128 research outputs found
Multiliteracies, Pedagogy and Identities:Teacher and Student Voices from a Toronto Elementary School
In this article, I draw on an ethnographic case study of one Toronto elementary school, as part of a Canadaâwide action research project: Multiliteracy Project (www.multiliteracies.ca). I have explored how Perminder, a gradeâ4 teacher, develâ oped a multiliteracies pedagogy, drawing on her own and her studentsâ identities and linguistic and cultural forms of capital to create learning opportunities for all students to access the English mainstream curriculum. Alternative pedagogical choices inâ cluded studentsâ creation of multimodal dual language âidentity textsâ (Cummins, Bismilla, Cohen, Giampapa, & Leoni, 2005a), and identity work, expanding literacy practices valued within Canadian classrooms. Key words: critical pedagogies, critical literacies, ESL/EAL, identities, Multilitâ eracy Project, urban schools Dans cet article, lâauteure part dâune Ă©tude de cas ethnographique portant sur une Ă©cole primaire de Toronto, Ă©tude rĂ©alisĂ©e dans le cadre dâun projet de rechercheâ action pancanadien, The Multiliteracy Project (www.multiliteracies.ca). Elle analyse comment Perminder, une enseignante de 4e annĂ©e, a mis au point une pĂ©dagogie en matiĂšre de multilitĂ©raties. Puisant dans sa propre identitĂ© et dans celles de ses Ă©lĂšves ainsi que dans diverses formes de capital linguistiques et culturelles, elle offre Ă tous ses Ă©lĂšves la possibilitĂ© dâapprendre et ainsi dâavoir accĂšs au curriculum standard en anglais. Parmi les choix pĂ©dagogiques novateurs figuraient la crĂ©ation par les Ă©lĂšves de « textes identitaires » (Cummins et coll. 2005a) multimodaux en deux langues et des travaux portant sur lâidentitĂ©, Ă©largissant ainsi les pratiques en matiĂšre de littĂ©raâ tie jugĂ©es utiles dans les classes canadiennes. Mots clĂ©s : pĂ©dagogies critiques, littĂ©raties critiques, ESL/EAL, identitĂ©s, The Multiliteracy Project, Ă©coles urbaines.
Fluxes in H\alpha and Ca II H and K for a sample of Southern stars
The main chromospheric activity indicator is the S index, which is esentially
the ratio of the flux in the core of the Ca II H and K lines to the continuum
nearby, and is well studied basically for stars from F to K. Another usual
chromospheric proxy is the H\alpha line, which is beleived to be tightly
correlated with the Ca II index. In this work we characterize both
chromospheric activity indicators, one associated with the H and K Ca II lines
and the other with H\alpha, for the whole range of late type stars, from F to
M. We present periodical medium-resolution echelle observations covering the
complete visual range, which were taken at the CASLEO Argentinean Observatory.
These observations are distributed along 7 years. We use a total of 917
flux-calibrated spectra for 109 stars which range from F6 to M5. We
statistically study these two indicators for stars of different activity levels
and spectral types. We directly derive the conversion factor which translate
the known S index to flux in the Ca II cores, and extend its calibration to a
wider spectral range. We investigate the relation between the activity
measurements in the calcium and hydrogen lines, and found that the usual
correlation observed is basically the product of the dependence of each flux
with stellar colour, and not the product of similar activity phenomena.Comment: 12 pages, including 11 figures and 2 tables. Accepted for publication
in Astronomy and Astrophysic
GJ 900: A new hierarchical system with low-mass components
Speckle interferometric observations made with the 6 m telescope of the
Special Astrophysical Observatory of the Russian Academy of Sciences in 2000
revealed the triple nature of the nearby ( mas)
low-mass young ( Myr) star GJ 900. The configuration of the triple
system allowed it to be dynamically unstable. Differential photometry performed
from 2000 through 2004 yielded - and -band absolute magnitudes and
spectral types for the components to be =6.660.08,
=9.150.11, =10.080.26, =4.840.08,
=6.760.20, =7.390.31, K5--K7,
M3--M4, M5--M6. The ``mass--luminosity''
relation is used to estimate the individual masses of the components:
,
,
. From the observations of the
components relative motion in the period 2000--2006, we conclude that GJ 900 is
a hierarchical triple star with the possible orbital periods
P80 yrs and P20 yrs. An analysis of the 2MASS
images of the region around GJ 900 leads us to suggest that the system can
include other very-low-mass components.Comment: 7 pages, 5 figure
Powerful Winds from Low-Mass Stars: V374 Peg
The rapid rotation (P=0.44 d) of the M dwarf V374Peg (M4) along with its
intense magnetic field point toward magneto-centrifugal acceleration of a
coronal wind. In this work, we investigate the structure of the wind of V374Peg
by means of 3D magnetohydrodynamical (MHD) numerical simulations. For the first
time, an observationally derived surface magnetic field map is implemented in
MHD models of stellar winds for a low mass star. We show that the wind of
V374Peg deviates greatly from a low-velocity, low-mass-loss rate solar-type
wind. We find general scaling relations for the terminal velocities, mass-loss
rates, and spin-down times of highly magnetized M dwarfs. In particular, for
V374Peg, our models show that terminal velocities across a range of stellar
latitudes reach ~(1500-2300) n_{12}^{-1/2} km/s, where n_{12} is the coronal
wind base density in units of 10^{12} cm^{-3}, while the mass-loss rates are
about 4 x 10^{-10} n_{12}^{1/2} Msun/yr. We also evaluate the angular-momentum
loss of V374Peg, which presents a rotational braking timescale ~28
