4,267 research outputs found
A Study of Juvenile Waiver
In a footnote to its recent decision, In re Dennis M, the California Supreme Court recommended, that juvenile officers and police be prepared to give their compulsory Miranda warning in terms that reflect the language and experience of today’s juveniles. This language stimulated our attempt to draft and test the efficacy of a simplified Miranda warning, potentially more understandable to juveniles, and consistent with juvenile law requirements. The purpose of this article is to relate the findings of an empirical study which sought to answer two questions: 1) should the Miranda warning be revised for the juvenile offender; and 2) does a minor have the capacity knowingly and intelligently to waive his Miranda rights
Far-UV Emission from Elliptical Galaxies at z=0.55
The restframe UV-to-optical flux ratio, characterizing the ``UV upturn''
phenomenon, is potentially the most sensitive tracer of age in elliptical
galaxies; models predict that it may change by orders of magnitude over the
course of a few Gyr. In order to trace the evolution of the UV upturn as a
function of redshift, we have used the far-UV camera on the Space Telescope
Imaging Spectrograph to image the galaxy cluster CL0016+16 at z=0.55. Our
25''x25'' field includes four bright elliptical galaxies, spectroscopically
confirmed to be passively evolving cluster members. The weak UV emission from
the galaxies in our image demonstrates that the UV upturn is weaker at a
lookback time 5.6 Gyr earlier than our own, as compared to measurements of the
UV upturn in cluster E and S0 galaxies at z=0 and z=0.375. These images are the
first with sufficient depth to demonstrate the fading of the UV upturn expected
at moderate redshifts. We discuss these observations and the implications for
the formation history of galaxies.Comment: 4 pages, Latex. 2 figures. Uses corrected version of emulateapj.sty
and apjfonts.sty (included). Accepted for publication in ApJ Letter
Pearls of Elschnig
This is a Photo Essay and does not contain an abstract
Far-Ultraviolet Emission from Elliptical Galaxies at z=0.33
We present far-ultraviolet (far-UV) images of the rich galaxy cluster
ZwCl1358.1+6245, taken with the Space Telescope Imaging Spectrograph on board
the Hubble Space Telescope (HST). When combined with archival HST observations,
our data provide a measurement of the UV-to-optical flux ratio in 8 early-type
galaxies at z=0.33. Because the UV flux originates in a population of evolved,
hot, horizontal branch (HB) stars, this ratio is potentially one of the most
sensitive tracers of age in old populations -- it is expected to fade rapidly
with lookback time. We find that the UV emission in these galaxies, at a
lookback time of 3.9 Gyr, is significantly weaker than it is in the current
epoch, yet similar to that in galaxies at a lookback time of 5.6 Gyr. Taken at
face value, these measurements imply different formation epochs for the massive
ellipticals in these clusters, but an alternative explanation is a "floor" in
the UV emission due to a dispersion in the parameters that govern HB
morphology.Comment: 4 pages, Latex. 2 figures. Uses corrected version of emulateapj.sty
and apjfonts.sty (included). Accepted for publication in ApJ Letter
Fischer-Tropsch-Type Production of Organic Materials in the Solar Nebula: Studies Using Graphite Catalysts and Measuring the Trapping of Noble Gases
The formation of abundant carbonaceous material in meteorites is a long standing problem and an important factor in the debate on the potential for the origin of life in other stellar systems. The Fischer-Tropsch-type (FTT) catalytic reduction of CO by hydrogen was once the preferred model for production of organic materials in the primitive solar nebula. We have demonstrated that many grain surfaces can catalyze both FTT and HB-type reactions, including amorphous iron and magnesium silicates, pure silica smokes as well as several minerals. Graphite is not a particularly good FTT catalyst, especially compared to iron powder or to amorphous iron silicate. However, like other silicates that we have studied, it gets better with exposure to CO. N2 and H2 over time: e.g., after formation of a macromolecular carbonaceous layer on the surfaces of the underlying gains. While amorphous iron silicates required only 1 or 2 experimental runs to achieve steady state reaction rates, graphite only achieved steady state after 6 or more experiments. We will present results showing the catalytic action of graphite grains increasing with increasing number of experiments and will also discuss the nature of the final "graphite" grains aster completion of our experiments
