Disentangling starlight

NGC 300. Credit: AIP/M. M. Roth

Disentangling starlight

Although they look like fuzzy patches of light, distant galaxies are actually made up of billions of stars and other astronomical intricacies. Telescopes are rarely powerful enough to study the ind...

Four hundred years ago, Galileo Galilei became the first person to point a telescope at the sky and prove that the hazy band of the Milky Way is actually composed of billions of individual stars. Astronomy has come a long way since then, and nowadays astronomers do not merely look at the stars, but also analyse their chemical composition, measure their rotation and velocity in space, and determine many other physical parameters to find out more about the Universe — all using a technique called spectroscopy, which is the study of the interaction of matter and light.

Stellar spectroscopy really started taking speed with the emergence of a technique called integral field spectroscopy about 25 years ago. This technique allows astronomers to obtain a 3D view of a galaxy in just one shot. It uses an Integral Field Unit (IFU) to divide the field of view into many segments — or pixels — to obtain a more comprehensive overview of the whole. The signal from each pixel is fed into a spectrograph which generates a light spectrum for each one. The result is therefore a data cube, a sort of "stack" of images, each at a different wavelength. The pixels in this case are rather lovingly named “spaxels”.

The integral field spectrographs developed at this time - such as the Potsdam Multi-aperture spectrophotometer (PMAS) [1] - still had a very low number of Spaxels by today's standards. PMAS, for example, only has 256 Spaxels, while a modern mobile phone camera has about 10 to 15 million pixels. A major step forward in 2014 was the installation of MUSE, the multi-unit Spectroscopic Explorer, at ESO's VLT in Chile. The AIP has essentially participated in the development of this instrument. MUSE hosts incredible 90,000 Spaxels and has excellent sensitivity.

Beyond the boarders of the Milky Way

The primary raison d’etre of MUSE is to study the origin and development of the Universe as a whole. As part of the guaranteed observation time available to the MUSE consortium, Martin Roth, department head of innoFSPEC at AIP, requested the use of the new instrument to observe the single stars in the spiral galaxy NGC 300. Similar observations had already been made for nearby galaxies in the so-called Local Group, but not for galaxies farther away - such as NGC 300. Six million light-years from the Milky Way it is located outside the Local Group and a "typical" spiral galaxy.

Thanks to the powerful instrument and specially developed software [2] [3], the team was able to identify individual stars with high clarity in NGC 300 as well as gaseous regions, supernova remnants, planetary nebulae and ionized hydrogen regions. Even distant background galaxies were faintly visible through the galaxy [4]. MUSE is special because it can look at light with a wide range of wavelengths, making many different objects and colours visible.

Technological plans for the future of exploring galactic past

The scientists hope to be able to observe a variety of stars in detail with other instruments. Under the leadership of the AIP, an international consortium for ESO is currently building the instrument 4MOST, which will enable the spectroscopy of up to 2,400 individual stars per single exposure in the Milky Way. The goal is to study millions of stars in the attempt to unravel our galaxy’s formation history and evolution, as part of a vibrant field of research called “galactic archaeology”.

By analogy with this, working with MUSE in the much further galaxy NGC 300 is already enabling "extragalactic archeology" for the first time ever. The enormous light collection capacity of the future Extremely Large Telescope (ELT) of ESO, combined with the extremely sharp image quality enabled by adaptive optics, promises extraordinarily interesting development prospects for this new field of research [5].


Data cube, generated by MUSE. (Credit: AIP)



[1] Roth, M.M., Kelz, A., Fechner, T., Hahn, T., Bauer, S.-M., Becker, T., Böhm, P., Christensen, L., Dionies, F., Paschke, J., Popow, E., Wolter, D., Schmoll, J., Laux, U., Altmann, W. 2005, "PMAS: The Potsdam Multi-Aperture Spectrophotometer. I. Design, Manufacture, and Performance", PASP 117, 620

[2] Kamann, S., Wisotzki, L., Roth, M. M. 2013, “Resolving stellar populations with crowded field 3D spectroscopy”, A&A 549, 71

[3] Husser, Tim-Oliver, Kamann, Sebastian, Dreizler, Stefan, Wendt, Martin, Wulff, Nina, Bacon, Roland, Wisotzki, Lutz, Brinchmann, Jarle, Weilbacher, Peter M., Roth, Martin M., Monreal-Ibero, Ana 2016, MUSE crowded field 3D spectroscopy of over 12 000 stars in the globular cluster NGC 6397. I. The first comprehensive HRD of a globular cluster, A&A 588, A148

[4] Roth, M. M., Sandin, C., Kamann, S., Husser, T.-O., Weilbacher, P. M., Monreal-Ibero, A., Bacon, R., den Brok, M., Dreizler, S., Kelz, A., Marino, R.A., Steinmetz, M. 2018, MUSE crowded field 3D spectroscopy in NGC300 I. First results from central fields, A&A 618, A3

[5] An Expanded View of the Universe -  Science with the  European Extremely Large Telescope, European Souther Observatory, Garching 2010, Hrsg. Mariya Lyubenova & Markus Kissler-Patig


The development of the tools PMAS, MUSE, and 4MOST was or is funded by the collaborative research of the Federal Ministry of Education and Research.

