ALBERT

Description: The Sun is the only star whose surface can be directly resolved at high resolution, and therefore constitutes an excellent test case to explore the physical origin of stellar radial-velocity (RV) variability. We present HARPS observations of sunlight scattered off the bright asteroid 4/Vesta, from which we deduced the Sun's activity-driven RV variations. In parallel, the Helioseismic and Magnetic Imager instrument on board the Solar Dynamics Observatory provided us with simultaneous high spatial resolution magnetograms, Dopplergrams and continuum images of the Sun in the Fe i 6173 Å line. We determine the RV modulation arising from the suppression of granular blueshift in magnetized regions and the flux imbalance induced by dark spots and bright faculae. The rms velocity amplitudes of these contributions are 2.40 and 0.41 m s –1 , respectively, which confirms that the inhibition of convection is the dominant source of activity-induced RV variations at play, in accordance with previous studies. We find the Doppler imbalances of spot and plage regions to be only weakly anticorrelated. Light curves can thus only give incomplete predictions of convective blueshift suppression. We must instead seek proxies that track the plage coverage on the visible stellar hemisphere directly. The chromospheric flux index $R^{\prime }_{HK}$ derived from the HARPS spectra performs poorly in this respect, possibly because of the differences in limb brightening/darkening in the chromosphere and photosphere. We also find that the activity-driven RV variations of the Sun are strongly correlated with its full-disc magnetic flux density, which may become a useful proxy for activity-related RV noise.

Description: At optical wavelengths, an exoplanet's signature is essentially reflected light from the host star – several orders of magnitude fainter. Since it is superimposed on the star spectrum its detection has been a difficult observational challenge. However, the development of a new generation of instruments like Echelle Spectrograph for Rocky Exoplanets and Stable Spectroscopic Observations (ESPRESSO) and next-generation telescopes like the European Extremely Large Telescope (E-ELT) put us in a privileged position to detect these planets’ reflected light as we will have access to extremely high signal-to-noise ratio spectra. With this work, we propose an alternative approach for the direct detection of the reflected light of an exoplanet. We simulated observations with ESPRESSO at Very Large Telescope (VLT) and high-resolution spectrograph (HIRES) at E-ELT of several star+planet systems, encompassing 10 h of the most favourable orbital phases. To the simulated spectra we applied the cross-correlation function to operate in a much higher signal-to-noise ratio domain than when compared with the spectra. The use of the cross-correlation function permitted us to recover the simulated planet signals at a level above 3 noise significance on several prototypical (e.g. Neptune-type planet with a 2 d orbit with the VLT at 4.4 noise significance) and real planetary systems (e.g. 55 Cnc e with the E-ELT at 4.9 noise significance). Even by using a more pessimistic approach to the noise level estimation, where systematics in the spectra increase the noise 2–3 times, the detection of the reflected light from large close-orbit planets is possible. We have also shown that this kind of study is currently within reach of current instruments and telescopes (e.g. 51 Peg b with the VLT at 5.2 noise significance), although at the limit of their capabilities.

Description: We present new measurements of the projected spin-orbit angle for six WASP hot Jupiters, four of which are new to the literature (WASP-61, -62, -76, and -78), and two of which are new analyses of previously measured systems using new data (WASP-71, and -79). We use three different models based on two different techniques: radial velocity measurements of the Rossiter–McLaughlin effect, and Doppler tomography. Our comparison of the different models reveals that they produce projected stellar rotation velocities ( v sin I s ) measurements often in disagreement with each other and with estimates obtained from spectral line broadening. The Boué model for the Rossiter–McLaughlin effect consistently underestimates the value of v sin I s compared to the Hirano model. Although v sin I s differed, the effect on was small for our sample, with all three methods producing values in agreement with each other. Using Doppler tomography, we find that WASP-61 b ( $\lambda =4{^{\circ}_{.}}0^{+17.1}_{\,\,\,-18.4}$ ), WASP-71 b ( $\lambda =-1{^{\circ}_{.}}9^{+7.1}_{\,\,\,-7.5}$ ), and WASP-78 b ( = –6 $_{.}^{\circ}$ 4 ± 5.9) are aligned. WASP-62 b ( $\lambda =19{^{\circ}_{.}}4^{+5.1}_{\,\,\,-4.9}$ ) is found to be slightly misaligned, while WASP-79 b ( $\lambda =-95{^{\circ}_{.}}2^{+0.9}_{\,\,\,-1.0}$ ) is confirmed to be strongly misaligned and has a retrograde orbit. We explore a range of possibilities for the orbit of WASP-76 b, finding that the orbit is likely to be strongly misaligned in the positive direction.

