With the upgrade of both the grating and detector for the OSIRIS spectrometer, there was a substantial increase in overall throughput for the instrument. In the table below, we have calculated the new spectroscopic zero points by applying the measured throughput values and scaling the limiting magnitudes appropriately.

Zero points are defined in the standard way:

Mag(zero point) = Mag(standard) + 2.5 * log (N/t)
where:

N = counts or electrons, depending upon calculation

t = time

N/t = counts or electrons per second
Spectroscopic Zero Points
Band Delivered (H2) Upgraded 2016 (H2RG)
J-Band 23.5 24.7
H-Band 24.3 25.3
K-Band 23.7 25.1

These sensitivity improvements are a result of a better grating reflectivity, increased detector sensitivity, and decreases in the detector noise both in dark current and read noise. In addition, the new focus stage improved the focus across the array so the PSF is tighter.

Gain Delivered (H2) Upgraded 2016 (H2RG)
DN/e- 0.23 0.465
e-/DN 4.35 2.15

Imager Zero Points

Method:

  • Aperture Radius:
  • Inner Annulus Radius:
  • Outer Annulus Radius:
  • Magnitude source:
  • Detector gain:
  • Date:
  • Star:
  • AO:
  •  75 pix
  • 150 pix
  • 200 pix
  • SIMBAD
  • 2.16 e-/DN
  • 2018-10-22
  • FS32
  • NGS, TT-only

Imager Zero Points
Imager Zero Points (2018, H2RG)
Band DN/s electrons/s
Y 25.33 26.17
J 25.99 26.82
H 26.58 27.41
Kp 25.78 26.62
FeII 23.54 24.38
Hcont 23.59 24.43
BrGamma 23.18 24.02
Kcont 22.83 23.67
HeI_B 23.36 24.02