply different cloud coverage on each hemisphere. Methane absorption could be absent at its hotspot but present over the rest of the planet.
    Print ISSN: 1745-3925
    Electronic ISSN: 1745-3933
    Topics: Physics
    Published by Oxford University Press
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  • 13
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    Three newly discovered sub-Jupiter-mass planets: WASP-69b and WASP-84b transit active K dwarfs and WASP-70Ab transits the evolved primary of a G4+K3 binary (2014)
    Oxford University Press
    Details
    Publication Date: 2014-10-10
    Description: We report the discovery of the transiting exoplanets WASP-69b, WASP-70Ab and WASP-84b, each of which orbits a bright star ( V  ~ 10). WASP-69b is a bloated Saturn-mass planet (0.26  M Jup , 1.06  R Jup ) in a 3.868-d period around an active, ~1-Gyr, mid-K dwarf. ROSAT detected X-rays 60±27 arcsec from WASP-69. If the star is the source then the planet could be undergoing mass-loss at a rate of ~10 12  g s –1 . This is one to two orders of magnitude higher than the evaporation rate estimated for HD 209458b and HD 189733b, both of which have exhibited anomalously large Lyman α absorption during transit. WASP-70Ab is a sub-Jupiter-mass planet (0.59  M Jup , 1.16  R Jup ) in a 3.713-d orbit around the primary of a spatially resolved, 9–10-Gyr, G4+K3 binary, with a separation of 3.3 arcsec (≥800 au). WASP-84b is a sub-Jupiter-mass planet (0.69  M Jup , 0.94  R Jup ) in an 8.523-d orbit around an active, ~1-Gyr, early-K dwarf. Of the transiting planets discovered from the ground to date, WASP-84b has the third-longest period. For the active stars WASP-69 and WASP-84, we pre-whitened the radial velocities using a low-order harmonic series. We found that this reduced the residual scatter more than did the oft-used method of pre-whitening with a fit between residual radial velocity and bisector span. The system parameters were essentially unaffected by pre-whitening.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 14
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    Colour-magnitude diagrams of transiting Exoplanets - II. A larger sample from photometric distances (2014)
    Oxford University Press
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    Publication Date: 2014-08-22
    Description: Colour–magnitude diagrams form a traditional way of presenting luminous objects in the Universe and compare them to each other. Here, we estimate the photometric distance of 44 transiting exoplanetary systems. Parallaxes for seven systems confirm our methodology. Combining those measurements with fluxes obtained while planets were occulted by their host stars, we compose colour–magnitude diagrams in the near and mid-infrared. When possible, planets are plotted alongside very low mass stars and field brown dwarfs, who often share similar sizes and equilibrium temperatures. They offer a natural, empirical, comparison sample. We also include directly imaged exoplanets and the expected loci of pure blackbodies. Irradiated planets do not match blackbodies; their emission spectra are not featureless. For a given luminosity, hot Jupiters’ daysides show a larger variety in colour than brown dwarfs do and display an increasing diversity in colour with decreasing intrinsic luminosity. The presence of an extra absorbent within the 4.5 μm band would reconcile outlying hot Jupiters with ultra-cool dwarfs’ atmospheres. Measuring the emission of gas giants cooler than 1000 K would disentangle whether planets’ atmospheres behave more similarly to brown dwarfs’ atmospheres than to blackbodies, whether they are akin to the young directly imaged planets, or if irradiated gas giants form their own sequence.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 15
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    Gaia's potential for the discovery of circumbinary planets (2014)
    Oxford University Press
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    Publication Date: 2014-12-17
