The NEID spectrometer, a new tool for the discovery of planets outside of our solar system, has now started its scientific mission at the WIYN 3.5 m telescope at Kitt Peak National Observatory, Arizona. 1)
Figure 1: An image of NEID's spectroscopic observations of the sun. NEID's spectral coverage extends significantly redder and bluer than the limits of human vision, enabling it to observe many critical spectral lines. NEID's design enables high spectral resolution, large wavelength coverage, and exquisite stability. The image is inspired by the classic image of the spectrum of the sun created by N. A. Sharpe, based on data obtained at the McMath Pierce Observatory, located at Kitt Peak, where NEID is also located (image credit: Dani Zemba, Guðmundur Stefánsson, and the NEID Team)
Note: The NEID spectrometer takes its name from the Tohono O'odham word meaning "to see," a name selected after consultation with the Tohono O'odham Nation.
"We are proud that NEID is available to the worldwide astronomical community for exoplanet discovery and characterization," said Jason Wright, professor of astronomy and astrophysics at Pennsylvania State University (PSU) and NEID project scientist. "I can't wait to see the results we and our colleagues around the world will produce over the next few years, from discovering new, rocky planets, to measuring the compositions of exoplanetary atmospheres, to measuring the shapes and orientations of planetary orbits, to characterization of the physical processes of these planets' host stars."
The newest and one of the most precise tools ever built to detect exoplanets, NEID will discover exoplanets by measuring the minute gravitational tug of these planets on their host star.
"We have reached an exciting milestone for NEID," said Sarah Logsdon, a scientist at NSF's NOIRLab and NEID instrument scientist. "After an extensive commissioning process, where NEID was put through its paces, NEID is embarking on its science mission, having demonstrated that it is indeed a state-of-the-art tool for studying planets outside of our solar system."
The gravitational tug of orbiting planets induces a periodic velocity shift on the host star — a "wobble" that can be measured by NEID. Jupiter for example induces a 13 meter per second wobble on our sun, but the Earth induces a wobble of only about 9 cm/s. NEID's single measurement precision is already better than 25 cm/s, enabling it to detect small wobbles with sufficient data.
"NEID represents the state of the art in Doppler spectroscopy radial velocity detection and characterization of exoplanets," said John Callas, NN-EXPLORE project manager for NASA's Exoplanet Exploration Program at the agency's Jet Propulsion Laboratory (JPL). "NEID will push the existing boundaries for searching for smaller exoplanets, probing beyond the challenges that have limited past generations of RV spectrographs."
Built as part of a joint NSF and NASA program, NEID's mission is to enable some of the highest precision measurements currently possible, as well as to attempt to chart a path to the discovery of terrestrial planets around other stars.
"NEID has now successfully passed its final NASA review, and is in full operations as a scientific discovery tool," said Fred Hearty, research professor at Penn State and project manager of NEID. "It was a real delight to work with this talented team, and a privilege to be a part of this group of professionals."
The seething convection on the surface of stars, threaded by invisible lines of magnetic force and marred by ever changing active regions and "starspots" can pose a substantial challenge to NEID's measurements. This stellar activity is one of the major impediments to enabling the detection of rocky planets like our own. For very small signals it is difficult to tell which are planets and which are just manifestations of stellar activity. However, the researchers added, there is one star for which we know the answer, because we know exactly how many planets orbit it — our sun. In addition to observing stars during the night, NEID will also look at the sun through a special smaller solar telescope that the team has developed.
"Thanks to the NEID solar telescope funded by the Heising-Simons Foundation, NEID won't sit idle during the day," said Eric Ford, professor of astronomy and astrophysics and director of Penn State's Center for Exoplanets and Habitable Worlds. "Instead, it will carry out a second mission, collecting a unique dataset that will enhance the ability of machine learning algorithms to recognize the signals of low-mass planets during the nighttime."
The solar telescope was designed and built by Andrea Lin, a Cecilia Payne-Gaposchkin Science Achievement Graduate Fellow in astronomy and astrophysics at Penn State, with Andy Monson, NEID's systems engineer.
