Alejandro Oscoz

FastCam: a new lucky imaging instrument for medium-sized telescopes

FastCam is an instrument jointly developed by the Spanish Instituto de Astrofísica de Canarias and the Universidad Politécnica de Cartagena designed to obtain high spatial resolution images in the optical wavelength range from ground-based telescopes. The instrument consists of a very low noise and very fast readout speed EMCCD camera capable of reaching the diffraction limit of medium-sized telescopes from 500 to 850 nm. FastCam incorporates a FPGAs-based device to save and evaluate those images minimally disturbed by atmospheric turbulence in real time. The undisturbed images represent a small fraction of the observations. Therefore, a special software package has been developed to extract, from cubes of tens of thousands of images, those with better quality than a given level. This is done in parallel with the data acquisition at the telescope. After the first tests in the laboratory, FastCam has been successfully tested in three telescopes: the 1.52-meter TCS (Teide Observatory), the 2.5-meter NOT, and the 4.2-meter WHT (Roque de los Muchachos Observatory). The theoretical diffraction limit of each telescope has been reached in the I band (850 nm) -0.15, 0.08 and 0.05 arcsec, respectively-, and similar resolutions have been also obtained in the V and R bands. Future work will include the development of a new instrument for the 10.4-meter GTC telescope on La Palma.

Time Delay of QSO 0957+561 and Cosmological Implications

We obtain the time delay between the arrival time of the A and B images of the QSO 0957+561. The results of applying two different methods (the discrete cross-correlation function and the dispersion estimation technique) to the observed light curves of the A and B images are presented. The adopted value (time delay) is of ΔτBA = 424 ± 3 days (1 σ). We have used this time delay as well as a recent measurement of the one-dimensional velocity dispersion of the main lensing galaxy (σgal) to estimate H0. Two H0 = H0(ΔτBA, σgal) relations based on different pictures of the lens galaxy, lead to H0 = 64+ 14−15 km s-1 Mpc-1 (2 σ) (softened power-law sphere) and H0 = 66+ 15−14 km s-1 Mpc-1 (2 σ) (King profile plus a point-mass at the center).

BVRI Photometry of QSO 0957+561A, B: Observations, New Reduction Method, and Time Delay

CCD observations of the gravitational lens system Q0957+561A, B in the BVRI bands are presented in this paper. The observations, taken with the 82 cm IAC-80 telescope at Teide Observatory, Spain, were made from the beginning of 1996 February to 1998 July, as part of an ongoing lens-monitoring program. Accurate photometry was obtained by simultaneously fitting a stellar two-dimensional profile on each component by means of DAOPHOT software. This alternative method is equal to and even improves on the results obtained with previous techniques. The final data set is characterized by its high degree of homogeneity, since it was obtained using the same telescope and instrumentation during a period of almost 3 yr. The resulting delay, obtained with a new method, the δ2 test, is of 425 ± 4 days, slightly higher than the value previously accepted (417 days), but concordant with the results obtained by other researchers.

The Influence of Microlensing on Time Delay Determinations in Double-imaged Quasars

The lag associated with the main peak of the cross-correlation function of the two light curves arriving from a double-imaged quasar is usually identified with the time delay between the components. However, short-timescale microlensing events can independently modify the light curve of each component, and when strong microlensing is present, the features of the cross-correlation function depend on both amplitude and shape of the microlensing events. This fact prevents a direct interpretation of the lag associated with the main peak as the true time delay. We present a new analysis of the light curves cross-correlation function including short-timescale microlensing. We discuss its application to the 1995/1996 optical photometry of Q0957+561, and determine the trend of a possible microlensing event taking place from JD 2,450,150 to 2,450,200.

Optical Photometry of Quasar 0957+561A, B

Observations of the gravitational lens system 0957+561A, B in the R band are presented in this Letter. The observations, taken with the 82 cm IAC-80 telescope, at Teide Observatory, Spain, were made from the beginning of 1996 February to June, as part of an on-going lens monitoring program to obtain the time delay between the two components of the system. By comparing our data with those previously published by Kundic et al., we infer that a large delay (>500 days) is inconsistent with both data sets.

