3,253 research outputs found
Ancient eruptions of Eta Carinae: A tale written in proper motions
We analyze eight epochs of Hubble Space Telescope H+[N II] imaging of
Eta Carinae's outer ejecta. Proper motions of nearly 800 knots reveal that the
detected ejecta are divided into three apparent age groups, dating to around
1250 A.D., to around 1550 A.D., and to during or shortly before the Great
Eruption of the 1840s. Ejecta from these groups reside in different locations
and provide a firm constraint that Eta Car experienced multiple major eruptions
prior to the 19th century. The 1250 and 1550 events did not share the same
axisymmetry as the Homunculus; the 1250 event was particularly asymmetric, even
one-sided. In addition, the ejecta in the S ridge, which have been associated
with the Great Eruption, appear to predate the ejection of the Homunculus by
several decades. We detect essentially ballistic expansion across multiple
epochs. We find no evidence for large-scale deceleration of the observed knots
that could power the soft X-ray shell by plowing into surrounding material,
suggesting that the observed X-rays arise instead from fast, rarefied ejecta
from the 1840s overtaking the older dense knots. Early deceleration and
subsequent coasting cannot explain the origin of the older outer
ejecta---significant episodic mass loss prior to the 19th century is required.
The timescale and geometry of the past eruptions provide important constraints
for any theoretical physical mechanisms driving Eta Car's behavior.
Non-repeating mechanisms such as the merger of a close binary in a triple
system would require additional complexities to explain the observations.Comment: 14 pages, 11 figures, accepted for publication in MNRA
Proper motions of collimated jets from intermediate-mass protostars in the Carina Nebula
We present proper motion measurements of 37 jets and HH objects in the Carina
Nebula measured in two epochs of H images obtained yrs apart
with HST/ACS. Transverse velocities in all but one jet are faster than km s, confirming that the jet-like H features identified by
Smith et al. (2010) trace outflowing gas. Proper motions constrain the location
of the jet-driving source and provide kinematic confirmation of the
intermediate-mass protostars that we identify for 20/37 jets. Jet velocities do
not correlate with the estimated protostar mass and embedded driving sources do
not have slower jets. Instead, transverse velocities (median km
s) are similar to those in jets from low-mass stars. Assuming a constant
velocity since launch, we compute jet dynamical ages (median yr).
If continuous emission from inner jets traces the duration of the most recent
accretion bursts, then these episodes are sustained longer (median
yr) than the typical decay time of an FU Orionis outburst. These jets can carry
appreciable momentum that may be injected into the surrounding environment. The
resulting outflow force, , lies between that measured in low- and
high-mass sources, despite the very different observational tracers used.
Smooth scaling of the outflow force argues for a common physical process
underlying outflows from protostars of all masses. This latest kinematic result
adds to a growing body of evidence that intermediate-mass star formation
proceeds like a scaled-up version of the formation of low-mass stars.Comment: accepted to MNRAS, 29 pages, 30 figures, 3 table
Proper motions of five OB stars with candidate dusty bow shocks in the Carina Nebula
We constrain the proper motions of five OB stars associated with candidate
stellar wind bow shocks in the Carina Nebula using HST ACS imaging over 9--10
year baselines. These proper motions allow us to directly compare each star's
motion to the orientation of its candidate bow shock. Although these stars are
saturated in our imaging, we assess their motion by the shifts required to
minimize residuals in their Airy rings. The results limit the direction of each
star's motion to sectors less than 90 degrees wide. None of the five stars are
moving away from the Carina Nebula's central clusters as runaway stars would
be, confirming that a candidate bow shock is not necessarily indicative of a
runaway star. Two of the five stars are moving tangentially relative to the
orientation of their candidate bow shocks, both of which point at the OB
cluster Trumpler 14. In these cases, the large-scale flow of the interstellar
medium, powered by feedback from the cluster, appears to dominate over the
motion of the star in producing the observed candidate bow shock. The remaining
three stars all have some component of motion toward the central clusters,
meaning that we cannot distinguish whether their candidate bow shocks are
indicators of stellar motion, of the flow of ambient gas, or of density
gradients in their surroundings. In addition, these stars' lack of outward
motion hints that the distributed massive-star population in Carina's South
Pillars region formed in place, rather than migrating out from the
association's central clusters.Comment: 13 pages, 5 figures, accepted for publication in MNRA
[Fe II] jets from intermediate-mass protostars in Carina
We present new HST/WFC3-IR narrowband [Fe II] images of protostellar jets in
the Carina Nebula. Combined with 5 previously published sources, we have a
sample of 18 jets and 2 HH objects. All of the jets we targeted with WFC3 show
bright infrared [Fe II] emission, and a few H candidate jets are
confirmed as collimated outflows based on the morphology of their [Fe II]
emission. Continuum-subtracted images clearly separate jet emission from the
adjacent ionization front, providing a better tracer of the collimated jet than
H and allowing us to connect these jets with their embedded driving
sources. The [Fe II] 1.64 m/H flux ratio measured in the jets is
times larger than in the adjacent ionization fronts. The
low-ionization jet core requires high densities to shield Fe against
further ionization by the FUV radiation from O-type stars in the H II region.
