Habitable Zones & Global Climate

A Harsh Test of Far-Field Scrambling with the Habitable Zone Planet Finder and the Hobby Eberly Telescope

By Keith Cowing
March 9, 2021
Filed under
A Harsh Test of Far-Field Scrambling with the Habitable Zone Planet Finder and the Hobby Eberly Telescope
An image of HET showing the dome housing the telescope, as well as the CCAS tower to the left of the dome. Credit: Marty Harris/McDonald Observatory. Right: Snapshots of the pupil viewing camera under afternoon sky illumination. The central obscuration with the PFIP, as well as the support strusses. Also visible are the fiber bundles on both sides of the central obscuration. The CCAS tower is visible in the top right image obscuring part of the pupil.

The Habitable zone Planet Finder (HPF) is a fiber fed precise radial velocity spectrograph at the 10 m Hobby Eberly Telescope (HET). Due to its fixed altitude design, the HET pupil changes appreciably across a track, leading to significant changes of the fiber far-field illumination.

HPF’s fiber scrambler is designed to suppress the impact of these illumination changes on the radial velocities — but the residual impact on the radial velocity measurements has yet to be probed on sky. We use GJ 411, a bright early type (M2) M dwarf to probe the effects of far-field input trends due to these pupil variations on HPF radial velocities (RVs). These large changes (∼ 2x) in pupil area and centroid present a harsh test of HPF’s far-field scrambling. Our results show that the RVs are effectively decoupled from these extreme far-field input changes due to pupil centroid offsets, attesting to the effectiveness of the scrambler design.

This experiment allows us to test the impact of these changes with large pupil variation on-sky, something we would not easily be able to do at a conventional optical telescope. While the pupil and illumination changes expected at these other telescopes are small, scaling from our results enables us to estimate and bound these effects, and show that they are controllable even for the new and next generation of RV instruments in their quest to beat down instrumental noise sources towards the goal of a few cm/s.

Shubham Kanodia, Samuel Halverson, Joe P. Ninan, Suvrath Mahadevan, Gudmundur Stefansson, Arpita Roy, Lawrence W. Ramsey, Chad F. Bender, Steven Janowiecki, William D. Cochran, Scott A. Diddams, Niv Drory, Michael Endl, Eric B. Ford, Fred Hearty, Andrew J. Metcalf, Andrew Monson, Paul Robertson, Christian Schwab, Ryan C. Terrien, Jason T. Wright

Comments: 16 pages. Accepted for publication in The Astrophysical Journal
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM)
Cite as: arXiv:2103.05148 [astro-ph.EP] (or arXiv:2103.05148v1 [astro-ph.EP] for this version)
Submission history
From: Shubham Kanodia
[v1] Tue, 9 Mar 2021 00:15:00 UTC (17,031 KB)

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