Alain Castera

SNIFS: a wideband integral field spectrograph with microlens arrays

SNIFS is an integral field spectrograph devoted to the observation of supernovae. This instrument is today in the manufacturing phase and should be able to observe supernovae at the end of this year (2003) on the 2.2m telescope of University Hawaii. The concept of SNIFS is to split the 6” x 6” field of view into 225 samples of 0.4” x 0.4” through a microlens array. Then the spectral decomposition of each sample is imaged on a 2k x 4k CCD. In order to cover all the large spectral range with a high resolution, the spectrograph is composed of two modules, one for the blue wavelengths (320 nm to 560nm)with a resolution around 1000 at 430 nm and one for the red wavelengths (520 nm to 1 µm) with a resolution around 1300 at 760 nm. First we will present the optical design and detail the function of each optical component. Then the mechanical design will be shown with some maps of the structure. Finally the first pictures taken during the alignments will be displayed.

The Drift Chambers Of The Nomad Experiment

Abstract We present a detailed description of the drift chambers used as an active target and a tracking device in the NOMAD experiment at CERN. The main characteristics of these chambers are a large area (3×3 m 2 ) , a self-supporting structure made of light composite materials and a low cost. A spatial resolution of 150 μm has been achieved with a single hit efficiency of 97%. 29.40.Cs; 29.40.Gx; 07.05.Kf; 13.15.+g Drift chambers; Spatial resolution; Tracking; Neutrino oscillations

The Nearby Supernova Factory

The Nearby Supernova Factory (SNfactory) is an ambitious project to find and study in detail approximately 300 nearby Type Ia supernovae (SNe Ia) at redshifts 0.03 < z < 0.08. This program will provide an exceptional data set of well-studied SNe in the nearby smooth Hubble flow that can be used as calibration for the current and future programs designed to use SNe to measure the cosmological parameters. The first key ingredient for this program is a reliable supply of Hubble-flow SNe systematically discovered in unprecedented numbers using the same techniques as those used in distant SNe searches. In 2002, 35 SNe were found using our test-bed pipeline for automated SN search and discovery. The pipeline uses images from the asteroid search conducted by the Near Earth Asteroid Tracking group at JPL. Improvements in our subtraction techniques and analysis have allowed us to increase our effective SN discovery rate to {approx}12 SNe/month in 2003.

Impact of noise covariance and nonlinearities in NIR H2RG detectors

We characterize at pixel level a NIR H2RG detector read with SIDECAR ASIC, similar to the detectors used in Euclids Near IR Spectrometer Photometer (NISP). We derive the full covariance matrix formulae, extending the results from previous publications, and compare them to data and simulations for NISP baseline operating modes. The nonlinear response of the detector is measured and high precision maps are derived for in-flight or on-ground correction. High precision maps of the conversion gain are also determined using the Photon Transfer Curve technique.

Impact of common modes correlations and time sampling on the total noise of a H2RG near-IR detector

We present the readout noise reduction methods and the 1/f noise response of an 2K × 2K HgCdTe detector similar to the detectors that will be used in the Near Infrared Spectrometer Photometer - one of the instruments of the future ESA mission named Euclid. Various algorithms of common modes subtraction are defined and compared. We show that the readout noise can be lowered by 60% using properly the references provided within the array. A predictive model of the 1/f noise with a given frequency power spectrum is defined and compared to data taken in a wide range of sampling frequencies. In view of this model the definition of ad-hoc readout noises for different sampling can be avoided.

Low noise flux estimate and data quality control monitoring in EUCLID-NISP cosmological survey

Euclid mission is designed to understand the dark sector of the universe. Precise redshift measurements are provided by H2RG detectors. We propose an unbiased method of fitting the flux with Poisson distributed and correlated data, which has an analytic solution and provides a reliable quality factor - fundamental features to ensure the goals of the mission. We compare our method to other techniques of signal estimation and illustrate the anomaly detection on the flight-like detectors. Although our discussion is focused on Euclid NISP instrument, much of what is discussed will be of interest to any mission using similar near-infrared sensors.

Comparison of hybrid and SIDECAR ASIC measurements

The readout noise of a H2RG HgCdTe NIR detector from Teledyne is measured at a temperature T=100K. In a previous work, we have analysed the evolution of the readout noise as a function of the number of reads in terms of the frequency power spectrum of the noise with our in-house hybrid readout electronics. The new measurements with the SIDECAR ASIC provided by Teledyne Imaging Sensors are compared to the previous ones. The noise power spectrum found can be used in a wide range of timing conditions and allows to predict the 1/f effects.

Extraction of the frequency spectrum of the noise of a HAWAII2RG NIR detector and impact on low-flux measurements

The readout noise of a H2RG HgCdTe NIR detector from Teledyne is measured at a temperature T=110K. It is shown that a Fowler mode with n = 240 allows to reach a noise of 2.63e (single read). A description of the power spectrum in terms of 3 parameters reproduces the variation of the noise as a function the number of Fowler samples, as well as its dependence on the periodicity of the sampling. The variance of the noise decreases with frequency with an effective power of 0.62 in our measurement domain. The behaviour of the detector under different experimental conditions can then be predicted.