NEID measures a spin-orbit angle for a long period planet

Background

The TESS mission continues to discover fruitful exoplanet systems ripe for various types of detailed study, including with NEID. Recently, we investigated the spin-orbit angle of a planet in the TOI-1670 system. The NEID team has investigated this kind of question before with other systems. Check out this post on TOI-2076 for a great primer on what the spin-orbit angle is and how we measure it with the Rossiter-McLaughlin (RM) effect. In summary, we use the color of the light that a planet blocks as it passes in front of the host star to measure the path it takes across the face of the star from our perspective. This then allows us to determine if the orbital plane is nicely perpendicular to the stellar spin axis (aligned) or not (misaligned).

NEID Data

TOI-1670 hosts two known transiting planets: the inner, planet b, is a typical sub-Neptune on an 11 day orbital period; the outer, planet c, is a Warm Jupiter on a 40 day orbital period. This is an interesting architecture, as we haven’t found many systems with small planets interior to Warm Jupiters. This prompted us to wonder, are the planets in this system well-aligned to the host star’s spin axis?

To answer this question, we observed TOI-1670 on the night of April 19/20, 2023 from Kitt Peak National Observatory in Arizona. The night started out a little less than perfect; there were wispy clouds above, and so the first 4 observations we took have larger error bars due to capturing fewer photons within the standardized 7-minute exposure times. But then, just as the planet was about to transit, the clouds parted way and conditions were ideal! In total, we collected 21 spectra, 15 of which were during the transit of planet c.

NEID RM data of TOI-1670c

The RM anomaly during transit of TOI-1670 c. NEID easily traces out the signal. The first 4 observations were taken through clouds and so they have larger error bars, but after these 4, conditions were ideal.

Using this data set, we determined that the 40-day orbital period Warm Jupiter, TOI-1670 c, is well aligned to its host star, finding the angle to be -0.3 +/- 2.2 degrees. This is a very tight constraint! The planet now joins 15 other Warm Jupiter planets (those with masses greater than 0.75 Jupiter masses and orbital periods longer than ~10 days) that are all found to be well aligned.

An Expected Result?

This is important because it puts the concept of alignment in a wider perspective. There is still much debate and uncertainty about how planets get into misaligned orbits. Leading theories mostly include dynamical interactions with other planets in the system and/or migration from the outer system to their current inner orbits. However, for misaligned planets that are very close in to their star, if they are massive enough (like Hot Jupiters), then they can actually realign their host stars to their new orbital plane through tidal interactions. Then, if we were to measure the spin-orbit angle, we would see an aligned orbit and would never know about the dynamical past of the system. However, for Warm Jupiters, because of their relatively wide separation from their host stars, they are not able to realign their star within the current lifetime of the Universe. So if we measure a misaligned orbit today, we can be sure there was some kind of dynamical history in the system. On the other hand, if we measure an aligned orbit, we can be almost sure that the planet formed in this aligned orbit and no realignment was needed.

Obliquity distributions

Comparing TOI-1670 with similar systems across 2 dimensions. Left: all Warm Jupiter host stars with measured obliquities shows that those around single stars are all well-aligned, while the only misaligned planets orbit stars in binary systems. Right: all planets in multi-planet systems shows that nearly all multi-planet systems are well aligned, with a few notable exceptions.

That’s what we have in TOI-1670 c: an aligned planet that likely formed in a dynamically “cold” environment and retained its primordial alignment. In many ways, this was the expected result. TOI-1670 hosts a multi planet system, and the kinds of dynamical interactions that would produce a misaligned orbit are also likely to disrupt the system and possibly eject all but one planet. Since we have multiple planets here, it’s most likely that there was not these dynamical interactions between planets; that is to say, all planets played nicely together in the early days of this system.

While it is an expected result, it is still a fascinating one. And one that shows off the precise RVs that NEID is able to measure. More of these kinds of measurements are in NEID’s future, stay tuned!

Learn More

The full details of our study of TOI-1670 c can be found in a research article for The Astrophysical Journal Letters, led by NEID Team member Jack Lubin.

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Constraining the Spin-Orbit angle of the Young Warm Neptune TOI-2076b with NEID

Beyond Discovery

High-resolution, super-precise instruments like NEID can do much more than just discover new exoplanets and measure their masses.  For certain planets, NEID may be able to detect molecules in their atmospheres, or–as we will see here–measure detailed properties of their orbits.  Today, we will look at the orbital properties of the young exoplanet TOI-2076b.  This exciting result was led by NEID team member Robert Frazier, and is published in full detail in a recent publication in the Astrophysical Journal Letters.

