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Le Borgne J.F.,Toulouse 1 University Capitole | Le Borgne J.F.,French National Center for Scientific Research | Poretti E.,Toulouse 1 University Capitole | Poretti E.,French National Center for Scientific Research | And 24 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

RR Lyr is one of the most studied variable stars. Its light curve has been regularly monitored since the discovery of its periodic variability in 1899. The analysis of all observed maxima allows us to identify two primary pulsation states, defined as pulsation over a long (P0 longer than 0.56684 d) and a short (P0 shorter than 0.56682 d) primary pulsation period. These states alternate with intervals of 13-16 yr, and are well defined after 1943. The 40.8-d periodical modulations of the amplitude and the period (i.e. the Blazhko effect) were noticed in 1916.We provide homogeneous determinations of the Blazhko period in the different primary pulsation states. The Blazhko period does not follow the variations of P0 and suddenly diminished from 40.8 d to around 39.0 d in 1975. The monitoring of these periodicities deserved, and still deserves, a continuous and intensive observational effort. For this purpose, we have built dedicated, transportable and autonomous small instruments, Very Tiny Telescopes (VTTs), to observe the times of maximum brightnessof RR Lyr. As immediate results, the VTTs recorded the last change of the P0 state in mid-2009 and extended the time coverage of the Kepler observations, thus recording a maximumO-C amplitude of the Blazhko effect at the end of 2008, followed by the historically smallest O-C amplitude in late 2013. This decrease is still ongoing and the VTTs are ready to monitor the expected increase in the next few years. © 2014 The Author Published by Oxford University Press on behalf of the Royal Astronomical Society. Source

This paper is a continuation of Miles et al. (2015) [Icarus] and Miles (2015b) [Icarus], which detail new observations of Comet 29P/Schwassmann-Wachmann, characterise its rotational period (~57d), and identify the presence of discrete sources of outburst on its nucleus: the latter ruling out amorphous-to-crystalline H2O ice transitions as the cause of its outbursts. Summary data are presented for 29P and a further 16 non-fragmenting comets which exhibit outbursts of >2 magnitudes. A comprehensive physicochemical mechanism is postulated to account for major outbursts based on melting of cometary ices and the exothermic dissolution of gases, especially CO and CO2 at pressures of 10-200kPa. The thermodynamics of enthalpy heating are described and heats of solution are calculated from gas-liquid solubility data yielding -6kJmol-1 for CO in CH4, and -15kJmol-1 for CO2 in CH3OH close to their freezing point. Heats of solution are ~6 times greater (per mole) than the enthalpy of fusion of the pure CH4 and CH3OH ices, enabling gas pressures of >~80kPa to continually melt these ices. Supervolatile O2 and N2 gases may also participate by dissolving exothermically in liquid CH4 and other hydrocarbons potentially reaching high mixing ratios. H2S and NH3 gases dissolve exothermically in CH3OH liberating up to 20kJmol-1 and 13kJmol-1, respectively, and all three hydrophilic species facilitate sintering of H2O ice in the near-surface of comets. Localised melting and consolidation is favoured in slowly-rotating cometary nuclei of intermediate dust/gas ratios, at pressures of ~1kPa, and temperatures as low as 50-65K where O2 and N2 are abundant. Nyctogenic processes on the night-time side of the nucleus restock desiccated surface layers, reseal the crust, enabling fractionation of solutes in sub-crustal liquid phases via fractional sublimation/distillation of non-polar, hydrophobic CH4 and other hydrocarbons; and by fractional crystallisation of polar, hydrophilic phases rich in aqueous CH3OH and other organic oxygenates, e.g. CH2O, able to form low melting point eutectic mixtures. A generalised outburst mechanism is described involving the containment of gases as solutes in cryomagma beneath consolidated surface crustal regions. Disruption of the crust and associated pressure loss render the cryomagma supersaturated, and the concomitant explosive exsolution of gases provokes a cometary outburst. The CO gas-exsolution mechanism operates at ~65 to 95K and accounts for activity of 29P and other distant comets up to rh=~15AU. A similar mechanism can operate at ~150 to 200K driven by CO2 in aqueous CH3OH and may account for rare outbursts of Jupiter-family comets such as 17P/Holmes. At least 10-15% of all periodic comets may be subject to gas-exsolution outbursts, the majority of which are weak and go undetected. Possible surface morphologies of the nucleus of Comet 29P are discussed. The mechanism may also explain the phenomenon of strong cometary outbursts triggering secondary events, as observed for 17P, 29P and 41P. © 2016 Elsevier Inc.All rights reserved. Source

