F. Gasparo

A Deep Large Binocular Telescope View of the Canes Venatici I Dwarf Galaxy

We present the first deep color-magnitude diagram of the Canes Venatici I (CVn I) dwarf galaxy from observations with the wide-field Large Binocular Camera on the Large Binocular Telescope. Reaching down to the main-sequence turnoff of the oldest stars, it reveals a dichotomy in the stellar populations of CVn I: it harbors an old (10 Gyr), metal-poor ( -->[ Fe/H ] ~ ? 2.0), and spatially extended population along with a much younger (~1.4-2.0 Gyr), 0.5 dex more metal-rich, and spatially more concentrated population. These young stars are also offset by + 40−20 --> pc to the east of the galaxy center. The data suggest that this young population, which represents ~3%-5% of the stellar mass of the galaxy within its half-light radius, should be identified with the kinematically cold stellar component found in a recent spectroscopic survey. CVn I therefore follows the behavior of the other remote MW dwarf spheroidals, which all contain intermediate-age and/or young populations: a complex star formation history is possible in extremely low mass galaxies.

Optimization of Planck-LFI on-board data handling

To asses stability against 1/f noise, the Low Frequency Instrument (LFI) on-board the Planck mission will acquire data at a rate much higher than the data rate allowed by the science telemetry bandwith of 35.5 Kbps. The data are processed by an on-board pipeline, followed on-ground by a decoding and reconstruction step, to reduce the volume of data to a level compatible with the bandwidth while minimizing the loss of information. This paper illustrates the on-board processing of the scientific data used by Planck/LFI to fit the allowed data-rate, an intrinsecally lossy process which distorts the signal in a manner which depends on a set of five free parameters (Naver, r1, r2, q, ) for each of the 44 LFI detectors. The paper quantifies the level of distortion introduced by the on-board processing as a function of these parameters. It describes the method of tuning the on-board processing chain to cope with the limited bandwidth while keeping to a minimum the signal distortion. Tuning is sensitive to the statistics of the signal and has to be constantly adapted during flight. The tuning procedure is based on a optimization algorithm applied to unprocessed and uncompressed raw data provided either by simulations, pre-launch tests or data taken in flight from LFI operating in a special diagnostic acquisition mode. All the needed optimization steps are performed by an automated tool, OCA2, which simulates the on-board processing, explores the space of possible combinations of parameters, and produces a set of statistical indicators, among them: the compression rate Cr and the processing noise Q. For Planck/LFI it is required that Cr = 2.4 while, as for other systematics, Q would have to be less than 10% of rms of the instrumental white noise. An analytical model is developed that is able to extract most of the relevant information on the processing errors and the compression rate as a function of the signal statistics and the processing parameters to be tuned. This model will be of interest for the instrument data analysis to asses the level of signal distortion introduced in the data by the on-board processing. The method was applied during ground tests when the instrument was operating in conditions representative of flight. Optimized parameters were obtained and inserted in the on-board processor and the performance has been verified against the requirements with the result that the required data rate of 35.5 Kbps has been achieved while keeping the processing error at a level of 3.8% of the instrumental white noise and well below the target 10% level.

Wide and deep near-UV (360 nm) galaxy counts and the extragalactic background light with the Large Binocular Camera

Context. Deep multicolour surveys are the main tool for exploring the formation and evolution of the very faint galaxies that are beyond the spectroscopic limit of present technology. The photometric properties of these faint galaxies are usually compared with current renditions of semianalytical models to provide constraints on the detailed treatment of the fundamental physical processes involved in galaxy formation and evolution, namely the mass assembly and the star formation. Aims. Galaxy counts over large sky areas in the 360 nm near-UV band are particularly difficult to obtain given the low efficiency of near-UV instrumentation, even at 8 m class telescopes. Observing in the near-UV bands can provide a first assessment of the distribution of star formation activity in distant (up to z ∼ 3) galaxies. A relatively large instrumental field of view helps to minimize the biases caused by cosmic variance. Methods. We obtained deep images in the 360 nm U band provided by the blue channel of the Large Binocular Camera at the prime focus of the Large Binocular Telescope. Over an area of � 0.4 sq. deg., we derived the galaxy number counts down to U = 27 in the Vega system (corresponding to U = 27.86 in the AB system) at a completeness level of 30% reaching the faintest current limit for this wavelength and sky area. Results. The shape of the galaxy number counts in the U band can be described by a double power-law, the bright side being consistent with the shape of shallower surveys of comparable or greater areas. The slope bends over significantly at U > 23.5 ensuring the convergence of the contribution by star-forming galaxies to the extragalactic background light in the near-UV band to a value that is more than 70% of the most recent upper limits derived for this band. We jointly compared our near-UV and K band counts collected from the literature with a few selected hierarchical CDM models, concentrating on specific critical issues in the physical description of the galaxy formation and evolution.