Obliquity:

All stars spin on their axis, same as a spinning top or the Earth. The Earth, and most of the other planets in the Solar System, orbit around the Sun in the direction that it spins, but this is not always the case. They can actually go around the star in any direction, and their orbits can be inclined in any way. The angle between the axis on which a star spins (stellar spin axis) and the axis of a planet’s orbit around the star (planet orbital axis) is called the stellar obliquity, and is visualized here:

Figure 1: An array of possible obliquities are shown in this figure with the obliquity angle shown in blue. The stellar spin axis is shown in dark yellow and the planet orbital axis is shown in green.

As can be seen in Figure 1, there’s a wide range of possible obliquities and orbits. They vary from the planet orbiting around the star’s equator to orbiting above the star’s poles. Planets with a small obliquity are known as well-aligned, while planets with a large obliquity are known as misaligned

Rossiter-McLaughlin effect:

Determining obliquity for stars and their exoplanets is difficult, requiring precise spectroscopic observations. It has only been done for around 200 exoplanets out of the over 5,000 confirmed exoplanets around almost 4,000 stars. Most of these have been determined using the Rossiter-McLaughlin (RM) effect. The RM effect occurs when a planet transits in front of its host star and blocks out light from the star as would be viewed by an observer. The RM effect is visualized in the following Figure:

Figure 2: In this figure, three different transits of an exoplanet in front of its host star and the resulting obliquity and RM curves are shown. Due to the star rotating on its axis, it causes one hemisphere to be blueshifted, and the other redshifted as seen from an observer on Earth. The path of the exoplanet in front of the star is shown with the thick black arrows. The dashed curves show the expected RV signal if the planet was not blocking any light, while the solid line is the ‘RM curve’ showing the expected RV variations during the transit. The shape of the curve is highly dependent on the obliquity of the star. Figure credit: WASP-Planets.net

As highlighted in Figure 2, as the star rotates on its axis, the light coming from the side spinning towards the observer is blueshifted, while the light coming from the side spinning away from the observer is redshifted. Thus when a transiting exoplanet blocks a part of the star spinning towards the observer, it is measured as a net redshift as the blueshifted light is reduced, and vice versa. This creates the distinctive curve of the Rossiter-McLaughlin effect, and is used to determine stellar obliquity.

History of Orbits:

Early determinations of stellar obliquities found that they were mostly small, just as we would predict based on the obliquity of planets in the Solar System. Earth’s obliquity is only 7.2 degrees, making it fairly well-aligned. However, starting in 2008, many planets started to be found to have high stellar obliquities. The sudden change in these observations and the physical causes were not known, and it broke the idea that planets all orbit on well-aligned orbits. As the discoveries continued, it was found that among Hot Jupiters—planets the size of Jupiter that are very close to their host stars, and make up the majority of obliquity measurements due to their ease of detection—there was a split into two populations: well-aligned, and misaligned Hot Jupiters. This obliquity bifurcation means that a systematic mechanism (or mechanisms) had to be occurring, but it remains to be seen whether this bifurcation is intrinsic just to Hot Jupiters or a broader range of planets, including in particular smaller planets which are more numerous, but have remained more difficult to measure due to their smaller sizes.

NEID Observations:

We leveraged the exquisite RV precision enabled by NEID to measure the obliquity of an exciting recently discovered young Neptune-sized planet called TOI-2076 b. TOI-2076 b is a warm and young (200 million years old, compared to 5 billion years for the Solar system) sub-Neptune (2.4 Earth radii) that orbits around its host star, TOI-2076, along with planets TOI-2076 c and TOI-2076 d. It was first discovered by a research effort led by Christina Hedges in 2022 (see paper here) using observations from NASA’s TESS (Transiting Exoplanet Survey Satellite). Using NEID, we conducted radial velocity measurements of TOI-2076 and observed the Rossiter-Mclaughlin effect.


In a single transit with NEID, we were able to determine that TOI-2076 b is well aligned with an obliquity of -3 +/- 16 degrees, as can be seen in Figure 3. What was interesting to see was that there was an overall upward curve in the RVs, as opposed to the flat to slightly downwards curve normally expected with the RM effect. The RV curve can be seen here:

Figure 3: The RM curve captured by NEID. The RVs are plotted against the Barycentric Julian Date (bottom), and time from mid transit in hours (top). The black dots are the measured radial velocity values from NEID, the red curve is the calculated model for the RM curve based on the RVs, and the blue shading highlights the 1 sigma credible interval of the best-fit model.

