Hans M. Günther

ARCUS

Performance of a double tilted-Rowland-spectrometer

Hans M. Günther and the ARCUS collaboration

Outline

  • ARCUS optical layout
    • Rowland design
    • in fact, two Rowland designs
    • tilted torus
    • select CCD locations
  • Resolving power
  • Order sorting and confusion
  • trade study: Boom
  • Tolerances

Chandra-like toy model

https://tinyurl.com/arcus-xray

Subaperturing toy model

  • Mirror scattering larger in plane of reflection than perpendicular
  • Multi-layer mirrors have narrow bandpass, but this helps
https://tinyurl.com/arcus-xray

CAT grating toy model

https://tinyurl.com/arcus-xray

2 CAT grating toy models

https://tinyurl.com/arcus-xray

2 CAT grating toy models

https://tinyurl.com/arcus-xray

ARCUS: Single energy

https://tinyurl.com/arcus-xray

CCD placement

FluxperCCD

Effective area and resolving power

Aeff 16 CCDs resolving power

Effective area and resolving power

averageres

Separating the two spectra

EQ Peg (an active star) observed for 100 ks, color scale is logarithmic FluxperCCD

Order sorting

FluxperCCD

Trade study: 3 vs 4 sided boom

https://tinyurl.com/arcus-xray

Losses through partial boom coverage

EQ Peg (and active star) observed for 100 ks, color scale is logarithmic Boom schematic boom loss

Losses through partial boom coverage

EQ Peg (and active star) observed for 100 ks, color scale is logarithmic Boom schematic boom aeff

Tolerances for CAT gratings

trans rot

Tolerances for CAT gratings

dvar

Summary

  • Design is based on Rowland geometry
  • Uses two optical axes to image zeroth order and dispersed light on fixed number of CCDs
  • Spectra can be separated and orders sorted
  • Small boom would reduce effective area, particularly at short wavelength
  • Tolerances are very forgiving