| 1. |
|
|
| 2. |
- Ameye, L., et al.
(författare)
-
Clinically oriented three-step strategy for assessment of adnexal pathology
- 2012
-
Ingår i: Ultrasound in Obstetrics & Gynecology. - : Wiley. - 1469-0705 .- 0960-7692. ; 40:5, s. 582-591
-
Tidskriftsartikel (refereegranskat)abstract
- Objective To determine the diagnostic performance of ultrasound-based simple rules, risk of malignancy index (RMI), two logistic regression models (LR1 and LR2) and real-time subjective assessment by experienced ultrasound examiners following the exclusion of masses likely to be judged as easy and 'instant' to diagnose by an ultrasound examiner, and to develop a new strategy for the assessment of adnexal pathology based on this. Methods 3511 patients with at least one persistent adnexal mass preoperatively underwent transvaginal ultrasonography to assess tumor morphology and vascularity. They were included in two consecutive prospective studies by the International Ovarian Tumor Analysis (IOTA) group: Phase 1 (1999-2005), development of the simple rules and logistic regression models LR1 and LR2, and Phase 2, a validation study (2005-2007). Results Almost half of the cases (43%) were identified as 'instant' to diagnose on the basis of descriptors applied to the database. To assess diagnostic performance in the more difficult 'non-instant' masses, we used only Phase 2 data (n = 1036). The sensitivity of LR2 was 88%, of RMI it was 41% and of subjective assessment it was 87%. The specificity of LR2 was 67%, of RMI it was 90% and of subjective assessment it was 86%. The simple rules yielded a conclusive result in almost 2/3 of the masses, where they resulted in sensitivity and specificity similar to those of real-time subjective assessment by experienced ultrasound examiners: sensitivity 89 vs 89% (P = 0.76), specificity 91 vs 91% (P = 0.65). When a three-step strategy was appliedwith easy 'instant' diagnoses as Step 1, simple rules where conclusive as Step 2 and subjective assessment by an experienced ultrasound examiner in the remaining masses as Step 3, we obtained a sensitivity of 92% and specificity of 92% compared with sensitivity 90% (P = 0.03) and specificity 93% (P = 0.44) when using real-time subjective assessment by experts in all tumors. Conclusion A diagnostic strategy using simple descriptors and ultrasound rules when applied to the variables contained in the IOTA database obtains results that are at least as good as those obtained by subjective assessment of a mass by an expert. Copyright. (C) 2012 ISUOG. Published by John Wiley & Sons, Ltd.
|
|
| 3. |
- Cruzalebes, P., et al.
(författare)
-
Measuring deviation from centrosymmetry for a source brightness distribution observed by spectro-interferometry
- 2014
-
Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 443:4, s. 3550-3563
-
Tidskriftsartikel (refereegranskat)abstract
- We report on the testing of the centrosymmetry parameter (CSP), an indicator of deviation from centrosymmetry of a source brightness distribution. This indicator is derived from the spectral distribution of the triple product measured over three baselines of an optical interferometer. Numerical simulations using parametric toy-models (separated or transiting binary, one-spot model), generated with the SPIDAST software, are applied to the VLTI/AMBER facility in the K band (2.2 mu m). The simulations show that, in case of centrosymmetry, the CSP parameter is in agreement with the usual phase of the spectral mean of the triple product (called GCP, global closure phase). To justify the preferential use of CSP rather than GCP, we show situations with asymmetric geometries for which GCP diagnoses centrosymmetry, while CSP does not. Using realistic Roche lobe-filling binary and hydrodynamic convective models, we show that CSP can also be used as an indicator for geometric similarity between physical and toy-models. Thus, dealing with real data, the toy-model parameters can be fitted on the measured CSP values, in order to assess the input-parameter values of the most suitable complex physical model that will be used to interpret the data.
|
|
| 4. |
- Fossati, L., et al.
