VTT

Vacuum Tower Telescope with open dome as seen from GREGOR.
Image of a sunspot around the core of Ca II H (width 1nm). Speckle reconstruction with KISIP. Observation and image reconstruction: Matthias Schubert, Nazaret Bello Gonzalez.

The German observatory in Tenerife is comprised of two major telescopes: The VTT and GREGOR.

The VTT (Vacuum Tower Telescope) is operated under the leadership of the KIS (60%) in cooperation with the AIP (20%) and the MPS (20%). It is a classical solar telescope: two Coelostat mirrors feed the sunlight into the telescope. The primary mirror has a diameter of 70 cm and a focal length of 46 m. The telescope is located in a building with a height of some 38 m spanning more than 10 floors.

The picture to the right shows an example of the image quality achievable with the VTT: a sunspot taken with a narrow band filter (1nm) around Ca II H. Its pixel size is 0.06 arc sec (and was recorded simultaneously during a TESOS observation. ????)

The VTT offers several large optical laboratories for all kinds of permanent and temporary optical setups. Dedicated, more permanent setups include:

 
TESOS/VIP

a 2D spectrometer based on three Fabry-Pérot interferometers with a telecentric design and a spectral resolution of 250,000. It covers the visible part of the spectrum and can be operated in intensity mode to record Stokes-I line profiles of 2D images, and in polarization mode to measure the full polarization state of the light along line profiles (I, Q, U, and V).

The Echelle spectrograph

a grating spectrograph with a predisperser, which allows to measure up to three different spectral bands at a spectral resolution of about 1 million. A reliable interaction with the telescope and the AO-Tip-Tilt system ensures that maps of solar regions-of-interest can be scanned.

TIP-I (Tenerife Infrared Polarimeter)

a near-infrared spectropolarimeter which is used together with the Echelle spectrograph to measure the Stokes profiles of near infrared spectral lines (1.0-1.8 μm) with high spectral and spatial resolution. The solar surface can be scanned using a scanning unit. (TIP II has been moved to GREGOR).

In addition the VTT offers optical benches that can be used for user-defined optical setups. Presently in commission are:

LARS (Absolute Reference Spectrograph)

a laser-frequency reference comb for the measurement of line positions on an absolute wavelength scale. 

HELLRIDE (HELioseismic Large Region Interferometric Device)

a Fabry-Pérot spectrometer that can scan 16 different solar lines, with 20 wavelength steps each, at a cadence of 60 seconds, in a field-of-view as large as 100×100 arcsec2. This instrument is outstanding as it provides unique data to study atmospheric waves, and will help to understand how the chromosphere is heated by shock waves.

An adaptive-optics system is permanently installed and available to all instruments; this leads to a substantial improvement of the image quality. On good days, this provides a spatial resolution of about 0.2 arcsec at 500 nm for short exposures, and of some 0.5 arcsec for exposures as long as 10 seconds.

The VTT is operated from mid-April to mid-December with some 240 observing days. Most of the time is used by German or Spanish scientists. To get infos on how to observe with the VTT, click 'Observing with VTT' in the left column of this web site.

Its high spatial resolution and wide offer of state-of-the-art instrumentation, turns the VTT into a first-class infrastructure for ground-based solar physics. It delivers excellent data and is of interest for a large number of scientists all over Europe and the world. Based on VTT data, an average of 20 original (refereed) articles are published every year. 

The science goals of VTT observing campaigns are typically in the field of one of the following topics of solar physics:

  • physics of convection
  • active region and flux emergence
  • magnetic fields and magnetoconvection
  • chromospheric emission and heating
  • solar oscillation