Planetary transits

The Darwin mission will not be carried out until the middle of the next decade. However, the COROT (Convection, Rotation and Planetary Transits) telescope was launched from the Baikonur cosmodrome in December 2006. The satellite, which weighs 630 kg, circles the Earth at a height of about 900 km in a polar orbit. The mission is planned to last 21/2 years, and more than 120,000 stars are to be observed. 

The water cycle in the biosphere determines the planetary transitions of various components such as aerosols, micro-organisms, and dissolved and suspended substances. 

Charbonneau D., Brown T. M., Latham D. W., and Mayor M. (2000) Detection of planetary transits across a Sun-like star. Astrophys. J. 529, L45-L48. 

RV searches and space based transit missions like ESA s Corot initially, and now NASA s Kepler mission, provide statistics of the occurrence of planets around Sun-like stars. NASA s Kepler telescope that mOTiitors stars for planetary transits was launched in 2009 and is observing one distant stellar field monitoring about 150,000 stars continuously for 5 years with sensitivity for detecting transits down to Earth-size planets around Sun-analogue stars. Several Kepler transit planet candidates from the first data release in February 2011 [9] and about 50 planets from the February 2012 data release [10], with radii consistent with rocky planet models, orbit their host stars in the so called Habitable Zone (see discussion below), providing first statistics of the number of planets and Earth-like planets (etaEarth) in the HZ (see e.g. [11]). 

Transit method planetary transits occur only when a planet crosses in front of its parent star s disk seen from Earth. If the planet is big enough then a small drop in the brightness of a star can be observed. The amount of the decrease in brightness depends on the size of the planet and the size of the star as well as on the distance of the planet from the star. Therefore, it is more probable to observe transits of giant planets that are relatively close to their central star. 

The dip in the absorption lines during a planetary transit is very small. Seager and Sasselov, 2000 [302] predict the possibility to observe a relative decrease in flux of about 10 ". In order to detect such small variation strong planet spectral features have to be observed and several absorption frequencies (Nal, KI, Hel) are proposed for observations. 

Hueso, R., Sanchez-Lavega, A. A three-dimensional model of moist convection for the giant planets II Saturn s water and ammonia moist convective storms. Icarus 172,255-271 (2004) Hui, L., Seager, S. Atmospheric lensing and oblateness effects during an extrasolar planetary transit. Astrophys. J. 572, 540-555 (2002)... 

Another family of feedbacks arises because the radical differences in the albedo (reflectivity) of ice, snow, and clouds compared to the rest of the planetary surface, which causes a loss of the absorption of solar radiation and thereby cools the planet. Indeed, the high albedo of snow and ice cover may be a factor that hastens the transition into ice ages once they have been initiated. Of course, the opposite holds due to decreasing albedo at the end of an ice age. As simple as this concept may appear to be, the cloud-albedo feedback is not easy to quantify because clouds reflect solar radiation (albedo effect) but absorb... 

The masses of the planets so far discovered vary between about 0.02 and 18 Jupiter masses. There are also very large variations in the values of the semi-major axis of the planetary orbits. If the first two methods for the discovery of extrasolar planets are compared (Doppler and transit methods), Doyle et al. (2000) point out the following facts around 40,000 photons are required to determine the transit of an extrasolar planet across the star HD 209548 using a photometer. But detection of the same system using variations in radial velocity requires 10 million photons. 

Abstract. We discuss new observations of 3He towards planetary nebulae (PNe) using the Very Large Array (VLA), the 305 m Arecibo telescope, which is now capable of observing the 3He+ spectral transition, and the recently commissioned 100 m Green Bank Telescope (GBT). 

The most direct, model independent, way to test the validity of the mixing solution is to measure the 3He abundance in the ejecta of low-mass stars, i.e. in planetary nebulae (PNe). The search for 3He in the ejecta of PNe via the 8.667 GHz spin-flip transition of 3He+, painstakingly carried out by Rood and coworkers at the Green Bank radiotelescope since 1992 (see summary of results in Balser et al. 1997), has produced so far one solid detection (NGC 3242, see Rood, Bania, Wilson 1992 confirmed with the Effelsberg radiotelescope by... 

Fig. 2. GBT Composite Spectrum of Planetary Nebulae. This 125.7 receiver hour integration is the spectral average of 4 PNe NGC3242 + NGC6543 + NGC6826 + NGC 7009. Shown are the Gaussian fits to the H171 r left) and 3He+ (right) transitions...

The S-form can be obtained by treating Copper Phthalocyanine Blue in benzene or toluene with aqueous sulfuric acid in the presence of a surfactant [21], The e-phase is produced by comminution of the a-, 7-, or 8-modification, for instance in a planetary ball mill. The mill base is then aftertreated in an organic solvent at elevated temperature. It is important to realize that the temperature, depending on the solvent, must be kept below the transition temperature at which the e-phase converts to the (3-modification (30 to 160°C). The e-modification is made best from the 7-phase, and the most preferred solvents are alcohols [22], For the industrially hitherto insignificant tt, X, and R-forms of Copper Phthalocyanine Blue (see [1], Vol. II, 34-35). 