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12 January | Observation Night with the Great Refractor

On Saturday, January 12, 2019, from 5 pm, the Leibniz Institute for Astrophysics Potsdam (AIP) and the Förderverein "Großer Refraktor" invite to a public observation night in the Great Refractor.


The event is part of the "100 Hours Astronomy" campaign that marks the 100th anniversary of the International Astronomical Union (IAU) 2019. From January 10th to 13th amateur and professional astronomers around the world will be inviting you to share knowledge and enthusiasm for astronomy in a variety of formats.


Admission is free, no registration required.

A donation for the preservation of the Great Refractor is welcome.


Venue: Great Refractor, Telegrafenberg, Potsdam


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Astronomy in the European Open Science Cloud

20 November 2018. First quarter 2019 sees the exciting launch of ESCAPE, one out of the five successfully retained Cluster projects, which the European Commission supports with €16 million to boo...

Nowadays, machine learning techniques are being used in many fields of science. Instead of developing complex codes, a computer learns how to solve otherwise time-consuming problems that involve much manual labor. Typically, a huge amount of data is a prerequisite to teach the computer how to identify patterns in the training set and enabling it without any human interaction to recognize similar features in new data.

European Open Science Cloud (EOSC) is a cloud for research data in Europe allowing for universal access to data; a single online platform where all European researchers will be able to find, access and re-use data produced by other scientists, and to deposit, analyse and share data they have been paid to produce. EOSC will help increase recognition of data intensive research and data science. Its architecture is developed as a data infrastructure commons serving the needs of scientists, providing both common functions and localised services delegated to community level. EOSC will federate existing resources across national data centres, European e-infrastructures and research infrastructures by gradually opening up its user base to the public sector and industry.

ESCAPE – « The European Science Cluster of Astronomy & Particle Physics ESFRI Research Infrastructures » answers the EOSC ambition in bringing People, Data, Services, Training, Publications, Projects & Organisations, all together in an integrated and federated environment. The project is led by CNRS, the French public research organisation, with a consortium of 31 partners including 27 European partner institutions.

The Optical Solar Physics group and the Super Computing and E-Science section at AIP will develop a Classification Engine for Solar and Stellar Spectra, which automatically identifies, classifies, and provides physical properties of solar and stellar atmospheres. This contribution by AIP to Escape's Foundation for Competence for Software and Service Innovation (COSSI) is embedded in a major effort bringing together machine and deep learning techniques from all branches of astronomy, astrophysics, solar physics, and high-energy particle physics.

ESCAPE press release and further information:


Scientific Contact: apl. Prof. Dr. Carsten Denker, 0331-7499-297,,
Dr. Harry Enke, 0331-7499 433,
Media contact: Dr. Janine Fohlmeister, 0331-7499 803,


The key areas of research at the Leibniz Institute for Astrophysics Potsdam (AIP) are cosmic magnetic fields and extragalactic astrophysics. A considerable part of the institute's efforts aim at the development of research technology in the fields of spectroscopy, robotic telescopes, and e-science. The AIP is the successor of the Berlin Observatory founded in 1700 and of the Astrophysical Observatory of Potsdam founded in 1874. The latter was the world's first observatory to emphasize explicitly the research area of astrophysics. The AIP has been a member of the Leibniz Association since 1992.

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IAU Symposium 354: Magnetfelder der Sonne und der Sterne

The Leibniz-Insitute for Astrophysics Potsdam (AIP) invites together with the New Jersey Institute of Technology to a symposium of the International Astronomical Union. It is going to take place du...

One of the puzzles of solar and stellar magnetism is related to the origin of extreme flare events. Despite the very weak magnetic cycle the Sun produced, in 2017 some of the strongest flares in the history of observations were seen. How are such observations related to the magnetism of stars that produce super-flares? What physical mechanism may cause such extreme events?  These and more questions will be discussed at the conference. The role of stellar magnetism in the interactions of stars and their planets is also of special interest for determining conditions for the habitability of planets.

The Symposium will include an open public session on solar eclipses and planetary transits. In particular, total solar eclipses provide high-resolution measurements of the magnetic field in the low corona, which cannot be obtained by any other means. The Symposium has thus been organized to embrace the total solar eclipse in Chile on July 2nd. In addition, this session will present a broad historical overview of solar eclipses, planetary transits, their role in astronomy, as well as a general talk on habitability of exoplanets.

More information and the registration form for the symposium can be found on the conference web page.


Web page:

Scientific Contact: Prof. K. G. Strassmeier, 0331-7499-223,

Press Contact: Franziska Gräfe, 0331-7499 803,

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AIP welcomes nominations for 2019 Wempe Award

7th November 2018. The Leibniz Institute for Astrophysics in Potsdam, Germany (AIP), is calling for nominations and applications for the Johann Wempe Award 2019.

In honour of Professor Johann Wempe (1906–1980), the last director of the former Astrophysical Observatory of Potsdam (AOP), the AIP grants the Johann Wempe award to outstanding scientists.


The award consists of a stipend to facilitate a research visit to the AIP of up to six months. The recipient may be either a promising young scientist who has already made notable achievements or a senior scientist, in recognition of his or her life's work. The recipient is expected to enrich the scientific life of the institute through a series of lectures in their area of expertise.


See also:

Application and nomination materials must arrive no later than December 31, 2018.

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