ALFOSC grisms #18 - #20
As of January 2015 we have a new set of VPH grisms available for
ALFOSC. The grisms were designed and assembled by Alessio Zanutta and
Prof. Andrea Bianco, from the Osservatorio Astronomico Di Brera (INAF,
Merate, Italy). The VPH gratings were made in Merate as part of the
PhD project of Alessio, aiming to develop new techniques for
fabricating VPH gratings.
Funding for the new grisms has been made possible by Prof. Johan Fynbo
and Prof. Hans Kjeldsen through an IDA grant (Instrument Center for
The new grisms #18 (blue), #19 (green), #20 (red) aim to replace
grisms #16, #7, #8, respectively, and are designed to give best
throughput while covering the optical wave range 353-984nm at a
1-arcsec slit resolution of R=800 - 1000. The achieved gain in peak
throughput is more than a factor 1.3 for the new blue and green
The new red grism outperforms the old grism #8 redwards from
Halpha, and by a factor 1.4 at 750nm. This new grism will
be valuable in combination with the new red-sensitive
fringe-suppressed CCD that is anticipated to arrive at NOT in 2015.
The new grisms have inbuilt order blocking filters, and consequently
the spectra are free of polluting second-order contribution.
The plot below shows for the new grisms the on-sky measured total
system efficiency of ALFOSC, the telescope and at airmass=1, while
using the 10-arcsec slit.
Preliminary design study by A. Zanutta,
Lab report by A. Zanutta, Sept 2014
Final report by A. Zanutta, Mar 2015
These grisms displace the object spectrum a few tens of pixels in the
spatial direction, with respect to the position of the object on the
Thanks to everyone involved!
In particular to: Alessio Zanutta,
Andrea Bianco, and Emilio Molinari
Johan Fynbo and Hans Kjeldsen
John Telting, Jan 2015