312 research outputs found
Calibration and data quality of warm IRAC
We present an overview of the calibration and properties of data from the IRAC instrument aboard the Spitzer Space Telescope taken after the depletion of cryogen. The cryogen depleted on 15 May 2009, and shortly afterward a two-month- long calibration and characterization campaign was conducted. The array temperature and bias setpoints were revised on 19 September 2009 to take advantage of lower than expected power dissipation by the instrument and to improve sensitivity. The final operating temperature of the arrays is 28.7 K, the applied bias across each detector is 500 mV and the equilibrium temperature of the instrument chamber is 27.55 K. The final sensitivities are essentially the same as the cryogenic mission with the 3.6 ÎŒm array being slightly less sensitive (10%) and the 4.5 ÎŒm array within 5% of the cryogenic sensitivity. The current absolute photometric uncertainties are 4% at 3.6 and 4.5 ÎŒm, and better than milli-mag photometry is achievable for long-stare photometric observations. With continued analysis, we expect the absolute calibration to improve to the cryogenic value of 3%. Warm IRAC operations fully support all science that was conducted in the cryogenic mission and all currently planned warm science projects (including Exploration Science programs). We expect that IRAC will continue to make ground-breaking discoveries in star formation, the nature of the early universe, and in our understanding of the properties of exoplanets
Structure and Colors of Diffuse Emission in the Spitzer Galactic First Look Survey
We investigate the density structure of the interstellar medium using new
high-resolution maps of the 8 micron, 24 micron, and 70 micron surface
brightness towards a molecular cloud in the Gum Nebula, made as part of the
Spitzer Space Telescope Galactic First Look Survey. The maps are correlated
with 100 micron images measured with IRAS. At 24 and 70 micron, the spatial
power spectrum of surface brightness follows a power law with spectral index
-3.5. At 24 micron, the power law behavior is remarkably consistent from the
0.2 degree size of our maps down to the 5 arcsecond spatial resolution. Thus,
the structure of the 24 micron emission is self-similar even at milliparsec
scales. The combined power spectrum produced from Spitzer 24 micron and IRAS 25
micron images is consistent with a change in the power law exponent from -2.6
to -3.5. The decrease may be due to the transition from a two-dimensional to
three-dimensional structure. Under this hypothesis, we estimate the thickness
of the emitting medium to be 0.3 pc.Comment: 13 Pages, 3 Figures, to be published in Astrophysical Journal
Supplement Series (Spitzer Special Issue), volume 154. Uses aastex v5.
Observations of Ultraluminous Infrared Galaxies with the Infrared Spectrograph on the Spitzer Space Telescope: Early Results on Mrk 1014, Mrk 463, and UGC 5101
We present spectra taken with the Infrared Spectrograph on Spitzer covering
the 5-38micron region of three Ultraluminous Infrared Galaxies (ULIRGs): Mrk
1014 (z=0.163), and Mrk 463 (z=0.051), and UGC 5101 (z=0.039). The continua of
UGC 5101 and Mrk 463 show strong silicate absorption suggesting significant
optical depths to the nuclei at 10microns. UGC 5101 also shows the clear
presence of water ice in absorption. PAH emission features are seen in both Mrk
1014 and UGC 5101, including the 16.4micron line in UGC 5101. The fine
structure lines are consistent with dominant AGN power sources in both Mrk 1014
and Mrk 463. In UGC 5101 we detect the [NeV] 14.3micron emission line providing
the first direct evidence for a buried AGN in the mid-infrared. The detection
of the 9.66micron and 17.03micron H emission lines in both UGC 5101 and
Mrk 463 suggest that the warm molecular gas accounts for 22% and 48% of the
total molecular gas masses in these galaxies.Comment: Accepted in ApJ Sup. Spitzer Special Issue, 4 pages, 3 figure
A Study of Heating and Cooling of the ISM in NGC 1097 with Herschel-PACS and Spitzer-IRS
NGC 1097 is a nearby Seyfert 1 galaxy with a bright circumnuclear starburst
