Index for Researchers
HDS Image Slicer
For detailed information about this image slicer, please refer
Tajitsu et al. 2012, PASJ, 64, 77.
In order to collect more photons into a narrow slit for high spectral
the image slicer (IS) can be used.
The IS reformats the 2D-image of a pinhole with 1''.5 diamteter (in the case of IS #1)
in the F/12.6 focal plane of the telescope into a
series of narrow slits which is imaged on the spectrograph entrance slit.
+ Focal Length Corrector
|Elongation along slit length
(λ > 5,000A for red settings ,
λ > 4,000A for blue settings)
(λ > 3,800A for red settings,
λ > 3,600A for blue settings)
(λ > 4,000A for red settings,
λ > 3,600A for blue settings)
||Fused quartz w/AR-coating
||> 83% (@4,000 ~ 7,000A)
||> 93% (@3,800 ~ 8,000A)
||> 73% (@4,000 ~ 8,000A)
In some cases, the proposal requesting image slicer may be switched to normal-slit
observations (and vice versa) if the observatory judges the requested observation can be
accomplished in either mode, due to operational reasons.
This applies to both normal and service programs.
The HDS ISs are basically designed for brighter targets (<∼15 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
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
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.
Expected observing efficiency
↑ Fraction of light that enters into the spectrograph
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 raw spectra
↑ 2D spectral format (IS #1)
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 guiding
↑ Slit Viewer (SV) image (IS #1)
The star on the left side is a companion (separation is ~3 arcseconds).