Deutsches SOFIA Institut (DSI)

ATUS

The 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 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) was 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.

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.

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)

 

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.

Pictures of ATUS

To the top of the page