Description: A decade ago, the detection of the first transiting extrasolar planet provided a direct constraint on its composition and opened the door to spectroscopic investigations of extrasolar planetary atmospheres. Because such characterization studies are feasible only for transiting systems that are both nearby and for which the planet-to-star radius ratio is relatively large, nearby small stars have been surveyed intensively. Doppler studies and microlensing have uncovered a population of planets with minimum masses of 1.9-10 times the Earth's mass (M[symbol:see text]), called super-Earths. The first constraint on the bulk composition of this novel class of planets was afforded by CoRoT-7b (refs 8, 9), but the distance and size of its star preclude atmospheric studies in the foreseeable future. Here we report observations of the transiting planet GJ 1214b, which has a mass of 6.55M[symbol:see text]), and a radius 2.68 times Earth's radius (R[symbol:see text]), indicating that it is intermediate in stature between Earth and the ice giants of the Solar System. We find that the planetary mass and radius are consistent with a composition of primarily water enshrouded by a hydrogen-helium envelope that is only 0.05% of the mass of the planet. The atmosphere is probably escaping hydrodynamically, indicating that it has undergone significant evolution during its history. The star is small and only 13 parsecs away, so the planetary atmosphere is amenable to study with current observatories.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Charbonneau, David -- Berta, Zachory K -- Irwin, Jonathan -- Burke, Christopher J -- Nutzman, Philip -- Buchhave, Lars A -- Lovis, Christophe -- Bonfils, Xavier -- Latham, David W -- Udry, Stephane -- Murray-Clay, Ruth A -- Holman, Matthew J -- Falco, Emilio E -- Winn, Joshua N -- Queloz, Didier -- Pepe, Francesco -- Mayor, Michel -- Delfosse, Xavier -- Forveille, Thierry -- England -- Nature. 2009 Dec 17;462(7275):891-4. doi: 10.1038/nature08679.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138, USA. dcharbonneau@cfa.harvard.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20016595" target="_blank"〉PubMed〈/a〉

Description: Of the over 400 known exoplanets, there are about 70 planets that transit their central star, a situation that permits the derivation of their basic parameters and facilitates investigations of their atmospheres. Some short-period planets, including the first terrestrial exoplanet (CoRoT-7b), have been discovered using a space mission designed to find smaller and more distant planets than can be seen from the ground. Here we report transit observations of CoRoT-9b, which orbits with a period of 95.274 days on a low eccentricity of 0.11 +/- 0.04 around a solar-like star. Its periastron distance of 0.36 astronomical units is by far the largest of all transiting planets, yielding a 'temperate' photospheric temperature estimated to be between 250 and 430 K. Unlike previously known transiting planets, the present size of CoRoT-9b should not have been affected by tidal heat dissipation processes. Indeed, the planet is found to be well described by standard evolution models with an inferred interior composition consistent with that of Jupiter and Saturn.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Deeg, H J -- Moutou, C -- Erikson, A -- Csizmadia, Sz -- Tingley, B -- Barge, P -- Bruntt, H -- Havel, M -- Aigrain, S -- Almenara, J M -- Alonso, R -- Auvergne, M -- Baglin, A -- Barbieri, M -- Benz, W -- Bonomo, A S -- Borde, P -- Bouchy, F -- Cabrera, J -- Carone, L -- Carpano, S -- Ciardi, D -- Deleuil, M -- Dvorak, R -- Ferraz-Mello, S -- Fridlund, M -- Gandolfi, D -- Gazzano, J-C -- Gillon, M -- Gondoin, P -- Guenther, E -- Guillot, T -- den Hartog, R -- Hatzes, A -- Hidas, M -- Hebrard, G -- Jorda, L -- Kabath, P -- Lammer, H -- Leger, A -- Lister, T -- Llebaria, A -- Lovis, C -- Mayor, M -- Mazeh, T -- Ollivier, M -- Patzold, M -- Pepe, F -- Pont, F -- Queloz, D -- Rabus, M -- Rauer, H -- Rouan, D -- Samuel, B -- Schneider, J -- Shporer, A -- Stecklum, B -- Street, R -- Udry, S -- Weingrill, J -- Wuchterl, G -- England -- Nature. 2010 Mar 18;464(7287):384-7. doi: 10.1038/nature08856.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Instituto de Astrofisica de Canarias, C. Via Lactea S/N, E-38205 La Laguna, Tenerife, Spain. hdeeg@iac.es〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20237564" target="_blank"〉PubMed〈/a〉

