HRS-2 Configurations

N.B., HRS-2 is still in early phases of development and much of the information on this page may be outdated!

HRS-2

HRS_ResPower_echelle_CrossDisp_fiber_skyfibers_slicer_gascell_binning

ResPower = 18k, 30k, 70k, or 105k These values set the slit width for resolving powers of 18,000, 30,000, 70,000, and 105,000, respectively
If you wish to use higher resolution modes below 4000 Å then consider using the special K configuration. This configuration has its best focus at the Ca K line. If you are interested in the higher resolution modes above 4400 Å then we suggest you don't use the special K version of the cross disperser.

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.

CrossDisp

Wavelength (Å) Wavelength (Å)

CrossDisp Begin Central End Orders CrossDisp Begin Central End Orders

N.B., HRS-2 is still in early phases of development and much of the information on this page may be outdated!
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
N.B., HRS-2 is still in early phases of development and much of the information on this page may be outdated!
The spectral coverage of a given order (its FSR or Free Spectral Range) is lambda/order number.
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:

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 = iodine gas cell out of beam

1 = iodine gas cell in beam

binning = 2x1, 2x2, 2x3, 2x4, 2x5, 2x6 (or 1xN) 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:

ResPower Binnings Recommended Binning(s)
(pixels per resolution element)

105k 2x1 (or 1x1) 2x1 (2.0)

70k 2x1 2x2 (or 1xN) 2x1 or 2x2 (4.0 or 2.0)

30k 2x2 2x3 2x4 (or 1xN) 2x3 (2.7)

18k 2x4 2x5 2x6 (or 1xN) 2x5 (3.2)

N.B., HRS-2 is still in early phases of development and much of the information on this page may be outdated!
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
NOTE: YOU PROBABLY SHOULD NOT USE COLUMN BINNING OF 1 BECAUSE YOUR READ NOISE WILL GROW TO BE SIGNIFICANT
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.

NOTE: YOU SHOULD PROBABLY USE OUR SUGGESTED BINNING; IF YOU OVER-RESOLVE THE LINE YOU WILL NOT GAIN ANY INFORMATION DUE TO FIBER SCRAMBLING; YOU WILL JUST HAVE A SQUARE PSF WITH MORE READNOISE
Example: with 2x3 binning and ResPower=30k (30,000), there are approximately 2.7 pixels per resolution element.

Clarifications or bug reports:

Contact Phillip MacQueen at pjm@astro.as.utexas.edu or (512) 471-1470.