Astronomical object | EPFL Graph Search

An astronomical object, celestial object, stellar object or heavenly body is a naturally occurring physical entity, association, or structure that exists within the observable universe. In astronomy, the terms object and body are often used interchangeably. However, an astronomical body or celestial body is a single, tightly bound, contiguous entity, while an astronomical or celestial object is a complex, less cohesively bound structure, which may consist of multiple bodies or even other objects with substructures. Examples of astronomical objects include planetary systems, star clusters, nebulae, and galaxies, while asteroids, moons, planets, and stars are astronomical bodies. A comet may be identified as both body and object: It is a body when referring to the frozen nucleus of ice and dust, and an object when describing the entire comet with its diffuse coma and tail. History Scientific Revolution and Copernican Revolution Astronomical objects such as stars, planets,

Precision Positioning of Microrobots for Multi-Object Spectrographs

Luzius Gregor Kronig

How does one study the evolution of the Milky Way, or the expansion of the Universe, or explore the mysteries of Dark energy? To investigate these complex topics, astronomers require data, and a great deal of it, in the form of the spectra of stars, galaxies, and quasars. In recent years remarkable efforts have been made to develop telescopes and instruments that can measure more light spectra in parallel than ever before. One solution for building these instruments, called Multi-Object Spectrographs, requires the use of several hundreds of small precise automated robots in the telescope's focal plane. Each robot can position an optical fiber with micrometer precision along the focal surface in order to capture and transmit the light of a celestial object to a spectrograph, which then measures the spectrum with great precision. In the future, new instruments will be able to measure over 10000 celestial objects simultaneously, which would consequently require the implementation of as many optical fiber positioners. To assure the development and successful operation of the instrument, every single fiber positioner requires design and validation testing. Tools for such quality assurance have yet to be developed. This thesis proposes solutions to verify, calibrate, control, and operate optical fiber positioners with two actuated rotation axes, serially linked. A metrology system is presented which is capable of accurately measuring position and alignment of the optical fiber, and a detailed model describing the correct behavior of the positioner is introduced. Based on the model, an automated measurement procedure enables calibration and validation of the positioners. The introduced measurement procedure identifies not only flaws in performance, but also various error sources, which help to detect possible design and manufacturing problems. Finally, a method is proposed on how to operate these positioners in the focal plane. Taken together, the results of this thesis can inform the present and future manufacturer of Multi-Object Spectrographs.

EPFL2020

Multi-band morpho-Spectral Component Analysis Deblending Tool (MuSCADeT): Deblending colourful objects

Frédéric Courbin, Rémy Elie Joseph

We introduce a new algorithm for colour separation and deblending of multi-band astronomical images called MuSCADeT which is based on Morpho-spectral Component Analysis of multi-band images. The MuSCADeT algorithm takes advantage of the sparsity of astronomical objects in morphological dictionaries such as wavelets and their differences in spectral energy distribution (SED) across multi-band observations. This allows us to devise a model independent and automated approach to separate objects with different colours. We show with simulations that we are able to separate highly blended objects and that our algoonfront our algoritrithm is robust against SED variations of objects across the field of view. To chm with real data, we use HST images of the strong lensing galaxy cluster MACS J1149+2223 and we show that MuSCADeT performs better than traditional profile-fitting techniques in deblending the foreground lensing galaxies from background lensed galaxies. Although the main driver for our work is the deblending of strong gravitational lenses, our method is fit to be used for any purpose related to deblending of objects in astronomical images. An example of such an application is the separation of the red and blue stellar populations of a spiral galaxy in the galaxy cluster Abell 2744. We provide a python package along with all simulations and routines used in this paper to contribute to reproducible research efforts.

Edp Sciences S A2016

The two-dimensional array of 2048 tilting micromirrors for astronomical spectroscopy

Michael David Canonica, Nico de Rooij, Wilfried Noell

In multi-object spectrometers, field selectors, which are located in the focal plane of the telescopes, are required for the selection of astronomical objects, such as stars or faint galaxies. We present a two-dimensional micromirror array as a field selector. Object selection is achieved through the precise tilting of micromirrors, which reflect the light of objects toward the spectrometer. These arrays were composed of 2048 (32 x 64) electrostatically actuated silicon micromirrors that measured 100 x 200 mu m(2). The micromirrors were addressed either by lines or individually using a line-column addressing scheme. The fabrication process of these devices involved three wafers and two wafer-level bondings. Characterization, by white light interferometry, revealed a tilt angle of 25 degrees at a voltage of 121 V, and a coated micromirror deformation below 10 nm. A fill factor of 82% and a contrast of 1000:1 were also observed. Demonstration of the line-column addressing scheme was achieved through its application to a sub-array of 2 x 2 micromirrors.

Institute of Physics2013

Precision Positioning of Microrobots for Multi-Object Spectrographs

Luzius Gregor Kronig

EPFL2020