J. Lillo-Box

A sub-Mercury-sized exoplanet

Since the discovery of the first exoplanets, it has been known that other planetary systems can look quite unlike our own. Until fairly recently, we have been able to probe only the upper range of the planet size distribution, and, since last year, to detect planets that are the size of Earth or somewhat smaller. Hitherto, no planets have been found that are smaller than those we see in the Solar System. Here we report a planet significantly smaller than Mercury. This tiny planet is the innermost of three that orbit the Sun-like host star, which we have designated Kepler-37. Owing to its extremely small size, similar to that of the Moon, and highly irradiated surface, the planet, Kepler-37b, is probably rocky with no atmosphere or water, similar to Mercury.

High-resolution imaging of Kepler planet host candidates - A comprehensive comparison of different techniques

The Kepler mission has discovered thousands of planet candidates. Currently, some of them have already been discarded; more than 200 have been confirmed by follow-up observations, and several hundreds have been validated. However, most of them are still awaiting for confirmation. Thus, priorities (in terms of the probability of the candidate being a real planet) must be established for subsequent observations. The motivation of this work is to provide a set of isolated (good) host candidates to be further tested by other techniques. We identify close companions of the candidates that could have contaminated the light curve of the planet host. We used the AstraLux North instrument located at the 2.2 m telescope in the Calar Alto Observatory to obtain diffraction-limited images of 174 Kepler objects of interest. The lucky-imaging technique used in this work is compared to other AO and speckle imaging observations of Kepler planet host candidates. We define a new parameter, the blended source confidence level (BSC), to assess the probability of an object to have blended non-detected eclipsing binaries capable of producing the detected transit. We find that 67.2% of the observed Kepler hosts are isolated within our detectability limits, and 32.8% have at least one visual companion at angular separations below 6 arcsec. We find close companions (below 3 arcsec) for the 17.2% of the sample. The planet properties of this sample of non-isolated hosts are revised. We report one possible S-type binary (KOI-3158). We also report three possible false positives (KOIs 1230.01, 3649.01, and 3886.01) due to the presence of close companions. The BSC parameter is calculated for all the isolated targets and compared to both the value prior to any high-resolution image and, when possible, to observations from previous high-spatial resolution surveys in the Kepler sample.

Kepler-91b: a planet at the end of its life Planet and giant host star properties via light-curve variations ,

Context. The evolution of planetary systems is intimately linked to the evolution of their host star. Our understanding of the whole planetary evolution process is based on the large planet diversity observed so far. To date, only few tens of planets have been discovered orbiting stars ascending the Red Giant Branch. Although several theories have been proposed, the question of how planets die remains open due to the small number statistics, making clear the need of enlarging the sample of planets around post-main sequence stars. Aims. In this work we study the giant star Kepler-91 (KIC 8219268) in order to determine the nature of a transiting companion. This system was detected by the Kepler Space Telescope, which identified small dims in its light cur ve with a period of 6.246580±0.000082 days. However, its planetary confirmation is needed due to th e large pixel size of the Kepler camera which can hide other stellar configurations able to mimic planet-like transit events. Methods. We analyse Kepler photometry to: 1) re-calculate transit parameters, 2) stud y the light-curve modulations, and 3) to perform an asteroseismic analysis (accurate stellar parameter det ermination) by identifying solar-like oscillations on the periodogram. We also used a high-resolution and high signal-to-noise ratio spec trum obtained with the Calar Alto Fiber-fed ´ Echelle spectrograph (CAFE) to measure stellar properties. Additionally, false-positiv e scenarios were rejected by obtaining high-resolution images with the AstraLux lucky-imaging camera on the 2.2 m telescope at the Calar Alto Observatory. Results. We confirm the planetary nature of the object transiting the s tar Kepler-91 by deriving a mass of Mp = 0.88 +0.17 −0.33 MJup and a planetary radius of Rp = 1.384 +0.011 −0.054 RJup. Asteroseismic analysis produces a stellar radius of R⋆ = 6.30± 0.16 R⊙ and a mass of M⋆ = 1.31± 0.10 M⊙. We find that its eccentric orbit ( e = 0.066 +0.013 −0.017 ) is just 1.32 +0.07 −0.22 R⋆ away from the stellar atmosphere at the pericenter. We also detected three small dims in the phase-folded light-curve. The combination of two of them agrees with the theoretical characteristics expected for secondary eclip se. Conclusions. Kepler-91b could be the previous stage of the planet engulfment, recently detected for BD+48 740. Our estimations show that Kepler-91b will be swallowed by its host star in less than 55 Myr. Among the confirmed planets around giant stars, this is the planetary-mass body closest to its host star. At pericen ter passage, the star subtends an angle of 48 ◦ , covering around 10% of the sky as seen from the planet. The planetary atmosphere seems to be inflated probably due to the high stellar irradiation.

