85 research outputs found
The nature of the progenitor of the Type II-P supernova 1999em
We present high quality ground-based VRI images of the site of the Type II-P
SN1999em (in NGC1637) taken before explosion, which were extracted from the
CFHT archive. We determine a precise position of the SN on these images to an
accuracy of 0.17''. The host galaxy is close enough (7.5 +/- 0.5 Mpc) that the
bright supergiants are resolved as individual objects, however we show that
there is no detection of an object at the SN position before explosion that
could be interpreted as the progenitor star. By determining the sensitivity
limits of the VRI data, we derive bolometric luminosity limits for the
progenitor. Comparing these to standard stellar evolutionary tracks which trace
evolution up to the point of core carbon ignition, we initially derive an upper
mass limit of approximately 12M_sol. However we present evolutionary
calculations that follow 7-12M_sol stars throughout their C-burning lifetime
and show that we can restrict the mass of the progenitor even further. Our
calculations indicate that progenitors initially of 8-10M_sol, undergoing
expected mass loss, can also be excluded because a second dredge up sends them
to somewhat higher luminosities than a star of initially 12M_sol. These results
limit the progenitor's initial main-sequence mass to a very narrow range of 12
+/- 1 M_sol. We discuss the similarities between the Type II-P SNe 1999em and
1999gi and their progenitor mass limits, and suggest that SN Type II-P
originate only in intermediate mass stars of 8-12M_sol, which are in the red
supergiant region and that higher mass stars produce the other Type II
sub-types. (Abridged).Comment: Replaced with accepted version to appear in ApJ, 30 pages, inc. 6
figure
Differential O and Si Abundances in M33 Early B Supergiants
We present non-LTE analyses of four M33 early B-supergiant stars and five
Galactic counterparts. This is the first time that B supergiants beyond the
Magellanic Clouds are analyzed by means of detailed Non-LTE techniques. Stellar
temperatures, gravities, microturbulences and Si abundances are derived for all
objects using the Si ionization equilibrium and the Balmer line wings. O
abundances are then also derived. Important approximations made during the
calculations are described, and their influence on the results is analyzed. It
is found that these approximations have no significant effect on the results at
any microturbulence. We find that a strict differential analysis is needed to
detect abundance differences. Thus we compare results line by line in M33 and
Galactic stars of stellar parameters as similar as possible. Three of the four
M33 stars turned out to be O deficient as compared to their Galactic
counterparts, and only one, close to the center of M33 (M33 1054) is found to
be moderately O enriched. From these differential analyses we find that our
data are compatible with a radial O gradient in M33 as that derived from HII
region data: we obtain -0.19+/-0.13 or -0.20+/-0.07 dex/kpc, depending on
whether B133 is included or not. Our data are also consistent with other
possibilities such as a steep increase of the O abundance in the inner region
(at projected distances less than 9 arcmin from the center of M33), followed by
a flat O abundance profile towards the outer parts of M33. Si shows the same
pattern, and it is shown that Si and O correlate well, as expected for
alpha-elements, supporting then the high value of the O abundance gradient in
M33 as compared to the Milky Way and other nearby spiral galaxies.Comment: Accepted for ApJ. Tentatively scheduled for Dec. 20, 2000. 44 pages,
9 tables, 18 figure
Terminal velocities of luminous, early-type SMC stars
Ultraviolet spectra from the Space Telescope Imaging Spectrograph (STIS) are
used to determine terminal velocities for 11 O and B-type giants and
supergiants in the Small Magellanic Cloud (SMC) from the Si IV and C IV
resonance lines. Using archival data from observations with the Goddard
High-Resolution Spectrograph and the International Ultraviolet Explorer
telescope, terminal velocities are obtained for a further five B-type
supergiants. We discuss the metallicity dependence of stellar terminal
velocities, finding no evidence for a significant scaling between Galactic and
SMC metallicities for Teff < 30,000 K, consistent with the predictions of
radiation driven wind theory for supergiant stars. A comparison of the
ratio between the SMC and Galactic samples, while
consistent with the above statement, emphasizes that the uncertainties in the
distances to galactic O-stars are a serious obstacle to a detailed comparison
with theory. For the SMC sample there is considerable scatter in this ratio at
a given effective temperature, perhaps indicative of uncertainties in stellar
masses.Comment: 28 pages, 8 figures, accepted by ApJ; minor revisions prior to
acceptanc
A Spectroscopic Study of Mass Outflows in the Interacting Binary RY Scuti
The massive interacting binary RY Scuti is an important representative of an
active mass-transferring system that is changing before our eyes and which may
be an example of the formation of a Wolf-Rayet star through tidal stripping.
