77 research outputs found
MEMS-based Speckle Spectrometer
We describe a new concept for a MEMS-based active spatial filter for
astronomical spectroscopy. The goal of this device is to allow the use of a
diffraction-limited spectrometer on a seeing limited observation at improved
throughput over a comparable seeing-limited spectrometer, thus reducing the
size and cost of the spectrometer by a factor proportional to r0/D (For the
case of a 10 meter telescope this size reduction will be approximately a factor
of 25 to 50). We use a fiber-based integral field unit (IFU) that incorporates
an active MEMS mirror array to feed an astronomical spectrograph. A fast camera
is used in parallel to sense speckle images at a spatial resolution of lambda/D
and at a temporal frequency greater than that of atmospheric fluctuations. The
MEMS mirror-array is used as an active shutter to feed speckle images above a
preset intensity threshold to the spectrometer, thereby increasing the
signal-to-noise ratio (SNR) of the spectrogram. Preliminary calculations
suggests an SNR improvement of a factor of about 1.4. Computer simulations have
shown an SNR improvement of 1.1, but have not yet fully explored the parameter
space.Comment: 11 pages, 5 figures, presented at SPIE Astronomical Telescopes and
Instrumentation, 24 - 31 May 2006, Orlando, Florida US
HexPak and GradPak: variable-pitch dual-head IFUs for the WIYN 3.5m Telescope Bench Spectrograph
We describe the design, construction, and expected performance of two new
fiber integral field units (IFUs) --- HexPak and GradPak --- for the WIYN 3.5m
Telescope Nasmyth focus and Bench Spectrograph. These are the first IFUs to
provide formatted fiber integral field spectroscopy with simultaneous sampling
of varying angular scales. HexPak and GradPak are in a single cable with a
dual-head design, permitting easy switching between the two different IFU heads
on the telescope without changing the spectrograph feed: the two heads feed a
variable-width double-slit. Each IFU head is comprised of a fixed arrangement
of fibers with a range of fiber diameters. The layout and diameters of the
fibers within each array are scientifically-driven for observations of
galaxies: HexPak is designed to observe face-on spiral or spheroidal galaxies
while GradPak is optimized for edge-on studies of galaxy disks. HexPak is a
hexagonal array of 2.9 arcsec fibers subtending a 40.9 arcsec diameter, with a
high-resolution circular core of 0.94 arcsec fibers subtending 6 arcsec
diameter. GradPak is a 39 by 55 arcsec rectangular array with rows of fibers of
increasing diameter from angular scales of 1.9 arcsec to 5.6 arcsec across the
array. The variable pitch of these IFU heads allows for adequate sampling of
light profile gradients while maintaining the photon limit at different scales.Comment: 10 pages, 4 figures, presented at SPIE, Astronomical Telescopes and
Instrumentation, 1 - 6 July 2012, Amsterdam, Netherland
Absorption spectrum of the quasar HS1603+3820 I. Observations and data analysis
We present the analysis of multi-wavelength observations of bright quasar
HS1603+3820: the optical data taken with the MMT and Keck telescopes, and X-ray
data obtained with the Chandra X-ray Observatory. The optical spectra contain a
very large number of absorption lines from numerous heavy elements. We derived
X-ray properties of HS1603. The quasar has the optical-to-X-ray slope index
alpha_ox of 1.70, which is on the high end of the typical range for radio quiet
QSOs. We found 49 individual heavy element absorption clouds, which can be
grouped into eleven distinct systems. We determined column densities and
redshifts of the individual components. Absorbers from the associated system
which is likely spatially closest to the QSO show large CIV to HI column
density ratio, reaching ca.20.Comment: Accepted for publication in A&A, 17 pages, 11 figures, 5 table
The NIR Upgrade to the SALT Robert Stobie Spectrograph
The near infrared (NIR) upgrade to the Robert Stobie Spectrograph (RSS) on
the Southern African Large Telescope (SALT), RSS/NIR, extends the spectral
coverage of all modes of the visible arm. The RSS/NIR is a low to medium
resolution spectrograph with broadband imaging, spectropolarimetric, and
Fabry-Perot imaging capabilities. The visible and NIR arms can be used
simultaneously to extend spectral coverage from approximately 3200 A to 1.6 um.
Both arms utilize high efficiency volume phase holographic gratings via
articulating gratings and cameras. The NIR camera is designed around a
2048x2048 HAWAII-2RG detector housed in a cryogenic dewar. The Epps optical
design of the camera consists of 6 spherical elements, providing sub-pixel rms
image sizes of 7.5 +/- 1.0 um over all wavelengths and field angles. The exact
long wavelength cutoff is yet to be determined in a detailed thermal analysis
and will depend on the semi-warm instrument cooling scheme. Initial estimates
place instrument limiting magnitudes at J = 23.4 and H(1.4-1.6 um) = 21.6 for
S/N = 3 in a 1 hour exposure well below the sky noise.Comment: 12 pages, 10 figures, presented at SPIE, Astronomical Telescopes and
Instrumentation, 24 - 31 May 2006, Orlando, Florida US
ESI, a new Keck Observatory echellette spectrograph and imager
The Echellette Spectrograph and Imager (ESI) is a multipurpose instrument
which has been delivered by the Instrument Development Laboratory of Lick
Observatory for use at the Cassegrain focus of the Keck II telescope. ESI saw
first light on August 29, 1999. ESI is a multi-mode instrument that enables the
observer to seamlessly switch between three modes during an observation. The
three modes of ESI are: An R=13,000-echellette mode; Low-dispersion prismatic
mode; Direct imaging mode. ESI contains a unique flexure compensation system
which reduces the small instrument flexure to negligible proportions.
