9,422 research outputs found
Modeling the Dust Spectral Energy Distributions of Dwarf Galaxies
Recent efforts on the modeling of the infrared spectral energy distributions
(SEDs) of dwarf galaxies are summarised here. The characterisation of the dust
properties in these low metallicity environments is just unfolding, as a result
of recently available mid-infrared to millimetre observations. From the limited
cases we know to date, it appears that the hard radiation fields that are
present in these star-bursting dwarf galaxies, as well as the rampent
energetics of supernovae shocks and winds have modified the dust properties, in
comparison with those in the Galaxy, or other gas and dust rich galaxies. The
sophistication of the SED models is limited by the availability of detailed
data in the mid infrared and particularly in the submillimetre to millimetre
regime, which will open up in the near future with space-based missions, such
as Herschel.Comment: 8 pages presented at "The Spectral Energy Distribution of Gas-Rich
Galaxies: Confronting Models with Data" Heidelberg (Germany), October 2004.
To be published in The Spectral Energy Distribution of Gas-Rich Galaxies, ed.
C. Popescu & R. Tuffs (Melville:AIP) in pres
Interstellar Gas in Low Mass Virgo Cluster Spiral Galaxies
We have measured the strengths of the [C II] 158 micron, [N II] 122 micron,
and CO (1 - 0) lines from five low blue luminosity spiral galaxies in the Virgo
Cluster, using the Infrared Space Observatory and the NRAO 12m millimeter
telescope. Two of the five galaxies have high L([C II)]/L(CO) and L(FIR)/L(CO)
ratios compared to higher mass spirals. These two galaxies, NGC 4294 and NGC
4299, have L([C II])/L(CO) ratios of >14,300 and 15,600, respectively, which
are similar to values found in dwarf irregular galaxies. This is the first time
that such enhanced L([C II])/L(CO) ratios have been found in spiral galaxies.
This result may be due to low abundances of dust and heavy elements, which can
cause the CO (1 - 0) measurements to underestimate the molecular gas content.
Another possibility is that radiation from diffuse HI clouds may dominate the
[C II] emission from these galaxies. Less than a third of the observed [C II]
emission arises from HII regions.Comment: 24 pages, Latex, 2 Figures, 6 Tables To appear in the Astronomical
Journal, July 199
The graceful exit in pre-big bang string cosmology
We re-examine the graceful exit problem in the pre-big bang scenario of
string cosmology, by considering the most general time-dependent classical
correction to the Lagrangian with up to four derivatives. By including possible
forms for quantum loop corrections we examine the allowed region of parameter
space for the coupling constants which enable our solutions to link smoothly
the two asymptotic low-energy branches of the pre-big bang scenario, and
observe that these solutions can satisfy recently proposed entropic bounds on
viable singularity free cosmologies.Comment: 14 pages, 6 figures, JHEP class. Added new section on the classical
correction and reference
Applications of inertial navigation and modern control theory to the all weather landing problem
Inertial navigation and automatic landing control theory applied to instrument landing proble
Modeling the physical properties in the ISM of the low-metallicity galaxy NGC4214
We present a model for the interstellar medium of NGC4214 with the objective
to probe the physical conditions in the two main star-forming regions and their
connection with the star formation activity of the galaxy. We used the spectral
synthesis code Cloudy to model an HII region and the associated
photodissociation region (PDR) to reproduce the emission of mid- and
far-infrared fine-structure cooling lines from the Spitzer and Herschel space
telescopes for these two regions. Input parameters of the model, such as
elemental abundances and star formation history, are guided by earlier studies
of the galaxy, and we investigated the effect of the mode in which star
formation takes place (bursty or continuous) on the line emission. Furthermore,
we tested the effect of adding pressure support with magnetic fields and
turbulence on the line predictions. We find that this model can satisfactorily
predict (within a factor of ~2) all observed lines that originate from the
ionized medium ([SIV] 10.5um, [NeIII] 15.6um, [SIII] 18.7um, [SIII] 33.5um, and
