ALBERT

Description: Star-like objects with effective temperatures of less than 2,700 kelvin are referred to as 'ultracool dwarfs'. This heterogeneous group includes stars of extremely low mass as well as brown dwarfs (substellar objects not massive enough to sustain hydrogen fusion), and represents about 15 per cent of the population of astronomical objects near the Sun. Core-accretion theory predicts that, given the small masses of these ultracool dwarfs, and the small sizes of their protoplanetary disks, there should be a large but hitherto undetected population of terrestrial planets orbiting them--ranging from metal-rich Mercury-sized planets to more hospitable volatile-rich Earth-sized planets. Here we report observations of three short-period Earth-sized planets transiting an ultracool dwarf star only 12 parsecs away. The inner two planets receive four times and two times the irradiation of Earth, respectively, placing them close to the inner edge of the habitable zone of the star. Our data suggest that 11 orbits remain possible for the third planet, the most likely resulting in irradiation significantly less than that received by Earth. The infrared brightness of the host star, combined with its Jupiter-like size, offers the possibility of thoroughly characterizing the components of this nearby planetary system.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Gillon, Michael -- Jehin, Emmanuel -- Lederer, Susan M -- Delrez, Laetitia -- de Wit, Julien -- Burdanov, Artem -- Van Grootel, Valerie -- Burgasser, Adam J -- Triaud, Amaury H M J -- Opitom, Cyrielle -- Demory, Brice-Olivier -- Sahu, Devendra K -- Bardalez Gagliuffi, Daniella -- Magain, Pierre -- Queloz, Didier -- England -- Nature. 2016 May 2;533(7602):221-4. doi: 10.1038/nature17448.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Institut d'Astrophysique et de Geophysique, Universite de Liege, Allee du 6 Aout 19C, 4000 Liege, Belgium. ; NASA Johnson Space Center, 2101 NASA Parkway, Houston, Texas, 77058, USA. ; Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA. ; Center for Astrophysics and Space Science, University of California San Diego, La Jolla, California 92093, USA. ; Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK. ; Astrophysics Group, Cavendish Laboratory, 19 J J Thomson Avenue, Cambridge, CB3 0HE, UK. ; Indian Institute of Astrophysics, Koramangala, Bangalore 560 034, India.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/27135924" target="_blank"〉PubMed〈/a〉

Description: Over the past decade, observations of giant exoplanets (Jupiter-size) have provided key insights into their atmospheres, but the properties of lower-mass exoplanets (sub-Neptune) remain largely unconstrained because of the challenges of observing small planets. Numerous efforts to observe the spectra of super-Earths--exoplanets with masses of one to ten times that of Earth--have so far revealed only featureless spectra. Here we report a longitudinal thermal brightness map of the nearby transiting super-Earth 55 Cancri e (refs 4, 5) revealing highly asymmetric dayside thermal emission and a strong day-night temperature contrast. Dedicated space-based monitoring of the planet in the infrared revealed a modulation of the thermal flux as 55 Cancri e revolves around its star in a tidally locked configuration. These observations reveal a hot spot that is located 41 +/- 12 degrees east of the substellar point (the point at which incident light from the star is perpendicular to the surface of the planet). From the orbital phase curve, we also constrain the nightside brightness temperature of the planet to 1,380 +/- 400 kelvin and the temperature of the warmest hemisphere (centred on the hot spot) to be about 1,300 kelvin hotter (2,700 +/- 270 kelvin) at a wavelength of 4.5 micrometres, which indicates inefficient heat redistribution from the dayside to the nightside. Our observations are consistent with either an optically thick atmosphere with heat recirculation confined to the planetary dayside, or a planet devoid of atmosphere with low-viscosity magma flows at the surface.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Demory, Brice-Olivier -- Gillon, Michael -- de Wit, Julien -- Madhusudhan, Nikku -- Bolmont, Emeline -- Heng, Kevin -- Kataria, Tiffany -- Lewis, Nikole -- Hu, Renyu -- Krick, Jessica -- Stamenkovic, Vlada -- Benneke, Bjorn -- Kane, Stephen -- Queloz, Didier -- England -- Nature. 2016 Apr 14;532(7598):207-9. doi: 10.1038/nature17169. Epub 2016 Mar 30.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Astrophysics Group, Cavendish Laboratory, JJ Thomson Avenue, Cambridge CB3 0HE, UK. ; Institut d'Astrophysique et de Geophysique, Universite of Liege, allee du 6 Aout 17, 4000 Liege, Belgium. ; Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA. ; Institute of Astronomy, University of Cambridge, Cambridge CB3 0HA, UK. ; NaXys, Department of Mathematics, University of Namur, 8 Rempart de la Vierge, 5000 Namur, Belgium. ; University of Bern, Center for Space and Habitability, Sidlerstrasse 5, CH-3012, Bern, Switzerland. ; Astrophysics Group, School of Physics, University of Exeter, Stocker Road, Exeter EX4 4QL, UK. ; Space Telescope Science Institute, Baltimore, Maryland 21218, USA. ; Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109, USA. ; Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, USA. ; Spitzer Science Center, MS 220-6, California Institute of Technology, Jet Propulsion Laboratory, Pasadena, California 91125, USA. ; Department of Physics and Astronomy, San Francisco State University, 1600 Holloway Avenue, San Francisco, California 94132, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/27027283" target="_blank"〉PubMed〈/a〉

Description: Results from exoplanet surveys indicate that small planets (super-Earth size and below) are abundant in our Galaxy. However, little is known about their interiors and atmospheres. There is therefore a need to find small planets transiting bright stars, which would enable a detailed characterization of this population of objects. We present the results of a search for the transit of the Earth-mass exoplanet α Centauri B b with the Hubble Space Telescope ( HST ). We observed α Centauri B twice in 2013 and 2014 for a total of 40 h. We achieve a precision of 115 ppm per 6-s exposure time in a highly saturated regime, which is found to be consistent across HST orbits. We rule out the transiting nature of α Centauri B b with the orbital parameters published in the literature at 96.6 per cent confidence. We find in our data a single transit-like event that could be associated with another Earth-sized planet in the system, on a longer period orbit. Our programme demonstrates the ability of HST to obtain consistent, high-precision photometry of saturated stars over 26 h of continuous observations.

