16393661
A Photometric Method for estimating CNO Abundances in Globular Clusters
Stromgren indices v and b are combined with broad-band index I, and a new index p, the short wavelength half of the v band, to estimate CN 4215A molecular absorption in a sample of stars in M22. The results have been used to estimate carbon and nitrogen abundances and suggest groups of stars within this cluster, each with a characteristic nitrogen abundance, but with a range of carbon abundances. The results suggest the possibility of stars consisting of material which has undergone CNO recycling two or three times. The method can be subsequently used for other globular clusters.
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.
119243801
Dynamic validation of the Planck-LFI thermal model
The Low Frequency Instrument (LFI) is an array of cryogenically cooled radiometers on board the Planck satellite, designed to measure the temperature and polarization anisotropies of the cosmic microwave backgrond (CMB) at 30, 44 and 70 GHz. The thermal requirements of the LFI, and in particular the stringent limits to acceptable thermal fluctuations in the 20 K focal plane, are a critical element to achieve the instrument scientific performance. Thermal tests were carried out as part of the on-ground calibration campaign at various stages of instrument integration. In this paper we describe the results and analysis of the tests on the LFI flight model (FM) performed at Thales Laboratories in Milan (Italy) during 2006, with the purpose of experimentally sampling the thermal transfer functions and consequently validating the numerical thermal model describing the dynamic response of the LFI focal plane. This model has been used extensively to assess the ability of LFI to achieve its scientific goals: its validation is therefore extremely important in the context of the Planck mission. Our analysis shows that the measured thermal properties of the instrument show a thermal damping level better than predicted, therefore further reducing the expected systematic effect induced in the LFI maps. We then propose an explanation of the increased damping in terms of non-ideal thermal contacts.
53706770
Design, development and verification of the 30 and 44 GHz front-end modules for the Planck Low Frequency Instrument
We give a description of the design, construction and testing of the 30 and 44 GHz Front End Modules (FEMs) for the Low Frequency Instrument (LFI) of the Planck mission to be launched in 2009. The scientific requirements of the mission determine the performance parameters to be met by the FEMs, including their linear polarization characteristics. The FEM design is that of a differential pseudo-correlation radiometer in which the signal from the sky is compared with a 4-K blackbody load. The Low Noise Amplifier (LNA) at the heart of the FEM is based on indium phosphide High Electron Mobility Transistors (HEMTs). The radiometer incorporates a novel phase-switch design which gives excellent amplitude and phase match across the band. The noise temperature requirements are met within the measurement errors at the two frequencies. For the most sensitive LNAs, the noise temperature at the band centre is 3 and 5 times the quantum limit at 30 and 44 GHz respectively. For some of the FEMs, the noise temperature is still falling as the ambient temperature is reduced to 20 K. Stability tests of the FEMs, including a measurement of the 1/f knee frequency, also meet mission requirements. The 30 and 44 GHz FEMs have met or bettered the mission requirements in all critical aspects. The most sensitive LNAs have reached new limits of noise temperature for HEMTs at their band centres. The FEMs have well-defined linear polarization characteristcs.
118335433
The Planck-LFI Radiometer Electronics Box Assembly
The Radiometer Electronics Box Assembly (REBA) is the control and data processing on board computer of the Low Frequency Instrument (LFI) of the Planck mission (ESA). The REBA was designed and built incorporating state of the art processors, communication interfaces and real time operating system software in order to meet the scientific performance of the LFI. We present a technical summary of the REBA, including a physical, functional, electrical, mechanical and thermal description. Aspects of the design and development, the assembly, the integration and the verification of the equipment are provided. A brief description of the LFI on board software is given including the Low-Level Software and the main functionalities and architecture of the Application Software. The compressor module, which has been developed as an independent product, later integrated in the application, is also described in this paper. Two identical engineering models EM and AVM, the engineering qualification model EQM, the flight model FM and flight spare have been manufactured and tested. Low-level and Application software have been developed. Verification activities demonstrated that the REBA hardware and software fulfil all the specifications and perform as required for flight operation.
43350860
Planck intermediate results. XIV. Dust emission at millimetre wavelengths in the Galactic plane
We use Planck HFI data combined with ancillary radio data to study the emissivity index of the interstellar dust emission in the frequency range 100–353 GHz, or 3–0.8 mm, in the Galactic plane. We analyse the region l = 20 ◦ –44 ◦ and |b |≤ 4 ◦ where the free-free emission can be estimated from radio recombination line data. We fit the spectra at each sky pixel with a modified blackbody model and two opacity spectral indices, βmm and βFIR, below and above 353 GHz, respectively. We find that βmm is smaller than βFIR, and we detect a correlation between this low frequency power-law index and the dust optical depth at 353 GHz, τ353. The opacity spectral index βmm increases from about 1.54 in the more diffuse regions of the Galactic disk, |b| = 3 ◦ –4 ◦ and τ353 ∼ 5 × 10 −5 , to about 1.66 in the densest regions with an optical depth of more than one order of magnitude higher. We associate this correlation with an evolution of the dust emissivity related to the fraction of molecular gas along the line of sight. This translates into βmm ∼ 1.54 for a medium that is mostly atomic and βmm ∼ 1.66 when the medium is dominated by molecular gas. We find that both the two-level system model and magnetic dipole emission by ferromagnetic particles can explain the results. These results improve our understanding of the physics of interstellar dust and lead towards a complete model of the dust spectrum of the Milky Way from far-infrared to millimetre wavelengths.
15013491
A SEARCH FOR THE OPTICAL COUNTERPART OF PSR B1951+32 IN THE SUPERNOVA REMNANT CTB 80
Using time-resolved two-dimensional aperture pho- tometry we have put upper limits on the pulsed emission from two proposed optical counterparts for PSR B1951+32. Our pulsed upper limits of mv;pulsed > 23:3, mb;pulsed > 24:4, for the first candidate and mv;pulsed > 23:6, mb;pulsed > 24:3 for the second, make it unlikely that either of these is, in fact, the pulsar. We discuss three further candidates, but also reject these on the basis of timing results. A search of a 5: 5 5: 00 5 area centred close to these stars failed to find any significant pulsations at the reported pulsar period.