The Dearth of UV-Bright Stars in M32: Implications for Stellar Evolution Theory
Using the Space Telescope Imaging Spectrograph on the Hubble Space Telescope,
we have obtained deep far-ultraviolet images of the compact elliptical galaxy
M32. When combined with earlier near-ultraviolet images of the same field,
these data enable the construction of an ultraviolet color-magnitude diagram of
the hot horizontal branch (HB) population and other hot stars in late phases of
stellar evolution. We find few post-asymptotic giant branch (PAGB) stars in the
galaxy, implying that these stars either cross the HR diagram more rapidly than
expected, and/or that they spend a significant fraction of their time
enshrouded in circumstellar material. The predicted luminosity gap between the
hot HB and its AGB-Manque (AGBM) progeny is less pronounced than expected,
especially when compared to evolutionary tracks with enhanced helium
abundances, implying that the presence of hot HB stars in this metal-rich
population is not due to (Delta Y)/(Delta Z) > 4. Only a small fraction (~2%)
of the HB population is hot enough to produce significant UV emission, yet most
of the UV emission in this galaxy comes from the hot HB and AGBM stars,
implying that PAGB stars are not a significant source of UV emission even in
those elliptical galaxies with a weak UV excess.Comment: Accepted for publication in The Astrophysical Journal. Latex, 18
pages, 18 black & white figures, in emulate-ApJ format. Figures 11 & 16 have
been degraded due to size constraints; the high-quality version of the paper
is at http://www.stsci.edu/~tbrown/research/m32fuv.pd
Stellar Models with Enhanced Abundances of C, N, O, Ne, Na, Mg, Si, S, Ca, and Ti, in Turn, at Constant Helium and Iron Abundances
Recent work has shown that most globular clusters have at least two
chemically distinct components, as well as cluster-to-cluster differences in
the mean [O/Fe], [Mg/Fe], and [Si/Fe] ratios at similar [Fe/H] values. In order
to investigate the implications of variations in the abundances of these and
other metals for H-R diagrams and predicted ages, grids of evolutionary
sequences have been computed for scaled solar and enhanced alpha-element
mixtures, and for mixtures in which the assumed [m/Fe] value for each of the
metals C, N, O, Ne, Na, Mg, Si, S, Ca, and Ti has been increased, in turn, by
0.4 dex at constant [Fe/H]. These tracks, together with isochrones for ages
from 6 to 14 Gyr, have been computed for -3.0 < [Fe/H] < -0.6, with helium
abundances Y = 0.25, 0.29, and 0.33 at each [Fe/H] value, using upgraded
versions of the Victoria stellar structure program and the Regina interpolation
code, respectively. Turnoff luminosity versus age relations from isochrones are
found to depend almost entirely on the importance of the CNO-cycle, and thereby
mainly on the abundance of oxygen. Since C, N, and O, as well as Ne and S, do
not contribute significantly to the opacities at low temperatures and
densities, variations in their abundances do not impact the Teff scale of red
giants. The latter is a strong function of the abundances of only Mg and Si
(and Fe, possibly to a lesser extent), because they are so abundant and because
they are strong sources of opacity at low temperatures. For these reasons, Mg
and Si also have important effects on the temperatures of main-sequence stars.
Due to their low abundances, Na, Ca, and Ti are of little consequence for
stellar models. The effects of varying the adopted solar metals mix and the
helium abundance at a fixed [Fe/H] are also briefly discussed.Comment: 27 pages, 18 figures; accepted and tentatively scheduled for
publication in ApJ, volume 755 (Aug 10, 2012 issue
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