382 research outputs found
The supernova: A stellar spectacle
The life of a star, the supernova, related objects and their importance in astronomy and science in general are discussed. Written primarily for science teachers of secondary school chemistry, physics, and earth sciences, the booklet contains a glossary, reference sources, suggested topics for discussion, and projects for individual or group assignment
Comments on an association in Vela
Evidence for an association near the Vela pulsar rests on the H-R diagram. Definite bunching occurs around the mean line. However this evidence is not supported by correlation of proper motions in the region. If the Vela pulsar is a member of this association, a rather large mass is implied, about 10 solar masses
Space and Ground Based Pulsation Data of Eta Bootis Explained with Stellar Models Including Turbulence
The space telescope MOST is now providing us with extremely accurate low
frequency p-mode oscillation data for the star Eta Boo. We demonstrate in this
paper that these data, when combined with ground based measurements of the high
frequency p-mode spectrum, can be reproduced with stellar models that include
the effects of turbulence in their outer layers. Without turbulence, the l=0
modes of our models deviate from either the ground based or the space data by
about 1.5-4.0 micro Hz. This discrepancy can be completely removed by including
turbulence in the models and we can exactly match 12 out of 13 MOST frequencies
that we identified as l=0 modes in addition to 13 out of 21 ground based
frequencies within their observational 2 sigma tolerances. The better agreement
between model frequencies and observed ones depends for the most part on the
turbulent kinetic energy which was taken from a 3D convection simulation for
the Sun.Comment: 13 pages, 7 figures, ApJ in pres
YREC: The Yale Rotating Stellar Evolution Code
The stellar evolution code YREC is outlined with emphasis on its applications
to helio- and asteroseismology. The procedure for calculating calibrated solar
and stellar models is described. Other features of the code such as a non-local
treatment of convective core overshoot, and the implementation of a
parametrized description of turbulence in stellar models, are considered in
some detail. The code has been extensively used for other astrophysical
applications, some of which are briefly mentioned at the end of the paper.Comment: 10 pages, 2 figures, ApSS accepte
Possible Signatures of a Cold-Flow Disk from MUSE using a z=1 galaxy--quasar pair towards SDSSJ1422-0001
We use a background quasar to detect the presence of circum-galactic gas
around a low-mass star forming galaxy. Data from the new Multi Unit
Spectroscopic Explorer (MUSE) on the VLT show that the host galaxy has a
dust-corrected star-formation rate (SFR) of 4.70.2 Msun/yr, with no
companion down to 0.22 Msun/yr (5 ) within 240 kpc (30"). Using a
high-resolution spectrum (UVES) of the background quasar, which is fortuitously
aligned with the galaxy major axis (with an azimuth angle of only
), we find, in the gas kinematics traced by low-ionization lines,
distinct signatures consistent with those expected for a "cold flow disk"
extending at least 12 kpc (). We estimate the mass accretion
rate to be at least two to three times larger than the SFR,
using the geometric constraints from the IFU data and the HI column density of
obtained from a {\it HST}/COS NUV spectrum. From
a detailed analysis of the low-ionization lines (e.g. ZnII, CrII, TiII, MnII,
SiII), the accreting material appears to be enriched to about 0.4
(albeit with large uncertainties: ), which is
comparable to the galaxy metallicity (), implying a
large recycling fraction from past outflows. Blue-shifted MgII and FeII
absorptions in the galaxy spectrum from the MUSE data reveal the presence of an
outflow. The MgII and FeII doublet ratios indicate emission infilling due to
scattering processes, but the MUSE data do not show any signs of fluorescent
FeII* emission.Comment: 17 pages, 11 figures, in press (ApJ), minor edits after the proofs.
Data available at http://muse-vlt.eu/science/j1422
Current Issues in Asteroseismology
In this contribution we briefly review some of the current issues and
promises for the future by asteroseismology. We are entering a new phase in
this field driven by the wealth of data that has been collected and data that
will soon be available for asteroseismology across the HR Diagram. Major
difficulties in the descriptions of stellar interiors that arose in the second
half of the 20th century may now be in part addressed and solved (this is the
expectation!) by asteroseismology with unprecedented precision. In this
contribution we list some of the key open questions in stellar physics, the
seismic data we expect to collect in the near future, and some techniques that
will provide the tools to connect data and models.Comment: 9 pages, 2 figures - to appear in Helioseismology, Asteroseismology
and MHD Connections, (Eds) L. Gizon et al., Journal of Physics Conference
Series, 2008 [Revision 1 - english; Revision 2 - references
Diffusive convective overshoot in core He-burning intermediate mass stars. I: the LMC metallicity
We present detailed evolutionary calculations focused on the evolution of
intermediate mass stars with 3 Msun < M < 9 Msun of metallicity typical of the
Large Magellanic Cloud (LMC), i.e. Z=0.008. We compare carefully the models
calculated by adopting a diffusive scheme for chemical mixing, in which nuclear
burning and mixing are self-consistently coupled, while the eddy velocities
beyond the formal convective core boundary are treated to decay exponentially,
and those calculated with the traditional instantaneous mixing approximation.
