207 research outputs found
An Ultraviolet and Near-Infrared View of NGC 4214: A Starbursting Core Embedded in a Low Surface Brightness Disk
During the Astro-2 Spacelab mission in 1995 March, the Ultraviolet Imaging Telescope (UIT) obtained far-UV (λ = 1500 A) imagery of the nearby Sm/Im galaxy NGC 4214. The UIT images have a spatial resolution of ~3'' and a limiting surface brightness, μ1500 > 25 mag arcsec-2, permitting detailed investigation of the intensity and spatial distribution of the young, high-mass stellar component. These data provide the first far-UV imagery covering the full spatial extent of NGC 4214. Comparison with a corresponding I-band image reveals the presence of a starbursting core embedded in an extensive low surface brightness disk. In the far-UV (FUV), NGC 4214 is resolved into several components: a luminous, central knot; an inner region (r 2.5 kpc) with ~15 resolved sources embedded in bright, diffuse emission; and a population of fainter knots extending to the edge of the optically defined disk (r ≈ 5 kpc). The FUV light, which traces recent massive star formation, is observed to be more centrally concentrated than the I-band light, which traces the global stellar population. The FUV radial light profile is remarkably well represented by an R1/4 law, providing evidence that the centrally concentrated massive star formation in NGC 4214 is the result of an interaction, possibly a tidal encounter, with a dwarf companion(s). The brightest FUV source produces ~8% of the global FUV luminosity. This unresolved source, corresponding to the Wolf-Rayet knot described by Sargent & Filippenko, is located at the center of the FUV light distribution, giving NGC 4214 an active galactic nucleus-like morphology. Another strong source is present in the I band, located 19'' west, 10'' north of the central starburst knot, with no FUV counterpart. The I-band source may be the previously unrecognized nucleus of NGC 4214 or an evolved star cluster with an age greater than ~200 Myr. The global star formation rate derived from the total FUV flux is consistent with rates derived using data at other wavelengths and lends support to the scenario of roughly constant star formation during the last few hundred million years at a level significantly enhanced relative to the lifetime averaged star formation rate. The hybrid disk/starburst-irregular morphology evident in NGC 4214 emphasizes the danger of classifying galaxies based on their high surface brightness components at any particular wavelength
Kepler Presearch Data Conditioning II - A Bayesian Approach to Systematic Error Correction
With the unprecedented photometric precision of the Kepler Spacecraft,
significant systematic and stochastic errors on transit signal levels are
observable in the Kepler photometric data. These errors, which include
discontinuities, outliers, systematic trends and other instrumental signatures,
obscure astrophysical signals. The Presearch Data Conditioning (PDC) module of
the Kepler data analysis pipeline tries to remove these errors while preserving
planet transits and other astrophysically interesting signals. The completely
new noise and stellar variability regime observed in Kepler data poses a
significant problem to standard cotrending methods such as SYSREM and TFA.
Variable stars are often of particular astrophysical interest so the
preservation of their signals is of significant importance to the astrophysical
community. We present a Bayesian Maximum A Posteriori (MAP) approach where a
subset of highly correlated and quiet stars is used to generate a cotrending
basis vector set which is in turn used to establish a range of "reasonable"
robust fit parameters. These robust fit parameters are then used to generate a
Bayesian Prior and a Bayesian Posterior Probability Distribution Function (PDF)
which when maximized finds the best fit that simultaneously removes systematic
effects while reducing the signal distortion and noise injection which commonly
afflicts simple least-squares (LS) fitting. A numerical and empirical approach
is taken where the Bayesian Prior PDFs are generated from fits to the light
curve distributions themselves.Comment: 43 pages, 21 figures, Submitted for publication in PASP. Also see
companion paper "Kepler Presearch Data Conditioning I - Architecture and
Algorithms for Error Correction in Kepler Light Curves" by Martin C. Stumpe,
et a
The Ultraviolet Imaging Telescope: Instrument and Data Characteristics
The Ultraviolet Imaging Telescope (UIT) was flown as part of the Astro
observatory on the Space Shuttle Columbia in December 1990 and again on the
Space Shuttle Endeavor in March 1995. Ultraviolet (1200-3300 Angstroms) images
of a variety of astronomical objects, with a 40 arcmin field of view and a
resolution of about 3 arcsec, were recorded on photographic film. The data
recorded during the first flight are available to the astronomical community
