arXiv subjects

Andreas Kelz

Publications and source records attributed to Andreas Kelz.

30 records · Page 2Linked to original sources

arXiv2015

MOSAIC: a Multi-Object Spectrograph for the E-ELT

The instrumentation plan for the European-Extremely Large Telescope foresees a Multi-Object Spectrograph (E-ELT MOS). The MOSAIC project is proposed by a European-Brazilian consortium, to provide a unique MOS facility for astrophysics, studies of the inter-galactic medium and for cosmology. The science cases range from spectroscopy of the most distant galaxies, mass assembly and evolution of galaxies, via resolved stellar populations and galactic archaeology, to planet formation studies. A further strong driver are spectroscopic follow-up observations of targets that will be discovered with the James Webb Space Telescope.

astro-ph.IM↗

arXiv2015

A MUSE map of the central Orion Nebula (M 42)

We present a new integral-field spectroscopic dataset of the central part of the Orion Nebula (M 42), observed with the MUSE instrument at the ESO VLT. We reduced the data with the public MUSE pipeline. The output products are two FITS cubes with a spatial size of ~5.9'x4.9' (corresponding to ~0.76 pc x 0.63 pc) and a contiguous wavelength coverage of 4595...9366 Angstrom, spatially sampled at 0.2". We provide two versions with a sampling of 1.25 Angstrom and 0.85 Angstrom in dispersion direction. Together with variance cubes these files have a size of 75 and 110 GiB on disk. They represent one of the largest integral field mosaics to date in terms of information content. We make them available for use in the community. To validate this dataset, we compare world coordinates, reconstructed magnitudes, velocities, and absolute and relative emission line fluxes to the literature and find excellent agreement. We derive a two-dimensional map of extinction and present de-reddened flux maps of several individual emission lines and of diagnostic line ratios. We estimate physical properties of the Orion Nebula, using the emission line ratios [N II] and [S III] (for the electron temperature $T_e$) and [S II] and [Cl III] (for the electron density $N_e$), and show two-dimensional images of the velocity measured from several bright emission lines.

astro-ph.GA↗

arXiv2013

The Influence of Motion and Stress on Optical Fibers

We report on extensive testing carried out on the optical fibers for the VIRUS instrument. The primary result of this work explores how 10+ years of simulated wear on a VIRUS fiber bundle affects both transmission and focal ratio degradation (FRD) of the optical fibers. During the accelerated lifetime tests we continuously monitored the fibers for signs of FRD. We find that transient FRD events were common during the portions of the tests when motion was at telescope slew rates, but dropped to negligible levels during rates of motion typical for science observation. Tests of fiber transmission and FRD conducted both before and after the lifetime tests reveal that while transmission values do not change over the 10+ years of simulated wear, a clear increase in FRD is seen in all 18 fibers tested. This increase in FRD is likely due to microfractures that develop over time from repeated flexure of the fiber bundle, and stands in contrast to the transient FRD events that stem from localized stress and subsequent modal diffusion of light within the fibers. There was no measurable wavelength dependence on the increase in FRD over 350 nm to 600 nm. We also report on bend radius tests conducted on individual fibers and find the 266 microns VIRUS fibers to be immune to bending-induced FRD at bend radii of R > 10cm. Below this bend radius FRD increases slightly with decreasing radius. Lastly, we give details of a degradation seen in the fiber bundle currently deployed on the Mitchell Spectrograph (formally VIRUS-P) at McDonald Observatory. The degradation is shown to be caused by a localized shear in a select number of optical fibers that leads to an explosive form of FRD. In a few fibers, the overall transmission loss through the instrument can exceed 80%.

astro-ph.IM↗

arXiv2012

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.

astro-ph.IM↗

arXiv2012

4MOST - 4-metre Multi-Object Spectroscopic Telescope

The 4MOST consortium is currently halfway through a Conceptual Design study for ESO with the aim to develop a wide-field (>3 square degree, goal >5 square degree), high-multiplex (>1500 fibres, goal 3000 fibres) spectroscopic survey facility for an ESO 4m-class telescope (VISTA). 4MOST will run permanently on the telescope to perform a 5 year public survey yielding more than 20 million spectra at resolution R~5000 (λ=390-1000 nm) and more than 2 million spectra at R~20,000 (395-456.5 nm & 587-673 nm). The 4MOST design is especially intended to complement three key all-sky, space-based observatories of prime European interest: Gaia, eROSITA and Euclid. Initial design and performance estimates for the wide-field corrector concepts are presented. We consider two fibre positioner concepts, a well-known Phi-Theta system and a new R-Theta concept with a large patrol area. The spectrographs are fixed configuration two-arm spectrographs, with dedicated spectrographs for the high- and low-resolution. A full facility simulator is being developed to guide trade-off decisions regarding the optimal field-of-view, number of fibres needed, and the relative fraction of high-to-low resolution fibres. Mock catalogues with template spectra from seven Design Reference Surveys are simulated to verify the science requirements of 4MOST. The 4MOST consortium aims to deliver the full 4MOST facility by the end of 2018 and start delivering high-level data products for both consortium and ESO community targets a year later with yearly increments.