Multiplicity in transiting planet-host stars - A lucky imaging study of Kepler candidates

Context. In the exoplanetary era, the Kepler spacecraft is causing a revolution by discovering thousands of new planet candidates. However, a follow-up program is needed to reject false candidates and fully characterize the bona-fide exoplanets. Aims. Our main aims are to 1./ detect and analyze close companions inside the typical Kepler point spread function (PSF) to study whether they are the responsible for the dimming found in Kepler light curves, 2./ study the change in the stellar and planetary parameters caused by an unresolved object, 3./ help validate the Kepler objects of interest (KOI) that do not have any object inside the Kepler PSF, and 4./ study the multiplicity rate of planet-host candidates. Such a large sample of observed planet-host candidates allows us to derive statistics for close (visual or bounded) companions to the harboring star. Methods. We present lucky imaging observations for a total of 98 KOIs. This technique is based on the acquisition of thousands of very-short-exposure-time images. A selection and combination of a small amount of the highest quality frames provides a high resolution image with objects having a 0.1 arcsec PSF. We apply this technique to carry out observations in the Sloan i and z filters of our Kepler candidates. Results. We find blended objects inside the Kepler PSF for a significant percentage of KOIs. On the one hand, only 58.2% of the hosts do not have any object within 6 arcsec. On the other hand, we find 19 companions closer than 3 arcsec in 17 KOIs. According to their magnitudes and i − z colors, 8 of them could be physically bound to the host star.

Gas and dust in the beta Pictoris moving group as seen by the Herschel Space Observatory

Context. Debris discs are thought to be formed through the collisional grinding of planetesimals, and then can be considered as the outcome of planet formation. Understanding the properties of gas and dust in debris discs can help us comprehend the architecture of extrasolar planetary systems. Herschel Space Observatory far-infrared (IR) photometry and spectroscopy have provided a valuable dataset for the study of debris discs gas and dust composition. This paper is part of a series of papers devoted to the study of Herschel-PACS observations of young stellar associations. Aims. This work aims at studying the properties of discs in the beta Pictoris moving group (BPMG) through far-IR PACS observations of dust and gas. Methods. We obtained Herschel-PACS far-IR photometric observations at 70, 100, and 160 μm of 19 BPMG members, together with spectroscopic observations for four of them. These observations were centred at 63.18 μm and 157 μm, aiming to detect [OI] and [CII] emission. We incorporated the new far-IR observations in the SED of BPMG members and fitted modified blackbody models to better characterise the dust content. Results. We have detected far-IR excess emission towards nine BPMG members, including the first detection of an IR excess towards HD 29391.The star HD 172555, shows [OI] emission, while HD 181296 shows [CII] emission, expanding the short list of debris discs with a gas detection. No debris disc in BPMG is detected in both [OI] and [CII]. The discs show dust temperatures in the range 55–264 K, with low dust masses (<6.6 × 10 −5 M⊕ to 0.2 M⊕) and radii from blackbody models in the range 3 to ∼82 AU. All the objects with a gas detection are early spectral type stars with a hot dust component.

One of the closest exoplanet pairs to the 3.2 mean motion resonance: K2-19b and c

Aims. The K2 mission has recently begun to discover new and diverse planetary systems. In December 2014, Campaign 1 data from the mission was released, providing high-precision photometry for similar to 22 000 objects over an 80-day timespan. We searched these data with the aim of detecting more important new objects. Methods. Our search through two separate pipelines led to the independent discovery of K2-19b and c, a two-planet system of Neptune-sized objects (4.2 and 7.2 R-circle plus), orbiting a K dwarf extremely close to the 3: 2 mean motion resonance. The two planets each show transits, sometimes simultaneously owing to their proximity to resonance and the alignment of conjunctions. Results. We obtained further ground-based photometry of the larger planet with the NITES telescope, demonstrating the presence of large transit timing variations (TTVs), and used the observed TTVs to place mass constraints on the transiting objects under the hypothesis that the objects are near but not in resonance. We then statistically validated the planets through the PASTIS tool,