(författare)
-
A detailed spectroscopic analysis of the open cluster NGC 5460
- 2011
-
Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 413:2, s. 1132-1144
-
Tidskriftsartikel (refereegranskat)abstract
- Within the context of a large project aimed at studying early F-, A- and late B-type stars, we present the abundance analysis of the photospheres of 21 members of the open cluster NGC 5460, an intermediate-age cluster (log t similar to 8.2) previously not studied with spectroscopy. Our study is based on medium- and high-resolution spectra obtained with the Fibre Large Array Multi Element Spectrograph (FLAMES) instrument of the European Southern Observatory/Very Large Telescope. We show that cluster members have a nearly solar metallicity and that there is evidence that the abundances of magnesium and iron are correlated with the effective temperature, exhibiting a maximum around T-eff = 10 500 K. No correlations are found between abundances and projected equatorial velocity, except for marginal evidence of barium being more abundant in slower than in faster rotating stars. We discovered two He-weak stars and a binary system where the hotter component is an HgMn star. We provide new estimates for the cluster distance (720 +/- 50 pc), age (log t = 8.2 +/- 0.1) and mean radial velocity (-17.9 +/- 5.2 km s-1).
|
|
| 5. |
- Van Holsbeke, C., et al.
(författare)
-
Acoustic streaming cannot discriminate reliably between endometriomas and other types of adnexal lesion: a multicenter study of 633 adnexal masses
- 2010
-
Ingår i: Ultrasound in Obstetrics & Gynecology. - : Wiley. - 1469-0705 .- 0960-7692. ; 35:3, s. 349-353
-
Tidskriftsartikel (refereegranskat)abstract
- Objective To determine the ability of acoustic streaming to discriminate between endometriomas and other adnexal masses. Methods We used data from 1938 patients with an adnexal mass included in Phase 2 of the International Ovarian Tumor Analysis (IOTA) study. All patients had been examined by transvaginal gray-scale and Doppler ultrasound following a standardized research protocol. Assessment of acoustic streaming was voluntary and was carried out only in lesions containing echogenic cyst fluid. Acoustic streaming was defined as movement of particles inside the cyst fluid during gray-scale and/or color Doppler examination provided that the probe had been held still for two seconds to ensure that the movement of the particles was not caused by movement of the probe or the patient. Only centers where acoustic streaming had been evaluated in > 90% of cases were included. Sensitivity, specificity, positive and negative likelihood ratios (LR+, LR-), and positive and negative predictive values (PPV and NPV) of acoustic streaming with regard to endometrioma were calculated. Results 460 (24%) masses were excluded because they were examined in centers where <= 90% of the masses with echogenic cyst fluid had been evaluated for the presence of acoustic streaming. Acoustic streaming was evaluated in 633 of 646 lesions containing echogenic cyst fluid. It was present in 19 (9%) of 209 endometriomas and in 55 (13%) of 424 other lesions. This corresponds to a sensitivity of absent acoustic streaming with regard to endometrioma of 91% (190/209), a specificity of 13% (55/424), LR+ of 1.04, LR- of 0.69, PPV of 34% (190/559) and NPV of 74% (55/74). Conclusions Acoustic streaming cannot discriminate reliably between endometrioinas and other adnexal lesions, and the presence of acoustic streaming does not exclude an endometrioma. Copyright (C) 2009 ISUOG. Published by John Wiley & Sons, Ltd.
|
|
| 6. |
- Van Holsbeke, C., et al.
