99 research outputs found
Observed and Physical Properties of Core-Collapse Supernovae
I use photometry and spectroscopy data for 24 Type II plateau supernovae to
examine their observed and physical properties. This dataset shows that these
objects encompass a wide range of ~5 mag in their plateau luminosities, their
expansion velocities vary by x5, and the nickel masses produced in these
explosions go from 0.0016 to 0.26 Mo. From a subset of 16 objects I find that
the explosion energies vary between 0.6x and 5.5x10^51 ergs, the ejected masses
encompass the range 14-56 Mo, and the progenitors' radii go from 80 to 600 Ro.
Despite this great diversity several regularities emerge, which reveal that
there is a continuum in the properties of these objects from the faint,
low-energy, nickel-poor SNe 1997D and 1999br, to the bright, high-energy,
nickel-rich SN 1992am. This study provides evidence that more massive
progenitors produce more energetic explosions, thus suggesting that the outcome
of the core collapse is somewhat determined by the envelope mass. I find also
that supernovae with greater energies produce more nickel. Similar
relationships appear to hold for Type Ib/c supernovae, which suggests that both
Type II and Type Ib/c supernovae share the same core physics. When the whole
sample of core collapse objects is considered, there is a continous
distribution of energies below 8x10^51 ergs. Far above in energy scale and
nickel production lies the extreme hypernova 1998bw, the only supernova firmly
associated to a GRB.Comment: 25 pages, 7 figures, accepted for Part 1 of Astrophysical Journa
Palomar 13: a velocity dispersion inflated by binaries ?
Recently, combining radial velocities from Keck/HIRES echelle spectra with
published proper motion membership probabilities, Cote et al (2002) observed a
sample of 21 stars, probable members of Palomar 13, a globular cluster in the
Galactic halo. Their projected velocity dispersion sigma_p = 2.2 +/-0.4 km/s
gives a mass-to-light ratio M/L_V = 40 +24/-17, about one order of magnitude
larger than the usual estimate for globular clusters. We present here radial
velocities measured from three different CCD frames of commissioning
observations obtained with the new ESO/VLT instrument FLAMES (Fibre Large Array
Multi Element Spectrograph). From these data, now publicly available, we
measure the homogeneous radial velocities of eight probable members of this
globular cluster. A new projected velocity dispersion sigma_p = 0.6-0.9 +/-0.3
km/s implies Palomar 13 mass-to-light ratio M/L_V = 3-7, similar to the usual
value for globular clusters. We discuss briefly the two most obvious reasons
for the previous unusual mass-to-light ratio finding: binaries, now clearly
detected, and more homogeneous data from the multi-fibre FLAMES spectrograph.Comment: 9 pages, 2 Postscript figure
Uncertainty inequalities on groups and homogeneous spaces via isoperimetric inequalities
We prove a family of uncertainty inequalities on fairly general groups
and homogeneous spaces, both in the smooth and in the discrete setting. The
crucial point is the proof of the endpoint, which is derived from a
general weak isoperimetric inequality.Comment: 17 page
The Blue Straggler and Main-sequence Binary Population of the Low-Mass Globular Cluster Palomar 13
We present high-precision VI photometry of stars from the middle of the giant
branch to about 5 magnitudes below the main-sequence turnoff in the globular
cluster Palomar 13 based on images obtained with the Keck II 10m telescope. We
tabulate a complete sample of blue stragglers in the cluster out to about 18
core radii. The blue straggler population is significantly more centrally
concentrated than the giant star sample, which is in turn significantly more
centrally concentrated than the main-sequence star sample. Palomar 13 has one
of the highest specific frequencies of blue stragglers of any known globular
cluster, but the specific frequency of blue stragglers in the outskirts of the
cluster does not increase as has been seen in denser clusters. We also identify
a group of faint blue stragglers (bluer than the turnoff, but having about the
same magnitude) that outnumbers the brighter stragglers by more than a factor
of 2. The cluster's color-magnitude diagram shows a large excess of stars to
the red of the main sequence, indicating that the cluster's binary fraction is
at least 30% +/- 4%, which appears to be similar to that of the low-mass
cluster E3 but significantly higher than that of the more massive clusters Pal
5 and NGC 288.Comment: 36 pages, 13 figures, 1 electronic table, accepted to A
Antithrombotic therapy in acute coronary syndrome: undertreatment of elderly?
The appropriate use of dual antiplatelet therapy (DAPT) in elderly patients with acute coronary syndrome (ACS) is largely debated. Due to the "demographic transition" in western countries, the elderly represent a growing percentage of patients admitted to hospitals for ACS, and among this high risk setting population most of early and late adverse outcomes occur. The presence of several concomitant "comorbidities" complicate the management strategy of both medical or invasive treatment and the clinical decision making process is challenging. Moreover, elderly people are constantly underrepresented in clinical trials and studies. As a result, there is no specific evidence about the optimal antithrombotic therapy in elderly and no specific recommendations are mentioned in the current ACS guidelines. Currently, the best practice for old people is still rudimentary and principally extrapolated from general cardiovascular guidelines. The management of elderly patients should be based on the evaluation of ischemic and hemorrhagic risk, life expectancy, comorbidities and parameters that are not included in the scores recommended by the current guidelines such as frailty and disability. In the era of "precision medicine", the evaluation of bleeding and ischaemic risk in elderly patients must be a dynamic process because of the risk changing over time. A"tailored therapy by individualized medicine" is the key of management strategy
Palomar 13: An Unusual Stellar System in the Galactic Halo
We have measured Keck/HIRES radial velocities for 30 candidate red giants in
the direction of Palomar 13: an object traditionally cataloged as a compact,
low-luminosity globular cluster. From a sample of 21 confirmed members, we find
a systemic velocity of 24.1 km/s and a projected, intrinsic velocity dispersion
of 2.2 km/s. Although small, this dispersion is several times larger than that
expected for a globular cluster of this luminosity and central concentration.