astro-ph.IM↗

arXiv2010

HETDEX pilot survey for emission-line galaxies - I. Survey design, performance, and catalog

We present a catalog of emission-line galaxies selected solely by their emission-line fluxes using a wide-field integral field spectrograph. This work is partially motivated as a pilot survey for the upcoming Hobby-Eberly Telescope Dark Energy Experiment (HETDEX). We describe the observations, reductions, detections, redshift classifications, line fluxes, and counterpart information for 397 emission-line galaxies detected over 169 sq.arcmin with a 3500-5800 Ang. bandpass under 5 Ang. full-width-half-maximum (FWHM) spectral resolution. The survey's best sensitivity for unresolved objects under photometric conditions is between 4-20 E-17 erg/s/sq.cm depending on the wavelength, and Ly-alpha luminosities between 3-6 E42 erg/s are detectable. This survey method complements narrowband and color-selection techniques in the search for high redshift galaxies with its different selection properties and large volume probed. The four survey fields within the COSMOS, GOODS-N, MUNICS, and XMM-LSS areas are rich with existing, complementary data. We find 104 galaxies via their high redshift Ly-alpha emission at 1.9 44 sq.arcsec which appear to be extended Ly-alpha nebulae. We also find three high-z objects with rest frame Ly-alpha equivalent widths above the level believed to be achievable with normal star formation, EW(rest)>240 Ang.

astro-ph.CO↗

arXiv2009

Astrochemistry and Astrophotonics for an Antarctic Observatory

Due to its location and climate, Antarctica offers unique conditions for long-period observations across a broad wavelength regime, where important diagnostic lines for molecules and ions can be found, that are essential to understand the chemical properties of the interstellar medium. In addition to the natural benefits of the site, new technologies, resulting from astrophotonics, may allow miniaturised instruments, that are easier to winterise and advanced filters to further reduce the background in the infrared.

astro-ph.IM↗

arXiv2008

Motivations for Imaging Spectroscopy at Dome C

Antarctica offers unique conditions for ground-based observations, such as low sky background in the infrared, improved seeing, and low turbulence and scintillation noise. These properties are particularly beneficial to imaging, precision photometry, and infrared observations. It may be less clear if Antarctica offers equally compelling advantages for spectroscopy, in particular in the optical domain. However, scientific programmes that make use of imaging (or 3D) spectroscopy for selected follow-up studies of IR surveys, long-term monitoring of extended targets and resolved stellar population studies in crowded fields, also benefit from the site conditions at Dome C.

astro-ph↗

arXiv2006

3D-Spectroscopy of extragalactic planetary nebulae as diagnostic probes for galaxy evolution

In addition to study extragalactic stellar populations in their integrated light, the detailed analysis of individual resolved objects has become feasible, mainly for luminous giant stars and for extragalactic planetary nebulae (XPNe) in nearby galaxies. A recently started project at the Astrophysical Institute Potsdam (AIP), called ``XPN--Physics'', aims to verify if XPNe are useful probes to measure the chemical abundances of their parent stellar population. The project involves theoretical and observational work packages.

astro-ph↗

arXiv2006

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.

astro-ph↗

arXiv2005

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.

astro-ph↗

arXiv2004

The Disk Mass project; science case for a new PMAS IFU module

We present our Disk Mass project as the main science case for building a new fiber IFU-module for the PMAS spectrograph, currently mounted at the Cassegrain focus of the 3.5m telescope on Calar Alto. Compared to traditional long-slit observations, the large light collecting power of 2-dimensional Integral Field Units dramatically improves the prospects for performing spectroscopy on extended low surface brightness objects with high spectral resolution. This enables us to measure stellar velocity dispersions in the outer disk of normal spiral galaxies. We describe some results from a PMAS pilot study using the existing lenslet array, and provide a basic description of the new fiber IFU-module for PMAS.

astro-ph↗