Prof. Dr. rer. nat. Alfred Krabbe

Barbara Klett

Dr.-Ing. Thomas Keilig

Deputy SMO Director (Kalifornien)
Dr. rer. nat Bernhard Schulz

Standortleiter AFRC & SOFIA Teleskop Manager
Dipl.-Ing. Michael Hütwohl

Standortleiter ARC & und Facility Scientist
Dr. rer. nat. Jürgen Wolf

Technology Advisor
Prof. Dr.-Ing. Jörg Wagner

Bildungs- und Öffentlichkeitsarbeit
Dr. rer. nat. Dörte Mehlert

Deutsches SOFIA Institut
Pfaffenwaldring 29
70569 Stuttgart

Tel. +49 (0)711/685-62379
Fax +49 (0)711/685-63596

Astronomical Telescope of the University of Stuttgart

The ATUS 0.6 meter Ritchey-Chrétien telescope, mounted on a
German equatorial Astro-Physics 3600GTO mount.
The fast Andor iXon EMCCD camera ("FPI") can be seen at the RC
focus; a QSI 632ws-8 camera is mounted at the guide scope ("FFI").

The Astronomical Telescope of the University of Stuttgart (ATUS) has been established by the university's Institute of Space Systems (IRS) with support of the Stratospheric Observatory for Infrared Astronomy (SOFIA), funded by the DLR Space Administration. The telescope is managed and operated by the German SOFIA Institute (DSI), a department of the IRS. For the university, the telescope serves as a training platform for aerospace engineering students in basic astronomy and in remote control of complex systems. M.Sc. and Ph.D. students use it as a research instrument for their engineering and astronomy projects. For SOFIA, it is used as a test platform to evaluate new hardware and software before the integration on the airborne observatory. In some cases, the telescope is also used to support SOFIA missions by providing preparatory or parallel measurements of a target or to conduct follow-up observations.

ATUS is a 0.6 meter fully reflective telescope in Ritchey-Chrétien configuration made by Officina Stellare, Italy. Its primary and secondary mirrors are made of the ultra-low-expansion glass ceramics CLEARCERAM-Z HS, supplied by Ohara Corporation, Japan. The primary mirror has a conically shaped backside to reduce its weight. The secondary mirror cell is motorized to shift the mirror along the optical axis for focusing. The optical tube assembly is a dual carbon fiber truss structure with titanium alloy joints. A German equatorial mount made by Astro-Physics (AP3600GTOPE) carries the telescope and allows slew speeds of up to 2.5 degrees per second. A precision encoder system at the polar axis of the mount provides nominal guiding accuracy better than 0.5 arcsec over periods of 20 minutes.

A third camera, the Wide Field Imager, is mounted sideways.
A mirror cover consisting of four flaps (opened in the picture) protects
the primary mirror from dirt and dust when the telescope is not in use.

The first and primary instrument at the Ritchey-Chrétien focus is a back-illuminated EMCCD camera made by Andor, Belfast combined with a 10-position filter wheel containing a Sloan filter set. The same camera and a similar filter set are used in SOFIA's new Focal Plane Imager (FPI+). It offers high quantum efficiency (ηPeak > 90%), high frame rates and virtually gap free imaging thanks to the sensor's frame-transfer architecture. Very low dark currents are achieved by the camera's thermoelectric cooler that cools the sensor as much as 95 K below ambient. The main telescope is complemented by a piggy-back mounted Wide Field Imager which consists of a ProLine Camera made by Fingerlakes Instrumentation with a back-illuminated e2v CCD47-20 sensor and a commercial 135 mm Canon telephoto lens. This setup is similar to the SOFIA Wide Field Imager. A 130 mm f/6 refractor can be used as a guide scope, or as an imager with an intermediate field size ("Fine Field Imager"). It has a camera made by Quantum Scientific Imaging, which employs a front-illuminated KAF-3200ME CCD.

ATUS is located at Sierra Remote Observatories (SRO) in the foothills of California's Sierra Nevada, a location with seeing conditions in the 1.0 to 1.5 arcsec range in summer. The telescope's control computer and software are set up for remote access via an internet connection. It is remotely operated from the SOFIA Science Center in Moffett Field, California and from Stuttgart, Germany.

Optical Characteristics of ATUS and its Instrumentation

ATUS Optical System

Optical configuration Ritchey-Chrétien
Clear aperture diameter of primary mirror, D 600 mm
Primary mirror focal ratio f/3
Clear aperture diameter of secondary mirror 222 mm
Diameter of secondary mirror baffle (central obscuration) 272 mm
Obscuration ratio, ε 45.3 %
Obscured area 20.6 %
Effective focal length, f (nominal) 4800 mm
Effective focal ratio (nominal) f/8
Diffraction limit, DAiry = 2.44 λ/D 0.46 arcsec

Main Camera ("Focal Plane Imager" / FPI)

Camera model Andor iXonEM+ DU-888E-C00-BV
Sensor type e2v CCD201-20, back-illuminated, frame transfer EMCCD
Sensor dimensions 1024 x 1024 pixel
Pixel size 13 x 13 µm2
Field of view on sky 9.53 x 9.53 arcmin2
Plate scale 0.56 arcsec/pixel
Mechanical shutter No
Filter wheel SBIG CFW-10; 10 positions for 1¼ inch filter cells
Available filters - Parfocal Astrodon Sloan 2nd generation filter set (g'2, r'2, i'2, z_s2, Y2) & clear filter (> 395 nm);
- Custom VR filter (500 - 700 nm bandpass)
- Opaque filter, used to record bias or dark frames
Achievable frame rates with... no binning 2x2 binning 4x4 binning
Full frame readout 8.9 fps 17.4 fps 33.5 fps
512 x 512 AOI 17.6 fps 34.0 fps 63.9 fps
32 x 32 AOI 205.3 fps 315.4 fps 427.3 fps