Barrado-Izagirre N.,University of the Basque Country | Rojas J.F.,University of the Basque Country | Hueso R.,University of the Basque Country | Sanchez-Lavega A.,University of the Basque Country | And 2 more authors.
Astronomy and Astrophysics | Year: 2013

Context. The general circulation of Jupiter's atmosphere at cloud level is dominated by a system of zonal jets that alternate in direction with latitude. The winds, measured in high-resolution images obtained by different space missions and the Hubble Space Telescope, are overall stable in their latitude location with small changes in intensity at particular jets. However, the atmosphere experiences repetitive changes in the albedo of particular belts and zones that are subject to large-scale intense disturbances that may locally influence the profile. Aims. The lack of high-resolution images has not allowed the wind system to be studied with the regularity required to assess its stability with respect to these major changes or to other types of variations (e.g., seasonality). To amend that, we present a study of the zonal wind profile of Jupiter using images acquired around the 2011 opposition by a network of observers operating small-size telescopes with apertures in the range 0.20-1 m. Methods. Using an automatic correlation technique, we demonstrate the capability to extract the mean zonal winds in observing periods close to the opposition. A broad collaboration with skilled amateur astronomers opens the possibility to regularly study short-and long-term changes in the jets of Jupiter. Results. We compare the 2011 Jovian wind profile to those previously obtained. The winds did not experience significant short-term changes over 2011 but show noteworthy variations at particular latitudes when compared with wind profiles from previous years. Most of these variations are related to major changes in the cloud morphology of the planet, in particular at 7 N where an intense eastward jet varies around 40 ms-1 in its intensity according to the development or not of the "dark projection" features, confirming previous results. © 2013 ESO. Source

Lohr M.E.,Open University Milton Keynes | Norton A.J.,Open University Milton Keynes | Kolb U.C.,Open University Milton Keynes | Boyd D.R.S.,British Astronomical Association
Astronomy and Astrophysics | Year: 2013

We report our investigation of 1SWASP J234401.81-212229.1, a variable with a 18 461.6 s period. After identification in a 2011 search of the SuperWASP archive for main-sequence eclipsing binary candidates near the distribution's short-period limit of ∼0.20 d, it was measured to be undergoing rapid period decrease in our earlier work, though later observations supported a cyclic variation in period length. Spectroscopic data obtained in 2012 with the Southern African Large Telescope did not, however, support the interpretation of the object as a normal eclipsing binary. Here, we consider three possible explanations consistent with the data: a single-star oblique rotator model in which variability results from stable cool spots on opposite magnetic poles; a two-star model in which the secondary is a brown dwarf; and a three-star model involving a low-mass eclipsing binary in a hierarchical triple system. We conclude that the latter is the most likely model. © 2013 ESO. Source

Frost M.,British Astronomical Association
Astrophysics and Space Science Proceedings | Year: 2015

Henry Beighton, FRS (1687-1743) was a polymath who played an important role in the early days of the Industrial Revolution. He was born in Chilvers Coton, Warwickshire, and supervised the steam engines which enabled the exploitation of the Warwickshire coalfield; he then used this expertise in Oxclose Colliery, Washington Fell, County Durham. He was the editor of The Ladies' Diary, the only significant mathematical journal in England during the early eighteenth century, and he used continental surveying techniques to produce an early accurate map of Warwickshire. I first got to know about Beighton when I came across the beautiful chart in Warwickshire Country Archives that he used to predict the 18 February 1736-1737 solar eclipse. There is a probable connection to Thomas Wright of County Durham, another astronomer who charted the eclipses which crossed Britain during the eighteenth century. © Springer International Publishing Switzerland 2015. Source

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