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NOTcam spectroscopy: flux calibration

Engineering array (SWIR1)

From data obtained on 2/7/2004, of the optical flux standard BD+26 2606 (G166-45; SP1446+259; V=9.7, J=8.7, H= 8.4, K=8.4 Alonso et al. 1994 A&ASS 107, 365), with the widest 'slit' (1mm pinhole), grism #1 and WFC, we obtained the following preliminary results.

At 1250 nm (approximate center of J band), the system efficiency (atmosphere, telescope, instrument, detector) is about 4%. At 1030 nm (approximate center of the Yn filter NOT #222), the system efficiency is about 3%, but these 3% are divided over the 6th and 7th order. Extrapolating this to H and K, using estimates for instrument and detector efficiencies, we get a total system efficiency for H and K of 5% and 6% respectively.

In the J band (6th order), the above star gives about 110 electrons/Angstrom/second, in the reduced spectrum. In the Z band (Yn filter, 1030nm, 7th order) we get about 75 e-/A/s. In the H band we observed approx 90 e-/A/s. In K we observed about 70 e-/A/s.

Science-grade array (SWIR3)

I have extrapolated the above results to derive estimates for the spectroscopic JHK efficiencies and countrates when using the new science array (installed Dec. 2007).

Expected count rates and efficiencies for science-grade array

J bandH bandK band
system efficiency 7% 8% 9%
photons/sec/Å   for SP1446+259 190140105

In June 2009 the star SP2209+178 was observed to calibrate the Yn-band efficiency.

Measured efficiency for science-grade array
date Yn band 7th orderYn band 6th order J band 6th orderJ band 5th order
June 2009 3.5% 4.7% 6.3% 8.2%

In June 2011 the star SP2209+178 was observed to calibrate the Y- and Z-band efficiency.

Measured efficiency for science-grade array
dateZ band 8th orderZ band 7th orderY band 7th order Y band 6th orderJ band 6th orderJ band 5th orderH bandK band
12 June 2011 3.7% 3.5% 4.7% 4.6% 4.5% 6.3% 7.0% 5.6%
photons/sec/Å 175 150 190 180 150 200 175 105

Exposure-time calculator

Currently, the above estimated efficiencies and countrates for the science-grade array are used in the exposure-time calculator.

John Telting (jht)

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