173 research outputs found
The Dust Sublimation Region of the Type 1 AGN NGC 4151 at a Hundred Microarcsecond Scale as Resolved by the CHARA Array Interferometer
No full textThe nuclear region of Type 1 active galactic nuclei (AGNs) has only been partially resolved so far in the near-infrared (IR), where we expect to see the dust sublimation region and the nucleus directly without obscuration. Here, we present the near-IR interferometric observation of the brightest Type 1 AGN NGC 4151 at long baselines of ∼250 m using the CHARA Array, reaching structures at hundred microarcsecond scales. The squared visibilities decrease down to as low as ∼0.25, definitely showing that the structure is resolved. Furthermore, combining with the previous visibility measurements at shorter baselines but at different position angles, we show that the structure is elongated perpendicular to the polar axis of the nucleus, as defined by optical polarization and a linear radio jet. A thin-ring fit gives a minor/major axis ratio of ∼0.7 at a radius ∼0.5 mas (∼0.03 pc). This is consistent with the case where the sublimating dust grains are distributed preferentially in the equatorial plane in a ring-like geometry, viewed at an inclination angle of ∼40°. The recent mid-IR interferometric finding of polar-elongated geometry at a pc scale, together with a larger-scale polar outflow as spectrally resolved by the Hubble Space Telescope, would generally suggest a dusty, conical and hollow outflow being launched, presumably in the dust sublimation region. This might potentially lead to a polar-elongated morphology in the near-IR, as opposed to the results here. We discuss a possible scenario where an episodic, one-off anisotropic acceleration formed a polar-fast and equatorially slow velocity distribution, having led to an effectively flaring geometry as we observe
Anterior superior alveolar nerve injury after extended endoscopic medial maxillectomy: a preclinical study to predict neurological morbidity
No full textEndoscopic medial maxillectomies (EMMs) are used to optimize exposure of the maxillary sinus and retromaxillary areas. Although in type D EMM (Sturmann-Canfield procedure) the anterior superior alveolar nerve (ASAN) is always at risk of injury, only 29% of patients complained of alveolar process and dental anesthesia. The purpose of this anatomical study is to assess the neural anastomotic network of the ASAN (ASAN-NAN) and describe different extensions of type D EMMs in a preclinical setting
Photoexcitation spectroscopy and material alteration with free-electron laser
No full textAs synchrotron radiation sources have been used for many experiments in the ultraviolet and X-ray regimes, the free-electron laser is an excellent source for a wide array of infrared-photon projects and applications. The free-electron laser delivers a beam of powerful tunable pulsed radiation which provides the opportunity for spatial and temporal localization of the energy delivered at any desired wavelength within the 2-10 mu m regime. One application discussed employs the free-electron laser for spectroscopy as a probe of electronic and vibrational structures. Another application uses the free-electron laser beam as a tool for altering materials in a fundamentally new way.LSELPRXVanderbilt univ,dept appl & engn sci,nashville,tn 37235. ecole polytech fed lausanne,inst phys appl,ch-1015 lausanne,switzerland. Sturmann, J, VANDERBILT UNIV,DEPT PHYS & ASTRON,CTR MOL & ATOM STUDIES & SURFACES,BOX 1807-B,NASHVILLE,TN 37235.ISI Document Delivery No.: WW08
The fundamental parameters of the roAp star 10 Aquilae
No full textContext. Owing to the strong magnetic field and related abnormal surface layers existing in rapidly oscillating Ap (roAp) stars, systematic errors are likely to be present when determining their effective temperatures, which potentially compromises asteroseismic studies of this class of pulsators.
Aims. Using the unique angular resolution provided by long-baseline visible interferometry, our goal is to determine accurate angular diameters of a number of roAp targets, so as to derive unbiased effective temperatures (Teff) and provide a Teff calibration for these stars.
Methods. We obtained long-baseline interferometric observations of 10 Aql with the visible spectrograph VEGA at the combined focus of the CHARA array. We derived the limb-darkened diameter of this roAp star from our visibility measurements. Based on photometric and spectroscopic data available in the literature, we estimated the star’s bolometric flux and used it, in combination with its parallax and angular diameter, to determine the star’s luminosity and effective temperature.
Results. We determined a limb-darkened angular diameter of 0.275 ± 0.009 mas and deduced a linear radius of R = 2.32 ± 0.09 R⊙. For the bolometric flux we considered two datasets, leading to an effective temperature of Teff = 7800 ± 170 K and a luminosity of L/L⊙ = 18 ± 1 or Teff = 8000 ± 210 K and L/L⊙ = 19 ± 2. Finally we used these fundamental parameters together with the large frequency separation determined by asteroseismic observations to constrain the mass and the age of 10 Aql, using the CESAM stellar evolution code. Assuming a solar chemical composition and ignoring all kinds of diffusion and settling of elements, we obtained a mass M/M⊙ ~ 1.92 and an age of ~780 Gy or a mass M/M⊙ ~ 1.95 and an age of ~740 Gy, depending on the derived value of the bolometric flux.
