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New Entry in High Precision Spectroscopy

As if I don’t have enough trouble figuring out acronyms, I now have to figure out how to pronounce acronyms. The issue comes up because a new NASA instrument now in use at Kitt Peak National Observatory is a spectrograph built at Penn State called NEID. Now NEID stands for NN-EXPLORE Exoplanet Investigations with Doppler spectroscopy. Here we have an acronym within an acronym, for NN-EXPLORE itself stands for the NASA-NSF Exoplanet Observational Research partnership that funds NEID.

Here’s the trick: The acronym NEID is not pronounced ‘NEE-id’ or ‘NEED’ but ‘NOO-id.’ The reason: Kit Peak is on land owned by the Tohono O’odham nation, and the latter pronunciation honors a verb that means something close to ‘to see’ in the Tohono O’odham language.

As a person fascinated with linguistics, I’m delighted to see this nod to a language whose very survival is threatened by the small number of speakers (count me as one infinitely cheered by the resurrection of Cornish, for example). And as one absorbed with exoplanet science, I note that NEID first light results were discussed at the recent meeting of the American Astronomical Society in Honolulu. The instrument is mounted on the WIYN 3.5-meter telescope at Kit Peak. The first observations were of 51 Pegasi, the first main sequence star found to host an exoplanet.

Here we’re in the realm of using radial velocity measurements to ferret out the slight stellar motion that indicates planets. The better we get at doing radial velocity calibration, the better, not only because we can discover new planets, but because we can use the method to characterize already known worlds. Thus TOI 700 d, that interesting habitable zone world we looked at yesterday, is a case of discovery by transit methods, but having measured its size, we can now use followup radial velocity readings to get a read on its density.

Image: The NEID instrument, mounted on the 3.5-meter WIYN telescope at the Kitt Peak National Observatory. The NASA-NSF Exoplanet Observational Research (NN-EXPLORE) partnership funds NEID (short for NN-EXPLORE Exoplanet Investigations with Doppler spectroscopy).Credit: NSF’s National Optical-Infrared Astronomy Research Laboratory/KPNO/NSF/AURA.

With NEID, we continue the movement in radial velocity studies down to measurements well below 1 meter per second. Long-time Centauri Dreams readers will know that for a long time, the HARPS spectrograph (High Accuracy Radial velocity Planet Searcher) at the ESO La Silla 3.6m telescope, has been considered the gold standard, taking us down to 1 meter per second, meaning that scientists could discern via Doppler methods the tiny pull of a planet on the star first towards us, and then away from Earth. The ESPRESSO instrument (Echelle Spectrograph for Rocky OxoPlanet and Stable Spectroscopic Observations) installed at the European Southern Observatory’s Very Large Telescope in Chile, takes us into centimeters per second range, which means detecting Earth-size habitable zone planets around Sun-like stars.

Image: The left side of this image shows light from the star 51 Pegasi spread out into a spectrum that reveals distinct wavelengths. The right-hand section shows a zoomed-in view of three wavelength lines from the star. Gaps in the lines indicate the presence of specific chemical elements in the star. Credit: Guðmundur Kári Stefánsson/Princeton University/NSF’s National Optical-Infrared Astronomy Research Laboratory/KPNO/NSF/AURA.

Can NEID likewise reach the realm of centimeters per second? At the AAS meeting, researchers described the instrument they are calling an ‘extreme precision Doppler spectrograph.’ Exploring radial velocity detection in this realm will demand the upgrades the NEID team has made to the observatory, allowing the spectrograph to achieve room temperature fluctuations below +/-0.2 degrees Celsius in the short term.

Vibration from the WIYN telescope also must be taken into account using high-precision accelerometers and speckle imaging data taken on-sky to achieve the needed precision. The team believes the instrument is capable of reaching 27 centimeters per second and perhaps lower. The goal of the ESPRESSO group is 10 centimeters per second. As we explore the capabilities of both instruments, we are revitalizing radial velocity and making it ever more relevant to the quest to discover and characterize small worlds that may support liquid water.

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{ 13 comments… add one }
  • Harry R Ray January 10, 2020, 18:08

    There is a third sub-meter spectrograph in operation called ESPRES, which Debra Fischer uses, although I do not know which telescope it is mounted on. I believe that at least 90% of the sky can be covered by at least one, and >40% by all three. This is important, because this astrocomb(or laser comb)technology is SO NEW that stars observable by ALL THREE can be used to VERIFY the precision of EACH ONE! It is IMPARITIVE that each of the three consortiums monitor AS MANY MUTUALLY OBSERVABLE STARS as possible abd publish their results as quick as possible to insure the reliability of this new technology.

    • Ronald January 11, 2020, 17:55

      Yes, I think you meant EXPRES.
      EXPRES will be installed on the 4.3-meter Discovery Channel Telescope operated by Lowell Observatory. It has a goal to achieve 10 cm/s radial velocity precision.
      I do not know when it will be operational.

      • Ashley Baldwin January 12, 2020, 12:31

        According to the website, EXPRES is opraional on the DCT, though if so, with hardly a fanfare. It was slated for the “100Earths” project but I’m not aware that has started.

