149 research outputs found
Probing the dusty stellar populations of the Local Volume Galaxies with JWST/MIRI
The Mid-Infrared Instrument (MIRI) for the {\em James Webb Space Telescope}
(JWST) will revolutionize our understanding of infrared stellar populations in
the Local Volume. Using the rich {\em Spitzer}-IRS spectroscopic data-set and
spectral classifications from the Surveying the Agents of Galaxy Evolution
(SAGE)-Spectroscopic survey of over a thousand objects in the Magellanic
Clouds, the Grid of Red supergiant and Asymptotic giant branch star ModelS
({\sc grams}), and the grid of YSO models by Robitaille et al. (2006), we
calculate the expected flux-densities and colors in the MIRI broadband filters
for prominent infrared stellar populations. We use these fluxes to explore the
{\em JWST}/MIRI colours and magnitudes for composite stellar population studies
of Local Volume galaxies. MIRI colour classification schemes are presented;
these diagrams provide a powerful means of identifying young stellar objects,
evolved stars and extragalactic background galaxies in Local Volume galaxies
with a high degree of confidence. Finally, we examine which filter combinations
are best for selecting populations of sources based on their JWST colours.Comment: 16 pages, 7 figures, 2 online tables; accepted for publication in Ap
Specsim: The MIRI Medium Resolution Spectrometer Simulator
MIRI, the Mid-InfraRed Instrument, is one of four instruments being built for
the James Webb Space Telescope, and is developed jointly between an
EuropeanConsortium and the US. In this paper we present a software data
simulator for one of MIRI's four instruments: the Integral Field Unit (IFU)
Medium Resolution Spectrometer (MIRI-MRS), the first mid-infrared IFU
spectrograph, and one of the first IFUs to be used in a space mission. To give
the MIRI community a preview of the properties of the MIRI-MRS data products
before the telescope is operational, the Specsim tool has been developed to
model, in software, the operation of the spectrometer. Specsim generates
synthetic data frames approximating those which will be taken by the instrument
in orbit. The program models astronomical sources and generates detector frames
using the predicted and measured optical properties of the telescope and MIRI.
These frames can then be used to illustrate and inform a range of operational
activities, including data calibration strategies and the development and
testing of the data reduction software for the MIRI-MRS. Specsim will serve as
a means of communication between the many consortium members by providing a way
to easily illustrate the performance of the spectrometer under different
circumstances, tolerances of components and design scenarios.Comment: 8 pages, 5 figures; A high resolution version is available at
http://www.roe.ac.uk/~npfl/Publications/lgw+06.ps.gz (Changed URL of high-res
version
Optical performance of the JWST MIRI flight model: characterization of the point spread function at high-resolution
The Mid Infra Red Instrument (MIRI) is one of the four instruments onboard
the James Webb Space Telescope (JWST), providing imaging, coronagraphy and
spectroscopy over the 5-28 microns band. To verify the optical performance of
the instrument, extensive tests were performed at CEA on the flight model (FM)
of the Mid-InfraRed IMager (MIRIM) at cryogenic temperatures and in the
infrared. This paper reports on the point spread function (PSF) measurements at
5.6 microns, the shortest operating wavelength for imaging. At 5.6 microns the
PSF is not Nyquist-sampled, so we use am original technique that combines a
microscanning measurement strategy with a deconvolution algorithm to obtain an
over-resolved MIRIM PSF. The microscanning consists in a sub-pixel scan of a
point source on the focal plane. A data inversion method is used to reconstruct
PSF images that are over-resolved by a factor of 7 compared to the native
resolution of MIRI. We show that the FWHM of the high-resolution PSFs were
5-10% wider than that obtained with Zemax simulations. The main cause was
identified as an out-of-specification tilt of the M4 mirror. After correction,
two additional test campaigns were carried out, and we show that the shape of
the PSF is conform to expectations. The FWHM of the PSFs are 0.18-0.20 arcsec,
in agreement with simulations. 56.1-59.2% of the total encircled energy
(normalized to a 5 arcsec radius) is contained within the first dark Airy ring,
over the whole field of view. At longer wavelengths (7.7-25.5 microns), this
percentage is 57-68%. MIRIM is thus compliant with the optical quality
requirements. This characterization of the MIRIM PSF, as well as the
deconvolution method presented here, are of particular importance, not only for