We find that: i) the physical and chemical behaviour of the models during the
H-burning phase is independent of the scheme used for the treatment of mixing
inside the CNO burning core; ii) the duration of the He-burning phase relative
to the MS phase is systematically longer in the diffusive models, due to a
slower redistribution of helium to the core from the outer layers; iii) the
fraction of time spent in the blue part of the clump, compared to the stay in
the red, is larger in the diffusive models. The differences described in points
ii) and iii) tend to vanish for M > Msun. In terms of the theoretical
interpretation of an open cluster stellar population, the differences
introduced by the use of a self-consistent scheme for mixing in the core with
adjacent exponential decay are relevant for ages in the range 80 Myr < t < 200
Myr. These results are robust, since they are insensitive to the choice of the
free-parameters regulating the extension of the extra-mixing region.Comment: 14 pages, 14 figure, accepted for publication on Astronomy &
Astrophysic
Core Overshoot: An Improved Treatment and Constraints from Seismic Data
We present a comprehensive set of stellar evolution models for Procyon A in
an effort to guide future measurements of both traditional stellar parameters
and seismic frequencies towards constraining the amount of core overshoot in
Procyon A and possibly other stars. Current observational measurements of
Procyon A when combined with traditional stellar modeling only place a large
upper limit on overshoot of alphaOV < 1.1. By carrying out a detailed pulsation
analysis, we further demonstrate, how p- and g-mode averaged spacings can be
used to gain better estimates of the core size. For both p- and g-modes, the
frequency spacings for models without overshoot are clearly separated from the
models with overshoot. In addition, measurements of the l=0 averaged small
p-mode spacings could be used to establish Procyon A's evolutionary stage. For
a fixed implementation of overshoot and under favorable circumstances, the
g-mode spacings can be used to determine the overshoot extent to an accuracy of
+-0.05 Hp. However, we stress that considerable confusion is added due to the
unknown treatment of the overshoot region. This ambiguity might be removed by
analyzing many different stars. A simple non-local convection theory developed
by Kuhfuss is implemented in our stellar evolution code and contrasted with the
traditional approaches. We show that this theory supports a moderate increase
of the amount of convective overshoot with stellar mass of Delta(alphaOV) =
+0.10 between 1.5 Msun and 15 Msun. This theory places an upper limit on
Procyon A's core overshoot extent of ~0.4 Hp which matches the limit imposed by
Roxburgh's integral criterion.Comment: 45 pages, 26 figures, accepted in Ap
Carfilzomib, bendamustine, and dexamethasone in patients with advanced multiple myeloma: The EMN09 phase 1/2 study of the European Myeloma Network
Background: Combined therapy with carfilzomib, bendamustine, and dexamethasone was evaluated in this multicenter phase 1/2 trial conducted within the European Myeloma Network (EMN09 trial). Methods: Sixty-three patients with relapsed/refractory multiple myeloma who had received 652 lines of prior therapy were included. The phase 1 portion of the study determined the maximum tolerated dose of carfilzomib with bendamustine set at 70 mg/m2 on days 1 and 8. After 8 cycles, responding patients received maintenance therapy with carfilzomib and dexamethasone until progression. Results: On the basis of the phase 1 results, the recommended phase 2 dose for carfilzomib was 27 mg/m2 twice weekly in weeks 1, 2, and 3. Fifty-two percent of patients achieved a partial response or better, and 32% reached a very good partial response or better. The clinical benefit rate was 93%. After a median follow-up of 21.9 months, the median progression-free survival was 11.6 months, and the median overall survival was 30.4 months. The reported grade 653 hematologic adverse events (AEs) were lymphopenia (29%), neutropenia (25%), and thrombocytopenia (22%). The main nonhematologic grade 653 AEs were pneumonia, thromboembolic events (10%), cardiac AEs (8%), and hypertension (2%). Conclusions: In heavily pretreated patients who have relapsed/refractory multiple myeloma, combined carfilzomib, bendamustine, and dexamethasone is an effective treatment option administered in the outpatient setting. Infection prophylaxis and attention to patients with cardiovascular predisposition are required
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