Optical Interferometry of early-type stars with PAVO@CHARA. I. Fundamental stellar properties

We present interferometric observations of 7 main-sequence and 3 giant stars with spectral types from B2 to F6 using the PAVO beam combiner at the CHARA array. We have directly determined the angular diameters for these objects with an average precision of 2.3%. We have also computed bolometric fluxes using available photometry in the visible and infrared wavelengths, as well as space-based ultraviolet spectroscopy. Combined with precise \textit{Hipparcos} parallaxes, we have derived a set of fundamental stellar properties including linear radius, luminosity and effective temperature. Fitting the latter to computed isochrone models, we have inferred masses and ages of the stars. The effective temperatures obtained are in good agreement (at a 3% level) with nearly-independent temperature estimations from spectroscopy. They validate recent sixth-order polynomial (B-V)-$T_\mathrm{eff}$ empirical relations \citep{Boyajian2012a}, but suggest that a more conservative third-order solution \citep{vanBelle2009} could adequately describe the (V-K)-$T_\mathrm{eff}$ relation for main-sequence stars of spectral type A0 and later. Finally, we have compared mass values obtained combining surface gravity with inferred stellar radius (\textit{gravity mass}) and as a result of the comparison of computed luminosity and temperature values with stellar evolutionary models (\textit{isochrone mass}). The strong discrepancy between isochrone and gravity mass obtained for one of the observed stars, $\gamma$\,Lyr, suggests that determination of the stellar atmosphere parameters should be revised.Comment: 13 pages, 9 figures, accepted for publication in MNRA

Diagnosis and grading of radiographic osteoporotic vertebral deformity by general radiologists after a brief self-learning period

Background: The expanded semi-quantitative (eSQ) osteoporotic vertebral deformity (OVD) classification has minimal, mild, moderate, moderately-severe, severe, and collapsed grades with <20%, 20-25%, >25%-1/3, >1/3-40%, >40%-2/3, >2/3 vertebral height loss respectively. This study evaluates the performance of using this grading criterion by radiology readers who did not have former training in OVD assessment. Methods: Spine radiographs of 44 elderly women with 278 normal appearing vertebrae and 65 OVDs were selected, with two senior readers agreed the reference reading. Three readers from Italy and three readers from China were invited to evaluate these radiographs after reading five reference articles including one detailing eSQ criteria with illustrative examples. Before the second round of reading, the readers were asked to read an additional explanatory document. For the readers in Italy an additional on-line demonstration was given on how to measure vertebral height loss in another five cases of OVD. Two Chinese readers had a third round of reading after a 90 minutes' on-line lecture. Results: The final absolute agreement rate with the reference reading (i.e., exactly the same grading as the reference) ranged between 46.2% to 68.2% for the six readers, and the final relative agreement (with one eSQ grade difference allowed) ranged between 78.5% to 92.5%. The >1 grade disagreement rate was all below 11%, and mostly below 7%. The missed OVD were mostly minimal grade. The rate for missing a ≥ mild OVD was <4.5%, and false positive rate was generally <1.4% among the final reading. If the minimal grade was removed and the remaining gradings were converted to Genant's semi-quantitative (GSQ) grading, the mean kappa values against the reference reading for SQ grades-1,2,3 were 0.813, 0.814, and 0.916 respectively. Conclusions: This study demonstrates good performance of the six learner readers for assessing radiographic after a brief self-learning period

A novel detection method for voltage sags

Author name used in this publication: K. W. E. ChengAuthor name used in this publication: X. D. XueAuthor name used in this publication: C. D. XuAuthor name used in this publication: Y. B. CheAuthor name used in this publication: D. H. WangAuthor name used in this publication: P. DongPower Electronics Research CentreRefereed conference paper2006-2007 > Academic research: refereed > Refereed conference paperVersion of RecordPublishe

Rotationally-modulated g-modes in the rapidly-rotating delta Scuti star Rasalhague (alpha Ophiuchi)

Despite a century of remarkable progress in understanding stellar interiors, we know surprisingly little about the inner workings of stars spinning near their critical limit. New interferometric imaging of these so-called ``rapid rotators'' combined with breakthroughs in asteroseismology promise to lift this veil and probe the strongly latitude-dependent photospheric characteristics and even reveal the internal angular momentum distribution of these luminous objects. Here, we report the first high precision photometry on the low-amplitude delta cuti variable star Rasalhague (alpha Oph, A5IV, 2.18 Msun, omega/omega_c~0.88) based on 30 continuous days of monitoring using the MOST satellite. We have identified 57+/-1 distinct pulsation modes above a stochastic granulation spectrum with a cutoff of ~26 cycles per day. Remarkably, we have also discovered that the fast rotation period of 14.5~hours modulates low-frequency modes (1-10 day periods) that we identify as a rich family of g-modes (|m| up to 7). The spacing of the g-modes is surprisingly linear considering Coriolis forces are expected to strongly distort the mode spectrum, suggesting we are seeing prograde ``equatorial Kelvin'' waves (modes l=m). We emphasize the unique aspects of Rasalhague motivating future detailed asteroseismic modeling -- a source with a precisely measured parallax distance, photospheric oblateness, latitude temperature structure, and whose low-mass companion provides an astrometric orbit for precise mass determinations.Comment: Accepted for publication in Astrophysical Journa

Development of an automotive HID electronic ballast based microprocessor

Author name used in this publication: D. H. WangAuthor name used in this publication: K. W. E. ChengAuthor name used in this publication: P. DongAuthor name used in this publication: X. D. XueAuthor name used in this publication: K. DingAuthor name used in this publication: Y. B. CheAuthor name used in this publication: C. D. XuPower Electronics Research CentreRefereed conference paper2006-2007 > Academic research: refereed > Refereed conference paperVersion of RecordPublishe

Imaging the Algol Triple System in H Band with the CHARA Interferometer

Algol (Beta Per) is an extensively studied hierarchical triple system whose inner pair is a prototype semi-detached binary with mass transfer occurring from the sub-giant secondary to the main-sequence primary. We present here the results of our Algol observations made between 2006 and 2010 at the CHARA interferometer with the Michigan Infrared Combiner in the H band. The use of four telescopes with long baselines allows us to achieve better than 0.5 mas resolution and to unambiguously resolve the three stars. The inner and outer orbital elements, as well as the angular sizes and mass ratios for the three components are determined independently from previous studies. We report a significantly improved orbit for the inner stellar pair with the consequence of a 15% change in the primary mass compared to previous studies. We also determine the mutual inclination of the orbits to be much closer to perpendicularity than previously established. State-of-the-art image reconstruction algorithms are used to image the full triple system. In particular an image sequence of 55 distinct phases of the inner pair orbit is reconstructed, clearly showing the Roche-lobe-filling secondary revolving around the primary, with several epochs corresponding to the primary and secondary eclipses

Allogenic Mesenchymal Stem Cell Transplantation Ameliorates Nephritis in Lupus Mice Via Inhibition of B-Cell Activation

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