Description: Exoplanets down to the size of Earth have been found, but not in the habitable zone--that is, at a distance from the parent star at which water, if present, would be liquid. There are planets in the habitable zone of stars cooler than our Sun, but for reasons such as tidal locking and strong stellar activity, they are unlikely to harbour water-carbon life as we know it. The detection of a habitable Earth-mass planet orbiting a star similar to our Sun is extremely difficult, because such a signal is overwhelmed by stellar perturbations. Here we report the detection of an Earth-mass planet orbiting our neighbour star alpha Centauri B, a member of the closest stellar system to the Sun. The planet has an orbital period of 3.236 days and is about 0.04 astronomical units from the star (one astronomical unit is the Earth-Sun distance).〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Dumusque, Xavier -- Pepe, Francesco -- Lovis, Christophe -- Segransan, Damien -- Sahlmann, Johannes -- Benz, Willy -- Bouchy, Francois -- Mayor, Michel -- Queloz, Didier -- Santos, Nuno -- Udry, Stephane -- England -- Nature. 2012 Nov 8;491(7423):207-11. doi: 10.1038/nature11572. Epub 2012 Oct 17.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Observatoire de Geneve, Universite de Geneve, 51 chemin des Maillettes, CH-1290 Sauverny, Switzerland. xavier.dumusque@unige.ch〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/23075844" target="_blank"〉PubMed〈/a〉

Description: Recent analyses of data from the NASA Kepler spacecraft have established that planets with radii within 25 per cent of the Earth's (R Earth symbol) are commonplace throughout the Galaxy, orbiting at least 16.5 per cent of Sun-like stars. Because these studies were sensitive to the sizes of the planets but not their masses, the question remains whether these Earth-sized planets are indeed similar to the Earth in bulk composition. The smallest planets for which masses have been accurately determined are Kepler-10b (1.42 R Earth symbol) and Kepler-36b (1.49 R Earth symbol), which are both significantly larger than the Earth. Recently, the planet Kepler-78b was discovered and found to have a radius of only 1.16 R Earth symbol. Here we report that the mass of this planet is 1.86 Earth masses. The resulting mean density of the planet is 5.57 g cm(-3), which is similar to that of the Earth and implies a composition of iron and rock.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Pepe, Francesco -- Cameron, Andrew Collier -- Latham, David W -- Molinari, Emilio -- Udry, Stephane -- Bonomo, Aldo S -- Buchhave, Lars A -- Charbonneau, David -- Cosentino, Rosario -- Dressing, Courtney D -- Dumusque, Xavier -- Figueira, Pedro -- Fiorenzano, Aldo F M -- Gettel, Sara -- Harutyunyan, Avet -- Haywood, Raphaelle D -- Horne, Keith -- Lopez-Morales, Mercedes -- Lovis, Christophe -- Malavolta, Luca -- Mayor, Michel -- Micela, Giusi -- Motalebi, Fatemeh -- Nascimbeni, Valerio -- Phillips, David -- Piotto, Giampaolo -- Pollacco, Don -- Queloz, Didier -- Rice, Ken -- Sasselov, Dimitar -- Segransan, Damien -- Sozzetti, Alessandro -- Szentgyorgyi, Andrew -- Watson, Christopher A -- England -- Nature. 2013 Nov 21;503(7476):377-80. doi: 10.1038/nature12768. Epub 2013 Oct 30.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Observatoire Astronomique de l'Universite de Geneve, 51 chemin des Maillettes, 1290 Versoix, Switzerland.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/24172902" target="_blank"〉PubMed〈/a〉

Description: Doppler spectroscopy was the first technique used to reveal the existence of extrasolar planetary systems hosted by solar-type stars. Radial-velocity surveys led to the detection of a rich population of super-Earths and Neptune-type planets. The numerous detected systems revealed a remarkable diversity. Combining Doppler measurements with photometric observations of planets transiting their host stars further provides access to the planet bulk density, a first step towards comparative exoplanetology. The development of new high-precision spectrographs and space-based facilities will ultimately lead us to characterize rocky planets in the habitable zone of our close stellar neighbours.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Mayor, Michel -- Lovis, Christophe -- Santos, Nuno C -- England -- Nature. 2014 Sep 18;513(7518):328-35. doi: 10.1038/nature13780.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Geneva Observatory, University of Geneva, 51 Chemin des Maillettes, 1290 Versoix, Switzerland. ; 1] Centro de Astrofisica e Departamento de Fisica e Astronomia, Faculdade de Ciencias, Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal. [2] Instituto de Astrofisica e Ciencias do Espaco, Centro de Astrofisica da Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/25230654" target="_blank"〉PubMed〈/a〉

