The Sloan Digital Sky Survey V (SDSS-V) Local Volume Mapper (LVM) is an ultra-wide field high spatial resolution IFU survey of the Milky Way, the Magellanic Clouds, and a sample of galaxies in the local volume. Observations are carried out with the LVM Instrument (LVM-I), a specially designed robotic telescope, instrument, and facility located at Las Campanas Observatory (LCO) in Chile. The LVM-I is hosted in a custom-built roll-off type enclosure that protects the hardware, allows for simultaneous observations towards different directions in the sky by the four LVM-I telescopes, provides a thermally controlled stable and clean environment for the LVM-I spectrographs, supplies all necessary utilities (e.g. power, communications, LN2 detector cooling) to the different LVM-I sub-systems, provides environmental telemetry and information, and integrates with the LVM-I control software to operate in an automated fashion. In this paper we discuss the design of the LVM-I enclosure, its construction, and an evaluation of its performance. The LVM-I was successfully integrated on-site and commissioned during the first half of 2023, with the enclosure design and performance meeting its requirements and allowing for the start of the SDSS-V LVM project science operations.
We describe the Sloan Digital Sky Survey Local Volume Mapper Instrument (LVM-I) construction, testing, and initial performance. The facility is designed to produce the first integral map of thousands of degrees of the Southern sky. The map will cover spectra from bluer than [O II] to 980 nm with a dispersion of over R = Δλ/λ > 4, 000 at Hα wavelength. Each spaxel will have a pitch of ∼35′′, and the survey will be conducted using four integral field units (IFUs) with an instantaneous field of view of 530 arcmin2. The LVM facility is designed to achieve the required sub-Rayleigh spectroscopy over large sky areas with outstanding spectrophotometric accuracy and precision. LVM-I is designed to produce this unique dataset using four siderostats on commercial mounts. The four beams are fed into 16-cm-diameter f/11.4 apochromatic objectives, and the sky is derotated with K mirrors. These telescopes produce an image of the field onto both guider cameras and a lenslet array. The array reimages the field at f/3.7 onto 107-micron-diameter fibers. Blue throughput is maximized with a short 18.5-m fiber run from the IFUs to the spectrographs. The fibers are reconfigured inside a splicing box to distribute the fibers from the four telescopes to three spectrographs. The spectrographs are near-copies of the Dark Energy Survey three-band f/1.7 spectrographs, which deliver sharp images over the entire chromatic range. Nine STA charge-coupled devices (CCDs), cooled with liquid-nitrogen dewars, are used for the survey. The LVM-I is controlled with custom Python software and distributed over various computers using power-over-ethernet networking. The system is housed in a custom enclosure with a roll-off roof to grant access to the sky. The enclosure allows all four telescopes to point all over the sky and measure the transmissivity of the atmosphere and the sky background. Some of the first-light data products are highlighted here.
Accurate positioning of opto-mechanical elements in the focal plane of large telescopes is a challenging requirements for many state of the art observational scientific applications. In particular high multiplexing multi object spectroscopy requires precise metrology tools for performing efficient observations and calibrations of the instruments. We have developed a metrology system based on modified commercial off-the-shelf components to reach high performances with a cost effective solution. Our system is based on the photogrammetry technique and on a number of fixed off-axis cameras. The cameras acquire images of the focal plane where metrology targets and references are located. The acquisition is based on Odroid-XU4, a single-board computer running on GNU/Linux. No moving parts in the setup ensures an extremely fast acquisition of the data. The calibration and metrology data processing is based on the computer vision library OpenCV. We present a prototype system and results of the camera calibrations and metrology tests obtained in our laboratory.
We are developing an optical adaptive optics (AO) system for small telescopes. An AO instrument in optical wavelength mounted on a 1-2 m class telescope located at a good seeing site will make it possible to achieve high angular resolution of 0.1-0.2 arcsec. Such capability will enable us to perform unique astronomical programs, as well as to provide good opportunity in education for both astronomy and engineering. In order to examine the AO capability on small telescopes, we developed an experimental AO instrument, in which inexpensive commercial devices are extensively used to reduce cost for development. We designed the weight and the physical size so small that it is portable and easy to be mounted on a small telescope, which is a unique feature of our AO instrument. After the engineering observations performed in Japan, we mounted it on the 1-m telescope of the European Southern Observatory of La Silla in Chile in March 2018 to examine the performance. We found that there were approximately 4 times and 5 times improvements in the full-width-halfmaximum (FWHM) and Strehl ratio of the PSF from the natural seeing, respectively. The best AO-corrected PSF obtained during the observation achieved FWHM=0.18 arcsec and the Strehl ratio = 0.18. Based on the detailed analysis of the timeseries wavefront and deformable-mirror-operation data, further improvement in AO performance is expected by adjustment of the system parameters. We succeeded in demonstrating the feasibility of an inexpensive optical AO system for small telescopes.
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