Utilizing new and previously published spectra, we present examples of how a
number of illustrative absorption and emission features vary during the binary
orbit. We identify spectral features associated with each component, calculate
a new, double-lined spectroscopic binary orbit, and find masses of 7.1 +/- 1.2
M_sun for the bright supergiant and 30.0 +/- 2.1 M_sun for the hidden massive
companion. Through tomographic reconstruction of the component spectra from the
composite spectra, we confirm the O9.7 Ibpe spectral class of the bright
supergiant and discover a B0.5 I spectrum associated with the hidden massive
companion; however, we suggest that the latter is actually the spectrum of the
photosphere of the accretion torus immediately surrounding the massive
companion. We describe the complex nature of the mass loss flows from the
system in the context of recent hydrodynamical models for beta Lyr, leading us
to conclude RY Scuti has matter leaving the system in two ways: 1) a bipolar
outflow from winds generated by the hidden massive companion, and 2) mass from
the bright O9.7 Ibpe supergiant flowing from the region near the L2 point to
fill out a large, dense circumbinary disk. This circumbinary disk (radius ~ 1
AU) may feed the surrounding double-toroidal nebula (radius ~ 2000 AU).Comment: 41 pages with 7 tables and 11 figures, accepted to Ap
Genetics, recombination and clinical features of human rhinovirus species C (HRV-C) infections; interactions of HRV-C with other respiratory viruses
To estimate the frequency, molecular epidemiological and clinical associations of infection with the newly described species C variants of human rhinoviruses (HRV), 3243 diagnostic respiratory samples referred for diagnostic testing in Edinburgh were screened using a VP4-encoding region-based selective polymerase chain reaction (PCR) for HRV-C along with parallel PCR testing for 13 other respiratory viruses. HRV-C was the third most frequently detected behind respiratory syncytial virus (RSV) and adenovirus, with 141 infection episodes detected among 1885 subjects over 13 months (7.5%). Infections predominantly targeted the very young (median age 6–12 months; 80% of infections in those <2 years), occurred throughout the year but with peak incidence in early winter months. HRV-C was detected significantly more frequently among subjects with lower (LRT) and upper respiratory tract (URT) disease than controls without respiratory symptoms; HRV-C mono-infections were the second most frequently detected virus (behind RSV) in both disease presentations (6.9% and 7.8% of all cases respectively). HRV variants were classified by VP4/VP2 sequencing into 39 genotypically defined types, increasing the current total worldwide to 60. Through sequence comparisons of the 5′untranslated region (5′UTR), the majority grouped with species A (n = 96; 68%, described as HRV-Ca), the remainder forming a phylogenetically distinct 5′UTR group (HRV-Cc). Multiple and bidirectional recombination events between HRV-Ca and HRV-Cc variants and with HRV species A represents the most parsimonious explanation for their interspersed phylogeny relationships in the VP4/VP2-encoding region. No difference in age distribution, seasonality or disease associations was identified between HRV-Ca and HRV-Cc variants. HRV-C-infected subjects showed markedly reduced detection frequencies of RSV and other respiratory viruses, providing evidence for a major interfering effect of HRV-C on susceptibility to other respiratory virus infections. HRV-C's disease associations, its prevalence and evidence for interfering effects on other respiratory viruses mandates incorporation of rhinoviruses into future diagnostic virology screening
Physical Parameters and Wind Properties of Galactic Early B Supergiants
We present optical studies of the physical and wind properties, plus CNO
chemical abundances, of 25 O9.5-B3 Galactic supergiants. We employ non-LTE,
line blanketed, extended model atmospheres, which provide a modest downward
revision in the effective temperature scale of early B supergiants of up to
1-2kK relative to previous non-blanketed results. The so-called `bistability
jump' at B1 (Teff ~ 21kK) from Lamers et al. is rather a more gradual trend
(with large scatter) from v_inf/v_esc ~ 3.4 for B0--0.5 supergiants above 24kK
to v_inf/v_esc ~ 2.5 for B0.7-1 supergiants with 20kK < Teff < 24kK, and
v_inf/v_esc ~ 1.9 for B1.5-3 supergiants below 20kK. This, in part, explains
the break in observed UV spectral characteristics between B0.5 and B0.7
subtypes as discussed by Walborn et al. We compare derived (homogeneous) wind
densities with recent results for Magellanic Cloud B supergiants and generally
confirm theoretical expectations for stronger winds amongst Galactic
supergiants. However, winds are substantially weaker than predictions from
current radiatively driven wind theory, especially at mid-B subtypes, a problem
which is exacerbated if winds are already clumped in the H-alpha line forming
region. In general, CNO elemental abundances reveal strongly processed material
at the surface of Galactic B supergiants, with mean N/C and N/O abundances 10
and 5 times higher than the Solar value, respectively, with HD 2905 (BC0.7 Ia)
indicating the lowest degree of processing in our sample, and HD 152236 (B1.5
Ia+) the highest.Comment: 18 pages, 9 figures, accepted for A&
Fear of cancer recurrence following allogeneic haematopoietic stem cell transplantation (HSCT) for haematological malignancy: A cross-sectional study.
