bHROS commissioning
bHROS was commissioned at Gemini South in July 2005, during a week when seeing conditions were excellent. Following a check of the target acquisition procedure, a range of observations were carried out to test the instrument, including several back to back observations of the same target with bHROS and GMOS in order to determine the throughput of bHROS relative to the absolute values previously measured for the GMOS 600B grating by Hook et al. (2004). In addition, a significant amount of time in the middle of two of the nights was used to test whether the science fold mirror (SFM) position was optimised for point sources. On the last 1.5 nights some science targets were observed.
Throughput @ 5500 A (large and small apertures)
For the GMOS 600B grating, Hook et al. (2004, PASP, 116, 425; Fig. 3b) have derived a thoughput of 39.5% at 5500A (this value appears to supersede an earlier quoted value of 47.5%), where the GMOS value is an absolute throughput including the GMOS optical components and detectors but excluding the throughput efficiencies of the atmosphere and the telescope. The bHROS throughputs derived relative to the GMOS 600B grating therefore also exclude the atmosphere and telescope.
Immediately prior to the bHROS commissioning run, bHROS and GMOS relative throughputs at 5500A were determined at 5500A by means of observations of the GCAL CuAr arc. A bHROS large aperture throughput of 16.4% was obtained then.
Relative throughput measurements obtained on the star HR 9087 (V=5.12) on July 22/23 and 23/24 are described in detail in Appendices A and B, respectively. Seeing correction estimates for the fraction of light falling on the bHROS apertures or GMOS slit were included.
For the July 22/23 observations
- 17.0% efficiency for bHROS with the large aperture (0.774 arcsec^2)
- 20.0% efficiency for bHROS with the small aperture (0.325 arcsec2)
For the July 23/24 observations
- 17.4% efficiency for bHROS with the large aperture fibre.
- 19.5% efficiency for bHROS with the small aperture fibre.
The results from July 22/23 are preferred because the bHROS and GMOS seeing conditions were very similar then, whereas the GMOS seeing on July 23/24 was markedly worse than for bHROS, necessitating a larger relative correction.
Further information
More information on bHROS performance and sensitivities can be obtained at the Gemini bHROS webpages here.
For further information on the results of this commissioning run and
science results with bHROS, please contact Prof. Mike Barlow.