Baseline Fit of the Interferometer What Is Happening

Baseline Fit of the Interferometer: What Is Happening By: Michelle Simon W. M. Keck Observatory Mentor: Jorg-Uwe Pott, Ben Berkey Home Institution: Pacific Lutheran University 1

What You Will See Today FThe vocabulary you may need to know FWhat was supposed to happen with the baseline FWhat actually happened before and after I arrived FWhat can be done to make the program work as desired 2

Vocabulary FInterferometer FBaseline Fb. Fit FPython Script 3

Why this project is needed and what an Interferometer does F An interferometer provides the ability to resolve objects that may not be resovable in a normal viewing with a single telescope. F A new instrument (ASTRA) is being added to the interferometer and requires more precise measurements of the baseline. 4

How the program b. Fit Works F Takes the measured fringes positions for each star which are found when the delay line matches the geometric delay. F Then derives the baseline vector from these positions, assuming a perfect rotation of each telescope. F The precision of the baseline fit is good enough to find the fringes with in 50 microns. 5

What is Happening (Physically) • The rotation of each telescope is imprecise and has yet to be predicted. 1. The azimuth motion can be repeated for each telescope but is not the same. 2. The rotation axis can change from night to night. 3. The up portion of the baseline vector may depend on the thickness of the azimuth oil bearing. 6

What is Happening (Programming) 1. Incorrect measurements that are extremely off. 2. b. Fit as is, is not designed for detailed monitoring of the interferometer baseline. 7

What I have done F Created multiple Python programs to ease the baseline analysis F Each program is documented to allow the future user to explore what has been done. F The programs help to establish the cause of bad data on the results of b. Fit, and allow to optimize the data selection. 8

Graphs Showing the Impact of Different Baseline Fits 9

What can cause b. Fit to go bad in a single night F Only observing a single star F Observing any number of stars but in small range of azimuth. F The variation in the up and constant terms of the baseline vector. 10

What's next. . . FThe team will further investigate what exactly causes the baseline to vary. FSee if the baseline variation can be predicted. 11

Acknowledgments: F Jorg – Uwe Pott F Ben Berkey F Cf. AO F W. M. Keck F Sarah Anderson F The Akamai Internship Program is funded by the Center for Adaptive Optics through its national Science Foundation Science and technology Center grant(#AST-987683) 12