Saturday, April 25, 2015

First Light for PEPSI

The LBT observatory from inside. Credit:

The Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) has received its first celestial light through the Large Binocular Telescope (LBT). Astronomers from the Leibniz Institute for Astrophysics Potsdam in Germany, showed the instruments incredible capabilities at different wavelengths and resolving powers. Among the first targets were several of the bright Gaia-ESO benchmark stars, magnetically active stars, solar-like stars with planets, a solar twin in M67, Jupiter’s four Galilean moons, and the bright Nova Sgr 2015b.

On April 1st, the 2 x 8.4m mirrors of LBT, effectively an 11.8m telescope, were turned to the K3 dwarf star HD 82106, and PEPSI received its first celestial photons through the world’s largest telescope. The instrument splits the stellar light into a spectrum with a wavelength resolution otherwise only obtainable in solar physics. The commissioning team of four AIP astronomers on the 3200m Mt. Graham in Arizona was preceded by a team of five who prepared the instrument for this event.

The star was only the first in a series of commissioning targets that test the instrument’s resolving powers at different wavelengths. Switching between resolution modes or between wavelength settings takes less than a minute and can be done any time. PEPSI is the only instrument that enables astronomers to point to bright stars as well as to faint quasars during the same night.

PEPSI is a fibre-feed high-resolution Echelle spectrograph for the Large Binocular Telescope (LBT) in Arizona. It is designed to utilize the two 8.4m apertures of the LBT in a unique spectropolarimetric mode. With two identical but independent polarimeters, mounted in each of the direct F/15 Gregorian foci, this will allow the simultaneous observation of circularly and linearly polarized light with high spectral and temporal resolution. Besides the polarimeters, integral (non-polarized) light can be feed to the spectrograph via two permanently mounted focus stations, thereby providing a high resolution standby spectrograph for the LBT Observatory.


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