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Ground-based astronomy has to correct astronomical observations from the impact of the atmospheric transparency and its variability.The current objective of several observatories is to achieve a sub-percent level monitoring of atmospheric transmission. A promising approach has been to combine internal calibration of the observations with various external meteorological data sources, upon avail-ability and depending on quality. In this paper we investigate the use of the NASA Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2) which is a general circulation model (GCM) and data assimilation system that renders freely available for any given site, at any time, all the parameters constraining atmospheric transmission. This paper demonstrates the extraction of the relevant atmospheric parameters for optical astronomy at two sites: Mauna Kea in Hawaii and Cerro Tololo InternationalObservatory in Chile. The temporal variability for the past eight years (annual, overnight and hourly), as well as the spatial gradients of ozone, precipitable water vapor, and aerosol optical depth is presented and their respective impacts on the atmospheric transparency is analyzed., Comment: 10 pages, 6 figures, accepted for publication in Journal of Astronomical Instrumentation

We propose a method to characterize thermal properties of ion irradiated materials. This method uses an ion beam as a heating source to create a hot spot on sample surface. Infrared imaging is used as a surface temperature mapping tool to record hot zone spreading. Since ion energy, ion flux, and ion penetration depth can be precisely controlled, the beam heating data is highly reliable and repeatable. Using a high speed infrared camera to capture lateral spreading of the hot zone, thermal diffusivity can be readily extracted. The proposed method has advantages in studying radiation induced thermal property changes, for which radiation damage can be introduced by using an irradiating beam over a relatively large beam spot and beam heating can be introduced by using a focused testing beam over a relatively small beam spot. These two beams can be switched without breaking vacuum. Thus thermal conductivity changes can be characterized in situ with ion irradiation. The feasibility of the technique is demonstrated on a single crystal quartz substrate.

We present measurements of the spectral response function of commercially-available Nikon 35mm photographic camera lenses for use in astronomical instrumentation. Our motivation for this work stems from the fact that several astronomical imaging systems have been deployed or proposed using this type of commercial lens. We have performed measurements of the relative and absolute spectral response function of five commercially-available photographic lenses. These measurements show that these lenses generally have >50% throughput across the entire optical window of 400nm < λ < 800nm.

Meeting the science goals for many current and future ground-based optical large-area sky surveys requires that the calibrated broadband photometry is stable in time and uniform over the sky to 1% precision or better. Past surveys have achieved photometric precision of 1-2% by calibrating the survey's stellar photometry with repeated measurements of a large number of stars observed in multiple epochs. The calibration techniques employed by these surveys only consider the relative frame-by-frame photometric zeropoint offset and the focal plane position-dependent illumination corrections, which are independent of the source color. However, variations in the wavelength dependence of the atmospheric transmission and the instrumental throughput induce source color-dependent systematic errors. These systematic errors must also be considered to achieve the most precise photometric measurements. In this paper, we examine such systematic chromatic errors using photometry from the Dark Energy Survey (DES) as an example. We define a natural magnitude system for DES and calculate the systematic errors on stellar magnitudes, when the atmospheric transmission and instrumental throughput deviate from the natural system. We conclude that the systematic chromatic errors caused by the change of airmass in each exposure, the change of the precipitable water vapor and aerosol in the atmosphere over time, and the non-uniformity of instrumental throughput over the focal plane, can be up to 2% in some bandpasses. We compare the calculated systematic chromatic errors with the observed DES data. For the test sample data, we correct these errors using measurements of the atmospheric transmission and instrumental throughput. The residual after correction is less than 0.3%. We also find that the errors for non-stellar objects are redshift-dependent and can be larger than those for stars at certain redshifts., 16 pages, 9 figures, AJ accepted

We present results from the spectrophotometric calibration of the new E2V CCD camera on the Swope telescope and of RetroCam on the DuPont Telescope. We measured the relative sensitivity of each pixel vs wavelength over the whole wavelength sensitivity range of each camera, for all the filters that will be used during the 5 years of the CSP2 survey. We used a tunable light source and fiber delivery system conceived and built in our lab to achieve +/-1% precision calibration from 300nm to 1100nm and +/-3% from 1100nm to 1800nm. Achieving this relatively high precision at low light levels was made possible by using Si, Ge and InGaAs photodiodes coupled to custom high gain amplifiers. Comparison of these results to results obtained 3 years before, allowed us to confirm that the intrinsic transmission bandpass of the filters has not changed over time but that the mirror reflectivity and the introduction of a new CCD camera drastically changed the total telescope sensitivity. The analysis of the spatial response of the new E2V CCD vs wavelength also shows a slight gradient in the color response of the CCD both in the UV and Infrared.

The Visible Integral-Field Replicable Unit Spectrograph (VIRUS) instrument will be installed at the Hobby-Eberly Telescope† in the near future. The instrument will be housed in two enclosures that are mounted adjacent to the telescope, via the VIRUS Support Structure (VSS). We have designed the enclosures to support and protect the instrument, to enable servicing of the instrument, and to cool the instrument appropriately while not adversely affecting the dome environment. The system uses simple HVAC air handling techniques in conjunction with thermoelectric and standard glycol heat exchangers to provide efficient heat removal. The enclosures also provide power and data transfer to and from each VIRUS unit, liquid nitrogen cooling to the detectors, and environmental monitoring of the instrument and dome environments. In this paper, we describe the design and fabrication of the VIRUS enclosures and their subsystems.

We present a conceptual design for a low resolution optical spectrograph for the Astronomical Observatory of Cordoba 1.54m telescope. The simple instrument is required to cover a broad wavelength range (4000A

The Visual Integral-Field Replicable Unit Spectrograph (VIRUS) instrument is a baseline array 150 identical fiber fed optical spectrographs designed to support observations for the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX). The collimator subassemblies of the instrument have been assembled in a production line and are now complete. Here we review the design choices and assembly practices used to produce a suite of identical low-cost spectrographs in a timely fashion using primarily unskilled labor.