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Yale Astronomy

Christmas Eve 2018

Dec 24, 2018 - Debra Fischer

It's been a few months since the last blog post, but my team has been working tirelessly on EXPRES. I wish I could make this look easy, but we are trying to do something that has never been done before. We've made so much progress and have reached the state-of-the-art 1 m/s precision. But our goal is far more ambitious. Some days success feels imminent, but then the finish line inches away. We keep our heads down and forge on.


Since the last post in September, we found and fixed the vacuum leak (a leaking optical fiber) and completed the thermal enclosure. We reinstalled the laser comb. We added extensive monitoring and archiving of temperature and pressures for many subcomponents in our instrument (special thanks to René Tronsgaard Rasmussen, from Denmark, who spent 3 months working with us at Yale). These data show that the thermal enclosure provided the desired stability. We sharpened our analysis code (thanks to Ryan Petersburg, Lily Zhao, and Joel Ong). John Michael Brewer and Lily continued development of the EXPRES data-taking manager. Happily, our extraction and analysis codes are performing beautifully. Prof Jessi Cisewski and her students are making exciting progress on disentangling photospheric velocities in our spectra, critical for Earth-detecting precision.

We received two major gifts this year. The Heising-Simons Foundation contributed funds for some telescope time in 2018. And an anonymous donation was made to support the brilliant John Michael Brewer for the next 3 years. I want to express my thanks for both of these incredible gifts. I have had many sleepless nights in the past two years, worrying that we had worked so hard for the last several years but might not have the funding to finish this project... worrying about the impact this would have on the graduate student thesis projects. This financial support has been renewing and when we succeed, it will be a shared victory with everyone who helped us.


We have reached 1 m/s measurement precision. However, standing between us and the extreme precision 0.1 m/s (10 cm/s) finish line: a persistant 6-minute sinusoidal oscillation in the laser comb data. This is a show-stopper for high precision. Impressively, if we could fit and remove the signal, the laser comb yields a wavelength solution that is stable at the centimeter-per-second level. That's our precision goal! A breakthrough occurred on Dec 5 when we briefly turned off the cryo-cooler on the CCD and the signal disappeared. That's not a solution (we have to keep the detector cold) but it was a great diagnostic test. The problem cannot be cryostat vibrations alone - the 6-minute oscillation we measure is far too slow to be vibrations. There must be a beat frequency with some other component, and Andy Szymkowiak has a clever insight for what might do this: (1) if the cryo-cooler is running at (say) 60.0287Hz (instead of 60.00 Hz, possible given the design of that component) and producing vibrations in the CCD with an amplitude of 45 nanometers and (2) if the laser comb spectral flattener is varying - e.g. from pulse width modulation or power line ripple, then the intensity in the laser comb would vary at 60 Hz, and the beating of those two sinusoidal frequencies would produce a "lovely sine wave" as the comb line intensity sweeps redward then blueward with a miniscule amplitude and a 6-minute period. Right now, we are trying to document the suspected 60 Hz intensity variation in the laser comb. If Andy's theory is correct, there are solutions. Unfortunately, it is now Christmas eve and no one except us seems to be working.

The real point here is to let you all know that I've been delaying a new post to the expres Blog, thinking that "tomorrow" we will have tracked this down so that I can report an instrumental precision of a few centimeters per second. But "tomorrow" has been a day away for two months now and I wanted to post a progress report before the end of the year. For any astronomers reading this: don't forget to thank the instrument builders who made your research possible. Innovative instruments are the lifeblood of astronomical discovery, but designing and building game-changing instruments can be thankless, invisible work. Today, we made some progress, tomorrow, we'll take another step. One day very soon, we'll make it across the finish line.

It is Christmas Eve! Santa, you know what I want (hint: the finish line). Happy Holidays, Merry Christmas and Happy New Year to everyone!

About Us

Photo from Lowell Observatory

The EXPRES team works on the discovery of planets orbiting stars other than our Sun, or exoplanets.

EXPRES is a next generation spectrograph that aims to break the record on current measurement precision with the goal of detecting small, rocky planets - similar to Earth - orbiting nearby stars. The instrument blends high resolution and extraordinary stability to produce the highest fidelity data.

This journey began long ago; our hope is that EXPRES will help humanity to explore the unknowns in the galaxy.

EXPRES is possible thanks to...

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2018: September, July, June, May, April, March.

News about EXPRES:

EXPRES Cast and Crew

  • Deputy Scientist - 100 Earths Project
    • John Michael Brewer
  • Professors
    • Debra Fischer, Astronomy
    • Jessi Cisewski, Statistics
    • Andrew Szymkowiak
  • Research Scientists
    • Colby Jurgenson
    • Tyler McCracken
    • David Sawyer
  • Graduate Students
    • Allen Davis
    • Ryan Blackman
    • Ryan Petersburg
    • Lily Zhao
    • Joel Ong
  • Undergraduate Students
    • Christopher Leet
    • Yonatan Zeff
    • Abby Mintz
  • Collaborators
    • Sally Dodson-Robinson, University of Delaware
    • Lars Buchhave, Danish National Space Institute
    • Gregory Henry, Tennessee State University
  • We Would Like to Expressly Thank
    • Steve Girvin, Yale University
    • Pieter van Dokkum, Yale University
    • Gábor Fűrész, MIT
    • Andy Szentgyorgyi, Harvard
    • Francesco Pepe, Geneva Observatory
    • Matteo Genoni, Brera Astronomical Observatory
    • Giorgio Pariani, Brera Astronomical Observatory
    • Marco Riva, Brera Astronomical Observatory
    • Ben Hardesty, Lowell Observatory
    • Frank Cornelius, Lowell Observatory