ChroTel - Chromospheric Telescope

ChroTel is a telescope to observe the solar chromosphere across the full disk. We acquire narrow-band filtergrams in the lines of Calcium II K (393.3 nm), H alpha (656.3 nm) and Helium I (1083.0 nm) with a cadence of less than a minute. As a special feature we can also derive He I Doppler maps (velocity maps) from these data. 

Latest ChroTel image: The chromosphere of the Sun

ChroTel is continously observing the Sun, weather permitting. The following display is showing the latest image. Examples of ChroTel images and a more detailed description of the instrument are provided below.

Calcium II K
H alpha
Helium 1083

Brief Introduction into ChroTel

ChroTel is a 10 cm aperture telescope to observe the chromosphere of the Sun. It was developed at the Kiepenheuer-Institute together with the High Altitude Observatory (HAO) in Boulder, USA. With a spatial resolution of about 2 arcsec it observes the solar chromosphere in its most prominent lines un the near UV, the red and the infrared (Ca II K, Hα and He I) using a 2048x2048 pixel CCD. ChroTel uses a two mirror system ("turret") next to the VTT building that relays a stabilized image of the solar disc into a laboratory within the VTT building (click on the video on the right to see it in operation). The heart of the optical lab is a filter system consisting of three narrow-band Lyot filters, of which one is tunable. The He I filter is tunable and observations are taken at seven wavelength positions fully covering the whole spectral line, giving full-disk chromospheric Doppler maps. Images in all channels (and the seven He I bands) can be taken with a cadence of below one minute. The following intensity maps show examples in all three channels.

The operation of ChroTel is automatic, as far as possible. The data with the full cadence will be temporarily stored on Tenerife and depending on interest and events on the Sun they are transferred to Freiburg. The ChroTel data will also serve as live images for VTT and Gregor and will be available over internet. The scientific data of ChroTel will be freely available for scientific and educational use.

Observing campaigns together with the Tenerife Infrared Polarimeter (TIP) at the VTT enable us to calibrate the Doppler shift maps derived from the seven filtergrams of ChroTel in the Helium I channel.


Die links dargestellten Daten zeigen interessante Strömungsmuster in flachen kühlen Bögen am Rand einer aktiven Region und unterstreichen das Potential von ChroTel für den regulären wissenschaftlichen Betrieb. Die Qualität von ChroTel kann anhand der Doppler-Karte in Helium I abgelesen werden, die eine aktive Region und das umgebende Netzwerk zeigt.

Mit ChroTel möchten wir untersuchen, wie die Chromosphäre der Sonne auf bestimmte Vorgänge und Prozesse in der Photosphäre reagiert. Von besonderem Interesse sind dabei Veränderungen des Netzwerks sowie bei großskaligen Ereignissen, wie z. B. Flares und koronalen Massenauswürfen (CMEs). Weiterhin wollen wir Erkenntnisse über die chromosphärische Quelle des Sonnenwindes gewinnen.