PURPOSE:The aim of this study was to quantify the prevalence of Fear of Cancer Recurrence (FCR) in patients with a prior haematology malignancy surviving more than one year post allogeneic haematopoietic stem cell transplantation (HSCT), and to identify the demographic, medical and psychological factors associated with FCR occurrence. METHOD:Participants were adult allogeneic HSCT recipients who had undergone the procedure for acute leukaemia or other haematological malignancy between the years 2000-2012 in Sydney, Australia. They completed a purpose designed survey and six other validated instruments which assessed FCR, psychological functioning, quality of life, demographic, social and clinical variables. RESULTS:Of the 364 respondents, approximately 11% of the sample lived with severe FCR while only 5% of subjects reported having no FCR. Variables significantly associated with higher FCR included unemployment, a shorter time (years) post-transplant, not attending to health screening (PAP smear), a secondary diagnosis of skin cancer, younger age, referral to a psychiatrist and taking psychotropic medication. Higher psychological distress (depression, anxiety, stress) and lower quality of life made a significant contribution to the prediction of FCR. CONCLUSIONS:Post HSCT follow-up care should include an assessment and discussion regarding FCR to balance both realistic and unrealistic cancer recurrence risks. Managing FCR is one of the most ubiquitous unmet needs of survivors of haematological disease and it is important that HSCT nurses are both aware of the fear, and are equipped with knowledge on how to help patients navigate it with realistic expectations
The B-Supergiant Components of the Double-Lined Binary HD1383
We present new results from a study of high quality, red spectra of the
massive binary star system HD 1383 (B0.5 Ib + B0.5 Ib). We determined radial
velocities and revised orbital elements (P = 20.28184 +/- 0.0002 d) and made
Doppler tomographic reconstructions of the component spectra. A comparison of
these with model spectra from non-LTE, line blanketed atmospheres indicates
that both stars have almost identical masses (M_2/M_1 = 1.020 +/- 0.014),
temperatures (T_eff = 28000 +/- 1000 K), gravities (log g = 3.25 +/- 0.25), and
projected rotational velocities (V sin i < 30 km/s). We investigate a number of
constraints on the radii and masses of the stars based upon the absence of
eclipses, surface gravity, stellar wind terminal velocity, and probable
location in the Perseus spiral arm of the Galaxy, and these indicate a range in
probable radius and mass of R/R_sun = 14 - 20 and M/M_sun = 16 - 35,
respectively. These values are consistent with model evolutionary masses for
single stars of this temperature and gravity. Both stars are much smaller than
their respective Roche radii, so the system is probably in a pre-contact stage
of evolution. A fit of the system's spectral energy distribution yields a
reddening of E(B-V)=0.55 +/- 0.05 and a ratio of total-to-selective extinction
of R=2.97 +/- 0.15. We find no evidence of H-alpha emission from colliding
stellar winds, which is probably the consequence of the low gas densities in
the colliding winds zone.Comment: Accepted for publication in ApJ: 20 pages, 5 figure
Longitudinal molecular microbial analysis of influenza-like illness in New York City, may 2009 through may 2010
<p>Abstract</p> <p>Background</p> <p>We performed a longitudinal study of viral etiology in samples collected in New York City during May 2009 to May 2010 from outpatients with fever or respiratory disease symptoms in the context of a pilot respiratory virus surveillance system.</p> <p>Methods</p> <p>Samples were assessed for the presence of 13 viruses, including influenza A virus, by MassTag PCR.</p> <p>Results</p> <p>At least one virus was detected in 52% of 940 samples analyzed, with 3% showing co-infections. The most frequently detected agents were rhinoviruses and influenza A, all representing the 2009 pandemic H1N1 strain. The incidence of influenza H1N1-positive samples was highest in late spring 2009, followed by a decline in summer and early fall, when rhinovirus infections became predominant before H1N1 reemerged in winter. Our study also identified a focal outbreak of enterovirus 68 in the early fall of 2009.</p> <p>Conclusion</p> <p>MassTag multiplex PCR affords opportunities to track the epidemiology of infectious diseases and may guide clinicians and public health practitioners in influenza-like illness and outbreak management. Nonetheless, a substantial proportion of influenza-like illness remains unexplained underscoring the need for additional platforms.</p
Distinguishing Molecular Features and Clinical Characteristics of a Putative New Rhinovirus Species, Human Rhinovirus C (HRV C)
Background: Human rhinoviruses (HRVs) are the most frequently detected pathogens in acute respiratory tract infections (ARTIs) and yet little is known about the prevalence, recurrence, structure and clinical impact of individual members. During 2007, the complete coding sequences of six previously unknown and highly divergent HRV strains were reported. To catalogue the molecular and clinical features distinguishing the divergent HRV strains, we undertook, for the first time, in silico analyses of all available polyprotein sequences and performed retrospective reviews of the medical records of cases in which variants of the prototype strain, HRV-QPM, had been detected
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