the verification of the optical quality and the MIRI calibration, but also for
scientific applications.Comment: 13 pages, submitted to SPIE Proceedings vol. 7731, Space Telescopes
and Instrumentation 2010: Optical, Infrared, and Millimeter Wav
The Mid-Infrared Instrument for the James Webb Space Telescope, V: Predicted Performance of the MIRI Coronagraphs
The imaging channel on the Mid-Infrared Instrument (MIRI) is equipped with
four coronagraphs that provide high contrast imaging capabilities for studying
faint point sources and extended emission that would otherwise be overwhelmed
by a bright point-source in its vicinity. Such bright sources might include
stars that are orbited by exoplanets and circumstellar material, mass-loss
envelopes around post-main-sequence stars, the near-nuclear environments in
active galaxies, and the host galaxies of distant quasars. This paper describes
the coronagraphic observing modes of MIRI, as well as performance estimates
based on measurements of the MIRI flight model during cryo-vacuum testing. A
brief outline of coronagraphic operations is also provided. Finally, simulated
MIRI coronagraphic observations of a few astronomical targets are presented for
illustration
The Origin of the Silicate Emission Features in the Seyfert 2 Galaxy, NGC 2110
The unified model of active galactic nuclei (AGN) predicts silicate emission
features at 10 and 18 microns in type 1 AGN, and such features have now been
observed in objects ranging from distant QSOs to nearby LINERs. More
surprising, however, is the detection of silicate emission in a few type 2 AGN.
By combining Gemini and Spitzer mid-infrared imaging and spectroscopy of NGC
2110, the closest known Seyfert 2 galaxy with silicate emission features, we
can constrain the location of the silicate emitting region to within 32 pc of
the nucleus. This is the strongest constraint yet on the size of the silicate
emitting region in a Seyfert galaxy of any type. While this result is
consistent with a narrow line region origin for the emission, comparison with
clumpy torus models demonstrates that emission from an edge-on torus can also
explain the silicate emission features and 2-20 micron spectral energy
distribution of this object. In many of the best-fitting models the torus has
only a small number of clouds along the line of sight, and does not extend far
above the equatorial plane. Extended silicate-emitting regions may well be
present in AGN, but this work establishes that emission from the torus itself
is also a viable option for the origin of silicate emission features in active
galaxies of both type 1 and type 2.Comment: ApJL, accepte
E-ELT/METIS
The Mid-infrared E-ELT Imager and Spectrograph (METIS) will be one of the first three scientific instruments on the European Extremely Large Telescope (E-ELT). It will be the only instrument to cover the thermal/mid-infrared wavelength range from 3-19 μm. METIS offers a number of scientifically important observing modes, including diffraction-limited imaging, low resolution slit spectroscopy, coronagraphy, and high resolution (R ˜ 100,000) integral field spectroscopy at very high sensitivity. This paper gives a brief summary of METIS and focuses on its unique discovery space in the area of protoplanetary disks, where METIS is quite complementary to ALMA and JWST
Dust in the inner regions of debris disks around A stars
We present infrared interferometric observations of the inner regions of two
A-star debris disks, beta Leo and zeta Lep, using the FLUOR instrument at the
CHARA interferometer on both short (30 m) and long (>200 m) baselines. For the
target stars, the short baseline visibilities are lower than expected for the
stellar photosphere alone, while those of a check star, delta Leo, are not. We
interpret this visibility offset of a few percent as a near-infrared excess
arising from dust grains which, due to the instrumental field of view, must be
located within several AU of the central star. For beta Leo, the near-infrared
excess producing grains are spatially distinct from the dust which produces the
previously known mid-infrared excess. For zeta Lep, the near-infrared excess
may be spatially associated with the mid-infrared excess producing material. We
present simple geometric models which are consistent with the near and
mid-infrared excess and show that for both objects, the near-infrared producing
material is most consistent with a thin ring of dust near the sublimation
radius with typical grain sizes smaller than the nominal radiation pressure
blowout radius. Finally, we discuss possible origins of the near-infrared
emitting dust in the context of debris disk evolution models.Comment: 20 pages, 2 figures, to appear in the Astrophysical Journa
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