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We present the variability processing and analysis that is foreseen for the Gaia mission within Coordination Unit 7 (CU7) of the Gaia Data Processing and Analysis Consortium (DPAC). A top level description of the tasks is given.
The measurement of the positions, distances, motions and luminosities of stars represents the foundations of modern astronomical knowledge. Launched at the end of the eighties, the ESA Hipparcos satellite was the first space mission dedicated to such measurements. Hipparcos improved position accuracies by a factor of 100 compared to typical ground-based results and provided astrometric and photometric multi-epoch observations of 118,000 stars over the entire sky. The impact of Hipparcos on astrophysics has been extremely valuable and diverse. Building on this important European success, the ESA Gaia cornerstone mission promises an even more impressive advance. Compared to Hipparcos, it will bring a gain of a factor 50 to 100 in position accuracy and of a factor of 10,000 in star number, collecting photometric, spectrophotometric and spectroscopic data for one billion celestial objects. During its 5-year flight, Gaia will measure objects repeatedly, up to a few hundred times, providing an unprecedented database to study the variability of all types of celestial objects. Gaia will bring outstanding contributions, directly or indirectly, to most fields of research in astrophysics, such as the study of our Galaxy and of its stellar constituents, and the search for planets outside the solar system.
Two upcoming large scale surveys, the ESA Gaia and LSST projects, will bring a new era in astronomy. The number of binary systems that will be observed and detected by these projects is enormous, estimations range from millions for Gaia to several tens of millions for LSST. We review some tools that should be developed and also what can be gained from these missions on the subject of binaries and exoplanets from the astrometry, photometry, radial velocity and their alert systems.
This study examined the inter-relationships between molluscs, heavy metal concentrations and trematode parasites. Littorina littorea (Mollusca: Gastropoda) were sampled seasonally from two sites in a tidal lagoon. Site A was close to the inflow of a polluted stream whilst site B was at the opposite end of the lagoon. The samples were analysed for lead, iron, copper and nickel. Metal concentrations in L. littorea varied with site, season and parasite infection, and exceeded comparative non-polluted concentrations for all metals in some samples. Parasitized periwinkles consistently had significantly lower levels of iron, copper and nickel than uninfected periwinkles.
We describe preliminary results from our study of multi-scale structures in Centaurus A (NGC 5128) obtained using the Chandra X-ray Observatory HRC-I observations. The high-angular resolution Chandra images reveal X-ray multi-scale structures in this object with unprecedented detail and clarity. The region surrounding the Cen A nucleus, believed to be associated with a supermassive black hole, shows structures on arcsecond scales clearly resolved from the central source.
The HIPPARCOS satellite observes 118,000 stars from a predefined list. Some 10% of these are known doubles or multiples, and another 2—3% may ultimately be found to be non-single with separations above 0″.l and magnitude–differences below 4–5. This paper describes briefly the special reduction methods used by NDAC (Northern Data Analysis Consortium) for treating these non-singles. A key feature is the use of the main reduction results to calibrate and collect the data for individual doubles in ‘case history files’. This enables a global solution of both absolute and relative parameters for a double to be carried out in a single step. Using provisional data tapes covering small parts of a 14-month interval, tests have been made of major parts of the double star reductions. These early results are compared with independent HIPPARCOS data and with ground–based speckle interferometry.
The Hipparcos satellite has a predefined observing program given by an Input Catalogue with 118 000 entries. This includes some 10 000 members of known double or multiple systems (with separations above 0.1 arcsec and magnitude-differences below 4-5), which are observably non-single and thus need a more complex reduction procedure. Also, a similar number of hitherto unknown doubles showing deviations from a single-star observation model will be included in the double-star reductions. A key feature in the NDAC reductions is the use of the main reduction results to calibrate and collect the data for individual doubles in ‘Case History Files’. This enables a global solution of both absolute and relative parameters for a double to be carried out later in a single solution. Using provisional data tapes covering small parts of a 14-month interval, tests have been made of major parts of the double star reductions. Comparisons with the main reduction results for single stars indicate that remaining calibration errors are below the 10 milliarcsec level. For known doubles, the solutions are good relative to the Input Catalogue at the expected 0.3 arcsec level, and for a few tens of systems observed with the star-mapper, the agreement is at the 0.05 arcsec level. A few hundred doubles not flagged in the Input Catalogue have also been detected and had their parameters provisionally determined. A detailed paper describing these methods and results has been accepted by Astronomy & Astrophysics.
The process of satellite attitude reconstruction carried out at RGO enables the assumed positions of the stars taken from INCA to be improved. The attitude reconstruction is determined from polynomial fits to the residuals between the observed StarMapper positions and those taken from INCA. The degree of the polynomial is such that smoothing occurs over a typical arc length of about 10°. The positions from different passes are combined, giving a typical internal accuracy for a star of 0"·02 in RA and Dec. The observations discussed here were accumulated from provisional magnetic tapes received from Darmstadt before the end of 1990.
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