"The solar telescope was fun project to work on," said Lin. "I look forward to using NEID for my doctoral dissertation research. One of my planned projects with NEID is to look for planets around K-dwarfs. These stars line up incredibly well with NEID's capabilities, and the radial velocity method in general, so I'm hoping to discover some small — hopefully terrestrial! — planets around nearby K-stars."
NEID's solar telescope marks the return of solar observations to Kitt Peak.
The sun points the way," said Suvrath Mahadevan, professor of astronomy and astrophysics at Penn State and principal investigator of NEID. "For decades the iconic, and now decommissioned, McMath Pierce telescope at Kitt Peak was the premier facility for studying the sun. NEID is now the bridge that connects exoplanet science to solar observations, the sun to the stars, and a bridge that connects Kitt Peak's history to its present and future."
All data from NEID's observations of the sun are being immediately released publicly to enable researchers to begin to address the stellar activity problem. The NASA Exoplanet Science Institute (NExScI) at Caltech / IPAC coordinates the data processing and will make the data available through the NEID science archive.
"NEID has been the incredible story of a team that has delivered, in record time of a little over four years that include seven months of stoppage for COVID and then working through the height of this pandemic, an instrument that sets a new standard and will produce breakthrough science," said WIYN Executive Director Jayadev Rajagopal.
The NEID instrument is funded by the joint NASA/NSF Exoplanet Observation Research Program, NN-EXPLORE, managed by JPL, a division of Caltech in Pasadena, California. The 3.5-meter WIYN Telescope is a partnership among Indiana University, the University of Wisconsin, Penn State, the University of Missouri-Columbia, Purdue University, NOIRLab and NASA.
The NEID team includes members at Penn State, JPL, NOIRLab, NASA Goddard Space Flight Center, the University of Pennsylvania, the University of Arizona, the University of Wisconsin, the National Institute of Standards and Technology / University of Colorado, Boulder (NIST/CU), the Space Telescope Science Institute, Macquarie University, Princeton University and Carleton College, and the University of California, Irvine.
The researchers are honored to be able to conduct their research on Iolkam Du'ag (Kitt Peak) in Arizona, a site with a very significant cultural role and reverence to the Tohono O'odham Nation. The NEID spectrometer takes its name from the Tohono O'odham word meaning "to see," a name selected after consultation with the Tohono O'odham Nation.
• July 20, 2021: It has been almost exactly five years since NEID was selected as the design for the extremely precise radial velocity instrument to be developed through the joint NN-EXPLORE (NASA-NSF EXoplanet Observational REsearch) exoplanet science program. As luck would have it, that five-year mark coincided with the instrument's Operational Readiness Review, which is the final acceptance stage before NEID is cleared for full-time science. We are happy to report that NEID passed the Operational Readiness Review, and the next observing semester will see the spectrometer in full science operations! 2)
Figure 2: Sunset over Kitt Peak National Observatory during NEID commissioning in January 2020 (photo credit: Paul Robertson)
- The NN-EXPLORE partnership will take advantage of the full National Optical Astronomy Observatory (NOAO) share of the 3.5-m Wisconsin, Indiana, Yale, and NOAO (WIYN) telescope on Kitt Peak. It will provide the community with the tools and access to conduct ground-based observations that advance exoplanet science, with particular emphasis on Kepler, K2, and (eventually) TESS follow-up observations. It will also provide observations that inform future NASA missions, such as the James Webb Space Telescope (JWST) and the Wide Field Infrared Survey Telescope (WFIRST) mission.
A challenging year
- NEID was delivered to WIYN in October 2019, and we began commissioning the instrument shortly thereafter. Commissioning is a period of time before a new telescopic instrument is released for science operations in which the instrument team works out all the bugs that are inherent in a newly-installed device, and characterizes its performance on sky for the first time. Our team spent many long nights in the 2019/2020 winter commissioning NEID. We were making good progress, but had to execute a rapid shutdown in March of 2020 when the COVID-19 pandemic caused a complete stop of operations at Kitt Peak National Observatory.
