We plan to deploy 4 NRES spectrographs to 4 sites: (Chile, Texas, South Africa, Israel) in 2017. In Chile and South Africa, each spectrograph will be coupled to 2 X 1m telesocpes. The Texas and Israel sites have only 1 X 1m telescope each. By the end of 2017, we thus expect to have 6 X 1m spectroscopically-capable telescopes, 4 in the southern hemisphere and 2 in the north.
We have parts for 2 more NRES spectrographs, but we have not yet worked out a schedule for deployment or a decision on sites.
The first NRES instrument (NRES-1) is complete, installed in its environmental chamber and attached to two 1m telescopes at CTIO (Chile).
The spectrograph performance parameters are close to the design targets.
Spectral dispersion and the dimensionless resolution R (the ratio of wavelength to the FWHM measured for ThAr emission lines) vary across each echelle order, but not from order to order; this is a consequence of the large incidence angle of light on the grating. The measured linewidths are about 4.15 pixels, almost independent of wavelength. The resolution R is about 44000 at the redmost end of each order, 55000 at the center, and 72000 at the blue end.
To estimate throughput, we measured the number of detected electrons per 4.15-pixel resolution element for two moderate-brightness Sun-like stars: HD76151 (V=6.0, Teff=5500) and HD115383 (V=5.22, Teff=6050). Scaled to V=10.0 and a 10-minute integration time, these measurements give:
450 nm | 550 nm | 650 nm | |
---|---|---|---|
HD76151 | 395 e- | 715 e- | 1055 e- |
HD115383 | 445 e- | 1045 e- | 1695 e- |
These numbers suggest better performance than our TESS target of S/N = 30 for V=11 at an integration time of 1 hour. Throughput will improve when the telescopes' optics are recoated.
We have obtained spectra of stars from 0.4 < V < 11.5 with exposure times 5 sec < Texp < 1 hr.
Environmental chamber servos have been tuned remotely since we left the site. Present temperature stability is better than 5 mK on timescales of 1 day.
Problems encountered:
NRES-2 is assembled and performs well in the lab. It has been moved into its environmental chamber (igloo). It will be packed for shipment to Texas in mid-June.
The data reduction pipeline corrects raw CCD images for bias, dark current, and stray light, extracts 1-dimensional spectra covering 67 echelle orders and 2 or 3 fibers, identifies about 800
ThAr emission lines from the calibration fiber and uses them to estimate a high-accuracy wavelength solution, and computes a radial velocity estimate. Results are written to a compressed tar file which is stored in a data archive. A searchable database of metadata will allow quick location and retrieval of data for any selected objects or observing times.
Work is proceeding on a queue system that will run the pipeline on an LCO server, so that the NRES pipeline will be invoked automatically for each incoming data file, performing near-real-time reduction of NRES data. We plan to make the pipeline available in three successive versions.
(v1 - due Aug 1) Performs automatic calibrations, extracts to 1-dimensional (per order) spectra, estimates wavelength solution from ThAr spectrum. Performs a rudimentary radial-velocity analysis, meant (at first) largely as a testbed for later improvements. Produces diagnostic plots and a tarball of intermediate and final data products.
(v2) Provide user access to and analysis of data from the exposure meter and from the autoguiders; also from the radial velocity analysis.
(v3) Perform an automated classification of the target star in terms of the parameters {Teff, log(g), log(Z), vsini}, and add information about this analysis and its result to the output tarball.
Schedule for remaining installations
UNIT | Site | # of Telescopes | Install Date |
---|---|---|---|
NRES-1 | CTIO Chile | 2 | 1 Feb 2017 |
NRES-2 | McDonald Obs. Texas | 1 | 1 Sept 2017 |
NRES-3 | SAAO South Africa | 2 | 1 Oct 2017 |
NRES-4 | Wise Obs. Israel | 1 | 1 Nov 2017 |
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