1,286 research outputs found
The Mass-Loss Return From Evolved Stars to The Large Magellanic Cloud VI: Luminosities and Mass-Loss Rates on Population Scales
We present results from the first application of the Grid of Red Supergiant
and Asymptotic Giant Branch ModelS (GRAMS) model grid to the entire evolved
stellar population of the Large Magellanic Cloud (LMC). GRAMS is a pre-computed
grid of 80,843 radiative transfer (RT) models of evolved stars and
circumstellar dust shells composed of either silicate or carbonaceous dust. We
fit GRAMS models to ~30,000 Asymptotic Giant Branch (AGB) and Red Supergiant
(RSG) stars in the LMC, using 12 bands of photometry from the optical to the
mid-infrared. Our published dataset consists of thousands of evolved stars with
individually determined evolutionary parameters such as luminosity and
mass-loss rate. The GRAMS grid has a greater than 80% accuracy rate
discriminating between Oxygen- and Carbon-rich chemistry. The global dust
injection rate to the interstellar medium (ISM) of the LMC from RSGs and AGB
stars is on the order of 1.5x10^(-5) solar masses/yr, equivalent to a total
mass injection rate (including the gas) into the ISM of ~5x10^(-3) solar
masses/yr. Carbon stars inject two and a half times as much dust into the ISM
as do O-rich AGB stars, but the same amount of mass. We determine a bolometric
correction factor for C-rich AGB stars in the K band as a function of J - K
color, BC(K) = -0.40(J-K)^2 + 1.83(J-K) + 1.29. We determine several IR color
proxies for the dust mass-loss rate (MLR) from C-rich AGB stars, such as log
(MLR) = (-18.90)/((K-[8.0])+3.37)-5.93. We find that a larger fraction of AGB
stars exhibiting the `long-secondary period' phenomenon are O-rich than stars
dominated by radial pulsations, and AGB stars without detectable mass-loss do
not appear on either the first-overtone or fundamental-mode pulsation
sequences.Comment: 19 pages, 19 figure
Imagining the Possible: Reflections on Teaching a Writing Methods Course for Pre-Service Undergraduate Secondary English/Language Arts Teachers
What\u27s possible in a teaching writing methods class? In this essay, the author provides a descriptive portrait of the undergraduate secondary writing methods course she teaches, focusing on five specific learning outcomes: teacher writing identities, knowledge of writer\u27s craft, grammatical awareness and an understanding of linguistic justice/injustice, writing workshop methodology, and genre-based unit and lesson planning. Course readings, assignments, and work samples are included
Keeping Things Going: Reflections on Teaching âTeaching Writingâ Online
What does it mean to âkeep things going onlineâ in an undergraduate teacher education course on teaching writing? In this article, a teacher educator describes how, in consultation with her students, she adapted a secondary English methods course on teaching writing to teach it online. While highlighting and celebrating what worked, she also reflects on lessons learned and teaching questions that continue to persist
Morphological Properties of PPNs: Mid-IR and HST Imaging Surveys
We will review our mid-infrared and HST imaging surveys of the circumstellar
dust shells of proto-planetary nebulae. While optical imaging indirectly probes
the dust distribution via dust-scattered starlight, mid-IR imaging directly
maps the distribution of warm dust grains. Both imaging surveys revealed
preferencially axisymmetric nature of PPN dust shells, suggesting that
axisymmetry in planetary nebulae sets in by the end of the asymptotic giant
branch phase, most likely by axisymmetric superwind mass loss. Moreover, both
surveys yielded two morphological classes which have one-to-one correspondence
between the two surveys, indicating that the optical depth of circumstellar
dust shells plays an equally important role as the inclination angle in
determining the morphology of the PPN shells.Comment: 6 pages + 8 figures, to appear in the proceedings of the conference,
"Post-AGB Objects (proto-planetary nebulae) as a Phase of Stellar Evolution",
Torun, Poland, July 5-7, 2000, eds. R. Szczerba, R. Tylenda, and S.K. Gorny.
Figures have been degraded to minimize the total file siz
Helping Students Choose a Reading Frame: Three Ways of Teaching Jacqueline Woodsonâs Harbor Me
Choice and autonomy in ways of reading are just as important as choice and autonomy in what to read. Teaching students different frames for reading novels provides students with essential tools for making meaning of texts. This article explores three frames using the middle grade novel Harbor Me
CO J = 2 - 1 Emission from Evolved Stars in the Galactic Bulge
We observe a sample of 8 evolved stars in the Galactic Bulge in the CO J = 2
- 1 line using the Submillimeter Array (SMA) with angular resolution of 1 - 4
arcseconds. These stars have been detected previously at infrared wavelengths,
and several of them have OH maser emission. We detect CO J = 2 - 1 emission
from three of the sources in the sample: OH 359.943 +0.260, [SLO2003] A12, and
[SLO2003] A51. We do not detect the remaining 5 stars in the sample because of
heavy contamination from the galactic foreground CO emission. Combining CO data
with observations at infrared wavelengths constraining dust mass loss from
these stars, we determine the gas-to-dust ratios of the Galactic Bulge stars
for which CO emission is detected. For OH 359.943 +0.260, we determine a gas
mass-loss rate of 7.9 (+/- 2.2) x 10^-5 M_Sun/year and a gas-to-dust ratio of
310 (+/- 89). For [SLO2003] A12, we find a gas mass-loss rate of 5.4 (+/- 2.8)
x 10^-5 M_Sun/year and a gas-to-dust ratio of 220 (+/- 110). For [SLO2003] A51,
we find a gas mass-loss rate of 3.4 (+/- 3.0) x 10^-5 M_Sun/year and a
gas-to-dust ratio of 160 (+/- 140), reflecting the low quality of our tentative
detection of the CO J = 2 - 1 emission from A51. We find the CO J = 2 - 1
detections of OH/IR stars in the Galactic Bulge require lower average CO J = 2
- 1 backgrounds.Comment: 40 pages, 16 figures, appeared in the 1 March 2013 issue of the
Astrophysical Journa
GEOGRAPHIC VARIATION WITHIN Apis koschevnikovi BUTTEL-REEPEN, 1906, IN BORNEO
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