AOLI: Adaptive Optics Lucky Imager: diffraction limited imaging in the visible on large ground-based telescopes

The highest resolution images ever taken in the visible were obtained by combining Lucky Imaging and low order adaptive optics. This paper describes a new instrument to be deployed on the WHT 4.2m and GTC 10.4 m telescopes on La Palma, with particular emphasis on the optical design and the expected system performance. A new design of low order wavefront sensor using photon counting CCD detectors and multi-plane curvature wavefront sensor will allow dramatically fainter reference stars to be used, allowing virtually full sky coverage with a natural guide star. This paper also describes a significant improvements in the efficiency of Lucky Imaging, important advances in wavefront reconstruction with curvature sensors and the results of simulations and sensitivity limits. With a 2 x 2 array of 1024 x 1024 photon counting EMCCDs, AOLI is likely to be the first of the new class of high sensitivity, near diffraction limited imaging systems giving higher resolution in the visible from the ground than hitherto been possible from space.

The AOLI low-order non-linear curvature wavefront sensor: a method for high sensitivity wavefront reconstruction

The Adaptive Optics Lucky Imager (AOLI) is a new instrument under development to demonstrate near diffraction limited imaging in the visible on large ground-based telescopes. We present the adaptive optics system being designed for the instrument comprising a large stroke deformable mirror, fixed component non-linear curvature wavefront sensor and photon-counting EMCCD detectors. We describe the optical design of the wavefront sensor where two photoncounting CCDs provide a total of four reference images. Simulations of the optical characteristics of the system are discussed, with their relevance to low and high order AO systems. The development and optimisation of high-speed wavefront reconstruction algorithms are presented. Finally we discuss the results of simulations to demonstrate the sensitivity of the system.

High-resolution optical imaging of the core of the globular cluster M15 with FastCam

We present high-resolution I-band imaging of the core of the globular cluster M15 obtained at the 2.5-m Nordic Optical Telescope with FastCam, a low readout noise L3CCD-based instrument. Short exposure times (30ms) were used to record 200 000 images (512×512 pixels each) over a period of 2 h and 43 min. The lucky imaging technique was then applied to generate a final image of the cluster centre with full width at half-maximum ∼0.1 arcsec and 13 × 13 arcsec^2 field of view. We obtained a catalogue of objects in this region with a limiting magnitude of I = 19.5. I-band photometry and astrometry are reported for 1181 stars. This is the deepest I-band observation of the M15 core at this spatial resolution. Simulations show that crowding is limiting the completeness of the catalogue. At shorter wavelengths, a similar number of objects have been reported using Hubble Space Telescope (HST)/Wide Field Planetary Camera observations of the same field. The cross-match with the available HST catalogues allowed us to produce colour–magnitude diagrams where we identify new blue straggler star candidates and previously known stars of this class.

Laboratory and telescope demonstration of the TP3-WFS for the adaptive optics segment of AOLI

This work was supported by the Spanish Ministry of Economy under the projects AYA2011-29024, ESP2014-56869-C2-2-P, ESP2015-69020-C2-2-R and DPI2015-66458-C2-2-R, by project 15345/PI/10 from the Fundacion Seneca, by the Spanish Ministry of Education under the grant FPU12/05573, by project ST/K002368/1 from the Science and Technology Facilities Council and by ERDF funds from the European Commission. The results presented in this paper are based on observations made with the William Herschel Telescope operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias. Special thanks go to Lara Monteagudo and Marcos Pellejero for their timely contributions.

Long-term Monitoring, Time Delay, and Microlensing in the Gravitational Lens System Q0142-100

We present 12 yr of monitoring of the gravitational lens Q0142-100 from the Teide Observatory. The data, taken from 1999 to 2010, comprise 105 observing nights with the IAC80 Telescope. The application of the δ{sup 2} method to the dataset leads to a value for the time delay between both components of the system of 72 ± 22 days (68% confidence level), consistent within uncertainties with the most recent results. With this value in mind a possible microlensing event is detected in Q0142-100.