Long-exposure images on the sky show FWHM spot diameters of 34 microns (0.34")
averaged over the entire field of view. These are the best non-AO images taken
in the visible at Keck Observatory to date. Maximum efficiencies are measured
to be 28% for the echellette mode and greater than 41% for low-dispersion
prismatic mode including atmospheric, telescope and detector losses. In this
paper we describe the instrument and its development. We also discuss the
performance-testing and some observational results.Comment: 10 pages, 14 figures, 8tables, accepted for publication in PASP, 15
April 200
Coronagraph design for an extreme adaptive optics system with spatially filtered wavefront sensing on segmented telescopes
High dynamic range coronagraphy targeted at discovering planets around nearby stars is often associated with monolithic, unobstructed aperture space telescopes. With the advent of extreme adaptive optics (ExAO) systems with thousands of sensing and correcting channels, the benefits of placing a near-infrared coronagraph on a large segmented mirror telescope become scientifically interesting. This is because increased aperture size produces a tremendous gain in achievable contrast at the same angular distance from a point source at Strehl ratios in excess of 90\% (and at lower Strehl ratios on future giant telescopes such as the Thirty Meter Telescope). We outline some of the design issues facing such a coronagraph, and model a band-limited coronagraph on an aperture with a Keck-like pupil. We examine the purely diffractive challenges facing the eXtreme AO Planetary Imager (XAOPI) given the Keck pupil geometry, notably its inter-segment gap spacing of 6~mm. Classical Lyot coronagraphs, with hard-edged occulting stops, are not efficient enough at suppressing diffracted light, given XAOPI's scientific goal of imaging a young Jupiter at a separation as close as 0.15 arcseconds (4λD at H on Keck) from its parent star. With a 4000 channel ExAO system using an anti-aliased spatially-filtered wavefront sensor planned for XAOPI, we wish to keep diffracted light due to coronagraphic design at least as low as the noise floor set by AO system limitations. We study the band-limited Lyot coronagraph (BLC) as a baseline design instead of the classical design because of its efficient light suppression, as well as its analytical simplicity. We also develop ways of investigating tolerancing coronagraphic mask fabrication by utilizing the BLC design's mathematical tractability
Keck spectroscopy and Spitzer Space Telescope analysis of the outer disk of the Triangulum Spiral Galaxy M33
In an earlier study of the spiral galaxy M33, we photometrically identified
arcs or outer spiral arms of intermediate age (0.6 Gyr - 2 Gyr) carbon stars
precisely at the commencement of the HI-warp. Stars in the arcs were
unresolved, but were likely thermally-pulsing asymptotic giant branch carbon
stars. Here we present Keck I spectroscopy of seven intrinsically bright and
red target stars in the outer, northern arc in M33. The target stars have
estimated visual magnitudes as faint as V \sim 25 mag. Absorption bands of CN
are seen in all seven spectra reported here, confirming their carbon star
status. In addition, we present Keck II spectra of a small area 0.5 degree away
from the centre of M33; the target stars there are also identified as carbon
stars. We also study the non-stellar PAH dust morphology of M33 secured using
IRAC on board the Spitzer Space Telescope. The Spitzer 8 micron image attests
to a change of spiral phase at the start of the HI warp. The Keck spectra
confirm that carbon stars may safely be identified on the basis of their red
J-K_s colours in the outer, low metallicity disk of M33. We propose that the
enhanced number of carbon stars in the outer arms are an indicator of recent
star formation, fueled by gas accretion from the HI-warp reservoir.Comment: 9 pages, 5 figures, accepted in A&
Host galaxies of luminous quasars: population synthesis of optical off-axis spectra
There is increasing evidence of a connection between AGN activity and galaxy
evolution. To obtain further insight into this potentially important
evolutionary phase, we analyse the properties of quasar host galaxies. In this
paper, we present a population synthesis modeling technique for off-axis
spectra, the results of which constrain host colour and the stellar ages of
luminous quasars (M_V(nuc)<-23). Our technique is similar to well established
quiescent-galaxy models, modified to accommodate scattered nuclear light (a
combination of atmospheric, instrumental and host galaxy scattered light)
observed off axis. In our model, subtraction of residual scattered quasar light
is performed, while simultaneously modeling the constituent stellar populations
of the host galaxy. The reliability of this technique is tested via a
Monte-Carlo routine in which the correspondence between synthetic spectra with
known parameters and the model output is determined. Application of this model
to a preliminary sample of 10 objects is presented and compared to previous
studies. Spectroscopic data was obtained via long-slit and integral-field unit
observations on the Keck and WIYN telescopes. We confirm that elliptical quasar
hosts are distinguishable (bluer) from inactive ellipticals in rest frame B-V
colour. Additionally, we note a trend for radio luminous (L_5GHz > 10^40 erg
s^-1) quasars to be located in redder host galaxies in comparison to their less
luminous radio counterparts. While the host colour and age of our radio
luminous sample is in close proximity to the green valley, our radio faint
sample is consistent with quiescent star-forming galaxies. However, further
observations are needed to confirm these results. Finally, we discuss future
applications for our technique on a larger sample of objects being obtained via
SALT and WIYN telescope observing campaigns.Comment: 18 pages, 10 figures, accepted for publication in MNRA
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