Instrumentation and Software


Technical illustration of 4MOST
Credit: 4MOST Consortium

4MOST is a major new facility, currently under construction under AIP leadership to create a wide-field, high-multiplex spectroscopic survey facility for the VISTA telescope at the Paranal Observatory of the European Southern Observatory (ESO) . Starting in 2023 as the principle instrument on the VISTA telescope, 4MOST will deploy 2436 optical fibres in a 4.2 square degree field-of-view to one high-resolution and two medium-resolution spectrographs. It will collect high quality spectra over a period of at least 10 years yielding spectra of over 40 million stars and more than 40 million galaxies at resolution R>5000 and of 5 million stars at R~20,000.

The 4MOST science goals are mostly driven by four key all-hemisphere, space-based observatories of prime European interest: Gaia and PLATO (Galactic Archeology), eROSITA (High-Energy Sky), and Euclid (Cosmology and Galaxy Evolution). These main science cases drive the Key Surveys covering a large fraction of the Southern sky, with bright time mostly devoted to the Milky Way disk and bulge areas and the Magellanic Clouds, and the dark/gray time essentially devoted to extra-galactic targets. In addition there will be a significant of the fibre-hours devoted to ESO's Community Surveys, making 4MOST a true general-purpose survey facility, capable of delivering spectra of samples of objects that are spread over a large fraction of the sky. 4MOST can also follow-up tens of thousands of VRO/LSST, eROSITA and SKA transients per year.

The Milky Way and Local Volume and the Dwarf Galaxies and the Galactic Halo sections at AIP are developing several of the main Galactic Archeology science cases to study the Milky Way halo, disk and bulge/bar components and the Magellanic clouds, and perform extensive simulations to test the feasibility of the science with 4MOST. We are furthermore contributing to instrument science, by contributing to commissioning, calibration, and science performance verification activities, and to the development of the operations scheme and software of 4MOST.



Two-dimensional map of the diffuse background levels for Gaia's Radial Velocity Spectrograph. Horizontal: time, one satellite rotation of about 6 hours in total, Vertical: position on the CCD, for 4 detectors in total.

Credit: Katja Weingrill, AIP

ESA's space mission Gaia measures the positions, distances, space motions and many physical characteristics of more than one and a half billion stars in our Galaxy and beyond. Since 2007 our research section has been involved in the Data Processing and Analysis Consortium (DPAC) that is responsible for the processing of Gaia's data with the final objective of producing the Gaia Catalogue.

The Radial Velocity Spectrograph (RVS) onboard Gaia is an integral field spectrograph (IFU). All accumulated Gaia data are processed in six month intervals to derive self-consistent, calibrated, astrometric and spectroscopic observations. As a consequence of the IFU nature of the RVS, neighbouring sources with similar across scan positions on the detector will create spectra that overlap the target spectrum. As these spectra cannot be measured, the background correction becomes a non trivial task and specific algorithms are developed for it. In order to identify potential problems early on and to minimize loss of valuable data it is therefore essential to have a daily monitoring system.

The Milky Way and the Local Volume section at AIP is responsible for modelling the spectral contribution of contaminating point sources to a target readout window, using as much information as is available from the source. In full mode, this will include atmospheric parameters to choose a template spectrum, radial and rotational velocity for line shift and broadening, the magnitude for the brightness and the relative position for the spatial and spectral contribution. But also extended sources contribute to the background spectrum. Instead of the point source background, the diffuse extended background is measured. This is done in empty, so called virtual object windows, that after cleaning of cosmic rays, defect, saturated or disturbed pixels, blends with targets and point sources contain nothing but the diffuse background arising from zodiacal light, or extended objects as nebulae.

Furthermore, together with the Dwarf Galaxies and the Galactic Halo and Supercomputing and E-Science sections, our section is developing a Gaia pipeline to extract astrometry and photometry of the most crowded regions on the sky (Globular Clusters, the Milky Way and Magellanic Cloud centres), that cannot be measured with the normal pipelines of Gaia due to the too high data rate. Since Gaia's science operation started in 2014, so-called Service Interface Function (SIF) images have been recorded with Gaia Sky Mapper in order to increase the completeness of Gaia in nine selected dense regions of the sky. In 2019 a new working group was formed within Gaia DPAC in order to create a software pipeline, that identifies new sources in these images. The AIP takes a main role in this SIF CF working group as both the main software developer and also the manager are located at AIP. 

Last update: 23. February 2021