77 research outputs found
Jewett, Town of and Laborers International Union of North America, Local 17
In the matter of Fact Finding Between Town of Jewett And Laborers International Union of North America, Local 17. PERB Case M2008-168. Before: Thomas B. Quimby, PERB-Appointed Fact Finder
Union-Management Training Programs in the Public Sector: The New York Experience
[Excerpt] New York State has a long history of union-management education and training programs, making it unique in public sector employment. This chapter examines the programs undertaken at both state and city levels, as well as the applicability of the New York experience to other public sector jurisdictions. Although the profile of the New York State and city work force differs from that of the rest of the nation, there is much of value here for educators, union leaders, and others involved in public sector employment
The Multiple Meanings of “Hybrid”: Studying Adult Student Experiences in Hybrid (Web-Enhanced) Classes While Learning How to do Qualitative Research
This paper has a two-fold or “hybrid” purpose: (1) to discuss the results of a qualitative study of adult students experiences of web-enhanced or hybrid classes, and (2) to briefly discuss the process of learning to do qualitative research while conducting this study in a qualitative research methods class
Type II Supernovae as Probes of Cosmology
- Constraining the cosmological parameters and understanding Dark Energy have
tremendous implications for the nature of the Universe and its physical laws.
- The pervasive limit of systematic uncertainties reached by cosmography
based on Cepheids and Type Ia supernovae (SNe Ia) warrants a search for
complementary approaches.
- Type II SNe have been shown to offer such a path. Their distances can be
well constrained by luminosity-based or geometric methods. Competing,
complementary, and concerted efforts are underway, to explore and exploit those
objects that are extremely well matched to next generation facilities.
Spectroscopic follow-up will be enabled by space- based and 20-40 meter class
telescopes.
- Some systematic uncertainties of Type II SNe, such as reddening by dust and
metallicity effects, are bound to be different from those of SNe Ia. Their
stellar progenitors are known, promising better leverage on cosmic evolution.
In addition, their rate - which closely tracks the ongoing star formation rate
- is expected to rise significantly with look- back time, ensuring an adequate
supply of distant examples.
- These data will competitively constrain the dark energy equation of state,
allow the determination of the Hubble constant to 5%, and promote our
understanding of the processes involved in the last dramatic phases of massive
stellar evolution.Comment: Science white paper, submitted to the Decadal committee Astro201
Hydrogen-poor superluminous stellar explosions
Supernovae (SNe) are stellar explosions driven by gravitational or
thermonuclear energy, observed as electromagnetic radiation emitted over weeks
or more. In all known SNe, this radiation comes from internal energy deposited
in the outflowing ejecta by either radioactive decay of freshly-synthesized
elements (typically 56Ni), stored heat deposited by the explosion shock in the
envelope of a supergiant star, or interaction between the SN debris and
slowly-moving, hydrogen-rich circumstellar material. Here we report on a new
class of luminous SNe whose observed properties cannot be explained by any of
these known processes. These include four new SNe we have discovered, and two
previously unexplained events (SN 2005ap; SCP 06F6) that we can now identify as
members. These SNe are all ~10 times brighter than SNe Ia, do not show any
trace of hydrogen, emit significant ultra-violet (UV) flux for extended periods
of time, and have late-time decay rates which are inconsistent with
radioactivity. Our data require that the observed radiation is emitted by
hydrogen-free material distributed over a large radius (~10^15 cm) and
expanding at high velocities (>10^4 km s^-1). These long-lived, UV-luminous
events can be observed out to redshifts z>4 and offer an excellent opportunity
to study star formation in, and the interstellar medium of, primitive distant
galaxies.Comment: Accepted to Nature. Press embargoed until 2011 June 8, 18:00 U
The Spectroscopic Diversity of Type Ia Supernovae
We present 2603 spectra of 462 nearby Type Ia supernovae (SN Ia) obtained
during 1993-2008 through the Center for Astrophysics Supernova Program. Most of
the spectra were obtained with the FAST spectrograph at the FLWO 1.5m telescope