Description: M-dwarf stars--hydrogen-burning stars that are smaller than 60 per cent of the size of the Sun--are the most common class of star in our Galaxy and outnumber Sun-like stars by a ratio of 12:1. Recent results have shown that M dwarfs host Earth-sized planets in great numbers: the average number of M-dwarf planets that are between 0.5 to 1.5 times the size of Earth is at least 1.4 per star. The nearest such planets known to transit their star are 39 parsecs away, too distant for detailed follow-up observations to measure the planetary masses or to study their atmospheres. Here we report observations of GJ 1132b, a planet with a size of 1.2 Earth radii that is transiting a small star 12 parsecs away. Our Doppler mass measurement of GJ 1132b yields a density consistent with an Earth-like bulk composition, similar to the compositions of the six known exoplanets with masses less than six times that of the Earth and precisely measured densities. Receiving 19 times more stellar radiation than the Earth, the planet is too hot to be habitable but is cool enough to support a substantial atmosphere, one that has probably been considerably depleted of hydrogen. Because the host star is nearby and only 21 per cent the radius of the Sun, existing and upcoming telescopes will be able to observe the composition and dynamics of the planetary atmosphere.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Berta-Thompson, Zachory K -- Irwin, Jonathan -- Charbonneau, David -- Newton, Elisabeth R -- Dittmann, Jason A -- Astudillo-Defru, Nicola -- Bonfils, Xavier -- Gillon, Michael -- Jehin, Emmanuel -- Stark, Antony A -- Stalder, Brian -- Bouchy, Francois -- Delfosse, Xavier -- Forveille, Thierry -- Lovis, Christophe -- Mayor, Michel -- Neves, Vasco -- Pepe, Francesco -- Santos, Nuno C -- Udry, Stephane -- Wunsche, Anael -- England -- Nature. 2015 Nov 12;527(7577):204-7. doi: 10.1038/nature15762.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA. ; Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138, USA. ; Observatoire de Geneve, Universite de Geneve, 51 chemin des Maillettes, 1290 Sauverny, Switzerland. ; Universite Grenoble Alpes, IPAG, F-38000 Grenoble, France. ; CNRS, IPAG, F-38000 Grenoble, France. ; Institut d'Astrophysique et de Geophysique, Universite de Liege, Allee du 6 Aout 17, Batiment B5C, 4000 Liege, Belgium. ; Institute for Astronomy, University of Hawaii at Manoa, Honolulu, Hawaii 96822, USA. ; Laboratoire d'Astrophysique de Marseille, UMR 6110 CNRS, Universite de Provence, 38 rue Frederic Joliot-Curie, 13388, Marseille Cedex 13, France. ; Departamento de Fisica, Universidade Federal do Rio Grande do Norte, 59072-970 Natal, Rio Grande do Norte, Brazil. ; Instituto de Astrofisica e Ciencias do Espaco, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal. ; Departamento de Fisica e Astronomia, Faculdade de Ciencias, Universidade do Porto, Rua Campo Alegre, 4169-007 Porto, Portugal.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/26560298" target="_blank"〉PubMed〈/a〉

Description: Context. An accurate characterization of the known exoplanet population is key to understanding the origin and evolution of planetary systems. Determining true planetary masses through the radial velocity (RV) method is expected to experience a great improvement thanks to the availability of ultra-stable echelle spectrographs. Aims. We took advantage of the extreme precision of the new-generation echelle spectrograph ESPRESSO to characterize the transiting planetary system orbiting the G2V star K2-38 located at 194 pc from the Sun with V ~ 11.4. This system is particularly interesting because it could contain the densest planet detected to date. Methods. We carried out a photometric analysis of the available K2 photometric light curve of this star to measure the radius of its two known planets, K2-38b and K2-38c, with Pb = 4.01593 ± 0.00050 d and Pc = 10.56103 ± 0.00090 d, respectively. Using 43 ESPRESSO high-precision RV measurements taken over the course of 8 months along with the 14 previously published HIRES RV measurements, we modeled the orbits of the two planets through a Markov chain Monte Carlo analysis, significantly improving their mass measurements. Results. Using ESPRESSO spectra, we derived the stellar parameters, Teff = 5731 ± 66, log g = 4.38 ± 0.11 dex, and [Fe/H] = 0.26 ± 0.05 dex, and thus the mass and radius of K2-38, M⋆ = 1.03−0.02+0.04 M⊕ and R⋆ = 1.06−0.06+0.09 R⊕. We determine new values for the planetary properties of both planets. We characterize K2-38b as a super-Earth with RP = 1.54 ± 0.14 R⊕ and Mp = 7.3−1.0+1.1 M⊕, and K2-38c as a sub-Neptune with RP = 2.29 ± 0.26 R⊕ and Mp = 8.3−1.3+1.3 M⊕. Combining the radius and mass measurements, we derived a mean density of ρp = 11.0−2.8+4.1 g cm−3 for K2-38b and ρp = 3.8−1.1+1.8 g cm−3 for K2-38c, confirming K2-38b as one of the densest planets known to date. Conclusions. The best description for the composition of K2-38b comes from an iron-rich Mercury-like model, while K2-38c is better described by a rocky-model with H2 envelope. The maximum collision stripping boundary shows how giant impacts could be the cause for the high density of K2-38b. The irradiation received by each planet places them on opposite sides of the radius valley. We find evidence of a long-period signal in the RV time-series whose origin could be linked to a 0.25–3 MJ planet or stellar activity.