15947685
Parallel Astronomical Data Processing with Python: Recipes for multicore machines
Abstract High performance computing has been used in various fields of astrophysical research. But most of it is implemented on massively parallel systems (supercomputers) or graphical processing unit clusters. With the advent of multicore processors in the last decade, many serial software codes have been re-implemented in parallel mode to utilize the full potential of these processors. In this paper, we propose parallel processing recipes for multicore machines for astronomical data processing. The target audience is astronomers who use Python as their preferred scripting language and who may be using PyRAF/IRAF for data processing. Three problems of varied complexity were benchmarked on three different types of multicore processors to demonstrate the benefits, in terms of execution time, of parallelizing data processing tasks. The native multiprocessing module available in Python makes it a relatively trivial task to implement the parallel code. We have also compared the three multiprocessing approaches—Pool/Map, Process/Queue and Parallel Python. Our test codes are freely available and can be downloaded from our website.
117023123
A new survey of variability in the core of M15 with TRIFFID-2
A two-week campaign of high-resolution imaging of the centre of M15 using the tip/tilt correcting TRIFFID-2 camera, followed by analysis with ISIS (image matching & subtraction software), has produced the most sensitive survey to date of variable stars in the central ~1x1 arcmin^2 - a total of 48 were detected -, and constrains the size of the dwarf nova population.
118356163
Advanced modelling of the Planck-LFI radiometers
The Low Frequency Instrument (LFI) is a radiometer array covering the 30-70 GHz spectral range on-board the ESA Planck satellite, launched on May 14th, 2009 to observe the cosmic microwave background (CMB) with unprecedented precision. In this paper we describe the development and validation of a software model of the LFI pseudo-correlation receivers which enables to reproduce and predict all the main system parameters of interest as measured at each of the 44 LFI detectors. These include system total gain, noise temperature, band-pass response, non-linear response. The LFI Advanced RF Model (LARFM) has been constructed by using commercial software tools and data of each radiometer component as measured at single unit level. The LARFM has been successfully used to reproduce the LFI behavior observed during the LFI ground-test campaign. The model is an essential element in the database of LFI data processing center and will be available for any detailed study of radiometer behaviour during the survey.
13718662
Planck 2013 results. XXVI. Background geometry and topology of the Universe
Maps of cosmic microwave background (CMB) temperature and polarization from the 2015 release of Planck data provide the highestquality full-sky view of the surface of last scattering available to date. This enables us to detect possible departures from a globally isotropic cosmology. We present the first searches using CMB polarization for correlations induced by a possible non-trivial topology with a fundamental domain that intersects, or nearly intersects, the last-scattering surface (at comoving distance χrec), both via a direct scan for matched circular patterns at the intersections and by an optimal likelihood calculation for specific topologies. We specialize to flat spaces with cubic toroidal (T3) and slab (T1) topologies, finding that explicit searches for the latter are sensitive to other topologies with antipodal symmetry. These searches yield no detection of a compact topology with a scale below the diameter of the last-scattering surface. The limits on the radius ℛi of the largest sphere inscribed in the fundamental domain (at log-likelihood ratio Δlnℒ > −5 relative to a simply-connected flat Planck best-fit model) are: ℛi > 0.97 χrec for the T3 cubic torus; and ℛi > 0.56 χrec for the T1 slab. The limit for the T3 cubic torus from the matched-circles search is numerically equivalent, ℛi > 0.97 χrec at 99% confidence level from polarization data alone. We also perform a Bayesian search for an anisotropic global Bianchi VIIh geometry. In the non-physical setting, where the Bianchi cosmology is decoupled from the standard cosmology, Planck temperature data favour the inclusion of a Bianchi component with a Bayes factor of at least 2.3 units of log-evidence. However, the cosmological parameters that generate this pattern are in strong disagreement with those found from CMB anisotropy data alone. Fitting the induced polarization pattern for this model to the Planck data requires an amplitude of −0.10 ± 0.04 compared to the value of + 1 if the model were to be correct. In the physically motivated setting, where the Bianchi parameters are coupled and fitted simultaneously with the standard cosmological parameters, we find no evidence for a Bianchi VIIh cosmology and constrain the vorticity of such models to (ω/H)0 < 7.6 × 10-10 (95% CL).
41221098
Planck intermediate results. XII: Diffuse Galactic components in the Gould Belt system
We perform an analysis of the diffuse low-frequency Galactic components in the southern
 part of the Gould Belt system (130° ≤ l ≤ 230° and
 −50° ≤ b ≤ −10°). Strong ultra-violet flux
 coming from the Gould Belt super-association is responsible for bright diffuse foregrounds
 that we observe from our position inside the system and that can help us improve our
 knowledge of the Galactic emission. Free-free emission and anomalous microwave emission
 (AME) are the dominant components at low frequencies
 (ν < 40 GHz), while synchrotron emission is
 very smooth and faint. We separated diffuse free-free emission and AME from synchrotron
 emission and thermal dust emission by using Planck data, complemented by
 ancillary data, using the correlated component analysis (CCA) component-separation method
 and we compared our results with the results of cross-correlation of foreground templates
 with the frequency maps. We estimated the electron temperature
 Te from Hα and free-free emission using two
 methods (temperature-temperature plot and cross-correlation) and obtained
 Te ranging from 3100 to 5200K for an effective fraction of
 absorbing dust along the line of sight of 30% (fd = 0.3). We
 estimated the frequency spectrum of the diffuse AME and recovered a peak frequency (in
 flux density units) of 25.5 ± 1.5 GHz. We verified the reliability of this result with
 realistic simulations that include biases in the spectral model for the AME and in the
 free-free template. By combining physical models for vibrational and rotational dust
 emission and adding the constraints from the thermal dust spectrum from
 Planck and IRAS, we are able to present a good description of the AME
 frequency spectrum for plausible values of the local density and radiation field.
119158588
Planck-LFI radiometers' spectral response
The Low Frequency Instrument (LFI) is an array of pseudo-correlation radiometers on board the Planck satellite, the ESA mission dedicated to precision measurements of the Cosmic Microwave Background. The LFI covers three bands centred at 30, 44 and 70 GHz, with a goal bandwidth of 20% of the central frequency. The characterization of the broadband frequency response of each radiometer is necessary to understand and correct for systematic effects, particularly those related to foreground residuals and polarization measurements. In this paper we present the measured band shape of all the LFI channels and discuss the methods adopted for their estimation. The spectral characterization of each radiometer was obtained by combining the measured spectral response of individual units through a dedicated RF model of the LFI receiver scheme. As a consistency check, we also attempted end-to-end spectral measurements of the integrated radiometer chain in a cryogenic chamber. However, due to systematic effects in the measurement setup, only qualitative results were obtained from these tests. The measured LFI bandpasses exhibit a moderate level of ripple, compatible with the instrument scientific requirements.
116935590
The Planck Telescope
In this paper we present an overview of the Telescope designed for ESA’s mission dedicated to map the Cosmic Microwave Background Anisotropies and Polarization. Two instrument, LFI and HFI, operate in an overall frequency range between 25 and 900 GHz and share the focal region of the 1.5 meter optimized aplanatic telescope. The optimization techniques adopted for the optical design and the telescope characteristic are reported and discussed.