8,101,553 research outputs found
Extreme multiplex spectroscopy at wide-field 4-m telescopes
We describe the design and science case for a spectrograph for the prime
focus of classical 4-m wide-field telescopes that can deliver at least 4000 MOS
slits over a 1 degree field. This extreme multiplex capability means that 25000
galaxy redshifts can be measured in a single night, opening up the
possibilities for large galaxy redshift surveys out to z~0.7 and beyond for the
purpose of measuring the Baryon Acoustic Oscillation (BAO) scale and for many
other science goals. The design features four cloned spectrographs and exploits
the exclusive possibility of tiling the focal plane of wide-field 4-m
telescopes with CCDs for multi-object spectroscopic purposes. In ~200 night
projects, such spectrographs have the potential to make galaxy redshift surveys
of ~6 million galaxies over a wide redshift range and thus may provide a
low-cost alternative to other survey routes such as WFMOS and SKA. Two of these
extreme multiplex spectrographs are currently being designed for the AAT
(NG1dF) and Calar Alto (XMS) 4-m class telescopes. NG2dF, a larger version for
the AAT 2 degree field, would have 12 clones and at least 12000 slits. The
clones use a transparent design including a grism in which all optics are
smaller than the clone square subfield so that the clones can be tightly packed
with little gaps between the contiguous fields. Only low cost glasses are used;
the variations in chromatic aberrations between bands are compensated by
changing one or two of the lenses adjacent to the grism. The total weight and
length is smaller with a few clones than a unique spectrograph which makes it
feasible to place the spectrograph at the prime focus.Comment: 8 pages, 4 figures, to appear in proceedings of Astronomical
Telescopes and Instrumentation, SPIE conference, Marseille, 23-28 June, 200
Suppression of the near-infrared OH night sky lines with fibre Bragg gratings - first results
The background noise between 1 and 1.8 microns in ground-based instruments is
dominated by atmospheric emission from hydroxyl molecules. We have built and
commissioned a new instrument, GNOSIS, which suppresses 103 OH doublets between
1.47 - 1.7 microns by a factor of ~1000 with a resolving power of ~10,000. We
present the first results from the commissioning of GNOSIS using the IRIS2
spectrograph at the AAT. The combined throughput of the GNOSIS fore-optics,
grating unit and relay optics is ~36 per cent, but this could be improved to
~46 per cent with a more optimal design. We measure strong suppression of the
OH lines, confirming that OH suppression with fibre Bragg gratings will be a
powerful technology for low resolution spectroscopy. The integrated OH
suppressed background between 1.5 and 1.7 microns is reduced by a factor of 9
compared to a control spectrum using the same system without suppression. The
potential of low resolution OH suppressed spectroscopy is illustrated with
example observations.
The GNOSIS background is dominated by detector dark current below 1.67
microns and by thermal emission above 1.67 microns. After subtracting these we
detect an unidentified residual interline component of ~ 860 +/ 210
ph/s/m^2/micron/arcsec^2. This component is equally bright in the suppressed
and control spectra. We have investigated the possible source of the interline
component, but were unable to discriminate between a possible instrumental
artifact and intrinsic atmospheric emission. Resolving the source of this
emission is crucial for the design of fully optimised OH suppression
spectrographs. The next generation OH suppression spectrograph will be focussed
on resolving the source of the interline component, taking advantage of better
optimisation for a FBG feed. We quantify the necessary improvements for an
optimal OH suppressing fibre spectrograph design.Comment: Accepted for publication in MNRAS. 15 pages, 18 figure
Stellar populations -- the next ten years
The study of stellar populations is a discipline that is highly dependent on
both imaging and spectroscopy. I discuss techniques in different regimes of
resolving power: broadband imaging (R~4), intermediate band imaging (R~16, 64),
narrowband spectral imaging (R~256, 1024, 4096). In recent years, we have seen
major advances in broadband all-sky surveys that are set to continue across
optical and IR bands, with the added benefit of the time domain, higher
sensitivity, and improved photometric accuracy. Tunable filters and integral
field spectrographs are poised to make further inroads into intermediate and
narrowband imaging studies of stellar populations. Further advances will come
from AO-assisted imaging and imaging spectroscopy, although photometric
accuracy will be challenging. Integral field spectroscopy will continue to have
a major impact on future stellar population studies, extending into the near
infrared once the OH suppression problem is finally resolved. A sky rendered
dark will allow a host of new ideas to be explored, and old ideas to be
revisited.Comment: Invited review, IAUS 241, "Stellar Populations as Building Blocks of
Galaxies," eds. Vazdekis, Peletier. 12 pages, 1 table. (The sideways table
should print ok; there are 10 columns.
Explicit semantic tasks are necessary to study semantic priming effects with high rates of repetition
Human fibroblast interferon RNA transcripts of different sizes in poly(I).poly(C) induced cells
Optical Tests of a 3.7-m diameter Liquid Mirror: Behavior under External Perturbations
We have built and tested a 3.7-m diameter liquid mirror that rotates on a
ball bearing. We have carried out extensive optical tests. We find that
although the ball bearing has a poor quality, the quality of the mirror, with
mercury layers 1-mm thick, is surprisingly good. Taken at face values the
instantaneous Strehl ratios indicate a mirror, that is not quite diffraction
limited but usable for astronomical applications. However, the large coning
error of the bearing (1.5 arcseconds P-V) induces an excessive wobble,
considerably worsening the time averaged PSF. The most interesting result of
the interferometry is that we do not see any evidence of the strong astigmatism
that may have been expected from Coriolis forces.Comment: PDF format, 34 pages, 12 figures, (some figures reduced, full size
figures in Applied Optics, Vol. 39, No 36, 5651
RICERCA È SVILUPPO 2020
Background, Research gap and Objective
This conference takes up the ambitious challenge of highlighting the positive exchange between scientific knowledge. Even if the Academy is characterized by disciplinary specialization, only rarely analysis and application developments do not need other forms of knowledge or do not involve other scientifically qualified context. Have approved both research works developed by multidisciplinary groups and sectoral works that considered further studies, scenarios and application cases with a multidisciplinary development
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