On the nights of Dec. 2-3, 2000 the mask-mode MOS at the TNG Low
Resolution Spectrograph DoLoRes was successfully commissioned. All the testing of mask
design and production and of telescope pointing gave excellent results. Unfortunately, due
to cloudy wheather, only the brightest targets could be observed. Science verification of
the performance of the MOS@TNG for deep spectroscopy will be done at due time. |
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Looking at the acquisition consolle while the first MOS exposures come out
from DoLoRes at the Telescopio Nazionale Galileo. |
Our first
commissioning target was a subsample of the globular clusters recently discovered in
M33 by Chandar, Bianchi & Ford (1999) using HST. Spectroscopy of extragalactic
clusters is intended to provide information on their ages and metallicities, and
ultimately on their formation mechanism.
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The pointing of the slits, as well as their quality, was excellent. Only two
steps were generally required to put all the targets within the slits. The pointing was
made faster by two reference pinholes corresponding to 2 relatively bright stars in the
field. An inclined slitlet was employed to observe two objects close to each other.
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The first light of MOS@TNG ! This is a
20 min spectrum of clusters in M33 observed through thin cirrus using 1.2" slitlets.
The grism was the MR-B (#2). Spectra taken with moderately tilted slits will be easily
reduced using the long-slit tasks of any reduction package. |
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The second target was a stellar sample in the open cluster Be17 (suggested by
Tosi, Bragaglia and coll.). Multiobject spectroscopy will provide in this case membership
information, so as individual stars will be securely placed in the HR diagram. |
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30 min exposure gave high S/N spectra for 21 stars in the field. We used the "high
resolution" B grism (#5) yielding a 4 A resolution with 1.2" slitlets. |
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Galaxy clusters represent the most classical target for multiobject
spectroscopy. We tested the behavior of MOS@TNG by observing Abell 951 (z=0.14),
a nearby cluster for which the redshift distribution is not known (suggested by G.
Fasano and coll.). Observations of more distant clusters were prevented by the bad
wheather.
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Good spectra of galaxies in A951 were obtained just with a 20 min exposure,
before thick cirrus forced us to stop observations. The grism was the LR-B, giving a 13 A
resolution with 1.2" slitlets. |
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The dome flat
fields taken with the same mask shows the excellent quality of the slits. It is important
that the masks are carefully dust-cleaned just before installation at the spectrograph.
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An example of comparison lamp spectra taken with the Th lamp and the LR-B
grism. The arcs on the rigth side are ghosts due to the grisms, and are currently under
investigation by the DoLoRes team.
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