Generation Ground-based Telescopes Research Articles

Multiband gravitational wave cosmology with stellar origin black hole binaries

Massive stellar origin black hole binaries (SBHBs), originating from stars above the pair-instability mass gap, are primary candidates for multiband gravitational wave (GW) observations. Here we study the possibility to use them as effective dark standard sirens to constrain cosmological parameters. The long lasting inspiral signal emitted by these systems is accessible by the future $Laser \; Interferometer \; Space \; Antenna$ (LISA), while the late inspiral and merger are eventually detected by third generation ground-based telescopes such as the $Einstein \; Telescope$ (ET). The direct measurement of the luminosity distance and the sky position to the source, together with the inhomogeneous redshift distribution of possible host galaxies, allow us to infer cosmological parameters by probabilistic means. The efficiency of this statistical method relies in high parameter estimation performances. We show that this multiband approach allows a precise determination of the Hubble constant H$_0$ with just ${\cal O}(10)$ detected sources. For selected SBHB population models, assuming $4$ ($10$) years of LISA observations, we find that H$_0$ is typically determined at $\sim 2\%$ ($\sim 1.5\%$), whereas $\Omega_m$ is only mildly constrained with a typical precision of $30\%$ ($20\%$). We discuss the origin of some outliers in our final estimates and we comment on ways to reduce their presence.

Wavelet methods in multi-conjugate adaptive optics

The next generation ground-based telescopes rely heavily on adaptive optics for overcoming the limitation of atmospheric turbulence. In the future adaptive optics modalities, like multi-conjugate adaptive optics (MCAO), atmospheric tomography is the major mathematical and computational challenge. In this severely ill-posed problem, a fast and stable reconstruction algorithm is needed that can take into account many real-life phenomena of telescope imaging. We introduce a novel reconstruction method for the atmospheric tomography problem and demonstrate its performance and flexibility in the context of MCAO. Our method is based on using locality properties of compactly supported wavelets, both in the spatial and frequency domains. The reconstruction in the atmospheric tomography problem is obtained by solving the Bayesian MAP estimator with a conjugate-gradient-based algorithm. An accelerated algorithm with preconditioning is also introduced. Numerical performance is demonstrated on the official end-to-end simulation tool OCTOPUS of European Southern Observatory.

Design of a Micro-Autonomous Robot for Use in Astronomical Instruments

A Micro-Autonomous Positioning System (MAPS) has been developed using micro-autonomous robots for the deployment of small mirrors within multi-object astronomical instruments for use on the next generation ground-based telescopes. The micro-autonomous robot is a two-wheel differential drive robot with a footprint of approximately 20 × 20 mm. The robot uses two brushless DC Smoovy motors with 125:1 planetary gearheads for positioning the mirror. This article describes the various elements of the overall system and in more detail the various robot designs. Also described in this article is the build and test of the most promising design, proving that micro-autonomous robot technology can be used in precision controlled applications.

Sensitivity analysis of test methods for aspheric off-axis mirrors

Following the Hubble Space Telescope (HST), the next generation James Webb Space Telescope (JWST) is being developed to be launched in a few years. JWST will be a segmented mirror telescope with a design much like that developed for ground-based telescopes over the past 20 years. Several segmented mirror telescopes are currently in operation, and next generation ground-based telescopes of the 30-m class are also being designed using segmented primary mirrors. Regardless of size, segmented primary mirror telescopes often require the use of aspheric segment mirrors. One of the key factors in fabrication of aspheric segment mirrors is feasibility of testing off-axis surfaces with high accuracy. A couple of test methods have been investigated for aspheric off-axis segments. As a case study, we apply these test methods to secondary segmented mirror models of the Giant Magellan Telescope. We derive required dimensions of test set-ups and assess sensitivity of optical alignment. Characteristics of the test methods are also discussed.

Ground-based telescope pointing and tracking optimization using a neural controller

Neural network models (NN) have emerged as important components for applications of adaptive control theories. Their basic generalization capability, based on acquired knowledge, together with execution rapidity and correlation ability between input stimula, are basic attributes to consider NN as an extremely powerful tool for on-line control of complex systems. By a control system point of view, not only accuracy and speed, but also, in some cases, a high level of adaptation capability is required in order to match all working phases of the whole system during its lifetime. This is particularly remarkable for a new generation ground-based telescope control system. Infact, strong changes in terms of system speed and instantaneous position error tolerance are necessary, especially in case of trajectory disturb induced by wind shake. The classical control scheme adopted in such a system is based on the proportional integral (PI) filter, already applied and implemented on a large amount of new generation telescopes, considered as a standard in this technological environment. In this paper we introduce the concept of a new approach, the neural variable structure proportional integral, (NVSPI), related to the implementation of a standard multi layer perceptron network in new generation ground-based Alt-Az telescope control systems. Its main purpose is to improve adaptive capability of the Variable structure proportional integral model, an already innovative control scheme recently introduced by authors [Proc SPIE (1997)], based on a modified version of classical PI control model, in terms of flexibility and accuracy of the dynamic response range also in presence of wind noise effects. The realization of a powerful well tested and validated telescope model simulation system allowed the possibility to directly compare performances of the two control schemes on simulated tracking trajectories, revealing extremely encouraging results in terms of NVSPI control robustness and reliability.