PMAS: The Potsdam Multi Aperture Spectrophotometer. II. The Wide Integral Field Unit PPak

PPak is a new fiber-based Integral Field Unit (IFU), developed at the Astrophysical Institute Potsdam, implemented as a module into the existing PMAS spectrograph. The purpose of PPak is to provide both an extended field-of-view with a large light collecting power for each spatial element, as well as an adequate spectral resolution. The PPak system consists of a fiber bundle with 331 object, 36 sky and 15 calibration fibers. The object and sky fibers collect the light from the focal plane behind a focal reducer lens. The object fibers of PPak, each 2.7 arcseconds in diameter, provide a contiguous hexagonal field-of-view of 74 times 64 arcseconds on the sky, with a filling factor of 60%. The operational wavelength range is from 400 to 900nm. The PPak-IFU, together with the PMAS spectrograph, are intended for the study of extended, low surface brightness objects, offering an optimization of total light-collecting power and spectral resolution. This paper describes the instrument design, the assembly, integration and tests, the commissioning and operational procedures, and presents the measured performance at the telescope.Comment: 14 pages, 21 figures, accepted at PAS

GREGOR Fabry-Perot Interferometer - status report and prospects

The GREGOR Fabry-Perot Interferometer (GFPI) is one of three first-light instruments of the German 1.5-meter GREGOR solar telescope at the Observatorio del Teide, Tenerife, Spain. The GFPI allows fast narrow-band imaging and post-factum image restoration. The retrieved physical parameters will be a fundamental building block for understanding the dynamic Sun and its magnetic field at spatial scales down to 50 km on the solar surface. The GFPI is a tunable dual-etalon system in a collimated mounting. It is designed for spectropolarimetric observations over the wavelength range from 530-860 nm with a theoretical spectral resolution of R ~ 250,000. The GFPI is equipped with a full-Stokes polarimeter. Large-format, high-cadence CCD detectors with powerful computer hard- and software enable the scanning of spectral lines in time spans equivalent to the evolution time of solar features. The field-of-view of 50" x 38" covers a significant fraction of the typical area of active regions. We present the main characteristics of the GFPI including advanced and automated calibration and observing procedures. We discuss improvements in the optical design of the instrument and show first observational results. Finally, we lay out first concrete ideas for the integration of a second FPI, the Blue Imaging Solar Spectrometer, which will explore the blue spectral region below 530 nm.Comment: 18 pages, 9 Figures, 4 Tables, "Astronomical Telescopes and Instrumentation", Amsterdam, 1-6 July 2012, SPIE Proc. 8446-276, in pres

Prototype development of the Integral-Field unit for VIRUS

VIRUS is a planned integral-field instrument for the Hobby-Eberly Telescope (HET). In order to achieve a large field-of-view and high grasp at reasonable costs, the approach is to replicate integral-field units (IFU) and medium sized spectrographs many times. The Astrophysical Institute Potsdam (AIP) contributes to VIRUS with the development and testing of the IFU prototype. This paper describes the optomechanical design and the manufacture of the fiber-based IFU subsystem. The initial VIRUS development aims to produce a prototype and to measure its performance. Additionally, techniques will be investigated to allow industrial replication of the highly specific fiber-bundle layout. This will be necessary if this technique is to be applied to the next generation of even larger astronomical instrumentation.Comment: 11 pages, 13 figures, to be published in SPIE proc. 627

The ERA2 facility: towards application of a fiber-based astronomical spectrograph for imaging spectroscopy in life sciences

Astronomical instrumentation is most of the time faced with challenging requirements in terms of sensitivity, stability, complexity, etc., and therefore leads to high performance developments that at first sight appear to be suitable only for the specific design application at the telescope. However, their usefulness in other disciplines and for other applications is not excluded. The ERA2 facility is a lab demonstrator, based on a high-performance astronomical spectrograph, which is intended to explore the innovation potential of fiber-coupled multi-channel spectroscopy for spatially resolved spectroscopy in life science, material sciences, and other areas of research.Comment: 10 pages, 9 figures, SPIE Conference "Astronomical Telescopes and Instrumentation" 2012, Amsterda

The STELLA Robotic Observatory on Tenerife

The Astrophysical Institute Potsdam (AIP) and the Instituto de Astrofísica de Canarias (IAC) inaugurated the robotic telescopes STELLA-I and STELLA-II (STELLar Activity) on Tenerife on May 18, 2006. The observatory is located on the Izaña ridge at an elevation of 2400 m near the German Vacuum Tower Telescope. STELLA consists of two 1.2 m alt-az telescopes. One telescope fiber feeds a bench-mounted high-resolution echelle spectrograph while the other telescope feeds a wide-field imaging photometer. Both scopes work autonomously by means of artificial intelligence. Not only that the telescopes are automated, but the entire observatory operates like a robot, and does not require any human presence on site