through the National Space Science Data Center (NSSDC); the data recorded
during the second flight will soon be available as well. This paper discusses
in detail the design, operation, data reduction, and calibration of UIT,
providing the user of the data with information for understanding and using the
data. It also provides guidelines for analyzing other astronomical imagery made
with image intensifiers and photographic film.Comment: 44 pages, LaTeX, AAS preprint style and EPSF macros, accepted by PAS
Kepler-16: A Transiting Circumbinary Planet
We report the detection of a planet whose orbit surrounds a pair of low-mass
stars. Data from the Kepler spacecraft reveal transits of the planet across
both stars, in addition to the mutual eclipses of the stars, giving precise
constraints on the absolute dimensions of all three bodies. The planet is
comparable to Saturn in mass and size, and is on a nearly circular 229-day
orbit around its two parent stars. The eclipsing stars are 20% and 69% as
massive as the sun, and have an eccentric 41-day orbit. The motions of all
three bodies are confined to within 0.5 degree of a single plane, suggesting
that the planet formed within a circumbinary disk.Comment: Science, in press; for supplemental material see
http://www.sciencemag.org/content/suppl/2011/09/14/333.6049.1602.DC1/1210923.Doyle.SOM.pd
UIT Astro-2 Observations of NGC 4449
The bright Magellanic irregular galaxy NGC 4449 was observed by the
Ultraviolet Imaging Telescope (UIT) during the Astro-2 Spacelab mission in
March, 1995. Far ultraviolet (FUV) images at a spatial resolution of ~3 arcsec
show bright star-forming knots that are consistent with the general optical
morphology of the galaxy and are often coincident with bright H II regions.
Comparison of FUV with H-alpha shows that in a few regions, sequential star
formation may have occurred over the last few Myr. The bright star forming
complexes in NGC 4449 are superposed on a smooth, diffuse FUV background that
may be associated with the H-alpha "froth."Comment: 4 pages, Latex with AIP proceedings macros, 2 EPS figures. To appear
in proceedings of U. Maryland October Astrophysics Conf., 1996, AIP pu
Oral Metallo-Beta-Lactamase Protects the Gut Microbiome From Carbapenem-Mediated Damage and Reduces Propagation of Antibiotic Resistance in Pigs
Antibiotics can damage the gut microbiome, leading to serious adventitious infections and emergence of antibiotic resistant pathogens. Antibiotic inactivation in the GI tract represents a strategy to protect colonic microbiota integrity and reduce antibiotic resistance. Clinical utility of this approach was established when SYN-004 (ribaxamase), an orally-administered beta-lactamase, was demonstrated to degrade ceftriaxone in the GI tract and preserve the gut microbiome. Ribaxamase degrades penicillins and cephalosporin beta-lactams, but not carbapenems. To expand this prophylactic approach to include all classes of beta-lactam antibiotics, a novel carbapenemase, formulated for oral administration, SYN-006, was evaluated in a porcine model of antibiotic-mediated gut dysbiosis. Pigs (20 kg, n = 16) were treated with the carbapenem, ertapenem (ERT), (IV, 30 mg/kg, SID) for 4 days and a cohort (n = 8) also received SYN-006 (PO, 50 mg, QID), beginning the day before antibiotic administration. ERT serum levels were not statistically different in ERT and ERT + SYN-006 groups, indicating that SYN-006 did not alter systemic antibiotic levels. Microbiomes were evaluated using whole genome shotgun metagenomics analyses of fecal DNA collected prior to and after antibiotic treatment. ERT caused significant changes to the gut microbiome that were mitigated in the presence of SYN-006. In addition, SYN-006 attenuated emergence of antibiotic resistance, including encoded beta-lactamases and genes conferring resistance to a broad range of antibiotics such as aminoglycosides and macrolides. SYN-006 has the potential to become the first therapy designed to protect the gut microbiome from all classes of beta-lactam antibiotics and reduce emergence of carbapenem-resistant pathogens
Ultraviolet Signposts of Resonant Dynamics in the Starburst-Ringed Sab Galaxy, M94 (NGC 4736)
M94 (NGC 4736) is investigated using images from the Ultraviolet Imaging
Telescope (FUV-band), Hubble Space Telescope (NUV-band), Kitt Peak 0.9-m
telescope (H-alpha, R, and I bands), and Palomar 5-m telescope (B-band), along
with spectra from the International Ultraviolet Explorer and Lick 1-m
telescopes. The wide-field UIT image shows FUV emission from (a) an elongated
nucleus, (b) a diffuse inner disk, where H-alpha is observed in absorption, (c)
a bright inner ring of H II regions at the perimeter of the inner disk (R = 48
arcsec. = 1.1 kpc), and (d) two 500-pc size knots of hot stars exterior to the
ring on diametrically opposite sides of the nucleus (R= 130 arcsec. = 2.9 kpc).