Description: WASP-80b is a missing link in the study of exoatmospheres. It falls between the warm Neptunes and the hot Jupiters and is amenable for characterization, thanks to its host star's properties. We observed the planet through transit and during occultation with Warm Spitzer . Combining our mid-infrared transits with optical time series, we find that the planet presents a transmission spectrum indistinguishable from a horizontal line. In emission, WASP-80b is the intrinsically faintest planet whose dayside flux has been detected in both the 3.6 and 4.5 μm Spitzer channels. The depths of the occultations reveal that WASP-80b is as bright and as red as a T4 dwarf, but that its temperature is cooler. If planets go through the equivalent of an L–T transition, our results would imply that this happens at cooler temperatures than for brown dwarfs. Placing WASP-80b's dayside into a colour–magnitude diagram, it falls exactly at the junction between a blackbody model and the T-dwarf sequence; we cannot discern which of those two interpretations is the more likely. WASP-80b's flux density is as low as GJ 436b at 3.6 μm; the planet's dayside is also fainter, but bluer than HD 189733Ab's nightside (in the [3.6] and [4.5] Spitzer bands). Flux measurements on other planets with similar equilibrium temperatures are required to establish whether irradiated gas giants, such as brown dwarfs, transition between two spectral classes. An eventual detection of methane absorption in transmission would also help lift that degeneracy. We obtained a second series of high-resolution spectra during transit, using HARPS. We reanalyse the Rossiter–McLaughlin effect. The data now favour an aligned orbital solution and a stellar rotation nearly three times slower than stellar line broadening implies. A contribution to stellar line broadening, maybe macroturbulence, is likely to have been underestimated for cool stars, whose rotations have therefore been systematically overestimated.

Description: Optical phase curves have become one of the common probes of exoplanetary atmospheres, but the information they encode has not been fully elucidated. Building on a diverse body of work, we upgrade the Flexible Modelling System to include scattering in the two-stream, dual-band approximation and generate plausible, three-dimensional structures of irradiated atmospheres to study the radiative effects of aerosols or condensates. In the optical, we treat the scattering of starlight using a generalization of Beer's law that allows for a finite Bond albedo to be prescribed. In the infrared, we implement the two-stream solutions and include scattering via an infrared scattering parameter. We present a suite of four-parameter general circulation models for Kepler-7b and demonstrate that its climatology is expected to be robust to variations in optical and infrared scattering. The westward and eastward shifts of the optical and infrared phase curves, respectively, are shown to be robust outcomes of the simulations. Assuming micron-sized particles and a simplified treatment of local brightness, we further show that the peak offset of the optical phase curve is sensitive to the composition of the aerosols or condensates. However, to within the measurement uncertainties, we cannot distinguish between aerosols made of silicates (enstatite or forsterite), iron, corundum or titanium oxide, based on a comparison to the measured peak offset (41° ± 12°) of the optical phase curve of Kepler-7b. Measuring high-precision optical phase curves will provide important constraints on the atmospheres of cloudy exoplanets and reduce degeneracies in interpreting their infrared spectra.

Description: Considerable progress has been made in recent years in observations of atmospheric signatures of giant exoplanets, but processes in rocky exoplanets remain largely unknown due to major challenges in observing small planets. Numerous efforts to observe spectra of super-Earths, exoplanets with masses of 1–10 Earth masses, have thus far revealed only featureless spectra. In this paper, we report a 4 detection of variability in the dayside thermal emission from the transiting super-Earth 55 Cancri e. Dedicated space-based monitoring of the planet in the mid-infrared over eight eclipses revealed the thermal emission from its dayside atmosphere varying by a factor of 3.7 between 2012 and 2013. The amplitude and trend of the variability are not explained by potential influence of star spots or by local thermal or compositional changes in the atmosphere over the short span of the observations. The possibility of large-scale surface activity due to strong tidal interactions possibly similar to Io, or the presence of circumstellar/circumplanetary material appear plausible and motivate future long-term monitoring of the planet.

Description: We present a yield simulator to predict the number and characteristics of planets, false positives and false alarms in transit surveys. The simulator is based on a galactic model and the planet occurrence rates measured by the Kepler mission. It takes into account the observation window function and measured noise levels of the investigated survey. Additionally, it includes vetting criteria to identify false positives. We apply this simulator to the Next Generation Transit Survey (NGTS), a wide-field survey designed to detect transiting Neptune-sized exoplanets. We find that red noise is the main limitation of NGTS up to 14 mag, and that its obtained level determines the expected yield. Assuming a red noise level of 1 mmag, the simulation predicts the following for a 4-yr survey: 4 ± 3 Super-Earths, 19 ± 5 Small Neptunes, 16 ± 4 Large Neptunes, 55 ± 8 Saturn-sized planets and 150 ± 10 Jupiter-sized planets, along with 4688 ± 45 eclipsing binaries and 843 ± 75 background eclipsing binaries. We characterize the properties of these objects to enhance the early identification of false positives and discuss follow-up strategies for transiting candidates.