arXiv subjects

E. Ortiz

Publications and source records attributed to E. Ortiz.

5 recordsLinked to original sources

arXiv2025

Link of the Zitterbewegung with the spin conductivity and the spin-textures of multiband systems

The Zitterbewegung phenomenon in multiband electronic systems is known to be subtly related to the charge conductivity, Berry curvature and the Chern number. Here we show that some spin-dependent properties as the optical spin conductivity, and intrinsic spin Hall conductivity are also entangled with the Zitterbewegung amplitudes. We also show that in multiband Dirac-type Hamiltonians, a direct link between the Zitterbewegung and the spin textures and spin transition amplitudes can be established. The later allow us to discern the presence or not of the Zitterbewegung oscillations by simply analyzing the spin or pseudo-spin textures. We provide examples of the applicability of our approach for Hamiltonian models that show the suppression of specific Zitterbewegung oscillations.

cond-mat.mes-hall↗

arXiv2022

Proton Penetration Efficiency over a High Altitude Observatory in Mexico

In association with a large solar flare on November 7, 2004, the solar neutron detectors located at Mt. Chacaltaya (5,250m) in Bolivia and Mt. Sierra Negra (4,600m) in Mexico recorded very interesting events. In order to explain these events, we have performed a calculation solving the equation of motion of anti-protons inside the magnetosphere. Based on these results, the Mt. Chacaltaya event may be explained by the detection of solar neutrons, while the Mt. Sierra Negra event may be explained by the first detection of very high energy solar neutron decay protons (SNDPs) around 6 GeV.

astro-ph.SR↗

arXiv2021

Optical-to-NIR magnitude measurements of the Starlink LEO Darksat satellite and effectiveness of the darkening treatment

Four observations of Starlink's LEO communication satellites, Darksat and STARLINK-1113, were conducted on two nights with two telescopes. The Chakana 0.6\,m telescope at the Ckoirama observatory (Chile) observed both satellites on 5\,Mar\,2020 (UTC) and 7\,Mar\,2020 (UTC) using a Sloan r' and Sloan i' filter, respectively. The ESO VISTA 4.1\,m telescope with the VIRCAM instrument observed both satellites on 5\,Mar\,2020 (UTC) and 7\,Mar\,2020 (UTC) in the NIR J-band and Ks-band, respectively. The calibration, image processing, and analysis of the Darksat images give r\,$\approx$\,5.6\,mag, i\,$\approx$\,5.0\,mag, J\,$\approx$\,4.2\,mag, and Ks\,$\approx$\,4.0\,mag when scaled to a range of 550\,km (airmass $=1$) and corrected for the solar incidence and observer phase angles. In comparison, the STARLINK-1113 images give r\,$\approx$\,4.9\,mag, i\,$\approx$\,4.4\,mag, J\,$\approx$\,3.8\,mag, and Ks\,$\approx$\,3.6\,mag when corrected for range, solar incidence, and observer phase angles. The data and results presented in this work show that the special darkening coating used by Starlink for Darksat has darkened the Sloan r' magnitude by 50\,\%, Sloan i' magnitude by 42\,\%, NIR J magnitude by 32\,\%, and NIR Ks magnitude by 28\,\%. The results show that both satellites increase in reflective brightness with increasing wavelength and that the effectiveness of the darkening treatment is reduced at longer wavelengths. This shows that the mitigation strategies being developed by Starlink and other LEO satellite operators need to take into account other wavelengths, not just the optical. This work highlights the continued importance of obtaining multi-wavelength observations of many different LEO satellites in order to characterise their reflective properties and to aid the community in developing impact simulations and developing mitigation tools.

astro-ph.IM↗

arXiv2020

First observations and magnitude measurement of Starlink's Darksat

Measure the Sloan g' magnitudes of the Starlink's STARLINK-1130 (Darksat) and 1113 LEO communication satellites and determine the effectiveness of the Darksat darkening treatment at 475.4\,nm. Two observations of the Starlink's Darksat LEO communication satellite were conducted on 2020/02/08 and 2020/03/06 using a Sloan r' and g' filter respectively. While a second satellite, STARLINK-1113 was observed on 2020/03/06 using a Sloan g' filter. The initial observation on 2020/02/08 was a test observation when Darksat was still manoeuvring to its nominal orbit and orientation. Based on the successful test observation, the first main observation was conducted on 2020/03/06 along with an observation of the second Starlink satellite. The calibration, image processing and analysis of the Darksat Sloan g' image gives an estimated Sloan g' magnitude of $7.46\pm0.04$ at a range of 976.50\,km. For STARLINK-1113 an estimated Sloan g' magnitude of $6.59\pm0.05$ at a range of 941.62\,km was found. When scaled to a range of 550\,km and corrected for the solar and observer phase angles, a reduction by a factor of two is seen in the reflected solar flux between Darksat and STARLINK-1113. The data and results presented in this work, show that the special darkening coating used by Starlink for Darksat has darkened the Sloan g' magnitude by $0.77\pm0.05$\,mag, when the range is equal to a nominal orbital height (550\,km). This result will serve members of the astronomical community modelling the satellite mega-constellations, to ascertain their true impact on both the amateur and professional astronomical communities. Concurrent and further observations are planned to cover the full optical and NIR spectrum, from an ensemble of instruments, telescopes and observatories.

astro-ph.IM↗

arXiv2008

Discovery of warm and dense molecular gas surrounding the ring nebula G79.29+0.46

We present for the first time the detection of mid-J CO line emission in the outskirts of an evolved massive star, which indicates the presence of warm and/or high density molecular gas. Aiming to learn about the interplay between evolved massive stars and their surroundings, we have carried out CO J=2-1, J=3-2, and (13)CO J=2-1 line observations in a 4'x4' field around the ring nebula G79.29+0.46, which is illuminated by a strong candidate to LBV star. The whole field shows extended predominant emission in both CO and (13)CO J=2-1 lines, which probably comes from the large cloud which contains the star forming region DR15. When this large-scale emission is removed, minor scales features become evident, particularly in the CO J=3-2 line, strikingly coincident with the ring nebula. The high critical density of CO J=3-2 (some 10^4 cm^(-3)) gives additional support for the association with the massive star, since high density molecular gas has more chances to survive in such a harsh environment. This structure may have been produced by the cumulative effect of a strong steady wind in the LBV stage or earlier, which has compressed the surviving parent molecular cloud. In addition, immersed within this CO feature, we have also discovered a higher density clump (at least several 10^5 cm^(-3)), unresolved by the telescope and probably having a higher kinetic temperature. Towards the clump, the presence of a jump of 14-16 km/s in the gas velocity may indicate the existence of a shockfront. This clump may have been created by at least one mass eruption, 10^3 - 10^4 yr ago. Thus, this work shows that not all the molecular gas is destroyed during massive star evolution, and consequently we are dealing with a new laboratory where one can learn about the mass-loss phenomena associated to the brief LBV stage.

astro-ph↗