Conclusions. For the first time, thanks to the unique capabilities of VEGA, we managed to determine an accurate angular diameter for a star smaller than 0.3 mas and to derive its fundamental parameters. In particular, by only combining our interferometric data and the bolometric flux, we derived an effective temperature that can be compared to those derived from atmosphere models. Such fundamental parameters can help for testing the mechanism responsible for the excitation of the oscillations observed in the magnetic pulsating stars
Fundamental properties of stars using asteroseismology from Kepler and CoRoT and interferometry from the CHARA Array
No full textWe present results of a long-baseline interferometry campaign using the PAVO beam combiner at the CHARA Array to measure the angular sizes of five main-sequence stars, one subgiant and four red giant stars for which solar-like oscillations have been detected by either Kepler or CoRoT. By combining interferometric angular diameters, Hipparcos parallaxes, asteroseismic densities, bolometric fluxes, and high-resolution spectroscopy, we derive a full set of near-model-independent fundamental properties for the sample. We first use these properties to test asteroseismic scaling relations for the frequency of maximum power (νmax) and the large frequency separation (Δν). We find excellent agreement within the observational uncertainties, and empirically show that simple estimates of asteroseismic radii for main-sequence stars are accurate to ≲ 4%. We furthermore find good agreement of our measured effective temperatures with spectroscopic and photometric estimates with mean deviations for stars between T eff = 4600-6200 K of -22 ± 32 K (with a scatter of 97K) and -58 ± 31 K (with a scatter of 93K), respectively. Finally, we present a first comparison with evolutionary models, and find differences between observed and theoretical properties for the metal-rich main-sequence star HD173701. We conclude that the constraints presented in this study will have strong potential for testing stellar model physics, in particular when combined with detailed modeling of individual oscillation frequencies. © 2012. The American Astronomical Society. All rights reserved
Different endoscopic surgical strategies in the management of inverted papilloma of the sinonasal tract: experience on 47 patients
No full textOBJECTIVE:
To demonstrate the potentials and limitations of three different endoscopic procedures employed for treatment of inverted papilloma (IP) of the sinonasal tract.
STUDY DESIGN:
Retrospective analysis of a cohort of patients treated at two University hospitals.
METHODS:
From January 1992 to June 2000, 47 patients with IP underwent endoscopic resection. Preoperative workup included multiple biopsies of the lesion and imaging evaluation by computed tomography or magnetic resonance imaging. Massive skull base erosion, intradural or intraorbital extension, extensive involvement of the frontal sinus, abundant scar tissue caused by previous surgery, or the concomitant presence of squamous cell carcinoma were considered absolute contraindications for a purely endoscopic approach. Three types of resection were used: ethmoidectomy with wide antrostomy and sphenoidotomy (type 1) for IPs confined to the middle meatus, medial maxillectomy with ethmoidectomy and sphenoidotomy (type 2) for IPs partially invading the maxillary sinus, and a Sturmann-Canfield operation (type 3) for IPs involving the mucosa of the alveolar recess or of the anterolateral corner of the maxillary sinus. All patients were followed by periodic endoscopic evaluations.
RESULTS:
Type 1, 2, and 3 resections were performed in 26, 15, and 6 patients, respectively. No recurrences were observed after a mean follow-up of 55 (range 30-132) months. One patient, who underwent a type 2 resection, developed a stenosis of the lacrimal pathways requiring endoscopic dacryocystorhinostomy.
CONCLUSIONS:
Our experience confirms that endoscopic surgery is an effective and safe method of treatment for most IPs. The availability of different endoscopic techniques allows the entity of the dissection to be modulated in relation to the extent of disease. Strict application of selection criteria, meticulous use of subperiosteal dissection in the involved areas, and regular follow-up evaluation are key elements for success
Different endoscopic surgical strategies in the management of inverted papilloma of the sinonasal tract: experience with 47 patients
No full textOBJECTIVE: To demonstrate the potentials and limitations of three different endoscopic procedures employed for treatment of inverted papilloma (IP) of the sinonasal tract. STUDY DESIGN: Retrospective analysis of a cohort of patients treated at two University hospitals. METHODS: From January 1992 to June 2000, 47 patients with IP underwent endoscopic resection. Preoperative workup included multiple biopsies of the lesion and imaging evaluation by computed tomography or magnetic resonance imaging. Massive skull base erosion, intradural or intraorbital extension, extensive involvement of the frontal sinus, abundant scar tissue caused by previous surgery, or the concomitant presence of squamous cell carcinoma were considered absolute contraindications for a purely endoscopic approach. Three types of resection were used: ethmoidectomy with wide antrostomy and sphenoidotomy (type 1) for IPs confined to the middle meatus, medial maxillectomy with ethmoidectomy and sphenoidotomy (type 2) for IPs partially invading the maxillary sinus, and a Sturmann-Canfield operation (type 3) for IPs involving the mucosa of the alveolar recess or of the anterolateral corner of the maxillary sinus. All patients were followed by periodic endoscopic evaluations. RESULTS: Type 1, 2, and 3 resections were performed in 26, 15, and 6 patients, respectively. No recurrences were observed after a mean follow-up of 55 (range 30-132) months. One patient, who underwent a type 2 resection, developed a stenosis of the lacrimal pathways requiring endoscopic dacryocystorhinostomy. CONCLUSIONS: Our experience confirms that endoscopic surgery is an effective and safe method of treatment for most IPs. The availability of different endoscopic techniques allows the entity of the dissection to be modulated in relation to the extent of disease. Strict application of selection criteria, meticulous use of subperiosteal dissection in the involved areas, and regular follow-up evaluation are key elements for succes