and reduced in a consistent manner, making data set well suited for studies of
SN Ia spectroscopic diversity. We study the spectroscopic and photometric
properties of SN Ia as a function of spectroscopic class using the
classification schemes of Branch et al. and Wang et al. The width-luminosity
relation appears to be steeper for SN Ia with broader lines. Based on the
evolution of the characteristic Si II 6355 line, we propose improved methods
for measuring velocity gradients, revealing a larger range than previously
suspected, from ~0 to ~400 km/s/day considering the instantaneous velocity
decline rate at maximum light. We find a weaker and less significant
correlation between Si II velocity and intrinsic B-V color at maximum light
than reported by Foley et al., owing to a more comprehensive treatment of
uncertainties and host galaxy dust. We study the extent of nuclear burning and
report new detections of C II 6580 in 23 early-time spectra. The frequency of C
II detections is not higher in SN Ia with bluer colors or narrower light
curves, in conflict with the recent results of Thomas et al. Based on nebular
spectra of 27 SN Ia, we find no relation between the FWHM of the iron emission
feature at ~4700 A and Dm15(B) after removing the two low-luminosity SN 1986G
and SN 1991bg, suggesting that the peak luminosity is not strongly dependent on
the kinetic energy of the explosion for most SN Ia. Finally, we confirm the
correlation of velocity shifts in some nebular lines with the intrinsic B-V
color of SN Ia at maximum light, although several outliers suggest a possible
non-monotonic behavior for the largest blueshifts.Comment: 36 pages (emulateapj), 23 figures. Accepted for publication in AJ.
Spectroscopic data available at
http://www.cfa.harvard.edu/supernova/SNarchive.html . New SNID template set
available at http://marwww.in2p3.fr/~blondin/software/snid/index.html . Minor
changes from v1 to conform to published versio
Nearby Supernova Factory Observations of SN 2007if: First Total Mass Measurement of a Super-Chandrasekhar-Mass Progenitor
We present photometric and spectroscopic observations of SN 2007if, an
overluminous (M_V = -20.4), red (B-V = 0.16 at B-band maximum), slow-rising
(t_rise = 24 days) type Ia supernova in a very faint (M_g = -14.10) host
galaxy. A spectrum at 5 days past B-band maximum light is a direct match to the
super-Chandrasekhar-mass candidate SN Ia 2003fg, showing Si II and C II at
~9000 km/s. A high signal-to-noise co-addition of the SN spectral time series
reveals no Na I D absorption, suggesting negligible reddening in the host
galaxy, and the late-time color evolution has the same slope as the Lira
relation for normal SNe Ia. The ejecta appear to be well mixed, with no strong
maximum in I-band and a diversity of iron-peak lines appearing in
near-maximum-light spectra. SN2007 if also displays a plateau in the Si II
velocity extending as late as +10 days, which we interpret as evidence for an
overdense shell in the SN ejecta. We calculate the bolometric light curve of
the SN and use it and the \ion{Si}{2} velocity evolution to constrain the mass
of the shell and the underlying SN ejecta, and demonstrate that SN2007 if is
strongly inconsistent with a Chandrasekhar-mass scenario. Within the context of
a "tamped detonation" model appropriate for double-degenerate mergers, and
assuming no host extinction, we estimate the total mass of the system to be 2.4
+/- 0.2 solar masses, with 1.6 +/- 0.1 solar masses of nickel-56 and with
0.3-0.5 solar masses in the form of an envelope of unburned carbon/oxygen. Our
modeling demonstrates that the kinematics of shell entrainment provide a more
efficient mechanism than incomplete nuclear burning for producing the low
velocities typical of super-Chandrasekhar-mass SNeIa.Comment: 23 pages, 13 figures, 4 tables, emulateapj format; v2 fixed some
typos and added a reference; v3 included minor copy-editing changes + fixed
typos in Figure 9, Table 4; accepted to Ap
The Subluminous and Peculiar Type Ia Supernova PTF09dav
PTF09dav is a peculiar subluminous type Ia supernova (SN) discovered by the
Palomar Transient Factory (PTF). Spectroscopically, it appears superficially
similar to the class of subluminous SN1991bg-like SNe, but it has several
unusual features which make it stand out from this population. Its peak
luminosity is fainter than any previously discovered SN1991bg-like SN Ia (M_B
-15.5), but without the unusually red optical colors expected if the faint
luminosity were due to extinction. The photospheric optical spectra have very
