The main goal of the third iteration of the High Accuracy Radial velocity Planet Searcher (HARPS3) is to search for Earth-like planets over a ten-year programme. As part of this search, spectropolarimetric observations have been envisioned foreseeing the need for new ways to reduce stellar activity jitter which obscures the 10 cm/sec radial velocity signal of such planets. HARPS3 has thus been designed with an insertable polarimetric sub-unit. This sub-unit consists of two superachromatic polymer retarders, one quarter-wave and one half-wave, to separately detect all Stokes parameters of a target, as well as a polarimetric beam splitter to separate the parallel polarimetric beams by 30 mm to feed the science fibers. In this paper we report on the currently nonfunctional polarimetric sub-unit of the HARPS3 spectrograph and discuss the upgrade expected before commissioning that will fix current issues. We discuss the possible observation schedule of polarimetric observations for the Terra Hunting Experiment and the potential impacts of polarimetric observations on mitigating stellar radial velocity jitter.
We present a description of A dual-Beam polarimetric Robotic Aperture for the Sun (ABORAS), to serve as a Solar input with a dedicated Stokes V polarimeter for the HARPS3 high-resolution spectrograph. ABORAS has three main science drivers: trying to understand the physics behind stellar variability, tracking the long term stability of HARPS3, and serve as a benchmark for Earth-sized exoplanet detection with HARPS3 by injecting an Earth RV signal into the data. By design, ABORAS will (together with the HARPS3 instrument) be able to measure 10cm/s variations in RV of the integrated Solar disk and detect integrated magnetic field levels at sub 1 Gauss level through circularly polarized light.
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