The structure of turbulence in the transition zone from a fully turbulent fluid to a nonfluid medium (often called the Prandtl layer) has been studied intensively (see, for instance, Williams and Elder, 1989). Well-known examples are the structure of the turbulent wind field above the land surface (known as the planetary boundary layer) or the mixing regime above the sediments of lakes and oceans (benthic boundary layer). The vertical variation of D(x) is schematically shown in Fig. 19.8b. Yet, in most cases it is sufficient to treat the boundary as if D(x) had the shape shown in Fig. 19.8a. 

The significance of collision-induced absorption for the planetary sciences is well established (Chapter 7) reviews and updates appeared in recent years [115, 165, 166, 169-173]. Numerous efforts are known to model experimental and theoretical spectra of the various hydrogen bands for the astrophysical applications [170, 174-181]. More recently, important applications of colhsional absorption in astrophysics were discovered in the cool and extremely dense stellar atmospheres of white dwarf stars [14, 43, 182-184], at temperatures from roughly 3000 to 6000 K. Under such conditions, large populations of vibra-tionally excited H2 molecules exist and collision-induced absorption extends well into the visible region of the spectrum and beyond. Numerous hot bands, high H2 overtone bands, and H2 rotovibrational sum and difference spectral bands due to simultaneous transitions that were never measured in the laboratory must be expected. Ab initio calculations of the collisional absorption processes in the dense atmospheres of such stars have yet to be provided so that the actual stellar emission spectra may be obtained more accurately than presently known. 

Tn the Rohr model of the hydrogen atom, the proton is a massive positive point charge about which the electron moves. By placing quantum mechanical conditions upon an otherwise classical planetary motion of the electron, Bohr explained the lines observed in optical spectra as transitions between discrete quantum mechanical energy states. Except for hvperfine splitting, which is a minute decomposition of spectrum lines into a group of closely spaced lines, the proton plays a passive role in the mechanics of the hydrogen atom, It simply provides the attractive central force field for the electron,... 

Many carbon rich stars also present an important emission at 11.3 pm associated with solid carbon and some of them present nebulosity of reflection as a consequence of the scattering of the circumstellar grains. There are indications that in the material ejected by these stars, carbon must exist, apart from CO molecules and solid grains, in some other form or species until now unknown, fullerenes are a possibility. Unfortunately, there is very little information about the presence of molecules of intermediate size (between 10 and 106 atoms) in circumstellar regions. There are bands in carbon rich planetary nebulae, for example those of 3.3,6.2,7.7, 8.6 and 11.3 pm which have not been detected in carbon stars but are observable in transition objects evolving between the giant red phase and the planetary nebula as for example, the Egg Nebula (Fig. 1.5) and the Red Rectangle. These infrared bands are normally associated with the vibration modes of materials based on carbon, possibly PAHs. But until now it has not been possible to make a conclusive identification of the carrier. 

The best evidence for a relation between carbon-particles and the diffuse interstellar bands comes from analysis of the Red Rectangle. The Red Rectangle is an usual mass-losing carbon star which is probably in transition into becoming a planetary nebula. Schmidt et al. (1980) using 6-20 A resolution discovered intense optical emission bands longward of 5400 A. With a higher spectral resolution of 1 A,... 

With current instruments it is possible to make spatial maps of the emission from different species in the Red Rectangle. These maps might provide valuable clues to the origin of different spectroscopic features. For example, in the spectrum of the Red Rectangle, the emission features which correspond to the diffuse interstellar bands are concentrated in what appears to be two hollow cones oriented perpendicular to the plane of this bipolar system (Schmidt Witt 1991). This hollow cone is similar to that proposed by Jura Kroto (1990) to explain the observed (Nguyen-Q-Rieu et al. 1986) HC,N emission (see around AFGL 2688, the Egg Nebula ), a very well studied carbon-rich object that appears to be in transition from a red giant to a planetary nebula. 

In our model, cap carbonates are explained as a result of high carbonate alkalinity in an ice-covered ocean, regardless of the specific mechanism for melting the snowball Earth. Ice could melt for a variety of reasons (e.g., greenhouse gases, a positive perturbation in solar forcing, a decrease in planetary albedo), but cap carbonates are expected to be produced as a result of the transition from high to low oceanic carbonate alkalinity. 

A unique perspective of the second edition is that it highlights the properties of minerals that make them compounds of interest to solid state chemists and physicists as well as to all earth and planetary scientists. This book will be useful as a textbook for advanced students as well as a valuable reference work for all research workers interested in the crystal chemistry, spectroscopy and geochemistry of the transition elements. 

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