ring, a strong large-scale bar and an active nucleus. We present a detailed
study of the spatial variation of the far infrared (FIR) [CII]158um and
[OI]63um lines and mid-infrared H2 emission lines as tracers of gas cooling,
and of the polycyclic aromatic hydrocarbon (PAH) bands as tracers of the
photoelectric heating, using Herschel-PACS, and Spitzer-IRS infrared spectral
maps. We focus on the nucleus and the ring, and two star forming regions (Enuc
N and Enuc S). We estimated a photoelectric gas heating efficiency
([CII]158um+[OI]63um)/PAH in the ring about 50% lower than in Enuc N and S. The
average 11.3/7.7um PAH ratio is also lower in the ring, which may suggest a
larger fraction of ionized PAHs, but no clear correlation with
[CII]158{\mu}m/PAH(5.5 - 14um) is found. PAHs in the ring are responsible for a
factor of two more [CII]158um and [OI]63um emission per unit mass than PAHs in
the Enuc S. SED modeling indicates that at most 25% of the FIR power in the
ring and Enuc S can come from high intensity photodissociation regions (PDRs),
in which case G0 ~ 10^2.3 and nH ~ 10^3.5 cm^-3 in the ring. For these values
of G0 and nH PDR models cannot reproduce the observed H2 emission. Much of the
the H2 emission in the starburst ring could come from warm regions in the
diffuse ISM that are heated by turbulent dissipation or shocks.Comment: 17 pages, 14 figures, 5 tables; accepted for publication in Ap
The infrared spectrograph on the Spitzer Space Telescope
The Infrared Spectrograph (IRS) is one of three science instruments on the Spitzer Space Telescope. The IRS comprises four separate spectrograph modules covering the wavelength range from 5.3 to 38 ÎŒm with spectral resolutions, R~90 and 650, and it was optimized to take full advantage of the very low background in the space environment. The IRS is performing at or better than the pre-launch predictions. An autonomous target acquisition capability enables the IRS to locate the mid-infrared centroid of a source, providing the information so that the spacecraft can accurately offset that centroid to a selected slit. This feature is particularly useful when taking spectra of sources with poorly known coordinates. An automated data reduction pipeline has been developed at the Spitzer Science Center
The Infrared Spectrograph on the Spitzer Space Telescope
The Infrared Spectrograph (IRS) is one of three science instruments on the
Spitzer Space Telescope. The IRS comprises four separate spectrograph modules
covering the wavelength range from 5.3 to 38micron with spectral resolutions, R
\~90 and 600, and it was optimized to take full advantage of the very low
background in the space environment. The IRS is performing at or better than
the pre-launch predictions. An autonomous target acquisition capability enables
the IRS to locate the mid-infrared centroid of a source, providing the
information so that the spacecraft can accurately offset that centroid to a
selected slit. This feature is particularly useful when taking spectra of
sources with poorly known coordinates. An automated data reduction pipeline has
been developed at the Spitzer Science Center.Comment: Accepted in ApJ Sup. Spitzer Special Issue, 6 pages, 4 figure
Variability Timescale and Spectral Index of Sgr A* in the Near Infrared: Approximate Bayesian Computation Analysis of the Variability of the Closest Supermassive Black Hole
Sagittarius A* (Sgr A*) is the variable radio, near-infrared (NIR), and X-ray
source associated with accretion onto the Galactic center black hole. We
present an analysis of the most comprehensive NIR variability dataset of Sgr A*
to date: eight 24-hour epochs of continuous monitoring of Sgr A* at 4.5 m
with the IRAC instrument on the Spitzer Space Telescope, 93 epochs of 2.18
m data from Naos Conica at the Very Large Telescope, and 30 epochs of 2.12
m data from the NIRC2 camera at the Keck Observatory, in total 94,929
measurements. A new approximate Bayesian computation method for fitting the
first-order structure function extracts information beyond current Fast Fourier
Transformation (FFT) methods of power spectral density (PSD) estimation. With a
