1,465 research outputs found
Creative Learning: A Curriculum for Preprimary Children. Unit 8, Dinosaur Era and Fossils
DINOSAUR ERA AND FOSSILS is one resource unit. It is hoped to serve as a resource to others as they guide the learning of young children. It is not a cut-and-dried, how-to-do-it book. But it is a collection of numerous learning experiences within the context of a unit setting. The various disciplines are not, and cannot, be separated; learning overlaps. With a central theme, young children will have many opportunities to examine, investigate, explore, experience and discover concepts of meaning. As the children approach the same concept from a number of experiences, they will have opportunities to formulate ideas, to test these ideas for validity and meaning, and to draw conclusions relevant for them
Cold Dust in Kepler's Supernova Remnant
The timescales to replenish dust from the cool, dense winds of Asymptotic
Giant Branch stars are believed to be greater than the timescales for dust
destruction. In high redshift galaxies, this problem is further compounded as
the stars take longer than the age of the Universe to evolve into the dust
production stages. To explain these discrepancies, dust formation in supernovae
(SNe) is required to be an important process but until very recently dust in
supernova remnants has only been detected in very small quantities. We present
the first submillimeter observations of cold dust in Kepler's supernova remnant
(SNR) using SCUBA. A two component dust temperature model is required to fit
the Spectral Energy Distribution (SED) with K and K. The total mass of dust implied for Kepler is -
1000 times greater than previous estimates. Thus SNe, or their progenitors may
be important dust formation sites.Comment: 12 pages, 2 figures, accepted to ApJL, corrected proof
The role of reproductive timing as a driver of genetic differentiation in populations of Pacific herring
There is growing recognition that maintaining diversity in life history traits contributes to the sustainable management of wild populations. One important life history characteristic is reproductive phenology, and it has been shown that differences in the timing of reproduction can act as a barrier to gene flow between populations. If the difference in reproductive timing determines the level of connectivity, one would expect that genetic differentiation between populations would increase as a function of difference in reproductive date. This pattern, known as “isolation by time” (IBT), has been observed in wild populations of salmonids containing early and late runs. Pacific herring in the Salish Sea also exhibit a wide diversity of spawn times; some populations start reproducing as early as January and reproductive activity in the region continues through May. Here, we test whether these temporal differences in reproduction influence the genetic population structure of herring. We collected adult herring from seven different locations in the Salish Sea during active spawning events (N = 48 per site). Samples were sequenced using a restriction site-associated (RAD) approach and approximately 3,000 polymorphic loci were genotyped in each sample. We found a positive correlation between genetic differentiation and difference in spawn date, with evidence of migration between populations with similar spawn timing. Several loci exhibited exceptionally steep gradients in allele frequencies, including one locus linked to the photoperiodic regulation of reproduction. Our discovery of IBT in Pacific herring support the adaptive significance of spawn timing and underscore the importance of conserving spawning time diversity in Puget Sound herring
An S-shaped outflow from IRAS 03256+3055 in NGC 1333
The IRAS source 03256+3055 in the NGC 1333 star forming region is associated
with extended sub-millimeter emission of complex morphology, showing multiple
clumps. One of these is found to coincide with the driving source of a bipolar
jet of S-shaped morphology seen in the emission lines of H_alpha and [SII] as
well as in the H2 emission lines in the K-band. Detailed images of the driving
source at the wavelengths of H_alpha and [SII] and in the I, J, H, and K bands
as well as a K-band spectrum and polarimetry are discussed. The near-infrared
morphology is characterized by a combination of line emission from the jet and
scattered light from a source with a steep continuum spectrum. The morphology
and proper motion of the jet are discussed in the context of a binary system
with a precessing disk. We conclude that the molecular core associated with
IRAS 03256+3055 consists of several clumps, only one of which shows evidence of
recent star formation at optical and near-infrared wavelengths.We also briefly
discuss a second, newly found near-infrared source associated with a compact
sub-millimeter continuum source near IRAS 03256+3055, and conclude that this
source may be physically unrelated the cluster of molecular clumps.Comment: 25 pages, including 5 figures. Accepted for publication in The
Astronomical Journa
A Submillimeter Study of the Star-Forming Region NGC7129
New molecular (13CO J=3-2) and dust continuum (450 and 850 micron) SCUBA maps
of the NGC7129 star forming region are presented, complemented by C18O J=3-2
spectra at several positions within the mapped region. The maps include the
Herbig Ae/Be star LkHalpha 234, the far-infrared source NGC 7129 FIRS2 and
several other pre-stellar sources embedded within the molecular ridge.
The SCUBA maps help us understand the nature of the pre-main sequence stars
in this actively star forming region. A deeply embedded submillimeter source,
SMM2, not clearly seen in any earlier data set, is shown to be a pre-stellar
core or possibly a protostar. The highest continuum peak emission is identified
with the deeply embedded source IRS6, a few arcseconds away from LkHalpha 234,
and also responsible for both the optical jet and the molecular outflow. The
gas and dust masses are found to be consistent, suggesting little or no CO
depletion onto grains. The dust emissivity index is lower towards the dense
compact sources, beta ~1 - 1.6, and higher, beta ~ 2.0, in the surrounding
cloud, implying small size grains in the PDR ridge, whose mantles have been
evaporated by the intense UV radiation.Comment: Accepted by Ap
The Hot Inner Disk of FU Ori
We have constructed a detailed radiative transfer disk model which reproduces
the main features of the spectrum of the outbursting young stellar object FU
Orionis from ~ 4000 angstrom, to ~ 8 micron. Using an estimated visual
extinction Av~1.5, a steady disk model with a central star mass ~0.3 Msun and a
mass accretion rate ~ 2e-4 Msun/yr, we can reproduce the spectral energy
distribution of FU Ori quite well. With the mid-infrared spectrum obtained by
the Infrared Spectrograph (IRS) on board the Spitzer Space Telescope, we
estimate that the outer radius of the hot, rapidly accreting inner disk is ~ 1
AU using disk models truncated at this outer radius. Inclusion of radiation
from a cooler irradiated outer disk might reduce the outer limit of the hot
inner disk to ~ 0.5 AU. In either case, the radius is inconsistent with a pure
thermal instability model for the outburst. Our radiative transfer model
implies that the central disk temperature Tc > 1000 K out to ~ 0.5 - 1 AU,
suggesting that the magnetorotational instability (MRI) can be supported out to
that distance. Assuming that the ~ 100 yr decay timescale in brightness of FU
Ori represents the viscous timescale of the hot inner disk, we estimate the
viscosity parameter (alpha) to be ~ 0.2 - 0.02 in the outburst state,
consistent with numerical simulations of MRI in disks. The radial extent of the
high mass accretion region is inconsistent with the model of Bell & Lin, but
may be consistent with theories incorporating both gravitational instability
and MRI.Comment: 32 pages, 10 figures, to appear in the Astrophysical Journa
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