Taken at face value, this dispersion implies a mass-to-light ratio of ~ 40 (in
solar units) based on the best-fit King-Michie model. The surface density
profile of Palomar 13 also appears to be anomalous among Galactic globular
clusters -- depending upon the details of background subtraction and
model-fitting, Palomar 13 either contains a substantial population of
"extra-tidal" stars, or it is far more spatially extended than previously
suspected. The full surface density profile is equally well-fit by a
King-Michie model having a high concentration and large tidal radius, or by a
NFW model. We examine -- and tentatively reject -- a number of possible
explanations for the observed characteristics of Palomar 13 (e.g., velocity
"jitter" among the red giants, spectroscopic binary stars, non-standard mass
functions, modified Newtonian dynamics), and conclude that the two most
plausible scenarios are either catastrophic heating during a recent
perigalacticon passage, or the presence of a massive dark halo. Thus, the
available evidence suggests that Palomar 13 is either a globular cluster which
is now in the process of dissolving into the Galactic halo, or a faint,
dark-matter-dominated stellar system (ABRIDGED).Comment: 31 pages, 13 postscript figures and 1 color gif image. Also available
at http://www.physics.rutgers.edu/ast/ast-rap.html. Accepted for publication
in the Astrophysical Journa
Tilted implants for full-arch rehabilitations in completely edentulous maxilla : a retrospective study
Purpose. The aims of this study were to assess the treatment outcome of immediately loaded full-arch fixed bridges anchored to both tilted and axially placed implants in the edentulous maxilla and to evaluate the incidence of biological and prosthetic complications. Materials and Methods. Thirty-four patients (18 women and 16 men) were included in the study. Each patient received a maxillary full-arch fixed bridge supported by two axial implants and two distal tilted implants. A total of 136 implants were inserted. Loading was applied within 48 hours of surgery and definitive restorations were placed 4 to 6 months later. Patients were scheduled for followup at 6, 12, 18, and 24 months and annually up to 5 years. At each followup plaque level and bleeding scores were assessed and every complication was recorded. Results. The overall follow-up range was 12 to 73 months (mean 38.8 months). No implant failures were recorded to date, leading to a cumulative implant survival rate of 100. Biological complications were recorded such as alveolar mucositis (11.8 patients), peri-implantitis (5.9 patients), and temporomandibular joint pain (5.9 patients). The most common prosthetic complications were the fracture or detachment of one or multiple acrylic teeth in both the temporary (20.6 patients) and definitive (17.7 patients) prosthesis and the minor acrylic fractures in the temporary (14.7 patients) and definitive (2.9 patients) prosthesis. Hygienic complications occurred in 38.2 patients. No patients' dissatisfactions were recorded. Conclusions. The high cumulative implant survival rate indicates that this technique could be considered a viable treatment option. An effective recall program is important to early intercept and correct prosthetic and biologic complications in order to avoid implant and prosthetic failures
Constraining Cosmic Evolution of Type Ia Supernovae
We present the first large-scale effort of creating composite spectra of
high-redshift type Ia supernovae (SNe Ia) and comparing them to low-redshift
counterparts. Through the ESSENCE project, we have obtained 107 spectra of 88
high-redshift SNe Ia with excellent light-curve information. In addition, we
have obtained 397 spectra of low-redshift SNe through a multiple-decade effort
at Lick and Keck Observatories, and we have used 45 UV spectra obtained by
HST/IUE. The low-redshift spectra act as a control sample when comparing to the
ESSENCE spectra. In all instances, the ESSENCE and Lick composite spectra
appear very similar. The addition of galaxy light to the Lick composite spectra
allows a nearly perfect match of the overall spectral-energy distribution with
the ESSENCE composite spectra, indicating that the high-redshift SNe are more
contaminated with host-galaxy light than their low-redshift counterparts. This
is caused by observing objects at all redshifts with the same slit width, which
corresponds to different projected distances. After correcting for the
galaxy-light contamination, subtle differences in the spectra remain. We have
estimated the systematic errors when using current spectral templates for
K-corrections to be ~0.02 mag. The variance in the composite spectra give an
estimate of the intrinsic variance in low-redshift maximum-light SN spectra of
~3% in the optical and growing toward the UV. The difference between the
maximum light low and high-redshift spectra constrain SN evolution between our
samples to be < 10% in the rest-frame optical.Comment: 22 pages, 22 figures, submitted to ApJ. Composite spectra can be
downloaded from http://astro.berkeley.edu/~rfoley/composite
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