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The LEECH Exoplanet Imaging Survey: Limits on Planet Occurrence Rates under Conservative Assumptions
摘要： We present the results of the largest L′ (3.8 μm) direct imaging survey for exoplanets to date, the Large Binocular Telescope Interferometer Exozodi Exoplanet Common Hunt (LEECH). We observed 98 stars with spectral types from B to M. Cool planets emit a larger share of their ?ux in L′ compared to shorter wavelengths, affording LEECH an advantage in detecting low-mass, old, and cold-start giant planets. We emphasize proximity over youth in our target selection, probing physical separations smaller than other direct imaging surveys. For FGK stars, LEECH outperforms many previous studies, placing tighter constraints on the hot-start planet occurrence frequency interior to ～20 au. For less luminous, cold-start planets, LEECH provides the best constraints on giant-planet frequency interior to ～20 au around FGK stars. Direct imaging survey results depend sensitively on both the choice of evolutionary model (e.g., hot- or cold-start) and assumptions (explicit or implicit) about the shape of the underlying planet distribution, in particular its radial extent. Arti?cially low limits on the planet occurrence frequency can be derived when the shape of the planet distribution is assumed to extend to very large separations, well beyond typical protoplanetary dust-disk radii (?50 au), and when hot-start models are used exclusively. We place a conservative upper limit on the planet occurrence frequency using cold-start models and planetary population distributions that do not extend beyond typical protoplanetary dust-disk radii. We ?nd that ?90% of FGK systems can host a 7–10 MJup planet from 5 to 50 au. This limit leaves open the possibility that planets in this range are common.
关键词： planetary systems,techniques: high angular resolution,planets and satellites: gaseous planets,stars: imaging
更新于2025-09-04 15:30:14
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The HARPS search for southern extra-solar planets
摘要： We present the analysis of the entire HARPS observations of three stars that host planetary systems: HD 1461, HD 40307, and HD 204313. The data set spans eight years and contains more than 200 nightly averaged velocity measurements for each star. This means that it is sensitive to both long-period and low-mass planets and also to the effects induced by stellar activity cycles. We modelled the data using Keplerian functions that correspond to planetary candidates and included the short- and long-term effects of magnetic activity. A Bayesian approach was taken both for the data modelling, which allowed us to include information from activity proxies such as log (R' HK) in the velocity modelling, and for the model selection, which permitted determining the number of significant signals in the system. The Bayesian model comparison overcomes the limitations inherent to the traditional periodogram analysis. We report an additional super-Earth planet in the HD 1461 system. Four out of the six planets previously reported for HD 40307 are confirmed and characterised. We discuss the remaining two proposed signals. In particular, we show that when the systematic uncertainty associated with the techniques for estimating model probabilities are taken into account, the current data are not conclusive concerning the existence of the habitable-zone candidate HD 40307 g. We also fully characterise the Neptune-mass planet that orbits HD 204313 in 34.9 days.
关键词： methods: data analysis,planetary systems,techniques: radial velocities,methods: statistical
更新于2025-09-04 15:30:14
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Chromatic line-profile tomography to reveal exoplanetary atmospheres: application to HD 189733b
摘要： Context. Transmission spectroscopy can be used to constrain the properties of exoplanetary atmospheres. During a transit, the light blocked from the atmosphere of the planet leaves an imprint in the light coming from the star. This has been shown for many exoplanets with both photometry and spectroscopy, using different analysis methods. Aims. We test chromatic line-profile tomography as a new tool to investigate exoplanetary atmospheres. The signal imprinted on the cross-correlation function (CCF) by a planet transiting its star is dependent on the planet-to-star radius ratio. We want to verify whether the precision reachable on the CCF obtained from a subset of the spectral orders of the HARPS spectrograph is high enough to determine the radius of a planet at different wavelengths. Methods. We analyze HARPS archival data of three transits of HD 189733b. We divide the HARPS spectral range into seven broad-bands, calculating for each band the ratio between the area of the out-of-transit CCF and the area of the signal imprinted by the planet on it during the full part of the transit. We take into account the effect of the limb darkening using the theoretical coefficients of a linear law. Averaging the results of three different transits allows us to obtain a good-quality broadband transmission spectrum of HD 189733b with a greater precision than that of the chromatic Rossiter McLaughlin effect. Results. We proved that chromatic line-profile tomography is an interesting way to reveal broadband transmission spectra of exoplanets: our analysis of the atmosphere of HD 189733b is in agreement with other ground- and space-based observations. The independent analysis of different transits emphasizes the probability that stellar activity plays a role in the extracted transmission spectrum. Therefore, care should be taken when claiming that Rayleigh scattering is present in the atmosphere of exoplanets orbiting active stars using only one transit.
关键词： techniques: spectroscopic,planetary systems,planets and satellites: atmospheres
更新于2025-09-04 15:30:14