arXiv subjects

Francisco J. Aceituno

Publications and source records attributed to Francisco J. Aceituno.

6 recordsLinked to original sources

arXiv2026

Size, shape, density, and atmospheric limit of (50000) Quaoar revealed from 14 years of stellar occultation

We present results from 28 stellar occultations by the large Trans-Neptunian Object (50000) Quaoar registered between 2018 and 2025. By performing a joint analysis of this occultation data-set, along with other 9 published events, we were able to fit an oblate ellipsoid shape, with equatorial semi-axes, a and b of 566.1+2.5-2.2 km, and a polar semi-axis, c, of 511.2+3.6-3.7 km. It provides an equivalent volumetric diameter of 1094.4 +/- 4.6 km and polar oblateness of 0.097 +/- 0.011. Considering an absolute magnitude of H = 2.79 +/- 0.35, we derive a geometric albedo of pV = 0.125 +/- 0.038. We have derived new upper limits to the surface pressure of a CH4 atmosphere of 0.15 nbar (1-sigma) and 0.65 nbar (3-sigma). We also provide a table with the 36 new astrometric positions for Quaoar. Using the new system mass derived from Weywot's orbit around Quaoar, we calculated a density of 1.760 +/- 0.109 g/cm3. Moreover, from the derived size and rotation period (8.8394 +/- 0.0002 hours (Ortiz et al. 2003)), we calculate that, if Quaoar is in Maclaurin hydrostatic equilibrium state, it would have a density of 1.859 +/- 0.200 g/cm3. This result, within the error bars, is compatible with the value we found. Therefore, this work shows that Quaoar can be a Maclaurin object, being eligible as a dwarf planet.

astro-ph.EP↗

arXiv2025

Intra-night optical polarization monitoring of blazars

Blazars are known for their extreme variability across the electromagnetic spectrum. Variability at very short timescales can push the boundaries between competing models offering us much needed discriminating power. This is particularly true for polarization variability that allows us to probe particle acceleration and high-energy emission models in blazars. Here we present results from the first pilot study of intra-night optical polarization monitoring conducted using RoboPol at the Skinakas Observatory and supplemented by observations from the Calar Alto, Perkins, and Sierra Nevada observatories. Our results show that while variability patterns can widely vary between sources, variability on timescales as short as minutes is prevalent in blazar jets. The amplitude of variations are typically small, a few percent for the polarization degree and less than 20 degrees for the polarization angle, pointing to a significant contribution to the optical emission from a turbulent magnetic field component, while the overall stability of the polarization angle over time points to a preferred magnetic field orientation.

astro-ph.HE↗

arXiv2025

Dust environment of long-period comet C/2023 A3 (Tsuchinshan-ATLAS)

We present a characterization of the dust environment of long-period comet C/2023 A3 (Tsuchinshan-ATLAS) by analyzing an extensive dataset, including dust tail images and photometric measurements, from 10 au pre-perihelion to 1.6 au post-perihelion, using our forward Monte Carlo code. For this analysis, we combine pre-perihelion images from the Zwicky Transient Facility with post-perihelion images from the Sierra Nevada Observatory (IAA-CSIC, Granada, Spain), along with both amateur and professional photometric measurements, including Af$ρ$ and magnitude data. We find that the dust loss rate increases monotonically from the assumed start of activity at a heliocentric distance of approximately 15 au down to 4 au inbound, where the comet exhibits a notable decrease in dust production by about one order of magnitude. Following this period of reduced activity, the dust production rate rises again toward perihelion, reaching a peak production rate of 10$^5$ kg s$^{-1}$. The size distribution of the particles follows a power law, with its index decreasing toward perihelion, along with a reduction in the minimum particle radius, leading to both brightness and dust mass being dominated by small particles at perihelion. The particle speeds exhibit a dependence on heliocentric distance ($r_h$) that closely follows the classical $r_h^{-0.5}$ law near perihelion but deviates at larger heliocentric distances. We demonstrate that the dependence of particle speeds on the cosine of the solar zenith angle at the emission point plays a significant role in shaping the synthetic dust tails and in the formation of a dark stripe along the tail axis observed in high spatial resolution images near the comet's perihelion.

astro-ph.EP↗

arXiv2024

CARMENES input catalog of M dwarfs: VII. New rotation periods for the survey stars and their correlations with stellar activity

Abridged: We measured photometric and spectroscopic $P_{\rm rot}$ for a large sample of nearby bright M dwarfs with spectral types from M0 to M9, as part of our continual effort to fully characterize the Guaranteed Time Observation programme stars of the CARMENES survey. We determine $P_{\rm rot}$ for 129 stars. Combined with the literature, we tabulate $P_{\rm rot}$ for 261 stars, or 75% of our sample. We evaluate the plausibility of all periods available for this sample by comparing them with activity signatures and checking for consistency between multiple measurements. We find that 166 of these stars have independent evidence that confirmed their $P_{\rm rot}$. There are inconsistencies in 27 periods, which we classify as debated. A further 68 periods are identified as provisional detections that could benefit from independent verification. We provide an empirical relation for the $P_{\rm rot}$ uncertainty as a function of the $P_{\rm rot}$ value, based on the dispersion of the measurements. We show that published formal errors seem to be often underestimated for periods $\gtrsim 10$ d. We highlight the importance of independent verification on $P_{\rm rot}$ measurements, especially for inactive M dwarfs. We examine rotation-activity relations with emission in X-rays, H$α$, Ca II H & K, and surface magnetic field strengths. We find overall agreement with previous works, as well as tentative differences in the partially versus fully convective subsamples. We show $P_{\rm rot}$ as a function of stellar mass, age, and galactic kinematics. With the notable exception of three transiting planet systems and TZ Ari, all known planet hosts in this sample have $P_{\rm rot} \gtrsim 15$ d. This indicates that important limitations need to be overcome before the radial velocity technique can be routinely used to detect and study planets around young and active stars.

astro-ph.SR↗

arXiv2015

Lunar impact flashes from Geminids, analysis of luminous efficiencies and the flux of large meteoroids on Earth

We analyze lunar impact flashes recorded by our team during runs in December 2007, 2011, 2013 and 2014. In total, 12 impact flashes with magnitudes ranging between 7.1 and 9.3 in V band were identified. From these, 9 events could be linked to the Geminid stream. Using these observations the ratio of luminous energy emitted in the flashes with respect to the kinetic energy of the impactors for meteoroids of the Geminid stream is estimated. By making use of the known Geminids meteoroid flux on Earth we found this ratio to be 2.1x10$^{-3}$ on average. We compare this luminous efficiency with other estimations derived in the past for other meteoroid streams and also compare it with other estimations that we present here for the first time by making use of crater diameter measurements. We think that the luminous efficiency has to be revised downward, not upward, at least for sporadic impacts. This implies an increase in the influx of kilogram-sized and larger bodies on Earth that has been derived thus far through the lunar impact flash monitoring technique.

astro-ph.EP↗

arXiv2010

T35: a small automatic telescope for long-term observing campaigns

The T35 is a small telescope (14") equipped with a large format CCD camera installed in the Sierra Nevada Observatory (SNO) in Southern Spain. This telescope will be a useful tool for the detecting and studying pulsating stars, particularly, in open clusters. In this paper, we describe the automation process of the T35 and show also some images taken with the new instrumentation.

astro-ph.IM↗