(författare)
-
Endometriomas: their ultrasound characteristics
- 2010
-
Ingår i: Ultrasound in Obstetrics & Gynecology. - : Wiley. - 1469-0705 .- 0960-7692. ; 35:6, s. 730-740
-
Tidskriftsartikel (refereegranskat)abstract
- Objectives To describe the ultrasound characteristics of endometriomas in pre- and postmenopausal patients and to develop rules that characterize endometriomas. Methods All patients included in the International Ovarian Tumor Analysis (IOTA) studies were used in our analysis. Patients with an adnexal mass were scanned by experienced sonologists using a standardized research protocol. The gold standard was the histology of the surgically removed adnexal mass. The gray-scale and Doppler ultrasound characteristics of the endometriomas were compared with those of other benign and malignant masses. Based on decision-tree analysis, the existing literature and clinical experience, ultrasound rules for the detection of endometriomas were created and evaluated. Results Of all 3511 patients included in the IOTA studies, 713 (20%) had endometriomas. Fifty-one per cent of the endometriomas were unilocular cysts with ground glass echogenicity of the cyst fluid. These characteristics were found less often among other benign tumors or malignancies, or among the small set of endometriomas (4%) that were found in postmenopausal patients. Based on the decision-tree analysis, the optimal rule to detect endometriomas was an adnexal mass in a premenopausal patient with ground glass echogenicity of the cyst fluid, one to four locules and no papillations with detectable blood flow'. Based on clinical considerations, the following rule: 'premenopausal status, ground glass echogenicity of the cyst fluid, one to four locules and no solid parts' seems preferable. Conclusions Several rules had a good ability to characterize endometriomas. The ultrasound characteristics of endometriomas differ between pre- and postmenopausal patients. Masses in postmenopausal women whose cystic contents have a ground glass appearance have a high risk of malignancy. Copyright (C) 2010 ISUOG. Published by John Wiley & Sons, Ltd.
|
|
| 7. |
- Bailey, J. D., et al.
(författare)
-
Magnetic field and atmospheric chemical abundances of the magnetic Ap star HD 318107
- 2011
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 535, s. A25-
-
Tidskriftsartikel (refereegranskat)abstract
- Context. A new generation of powerful and efficient spectropolarimeters has recently been used to provide the first sample of magnetic Ap stars of accurately known ages. Modelling of these data offer the possibility of significant new insights into the physics and main sequence evolution of these remarkable stars.Aims. New spectra have been obtained with the ESPaDOnS spectropolarimeter, and are supplemented with unpolarised spectra from the ESO UVES, UVES-FLAMES, and HARPS spectrographs, of the very peculiar large-field magnetic Ap star HD 318107, a member of the open cluster NGC 6405 and thus a star with a well-determined age. The available data provide sufficient material with which to re-analyse the first-order model of the magnetic field geometry and to derive chemical abundances of Si, Ti, Fe, Nd, Pr, Mg, Cr, Mn, O, and Ca.Methods. The models were obtained using ZEEMAN, a program which synthesises spectral line profiles for stars that have magnetic fields. The magnetic field structure was modelled with a low-order colinear multipole expansion, using coefficients derived from the observed variations of the field strength with rotation phase. The abundances of several elements were determined using spectral synthesis. After experiments with a very simple model of uniform abundance on each of three rings of equal width in co-latitude and symmetric about the assumed magnetic axis, we decided to model the spectra assuming uniform abundances of each element over the stellar surface.Results. The new magnetic field measurements allow us to refine the rotation period of HD 318107 to P = 9.7088 +/- 0.0007 days. Appropriate magnetic field model parameters were found that very coarsely describe the (apparently rather complex) field moment variations. Spectrum synthesis leads to the derivation of mean abundances for the elements Mg, Si, Ca, Ti, Cr, Fe, Nd, and Pr. All of these elements except for Mg and Ca are strongly overabundant compared to the solar abundance ratios. There is considerable evidence of non-uniformity, for example in the different values of < B(z)> found using lines of different elements.Conclusions. The present data set, while limited, is nevertheless sufficient to provide a useful first-order assessment of both the magnetic and surface abundance properties of HD 318107, making it one of the very few magnetic Ap stars of well-known age for which both of these properties have been studied.
|
|
| 8. |
- Klotz, D., et al.