    Description: The abundance and properties of planets orbiting binary stars – circumbinary planets – are largely unknown because they are difficult to detect with currently available techniques. Results from the Kepler satellite and other studies indicate a minimum occurrence rate of circumbinary giant planets of ~10 per cent, yet only a handful are presently known. Here, we study the potential of ESA's Gaia mission to discover and characterize extrasolar planets orbiting nearby binary stars by detecting the binary's periodic astrometric motion caused by the orbiting planet. We expect that Gaia will discover hundreds of giant planets around binaries with FGK-dwarf primaries within 200 pc of the Sun, if we assume that the giant planet mass distribution and abundance are similar around binaries and single stars. If on the other hand all circumbinary gas giants have masses lower than two Jupiter masses, we expect only four detections. Gaia is critically sensitive to the properties of giant circumbinary planets and will therefore make the detailed study of their population possible. Gaia 's precision is such that the distribution in mutual inclination between the binary and planetary orbital planes will be obtained. It also possesses the capacity to establish the frequency of planets across the Hertzsprung-Russell diagram, both as a function of mass and of stellar evolutionary state from pre-main sequence to stellar remnants. Gaia 's discoveries can reveal whether a second epoch of planetary formation occurs after the red giant phase.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 16
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    Circumbinary planets - why they are so likely to transit (2015)
    Oxford University Press
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    Publication Date: 2015-03-21
    Description: Transits on single stars are rare. The probability rarely exceeds a few per cent. Furthermore, this probability rapidly approaches zero at increasing orbital period. Therefore, transit surveys have been predominantly limited to the inner parts of exoplanetary systems. Here, we demonstrate how circumbinary planets allow us to beat these unfavourable odds. By incorporating the geometry and the three-body dynamics of circumbinary systems, we analytically derive the probability of transitability, a configuration where the binary and planet orbits overlap on the sky. We later show that this is equivalent to the transit probability, but at an unspecified point in time. This probability, at its minimum, is always higher than for single star cases. In addition, it is an increasing function with mutual inclination. By applying our analytical development to eclipsing binaries, we deduce that transits are highly probable, and in some case guaranteed. For example, a circumbinary planet revolving at 1 au around a 0.3 au eclipsing binary is certain to eventually transit – a 100 per cent probability – if its mutual inclination is greater than 0 $_{.}^{\circ}$ 6. We show that the transit probability is generally only a weak function of the planet's orbital period; circumbinary planets may be used as practical tools for probing the outer regions of exoplanetary systems to search for and detect warm to cold transiting planets.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 17
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    Transiting hot Jupiters from WASP-South, Euler and TRAPPIST: WASP-95b to WASP-101b (2014)
    Oxford University Press
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    Publication Date: 2014-04-11
    Description: We report the discovery of the transiting exoplanets WASP-95b, WASP-96b, WASP-97b, WASP-98b, WASP-99b, WASP-100b and WASP-101b. All are hot Jupiters with orbital periods in the range 2.1–5.7 d, masses of 0.5–2.8 M Jup and radii of 1.1–1.4 R Jup . The orbits of all the planets are compatible with zero eccentricity. WASP-99b produces the shallowest transit yet found by WASP-South, at 0.4 per cent. The host stars are of spectral type F2–G8. Five have metallicities of [Fe/H] from –0.03 to +0.23, while WASP-98 has a metallicity of –0.60, exceptionally low for a star with a transiting exoplanet. Five of the host stars are brighter than V = 10.8, which significantly extends the number of bright transiting systems available for follow-up studies. WASP-95 shows a possible rotational modulation at a period of 20.7 d. We discuss the completeness of WASP survey techniques by comparing to the HATnet project.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
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  • 18
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    A window on exoplanet dynamical histories: Rossiter-McLaughlin observations of WASP-13b and WASP-32b (2014)
    Oxford University Press
    Details
    Publication Date: 2014-04-19
    Description: 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 (). 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 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 per cent confidence) was identified for the WASP-32 system with P rot  = 11.6 ± 1.0 days. This rotation period is in agreement with the predicted stellar rotation period calculated from the stellar radius, R * , and v sin i if a stellar inclination of i *  = 90° is assumed. With the determined rotation period, the true 3D angle between the stellar rotation axis and the planetary orbit, , was found to be  = 11° ± 14°. We conclude with a discussion on the alignment of systems around cool host stars with T eff  〈 6150 K by calculating the tidal dissipation time-scale. We find that systems with short tidal dissipation time-scales are preferentially aligned and systems with long tidal dissipation time-scales have a broad range of obliquities.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
