EXPRES

51 Pegasi b

Sept 1, 2018 - Debra Fischer

The first exoplanet orbiting a sunlike star, 51 Pegasi, was detected in 1995 by Swiss Astronomers Michel Mayor and Didier Queloz using the Elodie spectrograph. In June 2018 we measured the velocities of this star with EXPRES and unambiguously see the signal from 51Peg b, the planet that launched the field of exoplanets. A comparison of the 1995 Mayor & Queloz data [1] and our EXPRES data [2] are shown for this star in the slide show below. Looking good!

However, we are planning to do better. Much better. We tallied a list of hardware issues that needed to be fixed on EXPRES.

1. after opening the vacuum chamber in mid-June, we were not able to get back to the same level of vacuum pressure (10^-6 Torr).
2. we measured a loss of 50% of our light at the pupil slicer.
3. we had ongoing problems locking the laser comb. The Menlo team identied a failing reference switch that needed to be replaced in Germany.
4. the focus of light into the fiber at the Front End Module seemed soft, which meant we were also losing light before injecting into the fiber.
5. the laser comb showed a one meter-per-second, 5.8-minute periodicity.
6. our measurements of temperature showed some drifts correlated with wavelength shifts.
7. the LED calibration light source was failing intermittently

Sigh... this is part of commissioning a new instrument... time to dig in! Telescope time is a precious commodity; not wanting to waste any time, we turned back all of our assigned nights in August, September, and October to work on these issues. We worked with the LED vendor Fiber Tech Optica (in Canada) to successfully make repairs to the cooling system. The pupil slicer vendor, Fraunhofer (in Germany), built a test mirror and helped grad students Ryan Petersburg and Ryan Blackman to improve the alignment, boosting the throughput to 90%. The Menlo team (in Germany) is now repairing the laser comb motor. The lesson here is that our vendors have been incredibly helpful, going above and beyond expectations. It's so important to have a good relationship with everyone who works on complex instruments like EXPRES. The students also refocused optics in the front end module, improving thoughput there [3].

This leaves 2 hardware issues. (1) the vacuum leak has been tough and frustrating. Suvrath Mahadavan (Penn State University) has been giving some advice and we have a plan - hopefully this will be fixed in the next few weeks. (2) the thermal stability is more straightforward - this will be fixed with a thermal enclosure that my son Ben Fischer is completing with craftsman precision.

Meanwhile, we've been working on software improvments. John Brewer has added more functionality to the EXPRES data taking GUI. An impressive paper let by undergrad Christopher Leet is about to be submitted; his research shows how to effectively identify contaminating spectral lines from the Earth's atmosphere [4]. Grad student Joel Ong, who dreams in Fourier Transforms, has developed a 2-d fitting for the laser comb lines; we should eventually reach our goal of 5 cm/s precision in laser comb [5]. He has also documented some (calibratable) structure in pixel positions in our detector. Grad student Lily Zhao is improving the spectral extraction code.

It's summer, so we should also have some fun. In July, I took a group of undergrads who were working on research at Yale this summer to NYC for lunch at the Chelsea Market and a trip to the American Museum of Natural History [6, 7]. Their price of admissions: everyone had to tell a joke on the train ride into the City. In August, the Heising Simons foundation held a "51 Peg b exoplanet summit" at the gorgeous Cavallo Point [8] in Sausolito - it was an amazing few days with lively presentations that helped to build collaborative spirt in our exoplanet community. I was able to show our first radial velocity data from EXPRES [2]: observations of the star 51 Peg being tugged around by a Jupiter-like planet in a 4.23-day orbit. The planet 51 Peg b is the name of the Heising-Simons program because it was the first exoplanet detected around a sunlike star (in 1995). This was a proof of concept for us and EXPRES nailed it - the velocities fall along the model line like beads on a string - and we have more improvements planned in the coming months.

August 2018 Slideshow

About Us

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.