A5067996366- Stellar, planetary, and galactic studies
- Astronomy and Astrophysical Research
- Astrophysics and Star Formation Studies
- Astro and Planetary Science
- Astronomical Observations and Instrumentation
- Digital Radiography and Breast Imaging
- Astrophysical Phenomena and Observations
- Advanced X-ray and CT Imaging
- Solar and Space Plasma Dynamics
- Gamma-ray bursts and supernovae
- Adaptive optics and wavefront sensing
- History and Developments in Astronomy
- Advanced Mathematical Theories
- Radiation Shielding Materials Analysis
- Spectroscopy Techniques in Biomedical and Chemical Research
- Radiation Dose and Imaging
- Power System Reliability and Maintenance
- Galaxies: Formation, Evolution, Phenomena
- Calibration and Measurement Techniques
- Radiation Effects and Dosimetry
- Quantum Dots Synthesis And Properties
- Pulsars and Gravitational Waves Research
- Inertial Sensor and Navigation
- Minerals Flotation and Separation Techniques
- X-ray Spectroscopy and Fluorescence Analysis
Universidade Federal de São Paulo
2013-2024
Institut d'Astrophysique de Paris
2019
Fundação de Amparo à Pesquisa do Espírito Santo
2019
Universidade Nove de Julho
2009
Universidade Franciscana
2007-2008
Universidade de São Paulo
2003-2008
Museu de Astronomia e Ciências Afins
2002-2005
Instituto de Geofísica y Astronomía
2005
Extensive spectral observations of η Carinae over the last cycle, and particularly around 2003.5 low-excitation event, have been obtained. The variability both narrow broad lines, when combined with data taken from two earlier cycles, reveal a common well-defined period. We cycle lengths derived many lines in optical spectrum those broad-band X-rays, near-infrared observations, obtained period length Ppres= 2022.7 ± 1.3 d.
This study presents a comparison of the X-ray transmission through microsized and nanosized materials. For this purpose CuO nanoparticles, with 13.4 nm average grain size, microparticles, mean particle size 56 μm, were incorporated separately to beeswax in concentration 5%. Results show that above material plates was almost same for beams generated at 60 102 kV tube voltages. However, radiation 26 30 voltages X-rays are more attenuated by nanostructured factor least 14%. suggest difference...
Spectroscopic monitoring of 141 southern field B type stars, 114 them known to exhibit the Be phenomenon, allowed estimation their projected rotational velocities, effective temperatures and superficial gravities from both line equivalent width fitting procedures. Stellar ages, masses bolometric luminosities were derived internal structure models. Without taking into account for effects gravity darkening, we notice occurrence phenomenon in later stages main sequence phase.
We explore the geometrical distortion and stellar circumstellar activity of α Eri (HD 10144), brightest Be star in sky. present a thorough discussion fundamental parameters object for an independent determination its rotational distortion. used atmosphere models evolutionary tracks calculated fast rotating early-type stars. If is rigid rotator, angular velocity rate 0.8, so that smaller than one inferred from recent interferometric measurements. then discuss surface using high resolution S/N...
A full description of the 5.5-yr low excitation events in Eta Carinae is presented. We show that they are not as simple and brief previously thought, but a combination two components. The first, 'slow variation' component, revealed by slow changes ionization level circumstellar matter across whole cycle caused gradual wind-wind collision shock-cone orientation, angular opening gaseous content. second, 'collapse' restricted to around minimum, due temporary global collapse shock. High energy...
Estimates of interstellar extinction are essential in a broad range astronomical research. In the last decades, several maps and models large scale Galaxy have been published. However, these developed different programming languages, with user interfaces input/output formats, which makes using comparing results from difficult. To address this issue, we tool called GALExtin (\url{http://www.galextin.org}) - that estimates based on both 3D models/maps 2D available. The only needs to provide...
We present the results of a high-accuracy (σ ≈ 0.005%) polarization monitoring Be star Achernar that was carried out between 2006 July 7 and November 5. Our indicate after near-quiescent phase from 1998 to 2002, is currently in an active has built circumstellar disk. detect variations both level position angle on timescales as short 1 hr long several weeks. Detailed modeling observed strongly suggests short-term originate discrete mass ejection events which produce transient inhomogeneities...
Prompted by peculiar spectroscopic variability observed in SDSS/APOGEE $H$-band spectra, we monitored the Be star HD 55606 using optical spectroscopy and found that it is an exotic double-lined binary (SB2) consisting of a hot, compact companion probably OB subdwarf (sdOB) star. Motion sdOB traced its impact on strong He~I lines, as radial velocity ($V_{r}$) variable, double-peaked emission profiles with narrow central absorption cores. Weak He II 4686 {\AA} associated detected most spectra....
The physical properties of stellar atmospheres in rapidly rotating massive stars, such as Be are critical to understanding their evolution and role progenitors supernovae. These which often have near-critical rotation, exhibit equatorial stretching gravity darkening, significantly complicates the determination parameters inclination angle. characterized by extreme rotational velocities, serve excellent candidates for exploring these phenomena. However, fundamental quantities polar radii...
The Be star π Aquarii shows a peculiar X-ray emission (γ Cas type) commonly attributed to its outer disk interacting with low-mass companion star, probably white dwarf. In this work, we study the long-term variability of optical spectra in order derive stellar and parameters specific epochs when major changes. We identified several spectral lines studied observation dates for Balmer, helium, silicon, iron detail. determined using atmosphere models, considering oblate geometry due fast...
