Observers’ and Proposers’ FAQ

This FAQ is written for proposers and the TAC for the 2020B NOAO call to use NEID on a shared risk basis. It represents the best current guidance from the instrument team regarding the instrument’s capabilities for that semester.

This document should not be read as a description or prescription of either the 2020B call or the TAC decision process, the parameters of which are the purview of NASA and NOAO, not the instrument team.

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1. May I propose technical modes or data products not described by the language in the call for proposals? For instance, asteroseismology, Doppler tomography of B star transiting planets, RVs of double-lined spectroscopic binaries, atmospheric transmission spectroscopy, or spectrophotometric measurements?

The operational modes and data reduction pipeline available in 2020B for NEID is focused on delivering precise RV measurements of bright, single, slowly rotating stars. All raw science and calibration frames (i.e. full 2D echellograms) and 1D wavelength-calibrated spectra will be available for proposers to perform their own custom data reductions.

Proposers may request to perform other kinds of science with data taken in the allowed observational modes with this understanding, and at the discretion of the TAC.

2. OK, but specifically, will NEID be able to perform spectrophotometry?

NEID will have an extremely stable throughput as a function of wavelength on long timescales because of its excellent guiding, excellent stability, excellent fiber scrambling, and the low-resolution spectra provided by its exposure meter. As such, it will likely enable good spectrophotometry.

However, spectrophotometric stability is not a design goal of either the instrument or the NExScI data reduction pipeline, and so proposers will likely need to perform their own spectrophotometric data reduction using raw data products, request spectrophotometric standards to calibrate the instrument, and determine the stability of the system on their own. Note that proposers would need to include the time required to obtain nonstandard calibration observations in their instrument time request.

3. What operational modes are available in 2020B?

The standard operational mode will be the HR (high resolution) mode with simultaneous etalon light in the calibration fiber.  The etalon is referenced to the laser frequency comb at the beginning and end of each night.

Users may request no simultaneous calibration light be present during exposures, but may not otherwise specify the brightness of the calibration light, which will be set by the instrument operator so as to not overwhelm the expected amount of light from the science fiber.

The instrument team anticipates that the HE fiber will have roughly twice the throughput of the HR fiber under typical conditions, and have roughly half the spectral resolution.

The exposure meter operations have not been finalized, but will be determined by the brightness of the target and optimized to deliver precise barycentric corrections. It will deliver 1D spectra of all five fibers at ~1 Hz time sampling at R~100 at moderate SNR, but cannot be more specific at this time. No special requests on its operations will be available for 2020B.

4. I’d like to observe a binary system. Where is the sky fiber with respect to the science fiber, and can I rotate the field to keep it off of the binary companion? How close can the binary be before spectral contamination in the science fiber becomes an issue? At what separation and contrast will binary stars detrimentally affect guiding performance?

The sky fiber is at a fixed position 40” from the science fiber and its orientation in the focal plane is not adjustable. The HR fiber spans 0.”92 on the sky and the “safe” separation for binaries to avoid contamination will depend on the seeing. The instrument team’s best, conservative guidance at this time is that binary companions within 10” could cause problems with either guiding or contamination or both.

5. What are the readout characteristics of the detector?

These will not be final until after commissioning, but the instrument team’s current best guidance is that per-exposure overhead of the NEID CCD will be around 30s, with read noise of around 4.5 electrons and dark current of less than 3 electrons/hour/pixel. The NEID spectral resolution element in HR mode is 5 pixels wide and the effective extraction height in the cross dispersion direction is around 6 pixels.

Nonstandard readout modes are not supported at this time.

6. I’m interested in observing a NEID standard star. May I propose for it?

Eight stars are currently designated “standard stars” for NEID:

Current expectations are that 2-3 stars on this list will be observed every night NEID is in operation, and these data will have zero proprietary period. There is no restriction on proposing additional observations of these targets, but the TAC may consider such science duplicative, and so proposers should justify the additional observations.

This list is subject to change in future semesters.

7. I’m interested in observing a star that I’m worried is on the instrument team’s GTO program. May I propose for it?

The NEID science team’s GTO targets are described in this paper. Stars on the GTO program are not proprietary targets and proposers may propose for them as they would for any other star. The TAC may consider observations beyond those acquired in the GTO program duplicative, and so proposers should justify the additional observations.

Briefly, most targets are mostly bright (V<7) and nearby, many being RV “classics” with many dozens of archival RV observations made over decades from Lick 3m, APF, Keck, HET, ELODIE, CORALIE, HARPS, and other instruments. The primary science goals include searching for nearby Habitable Zone terrestrial planets, identifying future direct imaging targets, evaluating known controversial and low-amplitude exoplanets. The NEID instrument team also anticipates using some GTO time to pursue targets of opportunity as they arise, including TESS targets.

GTO time will share the NEID queue with targets submitted via NN-EXPLORE and the other WIYN partners.

Earlier descriptions of the program are in the AAS poster on the GTO program here. The initial GTO target list is here.

8. May I request non-standard “internal” calibration frames (i.e. extra flats, darks, or calibration sources)?

Not at this time.