A fast photometry methodology is described. We use a cooled Ixon Ultra emCCD in photon counter mode to acquire data. A dissipation system is added to stabilize the temperature down to -96 C. The sensibility of this system makes it ideal even for small telescopes.
The wavefront sensor is an important part of active control for an Active Optics System (AOS). The wavefront sensibility of a beam compressor is experimentally tested on the 2.1m telescope at SPM. This is a simple wavefront sensor based on the wave propagation equation. A qualitative analysis of the experimental data is presented. It is concluded that the beam compressor has enough sensibility to be used as a wavefront sensor for the AOS.
The support system of the primary mirror of 2.1m telescope at SPM allows correction of some optical aberrations. A low cost Active Optics System (AOS) can be developed based on this property of the support system. Within the preliminary development of this system, computer simulations were being performed. The general propose of simulations was to find the optimal scheme for the wavefront control of the primary mirror. This paper presents results for the wavefront sensor of the AOS proposed for the 2.1m telescope at San Pedro Martir.
The Observatorio Astronomico Nacional at San Pedro Martir is situated on the summit of the San Pedro Martir Sierra in the Baja California peninsula of Mexico, at 2800m above sea level. For as long as three decades, a number of groups and individuals have gathered extremely valuable data leading to the site characterization for astronomical observations. Here we present a summary of the most important results obtained so far. The aspects covered are: weather, cloud coverage, local meteorology, atmospheric optical extinction, millimetric opacity, geotechnical studies, seeing, optical turbulence profiles, wind profiles and 3D simulations of atmospheric turbulence. The results place San Pedro Martir among the most favorable sites in the world for astronomical observations. It seems to be particularly well-suited for extremely large telescopes because of the excellent turbulence and local wind conditions, to mention but two characteristics. Long-term monitoring of some parameters still have to be undertaken. The National University of Mexico (UNAM) and other international institutions are putting a considerable effort in that sense.
The applicability of the curvature method for co-phasing of segmented mirrors is investigated by means of simulations for the case of strongly defocused images. The simulations are performed for both the monochromatic and the white light as well. A simple wavefront reconstruction from curvature signal was made. The reconstruction quality of the piston modes and the aberrations up to the fourth order is analyzed. The dependence of the Central Intensity Ratio for a segmented mirror as a function of the rms segment's aberrations is presented. The effect of turbulence-induced distortions on the quality of mirror co-phasing is analyzed. It is shown that the local pistons and the local tip-tilts can be measured directly from the curvature signal without any phase recovering procedure. The results obtained show that, even in the presence of the atmospheric turbulence, the curvature method is sensitive enough to detect the errors of segmented mirrors.
We demonstrate that the curvature equation can be modified using some properties of Distributions theory for segmented mirror techniques. It is shown that, additionally to the individual segment aberrations, the modified equation contains the information about the relative pistons and tip- tilts among the segments. The validity of the equation is verified by numerical simulations and by a laboratory experiment as well.
We have obtained the curvature signal from defocused images before and after the pupil image for a simplified segmented mirror model. We used white light interferometry in order to calibrate the relative piston difference between the segments. The first results of applying the Curvature Sensing method to measure this relative piston difference are presented.
The efficiency of off-axis adaptive astronomical systems is estimated for four astronomical sites: Paranal (Chili), Roque de los Muchachos (Canary Islands), San Pedro Martir (Mexico) and Observatoire de Haute Provence (France). The efficiency of interest is considered through the Strehl ratio of the corrected image calculated for V, J and K bands and for 8-m class telescopes. The experimental optical turbulence strength C<SUB>n</SUB><SUP>2</SUP>(z) profiles necessary for calculations have been measured with balloon flights and with the Generalized Scidar. It is found that this efficiency depends mainly on the C<SUB>n</SUB><SUP>2</SUP>(z) profile layered structure and on the turbulence strength.
A detailed analysis of anisotropy in the point spread function (PSF) associated with off-axis adaptive astronomical correction is presented. The results obtained are based on the experimental C<SUB>n</SUB><SUP>2</SUP> profile which has been recently measured at San Pedro Martir observatory (Mexico). It is found that the PSF has a complicated shape that depends strongly on the wavelength and on the separation between the guide and observed stars.
The University of Mexico 6.5m TIM telescope project has a 19 fully active segmented M1 and an active M2. Each 1.8m segment is a relative thin meniscus supported by three position hard points, computer controlled, and 16 force soft actuators which support the meniscus and can deform it. This project includes an AO system using a corrector mirror placed at a conjugated telescope pupil. We decided to specify the telescope optics in function of this AO system from the beginning and not specify the AO system in function of the telescope. In order to calculate the optical budget of the TIM we simulated, using a Monte Carlo technique e approach, the Strehl ratio of the telescope PSF as a function of the low order aberration values of the individual segments. The low order aberrations studied are the 'position' aberrations, as the piston and the tip-tilt between the segments, and the 'deformation' aberrations as the values for the deformation aberrations for each segment are comparable with the 'intrinsic' quality of the primary mirror of an active telescope as the NTT or our recently enhanced 2.1m UNAM telescope, if diffraction limited imaging for the complete primary is specified. This result shows that the technology for a correct support for the individual segments actually exist. The results obtained are used for the optical quality definition of the TIM 6.5m telescope.
We describe different works conducing to the adaptive optics system for the TIM 6.5m telescope. We show turbulence profiles result at our San Pedro Martir Observatory in Baja using the Generalized SCIDAR. We can conclude that the turbulence conditions in this site are comparable to the major observatories in the world. From these results and taken in account curvature AO simulations it is possible to predict the performances in limiting magnitude and sky coverage of different AO systems and telescopes in our observatory. We can also define the degree of the AO system for the TIM 6.5m telescope. We made a short description of our LOLA tip-tilt corrector system and the GUIELOA 19 elements curvature AO system. The calculation of the optics quality for the TIM 6.5m is briefly mentioned. Studies about the influence of the finite outerscale on the optical quality of AO corrected images are described.
The influence of the turbulence outer scale on the power spectrum (PS) of speckle interferograms and on the Strehl ratio obtained with low-order adaptive optics (AO) system is examined by numerical simulation. It is shown that the outer scale has a little positive effect the PS when the outer scale magnitude becomes less than the aperture diameter. The finite outer scale has a positive effect on the STrehl ratio of the uncorrected long-exposure image. It is also shown that the Strehl ratio produced by a second-order AO correction is affected quite strongly by the finite outer scale. For the more higher-order correction, the effect under study is very weak and it appears only when the outer scale magnitude becomes less than the aperture diameter.