[OIII] 88um), with the exception of [NeII] 12.8um and [NII] 122um, which may
arise from a lower ionization medium. In the PDR, the [OI] 63um, [OI] 145um,
and [CII] 157um lines are matched within a factor of ~5 and work better when
weak pressure support is added to the thermal pressure or when the PDR clouds
are placed farther away from the HII regions and have covering factors lower
than unity. Our models of the HII region agree with different evolutionary
stages found in previous studies, with a more evolved, diffuse central region,
and a younger, more compact southern region. However, the local PDR conditions
are averaged out on the 175 pc scales that we probe and do not reflect
differences observed in the star formation properties of the two regions.Comment: accepted for publication in A&
Supporting a Community of Pets
This capstone project highlights a community\u27s efforts to support in-need pets, particularly dogs and cats, as well as their owners. For this project, I organized and executed a multiple-week food drive focused specifically on collecting pet food. The objective of this project was to help diminish the rate of food insecurity found in pets within the Boise community, as well as bring a fresh sense of hope to pet owners who may be facing financial hardship or other personal challenges. Over nearly a month’s time, my pet food drive was able to raise over 750 pounds of food for those in need, and all of the collections were donated to a local St. Vincent de Paul Food Pantry to be distributed. With the help of many selfless donors, we, as a community, have had the opportunity to help support dozens of pets, individuals, and families because of this project\u27s creation
Extended Intensity Range Imaging
A single composite image with an extended intensive range is generated by combining disjoining regions from different images of the same scene. The set of images is obtained with a charge-couple device (CCD) set for different flux integration times. By limiting differences in the integration times so that the ranges of output pixel values overlap considerably, individual pixels are assigned the value measured at each spatial location that is in the most sensitive range where the values are both below saturation and are most precisely specified. Integration times are lengthened geometrically from a minimum where all pixel values are below saturation until all dark regions emerge from the lowest quantization level. the method is applied to an example scene and the effect the composite images have on traditional low-level imaging methods also is examined
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A multi-transition study of the cyclic molecule cyclopropenylidene (C2H2) in the galaxy.
We report results of multi-transition observations and modeling of the hydrocarbon ring molecule cyclopropenylidene (C\sb3H\sb2). From a survey of the 1\sb{10}-1\sb{01} (18 GHz) and 2\sb{12}-1\sb{01} (85 GHz) transitions in the Galaxy, we have found C\sb3H\sb2 present in a variety of sources including cold, dark clouds, giant molecular clouds, the envelope of a carbon star, and diffuse clouds. Up to 10 transitions of C\sb3H\sb2 ranging in wavelength from 1.3 cm to 1.3 mm were observed in the dark clouds L1498, L134N, B335 and toward several positions in TMC-1. The Large Velocity Gradient (LVG) approximation was used to model the observations. Optical depth values of C\sb3H\sb2, estimated from C\sp{13}C\sb2H\sb2 observations, are necessary to constrain the results since the range in excitation energies of the observed C\sb3H\sb2 transitions does not contrast sufficiently. The molecular hydrogen density in TMC-1 is estimated to be 3.7 10\sp4 cm\sp{-3}, while the fractional abundance of C{\sb3}H\sb2 relative to H\sb2 is 5.7 10\sp{-9}. Previous estimates assuming LTE conditions overestimate the abundance of C\sb3H\sb2. The abundance in the ridge component in Orion is estimated to be approximately 8 10\sp{-10} cm \sp{-2}. Gas phase chemical models can reproduce the high C\sb3H\sb2 abundance found in dark clouds under assumptions such as steady state conditions with (C) / (O) / 1.0, conditions of earlier evolutionary time, or \u27optimistic\u27 rate coefficients. However, large deuteration ratios (0.05 to 0.15) create difficulties for gas phase models
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