308 research outputs found
The 2-850 micron SED of starforming galaxies
We present preliminary results on a study of the 2--850 micron SEDs of a
sample of 30 FIRBACK galaxies selected at 170 micron. These sources are
representative of the brightest ~10% of the Cosmic Infrared Background. They
are a mixture of mostly local (z<~0.3) starforming galaxies, and a tail of
ULIGs that extend up to z~1, and are likely to be a similar population to faint
SCUBA sources. We use archival Spitzer IRAC and MIPS data to extend the
spectral coverage to the mid-IR regime, resulting in an unprecended (for this
redshift range) census of their infrared SEDs. This allows us to study in far
greater detail this important population linking the near-IR stellar emission
with PAH and thermal dust emission. We do this using a Markov Chain Monte Carlo
method, which easily allows for the inclusion of ~6 free parameters, as well as
an estimate of parameter uncertainties and correlations.Comment: 5 pages, 3 figures. Proceeding for the conference "Starbursts: From
30 Doradus to Lyman Break Galaxies", held in Cambridge (UK) in September,
200
AFC-Enabled Vertical Tail System Integration Study
This document serves as the final report for the SMAAART AFC-Enabled Vertical Tail System Integration Study. Included are the ground rule assumptions which have gone into the study, layouts of the baseline and AFC-enabled configurations, critical sizing information, system requirements and architectures, and assumed system properties that result in an NPV assessment of the two candidate AFC technologies
Performance Enhancement of a Full-Scale Vertical Tail Model Equipped with Active Flow Control
This paper describes wind tunnel test results from a joint NASA/Boeing research effort to advance active flow control (AFC) technology to enhance aerodynamic efficiency. A full-scale Boeing 757 vertical tail model equipped with sweeping jet actuators was tested at the National Full-Scale Aerodynamics Complex (NFAC) 40- by 80-Foot Wind Tunnel (40x80) at NASA Ames Research Center. The model was tested at a nominal airspeed of 100 knots and across rudder deflections and sideslip angles that covered the vertical tail flight envelope. A successful demonstration of AFC-enhanced vertical tail technology was achieved. A 31- actuator configuration significantly increased side force (by greater than 20%) at a maximum rudder deflection of 30deg. The successful demonstration of this application has cleared the way for a flight demonstration on the Boeing 757 ecoDemonstrator in 2015
Refined AFC-Enabled High-Lift System Integration Study
A prior trade study established the effectiveness of using Active Flow Control (AFC) for reducing the mechanical complexities associated with a modern high-lift system without sacrificing aerodynamic performance at low-speed flight conditions representative of takeoff and landing. The current technical report expands on this prior work in two ways: (1) a refined conventional high-lift system based on the NASA Common Research Model (CRM) is presented that is more representative of modern commercial transport aircraft in terms of stall characteristics and maximum Lift/Drag (L/D) ratios at takeoff and landing-approach flight conditions; and (2) the design trade space for AFC-enabled high-lift systems is expanded to explore a wider range of options for improving their efficiency. The refined conventional high-lift CRM (HL-CRM) concept features leading edge slats and slotted trailing edge flaps with Fowler motion. For the current AFC-enhanced high lift system trade study, the refined conventional high-lift system is simplified by substituting simply-hinged trailing edge flaps for the slotted single-element flaps with Fowler motion. The high-lift performance of these two high-lift CRM variants is established using Computational Fluid Dynamics (CFD) solutions to the Reynolds-Averaged Navier-Stokes (RANS) equations. These CFD assessments identify the high-lift performance that needs to be recovered through AFC to have the CRM variant with the lighter and mechanically simpler high-lift system match the performance of the conventional high-lift system. In parallel to the conventional high-lift concept development, parametric studies using CFD guided the development of an effective and efficient AFC-enabled simplified high-lift system. This included parametric trailing edge flap geometry studies addressing the effects of flap chord length and flap deflection. As for the AFC implementation, scaling effects (i.e., wind-tunnel versus full-scale flight conditions) are addressed, as are AFC architecture aspects such as AFC unit placement, number AFC units, operating pressures, mass flow rates, and steady versus unsteady AFC applications. These efforts led to the development of a novel traversing AFC actuation concept which is efficient in that it reduces the AFC mass flow requirements by as much as an order of magnitude compared to previous AFC technologies, and it is predicted to be effective in driving the aerodynamic