Disk-unresolved solar light shall be fed to the spectrograph from a small „Sun-as-a-star“ telescope and a fiber connection via the PEPSI calibration unit. Its aim is a) to provide an external comparison source for the UHR mode of PEPSI and its long-term stability and, b) to monitor the Sun for measuring line-bisector variations over an entire activity cycle. The spectral-resolution mode with 320,000 shall be used.
The SPRTV5. Alt-az mount. Dimensions are 190x120x250mm, mass approx, 8 kg. The box contains all gears, the two stepper motors and two limit switches. The solar visor is seen in the upper right corner. It consists of a four quadrant detector with a total filed of view 8 degrees. The actual sola-feed telescope would be mounted on the axis leaving the box to the right.
The solar tracker provides a program-supported autotrack mode based on a solar visor that automatically switches to continuous pre-computed tracking once the Sun has been lost, e.g. due to clouds. The tracker is connected to a PC through a RS232 link. The stepper resolution is 0.009 degrees (32″) and the positioning precision is 0.02 degrees (72″) relative to the mechanical zero position of the system. The actual telescope is based on a simple 10mm achromat with a solar-certified eyepiece which pupil plane is used to feed a 600µm fiber. The raw data flow is 500GB/day and the total archive need is 120TB/year and are determined from the goal to obtain three full-wavelength R=320,000 spectra with S/N of approx. 5,000:1 per day.
Envisioned integration scheme for a single S/N≈5000:1 spectrum. Calibration frames for CD#1 are taken before the science frames, for CD#2 they must be taken in the middle of the sequence, and for CD#3 can be taken after the science frames.
Latest CAD design for the SDI unit (view 1).
Latest CAD design for the SDI unit (view 1).
SDI test
Testing the SDI unit on the roof of the Schwarzschild house at AIP.
SDI controller box inside.
SDI GUI
Click on the image to view the SDI GUI in operation. Note that a transiting spot can be seen on the Sun.