(författare)
-
Catching the fish - Constraining stellar parameters for TX Piscium using spectro-interferometric observations
- 2013
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 550, s. A86-
-
Tidskriftsartikel (refereegranskat)abstract
- Context. Stellar parameter determination is a challenging task when dealing with galactic giant stars. The combination of different investigation techniques has proven to be a promising approach. Aims. We analyse archive spectra obtained with the Short Wavelength Spectrometer (SWS) onboard ISO, and new interferometric observations from the Very Large Telescope MID-infrared Interferometric instrument (VLTI/MIDI) of a very well studied carbon-rich giant: TXPsc. The aim of this work is to determine stellar parameters using spectroscopy and interferometry. Methods. The observations are used to constrain the model atmosphere, and eventually the stellar evolutionary model in the region where the tracks map the beginning of the carbon star sequence. Two different approaches are used to determine stellar parameters: (i) the "classic" interferometric approach where the effective temperature is fixed by using the angular diameter in the N-band (from interferometry) and the apparent bolometric magnitude; (ii) parameters are obtained by fitting a grid of state-of-the-art hydrostatic models to spectroscopic and interferometric observations. Results. We find good agreement between the parameters of the two methods. The effective temperature and luminosity clearly place TXPsc in the carbon-rich AGB star domain in the H-R-diagram. Current evolutionary tracks suggest that TXPsc became a C-star just recently, which means that the star is still in a "quiet" phase compared to the subsequent strong-wind regime. This agrees with the C/O ratio being only slightly greater than one.
|
|
| 9. |
- Klotz, D., et al.
(författare)
-
Geometrical model fitting for interferometric data : GEM-FIND
- 2012
-
Ingår i: Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series. - : SPIE.
-
Konferensbidrag (refereegranskat)abstract
- We developed the tool GEM-FIND that allows to constrain the morphology and brightness distribution of ob- jects. The software fits geometrical models to spectrally dispersed interferometric visibility measurements in the N-band using the Levenberg-Marquardt minimization method. Each geometrical model describes the bright- ness distribution of the object in the Fourier space using a set of wavelength-independent and/or wavelength- dependent parameters. In this contribution we numerically analyze the stability of our nonlinear fitting approach by applying it to sets of synthetic visibilities with statistically applied errors, answering the following questions: How stable is the parameter determination with respect to (i) the number of uv-points, (ii) the distribution of points in the uv-plane, (iii) the noise level of the observations?
|
|
| 10. |
- Klotz, D., et al.
(författare)
-
The geometry of the close environment of SV Piscium as probed by VLTI/MIDI
- 2012
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 541
-
Tidskriftsartikel (refereegranskat)abstract
- Context. SVPsc is an asymptotic giant branch (AGB) star surrounded by an oxygen-rich dust envelope. The mm-CO line profile of the object's outflow shows a clear double-component structure. Because of the high angular resolution, mid-IR interferometry may give strong constraints on the origin of this composite profile. Aims. The aim of this work is to investigate the morphology of the environment around SVPsc using high-angular resolution interferometry observations in the mid-IR with the Very Large Telescope MID-infrared Interferometric instrument (VLTI/MIDI). Methods. Interferometric data in the N-band taken at different baseline lengths (ranging from 32-64 m) and position angles (73-142 degrees) allow a study of the morphology of the circumstellar environment close to the star. The data are interpreted on the basis of 2-dimensional, chromatic geometrical models using the fitting software tool GEM-FIND developed for this purpose. Results. The results favor two scenarios: (i) the presence of a highly inclined, optically thin, dusty disk surrounding the central star; (ii) the presence of an unresolved binary companion at a separation of 13.7(-4.8)(+4.2) AU and a position angle of 121.8 degrees(-24.5)degrees(+15.4)degrees. NE. The derived orbital period of the binary is 38.1(-22.6)(+20.4) yr. This detection is in good agreement with hydrodynamic simulations showing that a close companion could be responsible for the entrainment of the gas and dust into a circumbinary structure.
|
|
| 11. |
- Maercker, Matthias, 1979, et al.
