Reduction of time-resolved space-based CCD photometry developed for MOST Fabry Imaging data

The MOST (Microvariability & Oscillations of STars) satellite obtains ultraprecise photometry from space with high sampling rates and duty cycles. Astronomical photometry or imaging missions in low Earth orbits, like MOST, are especially sensitive to scattered light from Earthshine, and all these missions have a common need to extract target information from voluminous data cubes. They consist of upwards of hundreds of thousands of two-dimensional CCD frames (or sub-rasters) containing from hundreds to millions of pixels each, where the target information, superposed on background and instrumental effects, is contained only in a subset of pixels (Fabry Images, defocussed images, mini-spectra). We describe a novel reduction technique for such data cubes: resolving linear correlations of target and background pixel intensities. This stepwise multiple linear regression removes only those target variations which are also detected in the background. The advantage of regression analysis versus background subtraction is the appropriate scaling, taking into account that the amount of contamination may differ from pixel to pixel. The multivariate solution for all pairs of target/background pixels is minimally invasive of the raw photometry while being very effective in reducing contamination due to, e.g., stray light. The technique is tested and demonstrated with both simulated oscillation signals and real MOST photometry.Comment: 16 pages, 23 figure

Towards a novel concept of imaging spectrograph

L'obiettivo della presente tesi è di introdurre una nuova concezione di fotorivelatore astrofisico, in grado di analizzare immediatamente la composizione spettrale di immagini bidimensionali. Prima di tutto, la sua innovativa tecnologia, che si basa sull'effetto superconduttivo dell'induttanza cinetica, è confrontata con lo standard dei dispositivi semiconduttivi ad accoppiamento di carica. Essi contano sull'effetto fotoelettrico e possono solo percepire l'intensità della luce su un periodo d'esposizione, di per sé, senza elementi dispersivi o filtri monocromatici dinnanzi. In questo contesto, riporto il risultato della mia collaborazione con l'Università di Oxford, dov'è in via di sviluppo uno spettrografo a campo integrale chiamato KIDSpec, operativo nella banda elettromagnetica che va dall'ultravioletto al vicino infrarosso. Sarà il primo strumento di tal sorta ad essere costruito al di fuori degli Stati Uniti d'America. Il mio compito consisteva nell'assemblare uno spettrometro ottico destinato ad uno studio di fattibilità di questo apparato. Quindi, le carenze del sistema ottico sono discusse in breve, in vista della sua implementazione. A seguire, le indagini ottiche attraverso cui esaminai la prestazione dello spettrometro, quanto alle sue risposte in fatto di diffrazione, a varî angoli d'uscita e lunghezze d'onda in ingresso. In aggiunta, si fornisce un'eziologia dei motivi circolari causati dalla fibra ottica ivi impiegata. Infine, sono esaminate alcune possibili applicazioni astrofisiche del nuovo tipo di rivelatore: particolare attenzione è data all'emergente frontiera della caratterizzazione esoplanetaria diretta

LSST Science Book, Version 2.0

A survey that can cover the sky in optical bands over wide fields to faint magnitudes with a fast cadence will enable many of the exciting science opportunities of the next decade. The Large Synoptic Survey Telescope (LSST) will have an effective aperture of 6.7 meters and an imaging camera with field of view of 9.6 deg^2, and will be devoted to a ten-year imaging survey over 20,000 deg^2 south of +15 deg. Each pointing will be imaged 2000 times with fifteen second exposures in six broad bands from 0.35 to 1.1 microns, to a total point-source depth of r~27.5. The LSST Science Book describes the basic parameters of the LSST hardware, software, and observing plans. The book discusses educational and outreach opportunities, then goes on to describe a broad range of science that LSST will revolutionize: mapping the inner and outer Solar System, stellar populations in the Milky Way and nearby galaxies, the structure of the Milky Way disk and halo and other objects in the Local Volume, transient and variable objects both at low and high redshift, and the properties of normal and active galaxies at low and high redshift. It then turns to far-field cosmological topics, exploring properties of supernovae to z~1, strong and weak lensing, the large-scale distribution of galaxies and baryon oscillations, and how these different probes may be combined to constrain cosmological models and the physics of dark energy.Comment: 596 pages. Also available at full resolution at http://www.lsst.org/lsst/sciboo

