Kanzelhöhe Observatory: Instruments, Data Processing and Data Products

Kanzelhöhe Observatory for Solar and Environmental Research (KSO) of the University of Graz (Austria) is in continuous operation since its foundation in 1943. Since the beginning, its main task was the regular observation of the Sun in full disc. In this long time span covering almost seven solar cycles, a substantial amount of data was collected, which is made available online. In this article we describe the separate processing steps from data acquisition to high level products for different observing wavelengths. First of all we present in detail the quality classification, which is important for further processing of the raw images. We show how we construct centre-to-limb variation (CLV) profiles and how we remove large scale intensity variations produced by the telescope optics in order to get images with uniform intensity and contrast. Another important point is an overview of the different data products from raw images to high contrast images with heliographic grids overlaid. As the data products are accessible via different sources, we also present how to get information about the availability and how to obtain these data. Finally, in an appendix, we describe in detail the information in the FITS headers, the file naming and the data hierarchy.

Validation of PSF models for HST and other space-based observations

ABSTRACT Forthcoming space-based observations will require high-quality point spread function (PSF) models for weak gravitational lensing measurements. One approach to generating these models is using a wavefront model based on the known telescope optics. We present an empirical framework for validating such models to confirm that they match the actual PSF to within requirements by comparing the models to the observed light distributions of isolated stars. We apply this framework to Tiny Tim, the standard tool for generating model PSFs for the Hubble Space Telescope (HST), testing its models against images taken by HST’s Advanced Camera for Surveys in the Wide Field Channel. We show that Tiny Tim’s models, in the default configuration, differ significantly from the observed PSFs, most notably in their sizes. We find that the quality of Tiny Tim PSFs can be improved through fitting the full set of Zernike polynomial coefficients that characterize the optics, to the point where the practical significance of the difference between model and observed PSFs is negligible for most use cases, resulting in additive and multiplicative biases both of order ∼4 × 10−4. We also show that most of this improvement can be retained through using an updated set of Zernike coefficients, which we provide.

Expected performances of the Characterising Exoplanet Satellite (CHEOPS)

Context. The CHaracterising ExOPlanet Satellite (CHEOPS) is a mission dedicated to the search for exoplanetary transits through high precision photometry of bright stars already known to host planets. The telescope will provide the unique capability of determining accurate radii for planets whose masses have already been measured from ground-based spectroscopic surveys. This will allow a first-order characterisation of the planets’ internal structure through the determination of the bulk density, providing direct insight into their composition. By identifying transiting exoplanets with high potential for in-depth characterisation, CHEOPS will also provide prime targets for future instruments suited to the spectroscopic characterisation of exoplanetary atmospheres. Aims. The CHEOPS simulator has been developed to perform detailed simulations of the data which is to be received from the CHEOPS satellite. It generates accurately simulated images that can be used to explore design options and to test the on-ground data processing, in particular, the pipeline producing the photometric time series. It is, thus, a critical tool for estimating the photometric performance expected in flight and to guide photometric analysis. It can be used to prepare observations, consolidate the noise budget, and asses the performance of CHEOPS in realistic astrophysical fields that are difficult to reproduce in the laboratory. Methods. The simulator has been implemented as a highly configurable tool called CHEOPSim, with a web-based user interface. Images generated by CHEOPSim take account of many detailed effects, including variations of the incident signal flux and backgrounds, and detailed modelling of the satellite orbit, pointing jitter and telescope optics, as well as the CCD response, noise and readout. Results. The simulator results presented in this paper have been used in the context of validating the data reduction processing chain, in which image time series generated by CHEOPSim were used to generate light curves for simulated planetary transits across real and simulated targets. Independent analysts were successfully able to detect the planets and measure their radii to an accuracy within the science requirements of the mission: for an Earth-sized planet with an orbital period of 50 days orbiting a Sun-like target with magnitude V = 6, the median measured value of the planet to star radius ratio, Rp/Rs, was 0.00923 ± 0.00054(stat) ± 0.00019(syst), compared to a true input value of 0.00916. For a Neptune-sized planet with an orbital period of 13 days orbiting a target with spectral type K5V and magnitude V = 12, the median measured value of Rp/Rs was 0.05038 ± 0.00061(stat) ± 0.00031(syst), compared to a true input value of 0.05.

Did Tim Paint a Vermeer?

Tim’s Vermeer is a recent documentary feature film following engineer and self-described non-artist Tim Jenison’s extensive efforts to “paint a Vermeer” by means of a novel optical telescope and mirror-comparator procedure. His efforts were inspired by the controversial claim that some Western painters as early as 1420 secretly built optical devices and traced passages in projected images during the execution of some of their works, thereby achieving a novel and compelling “optical look.” The authors examine the proposed telescope optics in historical perspective, the particular visual evidence adduced in support of the comparator hypothesis, and the difficulty and efficacy of the mirror-comparator procedure as revealed by an independent artist/copyist’s attempts to replicate the procedure. Specifically, the authors find that the luminance gradient along the rear wall in the duplicate painting is far from being rare, difficult, or even “impossible” to achieve as proponents claimed; in fact, such gradients appear in numerous Old Master paintings that show no ancillary evidence of having been executed with optics. There is indeed a slight bowing of a single contour in the Vermeer original, which one would normally expect to be straight; however, the optical explanation for this bowing implies that numerous other lines would be similarly bowed, but in fact all are straight. The proposed method does not explain some of the most compelling “optical” evidence in Vermeer’s works such as the small disk-shaped highlights, which appear like the blur spots that arise in an out-of-focus projected image. Likewise, the comparator-based explanations for the presence of pinprick holes at central vanishing points and the presence of underdrawings and pentimenti in several of Vermeer’s works have more plausible non-optical explanations. Finally, an independent experimental attempt to replicate the procedure fails overall to provide support for the telescope claim. In light of these considerations and evidence, the authors conclude that it is extremely unlikely that Vermeer used the proposed mirror-comparator procedure.

Development of a 22/43 GHz-band quasi-optical perforated plate and dual-band observation system of the Nobeyama 45 m telescope

We have developed a system of simultaneous observations in the 22 and 43 GHz bands using the Nobeyama 45 m telescope, and are also working to add the 86 GHz band. Multi-frequency observations are realized by mounting perforated plates in the optics as dichroic frequency-selective devices. This paper presents the development of the perforated plate for the 22 and 43 GHz bands and the results of the commissioning observations with this plate on the Nobeyama 45 m telescope. The perforated plate is designed to be installed in the large telescope optics with a physical beam diameter as large as $50\:$cm for transmitting the higher frequency (43 GHz) band and for reflecting the lower frequency (22 GHz) band. The developed plate achieves an insertion loss of $0.22\:$dB (5%) at $43\:$GHz. The effects of the mounted plate on the systematic offsets and on the accuracy degradation of pointing were confirmed to be negligible. The differences in the main-beam/aperture efficiencies from those without the plate were confirmed to be within a few percent points. In addition, we successfully detected interferometry fringes in a very long baseline interferometry (VLBI) observation using the 45 m telescope and the VLBI Exploration of Radio Astrometry (VERA) 20 m telescopes, which confirmed that the dual-band observation system is operationally effective in both single-dish and VLBI observations.