6,036 research outputs found
A MiMeS analysis of the magnetic field and circumstellar environment of the weak-wind O9 sub-giant star HD 57682
I will review our recent analysis of the magnetic properties of the O9IV star
HD 57682, using spectropolarimetric observations obtained with ESPaDOnS at the
Canada-France-Hawaii telescope within the context of the Magnetism in Massive
Stars (MiMeS) Large Program. I discuss our most recent determination of the
rotational period from longitudinal magnetic field measurements and Halpha
variability - the latter obtained from over a decade's worth of professional
and amateur spectroscopic observations. Lastly, I will report on our
investigation of the magnetic field geometry and the effects of the field on
the circumstellar environment.Comment: 2 pages, 2 figures, IAUS272 - Active OB Stars: Structure, Evolution,
Mass Loss and Critical Limit
Of?p stars: a class of slowly rotating magnetic massive stars
Only 5 Of?p stars have been identified in the Galaxy. Of these, 3 have been
studied in detail, and within the past 5 years magnetic fields have been
detected in each of them. The observed magnetic and spectral characteristics
are indicative of organised magnetic fields, likely of fossil origin, confining
their supersonic stellar winds into dense, structured magnetospheres. The
systematic detection of magnetic fields in these stars strongly suggests that
the Of?p stars represent a general class of magnetic O-type stars.Comment: Proceedings of IAUS 272: Active OB star
Measurements of Total Hemispherical Emissivity of Several Stably Oxidized Nickel-Titanium Carbide Cemented Hard Metals from 600 F to 1,600 F
The total hemispherical emissivity of several nickel-titanium carbide cemented hard metals have been measured over a temperature range from 600 F to l,600 F. A variety of cemented hard metals were obtained from the Kennametal Corporation. A brief discussion of the apparatus employed and the procedures used for this investigation is included. The results of the tests of specimens in the as-received and polished states indicate a nearly constant emissivity for each material tested over the temperature range considered and only slight differences in emissivity values for the different materials. Values obtained on the stably oxidized specimens range from 0.90 to 0.94 at 6000 F and o.88 to 0.92 at 1,600 F for the as-received specimens and from 0.82 to 0.89 at 600 F and 0.85 to 0.87 at 1,600 F for the polished specimens. The surface analysis of the oxidized materials as obtained by X-ray diffraction methods and metallographic techniques are presented as an aid to reproducing the surface on which these measurements were made
Discovery of the first tau Sco analogues: HD 66665 and HD 63425
The B0.2 V magnetic star tau Sco stands out from the larger population of
massive OB stars due to its high X-ray activity, peculiar wind diagnostics and
highly complex magnetic field. This paper presents the discovery of the first
two tau Sco analogues - HD 66665 and HD 63425, identified by the striking
similarity of their UV spectra to that of tau Sco. ESPaDOnS spectropolarimetric
observations were secured by the Magnetism in Massive Stars CFHT Large Program,
in order to characterize the stellar and magnetic properties of these stars.
CMFGEN modelling of optical ESPaDOnS spectra and archived IUE UV spectra showed
that these stars have stellar parameters similar to those of tau Sco. A
magnetic field of similar surface strength is found on both stars, reinforcing
the connection between the presence of a magnetic field and wind peculiarities.
However, additional phase-resolved observations will be required in order to
assess the potential complexity of the magnetic fields, and verify if the wind
anomalies are linked to this property.Comment: 6 pages, 2 tables, 3 figures. Accepted for publication in MNRAS. The
definitive version will be available at www.blackwel-synergy.co
Reproducibility of left ventricular mass measurements by two-dimensional and M-mode echocardiography
AbstractBoth two-dimensional and M-mode echocardiography provide accurate estimates of left ventricular mass. However, their reproducibility in serial studies has not been compared, although this issue is critical to evaluation of regression of hypertrophy. To determine which technique provides more reproducible estimates of left ventricular mass, three serial studies were performed prospectively in each of eight normal adults over 5 months. Both two-dimensional and M-mode echocardiograms were obtained at each of these 24 studies. Measurements were performed by two independent observers who did not know patient identity. For the two-dimensional method, left ventricular mass was determined with use of a computer light-pen system and the truncated ellipsoid formula. For the M-mode method, mass was calculated from Penn convention measurements with use of the cube formula.At study 1 the group mean left ventricular mass by two-dimensional echocardiography (115 ± 20 g) did not differ from that by M-mode study (127± 37 g, p = NS). However, serial estimates of left ventricular mass were more reproducible by two-dimensional echocardiography. The mean difference among the three serial two-dimensional studies in each individual was 4.8 ± 4 g (4.2 ± 3%) by the two-dimensional method, but was 18.5 ± 13 g (14.9 ± 10%) by the M-mode method (p = 0.01). Interobserver results for left ventricular mass by two-dimensional echocardiography correlated closely (r = 0.95, n = 24, p < 0.001).The superior reproducibility of two-dimensional echocardiographic estimates of left ventricular mass in normal adults supports the use of two-dimensional echocardiography when serial studies are to be performed
Discovery of a strong magnetic field in the rapidly rotating B2Vn star HR 7355
We report the detection of a strong, organized magnetic field in the
helium-variable early B-type star HR 7355 using spectropolarimetric data
obtained with ESPaDOnS on the 3.6-m Canada-France-Hawaii Telescope within the
context of the Magnetism in Massive Stars (MiMeS) Large Program. HR 7355 is
both the most rapidly rotating known main-sequence magnetic star and the most
rapidly rotating helium-strong star, with = 300 15 km s
and a rotational period of 0.5214404 0.0000006 days. We have modeled our
eight longitudinal magnetic field measurements assuming an oblique dipole
magnetic field. Constraining the inclination of the rotation axis to be between
and , we find the magnetic obliquity angle to be
between and , and the polar strength of the magnetic
field at the stellar surface to be between 13-17 kG. The photometric light
curve constructed from HIPPARCOS archival data and new CTIO measurements shows
two minima separated by 0.5 in rotational phase and occurring 0.25 cycles
before/after the magnetic extrema. This photometric behavior coupled with
previously-reported variable emission of the H line (which we confirm)
strongly supports the proposal that HR 7355 harbors a structured magnetosphere
similar to that in the prototypical helium-strong star, Ori E.Comment: 6 pages, 3 figures. Accepted for publication in MNRAS Letter
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