Confirmation of an exoplanet using the transit color signature: Kepler-418b, a blended giant planet in a multiplanet system

We announce confirmation of Kepler-418b, one of two proposed planets in this system. This is the first confirmation of an exoplanet based primarily on the transit color signature technique. We used the Kepler public data archive combined with multicolor photometry from the Gran Telescopio de Canarias and radial velocity follow-up using FIES at the Nordic Optical Telescope for confirmation. We report a confident detection of a transit color signature that can only be explained by a compact occulting body, entirely ruling out a contaminating eclipsing binary, a hierarchical triple, or a grazing eclipsing binary. Those findings are corroborated by our radial velocity measurements, which put an upper limit of ~1 Mjup on the mass of Kepler-418b. We also report that the host star is significantly blended, confirming the ~10% light contamination suspected from the crowding metric in the Kepler light curve measured by the Kepler team. We report detection of an unresolved light source that contributes an additional ~40% to the target star, which would not have been detected without multicolor photometric analysis. The resulting planet-star radius ratio is 0.110 +/- 0.0025, more than 25% more than the 0.087 measured by Kepler, leading to a radius of 1.20 +/- 0.16 Rjup instead of the 0.94 Rjup measured by the Kepler team. This is the first confirmation of an exoplanet candidate based primarily on the transit color signature, demonstrating that this technique is viable from ground for giant planets. It is particularly useful for planets with long periods such as Kepler-418b, which tend to have long transit durations. Additionally, multicolor photometric analysis of transits can reveal unknown stellar neighbors and binary companions that do not affect the classification of the transiting object but can have a very significant effect on the perceived planetary radius.Comment: accepted by Astronomy & Astrophysic

Earthshine observation of vegetation and implication for life detection on other planets - A review of 2001 - 2006 works

The detection of exolife is one of the goals of very ambitious future space missions that aim to take direct images of Earth-like planets. While associations of simple molecules present in the planet's atmosphere ($O_2$, $O_3$, $CO_2$ etc.) have been identified as possible global biomarkers, we review here the detectability of a signature of life from the planet's surface, i.e. the green vegetation. The vegetation reflectance has indeed a specific spectrum, with a sharp edge around 700 nm, known as the "Vegetation Red Edge" (VRE). Moreover vegetation covers a large surface of emerged lands, from tropical evergreen forest to shrub tundra. Thus considering it as a potential global biomarker is relevant. Earthshine allows to observe the Earth as a distant planet, i.e. without spatial resolution. Since 2001, Earthshine observations have been used by several authors to test and quantify the detectability of the VRE in the Earth spectrum. The egetation spectral signature is detected as a small 'positive shift' of a few percents above the continuum, starting at 700 nm. This signature appears in most spectra, and its strength is correlated with the Earth's phase (visible land versus visible ocean). The observations show that detecting the VRE on Earth requires a photometric relative accuracy of 1% or better. Detecting something equivalent on an Earth-like planet will therefore remain challenging, moreover considering the possibility of mineral artifacts and the question of 'red edge' universality in the Universe.Comment: Invited talk in "Strategies for Life Detection" (ISSI Bern, 24-28 April 2006) to appear in a hardcopy volume of the ISSI Space Science Series, Eds, J. Bada et al., and also in an issue of Space Science Reviews. 13 pages, 8 figures, 1 tabl

Subaru and Swift observations of V652 Herculis: resolving the photospheric pulsation