The HST/FOC image resolves the NUV emission from the nuclear region into a
bright core and a faint 20 arcsec. long ``mini-bar'' at a position angle of 30
deg. Optical and IUE spectroscopy of the nucleus and diffuse inner disk
indicates an approximately 10^7 or 10^8 yr-old stellar population from
low-level starbirth activity blended with some LINER activity. Analysis of the
H-alpha, FUV, NUV, B, R, and I-band emission along with other observed tracers
of stars and gas in M94 indicates that most of the star formation is being
orchestrated via ring-bar dynamics involving the nuclear mini-bar, inner ring,
oval disk, and outer ring. The inner starburst ring and bi-symmetric knots at
intermediate radius, in particular, argue for bar-mediated resonances as the
primary drivers of evolution in M94 at the present epoch. Similar processes may
be governing the evolution of the ``core-dominated'' galaxies that have been
observed at high redshift. The gravitationally-lensed ``Pretzel Galaxy''
(0024+1654) at a redshift of approximately 1.5 provides an important precedent
in this regard.Comment: revised figure 1 (corrected coordinate labels on declination axis);
19 pages of text + 19 figures (jpg files); accepted for publication in A
Kepler-21b: A 1.6REarth Planet Transiting the Bright Oscillating F Subgiant Star HD 179070
We present Kepler observations of the bright (V=8.3), oscillating star HD
179070. The observations show transit-like events which reveal that the star is
orbited every 2.8 days by a small, 1.6 R_Earth object. Seismic studies of HD
179070 using short cadence Kepler observations show that HD 179070 has a
frequencypower spectrum consistent with solar-like oscillations that are
acoustic p-modes. Asteroseismic analysis provides robust values for the mass
and radius of HD 179070, 1.34{\pm}0.06 M{\circ} and 1.86{\pm}0.04 R{\circ}
respectively, as well as yielding an age of 2.84{\pm}0.34 Gyr for this F5
subgiant. Together with ground-based follow-up observations, analysis of the
Kepler light curves and image data, and blend scenario models, we
conservatively show at the >99.7% confidence level (3{\sigma}) that the transit
event is caused by a 1.64{\pm}0.04 R_Earth exoplanet in a 2.785755{\pm}0.000032
day orbit. The exoplanet is only 0.04 AU away from the star and our
spectroscopic observations provide an upper limit to its mass of ~10 M_Earth
(2-{\sigma}). HD 179070 is the brightest exoplanet host star yet discovered by
Kepler.Comment: Accepted to Ap
Ultraviolet Signatures of Tidal Interaction in the Giant Spiral Galaxy, M101
We present new evidence for tidal interactions having occurred in the disk of
M101 in the last 10^8 - 10^9 years. Recent imaging of the far-ultraviolet
emission from M101 by the Shuttle-borne Ultraviolet Imaging Telescope (UIT)
reveals with unprecedented clarity a disk-wide pattern of multiple linear arm
segments (``crooked arms''). The deep FUV image also shows a faint outer spiral
arm with a (``curly tail'') feature that appears to loop around the supergiant
HII region NGC 5471 - linking this outlying starburst with the rest of the
galaxy. These FUV-bright features most likely trace hot O & B-type stars along
with scattered light from associated nebular dust. Counterparts of the
outermost ``crooked arms'' are evident in maps at visible wavelengths and in
the 21-cm line of HI. The inner-disk FUV arms are most closely associated with
H knots and the outer (downstream) sides of CO arms. Comparisons of the
``crooked arm'' and ``curly tail'' morphologies with dynamical simulations
yield the greatest similitude, when the non- axisymmetric forcing comes from a
combination of ``external interactions'' with one or more companion galaxies
and ``internal perturbations'' from massive objects orbiting within the disk.
We speculate that NGC 5471 represents one of these ``massive disturbers''
within the disk, whose formation followed from a tidal interaction between M101
and a smaller galaxy.Comment: Paper format (latex); length of paper (8); 4 gif figure files; uses
aas2pp4.sty AASTeX macro file; to be published in Part I of the Astrophysical
Journa
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