(författare)
-
Unexpectedly large mass loss during the thermal pulse cycle of the red giant star R Sculptoris
- 2012
-
Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 490:7419, s. 232-234
-
Tidskriftsartikel (refereegranskat)abstract
- The asymptotic giant branch star R Sculptoris is surrounded by a detached shell of dust and gas. The shell originates from a thermal pulse during which the star undergoes a brief period of increased mass loss. It has hitherto been impossible to constrain observationally the timescales and mass-loss properties during and after a thermal pulse - parameters that determine the lifetime on the asymptotic giant branch and the amount of elements returned by the star. Here we report observations of CO emission from the circumstellar envelope and shell around R Sculptoris with an angular resolution of 1.3 arcsec. What was hitherto thought to be only a thin, spherical shell with a clumpy structure, is revealed to contain a spiral structure. Spiral structures associated with circumstellar envelopes have been seen previously, from which it was concluded that the systems must be binaries. Using the data, combined with hydrodynamic simulations, we conclude that R Sculptoris is a binary system that underwent a thermal pulse approximately 1800 years ago, lasting approximately 200 years. About 0.003 Msun of mass was ejected at a velocity of 14.3 km s-1 and at a rate approximately 30 times higher than the prepulse mass-loss rate. This shows that approximately 3 times more mass is returned to the interstellar medium during and immediately after a pulse than previously thought.
|
|
| 12. |
- Paladini, C., et al.
(författare)
-
Detection of an asymmetry in the envelope of the carbon Mira R Fornacis using VLTI/MIDI
- 2012
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 544, s. L5-
-
Tidskriftsartikel (refereegranskat)abstract
- Aims. We present a study of the envelope morphology of the carbon Mira R For with VLTI/MIDI. This object is one of the few asymptotic giant branch (AGB) stars that underwent a dust-obscuration event. The cause of such events is still a matter of discussion. Several symmetric and asymmetric scenarios have been suggested in the literature.Methods. Mid-infrared interferometric observations were obtained separated by two years. The observations probe different depths of the atmosphere and cover different pulsation phases. The visibilities and the differential phases were interpreted using GEM-FIND, a tool for fitting spectrally dispersed interferometric observations with the help of wavelength-dependent geometric models.Results. We report the detection of an asymmetric structure revealed through the MIDI differential phase. This asymmetry is observed at the same baseline and position angle two years later. The observations are best simulated with a model that includes a uniform-disc plus a Gaussian envelope plus a point-source. The geometric model can reproduce both the visibilities and the differential phase signatures.Conclusions. Our MIDI data favour explanations of the R For obscuration event that are based on an asymmetric geometry. We clearly detect a photocentre shift between the star and the strongly resolved dust component. This might be caused by a dust clump or a substellar companion. However, the available observations do not allow us to distinguish between the two options. The finding has strong implications for future studies of the geometry of the envelope of AGB stars: if this is a binary, are all AGB stars that show an obscuration event binaries as well? Or are we looking at asymmetric mass-loss processes (i.e. dusty clumps) in the inner part of a carbon-rich Mira?
|
|
| 13. |
- Paladini, C., et al.
(författare)
-
To be or not to be asymmetric? VLTI and the mass loss geometry of red giants
- 2012
-
Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9780819491466 ; 8445, s. Art. no. 84451R-
-
Konferensbidrag (refereegranskat)abstract
- The mass-loss process is a key ingredient for our understanding in many fields of astrophysics, including stellar evolution and the enrichment of the interstellar medium (ISM) via stellar yields. We combined the capability of the VLTI/MIDI and VLT/VISIR instruments with very recent Herschel/PACS observations to characterize the geometry of mass loss from evolved red giants on the Asymptotic Giant Branch (AGB) at various scales. This paper describes the sample of objects, the observing strategy, the tool for the interpretation, and preliminary MIDI results for two targets: U Ant and θ Aps.
|
|
| 14. |
- Ramstedt, Sofia, et al.
