2,199 research outputs found
Refining the formation and early evolution of the Eastern North American Margin : new insights from multiscale magnetic anomaly analyses
Author Posting. Š American Geophysical Union, 2017. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Solid Earth 122 (2017): 8724â8748, doi:10.1002/2017JB014308.To investigate the oceanic lithosphere formation and early seafloor spreading history of the North Atlantic Ocean, we examine multiscale magnetic anomaly data from the Jurassic/Early Cretaceous age Eastern North American Margin (ENAM) between 31 and 40°N. We integrate newly acquired sea surface magnetic anomaly and seismic reflection data with publicly available aeromagnetic and composite magnetic anomaly grids, satellite-derived gravity anomaly, and satellite-derived and shipboard bathymetry data. We evaluate these data sets to (1) refine magnetic anomaly correlations throughout the ENAM and assign updated ages and chron numbers to M0âM25 and eight pre-M25 anomalies; (2) identify five correlatable magnetic anomalies between the East Coast Magnetic Anomaly (ECMA) and Blake Spur Magnetic Anomaly (BSMA), which may document the earliest Atlantic seafloor spreading or synrift magmatism; (3) suggest preexisting margin structure and rifting segmentation may have influenced the seafloor spreading regimes in the Atlantic Jurassic Quiet Zone (JQZ); (4) suggest that, if the BSMA source is oceanic crust, the BSMA may be M series magnetic anomaly M42 (~168.5 Ma); (5) examine the along and across margin variation in seafloor spreading rates and spreading center orientations from the BSMA to M25, suggesting asymmetric crustal accretion accommodated the straightening of the ridge from the bend in the ECMA to the more linear M25; and (6) observe anomalously high-amplitude magnetic anomalies near the Hudson Fan, which may be related to a short-lived propagating rift segment that could have helped accommodate the crustal alignment during the early Atlantic opening.J. A. G. and
M. T. thank the Department of Geology
and Geophysics at Texas A&M
University for their support of J. A. G.âs
PhD program. M. T. and M. R. K. thank
the Department of Earth and
Environmental Sciences at Michigan
State University for their support during
M. R. K.âs MS thesis project, included in
this study.2018-05-1
Mid-Infrared Observations of Class I/Flat-Spectrum Systems in Six Nearby Molecular Clouds
We have obtained new mid-infrared observations of 65 Class I/Flat-Spectrum
(F.S.) objects in the Perseus, Taurus, Chamaeleon I/II, Rho Ophiuchi, and
Serpens dark clouds. We detected 45/48 (94%) of the single sources, 16/16
(100%) of the primary components, and 12/16 (75%) of the secondary/triple
components of the binary/multiple objects surveyed. The composite spectral
energy distributions (SEDs) for all of our sample sources are either Class I or
F.S., and, in 15/16 multiple systems, at least one of the individual components
displays a Class I or F.S. spectral index. However, the occurrence of mixed
pairings, such as F.S. with Class I, F.S. with Class II, and, in one case, F.S.
with Class III, is surprisingly frequent. Such behaviour is not consistent with
that of multiple systems among T Tauri stars (TTS), where the companion of a
classical TTS also tends to be a classical TTS, although other mixed pairings
have been previously observed among Class II objects. Based on an analysis of
the spectral indices of the individual binary components, there appears to be a
higher proportion of mixed Class I/F.S. systems (65-80%) than that of mixed
Classical/Weak-Lined TTS (25-40%), demonstrating that the envelopes of Class I/
F.S. systems are rapidly evolving during this evolutionary phase. We report the
discovery of a steep spectral index secondary companion to ISO-ChaI 97,
detected for the first time via our mid-infrared observations. In our previous
near- infrared imaging survey of binary/multiple Class I/F.S. sources, ISO-ChaI
97 appeared to be single. With a spectral index of Alpha >= 3.9, the secondary
component of this system is a member of a rare class of very steep spectral
index objects, those with Alpha > 3. Only three such objects have previously
been reported, all of which are either Class 0 or Class I.Comment: 31 pages, 4 figures, 6 table
Dynamical Measurements of Black Hole Masses in Four Brightest Cluster Galaxies at 100 Mpc
We present stellar kinematics and orbit superposition models for the central
regions of four Brightest Cluster Galaxies (BCGs), based upon integral-field
spectroscopy at Gemini, Keck, and McDonald Observatories. Our integral-field
data span radii from < 100 pc to tens of kpc. We report black hole masses,
M_BH, of 2.1 +/- 1.6 x 10^10 M_Sun for NGC 4889, 9.7 + 3.0 - 2.6 x 10^9 M_Sun
for NGC 3842, and 1.3 + 0.5 - 0.4 x 10^9 M_Sun for NGC 7768. For NGC 2832 we
report an upper limit of M_BH < 9 x 10^9 M_Sun. Stellar orbits near the center
of each galaxy are tangentially biased, on comparable spatial scales to the
galaxies' photometric cores. We find possible photometric and kinematic
evidence for an eccentric torus of stars in NGC 4889, with a radius of nearly 1
kpc. We compare our measurements of M_BH to the predicted black hole masses
from various fits to the relations between M_BH and stellar velocity
dispersion, luminosity, or stellar mass. The black holes in NGC 4889 and NGC
3842 are significantly more massive than all dispersion-based predictions and
most luminosity-based predictions. The black hole in NGC 7768 is consistent
with a broader range of predictions.Comment: 24 pages, 18 figures. Accepted for publication in Ap
The Safe Dates program: 1-year follow-up results
OBJECTIVES: An earlier report described desirable 1-month follow-up effects of the Safe Dates program on psychological, physical, and sexual dating violence. Mediators of the program-behavior relationship also were identified. The present report describes the 1-year follow-up effects of the Safe Dates program. METHODS: Fourteen schools were in the randomized experiment. Data were gathered by questionnaires in schools before program activities and 1 year after the program ended. RESULTS: The short-term behavioral effects had disappeared at 1 year, but effects on mediating variables such as dating violence norms, conflict management skills, and awareness of community services for dating violence were maintained. CONCLUSIONS: The findings are considered in the context of why program effects might have decayed and the possible role of boosters for effect maintenance
