Evolution of "51Peg b-like" Planets

About one-quarter of the extrasolar giant planets discovered so far have orbital distances smaller than 0.1 AU. These ``51Peg b-like'' planets can now be directly characterized, as shown by the planet transiting in front the star HD209458. We review the processes that affect their evolution. We apply our work to the case of HD209458b, whose radius has been recently measured. We argue that its radius can be reproduced only when the deep atmosphere is assumed to be unrealistically hot. When using more realistic atmospheric temperatures, an energy source appears to be missing in order to explain HD209458b's large size. The most likely source of energy available is not in the planet's spin or orbit, but in the intense radiation received from the parent star. We show that the radius of HD209458b can be reproduced if a small fraction (~1%) of the stellar flux is transformed into kinetic energy in the planetary atmosphere and subsequently converted to thermal energy by dynamical processes at pressures of tens of bars.Comment: 11 pages including 9 figures. A&A, in press. Also available at http://www.obs-nice.fr/guillot/pegasi-planets

Pure hydrogen atmosphere for very cool white dwarfs

Microlensing events observed in the line of sight toward the LMC indicate that a significant fraction of the mass of the dark halo of the Galaxy is probably composed of white dwarfs. In addition, white dwarf sequences have now be observed in the HR diagrams of several globular clusters. Because of the unavailability of white dwarf atmospheres for Teff < 4000K, cooling time scales for white dwarfs older than ~ 10 Gyr are very uncertain. Moreover, the identification of a MACHO white dwarf population by direct observation depends on a knowledge of the colors and bolometric corrections of very-cool white dwarfs. In this paper we present the first detailed model atmospheres and spectra of very cool hydrogen white dwarfs for Teff < 4000K. We include the latest description of the opacities of hydrogen and significantly, we introduce a non-ideal equation of state in the atmosphere calculation. We find that due to strong absorption from H_2 in the infrared, very old white dwarfs are brightest in the V, R, and I bands, and we confirm that they become bluer in most color indices as they cool below Teff ~ 3500K.Comment: 6 LaTex pages and 3 postscript figures. To appear in Ap. J. Letter

First star formation with dark matter annihilation

We include an energy term based on Dark Matter (DM) self-annihilation during the cooling and subsequent collapse of the metal-free gas, in halos hosting the formation of the first stars in the Universe. We have found that the feedback induced on the chemistry of the cloud does modify the properties of the gas throughout the collapse. However, the modifications are not dramatic, and the typical Jeans mass within the halo is conserved throughout the collapse, for all the DM parameters we have considered. This result implies that the presence of Dark Matter annihilations does not substantially modify the Initial Mass Function of the First Stars, with respect to the standard case in which such additional energy term is not taken into account. We have also found that when the rate of energy produced by the DM annihilations and absorbed by the gas equals the chemical cooling (at densities yet far from the actual formation of a proto-stellar core) the structure does not halt its collapse, although that proceeds more slowly by a factor smaller than few per cent of the total collapse time.Comment: 12 pages, 8 figures, 3 tables; replaced with published version after minor change

Low-temperature gas opacity - AESOPUS: a versatile and quick computational tool

We introduce a new tool - AESOPUS: Accurate Equation of State and OPacity Utility Software - for computing the equation of state and the Rosseland mean (RM) opacities of matter in the ideal gas phase. Results are given as a function of one pair of state variables, (i.e. temperature T in the range 3.2 <= log(T) <= 4.5, and parameter R= rho/(T/10^6 K)^3 in the range -8 <= log(R) <= 1), and arbitrary chemical mixture. The chemistry is presently solved for about 800 species, consisting of almost 300 atomic and 500 molecular species. The gas opacities account for many continuum and discrete sources, including atomic opacities, molecular absorption bands, and collision-induced absorption. Several tests made on AESOPUS have proved that the new opacity tool is accurate in the results,flexible in the management of the input prescriptions, and agile in terms of computational time requirement. We set up a web-interface (http://stev.oapd.inaf.it/aesopus) which enables the user to compute and shortly retrieve RM opacity tables according to his/her specific needs, allowing a full degree of freedom in specifying the chemical composition of the gas. Useful applications may regard RM opacities of gas mixtures with i) scaled-solar abundances of metals, choosing among various solar mixture compilations available in the literature; ii) varying CNO abundances, suitable for evolutionary models of red and asymptotic giant branch stars and massive stars in the Wolf-Rayet stages; iii) various degrees of enhancement in alpha-elements, and C-N, Na-O and Mg-Al abundance anti-correlations, necessary to properly describe the properties of stars in early-type galaxies and Galactic globular clusters; iv) zero-metal abundances appropriate for studies of gas opacity in primordial conditions.Comment: 32 pages, 34 postscript figures, A&A in press; new section 4.1.2 showing first tests with stellar models, sections 2.2, 2.2.2 and 5 expanded; interactive web-page at http://stev.oapd.inaf.it/aesopu

The Formation of the First Stars in the Universe

In this review, I survey our current understanding of how the very first stars in the universe formed, with a focus on three main areas of interest: the formation of the first protogalaxies and the cooling of gas within them, the nature and extent of fragmentation within the cool gas, and the physics -- in particular the interplay between protostellar accretion and protostellar feedback -- that serves to determine the final stellar mass. In each of these areas, I have attempted to show how our thinking has developed over recent years, aided in large part by the increasing ease with which we can now perform detailed numerical simulations of primordial star formation. I have also tried to indicate the areas where our understanding remains incomplete, and to identify some of the most important unsolved problems.Comment: 74 pages, 4 figures. Accepted for publication in Space Science Review