combined fit of the data of all three observatories, the characteristic
coherence timescale of Sgr A* is minutes (
credible interval). The PSD has no detectable features on timescales down to
8.5 minutes ( credible level), which is the ISCO orbital frequency for a
dimensionless spin parameter . One light curve measured
simultaneously at 2.12 and 4.5 m during a low flux-density phase gave a
spectral index (). This
value implies that the Sgr A* NIR color becomes bluer during higher
flux-density phases. The probability densities of flux densities of the
combined datasets are best fit by log-normal distributions. Based on these
distributions, the Sgr A* spectral energy distribution is consistent with
synchrotron radiation from a non-thermal electron population from below 20 GHz
through the NIR.Comment: Accepted for publication in ApJ on May 30, 2018. A machine readable
version of the light curve data is included in the journal's online
publication. Version 2 includes proof correction
Enhanced Virulence of Chlamydia muridarum Respiratory Infections in the Absence of TLR2 Activation
Chlamydia trachomatis is a common sexually transmitted pathogen and is associated with infant pneumonia. Data from the female mouse model of genital tract chlamydia infection suggests a requirement for TLR2-dependent signaling in the induction of inflammation and oviduct pathology. We hypothesized that the role of TLR2 in moderating mucosal inflammation is site specific. In order to investigate this, we infected mice via the intranasal route with C. muridarum and observed that in the absence of TLR2 activation, mice had more severe disease, higher lung cytokine levels, and an exaggerated influx of neutrophils and T-cells into the lungs. This could not be explained by impaired bacterial clearance as TLR2-deficient mice cleared the infection similar to controls. These data suggest that TLR2 has an anti-inflammatory function in the lung during Chlamydia infection, and that the role of TLR2 in mucosal inflammation varies at different mucosal surfaces
MIPSGAL: A Survey of the Inner Galactic Plane at 24 and 70 ÎŒm
MIPSGAL is a 278 deg^2 survey of the inner Galactic plane using the Multiband Infrared Photometer for Spitzer aboard the Spitzer Space Telescope. The survey field was imaged in two passbands, 24 and 70 ÎŒm with resolutions of 6âł and 18âł, respectively. The survey was designed to provide a uniform, well-calibrated and well-characterized data set for general inquiry of the inner Galactic plane and as a longer-wavelength complement to the shorter-wavelength Spitzer survey of the Galactic plane: Galactic Plane Infrared Mapping Survey Extraordinaire. The primary science drivers of the current survey are to identify all high-mass (M > 5 Mâ) protostars in the inner Galactic disk and to probe the distribution, energetics, and properties of interstellar dust in the Galactic disk. The observations were planned to minimize data artifacts due to image latents at 24 ÎŒm and to provide full coverage at 70 ÎŒm. Observations at ecliptic latitudes within 15° of the ecliptic plane were taken at multiple epochs to help reject asteroids. The data for the survey were collected in three epochs, 2005 SeptemberâOctober, 2006 April, and 2006 October with all of the data available to the public. The estimated point-source sensitivities of the survey are 2 and 75 mJy (3 Ï) at 24 and 70 ÎŒm, respectively. Additional data processing was needed to mitigate image artifacts due to bright sources at 24 ÎŒm and detector responsivity variations at 70 ÎŒm due to the large dynamic range of the Galactic plane. Enhanced data products including artifact-mitigated mosaics and point-source catalogs are being produced with the 24 ÎŒm mosaics already publicly available from the NASA/IPAC Infrared Science Archive. Some preliminary results using the enhanced data products are described
Molecular excitation in the Interstellar Medium: recent advances in collisional, radiative and chemical processes
We review the different excitation processes in the interstellar mediumComment: Accepted in Chem. Re
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