906 research outputs found

    The Square Kilometre Array

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    The Square Kilometre Array (SKA) is intended as the next-generation radio telescope and will address fundamental questions in astrophysics, physics, and astrobiology. The international science community has developed a set of Key Science Programs: (1) Emerging from the Dark Ages and the Epoch of Reionization, (2) Galaxy Evolution, Cosmology, and Dark Energy, (3) The Origin and Evolution of Cosmic Magnetism, (4) Strong Field Tests of Gravity Using Pulsars and Black Holes, and (5) The Cradle of Life/Astrobiology. In addition, there is a design philosophy of "exploration of the unknown," in which the objective is to keep the design as flexible as possible to allow for future discoveries. Both a significant challenge and opportunity for the SKA is to obtain a significantly wider field of view than has been obtained with radio telescopes traditionally. Given the breadth of coverage of cosmic magnetism and galaxy evolution in this conference, I highlight some of the opportunities that an expanded field of view will present for other Key Science Programs.Comment: 8 pages; invited presentation at the Panoramic Radio Astronomy conference, Groningen, The Netherlands; 2009 June 2--

    Radio Observations of HD 80606 Near Planetary Periastron

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    This paper reports Very Large Array observations at 325 and 1425 MHz (90cm and 20cm) during and near the periastron passage of HD 80606b on 2007 November 20. We obtain flux density limits (3-sigma) of 1.7 mJy and 48 microJy at 325 and 1425 MHz, respectively, equivalent to planetary luminosity limits of 2.3 x 10^{24} erg/s and 2.7 x 10^{23} erg/s. These are well above the Jovian value (at 40 MHz) of 2 x 10^{18} erg/s. The motivation for these observations was that the planetary magnetospheric emission is driven by a stellar wind-planetary magnetosphere interaction so that the planetary luminosity would be elevated. Near periastron, HD 80606b might be as much as 3000 times more luminous than Jupiter. Recent transit observations of HD 80606b provide stringent constraints on the planetary mass and radius, and, because of the planet's highly eccentric orbit, its rotation period is likely to be "pseudo-synchronized" to its orbital period, allowing a robust estimate of the former. We are able to make robust estimates of the emission frequency of the planetary magnetospheric emission and find it to be around 60--90 MHz. We compare HD 80606b to other high-eccentricity systems and assess the detection possibilities for both near-term and more distant future systems. Of the known high eccentricity planets, only HD 80606b is likely to be detectable, as HD 20782B b and HD 4113b are both likely to have weaker magnetic field strengths. Both the forthcoming "EVLA low band" system and the Low Frequency Array may be able to improve upon our limits for HD 80606b, and do so at a more optimum frequency. If the low-frequency component of the Square Kilometre Array (SKA-lo) and a future lunar radio array are able to approach their thermal noise limits, they should be able to detect an HD 80606b-like planet, unless the planet's luminosity increases by substantially less than a factor of 3000.Comment: 9 pages; accepted for publication in A

    Two New and Remarkable Sightlines through the Galactic Center's Molecular Gas

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    Until now the known sources in the Galactic center with sufficiently smooth spectra and of sufficient brightness to be suitable for high resolution infrared absorption spectroscopy of interstellar gas occupied a narrow range of longitudes, from the central cluster of hot stars to approximately 30 pc east of the center. In order to more fully characterize the gas within the r ~ 180 pc central molecular zone it is necessary to find additional such sources that cover a much wider longitudinal range. We are in the process of identifying luminous dust-embedded objects suitable for spectroscopy within 1.2 deg in longitude and 0.1 deg in latitude of Sgr A* using the Spitzer GLIMPSE and the 2MASS catalogues. Here we present spectra of H3+ and CO towards two such objects, one located 140 pc west of Sgr A*, and the other located on a line of sight to the Sgr B molecular cloud complex 85 pc to the east of Sgr A*. The sightline to the west passes through two dense clouds of unusually high negative velocities and also appears to sample a portion of the expanding molecular ring. The spectra toward Sgr B reveal at least ten absorption components covering over 200 km/s and by far the largest equivalent width ever observed in an interstellar H3+line; they appear to provide the first near-infrared view into that hotbed of star formation.Comment: 13 pages, incl. 4 figures - accepted by ApJ Letters Dec 14, 2009; minor typos correcte

    A Search for Supernova-Remnant Masers Toward Unidentified EGRET Sources

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    Supernova remnants expanding into adjacent molecular clouds are believed to be sites of cosmic ray acceleration and sources of energetic gamma-rays. Under certain environmental conditions, such interactions also give rise to unusual OH masers in which the 1720 MHz satellite line dominates over the more common 1665/7 MHz emission. Motivated by the apparent coincidence of a handful of EGRET sources with OH(1720 MHz) maser-producing supernova remnants, we have carried out a search using the Very Large Array for new OH(1720 MHz) masers within the error regions of 11 unidentified EGRET sources at low Galactic latitude. While a previously known maser associated with an HII region was serendipitously detected, initial results indicate that no new masers were found down to a limiting flux of, typically, 50 mJy. We discuss the implications of this result on the nature of the unidentified Galactic EGRET sources.Comment: 5 pages, 1 figure. To appear in Proceedings, GAMMA2001 (Baltimore, MD, April 4-6, 2001), eds. N. Gehrels, C. Shrader, and S. Rit