We found that the curve of this slope changed depending on what range of wavelengths it was constructed from. Combining this with the star’s young age and clear brightness variations seen by TESS led us to attribute the overall upward trend in the RVs to starspots, regions of high magnetic activity analogous to Sun spots. Accounting for this slope, we had no difficulty in analyzing the RM effect and arriving at our measured obliquity. 

With this measurement, TOI-2076 b joins a small but growing sample of young planets in multi-planet systems with well-aligned orbits, and is the fourth planet with an age less than about 300 million years in a multi-transiting system with an obliquity measurement. A plot of exoplanets in systems with multiple transiting planets with measured obliquities is shown below to put our measurement into context. Some values have been left out due to high uncertainty on the age or obliquity.

Figure 4: A plot of planets in multiple transiting systems with measured obliquities. TOI-2076b is shown as a square and is highlighted in red. The orange points represent Warm and Cold Jupiter exoplanets and the green points represent Sub-Saturn exoplanets. The grayed out marker represents a Hot Jupiter.

The low obliquity of TOI-2076 b, and the presence of transit timing variations in the systemwhich are variations in timings of transits of planets in a multi-planet system that are capable of gravitationally tugging each other to and fro—suggest the TOI-2076 system likely formed from an already well aligned protoplanetary disk. We believe that the two other observed exoplanets in the system, TOI 2076 c and d, are also likely to have well-aligned orbits, although additional observations would be required to confirm this prediction. 

Lastly, TOI-2076 is also an exceptionally bright star, and so this provides the opportunity to characterize the atmospheres of all of the three transiting planets in the system with, for example, the recently launched James Webb Space Telescope (JWST), and would be among some of the known youngest multi-planet systems amenable for such observations.

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NEID Validates a Venus-like Exoplanet

Despite challenges caused by a global pandemic, the NEID team has adapted, and is already putting out important new exoplanet science.  Much of the early science efforts with NEID have focused on detailed characterization of new exoplanets discovered by the Transiting Exoplanet Survey Satellite, or TESS.  One of the first planets we studied was an Earth-sized planet orbiting a small nearby star.  The results of this study were detailed in a recent publication in the Astrophysical Journal led by NEID team member Corey Beard. Our results were also recently highlighted by AAS Nova, a blog that features novel and exciting new papers appearing in the American Astronomical Society Journals  Here, we will look at the highlights of this exciting planet system!

What’s Up With GJ 3929?

Thanks to the TESS mission, we were notified that Gliese (pronounced glees-y, and abbreviated as GJ) 3929, a cooler, redder star known as an M dwarf, might be hosting an exoplanet we hadn’t known about before. This candidate planet was reported to be about the size of Earth, but don’t start preparing your vacation plans yet: revolving around its star every 2.6 days, the planet GJ 3929b is basking in a lot of stellar radiation. With a surface temperature more likely to be close to Venus than Earth, we dubbed GJ 3929b a potential exo-Venus.

While the NEID team began follow-up work to confirm the planet right away, the planet signal eluded us. Could this planet be much lighter than we had previously thought, or was something else at play? It turned out to be the latter, which we discovered when the CARMENES team released an analysis that highlighted the transiting planet and a previously unseen non-transiting companion. Most likely, the mixing of the two signals confused our initial results, but with new data, a 2 planet model, and the extremely high precision of NEID, we were positioned to dive deeper into this system than had been done before.

Radial velocities of GJ 3929

A combination of radial velocity data taken by CARMENES, HPF, and NEID reveal the characteristic sine-wave-like shape of GJ 3929’s two planets.

If There’s an Atmosphere, We’ll Find It!

After the successful launch of the James Webb Space Telescope (JWST), many exoplanets are being framed in the context of atmospheric characterization: how easy is it to look at them with JWST and pick apart the chemicals in their atmosphere?

TSM of GJ 3929

We highlight a few planetary systems with a high Transit Spectroscopy Metric, or TSM. Planets with higher TSMs are easier to observe with JWST to characterize their atmospheres. Note that very few planets are as small as GJ 3929b, and yet still suitable for study with JWST.

Luckily, GJ 3929b is an extremely good target for JWST. Many factors can make transiting exoplanets favorable (or not) for atmospheric characterization, but for the most part a bigger planet, a smaller star, and a close distance to Earth all go a long way to make a planet feasible. The star GJ 3929 is on the small and close side, which helps make it possible. But the planet GJ 3929b is Earth-sized, which is definitely small when it comes to exoplanets. So why is it good for JWST then? Well, it’s true that if GJ 3929b were, say, Jupiter sized, it would be much easier to study with JWST. But it would be much less interesting, as we already have the capability of studying the atmospheres of hot Jupiters. What makes GJ 3929b great for JWST is that it is a small planet that can be studied with JWST; most cannot!