        The original idea wasn’t just about the instrument’s 10cms/sec sensitivity though, so much as the photospheric modelling it would use to lower disruptive stellar noise down to a threshold that would give a meaningful SNR. I guess it is this that is causing the operational delay.

        Always a software problem these days !

    • Ronald January 11, 2020, 17:59

      Those 3 will indeed, in my knowledge, be the only RV instruments capable of detecting terrestrial planets in the HZ of solar type stars.
      Until we get CODEX, on the European ELT. Around 2025?

      • Ashley Baldwin January 12, 2020, 12:22

        Not sure we will see a that now.

        The ESO are currently studying two new possible first generation instruments on the E-ELT , one of which is an alternative/upgrade to CODEX . A multi purpose high resolution optical integral field spectrograph,”HIRES” .

        HIRES is essentially a compromise between CODEX and EPIC – the original high resolution optical imaging and spectroscopy package .( the optical equivalent of METIS and originally slated as a second generation instrument given its complexity and cost ) With a maximum resolution of around 150000. Perfect for exoplanet science . Especially if combined with a high performance coronagraph ( contrast reduction 1e6 – 1e8) , polarimetric imager and ….most importantly of all – an extreme adaptive optics system . With the last by far in a way the most difficult technologically and financially . This all offers direct imaging of exoplanets in the visible spectrum and better still, “high definition imaging” ,or HDI.

        HDI cleverly combines direct imaging and polarimetry with ultra high resolution spectroscopy AND the massive photon gathering capacity of an ELT to give detailed exoplanet atmospheric characterisation ( it needs a whole lot of very sophisticated simulation and modelling first but that is a talk in itself !) .

        A technique described on this site a few years back by one of its main pioneers , Ignas Snellen from Leiden University . I’m sure Paul can supply the link.

        A lot of budget though , hence the extended consultation , but a serious exoplanet characterisation package – especially used with the pre-existing first generation NIR METIS instrument above.

      • Thomas R Mazanec January 14, 2020, 12:09

        Is CODEX one of Paul’s exoplanet projects?

        • Paul Gilster January 14, 2020, 13:01

          Still undergoing early feasibility studies. I’ve linked to it nonetheless.

  • Ronald January 10, 2020, 18:21

    The ESPRESSO instrument (…) takes us into centimeters per second range, which means detecting habitable zone planets around Sun-like stars.”

    Small addition: “which means detecting habitable zone *earth-sized* planets around Sun-like stars”.

    If I am not mistaken, that would require something like 20 cm/sec, which is within the range of ESPRESSO.

    • Paul Gilster January 10, 2020, 21:42

      Exactly right, Ronald. I’ll get that change into the text.

  • Robin Datta January 10, 2020, 23:25

    Why not a simpler name like Kitt Peak Exoplanet Doppler Spectroscope?

  • Rob Flores January 11, 2020, 2:09

    Finally, with the sensitivity of spectroscopy based radial
    velocity planet hunting we can fill a gap in knowledge that
    the Kepler mission could not give us.

    That is, how common are Earth twins +/- 10% around
    Smaller F,G, bigger K type stars in their habitable zones.

    You can make an inference or extrapolation from Kepler data that there should be many, but there could always be unknown combination factors that reduce the likelyhood of such planets. (I suspect that Earth twins in Sun like stars in the HZ, are rare (those kepler findings show a lot 1.3-1.5 ME and even though there is bias, a dearth of Earth twins would help explain Fermi Paradox.)

    • Ashley Baldwin January 12, 2020, 14:16

      Amid all the (understandable ) excitement over the inclusion of a high performance coronagraphic imager on WFIRST, it’s often forgotten that Scott Gaudi’s team are leading a microlensing survey of exoplanets with the same telescope – hopefully finding up to 4-5000 k exoplanets. About as many are known at present. Yes these planets are “one time” discoveries and cannot ever undergo detailed atmospheric characterisation. However taken together they will be the first large and totally representative sample of the exoplanet population . Very unlike the current population of 4000 or so planets discovered by mostly Doppler or Transit spectroscopy – and thus hugely biased to larger planets, orbiting closer in, to smaller stars .

      If the ESA Euclid telescope gets a mission extension ( as seems likely especially as unlike Kepler it has six reaction wheels ) the hope is it too will perform a further microlensing survey . All of which should give us a much more representative sample and breakdown of exoplanet mass distribution per orbital distribution per stellar class.

      For all its revolutionary contribution Kepler didn’t last long enough ( in primary non K2 guise) , amongst other reasons – including sensitivity and stellar noise baseline – to achieve its stated goal of discovering an Earth mass planet orbiting in the hab zone of a sun like star. TESS was never intended or able to do this either.

      Still hope for PLATO though.

      However the vital role of microlensing cannot be overstated in its contribution to exoplanet science.

      Go, go Gaudi & Co,

      In terms of the Fermi Paradox this is too often mistaken as some sort of physical law. In reality it’s eponymous creator simply meant it as a philosophical question framing what has become an existential subject. Given the reasons described above we are nowhere near providing any sort of answer either affirmative or negative.

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