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  • 19
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    Mass and period limits on the ringed companion transiting the young star J1407 (2014)
    Oxford University Press
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    Publication Date: 2014-11-14
    Description: The young (~16 Myr) pre-main-sequence star in Sco–Cen 1SWASP J140747.93–394542.6, hereafter referred to as J1407, underwent a deep eclipse in 2007 April, bracketed by several shallower eclipses in the surrounding 54 d. This has been interpreted as the first detection of an eclipsing ring system circling a substellar object (dubbed J1407b). We report on a search for this companion with Sparse Aperture Mask imaging and direct imaging with both the UT4 VLT and Keck telescopes. Radial velocity measurements of J1407 provide additional constraints on J1407b and on short period companions to the central star. Follow-up photometric monitoring using the Panchromatic Robotic Optical Monitoring and Polarimetry Telescopes (PROMPT)-4 and ROAD observatories during 2012–2014 has not yielded any additional eclipses. Large regions of mass–period space are ruled out for the companion. For circular orbits the companion period is constrained to the range 3.5–13.8 yr ( a ~= 2.2–5.6 au), and stellar masses (〉80 M Jup ) are ruled out at 3 significance over these periods. The complex ring system appears to occupy more than 0.15 of its Hill radius, much larger than its Roche radius and suggesting a ring structure in transition. Further, we demonstrate that the radial velocity of J1407 is consistent with membership in the Upper Cen–Lup subgroup of the Sco–Cen association, and constraints on the rotation period and projected rotational velocity of J1407 are consistent with a stellar inclination of i * ~= 68° ± 10°.
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    Electronic ISSN: 1365-2966
    Topics: Physics
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  • 20
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    An orbital period of 0.94 days for the hot-Jupiter planet WASP-18b (2009)
    Nature Publishing Group (NPG)
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    Publication Date: 2009-08-29
    Description: The 'hot Jupiters' that abound in lists of known extrasolar planets are thought to have formed far from their host stars, but migrate inwards through interactions with the proto-planetary disk from which they were born, or by an alternative mechanism such as planet-planet scattering. The hot Jupiters closest to their parent stars, at orbital distances of only approximately 0.02 astronomical units, have strong tidal interactions, and systems such as OGLE-TR-56 have been suggested as tests of tidal dissipation theory. Here we report the discovery of planet WASP-18b with an orbital period of 0.94 days and a mass of ten Jupiter masses (10 M(Jup)), resulting in a tidal interaction an order of magnitude stronger than that of planet OGLE-TR-56b. Under the assumption that the tidal-dissipation parameter Q of the host star is of the order of 10(6), as measured for Solar System bodies and binary stars and as often applied to extrasolar planets, WASP-18b will be spiralling inwards on a timescale less than a thousandth that of the lifetime of its host star. Therefore either WASP-18 is in a rare, exceptionally short-lived state, or the tidal dissipation in this system (and possibly other hot-Jupiter systems) must be much weaker than in the Solar System.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Hellier, Coel -- Anderson, D R -- Cameron, A Collier -- Gillon, M -- Hebb, L -- Maxted, P F L -- Queloz, D -- Smalley, B -- Triaud, A H M J -- West, R G -- Wilson, D M -- Bentley, S J -- Enoch, B -- Horne, K -- Irwin, J -- Lister, T A -- Mayor, M -- Parley, N -- Pepe, F -- Pollacco, D L -- Segransan, D -- Udry, S -- Wheatley, P J -- England -- Nature. 2009 Aug 27;460(7259):1098-100. doi: 10.1038/nature08245.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Astrophysics Group, Keele University, Staffordshire, ST5 5BG, UK. ch@astro.keele.ac.uk〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/19713926" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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