Context. The signal processing of multi-aperture monomode interferometers using multiaxial recombination, such as AMBER/VLTI, makes use of the modeling of the fringes in the image space called the ...“P2VM method”. This method was only validated on simulated data. Aims. We aim to validate the P2VM method on-sky, and to use the knowledge acquired during more than three years of use of the instrument to provide improved data processing algorithms. Methods. We compare the on-sky results of the P2VM algorithm with those provided by the standard, well known, and robust Fourier method. Results. We first prove that the current implementation of the P2VM method used in the AMBER data reduction is biased for intermediate and low flux measurements. We determine the physical origin of these biases, then modify the data model accordingly, and introduce an improved noise model. We demonstrate that the P2VM method, together with the more realistic data and noise models, give results that are now in accordance with those provided by the Fourier method.
We present a thorough study of the target-cleaning phase to estimate the healthiness of the target in a direct current (DC) magnetron sputtering deposition. The study is based on real-time plasma ...monitoring by means of optical emission spectroscopy during a traditional cleaning phase in an Ar atmosphere. In this work we demonstrate that intensities of Ar emission lines are sufficient indicators of the target cleanliness degree. To derive these results SiOxNy thin films were grown by reactive DC magnetron sputtering on silicon wafers for different deposition configurations of Ar, O2 and N2 fluxes. Refractive index of the resulting films is measured by in-situ spectroscopic-ellipsometry. A simple but robust estimator is used to determine the time when the target is ready to start deposition. Hence, this approach can be suited for an industrial environment since the time invested in the cleaning phase can be minimized avoiding the waste of material and time.
•Plasma spectroscopy is used to estimate the target cleanliness prior deposition.•The pre-sputtering phase is terminated until intensity of Ar emission is stable.•Different target materials require different duration of the pre-sputtering phase.
The young stellar object MWC 297 is an embedded B1.5Ve star exhibiting strong hydrogen emission lines and a strong near-infrared continuum excess. This object has been observed with the VLT ...interferometer equipped with the AMBER instrument during its first commissioning run. AMBER/VLTI is currently the only near infrared interferometer that can observe spectrally dispersed visibilities. MWC 297 has been spatially resolved in the continuum with a visibility of $0.50^{+0.08}_{-0.10}$ as well as in the Brγ emission line where the visibility decreases to $0.33\pm0.06$. This change in the visibility with wavelength can be interpreted by the presence of an optically thick disk responsible for the visibility in the continuum and of a stellar wind traced by the Brγ emission line and whose apparent size is 40% larger. We validate this interpretation by building a model of the stellar environment that combines a geometrically thin, optically thick accretion disk model consisting of gas and dust, and a latitude-dependent stellar wind outflowing above the disk surface. The continuum emission and visibilities obtained from this model are fully consistent with the interferometric AMBER data. They agree also with existing optical, near-infrared spectra and other broad-band near-infrared interferometric visibilities. We also reproduce the shape of the visibilities in the Brγ line as well as the profile of this line obtained at an higher spectral resolution with the VLT/ISAAC spectrograph, and those of the Hα and Hβ lines. The disk and wind models yield a consistent inclination of the system of approximately 20°. A picture emerges in which MWC 297 is surrounded by an equatorial flat disk that is possibly still accreting and an outflowing wind that has a much higher velocity in the polar region than at the equator. The AMBER/VLTI unique capability of measuring spectral visibilities therefore allows us for the first time to compare the apparent geometry of a wind with the disk structure in a young stellar system.
ABSTRACT The Cananea near-infrared camera (CANICA) is an instrument commissioned at the 2.12m telescope of the Guillermo Haro Astrophysical Observatory (OAGH) located in Cananea, Sonora, México. ...CANICA operates in the near-infrared at multiple bands including J(1.24µm), H(1.63µm) and K (2.12µm) broad-bands. CANICA in located at the Ritchey-Chrétien focal plane of the telescope, reimaging the f/12 beam into f/6 beam. The detector is a 1024 × 1024 HgCdTe HAWAII array of 18.5µm pixel size, covering a field of view of 5.5×5.5arcmin2, for a plate scale of 0.32arcsec/pixel. The camera is enclosed in a cryostat, cooled with liquid nitrogen to 77K. The cryostat contains the collimator, two 15-position filter wheels, single fixed reimaging optics and the detector.
In this work, we present the first AMBER observations, of the Wolf-Rayet and O (WR+O) star binary system y² Velorum. The AMBER instrument was used with the telescopes UT2, UT3, and UT4 on baselines ...ranging from 46m to 85m. It delivered spectrally dispersed visibilities, as well as differential and closure phases, with a resolution R = 1500 in the spectral band 1.95-2.17 micron. We interpret these data in the context of a binary system with unresolved components, neglecting in a first approximation the wind-wind collision zone flux contribution. We show that the AMBER observables result primarily from the contribution of the individual components of the WR+O binary system. We discuss several interpretations of the residuals, and speculate on the detection of an additional continuum component, originating from the free-free emission associated with the wind-wind collision zone (WWCZ), and contributing at most to the observed K-band flux at the 5% level. The expected absolute separation and position angle at the time of observations were 5.1±0.9mas and 66±15° respectively. However, we infer a separation of 3.62+0.11-0.30 mas and a position angle of 73+9-11°. Our analysis thus implies that the binary system lies at a distance of 368+38-13 pc, in agreement with recent spectrophotometric estimates, but significantly larger than the Hipparcos value of 258+41-31 pc.
Context. Interferometry can provide spatially resolved observations of massive star binary systems and their colliding winds, which thus far have been studied mostly with spatially unresolved ...observations. Aims. We present the first AMBER/VLTI observations, taken at orbital phase 0.32, of the Wolf-Rayet and O (WR+O) star binary system γ2 Velorum and use the interferometric observables to constrain its properties. Methods. The AMBER/VLTI instrument was used with the telescopes UT2, UT3, and UT4 on baselines ranging from 46 m to 85 m. It delivered spectrally dispersed visibilities, as well as differential and closure phases, with a resolution $R=1500$ in the spectral band 1.95-2.17 μm. We interpret these data in the context of a binary system with unresolved components, neglecting in a first approximation the wind-wind collision zone flux contribution. Results. Using WR- and O-star synthetic spectra, we show that the AMBER/VLTI observables result primarily from the contribution of the individual components of the WR+O binary system. We discuss several interpretations of the residuals, and speculate on the detection of an additional continuum component, originating from the free-free emission associated with the wind-wind collision zone (WWCZ), and contributing at most to the observed K-band flux at the 5% level. Based on the accurate spectroscopic orbit and the Hipparcos distance, the expected absolute separation and position angle at the time of observations were $5.1\pm0.9$ mas and $66\pm15$°, respectively. However, using theoretical estimates for the spatial extent of both continuum and line emission from each component, we infer a separation of 3.62$^{+0.11}_{-0.30}$ mas and a position angle of 73$^{+9}_{-11}$°, compatible with the expected one. Our analysis thus implies that the binary system lies at a distance of 368$^{+38}_{-13}$ pc, in agreement with recent spectrophotometric estimates, but significantly larger than the Hipparcos value of 258$^{+41}_{-31}$ pc.
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