RYTSI:
The RIT-Yale Tip-tilt Speckle Imager
| What is it?
Why make it? Who's involved? Current Status For More Information |
 |
 |
RYTSI is an optics box that is placed between the telescope mounting surface and a large format CCD detector to take speckle images of astronomical objects. From these speckle iamges, diffraction-limited image reconstructions can be made.
RYTSI uses a large format CCD to collect a grid of speckle images over the entire active area of the detector before full-frame readout. Shown above are two possible methods of filling the array. Two galvonometer scanning mirrors move the star image in a timed pattern over the CCD array.
(a) “typewriter mode” -- use the row-shift capability
of the CCD to advance rows of star images toward the serial register. Rows
are filled by moving the mirror in a direction parallel to the serial register.
(b) “raster mode” -- moveable mirror deflects
the star image in both imaging dimensions (serpentine step pattern).
RYTSI's optical design is actually pretty simple.
It's a two lens reimaging system with filter wheels and the tip-tilt mirrors
in the collimated beam between the two lenses, shown below.
 |
1) Speckle remains a fundamental tool in determining binary star orbits and stellar masses.
2) CCDs have improved dramatically in readout
speed and read noise in the last few years and will most likely continue
to do so. In the limit of zero read noise, a CCD is a linear photon-counting
detector of very high quantum efficiency. Meaning:
>
Fainter limiting magnitudes.
>
Reliable diffraction-limited photometric information!! (This has been a
tough problem in speckle up to the present.)
3) Hipparcos has identified ~3400 previously unknown doubles. With distances already known, we seek to identify which are gravitationally bound and determine orbits as well as component magnitudes and colors of these stars.
4) The instrument was designed for the Cassegrain focus of the WIYN Telescope. WIYN has outstanding median seeing conditions and superb optics, meaning higher signal-to-noise in the speckle patterns.
Elliott Horch and Reed Meyer have been the primary developers of the instrument. Zoran Ninkov (Center for Imaging Science, RIT) and Bill van Altena (Astronomy Department, Yale University) are also involved. Bill is the head of the Astrometry Group at Yale.
RYTSI was designed and prototyped in Room A110
at the Center for Imaging Science by Reed and Elliott. ModelMax, Inc.,
of Rochester, NY, was contracted to do the precision machining. RYTSI looked
like this in May of 2001:
 |
But by late June 2001, all the optics and electronics
were mounted inside the box:
 |
Then we took RYTSI out to the WIYN
Telescope at Kitt Peak National
Observatory. Mounted at the Nasmyth focus (the "WIYN Port"; the Cass
port was not available for this run), RYTSI looks like this:
|
Of course, we close the cover before making observations!!
Here's what RYTSI can do:
 |
The above is a single 2048x2048 CCD frame with
256 individual speckle images on it. This image took less than 20 seconds
to record and read out. Below is a 20-image blow up. It shows the speckle
nature of the images, as expected when viewing starlight through the atmosphere.
Actually, this object is a very close (~0.1 arcsec separation) double star.
If you look carefully in these images, you can see the "double image" effect
in this case. The second star is at about 11 o'clock relative to the first
star...
 |
With images like these, we hope to get differential photometry of many close binary star systems for the first time.
Contact Elliott Horch,
or check out our recent poster from
the AAS meeting, June 2001.