212 research outputs found
International Research Symposium on Talent Education, Part 5: The challenges of offering group class
This is the fifth installment in a series of articles reporting on a largeâscale demographic survey of North American Suzuki teachers. The last article in this series examined some of the perceived benefits of group class. In this article, we will review participantsâ perceptions of the challenges of group class. Participating teachers were asked to respond to the openâended question, "What is the greatest challenge of group class?" Their responses were coded and analyzed for important themes
International Research Symposium on Talent Education, Part 6: Parent education in Suzuki studios
This is the sixth installment in a series of articles reporting on a largeâscale demographic survey of North American Suzuki teachers. The previous article in this series examined some of the perceived challenges of group class. In this article, we will review teachers' descriptions of the parent education offerings within their studios. Teachers were asked to provide information about the structure, content, and intensity of their parent education programs. The survey questions included both initial education for new families entering their studios, as well as ongoing education for returning families
International Research Symposium on Talent Education, Part 4: The joys and benefits of Suzuki group class
This is the fourth article in a series reporting the findings of a large-scale demographic study of Suzuki teachers in Canada and the United States. Previous articles introduced the research, reporting on basic demographic statistics, teacher training, studio size, and structure of group classes. In this article we report on the results of an open-ended response question regarding the benefits of student participation in Suzuki group class
Effects of tidal interactions on the gas flows of elliptical galaxies
During a Hubble time, cluster galaxies may undergo several mutual encounters
close enough to gravitationally perturb their hot, X-ray emitting gas flows. We
ran several 2D, time dependent hydrodynamical models to investigate the effects
of such perturbations on the gas flow inside elliptical galaxies. In
particular, we studied in detail the modifications occurring in the scenario
proposed by D'Ercole et al. (1989), in which the galactic interstellar medium
produced by the aging galactic stellar population, is heated by SNIa at a
decreasing rate. We find that, although the tidal interaction in our models
lasts less than 1 Gyr, its effect extends over several Gyrs. The tidally
induced turbulent flows create dense filaments which cool quickly and accrete
onto the galactic center, producing large spikes in the global Lx. Once this
mechanism starts, it is fed by gravity and amplified by SNIa. In cooling flow
models without supernovae the amplitude of the Lx fluctuations due to the tidal
interaction is substantially reduced. We conclude that, if SNIa significantly
contribute to the energetics of the gas flows in ellipticals, then the observed
spread in the Lx-Lb diagram may be caused, at least in part, by this mechanism.
On the contrary, tidal interactions cannot be responsible for the observed
spread if the pure cooling flow scenario applies (abridged).Comment: 21 pages, 8 figures, to be published in ApJ (main journal
International Research Symposium on Talent Education, Part 3: What do Suzuki studios look like?
This is the third article in a series reporting the findings of a large-scale demographic study of 1128 North American SAA member teachers. The first article introduced the International Research Symposium on Talent Education and the group's current research interests. The second installment in the series focused on Suzuki teachers and included basic demographic information and information on teachers' training. In this article, we will explore what Suzuki studios look like, examining data such as studio size and structure of group classes
The effect of swimming on oral health status: competitive versus non-competitive athletes
Constraints on mass loss and self-enrichment scenarios for the globular clusters of the Fornax dSph
Recently, high-dispersion spectroscopy has demonstrated conclusively that
four of the five globular clusters (GCs) in the Fornax dwarf spheroidal galaxy
are very metal-poor with [Fe/H]<-2. The remaining cluster, Fornax 4, has
[Fe/H]=-1.4. This is in stark contrast to the field star metallicity
distribution which shows a broad peak around [Fe/H]=-1 with only a few percent
of the stars having [Fe/H]<-2. If we only consider stars and clusters with
[Fe/H]<-2 we thus find an extremely high GC specific frequency, SN=400,
implying by far the highest ratio of GCs to field stars known anywhere. We
estimate that about 1/5-1/4 of all stars in the Fornax dSph with [Fe/H]<-2
belong to the four most metal-poor GCs. These GCs could, therefore, at most
have been a factor of 4-5 more massive initially. Yet, the Fornax GCs appear to
share the same anomalous chemical abundance patterns known from Milky Way GCs,
commonly attributed to the presence of multiple stellar generations within the
