|NRES Unit||Site||Dome(s)||Camera||Mean Seeing at Site (arcsec)||Current status|
|NRES01||LSC (Chile)||B, C||fa09||1.0||Exposure meter not working|
|NRES02||ELP (Texas)||A, B||fa17||1.2||Exposure meter operational|
|NRES03||CPT (South Africa)||B, C||fa13||1.6||Exposure meter not working|
|NRES04||TLV (Israel)||A||fa18||TBD||Exposure meter not working|
Please see the Observatory Status page for the current status of each NRES unit.
The plot below shows the expected signal-to-noise ratio obtainable from NRES under good conditions; the actual SNR obtained may be lower due to clouds, acquisition inaccuracies, etc. The signal-to-noise per resolution element is estimated from the order of the spectrum that includes the Mg b lines (5167 - 5184 Å). The results from a set of test observations are scaled to an exposure time of 60s, and then a model is fit to the points with the highest quality spectra (i.e. successful acquisition and clear sky conditions). Although the scheduler regards the NRES units as identical, the commissioning observations have demonstrated that their performance somewhat differs. Those differences are predominantly driven by the state of the feeding telescope, not the spectrograph itself. We recommend setting the exposure time based on the performance of the lowest throughput NRES system, which is shown by the model below.
A signal-to-noise ratio of at least 25 is recommended in order to obtain precise RVs, and at least 40 for stellar parameter determination. These SNRs are difficult to obtain for targets with V>10.
Beyond the exposure time, NRES observations are subject to typical overheads. The overheads we've included in our database are the following:
The total, 667s, will be added to the exposure time of the request. You must make sure that your time window can accommodate the sum of exposure time plus overheads.
We recognize that the instrument performance is not yet at the level of its ultimate capability; we expect to continue to deliver significant improvements. We welcome your assistance in that effort. We encourage you to send us your criticism and your suggestions for improvements: Send email to firstname.lastname@example.org and put "NRES" in the subject line.