HRS Configurations

See the HRS Configurations Check to see if a configuration is valid or not
ResPower = 15k, 30k, 60k, or 120k
These values set the slit width for resolving powers of 15,000, 30,000, 60,000, and 120,000, respectively
echelle = blue, central, red
These values set the echelle rotation angle for changing the position of the orders on the CCD, primarily to move spectral features of interest off CCD defects.
  • Central: Default value. It is intended to center the orders on the CCD, and yield the (theoretical) wavelengths given below in the CrossDisp table. In practice, the blaze peaks are slightly to the red side of the CCD.
  • Blue: Causes the wavelength approximately at the blue end of the orders to be moved to the center of the CCD. The blaze peak of the order (peak efficiency) moves near the red edge of the CCD.
  • Red: Causes the wavelength approximately at the red end of the orders to be moved to the center of the CCD. The blaze peak of the order (peak efficiency) moves near the blue edge of the CCD.
Wavelength (Å) Wavelength (Å)
CrossDispBeginCentralEndOrders CrossDispBeginCentralEndOrders
316g4931 *3057 4931 6793200124 90 600g4739 *3751 4739 5732163129106
316g5936 4076 5936 7838150103 78 600g5271 4275 5271 6263143116 97
316g6948 5095 6948 8860120 88 69 600g5822 4814 5822 6793127105 90
316g7940 6114 7940 9861100 77 61 600g6302 5316 6302 7278115 97 84
316g8991 7109 8991**10917 86 68 56 600g6869 5879 6869 7838104 89 78
316g10022815210022**11757 76 61 52 600g7366 6369 7366 8375 96 83 73
316g109179125**10917**12737 67 56 48 600g7940 6948 7940 8861 88 77 69
600g8375 7456 8375 9406 82 73 65
600g8990 7940 8990 9861 77 68 62
600g9405 8491 940510362 72 65 59
*HRS+HET delivers very little flux below 4000 Å
**HRS+HET delivers very little flux above 10400 Å

These values set the rotation of the cross disperser to:

  • select which orders fall on the CCD
  • set how much inter-order space there is for sky fibers
The three wavelengths given above for each value of CrossDisp are the blaze (central) wavelengths of the blue-most order, the central order that falls between the two CCDs, and the red-most order.

The wavelengths given are for the echelle=central setting.

The shortest wavelength observable is 400nm, set by the filter for rejecting the 2nd order of the cross disperser, and by the HRS image quality (as specified and designed).

The longest wavelength observable is approximately 1050nm due to the drop in the CCD quantum efficiency.

The central wavelength of any order can be calculated from any other order of known central wavelength and order number (eg. those in the table) by using the relationship:

  • lambda * order = constant
eg. for 316g4931, where lambda=4931 and order=124, the central wavelength of order 150 is (4931*124)/150=4076.

The spectral coverage of a given order (its FSR or Free Spectral Range) is lambda/order number. eg. 316g4931: for order 124, lambda=4931 so FSR=39.8 Å

A filter is always used for rejecting the 2nd order of the cross disperser, and it is selected automatically.

fiber = 2as or 3as (as=arcsecond)
Angular diameter on the sky of the fiber to be used for feeding light from the telescope to the spectrometer.
An important consideration for observing faint objects is that the 3as fiber collects 225% more "sky" than the 2as fibers.
skyfibers = 0sky, 1sky, 2sky
The maximum number of sky fibers that can be used without order overlap depends upon the values of "CrossDisp" and "fiber". The limiting wavelengths are:
  • 316g and 2as: 4000+ for 0sky, 5880+ for 2sky
  • 316g and 3as: 4000+ for 0sky, 5880+ for 1sky, 7100+ for 2sky
  • 600g and 2as: 4000+ for 0sky, 4200+ for 2sky
  • 600g and 3as: 4000+ for 0sky, 4200+ for 1sky, 5100+ for 2sky
slicer = IS0 or IS1
  • 0 = no slicer
  • 1 = image slicer #1
    Available when fiber=3as, skyfibers=0sky, and ResPower is one of30k, 60k, or 120k. The increase in throughput verses the 3as fiber is 41%. Or ders overlap depending upon "CrossDisp" as follows:
    • all 316g settings: orders overlap below 5880 Å
    • all 600g settings: orders overlap below 4200 Å
gascell = GC0 or GC1
  • 0 = don't use the iodine gas cell
  • 1 = use the iodine gas cell as user specified elsewhere
binning = 1x1, 1x2, 1x3, 1x4, 1x5, 2x1, 2x2, 2x3, 2x4, 2x5
The format is (column binning)x(row binning), where
  • column binning is in the cross dispersion dimension
  • row binning is in the echelle dispersion dimension
Typical binnings for each "ResPower" are:

ResPowerBinningsRecommended Binning(s)
(pixels per resolution element)
120k 1x1 or 2x1 2x1(2.0)
60k1x1, 1x2, 2x1, or 2x22x1 or 2x2(4.0 or 2.0)
30k1x2, 2x2, 1x3, or 2x3 2x3(2.7)
15k1x4, 2x4, 1x5, or 2x5 2x5(3.2)

The width of the orders as a function of "fiber" is

  • for fiber = 2as: 13 pixels for column binning = 1
  • for fiber = 3as: 20 pixels for column binning = 1
The number of pixels per resolution element can be calculated as

(240,000)/(Resolving power)/(row binning)

Note that this value varies along the orders.

Example: with 2x3 binning and ResPower=30k (30,000), there are approximately 2.7 pixels per resolution element.

Example HRS configurations:
  • HRS_15k_central_316g7940_3as_2sky_IS0_GC0_2x5
  • HRS_30k_central_600g5271_2as_2sky_IS0_GC0_2x3
  • HRS_60k_central_316g5936_3as_0sky_IS0_GC0_2x1
  • HRS_120k_central_316g6948_3as_0sky_IS0_GC0_2x1
Clarifications or bug reports:

Contact Phillip MacQueen at or (512) 471-1470.