An Infrared Multiplicity Survey of Class I/Flat-Spectrum Systems in the Rho Ophiuchi and Serpens Molecular Clouds
We present new near- and mid-infrared observations of 19 Class
I/flat-spectrum young stellar objects in the nearby Rho Oph (d=125pc) and
Serpens (d=310pc) dark clouds. These observations are part of a larger
systematic infrared multiplicity survey of Class I/flat-spectrum objects in the
nearest dark clouds. We find 7/19 (37% +/- 14%) of the sources surveyed to be
multiple systems over a separation range of ~150 - 1800 AU. This is consistent
with the fraction of multiple systems found among older pre-main-sequence stars
in each of the Taurus, Rho Oph, Chamaeleon, Lupus, and Corona Australis
star-forming regions over a similar separation range. However, solar-type
main-sequence stars in the solar neighborhood have a fraction approximately
one-third that of our Class I/flat- spectrum sample (11% +/- 3%). This may be
attributed to evolutionary effects or environmental differences. An examination
of the spectral energy distributions of the SVS 20 and WL 1 binaries reveals
that the individual components of each source exhibit the same SED
classifications, similar to what one typically finds for binary T Tauri star
(TTS) systems, where the companion of a classical TTS also tends to be of the
same SED type.Comment: 30 pages, 10 figures, 4 tables, accepted for publication in the A
An Over-Massive Black Hole in the Compact Lenticular Galaxy NGC1277
All massive galaxies likely have supermassive black holes at their centers,
and the masses of the black holes are known to correlate with properties of the
host galaxy bulge component. Several explanations have been proposed for the
existence of these locally-established empirical relationships; they include
the non-causal, statistical process of galaxy-galaxy merging, direct feedback
between the black hole and its host galaxy, or galaxy-galaxy merging and the
subsequent violent relaxation and dissipation. The empirical scaling relations
are thus important for distinguishing between various theoretical models of
galaxy evolution, and they further form the basis for all black hole mass
measurements at large distances. In particular, observations have shown that
the mass of the black hole is typically 0.1% of the stellar bulge mass of the
galaxy. The small galaxy NGC4486B currently has the largest published fraction
of its mass in a black hole at 11%. Here we report observations of the stellar
kinematics of NGC 1277, which is a compact, disky galaxy with a mass of 1.2 x
10^11 Msun. From the data, we determine that the mass of the central black hole
is 1.7 x 10^10 Msun, or 59% its bulge mass. Five other compact galaxies have
properties similar to NGC 1277 and therefore may also contain over-sized black
holes. It is not yet known if these galaxies represent a tail of a
distribution, or if disk-dominated galaxies fail to follow the normal black
hole mass scaling relations.Comment: 7 pages. 6 figures. Nature. Animation at
http://www.mpia.de/~bosch/blackholes.htm
A Near-Infrared Multiplicity Survey of Class I/Flat-Spectrum Systems in Six Nearby Molecular Clouds
We present new near-IR observations of 76 Class I/flat-spectrum objects in
the nearby (d < 320 pc) Perseus, Taurus, Chamaeleon I and II, rho Ophiuchi, and
Serpens dark clouds. These observations are part of a larger systematic
infrared multiplicity survey of self-embedded objects in the nearest dark
clouds. When combined with the results of our previously published
near-infrared multiplicity survey, we find a restricted companion star fraction
of 14/79 (18% +/- 4%) of the sources surveyed to be binary or higher order
multiple systems over a separation range of ~300 - 2000 AU with a magnitude
difference K <= 4, and with no correction for background contamination
or completeness. This is consistent with the fraction of binary/multiple
systems found among older pre-main-sequence T Tauri stars in each of the
Taurus, rho Ophiuchi, and Chamaeleon star-forming regions over a similar
separation range, as well as the combined companion star fraction for these
regions. However, the companion star fraction for solar-type, and lower mass M
dwarf, main-sequence stars in the solar neighborhood in this separation range
(11% +/- 3%) is approximately one-half that of our sample. Together with
multiplicity statistics derived for previously published samples of Class 0 and
Class I sources, our study suggests that a significant number of
binary/multiple objects may remain to be discovered at smaller separations
among our Class I/flat-spectrum sample and/or most of the evolution of
binary/multiple systems occurs during the Class 0 phase of early stellar
evolution.Comment: 23 pages, 8 figures, to appear in the March 2004 A
Search for supersymmetry in events with b-quark jets and missing transverse energy in pp collisions at 7 TeV
Results are presented from a search for physics beyond the standard model
based on events with large missing transverse energy, at least three jets, and
at least one, two, or three b-quark jets. The study is performed using a sample
of proton-proton collision data collected at sqrt(s) = 7 TeV with the CMS
detector at the LHC in 2011. The integrated luminosity of the sample is 4.98
inverse femtobarns. The observed number of events is found to be consistent
with the standard model expectation, which is evaluated using control samples
in the data. The results are used to constrain cross sections for the
production of supersymmetric particles decaying to b-quark-enriched final
states in the context of simplified model spectra.Comment: Submitted to Physical Review
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