(författare)
-
The wonderful complexity of the Mira AB system
- 2014
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 570, s. Art. no. L14-
-
Tidskriftsartikel (refereegranskat)abstract
- We have mapped the (CO)-C-12(3-2) line emission around the Mira AB system at 0 ''.5 resolution using the Atacama Large Millimeter/submillimeter Array (ALMA). The CO map shows amazing complexity. The circumstellar gas has been shaped by different dynamical actors during the evolution of the system, and several morphological components can be identified. The companion is marginally resolved in continuum emission and is currently at 0 ''.487 +/- 0 ''.006 separation. In the main line component, centered on the stellar velocity, spiral arcs around Mira A are found. The spiral appears to be relatively flat and oriented in the orbital plane. An accretion wake behind the companion is clearly visible, and the projected arc separation is about 5 ''. In the blue wing of the line emission, offset from the main line, several large (similar to 5-10 '') opposing arcs are found. We tentatively suggest that this structure is created by the wind of Mira B blowing a bubble in the expanding envelope of Mira A.
|
|
| 15. |
- Sacuto, S., et al.
(författare)
-
Observing and modeling the dynamic atmosphere of the low mass-loss C-star R Sculptoris at high angular resolution
- 2011
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 525, s. A42-
-
Tidskriftsartikel (refereegranskat)abstract
- Context. We study the circumstellar environment of the carbon-rich star R Sculptoris using the near- and mid-infrared high spatial resolution observations from the ESO-VLTI focal instruments VINCI and MIDI, respectively. Aims. These observations aim at increasing our knowledge of the dynamic processes in play within the very close circumstellar environment where the mass loss of AGB stars is initiated. Methods. We first compare the spectro-interferometric measurements of the star at different epochs to detect the dynamic signatures of the circumstellar structures at different spatial and spectral scales. We then interpret these data using a self-consistent dynamic model atmosphere to discuss the dynamic picture deduced from the observations. Since the hydrodynamic computation needs stellar parameters as input, a considerable effort is first applied to determining these parameters. Results. Interferometric observations do not show any significant variability effect at the 16 m baseline between phases 0.17 and 0.23 in the K band, and for both the 15 m baseline between phases 0.66 and 0.97 and the 31 m baseline between phases 0.90 and 0.97 in the N band. We find fairly good agreement between the dynamic model and the spectrophotometric data from 0.4 to 25 mu m. The model agrees well with the time-dependent flux data at 8.5 mu m, whereas it is too faint at 11.3 and 12.5 mu m. The VINCI visibility measurements are reproduced well, meaning that the extension of the model is suitable in the K-band. In the mid-infrared, the model has the proper extension to reveal molecular structures of C2H2 and HCN located above the stellar photosphere. However, the windless model used is not able to reproduce the more extended and dense dusty environment. Conclusions. Among the different explanations for the discrepancy between the model and the measurements, the strong nonequilibrium process of dust formation is one of the most probable. The transition from windless atmospheres to models with considerable mass-loss rates occurs in a very narrow range of stellar parameters, especially for the effective temperature, the C/O ratio, and the pulsation amplitude. A denser sampling of such critical regions of the parameter space with additional models might lead to a better representation of the extended structures of low mass-loss carbon stars like R Sculptoris. The complete dynamic coupling of gas and dust and the approximation of grain opacities with the small-particle limit in the dynamic calculation could also contribute to the difference between the model and the data.
|
|
| 16. |
- Shulyak, D., et al.
(författare)
-
Analysis of surface structures of chemically peculiar stars with modern and future interferometers
- 2014
-
Ingår i: OPTICAL AND INFRARED INTERFEROMETRY IV. - : SPIE. - 9780819496140
-
Konferensbidrag (refereegranskat)abstract
- Interferometry is a very powerful observational technique known in astronomy for many decades. Its application to main-sequence stars, however, is still limited to only brightest objects. In this work we aim to explore the application of interferometry to a special class of main-sequence stars known as chemically peculiar (CP) stars. These stars demonstrate surface chemical abundance inhomogeneities (spots) that usually cover a considerable part of the stellar surface and induce a pronounced spectral and photometric variability. Interferometry thus has a potential to naturally resolve such spots in single stars, providing unique complementary information about spots sizes and contrasts. By means of numerical experiments we derive the actual interferometric requirements essential for the CP stars research that can be addressed in future instrument development. The first comparison between theoretical predictions and already available observations will also be discussed.
|
|
| 17. |
- Shulyak, D., et al.