Worldwide variations in artificial skyglow

Despite constituting a widespread and significant environmental change, understanding of artificial nighttime skyglow is extremely limited. Until now, published monitoring studies have been local or regional in scope, and typically of short duration. In this first major international compilation of monitoring data we answer several key questions about skyglow properties. Skyglow is observed to vary over four orders of magnitude, a range hundreds of times larger than was the case before artificial light. Nearly all of the study sites were polluted by artificial light. A non-linear relationship is observed between the sky brightness on clear and overcast nights, with a change in behavior near the rural to urban landuse transition. Overcast skies ranged from a third darker to almost 18 times brighter than clear. Clear sky radiances estimated by the World Atlas of Artificial Night Sky Brightness were found to be overestimated by ~25%; our dataset will play an important role in the calibration and ground truthing of future skyglow models. Most of the brightly lit sites darkened as the night progressed, typically by ~5% per hour. The great variation in skyglow radiance observed from site-to-site and with changing meteorological conditions underlines the need for a long-term international monitoring program

PMAS: The Potsdam Multi-Aperture Spectrophotometer. I. Design, Manufacture, and Performance

We describe the design, manufacture, commissioning, and performance of PMAS, the Potsdam Multi-Aperture Spectrophotometer. PMAS is a dedicated integral field spectrophotometer, optimized to cover the optical wavelength regime of 0.35--1um. It is based on the lens array -- fiber bundle principle of operation. The instrument employs an all-refractive fiber spectrograph, built with CaF2 optics, to provide good transmission and high image quality over the entire nominal wavelength range. A set of user-selectable reflective gratings provides low to medium spectral resolution in first order of approx. 1.5, 3.2, and 7 A, depending on the groove density (1200, 600, 300 gr/mm). While the standard integral field unit (IFU) uses a 16x16 element lens array, which provides seeing-limited sampling in a relatively small field-of-view (FOV) in one of three magnifications (8x8, 12x12, or 16x16 arcsec^2, respectively), a recently retrofitted bare fiber bundle IFU (PPak) expands the FOV to a hexagonal area with a footprint of 65x74 arcsec^2. Other special features include a cryogenic CCD camera for field acquisition and guiding, a nod-shuffle mode for beam switching and improved sky background subtraction, and a scanning Fabry-Perot etalon in combination with the standard IFU (PYTHEAS mode). PMAS was initially designed and built as an experimental traveling instrument with optical interfaces to various telescopes (Calar Alto 3.5m, ESO-VLT, LBT). It is offered as a common user instrument at Calar Alto under contract with MPIA Heidelberg since 2002.Comment: accepted for publication in PASP, 18 pages, 21 figure

Worldwide variations in artificial skyglow

Despite constituting a widespread and significant environmental change, understanding of artificial nighttime skyglow is extremely limited. Until now, published monitoring studies have been local or regional in scope and typically of short duration. In this first major international compilation of monitoring data we answer several key questions about skyglow properties. Skyglow is observed to vary over four orders of magnitude, a range hundreds of times larger than was the case before artificial light. Nearly all of the study sites were polluted by artificial light. A non-linear relationship is observed between the sky brightness on clear and overcast nights, with a change in behavior near the rural to urban landuse transition. Overcast skies ranged from a third darker to almost 18 times brighter than clear. Clear sky radiances estimated by the World Atlas of Artificial Night Sky Brightness were found to be overestimated by ~25%; our dataset will play an important role in the calibration and ground truthing of future skyglow models. Most of the brightly lit sites darkened as the night progressed, typically by ~5% per hour. The great variation in skyglow radiance observed from site-to-site and with changing meteorological conditions underlines the need for a long-term international monitoring program

Worldwide variations in artificial skyglow

Despite constituting a widespread and significant environmental change, understanding of artificial nighttime skyglow is extremely limited. Until now, published monitoring studies have been local or regional in scope, and typically of short duration. In this first major international compilation of monitoring data we answer several key questions about skyglow properties. Skyglow is observed to vary over four orders of magnitude, a range hundreds of times larger than was the case before artificial light. Nearly all of the study sites were polluted by artificial light. A non-linear relationship is observed between the sky brightness on clear and overcast nights, with a change in behavior near the rural to urban landuse transition. Overcast skies ranged from a third darker to almost 18 times brighter than clear. Clear sky radiances estimated by the World Atlas of Artificial Night Sky Brightness were found to be overestimated by ,25%; our dataset will play an important role in the calibration and ground truthing of future skyglow models. Most of the brightly lit sites darkened as the night progressed, typically by ,5% per hour. The great variation in skyglow radiance observed from site-to-site and with changing meteorological conditions underlines the need for a long-term international monitoring program