The UltraViolet Imaging Telescope (UVIT):
The UltraViolet Imaging Telescope will perform imaging
simultaneously in three channels: 130-180 nm, 180-300 nm, and
320-530 nm. The field of view is a circle of ~ 28 arcmin diameter
and the angular resolution is 1.8" for the ultraviolet
channels and 2.5" for the visible channel. In each of the three
channels a spectral band can be selected through a set of
filters mounted on a wheel; in addition, for the two ultraviolet
channels a grating can be selected in the wheel to do slit-less
spectroscopy with a resolution of ~ 100.
The configuration of UVIT on board ASTROSAT
The instrument is configured as two telescopes: one is for the
FUV (130-180 nm) channel, and the other is for simultaneous
imaging in the NUV (180-300 nm) & VIS (320-530 nm) channels.
Each of the two telescopes is a f/12 Ritchey-Chretien
combination with a primary mirror of ~380 mm diameter and
a plate scale of ~ 24 micron per arcsec.
All the three channels use MCP-based intensified CMOS imaging
detectors for recording images in either (high gain) photon
counting mode or in (low gain) integrating mode in which
individual photons cannot be distinguished. Typically, photon
counting mode is used for the two ultraviolet channels which
have a small flux, and integration mode is used for the VIS
channel which has a high flux. Special attention has been
paid to minimize the photo-cathode/MCP gap to get a spatial
resolution of ~ 25 micron FWHM, i.e. ~ 1" on the plate scale
of the telescopes, in the photon counting mode.
The ultraviolet images are typically taken at ~ 30 frames/s;
for specific observations, depending on the size of the
selected field, images of a partial field can be taken up
to a rate of 200 frames/s. The time of each frame can be
tracked to an absolute accuracy of 5 ms.
The effective area of the telescope depends on the chosen
channel and the filter: it is ~ 15 sq cm for the FUV channel
which only use crystal filters, and it is in range 15-40 sq cm
for the various filters in NUV & VIS channels.
Click to use the current version of the
UVIT Exposure Time Calculator
See also the
UVIT page at IIA
for additional information.