(författare)
-
Interferometry of chemically peculiar stars : theoretical predictions versus modern observing facilities
- 2014
-
Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 443:2, s. 1629-1642
-
Tidskriftsartikel (refereegranskat)abstract
- By means of numerical experiments we explore the application of interferometry to the detection and characterization of abundance spots in chemically peculiar (CP) stars using the brightest star epsilon UMa as a case study. We find that the best spectral regions to search for spots and stellar rotation signatures are in the visual domain. The spots can clearly be detected already at a first visibility lobe and their signatures can be uniquely disentangled from that of rotation. The spots and rotation signatures can also be detected in near-infrared at low spectral resolution but baselines longer than 180 m are needed for all potential CP candidates. According to our simulations, an instrument like VEGA (or its successor e. g. Fibered and spectrally Resolved Interferometric Equipment New Design) should be able to detect, in the visual, the effect of spots and spots+rotation, provided that the instrument is able to measure V-2 approximate to 10(-3), and/or closure phase. In infrared, an instrument like AMBER but with longer baselines than the ones available so far would be able to measure rotation and spots. Our study provides necessary details about strategies of spot detections and the requirements for modern and planned interferometric facilities essential for CP star research.
|
|
| 18. |
|
|
| 19. |
- Van Holsbeke, C., et al.
(författare)
-
Prospective external validation of the 'ovarian crescent sign' as a single ultrasound parameter to distinguish between benign and malignant adnexal pathology
- 2010
-
Ingår i: Ultrasound in Obstetrics & Gynecology. - : Wiley. - 1469-0705 .- 0960-7692. ; 36:1, s. 81-87
-
Tidskriftsartikel (refereegranskat)abstract
- Objective To determine the sensitivity and specificity of the 'ovarian crescent sign' (OCS) - a rim of normal ovarian tissue seen adjacent to an ipsilateral adnexal mass as a sonographic feature to discriminate between benign and malignant adnexal masses. Methods The patients included were a subgroup of patients participating in the International Ovarian Tumor Analysis (IOTA) Phase 2 study, which is an international multicenter study. The subgroup comprised 1938 patients, with an adnexal mass, recruited from 19 ultrasound centers in different countries. All patients were scanned using the same standardized ultrasound protocol. Information on more than 40 demographic and ultrasound variables were collected, but the evaluation of the OCS was optional. Only patients from centers that had evaluated the OCS in >= 90% of their cases were included. The gold standard was the histological diagnosis of the adnexal mass. The ability of the OCS to discriminate between borderline or invasively malignant vs. benign adnexal masses, as well as between invasively malignant vs. other (benign and borderline) tumors, was determined and compared with the performance of subjective evaluation of ultrasound findings by the ultrasound examiner. Results The OCS was evaluated in 1377 adnexal masses from 12 centers, 938 (68%) masses being benign, 86 (6%) borderline, 305 (22%) primary invasive and 48 (3%) metastases. The OCS was present in 398 (42%) of 938 benign masses, in 14 (16%) of 86 borderline tumors, in 18 (6%) of 305 primary invasive tumors (one malignant struma ovarii, one uterine clear cell adenocarcinoma and 16 epithelial carcinomas, i.e. four Stage I and 12 Stage II-IV) and in two (4%) of 48 ovarian metastases. Hence, the sensitivity and specificity for absent OCS to identify a malignancy was 92% and 42%, respectively, and the positive and negative likelihood ratios (LR+ and LR-, respectively) were 1.60 and 0.18. Subjective impression performed significantly better than the OCS. Sensitivity and specificity were 90% and 92%, respectively, LR+ was 11.0 and LR- was 0.10. For discrimination between invasive vs. benign or borderline tumors, the sensitivity for absent OCS was 94%, the specificity was 40%, the LR+ was 1.58 and the LR- was 0.14. Conclusion This study confirms previous reports that the presence of the OCS decreases the likelihood of invasive malignancy in adnexal masses. However it is a poor discriminator between benign and malignant adnexal masses. Copyright (C) 2010 ISUOG. Published by John Wiley & Sons, Ltd.
|
|
