3,908 research outputs found
Development of a general purpose airborne simulator
Variable stability system development for General Purpose Airborne Simulator /GPAS
A Tentative Detection of the Cosmic Infrared Background at 3.5 microns from COBE/DIRBE Observations
Foreground emission and scattered light from interplanetary dust (IPD)
particles and emission from Galactic stellar sources are the greatest obstacles
for determining the cosmic infrared background (CIB) from diffuse sky
measurements in the ~ 1 to 5 micron range. We use ground-based observational
limits on the K-band intensity of the CIB in conjunction with skymaps obtained
by the Diffuse Infrared Background Experiment (DIRBE) on the COBE satellite to
reexamine the limits on the CIB at 1.25, 3.5, and 4.9 microns. Adopting a CIB
intensity of 7.4 nW m-2 sr-1 at 2.2 microns, and using the 2.2 micron DIRBE
skymap from which the emission from IPD cloud has been subtracted, we create a
spatial template of the Galactic stellar contribution to the diffuse infrared
sky. This template is then used to subtract the contribution of the diffuse
Galactic stellar emission from the IPD-emission-subtracted DIRBE skymaps. The
DIRBE 100 micron data are used to estimate the small contribution of emission
from interstellar dust at 3.5 and 4.9 microns. Our method significantly reduces
the errors associated with the subtraction of Galactic starlight, leaving only
the IPD emission component as the primary obstacle for the detection of the CIB
at these wavelengths. This analysis leads to a tentative detection of the CIB
at 3.5 microns. The cosmological implications of these results are discussed in
the paper.Comment: 8 pages, AASTeX, 2 embedded EPS figures. Accepted for publication in
ApJ Letter
Properties and Spatial Distribution of Dust Emission in the Crab Nebula
The nature and quantity of dust produced in supernovae (SNe) is still poorly understood. Recent IR observations of freshly-formed dust in supernova remnants (SNRs) have yielded significantly lower dust masses than predicted by theoretical models and observations high-redshift galaxies. The Crab Nebula's pulsar wind is thought to be sweeping up freshly-formed SN dust along with the SN ejecta. The evidence for this dust was found in the form of an IR bump in the integrated spectrum of the Crab and in extinction against the synchrotron nebula that revealed the presence of dust in the filament cores. We present the first spatially-resolved emission spectra of dust in the Crab Nebula acquired with the Spitzer Space Telescope. The IR spectra are dominated by synchrotron emission and show forbidden line emission from both sides of the expanding nebula, including emission from [S III], [Si II], [Ne II], [Ne III], [Ne V], [Ar III], [Ar V], [Fe II], and [Ni II]. We extrapolated a synchrotron spectral data cube from the Spitzer 3.6 and 4.5 micron images, and subtracted this contribution from our 15-40 micron spectral data to produce a map of the residual continuum emission from dust. The emission appears to be concentrated along the ejecta filaments and is well described by astronomical silicates at an average temperature of 65 K. The estimated mass of dust in the Crab Nebula is 0.008 solar masses
Determination of the Far-Infrared Cosmic Background Using COBE/DIRBE and WHAM Data
Determination of the cosmic infrared background (CIB) at far infrared
wavelengths using COBE/DIRBE data is limited by the accuracy to which
foreground interplanetary and Galactic dust emission can be modeled and
subtracted. Previous determinations of the far infrared CIB (e.g., Hauser et
al. 1998) were based on the detection of residual isotropic emission in skymaps
from which the emission from interplanetary dust and the neutral interstellar
medium were removed. In this paper we use the Wisconsin H-alpha Mapper (WHAM)
Northern Sky Survey as a tracer of the ionized medium to examine the effect of
this foreground component on determination of the CIB. We decompose the DIRBE
far infrared data for five high Galactic latitude regions into H I and H-alpha
correlated components and a residual component. We find the H-alpha correlated
component to be consistent with zero for each region, and we find that addition
of an H-alpha correlated component in modeling the foreground emission has
negligible effect on derived CIB results. Our CIB detections and 2 sigma upper
limits are essentially the same as those derived by Hauser et al. and are given
by nu I_nu (nW m-2 sr-1) < 75, < 32, 25 +- 8, and 13 +- 3 at 60, 100, 140, and
240 microns, respectively. Our residuals have not been subjected to a detailed
anisotropy test, so our CIB results do not supersede those of Hauser et al. We
derive upper limits on the 100 micron emissivity of the ionized medium that are
typically about 40% of the 100 micron emissivity of the neutral atomic medium.
This low value may be caused in part by a lower dust-to-gas mass ratio in the
ionized medium than in the neutral medium, and in part by a shortcoming of
using H-alpha intensity as a tracer of far infrared emission.Comment: 38 pages, 8 figures. Accepted for publication in Ap
The international origins of Hannah Arendt’s historical method
This article examines the multiple ways in which Hannah Arendt’s thought arose historically and in international context, but also how we might think about history and theory in new ways with Arendt. It is commonplace to situate Arendt’s political and historical thought as a response to totalitarianism. However, far less attention has been paid to the significance of other specifically and irreducibly international experiences and events. Virtually all of her singular contributions to political and international thought were influenced by her lived experiences of and historical reflections on statelessness and exile, imperialism, transnational totalitarianism, world wars, the nuclear revolution, the founding of Israel, war crimes trials, and the war in Vietnam. Yet we currently lack a comprehensive reconstruction of the extent to which Arendt’s thought was shaped by the fact of political multiplicity, that there are not one but many polities existing on earth and inhabiting the world. This neglect is surprising in light of the significant ‘international turn’ in the history of thought and intellectual history; the growing interest in Arendt’s thought within international theory; and, above all, Arendt’s own unwavering commitment to plurality not simply as a characteristic of individuals but as an essential and intrinsically valuable effect of distinct territorial entities. The article examines the historical and international context of Arendt’s historical method, including her critique of process- and development-oriented histories that remain current in different social science fields, setting out and evaluating her alternative approach to historical writing
A Near-Infrared Spectrometer to Measure Zodiacal Light Absorption Spectrum
We have developed a high throughput infrared spectrometer for zodiacal light fraunhofer lines measurements. The instrument is based on a cryogenic dual silicon Fabry-Perot etalon which is designed to achieve high signal to noise Fraunhofer line profile measurements. Very large aperture silicon Fabry-Perot etalons and fast camera optics make these measurements possible. The results of the absorption line profile measurements will provide a model free measure of the zodiacal Light intensity in the near infrared. The knowledge of the zodiacal light brightness is crucial for accurate subtraction of zodiacal light foreground for accurate measure of the extragalactic background light after the subtraction of zodiacal light foreground. We present the final design of the instrument and the first results of its performance
Is the Cygnus Loop two supernova remnants?
The Cygnus Loop is classified as a middle-aged supernova remnant (SNR)
located below the Galactic equator (l=74, b=-8.6) and 770 pc away from us. Its
large size and little confusion with Galactic emission makes it an ideal test
ground for evolutionary and structural theories of SNRs. New radio continuum
mapping of the Cygnus Loop at 2695 MHz with the Effelsberg 100-m telescope
provides indications that the Cygnus Loop consists of two separate SNRs.
Combining this result with data from the literature we argue that a secondary
SNR exists in the south with a recently detected neutron star close to its
center. Two interacting SNRs seem to be the best explanation to account for the
Cygnus Loop observations at all wavelengths.Comment: 4 pages, 2 figures, Astron. Astrophys., accepte
- …