119327970
A MERLIN Observation of PSR B1951+32 and Its Associated Plerion
In an investigative 16 hr L-band observation using the MERLIN radio interferometric array, we have resolved both the pulsar PSR B1951+32 and the structure within the flat spectral radio continuum region, believed to be the synchrotron nebula associated with the interaction of the pulsar and its "host" supernova remnant CTB 80. The extended structure we see, significant at ~4.5 σ, is of dimensions 25 × 075 and suggests a sharp bow-shaped arc of shocked emission, which is correlated with a similar structure observed in lower resolution radio maps and X-ray images. Using this MERLIN data as a new astrometric reference for other multiwavelength data, we can place the pulsar at one edge of the HST reported optical synchrotron knot, ruling out previously suggested optical counterparts and allowing an elementary analysis of the optical synchrotron emission that appears to trail the pulsar. The latter is possibly a consequence of pulsar wind replenishment, and we suggest that the knot is a result of magnetohydrodynamic (MHD) instabilities. These being so, it suggests a dynamical nature to the optical knot, which will require high-resolution optical observations to confirm.
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.
15893587
PSR B1951+32 and PSR J0537-6910 - where are the optical counterparts?
There remain several definitive -ray pulsars that are as yet undetected in the optical regime. A clas- sic case is the pulsar PSR B1951+32, associated with the complex CTB 80 SNR. Previous ground based high speed 2-d optical studies have ruled out candidates to mV � 24. Hester (2000) has reported an analysis of archival HST/WFPC2 observations of the CTB 80 complex which suggest a compact synchrotron nebula coincident with the pulsar's radio position. Performing a similar analysis, we have identified a possible optical counterpart within this synchrotron nebula at mV � 25.5, and another optical counterpart candidate nearby at mV �24.2. PSR J0537-6910 is a young (canonical age � 5000 years), 16ms pulsar in the LMC. We report a search for op- tical pulsations from the region around the X-ray position. We see no obvious candidate exhibiting optical pulsations at the X-ray period, with a 3� upper limit of mV �23.6. We have also examined recent Chandra results (Wang et al. 2001) and show that their X-ray-Optical astrometry is in error by about 7".
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.
2326076
Detection of new optical counterpart candidates to PSR B1951+32 with HST/WFPC2
There remain several definitive-ray pulsars that are as yet undetected in the optical regime. A classic case is the pulsar PSR B1951+32, associated with the complex CTB 80 SNR. Previous ground based high speed 2-d optical studies have ruled out candidates to mV 24. Hester (2000a) has reported an analysis of archival HST/WFPC2 observations of the CTB 80 complex which suggest a compact synchrotron nebula coincident with the pulsar's radio position. Performing a similar analysis, we have identified a possible optical counterpart within this synchrotron nebula at mV 25:5 26, and another optical counterpart candidate nearby at mV 24:5. We assess the reality of these counterpart candidates in the context of existing models of pulsar emission.
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.
23277998
Planck intermediate results. XIX. An overview of the polarized thermal emission from Galactic dust
This paper presents an overview of the polarized sky as seen by Planck HFI at 353 GHz, which is the most sensitive Planck channel for dust polarization. We construct and analyse maps of dust polarization fraction and polarization angle at 1° resolution, taking into account noise bias and possible systematic effects. The sensitivity of the Planck HFI polarization measurements allows for the first time a mapping of Galactic dust polarized emission on large scales, including low column density regions. We find that the maximum observed dust polarization fraction is high (p_(max) = 19.8%), in particular in some regions of moderate hydrogen column density (N_H < 2 × 10^(21) cm^(-2)). The polarization fraction displays a large scatter at N_H below a few 10^(21) cm^(-2). There is a general decrease in the dust polarization fraction with increasing column density above N_H ≃ 1 × 10^(21) cm-2 and in particular a sharp drop above N_H ≃ 1.5 × 10^(22) cm^(-2). We characterize the spatial structure of the polarization angle using the angle dispersion function. We find that the polarization angle is ordered over extended areas of several square degrees, separated by filamentary structures of high angle dispersion function. These appear as interfaces where the sky projection of the magnetic field changes abruptly without variations in the column density. The polarization fraction is found to be anti-correlated with the dispersion of polarization angles. These results suggest that, at the resolution of 1°, depolarization is due mainly to fluctuations in the magnetic field orientation along the line of sight, rather than to the loss of grain alignment in shielded regions. We also compare the polarization of thermal dust emission with that of synchrotron measured with Planck, low-frequency radio data, and Faraday rotation measurements toward extragalactic sources. These components bear resemblance along the Galactic plane and in some regions such as the Fan and North Polar Spur regions. The poor match observed in other regions shows, however, that dust, cosmic-ray electrons, and thermal electrons generally sample different parts of the line of sight.
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.
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.
28387065
Planck pre-launch status: Calibration of the Low Frequency Instrument flight model radiometers
The Low Frequency Instrument (LFI) on-board the ESA Planck satellite carries eleven radiometer subsystems, called radiometer chain assemblies (RCAs), each composed of a pair of pseudo-correlation receivers. We describe the on-ground calibration campaign performed to qualify the flight model RCAs and to measure their pre-launch performances. Each RCA was calibrated in a dedicated flight-like cryogenic environment with the radiometer front-end cooled to 20 K and the back-end at 300 K, and with an external input load cooled to 4 K. A matched load simulating a blackbody at different temperatures was placed in front of the sky horn to derive basic radiometer properties such as noise temperature, gain, and noise performance, e.g. 1/f noise. The spectral response of each detector was measured as was their susceptibility to thermal variation. All eleven LFI RCAs were calibrated. Instrumental parameters measured in these tests, such as noise temperature, bandwidth, radiometer isolation, and linearity, provide essential inputs to the Planck-LFI data analysis.
118459459
Planck-LFI flight model feed horns
The Low Frequency Instrument is optically interfaced with the ESA Planck telescope through 11 corrugated feed horns each connected to the Radiometer Chain Assembly (RCA). This paper describes the design, the manufacturing and the testing of the flight model feed horns. They have been designed to optimize the LFI optical interfaces taking into account the tight mechanical requirements imposed by the Planck focal plane layout. All the eleven units have been successfully tested and integrated with the Ortho Mode transducers.