n_{12}^{-1/2} Myr. Compared to observationally derived values from period
distributions of stars in open clusters, this suggests that V374Peg may have
low coronal base densities (< 10^{11} cm^{-3}). We show that the wind ram
pressure of V374Peg is about 5 orders of magnitude larger than for the solar
wind. Nevertheless, a small planetary magnetic field intensity (~ 0.1G) is able
to shield a planet orbiting at 1 AU against the erosive effects of the stellar
wind. However, planets orbiting inside the habitable zone of V374Peg, where the
wind ram pressure is higher, might be facing a more significant atmospheric
erosion. In that case, higher planetary magnetic fields of, at least, about
half the magnetic field intensity of Jupiter, are required to protect the
planet's atmosphere.Comment: 13 pages, 5 figures, 1 table. MNRAS in pres
The GAPS programme at TNG XXII. The GIARPS view of the extended helium atmosphere of HD189733 b accounting for stellar activity
Exoplanets orbiting very close to their host star are strongly irradiated.
This can lead the upper atmospheric layers to expand and evaporate into space.
The metastable helium (HeI) triplet at 1083.3nm has recently been shown to be a
powerful diagnostic to probe extended and escaping exoplanetary atmosphere. We
perform high-resolution transmission spectroscopy of the transiting hot Jupiter
HD189733b with the GIARPS (GIANO-B + HARPS-N) observing mode of the Telescopio
Nazionale Galileo, taking advantage of the simultaneous optical+near infrared
spectral coverage to detect HeI in the planet's extended atmosphere and to
gauge the impact of stellar magnetic activity on the planetary absorption
signal. Observations were performed during five transit events of HD189733b. By
comparison of the in- and out-of-transit GIANO-B observations we compute
high-resolution transmission spectra, on which we perform equivalent width
measurements and light-curves analyses to gauge the excess in-transit
absorption in the HeI triplet. We detect an absorption signal during all five
transits. The mean in-transit absorption depth amounts to 0.75+/-0.03%. We
detect night-to-night variations in the HeI absorption signal likely due to the
transit events occurring in presence of stellar surface inhomogeneities. We
evaluate the impact of stellar-activity pseudo-signals on the true planetary
absorption using a comparative analysis of the HeI and the H lines. We
interpret the time-series of the HeI absorption lines in the three nights not
affected by stellar contamination -exhibiting a mean in-transit absorption
depth of 0.77+/-0.04%- using a 3-d atmospheric code. Our simulations suggest
that the helium layers only fill part of the Roche lobe. Observations can be
explained with a thermosphere heated to 12000 K, expanding up to
1.2 planetary radii, and losing 1 g/s of metastable helium.Comment: 17 pages, 17 figures, accepted for publication in A&
RACE-OC Project: Rotation and variability in the epsilon Chamaeleontis, Octans, and Argus stellar associations
We aim at determining the rotational and magnetic-related activity properties
of stars at different stages of evolution. We focus our attention primarily on
members of young stellar associations of known ages. Specifically, we extend
our previous analysis in Paper I (Messina et al. 2010, A&A 520, A15) to 3
additional young stellar associations beyond 100 pc and with ages in the range
6-40 Myr: epsilon Chamaeleontis (~6 Myr), Octans (~20 Myr), and Argus (~40
Myr). Additional rotational data of eta Chamaeleontis and IC2391 clusters are
also considered. Rotational periods were determined from photometric
time-series data obtained by the All Sky Automated Survey (ASAS) and the Wide
Angle Search for Planets (SuperWASP) archives. With the present study we have
completed the analysis of the rotational properties of the late-type members of
all known young loose associations in the solar neighborhood. Considering also
the results of Paper I, we have derived the rotation periods of 241 targets:
171 confirmed, 44 likely, 26 uncertain. The period of the remaining 50 stars
known to be part of loose associations still remains unknown. This rotation
period catalogue, and specifically the new information presented in this paper
at ~6, 20, and 40 Myr, contributes significantly to a better observational
description of the angular momentum evolution of young stars.Comment: Accepted by Astronomy & Astrophysics. Onlines figures will be
available at CD
Detection of the lithium depletion boundary in the young open cluster IC 4665
The so-called lithium depletion boundary (LDB) provides a secure and
independent tool for deriving the ages of young open clusters.In this context,
our goal is to determine membership for a sample of 147 photometrically
selected candidates of the young open cluster IC 4665 and to use confirmed
members to establish an age based on the LDB. Employing the FLAMES multi-object
spectrograph on VLT/UT2, we have obtained intermediate-resolution spectra of
the cluster candidates. The spectra were used to measure radial velocities and
to infer the presence of the Li I 670.8 nm doublet and Halpha emission. We have
identified 39 bona fide cluster members based on radial velocity, Halpha
emission, and Li absorption. The mean radial velocity of IC 4665 is found to be
vrad=-15.95 +/- 1.13 km/s. Confirmed cluster members display a sharp transition
in magnitude between stars with and without lithium, both in the Im vs. Im-z
and in the Ks vs. Im-Ks diagrams.From this boundary, we deduce a cluster age of
27.7^(+4.2)_(-3.5) +/- 1.1 +/- 2 Myr. IC 4665 is the fifth cluster for which an
LDB age has been determined, and it is the youngest cluster among these five.
