HDS Image Slicer

We are planning to open a new Image Slicer (IS) for HDS open use in S11B.
Please note that the operation of the IS will be in a shared-risk mode.
The observer who wants to use this IS must make contact with the HDS support astronomer.
For detailed information about this image slicer, please refer Tajitsu et al. 2012 PASJ in press.

In order to collect more photons into a narrow slit for high spectral resolving power, the image slicer (IS) can be used. The IS reformats the 2D-image of a pinhole with 1''.5 diamteter in the F/12.6 focal plane of the telescope into a series of narrow slits (0''.3 width ×5) which is imaged on the spectrograph entrance slit.

Type	Bowen-Walraven type
Entrance opening	φ1''.5 circle
Slit width	0''.3 (R~110,000)
Slit length	7''.9 (λ > 5,000A for the red , λ > 4,000A for the blue setting)
Number of slices	5
Efficiency	> 80% (@4,000 ~ 7,000A)
manufactured by	OptCraft

The IS is basically designed for brighter targets (<10~12 mag).
Since we have never had actual results for fainter targets and need to make sure the performance of the IS, we recommend to use the IS for relatively brighter ones during the shared-risk mode operation.
For fainter targets, observers must give care to the following points.

Due to the spread of the spectrum along the slit length direction, the increase of total dark currents and read out noises in allover pixels cannot be ignored for fainter targets. Please check carefully the resultant S/N ratio in HDS ETC for your targets.

With the IS, the telescope guiding during exposures usually uses the light of the target itself leaking from the IS's pinhole (see below).

The telescope focus must be adjusted not for the slit viewer (pihhole) but for the IS's optics (the difference is ~ 0.4mm in the secondary mirror of the telescope.). Therefore, the telescope guinding might be difficult for fainter targets.

The offset auto-guider camera does not have its indemendent mechanism for focus shifting. So, if we use the offset auto-guider, the guiding might be unstable during the IS observation.

Considering these problems for guiding and limited space along the slit length direction, it is difficut to remove sky background from the spectrum taken with the IS.

The IS is manually inserted into the beam and bolted by hand just before the HDS entrance slit unit. Therefore, the insertion and the retraction of the IS during the night operation might not be recommended. It takes 10 minutes at least, including the changes of foci of the telescope and the collimator of the spectrograph.

↑ Optical Transmittion of the Image Slicer
measured at the center of each echelle order, using flat lamp frames.

↑ Gain of the Image Slicer
The actual gain with respect to a standard observation through a narrow slit depends on the value of the seeing.
Use HDS ETC to check more detailed gain for your desired targets.

↑ 2D spectral format
Basically, the spectrum with the IS can be extracted as one large aperture with 7''.9 slit length on the IRAF reduction package.

↑ Slit Viewer (SV) image
The star on the left side is a companion (separation is ~3 arcseconds).