High-resolution spectroscopy with the Subaru High Dispersion Spectrograph, and Swift ultraviolet photometry are presented for the pulsating extreme helium star V652 Her. Swift provides the best relative ultraviolet photometry obtained to date, but shows no direct evidence for a shock at ultraviolet or X-ray wavelengths. Subaru has provided high spectral and high temporal resolution spectroscopy over six pulsation cycles (and eight radius minima). These data have enabled a line-by-line analysis of the entire pulsation cycle and provided a description of the pulsating photosphere as a function of optical depth. They show that the photosphere is compressed radially by a factor of at least 2 at minimum radius, that the phase of radius minimum is a function of optical depth and the pulse speed through the photosphere is between 141 and 239 km s−1 (depending how measured) and at least 10 times the local sound speed. The strong acceleration at minimum radius is demonstrated in individual line profiles; those formed deepest in the photosphere show a jump discontinuity of over 70 kms−1 on a time-scale of 150 s. The pulse speed and line profile jumps imply a shock is present at minimum radius. These empirical results provide input for hydrodynamical modelling of the pulsation and hydrodynamical plus radiative transfer modelling of the dynamical spectra

Aerosols and Water Ice in Jupiter's Stratosphere from UV-NIR Ground-based Observations

Jupiter's atmosphere has been sounded in transmission from the UV to the IR, as if it were a transiting exoplanet, by observing Ganymede while passing through Jupiter's shadow. The spectra show strong extinction due to the presence of aerosols and haze in Jupiter's atmosphere and strong absorption features of methane. Here, we report a new detailed analysis of these observations, with special emphasis on the retrievals of the vertical distribution of the aerosols and their sizes, and the properties and distribution of the stratospheric water ice. Our analysis suggests the presence of aerosols near the equator in the altitude range of 100 hPa up to at least 0.01 hPa, with a layer of small particles (mean radius of 0.1 μm) in the upper part (above 0.1 hPa), an intermediate layer of aerosols with a radius of 0.3 μm, extending between ∼10 and 0.01 hPa, and a layer with larger sizes of ∼0.6 μm at approximately 100-1 hPa. The corresponding loads for each layer are ∼2 × 10 g cm, ∼3.4 × 10 g cm, and ∼1.5 × 10 g cm, respectively, with a total load of ∼2.0 × 10 g cm. The lower and middle layers agree well with previous measurements; but the finer particles of 0.1 μm above 0.01 hPa have not been reported before. The spectra also show two broad features near 1.5 and 2.0 μm, which we attribute to a layer of very small (∼10 nm) HO crystalline ice in Jupiter's lower stratosphere (∼0.5 hPa). While these spectral signatures seem to be unequivocally attributable to crystalline water ice, they require a large amount of water ice to explain the strong absorption features.© 2018. The American Astronomical Society. All rights reserved.We are very grateful to Rafael Escribano, Victor Herrero, Anni Maattanen, Beatriz Mate, Agustin Sanchez-Lavega, and Miguel Angel Satorre for very valuable discussions on the water ice topic. The IAA team was supported by the Spanish MICINN under projects ESP2014-54362-P, ESP2017-87143-R, and EC FEDER funds. This work is also partly financed by the Spanish Ministry of Economics and Competitiveness through grant ESP2013-48391-C4-2-R. M.G.C. is also supported by the MINECO under its >Ramon y Cajal> subprogram

Biomarkers in disk-averaged near-UV to near-IR Earth spectra using Earthshine observations

We analyse the detectability of vegetation on a global scale on Earth's surface. Considering its specific reflectance spectrum showing a sharp edge around 700 nm, vegetation can be considered as a potential global biomarker. This work, based on observational data, aims to characterise and to quantify this signature in the disk-averaged Earth's spectrum. Earthshine spectra have been used to test the detectability of the "Vegetation Red Edge" (VRE) in the Earth spectrum. We obtained reflectance spectra from near UV (320 nm) to near IR (1020 nm) for different Earth phases (continents or oceans seen from the Moon) with EMMI on the NTT at ESO/La Silla, Chile. We accurately correct the sky background and take into account the phase-dependent colour of the Moon. VRE measurements require a correction of the ozone Chappuis absorption band and Rayleigh plus aerosol scattering. Results : The near-UV spectrum shows a dark Earth below 350 nm due to the ozone absorption. The Vegetation Red Edge is observed when forests are present (4.0% for Africa and Europe), and is lower when clouds and oceans are mainly visible (1.3% for the Pacific Ocean). Errors are typically $\pm0.5$, and $\pm1.5$ in the worst case. We discuss the different sources of errors and bias and suggest possible improvements. We showed that measuring the VRE or an analog on an Earth-like planet remains very difficult (photometric relative accuracy of 1% or better). It remains a small feature compared to atmospheric absorption lines. A direct monitoring from space of the global (disk-averaged) Earth's spectrum would provide the best VRE follow-up.Comment: Accepted for publication in A&A. 9 pages, 8 figure