The First Stars

The first stars to form in the Universe -- the so-called Population III stars -- bring an end to the cosmological Dark Ages, and exert an important influence on the formation of subsequent generations of stars and on the assembly of the first galaxies. Developing an understanding of how and when the first Population III stars formed and what their properties were is an important goal of modern astrophysical research. In this review, I discuss our current understanding of the physical processes involved in the formation of Population III stars. I show how we can identify the mass scale of the first dark matter halos to host Population III star formation, and discuss how gas undergoes gravitational collapse within these halos, eventually reaching protostellar densities. I highlight some of the most important physical processes occurring during this collapse, and indicate the areas where our current understanding remains incomplete. Finally, I discuss in some detail the behaviour of the gas after the formation of the first Population III protostar. I discuss both the conventional picture, where the gas does not undergo further fragmentation and the final stellar mass is set by the interplay between protostellar accretion and protostellar feedback, and also the recently advanced picture in which the gas does fragment and where dynamical interactions between fragments have an important influence on the final distribution of stellar masses.Comment: 72 pages, 4 figures. Book chapter to appear in "The First Galaxies - Theoretical Predictions and Observational Clues", 2012 by Springer, eds. V. Bromm, B. Mobasher, T. Wiklin

An Educated Guess on the Workplace Attenuation Variability of Ear Muffs

The attenuation variability of hearing protector devices plays a primary role in determining compliance, or lack of, with occupational noise exposure limits. This study presents an estimate of the ear muff attenuation variability, which includes several factors (biological diversity, positioning, sound field, ageing) for which specific information from laboratory studies is available. A mean value of the attenuation variability for ear muffs σFR = 4.8 dB is found. This value is about 65% larger than the typical value measured according to existing test standards. Being marginally smaller than the mean variability resulting from field measurements, and certainly within the wide range of fluctuations of the latter, it represents a robust and reliable quantity for application in any workplace environment

Low scan rate DSC study of the monoclinic-tetragonal transition in zirconia

The effect of heating and cooling rates on the DSC (differential scanning calorimetry) heat flux peak of the monoclinic-tetragonal transition of zirconia was investigated in the 0.4-20 °C/min scan rate range. While the peak position, shape and area at high to moderate scan rates are consistent with existing literature data, a 'step change' (i.e., a peak-less baseline shift) was observed for the extremely slow heating rate of 0.4 °C/min. As expected, peak profiles in the heating and cooling transitions are markedly different, the peak shape being strongly asymmetrical for the t → m transition, but very closely symmetrical for the m → t transition. As the cooling rate is lowered, the t → m peak is increasingly splitted into multiple components, whose individual properties have been fitted using Gamma distribution functions

Ispezione di tubazioni mediante onde ultrasoniche guidate: Linea Guida ISPESL

L\u2019esigenza dello sviluppo di una regolamentazione tecnica concernente l\u2019esercizio in sicurezza delle tubazioni ai sensi dell\u2019art. 3 del D.M. 329/2004, ha determinato, nel settore ispettivo, interesse verso approcci diagnostici non distruttivi a carattere innovativo. In tal senso, il metodo non distruttivo ad onde guidate, gi\ue0 ampiamente sperimentato a livello internazionale, assume una particolare rilevanza proprio per la peculiarit\ue0 all\u2019uso specifico su tubazioni per controlli di screening. Le onde guidate infatti, propagandosi lungo la tubazione con modesta attenuazione, consentono di ispezionare velocemente tratti di conduttura anche di notevole lunghezza, mediante l\u2019installazione, in una zona limitata, di un sistema di eccitazione/ricezione. Poich\ue9 nella loro propagazione esse interessano l\u2019intero volume, le onde risultano egualmente sensibili a difetti che determinano variazioni dello spessore o della geometria sia della superficie interna che di quella esterna del tubo. Il metodo \ue8 pertanto particolarmente indicato per il controllo di tratti interrati, incamiciati, sovrappassi ed altre installazioni la cui accessibilit\ue0 sia oggettivamente complessa o problematica. Il lavoro riporta i risultati di alcune specifiche applicazioni, evidenziando i vantaggi del metodo e, al contempo, le limitazioni applicative come anche una panoramica delle specifiche tecniche e relative potenzialit\ue0 diagnostiche. Infine, viene presentato un algoritmo originale di valutazione dell'adeguatezza all'uso del controllo mediante onde guidate per le diverse tipologie d'installazione

Low scan rate DSC study of the monoclinic-tetragonal transition in zirconia

The effect of heating and cooling rates on the DSC (differential scanning calorimetry) heat flux peak of the monoclinic-tetragonal transition of zirconia was investigated in the 0.4-20 °C/min scan rate range. While the peak position, shape and area at high to moderate scan rates are consistent with existing literature data, a 'step change' (i.e., a peak-less baseline shift) was observed for the extremely slow heating rate of 0.4 °C/min. As expected, peak profiles in the heating and cooling transitions are markedly different, the peak shape being strongly asymmetrical for the t → m transition, but very closely symmetrical for the m → t transition. As the cooling rate is lowered, the t → m peak is increasingly splitted into multiple components, whose individual properties have been fitted using Gamma distribution functions