Instrumentation at the VTT 2015

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.

General Setup

The German Vacuum Tower Telescope (VTT) has a diameter of 70 cm and a focal length of 45.95 m. It is equipped with an adaptive optics system (Kiepenheuer Adaptive Optics system, KAOS). The corrected beam can be fed to all instruments listed below. Some of the instruments can be used simultaneously as will be described at the end of this overview.

 

A list of available broad and narrow band interference filters: vtt_filterlist.pdf.

Spectrograph

The Echelle spectrograph has a spectral resolution of > 750 000 and is a powerful tool for diagnostic spectroscopy. For spectropolarimetry the Tenerife Infrared Polarimeter (TIP, see below) can be integrated into the spectrograph. Up to three wavelength regions can be selected by the predisperser and can be observed simultaneously. Three gratings with different blaze angles are available to optimize the light throughput. Data acquisition is performed with up to three of the following CCDs: PCO 1, PCO 2, & Sensicam (more details on CCDs below). On the slit (focal plane of telescope), the image scale is 4.49 arcsec/mm. The image scale in the focal plane of the spectrograph is 8.98 arcsec/mm. For technical information and if you want to know which combination of spectral lines can be observed simultaneously please contact Thomas Kentischer (tk@leibniz-kis.de ). 

Data calibration packages (sophisticated flat fielding routines) to produce science-ready data is available.

Low-dispersion spectrograph with large spectral range

Ca II H and Ca II K line with low dispersion spectrograph (black line). The over-plotted red line corresponds to the FTS profile.

Another high-resolution spectrograph is also available at VTT with a spectral resolution of about 100 000. Compared to the Echelle spectrograph, it provides a much wider spectral range, about 4.5 nm (see Figure for the Ca II H and K spectrum, 4072 pixels with 11 mA per pixel). There is a special grating for this purpose which replaces the standard predisperser-grating. Data acquisition is performed with a single PCO camera placed at the position of the predisperser focus. The slit length corresponds to 90 arcsec and fits well onto the PCO camera with 0.0849 arcsec /px. Please contact Thomas Kentischer or Reza Rezaei ) for more information.

LARS

LARS (Lars is an Absolute Reference Spectrograph) is an instrument for precision solar spectroscopy in applications that do not require high spatial or temporal resolution but a high signal to noise ratio and an accurate wavelength calibration. It is based on the existing VTT echelle spectrograph (R > 750 000) extended with a single mode fiber feed (SMFF) and a laser frequency comb (LFC) based wavelength calibration system. The fiber feed picks up light from the VTT focal plane with a field of view of three arcseconds on the sky. It enables a high spectral purity with low instrumental straylight and superior flatfield correction with a tungsten flatfield lamp. With the LFC an absolute wavelength calibration of better than one meter per second is possible. For more information please contact Johannes Löhner-Böttcher or Thomas Kentischer.

TESOS: Triple Etalon SOlar Spectrometer

This instrument performs 2D spectroscopy. Three Fabry-Perot interferometer (etalons) are tuned to scan through a solar absorption line. For each wavelength, 2D images of a narrow band (spectral resolution of 280 000) and of a broad band image are recorded. Approximately 100 wavelength positions can be recorded within 40 seconds. A data reduction software package is available. TESOS can be used simultaneously with TIP (cf. Sect. 8). More information: Thomas Kentischer. Technical support during observation is provided. Data calibration routines are available.

Relevant publication:

Tritschler, Schmidt, Langhans, & Kentischer, 2002, Solar Physics 211, 17: ”High-resolution solar spectroscopy with TESOS - Upgrade from a double to a triple system”.

Kentischer, Schmidt, Sigwarth, & Uexkuell, 1998, A&A 340, 569: ”TESOS, a double Fabry-Perot instrument for solar spectrocopy”. von der Lühe & Kentischer, 2000, A&AS 146, 499: ”High spatial resolution performance of a triple Fabry-Perot filtergraph”.

Manual: How to use TESOS/VIP.

TESOS/VIP: Visible Imaging Polarimeter

TESOS can be extended to operate as a polarimeter to measure the four Stokes parameter at wavelengths between 600 and 660 nm. It can also be used as a simple V-polarimeter. VIP was developed as a collaboration between the Instituto de Astrofisico de Andalucia and the KIS. First light images can be viewed at the KIS archive of the images of the month. If you are interested to observe with VIP@TESOS please contact Thomas Kentischer.

Technical support during observation and for data reduction is provided.

Relevant publication:

Beck, Bellot Rubio, Kentischer Tritschler, & del Toro Iniesta, 2010, A&A 520, A115:
”Two-dimensional solar spectropolarimetry with the KIS/IAA Visible Imaging Polarimeter ”.

HELLRIDE

HELLRIDE stands for HELioseismological Large Regions Interferometric DEvice. It is a new Fabry-Pérot based spectrometer specifically designed to record the Doppler shifts of a large number of solar spectral lines in a quasi-simultaneous and multitarget mode. It will be used to carry out helioseismic investigations of the solar atmosphere and to analyze footpoint flows of coronal loops. Solar flares may be a further target in a future upgraded mode. Please consult Joe Staiger for information.

Optical Lab Space

The VTT offers an optical lab, where users can temporarilly install their own instrumental setup. The optical bench is fed with Solar Light via an adjustable 45 degree mirror in the first flor (in the same way as TESOS is fed with light). For information please contact Thomas Kentischer.

Spectrograph and Imaging

Three CCDs are available: PCO 1, PCO 2, and Sensicam. PCO2 has a wedged window and is suited for observations with high spectral resolution.

Speckle Cameras and code (DALSA II and Sensicam)

For performing imaging at diffraction limited spatial resolution, the VTT is equipped with two high cadence camera: Sensicam and DALSA II. These CCD cameras can be operated in the speckle burst mode or in the frame selection mode. For performing the speckle reconstruction, a user friendly (click & go) speckle reconstruction code KISIP (Kiepenheuer Institut Speckle Imaging Package, extended Knox-Thompson method) can be provided. For information and observing requests contact Oskar von der Lühe.

Relevant publication:

  • Wöger & v.d. Lühe 2006: ”KISIP: a software package for speckle interferometry of adaptive optics corrected solar data”. Advanced Software and Control for Astronomy II. Edited by Bridger, Alan; Radziwill, Nicole M. Proceedings of the SPIE, Volume 7019, pp. 70191E-70191E-8 (2008).
  • Mikurda, von der Lühe, & Wöger, 2003, AN supplement 324, p112: ”Solar Imaging with an Extended Knox- Thompson Technique”.

Multiwavelength observations with combined instruments

A dichroic beam splitter allows to reflect the short wavelengths (λ < 800 nm) into any instrument on the first floor (TESOS, optical bench) and to transmit the near infrared to the Echelle spectrograph (with or without TIP). Alternatively, a gray 50:50 beam splitter can also be used for simultaneous observations in the visible.