Abstract In this work we present a grid of LTE and non-LTE synthetic spectra hot DA white dwarfs (WDs). addition to its usefulness for the determination fundamental stellar parameters isolated WDs in binaries, will be interest construction theoretical libraries studies from integrated light. The spectral covers both wide temperature gravity range, with 17,000 K ≤ T eff 100,000 7.0 <?CDATA $\mathrm{log}g$?> 9.5. models are built pure hydrogen cover wavelength range 900 Å 2.5 μ m....
In this paper we present new results on stellar fundamental parameters for early B and Be field stars observed in the southern hemisphere: effective temperature, superficial gravity, projected rotation velocity. The estimation of their velocities is made by two successive methods. We first obtain an initial value based Fourier transforms He I λ4471 line 34 with magnitudes range 0.5 ≤ mv 10, followed a more accurate fitting procedure lines non-LTE model profiles. This yields velocity...
Star rotation offers us a large horizon for the study of many important physical issues pertaining to stellar evolution. Currently, four methods are widely used infer velocities, namely those related line width calibrations, on fitting synthetic spectra, interferometry, and Fourier transforms (FTs) profiles. Almost all estimations projected velocities using method in literature have been addressed with use linear limb-darkening (LD) approximations during evaluation profiles their cosine FTs,...
Context. Estimating the physical states of surfaces fast-rotating stars is challenging due to several intrinsic processes, which include radiative flux inhomogeneities on photosphere induced by rotation and circumstellar signatures in their spectra. The analysis spectra ultimately requires use synthetic grids accounting for all these processes. Aims. In this paper, we present ‘von ZeiPEl’s code gravity darKening specTRal synthesis’ (ZPEKTR) code, designed perform spectral synthesis stars,...
In this study, scattered x-ray distributions were produced by irradiating a tissue equivalent phantom under clinical mammographic conditions using Mo/Mo, Mo/Rh and W/Rh anode/filter combinations, for 25 30 kV tube voltages. Energy spectra of the x-rays have been measured with Cd0.9Zn0.1Te (CZT) detector scattering angles between 30° 165°. Measurement correction processes evaluated through comparison values half-value layer (HVL) air kerma calculated from corrected an ionization chamber in...
Line profile variations (lpv) in He i, Fe ii, Mg ii and Si transitions were detected the Be star η Cen (HD 127972) by means of high resolution spectroscopic observations obtained six epochs from May 1996 to April 2001. They interpreted terms nonradial pulsations (NRPs). Time analysis was performed using Cleanest algorithm showed following frequencies with order significance: 0.61 c/d, 1.48 3.81 5.31 9.24 c/d 10.35 c/d. From phase variation diagrams we estimated mode degrees range 3–8. If...
The increase in the X-ray absorption due to gold nanoparticles was investigated by using aqueous solutions containing (Au) nanoparticles. A sample with 15 nm size and 0.5 mg/mL concentration a distilled water were used. Transmitted beams through samples registered CdTe detector an ionization chamber. Results show enhancement range 20%–6% for generated from 20 kV 120 tube voltages, respectively. that use of nanoparticles, even at low concentrations, should result significant contrast low-energy beams.
The protective shielding design of a mammography facility requires the knowledge scattered radiation by patient and image receptor components. shape intensity secondary x-ray beams depend on kVp applied to tube, target/filter combination, primary field size, scattering angle. Currently, calculations for facilities are performed based scatter fraction data target/filter, even though modern equipment is designed with different anode/filter combinations. In this work we present evaluated...
Aims. We investigate the time-varying patterns in line profiles, V/R, and radial velocity of Be star HD 173948 (λ Pavonis).
In this work we evaluate the effectiveness of computed tomography images as a tool to determine magnetic nanoparticle biodistribution over biological tissues. For purpose, for nanoparticles, composed Fe3O4, coated with 2,3-dimercaptosuccinic acid (DMSA), were generated at several material concentrations. The comparison CT numbers, calculated from these clinical conditions, typical numbers tissues, shows that detection in most tissues is only possible high
Context. Currently, one of the standard procedures used to determine stellar and wind parameters massive stars involves comparing observed spectral lines with a grid synthetic lines. These are calculated using non-local thermodynamic equilibrium radiative transfer codes. In this procedure, after estimating stellar-projected rotational speed ( v sin i ), all models need be convolved value in order perform comparison line estimate parameters. Aims. work, we propose methodology deconvolve...
Distributions of true rotational velocities as a function spectral type for different luminosity class groups B and Be Stars are compared. While the distributions stars differ clearly from one to another, those less, which indicates that due effects many considered more evolved than they actually are. ‘select’ narrow range display phenomenon latter types rotate only marginally faster early ones.
A study on the photosphere and disc of Be star $\beta$ Psc is presented. We recover almost 40 years high-resolution spectroscopic observations additional data gathered from BeSS database. evaluate photospheric parameters SED fittings state-of-the-art non-LTE model atmospheres to observed helium, carbon, silicon magnesium line profiles. Our models include stellar geometric deformation as well co-latitude dependence temperature gravity, aiming derive effects rotation parameters. estimate...
A new grid of detailed atmosphere model spectra for hot and moderately cool subdwarf stars is presented. High-resolution synthetic photometry are calculated in the range from 1000{\AA} to 10,000{\AA} using Non-LTE fully line-blanketed structures. Our covers eight temperatures within 10,000<Teff [K]<65,000, three surface gravities 4.5<logg [cgs]<6.5, two helium abundances matching extreme helium-rich helium-poor scenarios, limiting metallicity boundaries regarding both solar ([Fe/H] = 0)...