Photoconductive and third-order nonlinear optical properties exhibited by Cu2ZnSnS4 nanostructures are presented. The samples were synthetized in thin film form by a spray pyrolysis processing route. ...Distinctions in the photoconductive behavior throughout the samples were clearly noted by modulating their optoelectronic response dependent on electrical frequency. Vectorial two-wave mixing experiments were carried out at a 532 nm wavelength provided by a Nd:YAG laser system to study the optical nonlinearities in the samples. An induced transparency effect was observed during nanosecond single-beam experiments in the nanostructures reported. Quantum and thermal processes were considered to be the main physical mechanism responsible for the photo-electrical phenomena and nonlinear refraction in the nanostructures. Potential applications for developing nanophotonic and nanoelectronic instrumentation systems can be contemplated.
We present the polarimetric measurements of the asteroid (16) Psyche for its whole rotational phase. Observations were conducted in the facilities of the OAN-SPM with a double beam polarizer (POLIMA ...2) coupled to the 84 cm telescope in September 2019. Polarimetric lightcurves are valuable because they might provide useful information about the geometric albedo and surface properties of atmosphereless bodies.
The upcoming NASA mission to visit Psyche will verify most of the ground-based observations, however, there is a lack of polarimetric lightcurves, which could be useful for a more precise determination of the surface properties.
Polarimetry relies on relative flux variation of orthogonal polarization states to determine Stokes parameters. The aim, in this work, is to measure the amount of linearly polarized light reflected by the asteroid (16) Psyche.
The polarimetric lightcurve was obtained for a rotation period, and an amplitude of 0.14 ± 0.03% was measured for a phase angle of ∼17°. From a comparison between the polarization curve with the corresponding photometric lightcurve, we found that the latter is possibly affected by both albedo and shape.
Our results show evidence of albedo variegation, which is in agreement with the albedo map of (16) Psyche obtained with different observational techniques.
∙A single maximum in polarization was observed in the rotation period, a possible explanation is an isolated spot with different surface properties.∙The maximum on the rotational phase polarization curve, suggest the presence of a low albedo region, this observation is in agreement with the albedo map reported by Ferrais et al., 2020) obtained by high angular resolution images and modeling.∙The photometric lightcurve is clearly dominated by asteroid shape, while albedo contribution, related to the maximum in the polarization curve, is low enough to be detected by photometry only.∙Even when polarimetric measurements are strong indicatives of albedo variation along the surface, it will be until the moment that the data from NASA's mission are at disposal that our interpretations over the polarimetric results could be confirmed or confronted.
Abstract
We present a new pipeline based on the Support Vector Machine algorithm to confirm the detection and perform classification of small solar system objects by serendipitous stellar ...occultations. This pipeline is designed to analyze light curves and to identify the occultation events and the classification of the occulting bodies according to their size, typically from a fraction to a few kilometers, and their distance from the Sun, typically a few tens of astronomical units. The input light curves for this pipeline were obtained from the event simulator for the Trans-Neptunian Automated Occultation Survey (TAOS II). We explore parameters affecting occultation light curves such as spectral type, apparent magnitude and finite angular size of the occulted star, angle from opposition, and readout cadence for the observations; also we assumed a Poisson noise distribution as expected from the TAOS II project. We find that occultation events, especially by trans-Neptunian objects with diameters ≥2 km are detected with 99.99%, 99.53%, and 86% efficiency for stars with a visual apparent magnitude of 12, 14, and 16, respectively at 0.05 s of exposure time. In terms of size and distance classification the overall accuracy is 94%. However, for smaller objects the confirmation and classification depends mostly upon the signal-to-noise ratio.
Abstract
In this paper we present multiband speckle interferometric measurements of double stars performed at the 2.1 m telescope of the Observatorio Astronómico Nacional, San Pedro Mártir, México. ...We focused our efforts on objects from the Washington Double Star Catalog that were observed during five runs allocated in 2018 and 2019. We report here 2101 astrometric and 2027 photometric measurements of 631 pairs, with angular separations ranging from 0.″05 to 6.″09, including 1622 measurements with separations smaller than 1″, and a magnitude difference up to 5.99 mag through the
V
filter, 5.46 mag for the
R
filter, and 5.85 mag for the
I
filter. We estimated a mean error in separation of 12 mas, 1.°1 in position angle, and 0.14 mag for the magnitude difference. We confirmed 58 double stars discovered by Hipparcos. For the first time we are presenting astrometric measurements for 7 systems listed at the Washington Double Star Catalog as being suspected binaries, which did not have a secondary confirmation, and 15 stars with only one published measurement. We identified a new close companion with a mean angular separation of 0.″10, detected in a previously known pair. Finally, we present a correction to two previously published orbital solutions of two visual binaries.
We present a new occultation event simulator for the Trans-Neptunian Automated Occultation Survey (TAOS II). We have developed a method to compute occultation shadows by small objects with ...non-circular apparent shapes (as may result from an intrinsic morphology or from the projection of a contact binary). The new simulator calculates diffraction features in the occultation shadows, as well as resulting light curves as would be measured by the TAOS II survey system. We include effects such as the spectral type and finite angular size of the occulted star. We find that occultation events, especially by Trans-Neptunian Objects with diameters ∼3 km may be misidentified or mischaracterized when not taking non-spherical shapes into account.