unusual strong lines of Sc II and Mg I, with possible Sr II, together with
stronger than average Ti II and low velocities of ~6000 km/s. The host galaxy
of PTF09dav is ambiguous. The SN lies either on the extreme outskirts (~41kpc)
of a spiral galaxy, or in an very faint (M_R>-12.8) dwarf galaxy, unlike other
1991bg-like SNe which are invariably associated with massive, old stellar
populations. PTF09dav is also an outlier on the light-curve-width--luminosity
and color--luminosity relations derived for other sub-luminous SNe Ia. The
inferred 56Ni mass is small (0.019+/-0.003Msun), as is the estimated ejecta
mass of 0.36Msun. Taken together, these properties make PTF09dav a remarkable
event. We discuss various physical models that could explain PTF09dav. Helium
shell detonation or deflagration on the surface of a CO white-dwarf can explain
some of the features of PTF09dav, including the presence of Sc and the low
photospheric velocities, but the observed Si and Mg are not predicted to be
very abundant in these models. We conclude that no single model is currently
capable of explaining all of the observed signatures of PTF09dav.Comment: Accepted for publication in Ap
Supernova 2007bi as a pair-instability explosion
Stars with initial masses 10 M_{solar} < M_{initial} < 100 M_{solar} fuse
progressively heavier elements in their centres, up to inert iron. The core
then gravitationally collapses to a neutron star or a black hole, leading to an
explosion -- an iron-core-collapse supernova (SN). In contrast, extremely
massive stars (M_{initial} > 140 M_{solar}), if such exist, have oxygen cores
which exceed M_{core} = 50 M_{solar}. There, high temperatures are reached at
relatively low densities. Conversion of energetic, pressure-supporting photons
into electron-positron pairs occurs prior to oxygen ignition, and leads to a
violent contraction that triggers a catastrophic nuclear explosion. Tremendous
energies (>~ 10^{52} erg) are released, completely unbinding the star in a
pair-instability SN (PISN), with no compact remnant. Transitional objects with
100 M_{solar} < M_{initial} < 140 M_{solar}, which end up as iron-core-collapse
supernovae following violent mass ejections, perhaps due to short instances of
the pair instability, may have been identified. However, genuine PISNe, perhaps
common in the early Universe, have not been observed to date. Here, we present
our discovery of SN 2007bi, a luminous, slowly evolving supernova located
within a dwarf galaxy (~1% the size of the Milky Way). We measure the exploding
core mass to be likely ~100 M_{solar}, in which case theory unambiguously
predicts a PISN outcome. We show that >3 M_{solar} of radioactive 56Ni were
synthesized, and that our observations are well fit by PISN models. A PISN
explosion in the local Universe indicates that nearby dwarf galaxies probably
host extremely massive stars, above the apparent Galactic limit, perhaps
resulting from star formation processes similar to those that created the first
stars in the Universe.Comment: Accepted version of the paper appearing in Nature, 462, 624 (2009),
including all supplementary informatio
PTF11eon/SN2011dh: Discovery of a Type IIb Supernova From a Compact Progenitor in the Nearby Galaxy M51
On May 31, 2011 UT a supernova (SN) exploded in the nearby galaxy M51 (the
Whirlpool Galaxy). We discovered this event using small telescopes equipped
with CCD cameras, as well as by the Palomar Transient Factory (PTF) survey, and
rapidly confirmed it to be a Type II supernova. Our early light curve and
spectroscopy indicates that PTF11eon resulted from the explosion of a
relatively compact progenitor star as evidenced by the rapid shock-breakout
cooling seen in the light curve, the relatively low temperature in early-time
spectra and the prompt appearance of low-ionization spectral features. The
spectra of PTF11eon are dominated by H lines out to day 10 after explosion, but
initial signs of He appear to be present. Assuming that He lines continue to
develop in the near future, this SN is likely a member of the cIIb (compact
IIb; Chevalier and Soderberg 2010) class, with progenitor radius larger than
that of SN 2008ax and smaller than the eIIb (extended IIb) SN 1993J progenitor.
Our data imply that the object identified in pre-explosion Hubble Space
Telescope images at the SN location is possibly a companion to the progenitor
or a blended source, and not the progenitor star itself, as its radius (~10^13
cm) would be highly inconsistent with constraints from our post-explosion
photometric and spectroscopic data
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