Thus, the LDB is established from relatively bright stars still in the
contracting pre-main sequence phase. The mass of the boundary is M*=0.24 +/-
0.04 Msun. The LDB age agrees well with the ages derived from isochrone fitting
of both low and high mass, turn-off stars, a result similar to what is found in
the slightly older NGC 2547.Comment: 13 pages, A&A in pres
Museum education, cultural sustainability, and English language teaching in Spain
The collaborative action research project presented analysed the potential of museum education to radically transform the way in which English was taught and learnt in three diverse elementary, middle, and high-school contexts in the province of ValĂšncia (Spain). Insights from museum education and New Literacy Studies were used to expand upon the pedagogical affordances of the material and multimodal dimensions of English language teaching, in order to generate more opportunities for student motivation and engagement by connecting with the learners' home and community cultures, identities, languages, and literacies. To assess the impact of the project, a variety of qualitative strategies were used (including classroom recordings, student interviews and questionnaires, and photographs). A model for culturally sustaining pedagogy was suggested, which school and museum educators may use to inform their practice
The age-mass-metallicity-activity relation for solar-type stars: comparisons with asteroseismology and the NGC 188 open cluster
Context. The Mount Wilson Caâii index log is the accepted standard metric of calibration for the chromospheric activity versus age relation for FGK stars. Recent results claim its inability to discern activity levels, and thus ages, for stars older than ~2 Gyr, which would severely hamper its application to date disk stars older than the Sun.
Aims. We present a new activity-age calibration of the Mt. Wilson index that explicitly takes mass and [Fe/H] biases into account; these biases are implicit in samples of stars selected to have precise ages, which have so far not been appreciated.
Methods. We show that these selection biases tend to blur the activity-age relation for large age ranges. We calibrate the Mt. Wilson index for a sample of field FGK stars with precise ages, covering a wide range of mass and [Fe/H] , augmented with data from the Pleiades, Hyades, Mâ67 clusters, and the Ursa Major moving group.
Results. We further test the calibration with extensive new Gemini/GMOS log ()R'HK) data of the old, solar [Fe/H] clusters, Mâ67 and NGC 188. The observed NGC 188 activity level is clearly lower than Mâ67. We correctly recover the isochronal age of both clusters and establish the viability of deriving usable chromospheric ages for solar-type stars up to at least ~6 Gyr, where average errors are ~0.14 dex provided that we explicitly account for the mass and [Fe/H] dimensions. We test our calibration against asteroseismological ages, finding excellent correlation (Ï = + 0.89). We show that our calibration improves the chromospheric age determination for a wide range of ages, masses, and metallicities in comparison to previous age-activity relations
X-Ray Spectroscopy of Stars
(abridged) Non-degenerate stars of essentially all spectral classes are soft
X-ray sources. Low-mass stars on the cooler part of the main sequence and their
pre-main sequence predecessors define the dominant stellar population in the
galaxy by number. Their X-ray spectra are reminiscent, in the broadest sense,
of X-ray spectra from the solar corona. X-ray emission from cool stars is
indeed ascribed to magnetically trapped hot gas analogous to the solar coronal
plasma. Coronal structure, its thermal stratification and geometric extent can
be interpreted based on various spectral diagnostics. New features have been
identified in pre-main sequence stars; some of these may be related to
accretion shocks on the stellar surface, fluorescence on circumstellar disks
due to X-ray irradiation, or shock heating in stellar outflows. Massive, hot
stars clearly dominate the interaction with the galactic interstellar medium:
they are the main sources of ionizing radiation, mechanical energy and chemical
enrichment in galaxies. High-energy emission permits to probe some of the most
important processes at work in these stars, and put constraints on their most
peculiar feature: the stellar wind. Here, we review recent advances in our
understanding of cool and hot stars through the study of X-ray spectra, in
particular high-resolution spectra now available from XMM-Newton and Chandra.
We address issues related to coronal structure, flares, the composition of
coronal plasma, X-ray production in accretion streams and outflows, X-rays from
single OB-type stars, massive binaries, magnetic hot objects and evolved WR
stars.Comment: accepted for Astron. Astrophys. Rev., 98 journal pages, 30 figures
(partly multiple); some corrections made after proof stag
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