Colder and Hotter: Interferometric Imaging of _ Cassiopeiae and _ Leonis
No full textNear-infrared interferometers have recently imaged a number of rapidly rotating A-type stars, finding levels of gravity darkening inconsistent with theoretical expectations. Here, we present new imaging of both a cooler star _ Cas (F2IV) and a hotter one _ Leo (B7V) using the CHARA array and the MIRC instrument at the H band. Adopting a solid-body rotation model with a simple gravity darkening prescription, we modeled the stellar geometric properties and surface temperature distributions, confirming that both stars are rapidly rotating and show gravity darkening anomalies. We estimate the masses and ages of these rapid rotators on L - R pol and H-R diagrams constructed for non-rotating stars by tracking their non-rotating equivalents. The unexpected fast rotation of the evolved sub-giant _ Cas offers a unique test of the stellar core-envelope coupling, revealing quite efficient coupling over the past ~0.5 Gyr. Lastly, we summarize all our interferometric determinations of the gravity darkening coefficient for rapid rotators, finding that none match the expectations from the widely used von Zeipel gravity darkening laws. Since the conditions of the von Zeipel law are known to be violated for rapidly rotating stars, we recommend using the empirically derived _ = 0.19 for such stars with radiation-dominated envelopes. Furthermore, we note that no paradigm exists for self-consistently modeling heavily gravity-darkened stars that show hot radiative poles with cool convective equators.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90751/1/0004-637X_732_2_68.pd
JOUVENCE OF FLUOR: UPGRADES OF A FIBER BEAM COMBINER AT THE CHARA ARRAY
No full textThe FLUOR (Fiber Linked Unit for Optical Recombination) interferometric beam combiner located at the CHARA Array on Mt. Wilson, California has recently undergone a program of major upgrades known as Jouvence of FLUOR (JouFLU). These upgrades seek to improve the precision, use, and observing efficiency of FLUOR as well as introduce new modes of operation. A Fourier Transform Spectrograph (FTS) mode and a spectral dispersion mode have been added to improve calibration and data collection. New mechanized stages and new cameras have been added to FLUOR for alignment and pupil plane imaging. Entirely new control/command software has been written for FLUOR which brings it into compliance with CHARA software standards. This allows for continued software upgrades and full remote operation capability. The new JouFLU instrument is now operating on sky and is expected to achieve accurate interferometric visibility amplitude measurements with 0.1 to 0.3 % precision
The fundamental parameters of the Ap star 78 Virginis
No full textContext. Determining the effective temperature of Ap stars, including the roAp stellar pulsators, is a difficult task owing to their strong magnetic field and their related spotted surfaces. It is, however, an important step towards constraining models of their complex atmosphere and testing proposed pulsation excitation mechanisms.
Aims. Using the unique angular resolution provided by long-baseline visible interferometry, we aim at deriving accurate angular diameters of a number of Ap targets, so as to determine their unbiased effective temperature (Teff) and their accurate position in the Hertzsprung-Russell diagram, to estimate their mass and age, and to test non-adiabatic pulsation models. Interferometric results on four Ap stars have been published in earlier works. Here we report the results on a fifth, significantly hotter star.
Methods. We observed 78 Vir with the visible spectrograph VEGA installed at the combined focus of the CHARA long-baseline optical array. We derived the limb-darkened diameter of this Ap star from our interferometric measurements. Based on photometric and spectroscopic data available in the literature, we estimated the star’s bolometric flux and used it, in combination with its parallax and angular diameter, to determine the star’s luminosity and effective temperature. We then used the derived fundamental parameters to perform a non-adiabatic pulsation analysis.
Results. We determined a limb-darkened angular diameter of 0.346 ± 0.006 mas and deduced a linear radius of R = 2.11 ± 0.04 R⊙. Considering a bolometric flux of 2.73 ± 0.20 10-7 erg/cm2/s we obtained a luminosity of L/L⊙ = 27 ± 2 and an effective temperature of Teff = 9100 ± 190 K. The non-adiabatic pulsation modeling allows us to predict that high overtone pulsations could be excited in 78 Vir at frequencies ranging from 1.2 to 1.9 mHz, provided that the magnetic field is capable of suppressing envelope convection in the polar regions.
Conclusions. Visible long-baseline interferometry is a unique means of deriving accurate fundamental parameters of Ap stars. The Ap star 78 Vir is found to be a promising roAp-star candidate and one that would allow us to extend recent tests on the roAp stars’ excitation mechanism towards the blue edge of the instability strip. Asteroseismic data of this star would, therefore, be of strong interest
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