2,687 research outputs found
Red Supergiants in the Andromeda Galaxy (M31)
Red supergiants are a short-lived stage in the evolution of moderately
massive stars (10-25Mo), and as such their location in the H-R diagram provides
an exacting test of stellar evolutionary models. Since massive star evolution
is strongly affected by the amount of mass-loss a star suffers, and since the
mass-loss rates depend upon metallicity, it is highly desirable to study the
physical properties of these stars in galaxies of various metallicities. Here
we identify a sample of red supergiants in M31 (the most metal-rich of the
Local Group galaxies) and derive their physical properties by fitting MARCS
atmosphere models to moderate resolution optical spectroscopy, and from V-K
photometry.Comment: Accepted for publication in the Astrophysical Journa
The High-Metallicity Explosion Environment of the Relativistic Supernova 2009bb
We investigate the environment of the nearby (d ~ 40Mpc) broad-lined Type Ic
supernova SN 2009bb. This event was observed to produce a relativistic outflow
likely powered by a central accreting compact object. While such a phenomenon
was previously observed only in long-duration gamma-ray bursts (LGRBs), no LGRB
was detected in association with SN 2009bb. Using an optical spectrum of the SN
2009bb explosion site, we determine a variety of ISM properties for the host
environment, including metallicity, young stellar population age, and star
formation rate. We compare the SN explosion site properties to observations of
LGRB and broad-lined SN Ic host environments on optical emission line ratio
diagnostic diagrams. Based on these analyses, we find that the SN 2009bb
explosion site has a very high metallicity of ~2x solar, in agreement with
other broad-lined SN Ic host environments and at odds with the low-redshift
LGRB host environments and recently proposed maximum metallicity limits for
relativistic explosions. We consider the implications of these findings and the
impact that SN 2009bb's unusual explosive properties and environment have on
our understanding of the key physical ingredient that enables some SNe to
produce a relativistic outflow.Comment: 7 pages, 4 figures, 1 table; accepted for publication in ApJ Letters
(replaced to include missing figure
A Spectroscopic Study of Type Ibc Supernova Host Galaxies from Untargeted Surveys
We present the largest spectroscopic study of the host environments of Type
Ibc supernovae (SN Ibc) discovered exclusively by untargeted SN searches. Past
studies of SN Ibc host environments have been biased towards high-mass,
high-metallicity galaxies by focusing on SNe discovered in galaxy-targeted SN
searches. Our new observations more than double the total number of
spectroscopic stellar population age and metallicity measurements published for
untargeted SN Ibc host environments, and extend to a median redshift about
twice as large as previous statistical studies (z = 0.04). For the 12 SNe Ib
and 21 SNe Ic in our metallicity sample, we find median metallicities of
log(O/H)+12 = 8.48 and 8.61, respectively, but determine that the discrepancy
in the full distribution of metallicities is not statistically significant.
This median difference would correspond to only a small difference in the mass
loss via metal-line driven winds (<30%), suggesting this does not play the
dominant role in distinguishing SN Ib and Ic progenitors. However, the median
metallicity of the 7 broad-lined SN Ic (SN Ic-BL) in our sample is
significantly lower, log(O/H)+12 = 8.34. The age of the young stellar
population of SN Ic-BL host environments also seems to be lower than for SN Ib
and Ic, but our age sample is small. A synthesis of SN Ibc host environment
spectroscopy to date does not reveal a significant difference in SN Ib and Ic
metallicities, but reinforces the significance of the lower metallicities for
SN Ic-BL. This combined sample demonstrates that galaxy-targeted SN searches
introduce a significant bias for studies seeking to infer the metallicity
distribution of SN progenitors, and we identify and discuss other systematic
effects that play smaller roles. We discuss the path forward for making
progress on SN Ibc progenitor studies in the LSST era.Comment: 27 pages, 12 Figures, V2 as accepted by ApJ, more information at
http://www.cfa.harvard.edu/~nsanders/papers/Ibchosts/summary.htm
Service Platform for Converged Interactive Broadband Broadcast and Cellular Wireless
A converged broadcast and telecommunication
service platform is presented that is able to create, deliver, and
manage interactive, multimedia content and services for consumption
on three different terminal types. The motivations of
service providers for designing converged interactive multimedia