performance of a mechanical simplified high-lift system close to that of the reference conventional high-lift system. Conceptual system integration studies were conducted for the AFC-enhanced high-lift concept applied to a NASA Environmentally Responsible Aircraft (ERA) reference configuration, the so-called ERA-0003 concept. The results from these design integration assessments identify overall system performance improvement opportunities over conventional high-lift systems that suggest the viability of further technology maturation efforts for AFC-enabled high lift flap systems. To that end, technical challenges are identified associated with the application of AFC-enabled high-lift systems to modern transonic commercial transports for future technology maturation efforts
Simulating the Spitzer mid-IR color-color diagrams
We use a simple parameterization of the mid-IR spectra of a wide range of
galaxy types in order to predict their distribution in the Infrared Array
Camera (IRAC) 3.6um, 4.5um, 5.8um, and 8.0um and Multiband Photometer for
Spitzer (MIPS) 24um color-color diagrams. We distinguish three basic spectral
types by the energetically dominant component in the 3--12 micron regime:
stellar-dominated; PAH-dominated; and continuum-dominated. We have used a
Markov chain Monte Carlo (MCMC) approach to arrive at a more systematic and
robust representation of the mid-IR spectra of galaxies than more traditional
approaches. We find that IRAC color-color plots are well suited to
distinguishing the above spectral types, while the addition of 24 micron data
allows us to suggest practical 3-color cuts which preferentially select higher
redshift sources of specific type. We compare our simulations with the
color-color plot obtained by the Spitzer First Look Survey (FLS) and find
reasonable agreement. Lastly, we discuss other applications as well as future
directions for this work.Comment: 20p, 12figures, submitted to Ap
Accurate Wavenumbers for Mid-Infrared Fine-Structure Lines
We present accurate new wavenumbers for a set of 13 mid-infrared
fine-structure lines. The wavenumbers were determined from observations of the
planetary nebula NGC 7027 and of the red supergiant Alpha Scorpii. Most of the
new wavenumbers are good to within 0.0025%, or 8 km/s. We provide details on
the measurements and present an analysis of the errors. In addition, we present
the first observations of hyperfine splitting in the [Na IV] 1106 cm-1 line.Comment: 12 pages text, 2 postscript figures, uses AASTeX macros, figures are
gzipped and uuencode
Measurement of Galactic Logarithmic Spiral Arm Pitch Angle Using Two-Dimensional Fast Fourier Transform Decomposition
A logarithmic spiral is a prominent feature appearing in a majority of
observed galaxies. This feature has long been associated with the traditional
Hubble classification scheme, but historical quotes of pitch angle of spiral
galaxies have been almost exclusively qualitative. We have developed a
methodology, utilizing two-dimensional fast Fourier transformations of images
of spiral galaxies, in order to isolate and measure the pitch angles of their
spiral arms. Our technique provides a quantitative way to measure this
morphological feature. This will allow comparison of spiral galaxy pitch angle
to other galactic parameters and test spiral arm genesis theories. In this
work, we detail our image processing and analysis of spiral galaxy images and
discuss the robustness of our analysis techniques.Comment: 23 pages, 22 figures, and 3 Tables; published in ApJS 199, 33
http://iopscience.iop.org/0067-0049/199/2/33/; software available for
download at http://dafix.uark.edu/~ages/downloads.html and
http://astro.host.ualr.edu/2DFFT
A Sample of Ultra Steep Spectrum Sources Selected from the Westerbork In the Southern Hemisphere (WISH) survey
The 352 MHz Westerbork In the Southern Hemisphere (WISH) survey is the
southern extension of the WENSS, covering 1.60 sr between -9 < DEC < -26 to a
limiting flux density of ~18 mJy (5sigma). Due to the very low elevation of the
observations, the survey has a much lower resolution in declination than in
right ascension (54" x 54"cosec(DEC)). A correlation with the 1.4 GHz NVSS
shows that the positional accuracy is less constrained in declination than in
right ascension, but there is no significant systematic error. We present a
source list containing 73570 sources.
We correlate this WISH catalogue with the NVSS to construct a sample of faint
Ultra Steep Spectrum (USS) sources, which is accessible for follow-up studies
with large optical telescopes in the southern hemisphere. This sample is aimed
at increasing the number of known high redshift radio galaxies to allow
detailed follow-up studies of these massive galaxies and their environments in
the early Universe.Comment: 12 Pages, including 5 PostScript figures. Accepted for publication in
Astronomy & Astrophysics. The full WISH catalog with 73570 sources is
available from http://www.strw.leidenuniv.nl/wenss
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