Gas and dust in the TW Hydrae association as seen by the Herschel Space Observatory

Context. Circumstellar discs are the places where planets form, therefore knowledge of their evolution is crucial for our understanding of planet formation. The Herschel Space Observatory is providing valuable data for studying disc systems, thanks to its sensitivity and wavelength coverage. This paper is one of several devoted to analysing and modelling Herschel-PACS observations of various young stellar associations from the GASPS open time key programme. Aims. The aim of this paper is to elucidate the gas and dust properties of circumstellar discs in the ~10 Myr TW Hya association (TWA) using new far-infrared (IR) imaging and spectroscopy from Herschel-PACS. Methods. We obtained far-IR photometric data at 70, 100, and 160 μm of 14 TWA members; spectroscopic observations centred on the [OI] line at 63.18 μm were also obtained for 9 of the 14. The new photometry for each star was incorporated into its full spectral energy distribution. Results. We detected excess IR emission that is characteristic of circumstellar discs from five TWA members, and computed upper limits for another nine. Two TWA members (TWA 01 and TWA 04B) also show [OI] emission at 63.18 μm. Discs in the TWA association display a variety of properties, with a wide range of dust masses and inner radii, based on modified blackbody modelling. Both transitional and debris discs are found in the sample. Models for sources with a detected IR excess give dust masses in the range from ~0.15 M_⊕ to ~63 M_⊕

Kepler-432 b: a massive planet in a highly eccentric orbit transiting a red giant

We report the first disclosure of the planetary nature of Kepler-432 b (aka Kepler object of interest KOI-1299.01). We accurately constrained its mass and eccentricity by high-precision radial velocity measurements obtained with the CAFE spectrograph at the CAHA 2.2-m telescope. By simultaneously fitting these new data and Kepler photometry, we found that Kepler-432 b is a dense transiting exoplanet with a mass of Mp = 4.87 ± 0.48 MJup and radius of Rp = 1.120 ± 0.036RJup. The planet revolves every 52. 5d around a K giant star that ascends the red giant branch, and it moves on a highly eccentric orbit with e = 0.535 ± 0.030. By analysing two near-IR high-resolution images, we found that a star is located at 1.1 �� from Kepler-432, but it is too faint to cause significant effects on the transit depth. Together with Kepler-56 and Kepler-91, Kepler-432 occupies an almost-desert region of parameter space, which is important for constraining the evolutionary processes of planetary systems.

Photodynamical mass determination of the multiplanetary system K2-19

K2-19 is the second multiplanetary system discovered with K2 observations. The system is composed of two Neptune size planets close to the 3: 2 mean-motion resonance. To better characterize the system we obtained two additional transit observations of K2-19b and five additional radial velocity observations. These were combined with K2 data and fitted simultaneously with the system dynamics ( photodynamical model) which increases the precision of the transit time measurements. The higher transit time precision allows us to detect the chopping signal of the dynamic interaction of the planets that in turn permits to uniquely characterize the system. Although the reflex motion of the star was not detected, dynamic modelling of the system allowed us to derive planetary masses of M-b = 44 +/- 12 M-circle plus and M-c = 15.9 +/- 7.0 M-circle plus for the inner and the outer planets, respectively, leading to densities close to Uranus. We also show that our method allows the derivation of mass ratios using only the 80 d of observations during the first campaign of K2.

Radial velocity confirmation of Kepler-91 b - Additional evidence of its planetary nature using the Calar Alto/CAFE instrument

The object transiting the star Kepler-91 was recently assessed as being of planetary nature. The confirmation was achieved by analysing the light-curve modulations observed in the Kepler data. However, quasi-simultaneous studies claimed a self-luminous nature for this object, thus rejecting it as a planet. In this work, we apply an {independent} approach to confirm the planetary mass of Kepler-91b by using multi-epoch high-resolution spectroscopy obtained with the Calar Alto Fiber-fed Echelle spectrograph (CAFE). We obtain the physical and orbital parameters with the radial velocity technique. In particular, we derive a value of