services, which are crafted for their individual requirements, are
investigated. The overall design of the system is presented with
particular emphasis placed on the operational features of each
of the sub-systems, the flows of media and metadata through the
sub-systems and the formats and protocols required for inter-communication
between them. The key features of tools required for
creating converged interactive multimedia content for a range of
different end-user terminal types are examined. Finally possible
enhancements to this system are discussed. This study is of particular
interest to those organizations currently conducting trials
and commercial launches of DVB-H services because it provides
them with an insight of the various additional functions required
in the service provisioning platforms to provide fully interactive
services to a range of different mobile terminal types
SN 2010ay is a Luminous and Broad-lined Type Ic Supernova within a Low-metallicity Host Galaxy
We report on our serendipitous pre-discovery detection and detailed follow-up
of the broad-lined Type Ic supernova (SN) 2010ay at z = 0.067 imaged by the
Pan-STARRS1 3pi survey just ~4 days after explosion. The SN had a peak
luminosity, M_R ~ -20.2 mag, significantly more luminous than known GRB-SNe and
one of the most luminous SNe Ib/c ever discovered. The absorption velocity of
SN 2010ay is v_Si ~ 19,000 km/s at ~40 days after explosion, 2-5 times higher
than other broad-lined SNe and similar to the GRB-SN 2010bh at comparable
epochs. Moreover, the velocity declines ~2 times slower than other SNe Ic-BL
and GRB-SNe. Assuming that the optical emission is powered by radioactive
decay, the peak magnitude implies the synthesis of an unusually large mass of
56 Ni, M_Ni = 0.9 M_solar. Modeling of the light-curve points to a total ejecta
mass, M_ej ~ 4.7 M_sol, and total kinetic energy, E_K ~ 11x10^51 ergs. The
ratio of M_Ni to M_ej is ~2 times as large for SN 2010ay as typical GRB-SNe and
may suggest an additional energy reservoir. The metallicity (log(O/H)_PP04 + 12
= 8.19) of the explosion site within the host galaxy places SN 2010ay in the
low-metallicity regime populated by GRB-SNe, and ~0.5(0.2) dex lower than that
typically measured for the host environments of normal (broad-lined) Ic
supernovae. We constrain any gamma-ray emission with E_gamma < 6x10^{48} erg
(25-150 keV) and our deep radio follow-up observations with the Expanded Very
Large Array rule out relativistic ejecta with energy, E > 10^48 erg. We
therefore rule out the association of a relativistic outflow like those which
accompanied SN 1998bw and traditional long-duration GRBs, but place
less-stringent constraints on a weak afterglow like that seen from XRF 060218.
These observations challenge the importance of progenitor metallicity for the
production of a GRB, and suggest that other parameters also play a key role.Comment: 19 pages, 10 figures, V3 has revisions following referee's report;
more information at
http://www.cfa.harvard.edu/~nsanders/papers/2010ay/summary.htm
Compilability of Abduction
Abduction is one of the most important forms of reasoning; it has been
successfully applied to several practical problems such as diagnosis. In this
paper we investigate whether the computational complexity of abduction can be
reduced by an appropriate use of preprocessing. This is motivated by the fact
that part of the data of the problem (namely, the set of all possible
assumptions and the theory relating assumptions and manifestations) are often
known before the rest of the problem. In this paper, we show some complexity
results about abduction when compilation is allowed
Theorem on the Distribution of Short-Time Particle Displacements with Physical Applications
The distribution of the initial short-time displacements of particles is
considered for a class of classical systems under rather general conditions on
the dynamics and with Gaussian initial velocity distributions, while the
positions could have an arbitrary distribution. This class of systems contains
canonical equilibrium of a Hamiltonian system as a special case. We prove that
for this class of systems the nth order cumulants of the initial short-time
displacements behave as the 2n-th power of time for all n>2, rather than
exhibiting an nth power scaling. This has direct applications to the initial
short-time behavior of the Van Hove self-correlation function, to its
non-equilibrium generalizations the Green's functions for mass transport, and
to the non-Gaussian parameters used in supercooled liquids and glasses.Comment: A less ambiguous mathematical notation for cumulants was adopted and
several passages were reformulated and clarified. 40 pages, 1 figure.
Accepted by J. Stat. Phy
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