- The WIYN telescope was shut down for 8 months, during which time we opened NEID in order to tweak the instrument in response to some issues we noticed during the early commissioning phase. The combination of the extended shutdown and the fact that we had opened the instrument meant that when we returned to operations in November 2020, we essentially had to start commissioning all over again. Thus, for two winters in a row the NEID team endured 12-hour nights of observing for up to a week at a time in order to get the instrument commissioned. It's safe to say that nobody else has ever endured a commissioning process quite like this one!
So does it work?
- In a word—yes! From December 2020 to April 2021, we ran a host of experiments to establish the reliability, precision, and limitations of NEID and its associated subsystems. The bulk of our time on sky was dedicated to the fairly standard practice of making many measurements of Doppler-stable stars in order to probe the spectrometer's limiting velocity measurement precision. On the other hand, we also conducted some fairly odd experiments (lovingly dubbed "torture tests") in which we deliberately made measurements with the telescope and instrument in strange configurations. These tests included observing targets far too close to the Moon, observing targets too low on the sky, and observing with the telescope dome covering half the primary mirror of the telescope!
Figure 3: NEID radial velocity measurements of the quiet star tau Ceti. Our on-sky measurements are stable to better than 50 cm/s, which indicates the instrument itself is even more stable (image credit: NEID Team)
- What we learned is that across a wide variety of targets, and in a wide variety of conditions, NEID offers radial velocity measurement precision that rivals the best facilities in the world. Our measurements of stable stars consistently show variability less than 1 meter per second. This on-sky stability reflects a combination of noise sources, including the instrument, statistical fluctuations (so-called "photon noise"), and the star's inherent atmospheric variability. Thus, while it is hard to pin down an exact number, we are assured that NEID's instrument-limited measurement precision is significantly better than 1 meter per second.
- Now the fun begins, as NEID is cleared for full-time science. The community is clearly excited for NEID; there is so much demand for the instrument that more than 60 percent of all WIYN nights in the 2021B observing semester will use NEID! If you are interested in proposing an observing program for NEID, we encourage you to see the WIYN Observatory's NEID page for more details.
• March 3, 2020: An article discussing the innovative technology used in the NEID Spectrometer is featured in this month's issue of IEEE Spectrum Magazine. IEEE Spectrum is the official magazine of the Institute of Electrical and Electronics Engineers, a professional society dedicated to the advancement of technology. 3)
- The article was authored by NEID team members Jason Wright and Cullen Blake, and features behind-the-scenes photos from NEID's development and installation. Head over to IEEE and check it out!
• January 16 2020: NEID sees its first light on 51 Pegasi, the host star around which Michel Mayor and Didier Queloz discovered the first exoplanet to orbit a solar type star in 1995! 4)
Figure 4: NEID Project Scientist Jason Wright at the Press Release at AAS 235, announcing the first light of NEID (image credit: Shubham Kanodia)
Figure 5: First light spectrum of 51 Pegasi as captured by NEID on the WIYN telescope with blowup of a small section of the spectrum. The right panel shows the light from the star, highly dispersed by NEID, from short wavelengths (bluer colors) to long wavelengths (redder colors). The colors shown, which approximate the true color of the starlight at each part of image, are included for illustrative purposes only. The region in the small white box in the right panel, when expanded (left panel), shows the spectrum of the star (longer dashed lines) and the light from the wavelength calibration source (dots). Deficits of light (dark interruptions) in the stellar spectrum, are due to stellar absorption lines — "fingerprints" of the elements that are present in the atmosphere of the star. By measuring the subtle motion of these features, to bluer or redder wavelengths, astronomers can detect the "wobble" of the star produced in response to its orbiting planet (image credit: Guðmundur Kári Stefánsson/Princeton University/Penn State/NSF's National Optical-Infrared Astronomy Research Laboratory/KPNO/AURA)
• December 2, 2020: This week, the NEID instrument team was recognized by NASA with the Group Achievement Award, which is presented to groups who have distinguished themselves through outstanding contributions to NASA's mission. The award citation to the NEID team is: "For the development and delivery of the state-of-the-art NEID radial velocity spectrograph and port adapter to the WIYN 3.5-meter telescope on Kitt Peak."
