Machine Learning Based Real Bogus System for HSC-SSP Moving Object Detecting Pipeline [IMA]

http://arxiv.org/abs/1704.06413


The machine learning techniques are widely applied in many modern optical sky surveys, i.e. Pan-STARRS1, PTF/iPTF and Subaru/Hyper Suprime-Cam survey, to reduce the human intervention for data verification. In this study, we have established a machine learning based real-bogus system to reject the false detections in the HSC-SSP source catalog. Therefore the HSC-SSP moving object detection pipeline can operate more effectively due to the much less false positives inputs. To train the real-bogus system, we use the stationary sources as the real training set and the `flagged’ data as the bogus set. The training set contains 49 features, which, in majority, are the photometry measurements and shape moments generating from the HSC image reduction pipeline (hscPipe). Our system can reach a true positive rate (tpr) ~ 96% with a false positive rate (fpr) ~ 1% or tpr ~ 99% at fpr ~ 5%. Therefore we conclude that the stationary sources are decent real training samples, and using photometry measurements and shape moments can reject the false positives effectively.

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H. Lin, Y. Chen, J. Wang, et. al.
Mon, 24 Apr 17
3/54

Comments: 16 pages, 4 figures, submitted to PASJ HSC special issue

Mirror Position Determination for the Alignment of Cherenkov Telescopes [IMA]

http://arxiv.org/abs/1704.06494


Imaging Atmospheric Cherenkov Telescopes (IACTs) need imaging optics with large apertures to map the faint Cherenkov light emitted in extensive air showers onto their image sensors. Segmented reflectors fulfill these needs using mass produced and light weight mirror facets. However, as the overall image is the sum of the individual mirror facet images, alignment is important. Here we present a method to determine the mirror facet positions on a segmented reflector in a very direct way. Our method reconstructs the mirror facet positions from photographs and a laser distance meter measurement which goes from the center of the image sensor plane to the center of each mirror facet. We use our method to both align the mirror facet positions and to feed the measured positions into our IACT simulation. We demonstrate our implementation on the 4 m First Geiger-mode Avalanche Cherenkov Telescope (FACT).

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J. Adam, M. Ahnen, D. Baack, et. al.
Mon, 24 Apr 17
12/54

Comments: 11 figures, small ray tracing performance simulation, and implementation demonstration

Lunar laser ranging in infrfared at hte Grasse laser station [IMA]

http://arxiv.org/abs/1704.06443


For many years, lunar laser ranging (LLR) observations using a green wavelength have suffered an inhomogeneity problem both temporally and spatially. This paper reports on the implementation of a new infrared detection at the Grasse LLR station and describes how infrared telemetry improves this situation. Our first results show that infrared detection permits us to densify the observations and allows measurements during the new and the full Moon periods. The link budget improvement leads to homogeneous telemetric measurements on each lunar retro-reflector. Finally, a surprising result is obtained on the Lunokhod 2 array which attains the same efficiency as Lunokhod 1 with an infrared laser link, although those two targets exhibit a differential efficiency of six with a green laser link.

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C. Courde, J. Torre, E. Samain, et. al.
Mon, 24 Apr 17
37/54

Comments: N/A

Removing visual bias in filament identification: a new goodness-of-fit measure [IMA]

http://arxiv.org/abs/1704.06377


Different combinations of input parameters to filament identification algorithms, such as Disperse and FilFinder, produce numerous different output skeletons. The skeletons are a one pixel wide representation of the filamentary structure in the original input image. However, these output skeletons may not necessarily be a good representation of that structure. Furthermore, a given skeleton may not be as good a representation as another. Previously there has been no mathematical goodness-of-fit' measure to compare output skeletons to the input image. Thus far this has been assessed visually, introducing visual bias. We propose the application of the mean structural similarity index (MSSIM) as a mathematical goodness-of-fit measure. We describe the use of the MSSIM to find the output skeletons most mathematically similar to the original input image (the optimum, orbest’, skeletons) for a given algorithm, and independently of the algorithm. This measure makes possible systematic parameter studies, aimed at finding the subset of input parameter values returning optimum skeletons. It can also be applied to the output of non-skeleton based filament identification algorithms, such as the Hessian matrix method. The MSSIM removes the need to visually examine thousands of output skeletons, and eliminates the visual bias, subjectivity, and limited reproducibility inherent in that process, representing a major improvement on existing techniques. Importantly, it also allows further automation in the post-processing of output skeletons, which is crucial in this era of `big data’.

