Processing and compression of noise-dominated data: application to the cosmic microwave background data on board the Planck satellite

We address the problem of encoding and compressing data dominated by noise. Information is decomposed into 'reference' sequences plus arrays containing noisy differences susceptible to being described by a known probability distribution. One can then give reliable estimates of the optimal compression rates by estimating the corresponding Shannon entropy. As a working example, this idea is applied to an idealized model of the cosmic microwave background (CMB) data on board the Planck satellite. Data reduction is a critical issue in space missions because the total information that can be downloaded to Earth is sometimes limited by telemetry allocation. Similar limitations might arise in remotely operated ground based telescopes. This download-rate limitation could reduce the amount of diagnostics sent on the stability of the instruments and, as a consequence, curb the final sensitivity of the scientific signal. Our proposal for Planck consists of taking differences of consecutive circles at a given sky pointing. To a good approximation, these differences could be made independent of the external signal, so that they are dominated by thermal (white) instrumental noise, which is simpler to model than the sky signal. Similar approaches can be found in other individual applications. Generic simulations and analytical predictions show that high compression rates,     can be obtained with minor or zero loss of sensitivity. Possible effects of digital distortion are also analysed. The proposed scheme is flexible and reliable enough to be optimized in relation to other critical aspects of the corresponding application. For Planck , this study constitutes an important step towards a more realistic modelling of the final sensitivity of the CMB temperature anisotropy maps.     

Probing the circumstellar structure of Herbig Ae/Be stars

We present Hα spectropolarimetry observations of a sample of 23 Herbig Ae/Be stars. A change in the linear polarization across Hα is detected in a large fraction of the objects, which indicates that the regions around Herbig stars are flattened (disc-like) on small scales. A second outcome of our study is that the spectropolarimetric signatures for the Ae stars differ from those of the Herbig Be stars, with characteristics changing from depolarization across Hα in the Herbig Be stars, to line polarizations in the Ae group. The frequency of depolarizations detected in the Herbig Be stars (seven out of 12) is particularly interesting as, by analogy with classical Be stars, it may be the best evidence to date that the higher-mass Herbig stars are surrounded by flattened structures. For the Herbig Ae stars, nine out of 11 show a line polarization effect that can be understood in terms of a compact Hα emission that is itself polarized by a rotating disc-like circumstellar medium. The spectropolarimetric difference between the Herbig Be and Ae stars may be the first indication that there is a transition in the Hertzsprung–Russell diagram from magnetic accretion at spectral type A to disc accretion at spectral type B. Alternatively, the interior polarized line emission apparent in the Ae stars may be masked in the Herbig Be stars owing to their higher levels of Hα emission.     

JHK standard stars for large telescopes: the UKIRT Fundamental and Extended lists

We present high-precision JHK photometry with the 3.8-m UK Infrared Telescope (UKIRT) of 82 standard stars, 28 from the widely used preliminary list known as the 'UKIRT Faint Standards', referred to here as the Fundamental List, and 54 additional stars referred to as the Extended List. The stars have 9.4< K <15.0 and all or most should be readily observable with imaging array detectors in normal operating modes on telescopes of up to 10-m aperture. Many are accessible from the southern hemisphere. Arcsec-accuracy positions (J2000, epoch ∼1998) are given, together with optical photometry and spectral types from the literature, where available, or inferred from the J − K colour. K -band finding charts are provided for stars with proper motions exceeding 0.3 arcsec yr⁻¹. We discuss some pitfalls in the construction of flat-fields for array imagers and a method to avoid them. On 30 nights between late 1994 and early 1998 the stars from the Fundamental List, which were used as standards for the whole programme, were observed on an average of 10 nights each, and those from the Extended List on an average of six nights. The average internal standard error of the mean results for the K magnitudes is 0.005 mag; for the J − H colours it is 0.003 mag for the Fundamental List stars and 0.005 mag for those of the Extended List; for H − K the average is 0.004 mag. The results are on the natural system of the IRCAM3 imager, which used a 256×256 InSb detector array with 'standard' JHK filters, behind gold-coated fore-optics and a gold- or silver-dielectric coated dichroic. We give colour transformations on to the CIT, Arcetri and LCO/Palomar NICMOS systems, and preliminary transformations on to the system defined by the new Mauna Kea Observatory near-infrared filter set.     

Prospects for spectroscopic reflected-light planet searches

High-resolution spectroscopic searches for the starlight reflected from close-in extrasolar giant planets have the capability of determining the optical albedo spectra and scattering properties of these objects. When combined with radial velocity measurements they also yield the true mass of the planet. To date, only two such planets have been targeted for reflected-light signals, yielding upper limits on the optical albedos of the planets. Here we examine the prospects for future searches of this kind. We present Monte Carlo estimates of prior probability distributions for the orbital velocity amplitudes and planet/star flux ratios of six bright stars known to harbour giant planets in orbits with periods of less than 5 d. Using these estimates, we assess the viability of these targets for future reflected-light searches using 4- and 8-m class telescopes.     

Spatial modeling of environmental vulnerability of marine finfish aquaculture using GIS-based neuro-fuzzy techniques

Combining GIS with neuro-fuzzy modeling has the advantage that expert scientific knowledge in coastal aquaculture activities can be incorporated into a geospatial model to classify areas particularly vulnerable to pollutants. Data on the physical environment and its suitability for aquaculture in an Irish fjard, which is host to a number of different aquaculture activities, were derived from a three-dimensional hydrodynamic and GIS models. Subsequent incorporation into environmental vulnerability models, based on neuro-fuzzy techniques, highlighted localities particularly vulnerable to aquaculture development.The models produced an overall classification accuracy of 85.71%, with a Kappa coefficient of agreement of 81%, and were sensitive to different input parameters. A statistical comparison between vulnerability scores and nitrogen concentrations in sediment associated with salmon cages showed good correlation.Neuro-fuzzy techniques within GIS modeling classify vulnerability of coastal regions appropriately and have a role in policy decisions for aquaculture site selection.