The Large Binocular Camera: description and performances of the first binocular imager

Since the very beginning of 2008, the Large Binocular Telescope (LBT) is officially equipped with its first binocular instrument ready for science observations: the Large Binocular Camera (LBC). This is a double CCD imager, installed at the prime focus stations of the two 8.4m telescopes of LBT, able to obtain deep and wide field images in the whole optical spectrum from UV to NIR wavelengths. We present here the overall architecture of the instrument, a brief hardware review of the two imagers and notes how observations are carried on. At the end we report preliminary results on the performances of the instrument along with some images obtained during the first months of observations in binocular mode.

The double Prime Focus camera for the Large Binocular Telescope

The Prime Focus for the Large Binocular Telescope are a couple of Prime Focus stations each equipped with four 4kx2k CCDs and a six lenses corrector with an aspheric surface and the first lens as large as roughly 800mm in diameter. These cameras will cover almost half degree of Field of View on 8m-class telescopes with unprecedented velocity of F/1.4. The two units are optimized for the Red and Blue portions of the visible wavelength and additionally an extension to J and H bands is foreseen. An overview of the project, including the optomechanics, the cryogenics, the electronics, and the software is given along with a preliminary account of lessons learned and on how much the second unit, the Red one, the schedule of which is shifted with respect to the Blue one by several months, will take advantage from the experience gained in the Blue unit assembly and integration.

A near-ultraviolet view of the inner region of M 31 with the large binocular telescope

Aims. We present a 900 s, wide-field U image of the inner region of the Andromeda galaxy obtained during the commissioning of the blue channel of the Large Binocular Camera mounted on the prime focus of the Large Binocular Telescope. Methods. Relative photometry and absolute astrometry of individual sources in the image was obtained along with morphological parameters aimed at discriminating between stars and extended sources, e.g. globular clusters. Results. The image unveils the near-ultraviolet view of the inner ring of star formation recently discovered in the infrared by the Spitzer Space Telescope and shows in great detail the fine structure of the dust lanes associated with the galaxy inner spiral arms. The capabilities of the blue channel of the Large Binocular Camera at the Large Binocular Telescope (LBC-Blue) are probed by direct comparison with ultraviolet GALEX observations of the same region in M 31. We discovered 6 new candidate stellar clusters in this high-background region of M 31. We also recovered 62 bona-fide globulars and 62 previously known candidates from the Revised Bologna Catalogue of the M 31 globular clusters, and firmly established the extended nature of 19 of them.

The Blue Channel of the Large Binocular Camera

The Large Binocular Camera (LBC) is the optical imager that will operate at the prime foci of the Large Binocular Telescope (LBT). LBC is composed of two separated large field (27 arcmin) cameras, one optimized for the UBV bands (blue channel) and the second for the VRIZ bands (red channel). An optical corrector balances the aberrations induced by the fast (F#=1.14) parabolic 8.4 m primary mirrors of LBT, assuring that 80% of the PSF encircled energy falls within one pixel across more than the 90% of the field. The focal plane equipment consists of an array of four E2V-4290 chips (4.5K×2K) for the acquisition of science images, and by two E2V-4210 chips (2K×0.5K) placed at both lateral sides of the scientific array, dedicated to the guide and active optics systems. The blue channel was installed on LBT in late 2004, and it is in the commissioning phase now. The hardware has been fully tested and the camera software with the Telescope Control Software (TCS) will be integrated and commissioned in Summer 2005. The science validation phase is expected to begin in October 2005.