The Herschel view of GAS in Protoplanetary Systems (GASPS): First comparisons with a large grid of models

The Herschel GASPS key program is a survey of the gas phase of protoplanetary discs, targeting 240 objects which cover a large range of ages, spectral types, and disc properties. To interpret this large quantity of data and initiate self-consistent analyses of the gas and dust properties of protoplanetary discs, we have combined the capabilities of the radiative transfer code MCFOST with the gas thermal balance and chemistry code ProDiMo to compute a grid of ≈300  000 disc models (DENT). We present a comparison of the first Herschel/GASPS line and continuum data with the predictions from the DENT grid of models. Our objective is to test some of the main trends already identified in the DENT grid, as well as to define better empirical diagnostics to estimate the total gas mass of protoplanetary discs. Photospheric UV radiation appears to be the dominant gas-heating mechanism for Herbig stars, whereas UV excess and/or X-rays emission dominates for T Tauri stars. The DENT grid reveals the complexity in the analysis of far-IR lines and the difficulty to invert these observations into physical quantities. The combination of Herschel line observations with continuum data and/or with rotational lines in the (sub-)millimetre regime, in particular CO lines, is required for a detailed characterisation of the physical and chemical properties of circumstellar discs

Reionization History from Coupled CMB/21cm Line Data

We study CMB secondary anisotropies produced by inhomogeneous reionization by means of cosmological simulations coupled with the radiative transfer code CRASH. The reionization history is consistent with the WMAP Thomson optical depth determination. We find that the signal arising from this process dominates over the primary CMB component for l > 4000 and reaches a maximum amplitude of l(l+1)C_l/2\pi ~ 1.6 x 10^{-13} on arcmin scale, i.e. l as large as several thousands. We then cross-correlate secondary CMB anisotropy maps with neutral hydrogen 21cm line emission fluctuations obtained from the same simulations. The two signals are highly anti-correlated on angular scales corresponding to the typical size of HII regions (including overlapping) at the 21cm map redshift. We show how the CMB/21cm cross-correlation can be used to: (a) study the nature of the reionization sources, (b) reconstruct the cosmic reionization history, (c) infer the mean cosmic ionization level at any redshift. We discuss the feasibility of the proposed experiment with forthcoming facilities.Comment: 7 pages, 5 figures, MNRAS in pres

Numerical study of jets produced by conical wire arrays on the Magpie pulsed power generator

The aim of this work is to model the jets produced by conical wire arrays on the MAGPIE generator, and to design and test new setups to strengthen the link between laboratory and astrophysical jets. We performed the modelling with direct three-dimensional magneto-hydro-dynamic numerical simulations using the code GORGON. We applied our code to the typical MAGPIE setup and we successfully reproduced the experiments. We found that a minimum resolution of approximately 100 is required to retrieve the unstable character of the jet. We investigated the effect of changing the number of wires and found that arrays with less wires produce more unstable jets, and that this effect has magnetic origin. Finally, we studied the behaviour of the conical array together with a conical shield on top of it to reduce the presence of unwanted low density plasma flows. The resulting jet is shorter and less dense.Comment: Accepted for publication in Astrophysics & Space Science. HEDLA 2010 conference procedings. Final pubblication will be available on Springe

Science at mid-infrared wavelengths with large telescopes

For background-limited observations such as those at mid-infrared wavelengths, an increase in telescope aperture not only improves the angular resolution (as it does at all wavelengths) but also leads to very large increases in sensitivity because of the reduced background within the diffraction-limited point spread function. In this presentation we look at the magnitude of that increase for several different operational modes of mid-infrared instrumentation, and we consider some of the implications for science on the current generation of 8-10 meter telescopes

What’s Cool About Hot Stars? Cataclysmic Variables in the Mid-Infrared

We review recent results from mid-infrared observations of cataclysmic variables with the Spitzer Space Telescope. In general, these observations have revealed mid-infrared excesses, above the level expected from the stellar and accretion components, in numerous systems. This excess can be modeled as originating from circumstellar and/or circumbinary dust. We present an overview of spectral energy distributions spanning the ultraviolet to the mid-infrared, as well as mid-infrared light curves, of disk-accreting and magnetic cataclysmic variables. Physically realistic models constructed to reproduce these data indicate that the mid-infrared luminosity of many cataclysmic variables is dominated by emission from warm (T < 2000 K) dust. The presence and characteristics of dust in cataclysmic variables has potentially important implications for the secular evolution scenario for interacting binary stars

