MAORY is one of the four instruments for the E-ELT approved for construction. It is an adaptive optics module offering two compensation modes: multi-conjugate and single-conjugate adaptive optics. The project has recently entered its phase B. A system-level overview of the current status of the project is given in this paper.
With the aim of paving the road for future accurate astrometry with MICADO at the European-ELT, we performed an astrometric study using two different but complementary approaches to investigate two critical components that contribute to the total astrometric accuracy. First, we tested the predicted improvement in the astrometric measurements with the use of an atmospheric dispersion corrector (ADC) by simulating realistic images of a crowded Galactic globular cluster. We found that the positional measurement accuracy should be improved by up to ∼ 2 mas with the ADC, making this component fundamental for high-precision astrometry. Second, we analysed observations of a globular cluster taken with the only currently available Multi-Conjugate Adaptive Optics assisted camera, GeMS/GSAOI at Gemini South. Making use of previously measured proper motions of stars in the field of view, we were able to model the distortions affecting the stellar positions. We found that they can be as large as ∼ 200 mas, and that our best model corrects them to an accuracy of ∼ 1 mas. We conclude that future astrometric studies with MICADO requires both an ADC and an accurate modelling of distortions to the field of view, either through an a-priori calibration or an a-posteriori correction.
GeMS is the multi-conjugate adaptive optics instrument at the Gemini South telescope in Chile, the first facility-class MCAO system and the first to use laser guide stars. During its science verification period we have observed the Galactic globular cluster NGC 1851 and here we discuss the optimization of the analysis techniques that we adopt to extract science-ready photometric measurements. We use the large number of stars in the field of view to determine with high accuracy the PSF model for the profile fitting photometry. Understanding the correct techniques not only has proven useful with GeMS data but will be valuable on the next generation of Extremely Large Telescopes, where MCAO will be a central technology.
We overview the current status of photometric analyses of images collected with Multi Conjugate Adaptive Optics (MCAO) at 8–10m class telescopes that operated, or are operating, on sky. Particular attention will be payed to resolved stellar population studies. Stars in crowded stellar systems, such as globular clusters or in nearby galaxies, are ideal test-particles to test AO performance. We will focus the discussion on photometric precision and accuracy reached nowadays. We briefly describe our project on stellar photometry and astrometry of Galactic globular clusters using images taken with GeMS at the Gemini South telescope. We also present the photometry performed with DAOPHOT suite of programs into the crowded regions of these globulars reaching very faint limiting magnitudes Ks ∼21.5 mag on moderately large fields of view (∼1.5 arcmin squared). We highlight the need for new algorithms to improve the modeling of the complex variation of the Point Spread Function (PSF) across the field of view. Finally, we outline the role that large samples of stellar standards plays in providing a detailed description of the MCAO performance and in precise and accurate colour-magnitude diagrams.
Multi-conjugate adaptive optics can achieve diffraction limited images over a field of arcminutes and is a central technology for the future ELTs: Gemini/GeMS is the first facility-class LGS MCAO system to operate. With it we have taken images in J and Ks bands of the globular cluster NGC 1851 for which we also have HST/ACS observations in the visible. In this paper we present the deepest to date near-infrared photometry of NGC 1851 providing a wide colour baseline CMD that reaches the lower main sequence to have a new insight into the stellar populations of this globular cluster. The use of the GGCs' lower main sequence knee to determine its age is one of the science drivers for the observation of GGCs with MCAO given its visibility in the infrared and because it requires high Strehl ratios to measure the faint stars' photometry. In addition to the stellar population analysis, these data allow to examine the photometric performance of the instrument using a large number of point sources distributed across the field.
We analyze the photometric performance of the instrument and the field dependence of the PSF, a central part on the prediction and improvement of the performance of future LGS MCAO systems like NFIRAOS for the Thirty Meter Telescope.
We present data collected using the camera PISCES coupled with the Firt Light Adaptive Optics (FLAO) mounted at the Large Binocular Telescope (LBT). The images were collected for two different pointings by using two natural guide stars with an apparent magnitude of R ~< 13 mag. During these observations the seeing was on average ~0.9 arcsec. The AO performed very well, in fact the images display a mean FWHM of 0.05 arcsec and of 0.06 arcsec in the J– and in the Ks–band, respectively. The Strehl ratio on the quoted images reaches 13–30% (J) and 50–65% (Ks), in the off and in the central pointings respectively. On the basis of this sample we have reached a J–band limiting magnitude of ~22.5 mag and the deepest Ks–band limiting magnitude ever obtained in a crowded stellar field: Ks ~23 mag. J–band images display a complex change in the shape of the PSF when moving at larger radial distances from the natural guide star. In particular, the stellar images become more elongated in approaching the corners of the J-band images whereas the Ks–band images are more uniform. We discuss in detail the strategy used to perform accurate and deep photometry in these very challenging images. In particular we will focus our attention on the use of an updated version of ROMAFOT based on asymmetric and analytical Point Spread Functions. The quality of the photometry allowed us to properly identify a feature that clearly shows up in NIR bands: the main sequence knee (MSK). The MSK is independent of the evolutionary age, therefore the difference in magnitude with the canonical clock to constrain the cluster age, the main sequence turn off (MSTO), provides an estimate of the absolute age of the cluster. The key advantage of this new approach is that the error decreases by a factor of two when compared with the classical one. Combining ground–based Ks with space F606W photometry, we estimate the absolute age of M15 to be 13.70± 0.80 Gyr.