clusters. The extreme ratio of metal-poor GC- versus field stars in the Fornax
dSph is difficult to reconcile with scenarios for self-enrichment and early
evolution of GCs in which a large fraction (90%-95%) of the first-generation
stars have been lost. It also suggests that the GCs may not have formed as part
of a larger population of now disrupted clusters with an initial power-law mass
distribution. The Fornax dSph may be a rosetta stone for constraining theories
of the formation, self-enrichment and early dynamical evolution of star
clusters.Comment: 4 pages, 2 figures, accepted for A&A Letter
Rapidly rotating second-generation progenitors for the blue hook stars of {\omega} Cen
Horizontal Branch stars belong to an advanced stage in the evolution of the
oldest stellar galactic population, occurring either as field halo stars or
grouped in globular clusters. The discovery of multiple populations in these
clusters, that were previously believed to have single populations gave rise to
the currently accepted theory that the hottest horizontal branch members (the
blue hook stars, which had late helium-core flash ignition, followed by deep
mixing) are the progeny of a helium-rich "second generation" of stars. It is
not known why such a supposedly rare event (a late flash followed by mixing) is
so common that the blue hook of {\omega} Cen contains \sim 30% of horizontal
branch stars 10 , or why the blue hook luminosity range in this massive cluster
cannot be reproduced by models. Here we report that the presence of helium core
masses up to \sim 0.04 solar masses larger than the core mass resulting from
evolution is required to solve the luminosity range problem. We model this by
taking into account the dispersion in rotation rates achieved by the
progenitors, whose premain sequence accretion disc suffered an early disruption
in the dense environment of the cluster's central regions where
second-generation stars form. Rotation may also account for frequent
late-flash-mixing events in massive globular clusters.Comment: 44 pages, 8 figures, 2 tables in Nature, online june 22, 201
A New View of the Circumstellar Environment of SN 1987A
We summarize the analysis of a uniform set of both previously-known and
newly-discovered scattered-light echoes, detected within 30" of SN 1987A in ten
years of optical imaging, and with which we have constructed the most complete
three-dimensional model of the progenitor's circumstellar environment.
Surrounding the SN is a richly-structured bipolar nebula. An outer,
double-lobed ``peanut,'' which we believe is the contact discontinuity between
the red supergiant and main sequence winds, is a prolate shell extending 28 ly
along the poles and 11 ly near the equator. Napoleon's Hat, previously believed
to be an independent structure, is the waist of this peanut, which is pinched
to a radius of 6 ly. Interior, the innermost circumstellar material lies along
a cylindrical hourglass, 1 ly in radius and 4 ly long, which connects to the
peanut by a thick equatorial disk. The nebulae are inclined 41o south and 8o
east of the line of sight, slightly elliptical in cross section, and marginally
offset west of the SN. The 3-D geometry of the three circumstellar rings is
studied, suggesting the equatorial ring is elliptical (b/a<0.98), and spatially
offset in the same direction as the hourglass. Dust-scattering models suggest
that between the hourglass and bipolar lobes: the gas density drops from 1--3
cm^{-3} to >0.03 cm^{-3}; the maximum dust-grain size increases from ~0.2
micron to 2 micron; and the Si:C dust ratio decreases. The nebulae have a total
mass of ~1.7 Msun, yielding a red-supergiant mass loss around 5*10^{-6} Msun
yr^{-1}.Comment: Accepted for publication in ApJ 2/14/05. 16 pages in emualteapj
forma
Building the Galactic halo from globular clusters: evidence from chemically unusual red giants
We present a spectroscopic search for halo field stars that originally formed
in globular clusters. Using moderate-resolution SDSS-III/SEGUE-2 spectra of 561
red giants with typical halo metallicities (-1.8 < [Fe/H] < -1.0), we identify
16 stars, 3% of the sample, with CN and CH bandstrength behavior indicating
depleted carbon and enhanced nitrogen abundances relative to the rest of the
data set. Since globular clusters are the only environment known in which stars
form with this pattern of atypical light-element abundances, we claim that
these stars are second-generation globular cluster stars that have been lost to
the halo field via normal cluster mass-loss processes. Extrapolating from
theoretical models of two-generation globular cluster formation, this result
suggests that globular clusters contributed significant numbers of stars to the
construction of the Galactic halo: we calculate that a minimum of 17% of the
present-day mass of the stellar halo was originally formed in globular
clusters. The ratio of CN-strong to CN-normal stars drops with Galactocentric
distance, suggesting that the inner-halo population may be the primary
repository of these stars.Comment: 9 pages including 8 figures, A&A accepte
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