In this paper we study the effects of systematic noise and atmospheric turbulence on image quality and signal-to-noise ratio for high cadence (∼20 fps) observations, in the context of fortuitous ...stellar occultation surveys. We performed an analysis of the spatial distribution of the weighted centroid of a reference star, in the X and Y direction (in the detector), and we also analyze the FWHM behavior to study the effect on the stellar profile. This information allowed us to find both the shift and the deformation of each image, which are the most significant effects of atmospheric turbulence on such images. Our observations were carried out at the 84 cm telescope of the San Pedro Mártir Observatory, located in Ensenada, Baja California, México. In order to isolate the atmospheric turbulence contribution on image quality and motion, the systematic noise due to telescope motion and other low frequency components were filtered-out from the distribution curve for the centroids. We used the APPHi pipeline as our analysis tool to study the effect of the size of the Region of Interest (ROIs) on energy loss in the photometry of the stars. We find for example that using ROI of 7 × 7 pixels in our study, the shifting and deformation of the images will produce an energy loss of ∼10%, for more than 9% of the observations, even after removing the systematic noise. Such energy loss can be comparable to the flux drop expected for some TNO occultations, thus leading to spurious detections. We also find that the algorithm developed to calculate an optimal ROI in the APPHi pipeline, makes a good compromise between avoiding the flux loss and keeping a reasonably small ROI, to reduce the data storage requirements and maximize the number of stars that can be simultaneously observed while limiting the overlap of ROIs for stars which are very close to each other.
The two rings of (50000) Quaoar Pereira, C. L.; Sicardy, B.; Morgado, B. E. ...
Astronomy & astrophysics,
05/2023, Letnik:
673
Journal Article
Recenzirano
Odprti dostop
Context.
Quaoar is a classical trans-Neptunian object (TNO) with an area-equivalent diameter of 1100 km and an orbital semi-major axis of 43.3 astronomical units. Based on stellar occultations ...observed between 2018 and 2021, an inhomogeneous ring (Q1R, i.e., Quaoar’s first ring) has been detected around this body.
Aims.
A new stellar occultation by Quaoar was observed on August 9, 2022, with the aim of improving Quaoar’s shape models and the physical parameters of Q1R, while searching for additional material around the body.
Methods.
The occultation provided nine effective chords across Quaoar, pinning down its size, shape, and astrometric position. Large facilities, such as Gemini North and the Canada-France-Hawaii Telescope (CFHT), were used to obtain high acquisition rates and signal-to-noise ratios. The light curves were also used to characterize the Q1R ring (radial profiles and orbital elements).
Results.
Quaoar’s elliptical fit to the occultation chords yields the limb with an apparent semi-major axis of 579.5 ± 4.0 km, apparent oblateness of 0.12 ± 0.01, and area-equivalent radius of 543 ± 2 km. Quaoar’s limb orientation is consistent with Q1R and Weywot orbiting in Quaoar’s equatorial plane. The orbital radius of Q1R is refined to a value of 4057 ± 6 km. The radial opacity profile of the more opaque ring profile follows a Lorentzian shape that extends over 60 km, with a full width at half maximum (FWHM) of ∼5 km and a peak normal optical depth of 0.4. Besides the secondary events related to the already reported rings, new secondary events detected during the August 2022 occultation in three different data sets are consistent with another ring around Quaoar with a radius of 2520 ± 20 km, assuming the ring is circular and co-planar with Q1R. This new ring has a typical width of 10 km and a normal optical depth of ∼0.004. Just as Q1R, it also lies outside Quaoar’s classical Roche limit.
Abstract
We present the results from four stellar occultations by (486958) Arrokoth, the flyby target of the
New Horizons
extended mission. Three of the four efforts led to positive detections of the ...body, and all constrained the presence of rings and other debris, finding none. Twenty-five mobile stations were deployed for 2017 June 3 and augmented by fixed telescopes. There were no positive detections from this effort. The event on 2017 July 10 was observed by the Stratospheric Observatory for Infrared Astronomy with one very short chord. Twenty-four deployed stations on 2017 July 17 resulted in five chords that clearly showed a complicated shape consistent with a contact binary with rough dimensions of 20 by 30 km for the overall outline. A visible albedo of 10% was derived from these data. Twenty-two systems were deployed for the fourth event on 2018 August 4 and resulted in two chords. The combination of the occultation data and the flyby results provides a significant refinement of the rotation period, now estimated to be 15.9380 ± 0.0005 hr. The occultation data also provided high-precision astrometric constraints on the position of the object that were crucial for supporting the navigation for the
New Horizons
flyby. This work demonstrates an effective method for obtaining detailed size and shape information and probing for rings and dust on distant Kuiper Belt objects as well as being an important source of positional data that can aid in spacecraft navigation that is particularly useful for small and distant bodies.
The absorptive and refractive third order nonlinear optical properties exhibited by a ZnO thin solid film with fluorine nanoparticles were studied with picosecond and femtosecond pulses using ...different techniques. We were able to evaluate the photoconductivity of the material and the quenching of the induced birefringence observed in the presence of two-photon absorption. The samples were prepared by a chemical spray deposition technique. In order to investigate the different contributions of the third order nonlinearities of the film, we analyzed the vectorial self-diffraction effect and the optical Kerr transmittance observed in the sample. A dominantly absorptive nonlinearity was measured at a 532 nm wavelength with 50 ps pulses, while nonlinear refraction was found to be negligible in this regime. On the other side, a pure electronic refractive third order nonlinearity without the contribution of nonlinear absorption was detected at 830 nm with 80 fs pulse duration. A quasi-instantaneous optical response and a strong enhancement in the ultrafast nonlinear refraction with the inhibition of the picosecond two-photon absorption mechanism were measured for the case of the femtosecond excitation.
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