Guide Scope ("Fine Field Imager" / FFI)

Optical configuration Apochromatic refractor
Clear aperture diameter 130 mm
Focal ratio f/6
Camera model QSI 632ws-8
Sensor type ON Semiconductor (formerly Kodak) KAF-3200ME; front illuminated, full frame CCD with microlenses and enhanced response towards blue wavelengths
Sensor dimensions 2184 x 1472 pixel
Pixel size 6.8 x 6.8 µm2
Field of view on sky 65.4 x 44.1 arcmin2
Plate scale 1.80 arcsec/pixel
Mechanical shutter Yes
Filter wheel Integrated in camera; 8 positions for 1¼ inch filter cells
Available filters Parfocal filter set, consisting of
- Astrodon Sloan 1st generation filter set (g', r', i', z')
- Narrowband H-α, O-III, S-II filters (3 nm bandpass)
- Clear filter (> 395 nm)
Readout speed, unbinned 2.78 s (full frame)
2.17 s (128 x 128 AOI)
ATUS close-up view ATUS Wide Field Imager
Close-up view of the secondary mirror assembly and focus mechanism of ATUS. The primary mirror cover is closed is this picture. The front truss is usually covered by a fabric shroud to protect the optics from any potential stray light and dust. The Wide Field Imager uses a commercial Canon EF 135mm f/2.8 telephoto lens and an Arduino microcontroller for focussing.

Wide Field Imager (WFI)

Optical configuration Commercial telephoto lens
Focal length, f 135 mm
Camera model Custom FLI ProLine PL4720
Sensor type e2v CCD47-20; back-illuminated, frame transfer CCD
Sensor dimensions 1024 x 1024 pixel
Pixel size 13 x 13 µm2
Field of view on sky 5.65 x 5.65 deg2
Plate scale 19.9 arcsec/pixel
Mechanical shutter No
Filter wheel FLI CFW-2-7; 7 positions for 50 mm filter substrates
Available filters - Parfocal Johnson/Bessel filter set (UBVRI)
- Opaque filter, used to record bias or dark frames
Frame rates, unbinned 1.5 fps (full frame)
5.6 fps (128 x 128 AOI)


  1. Sickafoose, A.A., Bosh, A.S., Levine, S.E., Zuluaga, C.A., Genade, A., Schindler, K., Lister, T.A., et al., 2019. A stellar occultation by Vanth, a satellite of (90482) Orcus. Icarus, 319, pp.657–668. DOI: 10.1016/j.icarus.2018.10.016.
  2. Bosh, A.S., Sickafoose, A.A., Levine, S.E., Zuluaga, C.A., Genade, A., Schindler, K., Lister, T.A., et al., 2018. The 2017 occultation by Vanth: a revised analysis. AAS/Division for Planetary Sciences Meeting Abstracts, 50, p.311.01.
  3. Sickafoose, A.A., Levine, S.E., Bosh, A.S., Zuluaga, C.A., Person, M.J. & Schindler, K., 2018. Pluto’s atmosphere after New Horizons: results from stellar occultations in 2017 and 2018. AAS/Division for Planetary Sciences Meeting Abstracts, 50, p.502.02.
  4. Sickafoose, A.A., Bosh, A.S., Levine, S.E., Zuluaga, C.A., Genade, A., Schindler, K., Lister, T.A., et al., 2017. A 2017 stellar occultation by Orcus/Vanth. AAS/Division for Planetary Sciences Meeting Abstracts, 49, p.216.02.
  5. Bosh, A.S., Zuluaga, C.A., Levine, S.E., Sickafoose, A.A., Genade, A., Schindler, K., Lister, T.A., et al., 2017. Astrometry of the Orcus/Vanth occultation on UT 7 March 2017. AAS/Division for Planetary Sciences Meeting Abstracts, 49, p.216.01.
  6. Schindler, K., Wolf, J., Bardecker, J., Olsen, A., Müller, T., Kiss, C., Ortiz, J.L., et al., 2017. Results from a triple chord stellar occultation and far-infrared photometry of the trans-Neptunian object (229762) 2007 UK126. A&A, 600, p.A12. DOI: 10.1051/0004-6361/201628620.
  7. Schindler, K., Lang, D., Moore, L., Hümmer, M., Wolf, J. & Krabbe, A., 2016. Computer-aided star pattern recognition with astrometry.net: in-flight support of telescope operations on SOFIA. Proc. SPIE, 9913, pp.991307-991307–14. DOI: 10.1117/12.2231531.
  8. Zintz, K., 2015. Stuttgarter Projekt Atus: Ein ferngesteuertes Teleskop für die Uni (Stuttgart’s project Atus: A remotely controlled telescope for the university). Stuttgarter Zeitung, 13 November 2015.
  9. Timerson, B., Durech, J., Beard, T., McPartlin, C., Morgan, W., Schindler, K., Wolf, J., et al., 2015. Asteroidal Occultation by 82 Alkmene and the Inversion Model Match. Minor Planet Bulletin, 42, pp.129–131.