Engineering Observations in 2012

This page summarizes the results of engineering observations of FOCAS in October (with CsIR) and December 2012 (with CsOpt) after the recovery work from the telescope cooling system incident in 2011.

(Last updated : 2/1/2013)

System Efficiency

    Comparison to 2010 data

    Comparison of the system efficiency including the atmosphere and telescope before (black-dot) and after (red, blue) the incident. All of the data are calculated from observations of the flux standard G191-B2B at similar airmasses (1.2-1.3). Absolute flux is taken from the STIS/NICMOS data of CALSPEC.

    It is clear that the system efficiency is completely recovered. A slightly better efficiency in the new data might be due to the absence of the Atmospheric Dispersion Corrector (ADC).

    Other Grisms

    System efficiency measured using the other grisms in December 2012 with CsOpt secondary. Efficiency with 300B/R grisms and a scaled quantum-efficiency curve of the detector are also shown for comparison.

Zero-point Magnitudes

Oct. 2010 (CsOpt+ADC)Oct. 2012 (CsIR)Dec. 2012 (CsOpt)
U 24.324.524.7
B 28.028.328.3
V 28.328.428.4
R 28.228.328.3
I 27.928.028.0

Multi-Object Spectroscopy (MOS)

Multi-object spectroscopic observation of Mrk 6 field.

MOS observations using masks created from FOCAS and Suprime-Cam images have been successfully done. However, the absence of ADC causes a difference in the plate scale and temporal procedures are necessary in the mask design process.


    Unpolarized Standard Star

    Linear spectropolarimetric observation of the unpolarized standard star G191B2B. The instrumental polarization is found to be smaller than 0.1%.

    Strongly Polarized Standard Stars

    Instrumental polarization position angle of the strongly polarized standard star BD+64d106 compared with that of polarizing filters. In this plot, the PA of polarizing filters are shifted to match BD+64d106. The variation of PA is caused by the wavelength dependence of the equivalent optical axis of the half-waveplate and consistent with the previous measurement shown in this page.

    The position angles (LEFT) and degrees of polarization (RIGHT) strongly polarized standard stars obtained from V-band imaging- (Hiltner 960 and VI Cyg #12) or spectro-polarimetric (BD+64d106 and BD+59d389) observations. The data from literatures are summarized in this page. From the left plot, the PA of the polarizing filter for UVOpt (< 800nm) is found to be 75°.7 (±0.5). The PA of the other filter for NIR (> 600nm) is 37°.1 .

    Ghost from Half-Wave Plate

    The half-wave plate was damaged in an accident during the recovery work which caused small cracks at its centeral portion. Although the performance of polarimetric function is similar to before as shown above, it is found that the cracks create additional ghost images.

    This is a V-band image of Hiltner 960 field. The ghosts due to the half-wave plate are indicated by the green circles. Their positions change with the angle of the wave plate. The red circle shows a ghost probably created by the Wollaston prism which had already existed before the incident and does not move with the wave plate angle. The brightness of these ghosts are below 1/1000 of the main body of Hiltner 960. They can be a problem for imaging polarimetric observation of faint target(s) in a crowded field.


FOCAS attached to the telescope
(Oct. 4, 2012)
telescope balancing with FOCAS
(Oct. 4, 2012)
M15 image in R-band
(Oct. 6, 2012, seeing ~0".55)

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