Enabling New ALMA Science with Improved Support for Time-Domain Observations [IMA]


While the Atacama Large Millimeter/submillimeter Array (ALMA) is a uniquely powerful telescope, its impact in certain fields of astrophysics has been limited by observatory policies rather than the telescope’s innate technical capabilities. In particular, several observatory policies present challenges for observations of variable, mobile, and/or transient sources — collectively referred to here as “time-domain” observations. In this whitepaper we identify some of these policies, describe the scientific applications they impair, and suggest changes that would increase ALMA’s science impact in Cycle 6 and beyond.
Parties interested in time-domain science with ALMA are encouraged to join the ALMA Time-domain Special Interest Group (ATSIG) by signing up for the ATSIG mailing list at https://groups.google.com/group/alma-td-sig .

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K. Alexander, E. Berger, G. Bower, et. al.
Thu, 16 Mar 17

Comments: 9 pages; whitepaper submitted to the ALMA Science Advisory Council; corresponding author P. K. G. Williams (pwilliams@cfa.harvard.edu)

Exponential Distance Relation and Near Resonances in the Trappist-1 Planetary System [IMA]


We report in this paper a new exponential relation distance of planets in the newly discovered exoplanetary system of the Trappist-1 star, and we comment on near orbital mean motion resonances among the seven planets. We predict that possible smaller planets could be found inside the orbit of the innermost discovered Planet b.

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V. Pletser and L. Basano
Thu, 16 Mar 17

Comments: 6 pages, 2 figures, 5 Tables

LSDCat: Detection and cataloguing of emission line sources in integral-field spectroscopy datacubes [IMA]


We present a robust, efficient, and user-friendly algorithm for detecting faint emission line sources in large integral-field spectroscopic datacubes. together with the public release of the software package LSDCat (Line Source Detection and Cataloguing). LSDCat uses a 3-dimensional matched filter approach, combined with thresholding in signal-to-noise, to build a catalogue of individual line detections. In a second pass, the detected lines are grouped into distinct objects, and positions, spatial extents, and fluxes of the detected lines are determined. LSDCat requires only a small number of input parameters, and we provide guidelines for choosing appropriate values. The software is coded in Python and capable to process very large datacubes in a short time. We verify the implementation with a source insertion and recovery experiment utilising a real datacube taken with the MUSE instrument at the ESO Very Large Telescope.

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E. Herenz and L. Wisotzki
Thu, 16 Mar 17

Comments: 14 pages. Accepted for publication in Astronomy & Astrophysics. The LSDCat software is available at this https URL

Digital receivers for low-frequency radio telescopes UTR-2, URAN, GURT [IMA]


This paper describes digital radio astronomical receivers used for decameter and meter wavelength observations. This paper describes digital radio astronomical receivers used for decameter and meter wavelength observations. Since 1998, digital receivers performing on-the-fly dynamic spectrum calculations or waveform data recording without data loss have been used at the UTR-2 radio telescope, the URAN VLBI system, and the GURT new generation radio telescope. Here we detail these receivers developed for operation in the strong interference environment that prevails in the decameter wavelength range. Data collected with these receivers allowed us to discover numerous radio astronomical objects and phenomena at low frequencies, a summary of which is also presented.

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V. Zakharenko, A. Konovalenko, P. Zarka, et. al.
Tue, 14 Mar 17

Comments: 24 pages, 15 figures

Gain factor and parameter settings optimization of the new gamma-ray burst polarimeter POLAR [IMA]


As a space-borne detector POLAR is designed to conduct hard X-ray polarization measurements of gamma-ray bursts on the statistically significant sample of events and with an unprecedented accuracy. During its development phase a number of tests, calibrations runs and verification measurements were carried out in order to validate instrument functionality and optimize operational parameters. In this article we present results on gain optimization togeter with verification data obtained in the course of broad laboratory and environmental tests. In particular we focus on exposures to the $^{137}$Cs radioactive source and determination of the gain dependence on the high voltage for all 1600 detection channels of the polarimeter. Performance of the instrument is described in detail with respect to the dynamic range, energy resolution and temperature dependence. Gain optimization algorithms and response non-uniformity studies are also broadly discussed. Results presented below constitute important parts for development of the POLAR calibration and operation database.

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X. Zhang, W. Hajdas, H. Xiao, et. al.
Tue, 14 Mar 17

Comments: 22 pages, 14 figures

Design and experimental test of an optical vortex coronagraph [IMA]


The optical vortex coronagraph (OVC) is one of the promising ways for direct imaging exoplanets because of its small inner working angle and high throughput. This paper presents the design and laboratory demonstration performance at 633nm and 1520nm of the OVC based on liquid crystal polymers (LCP). Two LCPs has been manufactured in partnership with a commercial vendor. The OVC can deliver a good performance in laboratory test and achieve the contrast of the order 10^-6 at angular distance 3{\lambda}/D, which is able to image the giant exoplanets at a young stage in combination with extreme adaptive optics.

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C. Liu, D. Ren, Y. Zhu, et. al.
Tue, 14 Mar 17

Comments: 8 pages and 6 figures

Canvas and Cosmos: Visual Art Techniques Applied to Astronomy Data [IMA]


Bold colour images from telescopes act as extraordinary ambassadors for research astronomers because they pique the public’s curiosity. But are they snapshots documenting physical reality? Or are we looking at artistic spacescapes created by digitally manipulating astronomy images? This paper provides a tour of how original black and white data, from all regimes of the electromagnetic spectrum, are converted into the colour images gracing popular magazines, numerous websites, and even clothing. The history and method of the technical construction of these images is outlined. However, the paper focuses on introducing the scientific reader to visual literacy (e.g.human perception) and techniques from art (e.g. composition, colour theory) since these techniques can produce not only striking but politically powerful public outreach images. When created by research astronomers, the cultures of science and visual art can be balanced and the image can illuminate scientific results sufficiently strongly that the images are also used in research publications. Included are reflections on how they could feedback into astronomy research endeavours and future forms of visualization as well as on the relevance of outreach images to visual art.

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J. English
Tue, 14 Mar 17

Comments: This is the submitted version (and lacks a couple of references, has lower quality figures, etc). 51 pages, 26 images. The paper has been published in IJMPD. For images by the author see this https URL