While it’s too early to say whether or not GJ 3929b has an atmosphere or not, it is perfectly plausible. Current models of planet formation allow for a primordial atmosphere that appeared with the planet when it first formed, or an atmosphere that appeared later by volatile gases leaking out of the inside of the planet.  Of course, it is also possible that the planet has no atmosphere at all. Time will tell what kind of environment ends up existing on GJ 3929b!

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NEID Passes Operational Readiness Review

It’s been a long time coming!

As of this writing, 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 NASA and the NSF’s joint NN-EXPLORE 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!

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.

Sunset over Kitt Peak National Observatory during NEID commissioning in January 2020. [Photo credit: Paul Robertson]

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!

tau Ceti RVs

NEID radial velocity measurements of the quiet star tau Ceti. Our on-sky measurements are stable to better than 50 centimeters per second, which indicates the instrument itself is even more stable.

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.

What’s next?

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.

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NEID graces the cover of IEEE Spectrum

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.

NEID’s cover image on IEEE Spectrum Magazine

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!

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NEID Team Receives NASA Group Achievement Award

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.

Members of the NEID team and KPNO astronomers celebrating NEID’s first light at WIYN. Image credit: Dave Summers

Congratulations to the entire NEID team on this award!

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NEID sees its first light on 51 Peg!

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!

NEID Project Scientist Jason Wright at the Press Release at AAS 235, announcing the first light of NEID

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.
Credit: Guðmundur Kári Stefánsson/Princeton University/Penn State/NSF’s National Optical-Infrared Astronomy Research Laboratory/KPNO/AURA

 

See associated coverage –

 

 

 

 

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NEID has shipped for WIYN!

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.

Lift off the loading dock

The fork-lift ride

Safely in the truck

All loaded up and ready to go!

The truck will be getting to WIYN, Kitt Peak on Monday when the team members will unload it. The second truck, will leave Penn State on November 1st containing the Laser Frequency Comb.

Stay tuned for more commissioning updates!

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Successful Pre-Ship Review!

NEID successfully passed its Pre Ship Review, held on the 17th and 18th of September 2019, at the Penn Stater Hotel & Conference Center. Time to ship to WIYN!

 

NEID team picture. Regrettably Ryan Terrien and Emily Lubar could not make it for the group photo.

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Alignment, Integration and Verification (AI&V) has begun!

After many months of careful coating and testing, all of NEID’s optical components have arrived safely at Penn State. For the instrument team, this means it’s go time. We’ve begun the process of adding optics to the instrument while our systems engineer, Andy Monson, begins the meticulous process of aligning the optical components. During this process we are also putting many components into the instrument for the first time. We will be fitting, checking, and double checking that all components fit the way we designed them and that nothing is in the way of the light path (or the “chief ray”) through the instrument.

Here are a few of the NEID team members working hard to carefully install and test NEID’s optical components

Light enters the instrument through optical fibers that bring light directly from the focus of the WIYN 3.5m telescope at Kitt Peak National Observatory (where NEID will be commissioned in 2019). The first big component the light interacts with is a parabolic mirror.

Here is our Systems Engineer Andy Monson inspecting the parabolic mirror after it arrived at Penn State freshly coated.

NEID’s parabolic mirror redirects the light to the NEID echelle grating which splits the light into the many wavelengths that made up the original beam. To read more about how an echelle grating works and why they’re wonderful, see this post about HPF’s grating. The light, which the grating has spread into its separate wavelengths, is redirected by the parabola to the prism. The prism disperses the light side-to-side such that the light is now in a 2-Dimensional format.

This is the NEID grating in its mount 

Here is a snap shot of the process of moving the prism onto its base. We had to lift the prism carefully with a suction cup because the optical surfaces on the sides cannot be touched! 

Here is the Prism up close. You can see a reflection of what is happening off to the right where NEID project manager Fred Hearty is preparing to assemble the rest of the prism mount

 The 2D format is important because we need the light to be recordable within the area of out 2D Silicon detector. To focus the 2D light’s foot print onto this detector, we have the NEID camera.

The detector records the light digitally which we use computers to search for tiny Doppler shifts in the spectra. These shifts in the stellar spectra may indicate the presence of a planet around that star. To get light to the detector, our Alignment, Integration and Verification phase must go well. Wish us luck!  

The detector is housed in the chamber on the end of the camera shown below. The purpose of the copper block is to cool the detector by connecting to the liquid nitrogen tank below the instrument.

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