Deciphering Spectral Fingerprints of Habitable Extrasolar Planets

In this paper we discuss how we can read a planets spectrum to assess its habitability and search for the signatures of a biosphere. After a decade rich in giant exoplanet detections, observation techniques have now reached the ability to find planets of less than 10 MEarth (so called Super-Earths) that may potentially be habitable. How can we characterize those planets and assess if they are habitable? The new field of extrasolar planet search has shown an extraordinary ability to combine research by astrophysics, chemistry, biology and geophysics into a new and exciting interdisciplinary approach to understand our place in the universe. The results of a first generation mission will most likely result in an amazing scope of diverse planets that will set planet formation, evolution as well as our planet in an overall context.Comment: 17 pages, 10 figures, Astrobiology, 10, 1, 201

Notes on disentangling of spectra II. Intrinsic line-profile variability due to Cepheid pulsations

The determination of pulsation velocities from observed spectra of Cepheids is needed for the Baade-Wesselink calibration of these primary distance markers. The applicability of the Fourier-disentangling technique for the determination of pulsation velocities of Cepheids and other pulsating stars is studied. The KOREL-code was modified to enable fitting of free parameters of a prescribed line-profile broadening function corresponding to the radial pulsations of the stellar atmosphere. It was applied to spectra of delta Cep in the H-alpha region observed with the Ondrejov 2-m telescope. The telluric lines were removed using template-constrained disentangling, phase-locked variations of line-strengths were measured and the curves of pulsational velocities obtained for several spectral lines. It is shown that the amplitude and phase of the velocities and line-strength variations depend on the depth of line formation and the excitation potential. The disentangling of pulsations in the Cepheid spectra may be used for distance determination

Projection effects in the spectra of early-type pulsating stars

The relation between the surface velocity of a pulsating star in the star's inertial frame and the apparent expansion velocity measured by a remote observer has been classically formulated in terms of a projection factor p. This factor depends on the relative limb darkening in continuum and spectral lines and may therefore be a function of composition. We have computed synthetic spectra to investigate the behaviour of p and, indeed, of the apparent line profile for radially pulsating stars over a range of temperature and gravity with hydrogen-rich and hydrogen-poor atmospheres. We have subsequently derived values of p suitable for the interpretation of velocity measurements of pulsating early type stars. Effective temperature has the most important influence on p: a change of 10 000 K in Teff introduces a change of 2-3 per cent with important consequences for measurements of stellar radii to an accuracy ${< }1\%$

On the impact of supply voltage variation on the statistical reliability of a Spin-transfer-torque MRAM (STT-MRAM)

The Spin-Transfer-Torque Magnetic Random Access Memory (STT-MRAM) presents as a promising alternative to today embedded memories due to its reduced read/write latency and high integration capability. Today aggressive technology scaling requirements, affects also the STT-MRAM by means of fabrication induced process variability and aging phenomena. These issues make reliability prediction a major concern. In this paper, we provide a methodology for predicting the reliability of an STT-MRAM based memory. The reliability prediction is performed at cell level, accounting for fabrication induced variability and aging phenomena simultaneously affecting the nMOS and MTJ devices. In addition, the effect of supply voltage variation on the cell reliability is also studied. The results show that a negative variation of the supply voltage highly degrades the cell reliability