Figure 6: Members of the NEID team and KPNO astronomers celebrating NEID's first light at WIYN (image credit: Dave Summers)
• October 25, 2019: This morning the first truck left from Penn State for WIYN university. This truck along with NEID also contains the etalon and the calibration bench for the system. It was surely a nerve wracking few bits when the entire instrument was suspended off the fork-lift while it was being put into the truck.
Figure 7: NEID instrument package lift off the loading dock (image credit: PSU)
• June 27, 2018: Optical fibers are thin waveguides made of glass and are used for transportation of light. Widely used in the telecommunication industry, in the 1980s they started to be used in astronomy to couple light from the telescope focus to highly specialized and sophisticated instruments located elsewhere, eg. in the observatory basement (Heacox 1986). 5)
- Fibers typically have three layers, the core, cladding and buffer (Figure 8).Fibers and operate on the principle of total internal reflection (TIR) : the core and cladding are made from glass, and the refractive index of the core is higher than that of the cladding to enable TIR. The role of the buffer, on the other hand, is to provide protection to these fragile glass strands.
- For an extreme RV precision instrument like NEID, optical fibers offer various advantages, some of these are :
1) By decoupling the instrument from the telescope focus, they allow for the instrument to be quite heavy and sophisticated (NEID weighs about a couple metric tons!) . Further, it allows the instrument to be housed in the basement of the WIYN telescope in a room with temperature control to the level of 1 degree Celsius or better.
Figure 9: WIYN basement showing the location of NEID, the laser frequency comb and the electronics rack/s (image credit: PSU)
2) Having the instrument in the basement also means a near constant gravitational vector for the instrument. An instrument at the Cassegrain focus of the telescope would move constantly as the telescope tracks the target. This is important to prevent a variable sag or bending of the optics or mounts in the instrument.
3) The fiber provides a degree of scrambling for the light. This means that illumination at the output end of the fiber is less sensitive to the the location of the star on the input face. This is important to average over any illumination changes or guiding errors of the telescope (See Halverson & Roy et al. 2015).
NEID Fiber Train
Shown below is the entire fiber train for NEID. Here, we shall go over some of the components.
Figure 10: Overview of the NEID fiber train (image credit: PSU)
Fiber puck and polishing
- NEID has two different operating modes, High Resolution (HR) for the brighter targets for maximum RV precision, and High Efficiency (HE) for the fainter targets, with higher throughput. To enable this, the HR mode has smaller fibers (64 micron core) while the HE mode fibers are bigger with ~100 micron cores to allow for higher efficiency.
- For the HR mode we have three fibers – Sky, Science and Calibration ; whereas the HE mode has only Science and Sky (bigger fibers take up more detector real estate). The Science fiber, of course, is where the stellar light enters the instrument. The Calibration fiber in the HR mode is used for simultaneous wavelength calibration of the stellar spectrum. The Sky fiber is used for a variety of telluric corrections.
- This combination of HE and HR mode fibers are inserted into a fused silica puck manufactured by Femtoprint using a combination of a femtosecond laser and hydrogen fluoride etching. This is shown in Figure 11.
- After inserting the fibers in the puck they are epoxi-ed into place using Epotek 301 – 2; once this epoxy dries, we polish the puck. For the polishing we use a custom made polishing jig which attaches the puck shown above to the polishing arm on the table. It then moves in a ‘figure of 8' pattern to polish the fiber. To do this we start with a coarse 60 µm grit, and progressively move to smoother grits as 12, 5, 3, 1, 0.3 um grits of silicon carbide, aluminum oxide and diamond.
• August 2, 2016: It has been a busy summer for NEID and its team. Now that the project has officially started, there are many tasks that must be done in a short amount of time. Plans must be made, parts must be ordered, and blogs must be written! Out of all this excitement and bustle, though, there is one important takeaway: NEID construction is underway! Today we will briefly highlight the effort our summer students have put into fabricating NEID's environment control system. 6)
In order to achieve the sub-meter-per-second Doppler velocity measurement precision required of NEID, there are dozens of sources of instrumental error that must be controlled as tightly as possible. One of those variables is the thermo-mechanical stability of the spectrograph and its optics. As the temperature changes within the instrument, the glass optics or their mounts will change shape or position slightly. Temperature and pressure changes will also affect the index of refraction of any air in the instrument, altering the motion of photons. The impact of these environmental changes on our measurements of the stellar spectra can be much greater than the changes we expect to see from orbiting exoplanets, so they must be mitigated!
