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Overview

HRS Throughput Estimates per Resolution Element

It is important for the PI to realize that due to the design of the HET the effective collecting area changes over a trajectory. Near the end of a trajectory the HET has half the collecting area that it has near the middle. As such two medium length visits centered on middle of a track could be more valuable than a single long visit. All throughput estimates are based upon center of track efficiency.

Try our HRS Throughput Calculator.

To see the effect of changing exposure times in a moving aperture try the HET Filling Factor Calculator.

The measured throughput for the HRS is given below determined relative to the LRS throughput curve. The latter was corrected for seeing and slit losses. We provide the abovementioned throughput calculator to obtain your own values.

The following is based on experience and feedback from users(based on 2.0" FWHM)

Configuration	V Mag.	Time	S/N @ Peak of order w/ Wavelength
R=15,000 3" fiber	14	1800	100 @ 5800 Å
R=15,000 2" fiber	13.6	1800	100 @ 5800 Å
R=30,000 3" fiber	12.5	1800	100 @ 5800 Å
R=30,000 2" fiber	12.1	1800	100 @ 5800 Å
R=60,000 3" fiber	10.5	1800	100 @ 5000 Å
R=60,000 2" fiber	10.1	1800	100 @ 5000 Å
R=120,000 3" fiber	9.3	1800	100 @ 6440 Å
R=120,000 2" fiber	8.9	1800	100 @ 6440 Å

where S/N assumes the Poisson noise limited regime with no sky subtraction. If you observe much fainter objects or on a very bright sky background, readout or background noise may factor strongly. See the observing tips for HRS.

The above assumes that the iodine cell is not being used. Transmission through the iodine cell is approximately 70%.

A useful analysis by George Trammell at PSU of a spectrophotometric standard taken with the R=30k setup under poor seeing IQ=2.3" yields the following throughput at blaze center for each order. Despite the atypically poor image quality, the relative throughput of the orders is indicative.