High jet densities imply high mass-loss rates, consistent with the
intermediate-mass driving sources we identify for 13 jets. The remaining jets
emerge from opaque globules that obscure emission from the protostar. In many
respects, the HH jets in Carina look like a scaled-up version of the jets
driven by low-mass protostars. Altogether, these observations suggest that [Fe
II] emission is a reliable tracer of dense, irradiated jets driven by
intermediate-mass protostars. We argue that highly collimated outflows are
common to more massive protostars, and that they suggest the outflow physics
inferred for low-mass stars formation scales up to at least
M.Comment: 24 pages, 23 figures, accepted for publication in MNRA
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Placement of Outdoor Exercise Equipment and Physical Activity: A Quasi-Experimental Study in Two Parks in Southern California.
To reduce the burden of chronic disease, the Centers for Disease Control and Prevention (CDC) funded the Orange County Partnerships to Improve Health (OC-PICH) project in Orange County, California. One of the strategies included adding outdoor exercise equipment (OEE) in two parks in Garden Grove and Anaheim. Using a quasi-experimental pre-post design, we evaluated park users' physical activity levels before and after OEE installation using the System for Observing Play and Recreation in Communities (SOPARC). The OEE was installed along a walking path in Edison Park (Anaheim) and grouped within a single area (a "fitness zone") in Garden Grove Park. In both parks, there were significantly greater odds of high-intensity physical activity overall after the installation-19% higher odds in Anaheim, and 23% higher odds in Garden Grove. However, the fitness zone area in Garden Grove had substantially higher odds of increased physical activity post-intervention (OR = 5.29, CI: 3.76-7.44, p < 0.001). While the increases in physical activity levels are consistent with past studies that link OEE to higher levels of physical activity among park users, our findings also suggest that the location and placement of equipment within a park may be an important factor to consider when improving park amenities for physical activity
Middle and elementary school students’ changes in self-determined motivation in a basketball unit taught using the Tactical Games Model
Studies examining student motivation levels suggest that this is a significant factor in students’ engagement in physical education and may be positively affected when teachers employ alternative pedagogical models such as game-centered approaches (GCAs). The aim of this study was to investigate changes in self-determined motivation of students as they participated in a GCA-basketball unit taught using the Tactical Games Model (TGM). Participants were 173 students (84 girls), 79 middle school (45 girls) and 94 (39 girls) elementary school students from four seventh and five fourth/fifth grade co-educational classes. Two teachers taught 32 (middle) and 33 (elementary) level one TGM basketball lessons. Need satisfaction and self-determined motivation data were collected using a previously validated instrument, while lesson context and teacher behavior data were recorded using systematic observation instruments. Repeated measures MANOVAs were employed to examine pre-posttest differences. Results revealed a significant main effect for time in need satisfaction for both middle (relatedness increased) and elementary school students (autonomy decreased) and a significant main effect in self-determined motivation for middle school students only (introjected regulation, external regulation, and amotivation all increased). Approximately 48%/42% (middle/elementary) of lesson time was game play, 22%/22% skill practice, 17%/17% management, and 13%/19% knowledge. The primary teacher behaviors used were instruction, management, specific observation, corrective feedback and modelling. Results indicate that it is important for future research to pay greater attention to the contextual factors associated with the application of the TGM, such as the students’ previous exposure to TGM lessons, and the teachers’ training and experience in utilizing the TGM. Indeed, results of the present study demonstrate that a longer-term commitment to the TGM is necessary to reduce controlling teacher behaviors, which will lead to positive changes in students’ need satisfaction and self-determined motivation. Future research is therefore needed to embrace this challenge to provide an increased evidence-base for GCAs such as the TGM
Book review: national and state identity in Turkey: the transformation of the Republic’s status in the international system by Toni Alaranta
In National and State Identity in Turkey: The Transformation of the Republic’s Status in the International System, Toni Alaranta examines the impact that the Justice and Development Party (AKP) has had on various strands of Turkish national identity since coming to power in 2002. Although Megan Smith highlights some structural oversimplifications in the book, she nonetheless positions Alaranta’s study as a rich and valuable account of contemporary Turkish identity politics
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