Like its predecessor spectrograph the Habitable-zone Planet Finder (HPF), NEID will be outfitted with an ECS (Environmental Control System) to keep the temperature and pressure within the spectrograph as stable as possible. The entire spectrograph will be surrounded by a temperature-controlled aluminum box called a "radiation shield," which itself is encased in a high-quality vacuum chamber. The high vacuum eliminates heat transport by convection, making it much easier for us to control the temperature of the radiation shield—and thus the instrument itself—to a very precise degree. On the HPF blog, we showed that by using the HPF ECS to simulate conditions for NEID, we could control the instrument's temperature to better than a thousandth of a degree! This level of precision is required to make the instrument sensitive to Earth-like planets.
Figure 12: The HPF and NEID instruments, with critical elements of the environmental control system highlighted (image credit: PSU)
Another requirement for NEID is that it must fit within approximately the same physical dimensions as HPF in order to be housed in the WIYN Telescope's instrument room. As a result, the NEID vacuum chamber and radiation shield will look very similar to HPF's. The image above shows the two instruments, highlighting some of the similarities and differences.
The vacuum chamber is the first major component that must be fabricated for the NEID project. The instrument has to have a home, after all! Thus, while the vacuum chamber itself is being built by our collaborators at Pulseray, the team at Penn State has been busy working on everything that goes inside it. Let's take a quick look.
Let's build it—again!
Because NEID utilizes nearly all of the technology we developed for HPF, it is much quicker and easier to build a second system. Many of the growing pains of achieving sub-milliKelvin temperature control have already been experienced, and we can simply get things right the first time. With that said, this is still no easy job! As shown in the figure above, NEID has twice as many active heaters as HPF, and the sheer amount of cabling required to operate so many heaters and thermometers is daunting. The optical bench is also larger for NEID, leaving less space to work with during assembly, so the design and application of the multi-layer insulation must also be carefully considered.
Figure 13: Students Demetrius Tuggle, David Conran, and Joe Smolsky assemble a wiring harness for the NEID ECS (image credit: PSU)
One advantage of building an instrument at a world-class university like Penn State is that there is never a shortage of talented young scientists to help with major projects. We are fortunate to have four undergraduates—David Conran and Adam Dykhouse from Penn State, Joe Smolsky from the University of Nebraska at Omaha, and Demetrius Tuggle from the Ohio State University—helping us to fabricate the NEID ECS over the summer.
With the help of these hardworking students, fabrication of the environment control system's heaters, thermometers, control electronics, and the half-mile or so of associated cabling is nearly complete! Assembly of the many MLI blankets is now underway as well.
Figure 14: Gudmundur Stefansson supervises the assembly of an MLI blanket (image credit: PSU)
Moving so fast on the first major component of the NEID instrument is not just critical for completing a subsystem before classes start again in the Fall. It is essential for keeping to NEID's aggressive project schedule and having the instrument ready to follow up all of the exciting exoplanets that NASA's Transiting Exoplanet Survey Satellite (TESS), to be launched in 2017, will discover.
1) Suvrath Mahadevan and Sam Sholtis, "From the sun to the stars: A journey of exoplanet discovery begins," Penn State News, 20 July 2021, URL: https://news.psu.edu/story/664079/2021/
3) "Atomically Precise Sensors Could Detect Another Earth - Tiny wobbles of distant stars may soon help reveal life-sustaining worlds," IEEE Spectrum, 25 February 2021, URL: https://spectrum.ieee.org/sensors/imagers/
4) "NEID sees its first light on 51 Peg!," PSU, 16 January 2020, URL: https://neid.psu.edu/2020/01/16/neid-has-its-first-light-on-51-peg/
The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: "Observation of the Earth and Its Environment: Survey of Missions and Sensors" (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (firstname.lastname@example.org).