54,701 research outputs found
Resolving stellar populations with crowded field 3D spectroscopy
(Abridged) We describe a new method to extract spectra of stars from
observations of crowded stellar fields with integral field spectroscopy (IFS).
Our approach extends the well-established concept of crowded field photometry
in images into the domain of 3-dimensional spectroscopic datacubes. The main
features of our algorithm are: (1) We assume that a high-fidelity input source
catalogue already exists and that it is not needed to perform sophisticated
source detection in the IFS data. (2) Source positions and properties of the
point spread function (PSF) vary smoothly between spectral layers of the
datacube, and these variations can be described by simple fitting functions.
(3) The shape of the PSF can be adequately described by an analytical function.
Even without isolated PSF calibrator stars we can therefore estimate the PSF by
a model fit to the full ensemble of stars visible within the field of view. (4)
By using sparse matrices to describe the sources, the problem of extracting the
spectra of many stars simultaneously becomes computationally tractable. We
present extensive performance and validation tests of our algorithm using
realistic simulated datacubes that closely reproduce actual IFS observations of
the central regions of Galactic globular clusters. We investigate the quality
of the extracted spectra under the effects of crowding. The main effect of
blending between two nearby stars is a decrease in the S/N in their spectra.
The effect increases with the crowding in the field in a way that the maximum
number of stars with useful spectra is always ~0.2 per spatial resolution
element. This balance breaks down when exceeding a total source density of ~1
significantly detected star per resolution element. We close with an outlook by
applying our method to a simulated globular cluster observation with the
upcoming MUSE instrument at the ESO-VLT.Comment: accepted for publication in A&A, 19 pages, 19 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.
A time-dependent Schr\"odinger equation for molecular core-hole dynamics
X-ray spectroscopy is an important tool for the investigation of matter. X
rays primarily interact with inner-shell electrons creating core (inner-shell)
holes that will decay on the time scale of attoseconds to few femtoseconds
through electron relaxations involving the emission of a photon or an electron.
The advent of femtosecond x-ray pulses expands x-ray spectroscopy to the time
domain and will eventually allow the control of core-hole population on
timescales comparable to core-vacancy lifetimes. For both cases, a theoretical
approach that accounts for the x-ray interaction while the electron relaxations
occur is required. Here we describe a time-dependent framework, based on
solving the time-dependent Schr\"odinger equation, that is suitable for
describing the induced electron and nuclear dynamics
Deployable Payloads with Starbug
We explore the range of wide field multi-object instrument concepts taking
advantage of the unique capabilities of the Starbug focal plane positioning
concept. Advances to familiar instrument concepts, such as fiber positioners
and deployable fiber-fed IFUs, are discussed along with image relays and
deployable active sensors. We conceive deployable payloads as components of
systems more traditionally regarded as part of telescope systems rather than
instruments - such as adaptive optics and ADCs. Also presented are some of the
opportunities offered by the truly unique capabilities of Starbug, such as
microtracking to apply intra-field distortion correction during the course of
an observation.Comment: 12 pages, 8 figures, to be published in Proc. SPIE 6273
"Opto-Mechanical Technologies for Astronomy
Integral-field spectroscopy of the quadruple QSO HE 0435-1223: Evidence for microlensing
We present the first spatially resolved spectroscopic observations of the
recently discovered quadruple QSO and gravitational lens HE0435-1223. Using the
Potsdam Multi-Aperture Spectrophotometer (PMAS), we show that all four QSO
components have very similar but not identical spectra. In particular, the
spectral slopes of components A, B, and D are indistinguishable, implying that
extinction due to dust plays no major role in the lensing galaxy. While also
the emission line profiles are identical within the error bars, as expected
from lensing, the equivalent widths show significant differences between
components. Most likely, microlensing is responsible for this phenomenon. This
is also consistent with the fact that component D, which shows the highest
relative continuum level, has brightened by 0.07 mag since Dec 2001. We find
that the emission line flux ratios between the components are in better
agreement with simple lens models than broad band or continuum measurements,
but that the discrepancies between model and data are still unacceptably large.
Finally, we present a detection of the lensing galaxy, although this is close
to the limits of the data. Comparing with a model galaxy spectrum, we obtain a
redshift estimate of z_lens=0.44+-0.02.Comment: 9 pages, 7 figures, accepted for publication in A&
Coupling MOAO with Integral Field Spectroscopy: specifications for the VLT and the E-ELT
[Abridged] We have developed an end-to-end simulation to specify the science
requirements of a MOAO-fed integral field spectrograph on either an 8m or 42m
telescope. Our simulations re-scales observations of local galaxies or results
from numerical simulations of disk or interacting galaxies. For the current
analysis, we limit ourselves to a local disk galaxy which exhibits simple
rotation and a simulation of a merger. We have attempted to generalize our
results by introducing the simple concepts of "PSF contrast" which is the
amount of light polluting adjacent spectra which we find drives the smallest EE
at a given spatial scale. The choice of the spatial sampling is driven by the
"scale-coupling", i.e., the relationship between the IFU pixel scale and the
size of the features that need to be recovered by 3D spectroscopy in order to
understand the nature of the galaxy and its substructure. Because the dynamical
nature of galaxies are mostly reflected in their large-scale motions, a
relatively coarse spatial resolution is enough to distinguish between a
rotating disk and a major merger. Although we used a limited number of
morpho-kinematic cases, our simulations suggest that, on a 42m telescope, the
choice of an IFU pixel scale of 50-75 mas seems to be sufficient. Such a coarse
sampling has the benefit of lowering the exposure time to reach a specific
signal-to-noise as well as relaxing the performance of the MOAO system. On the
other hand, recovering the full 2D-kinematics of z~4 galaxies requires high
signal-to-noise and at least an EE of 34% in 150 mas (2 pixels of 75 mas).
Finally, we carried out a similar study at z=1.6 with a MOAO-fed spectrograph
for an 8m, and find that at least an EE of 30% at 0.25 arcsec spatial sampling
is required to understand the nature of disks and mergers.Comment: 17 pages, 20 figures, accepted for publication in the MNRA
Supermassive black holes from OASIS and SAURON integral-field kinematics
Supermassive black holes are a key element in our understanding of how
galaxies form. Most of the progress in this very active field of research is
based on just ~30 determinations of black hole mass, accumulated over the past
decade. We illustrate how integral-field spectroscopy, and in particular our
OASIS modeling effort, can help improve the current situation.Comment: 4 pages, 2 figures, LaTeX. To appear in the proceedings of IAU
Symposium 245 "Formation and Evolution of Galaxy Bulges", M. Bureau, E.
Athanassoula, and B. Barbuy, ed
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