Curved Herbig-Haro Jets: Simulations and Experiments

Herbig-Haro jets often show some degree of curvature along their path, in many cases produced by the ram pressure of a side-wind. We present simulations of both laboratory and astrophysical curved jets and experimental results from laboratory experiments. We discuss the properties and similarities of the laboratory and astrophysical flow, which show the formation of internal shocks and working surfaces. In particular the results illustrate how the break-up of the bow-shock and clumps in the flow are produced without invoking jet variability; we also discuss how jet rotation reduces the growth of the Rayleigh-Taylor instability in curved jets.Comment: 15 pages, 5 figure, accepted to be published in The Astrophysical Journa

HIV-associated progressive multifocal leukoencephalopathy. Current perspectives

Progressive multifocal leukoencephalopathy (PML) is a demyelinating disease of the central nervous system, caused by the polyomavirus JC and occurring almost exclusively in the context of severe immune depression. AIDS represents the most common predisposing condition for PML development. Antiretroviral treatment has reduced PML incidence in HIV-infected subjects, but the disease remains a severe and life-threatening complication of AIDS, considering thus far the lack of an effective anti-JC virus (JCV) direct-acting antiviral drug. In the last decade, the use of monoclonal antibodies for treating immune-based diseases evidenced new predisposing conditions for PML development, promoting a renewed interest in PML pathogenesis. In this article, we review the current knowledge on JCV epidemiology and AIDS-associated PML incidence, JCV viral cycle, pathogenesis, and the interplay with HIV infection. We give an updated overview of diagnostic and prognostic tools available for PML diagnosis and describe past and current therapeutic approaches, including new strategies for PML cure

Tracing the Origins and Evolution of Small Planets using Their Orbital Obliquities

We recommend an intensive effort to survey and understand the obliquity distribution of small close-in extrasolar planets over the coming decade. The orbital obliquities of exoplanets--i.e., the relative orientation between the planetary orbit and the stellar rotation--is a key tracer of how planets form and migrate. While the orbital obliquities of smaller planets are poorly explored today, a new generation of facilities coming online over the next decade will make such observations possible en masse. Transit spectroscopic observations with the extremely large telescopes will enable us to measure the orbital obliquities of planets as small as $\sim2R_{\oplus}$ around a wide variety of stars, opening a window into the orbital properties of the most common types of planets. This effort will directly contribute to understanding the formation and evolution of planetary systems, a key objective of the National Academy of Sciences' Exoplanet Science Strategies report.Comment: Submitted to the Astro2020 call for science white papers. 7 pages, 2 figure

The Five Planets in the Kepler-296 Binary System All Orbit the Primary: A Statistical and Analytical Analysis

Kepler-296 is a binary star system with two M-dwarf components separated by 0.2 arcsec. Five transiting planets have been confirmed to be associated with the Kepler-296 system; given the evidence to date, however, the planets could in principle orbit either star. This ambiguity has made it difficult to constrain both the orbital and physical properties of the planets. Using both statistical and analytical arguments, this paper shows that all five planets are highly likely to orbit the primary star in this system. We performed a Markov-Chain Monte Carlo simulation using a five transiting planet model, leaving the stellar density and dilution with uniform priors. Using importance sampling, we compared the model probabilities under the priors of the planets orbiting either the brighter or the fainter component of the binary. A model where the planets orbit the brighter component, Kepler-296A, is strongly preferred by the data. Combined with our assertion that all five planets orbit the same star, the two outer planets in the system, Kepler-296 Ae and Kepler-296 Af, have radii of 1.53 +/- 0.26 and 1.80 +/- 0.31 R_earth, respectively, and receive incident stellar fluxes of 1.40 +/- 0.23 and 0.62 +/- 0.10 times the incident flux the Earth receives from the Sun. This level of irradiation places both planets within or close to the circumstellar habitable zone of their parent star.Comment: Accepted for publication in Ap

Observations of Binary Stars with the Differential Speckle Survey Instrument. II. Hipparcos Stars Observed in 2010 January and June

The results of 497 speckle observations of Hipparcos stars and selected other targets are presented. Of these, 367 were resolved into components and 130 were unresolved. The data were obtained using the Differential Speckle Survey Instrument at the WIYN 3.5 m Telescope. (The WIYN Observatory is a joint facility of the University of Wisconsin-Madison, Indiana University, Yale University, and the National Optical Astronomy Observatories.) Since the first paper in this series, the instrument has been upgraded so that it now uses two electron-multiplying CCD cameras. The measurement precision obtained when comparing to ephemeris positions of binaries with very well known orbits is approximately 1-2 mas in separation and better than 0°.6 in position angle. Differential photometry is found to be in very good agreement with Hipparcos measures in cases where the comparison is most relevant. We derive preliminary orbits for two systems