Maximum Entropy Limit of Small-scale Magnetic Field Fluctuations in the Quiet Sun

The observed magnetic field on the solar surface is characterized by a very complex spatial and temporal behavior. Although feature-tracking algorithms have allowed us to deepen our understanding of this behavior, subjectivity plays an important role in the identification and tracking of such features. In this paper, we continue studies Gorobets, A. Y., Borrero, J. M., & Berdyugina, S. 2016, ApJL, 825, L18 of the temporal stochasticity of the magnetic field on the solar surface without relying either on the concept of magnetic features or on subjective assumptions about their identification and interaction. We propose a data analysis method to quantify fluctuations of the line-of-sight magnetic field by means of reducing the temporal field's evolution to the regular Markov process. We build a representative model of fluctuations converging to the unique stationary (equilibrium) distribution in the long time limit with maximum entropy. We obtained different rates of convergence to the equilibrium at fixed noise cutoff for two sets of data. This indicates a strong influence of the data spatial resolution and mixing-polarity fluctuations on the relaxation process. The analysis is applied to observations of magnetic fields of the relatively quiet areas around an active region carried out during the second flight of the Sunrise/IMaX and quiet Sun areas at the disk center from the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory satellite.Comment: 11 pages, 5 figures, The Astrophysical Journal Supplement Series (accepted

The 2.5 m Telescope of the Sloan Digital Sky Survey

We describe the design, construction, and performance of the Sloan Digital Sky Survey Telescope located at Apache Point Observatory. The telescope is a modified two-corrector Ritchey-Chretien design which has a 2.5-m, f/2.25 primary, a 1.08-m secondary, a Gascoigne astigmatism corrector, and one of a pair of interchangeable highly aspheric correctors near the focal focal plane, one for imaging and the other for spectroscopy. The final focal ratio is f/5. The telescope is instrumented by a wide-area, multiband CCD camera and a pair of fiber-fed double spectrographs. Novel features of the telescope include: (1) A 3 degree diameter (0.65 m) focal plane that has excellent image quality and small geometrical distortions over a wide wavelength range (3000 to 10,600 Angstroms) in the imaging mode, and good image quality combined with very small lateral and longitudinal color errors in the spectroscopic mode. The unusual requirement of very low distortion is set by the demands of time-delay-and-integrate (TDI) imaging; (2) Very high precision motion to support open loop TDI observations; and (3) A unique wind baffle/enclosure construction to maximize image quality and minimize construction costs. The telescope had first light in May 1998 and began regular survey operations in 2000.Comment: 87 pages, 27 figures. AJ (in press, April 2006

Conceptual design of the International Axion Observatory (IAXO)

The International Axion Observatory (IAXO) will be a forth generation axion helioscope. As its primary physics goal, IAXO will look for axions or axion-like particles (ALPs) originating in the Sun via the Primakoff conversion of the solar plasma photons. In terms of signal-to-noise ratio, IAXO will be about 4-5 orders of magnitude more sensitive than CAST, currently the most powerful axion helioscope, reaching sensitivity to axion-photon couplings down to a few $\times 10^{-12}$ GeV$^{-1}$ and thus probing a large fraction of the currently unexplored axion and ALP parameter space. IAXO will also be sensitive to solar axions produced by mechanisms mediated by the axion-electron coupling $g_{ae}$ with sensitivity $-$for the first time$-$ to values of $g_{ae}$ not previously excluded by astrophysics. With several other possible physics cases, IAXO has the potential to serve as a multi-purpose facility for generic axion and ALP research in the next decade. In this paper we present the conceptual design of IAXO, which follows the layout of an enhanced axion helioscope, based on a purpose-built 20m-long 8-coils toroidal superconducting magnet. All the eight 60cm-diameter magnet bores are equipped with focusing x-ray optics, able to focus the signal photons into $\sim 0.2$ cm$^2$ spots that are imaged by ultra-low-background Micromegas x-ray detectors. The magnet is built into a structure with elevation and azimuth drives that will allow for solar tracking for $\sim$12 h each day.Comment: 47 pages, submitted to JINS