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C. Green, M. Cunningham, J. Dawson, et. al.
Mon, 24 Apr 17
44/54

Comments: 8 pages, 3 figures, Accepted for publication in ApJL, April 2017

A compact and modular X and gamma-ray detector with a CsI scintillator and double-readout Silicon Drift Detectors [IMA]

http://arxiv.org/abs/1704.06122


A future compact and modular X and gamma-ray spectrometer (XGS) has been designed and a series of prototypes have been developed and tested. The experiment envisages the use of CsI scintillator bars read out at both ends by single-cell 25 mm2 Silicon Drift Detectors. Digital algorithms are used to discriminate between events absorbed in the Silicon layer (lower energy X rays) and events absorbed in the scintillator crystal (higher energy X rays and gamma-rays). The prototype characterization is shown and the modular design for future experiments with possible astrophysical applications (e.g. for the THESEUS mission proposed for the ESA M5 call) are discussed.

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R. Campana, F. Fuschino, C. Labanti, et. al.
Fri, 21 Apr 17
18/73

Comments: 10 pages, 11 figures. Published in Proceeding of SPIE Astronomical Telescopes and Instrumentation 2016

Integrated optics prototype beam combiner for long baseline interferometry in the L and M bands [IMA]

http://arxiv.org/abs/1704.05846


In the last few years, integrated optics (IO) beam combiners have facilitated the emergence of 4-telescope interferometers such as PIONIER or GRAVITY, boosting the imaging capabilities of the VLTI. However, the spectral range beyond 2.2microns is not ideally covered by the conventional silica based IO. Here, we propose to consider new laser-written IO prototypes made of GLS glasses, a material that permits access to the mid-infrared spectral regime. Our goal is to conduct a full characterization of our mid-IR IO 2-telescope coupler in order to measure the performance levels directly relevant for long-baseline interferometry. We focus in particular on the exploitation of the L and M astronomical bands. We use a dedicated Michelson-interferometer setup to perform Fourier Transform spectroscopy on the coupler and measure its broadband interferometric performance. We also analyze the polarization properties of the coupler, the differential dispersion and phase degradation as well as the modal behavior and the total throughput. We measure broadband interferometric contrasts of 94.9% and 92.1% for unpolarized light in the L and M bands. Spectrally integrated splitting ratios are close to 50% but show chromatic dependence over the considered bandwidths. Additionally, the phase variation due to the combiner is measured and does not exceed 0.04rad and 0.07rad across the band L and M band, respectively. The total throughput of the coupler including Fresnel and injection losses from free-space is 25.4%. The laser-written IO GLS prototype combiners prove to be a reliable technological solution with promising performance for mid-infrared long-baseline interferometry. In the next steps, we will consider more advanced optical functions as well as a fiber-fed input and revise the optical design parameters in order the further enhance the total throughput and achromatic behavior.

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J. Tepper, L. Labadie, R. Diener, et. al.
Fri, 21 Apr 17
58/73

Comments: N/A

The Hyper Suprime-Cam SSP Survey: Overview and Survey Design [IMA]

http://arxiv.org/abs/1704.05858


Hyper Suprime-Cam (HSC) is a wide-field imaging camera on the prime focus of the 8.2m Subaru telescope on the summit of Maunakea. A team of scientists from Japan, Taiwan and Princeton University is using HSC to carry out a 300-night multi-band imaging survey of the high-latitude sky. The survey includes three layers: the Wide layer will cover 1400 deg$^2$ in five broad bands ($grizy$), with a $5\,\sigma$ point-source depth of $r \approx 26$. The Deep layer covers a total of 26~deg$^2$ in four fields, going roughly a magnitude fainter, while the UltraDeep layer goes almost a magnitude fainter still in two pointings of HSC (a total of 3.5 deg$^2$). Here we describe the instrument, the science goals of the survey, and the survey strategy and data processing. This paper serves as an introduction to a special issue of the Publications of the Astronomical Society of Japan, which includes a large number of technical and scientific papers describing results from the early phases of this survey.

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H. Aihara, N. Arimoto, R. Armstrong, et. al.
Fri, 21 Apr 17
69/73

Comments: 14 pages, 6 figures, 4 tables. Submitted to Publications of the Astronomical Society of Japan