72 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
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
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
The ultra-cool white dwarf companion of PSR J0751+1807
We present optical and near-infrared observations with Keck of the binary
millisecond pulsar PSR J0751+1807. We detect a faint, red object - with
R=25.08+-0.07, B-R=2.5+-0.3, and R-I=0.90+-0.10 - at the celestial position of
the pulsar and argue that it is the white dwarf companion of the pulsar. The
colours are the reddest among all known white dwarfs, and indicate a very low
temperature, Teff~4000 K. This implies that the white dwarf cannot have the
relatively thick hydrogen envelope that is expected on evolutionary grounds.
Our observations pose two puzzles. First, while the atmosphere was expected to
be pure hydrogen, the colours are inconsistent with this composition. Second,
given the low temperature, irradiation by the pulsar should be important, but
we see no evidence for it. We discuss possible solutions to these puzzles.Comment: 9 pages, 3 figures, accepted for publication in A&
A Study of Interstellar Gas and Stars in the Gravitationally Lensed Galaxy `The Cosmic Eye' from Rest-Frame Ultraviolet Spectroscopy
We report the results of a study of the rest-frame UV spectrum of the Cosmic
Eye, a luminous Lyman break galaxy at z=3.07331 gravitationally lensed by a
factor of 25. The spectrum, recorded with the ESI spectrograph on the Keck II
telescope, is rich in absorption features from the gas and massive stars in
this galaxy. The interstellar absorption lines are resolved into two components
of approximately equal strength and each spanning several hundred km/s in
velocity. One component has a net blueshift of -70 km/s relative to the stars
and H II regions and presumably arises in a galaxy-scale outflow similar to
those seen in most star-forming galaxies at z = 2-3. The other is more unusual
in showing a mean redshift of +350 km/s relative to the systemic redshift;
possible interpretations include a merging clump, or material ejected by a
previous star formation episode and now falling back onto the galaxy, or more
simply a chance alignment with a foreground galaxy. In the metal absorption
lines, both components only partially cover the OB stars against which they are
being viewed. We tentatively associate the redshifted component with the strong
damped Lyman alpha line, indicative of a column density N(H I) = (3.0 +/- 0.8)
x 10(21) atoms/cm2, and propose that it provides the dust `foreground screen'
responsible for the low ratio of far-infrared to UV luminosities of the Cosmic
Eye. Compared to other well-studied examples of strongly lensed galaxies, we
find that the young stellar population of the Cosmic Eye is essentially
indistinguishable from those of the Cosmic Horseshoe and MS 1512-cB58, while
the interstellar spectra of all three galaxies are markedly different,
attesting to the real complexity of the interplay between starbursts and
ambient interstellar matter in young galaxies (abridged).Comment: 14 pages, 6 Figures, Accepted for publication in Monthly Notices of
the Royal Astronomical Society after minor revision
Implications of Dramatic Broad Absorption Line Variability in the Quasar FBQS J1408+3054
We have observed a dramatic change in the spectrum of the formerly heavily
absorbed `overlapping-trough' iron low-ionization broad absorption line
(FeLoBAL) quasar FBQS J1408+3054. Over a time span of between 0.6 to 5
rest-frame years, the Mg II trough outflowing at 12,000 km/s decreased in
equivalent width by a factor of two and the Fe II troughs at the same velocity
disappeared. The most likely explanation for the variability is that a
structure in the BAL outflow moved out of our line of sight to the ultraviolet
continuum emitting region of the quasar's accretion disk. Given the size of
that region, this structure must have a transverse velocity of between 2600
km/s and 22,000 km/s. In the context of a simple outflow model, we show that
this BAL structure is located between approximately 5800 and 46,000
Schwarzschild radii from the black hole. That distance corresponds to 1.7 to 14
pc, 11 to 88 times farther from the black hole than the H-beta broad-line
region. The high velocities and the parsec-scale distance for at least this one
FeLoBAL outflow mean that not all FeLoBAL outflows can be associated with
galaxy-scale outflows in ultraluminous infrared galaxies transitioning to
unobscured quasars. The change of FBQS J1408+3054 from an FeLoBAL to a LoBAL
quasar also means that if (some) FeLoBAL quasars have multiwavelength
properties which distinguish them from HiBAL quasars, then some LoBAL quasars
will share those properties. Finally, we extend previous work on how
multiple-epoch spectroscopy of BAL and non-BAL quasars can be used to constrain
the average lifetime of BAL episodes (currently >60 rest-frame years at 90%
confidence).Comment: Final version to appear in MNRAS: references added and factor of 2
underestimate of accretion disk size corrected, resulting in absorber
constrained to be somewhat closer to the black hole. For an animated gif
showing the spectral evolution of the broad absorption line troughs in this
quasar, see http://www.yorku.ca/phall/film19952009.gi
Astronomical Spectroscopy
Spectroscopy is one of the most important tools that an astronomer has for
studying the universe. This chapter begins by discussing the basics, including
the different types of optical spectrographs, with extension to the ultraviolet
and the near-infrared. Emphasis is given to the fundamentals of how
spectrographs are used, and the trade-offs involved in designing an
observational experiment. It then covers observing and reduction techniques,
noting that some of the standard practices of flat-fielding often actually
degrade the quality of the data rather than improve it. Although the focus is
on point sources, spatially resolved spectroscopy of extended sources is also
briefly discussed. Discussion of differential extinction, the impact of
crowding, multi-object techniques, optimal extractions, flat-fielding
considerations, and determining radial velocities and velocity dispersions
provide the spectroscopist with the fundamentals needed to obtain the best
data. Finally the chapter combines the previous material by providing some
examples of real-life observing experiences with several typical instruments.Comment: An abridged version of a chapter to appear in Planets, Stars and
Stellar Systems, to be published in 2011 by Springer. Slightly revise
Optical and infrared observations of the Type IIP SN2002hh from day 3 to 397
We present optical and infrared (IR) observations of the type IIP SN2002hh
from 3 to 397 days after explosion. The optical spectroscopic (4-397d) and
photometric (3-278d) data are complemented by spectroscopic (137-381d) and
photometric (137-314d) data acquired at IR wavelengths. This is the first time
L-band spectra have ever been successfully obtained for a supernova at a
distance beyond the Local Group. The VRI light curves in the first 40 days
reveal SN2002hh to be a SN IIP (plateau) - the most common of all core-collapse
supernovae. SN2002hh is one of the most highly extinguished supernovae ever
investigated. To provide a good match between its early-time spectrum and a
coeval spectrum of the Type IIP SN1999em, as well as maintaining consistency
with KI interstellar absorption, we invoke a 2-component extinction model. One
component is due to the combined effect of the interstellar medium of our Milky
Way Galaxy and the SN host galaxy, while the other component is due to a "dust
pocket" where the grains have a mean size smaller than in the interstellar
medium. The early-time optical light curves of SNe 1999em and 2002hh are
generally well-matched, as are the radioactive tails of these two SNe and
SN1987A. The late-time similarity of the SN2002hh optical light curves to those
of SN1987A, together with measurements of the optical/IR luminosity and [FeII]
1.257mu emission indicate that 0.07 +- 0.02 Msun of Ni 56 was ejected by
SN2002hh. [... ABRIDGED...] From the [OI] 6300,6364 A doublet luminosity we
infer a 16-18 Msun main-sequence progenitor star. The progenitor of SN2002hh
was probably a red supergiant with a substantial, dusty wind.Comment: 32 pages, 30 figures, accepted for publication in MNRA
- …