The observational picture of the enigmatic O-type spectrum variable HD 191612 has been sharpened substantially. A symmetrical, low-amplitude light curve with a period near 540 days has recently been ...reported from Hipparcos photometry. This period satisfies all of the spectroscopy since at least 1982, including extensive new observations during 2003 and 2004, and it has predicted the next transition during 2004 September - October. Measurements of the Ha equivalent width reveal a sharp emission peak in the phase diagram, in contrast to the apparently sinusoidal light curve. The He II absorption-line strength is essentially constant, while He I varies strongly, possibly filled in by emission in the O6 state, thus producing the apparent spectral type variations. The O8 state appears to be the "normal" one. Two intermediate O7 observations have been obtained, which fall at the expected phases, but these are the only modern observations of the transitions so far. The period is too long for rotation or pulsation; although there is no direct evidence as yet for a companion, a model in which tidally induced oscillations drive an enhanced wind near periastron of an eccentric orbit appears promising. Further observations during the now predictable transitions may provide a critical test. Ultraviolet and X-ray observations during both states will likely also prove illuminating.
Abstract Although rare, numerous case reports suggest that thebesian veins confer increased morbidity and mortality. No study has evaluated their effects on cardiac structure or long term patient ...outcomes. Patients undergoing coronary angiogram at the study institution between October 2002 and January 2015 were assessed for a diagnosis of prominent thebesian veins. A matched control group was created and comparisons between clinical, echocardiographic, and survival measures were made. Of 50,116 total patients, 31 (0.06%) were found to have prominent thebesian veins on angiography and were compared to a matched control group of 596 patients. Patients were matched for age, sex, angiogram date, location and extent of coronary disease, and dominance. Demographic and clinical data were similar between cohorts, with a median follow-up period of 26 months. Patients with thebesian veins had lower Doppler E wave (0.7 versus 0.8; p=0.007) and A wave (0.6 versus 0.8; p=0.001) mitral inflow velocities suggesting some decrease in normal mitral inflow, potentially due to direct shunting into the ventricle from the thebesian vein network. However, there was no observed difference in left ventricular size or ejection fraction between groups. There was also no significantly increased mortality associated with the presence of thebesian veins (hazard ratio 1.11, 95% CI 0.58, 2.13). In conclusion, while previous reports have suggested adverse outcomes from thebesian veins, our case –control study demonstrated no significant associated adverse cardiac structural changes or increase in mortality, although patients with thebesian veins were noted to have a decrease in mitral inflow velocities.
The evolution and fate of massive stars are thought to be affected by
rotationally induced internal mixing. The surface boron abundance is a
sensitive tracer of this in early B-type main sequence ...stars. We test current
stellar evolution models of massive main sequence stars which include
rotational mixing through a systematic study of their predicted surface boron
depletion. We construct a dense grid of rotating single star models using MESA,
for which we employ a new nuclear network which follows all the stable isotopes
up to silicon, including lithium, beryllium, boron, as well as the radioactive
isotope aluminium-26. We also compile the measured physical parameters of the
90 Galactic early B-type stars with boron abundance information. We then
compare each observed stars with our models through a Bayesian analysis, which
yields the mixing efficiency parameter with which the star is reproduced the
best, and the probability that it is represented by the stellar models. We find
that about two-thirds of the sample stars are well represented by the stellar
models, with the best agreement achieved for a rotational mixing efficiency of
~50% compared to the widely adopted value. The remaining one third of the
stars, of which many are strongly boron depleted slow rotators, are largely
incompatible with our models, for any rotational mixing efficiency. We
investigate the observational incidence of binary companions and surface
magnetic fields, and discuss their evolutionary implications. Our results
confirm the concept of rotational mixing in radiative stellar envelopes. On the
other hand, we find that a different boron depletion mechanism, and likely a
different formation path, is required to explain about one-third of the sample
stars. The large spread in the surface boron abundances of these stars may hold
a clue to understanding their origin.
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