15 research outputs found
Comet nuclei activity simulation using percolation theory on comet 67P/Churyumov– Gerasimenko
Comets, remnants of the solar system\u27s formation, exhibits partially unexplained outbursts that are closely tied to the physical structure of the nucleus. To investigate outbursts, we employed pore network modeling techniques, such as the Bower-Watson algorithm and Voronoi diagrams, to better represent the nucleus\u27 complex porous structure and simulate gas transfer processes. We examined heat diffusion in the comet\u27s subsurface and its influence on crystallization. The extra heat generated by crystallization can shift the crystalline front deeper into the nucleus, accelerating subsurface evaporation rates. This process results in the formation of a thicker ice mantle with reduced porosity on the surface, trapping evaporated gas in the underlying layers. As gas pressure accumulates over time, the mantle eventually succumbs to the buildup. By applying percolation theory, we identified the critical point at which trapped gas breaks through the surface, ultimately leading to a better understanding of comet outburst formation
Statistical and numerical approaches for modelling and optimising Laser micromachining process-review
This chapter presents the modelling and optimization techniques commonly used in
engineering applications especially in Laser Micromachining process. Design of Experiment
DOE (Response Surface Method and Taguchi), Artificial Neural Network (ANN), Genetic
Algorithm (GA), and Particle swarm optimization (PSO) and mixed techniques are explained
briefly. Furthermore, a review of laser micromachining processes parameters optimization was
studied. Recent researches which used different approaches for modelling and optimization
was presented
A close-in puffy Neptune with hidden friends : the enigma of TOI 620
We present the validation of a transiting low-density exoplanet orbiting the M2.5 dwarf TOI 620 discovered by the NASA Transiting Exoplanet Survey Satellite (TESS) mission. We utilize photometric data from both TESS and ground-based follow-up observations to validate the ephemerides of the 5.09 day transiting signal and vet false-positive scenarios. High-contrast imaging data are used to resolve the stellar host and exclude stellar companions at separations ≳0farcs2. We obtain follow-up spectroscopy and corresponding precise radial velocities (RVs) with multiple precision radial velocity (PRV) spectrographs to confirm the planetary nature of the transiting exoplanet. We calculate a 5σ upper limit of MP < 7.1 M⊕ and ρP < 0.74 g cm−3, and we identify a nontransiting 17.7 day candidate. We also find evidence for a substellar (1–20 MJ) companion with a projected separation ≲20 au from a combined analysis of Gaia, adaptive optics imaging, and RVs. With the discovery of this outer companion, we carry out a detailed exploration of the possibilities that TOI 620 b might instead be a circum-secondary planet or a pair of eclipsing binary stars orbiting the host in a hierarchical triple system. We find, under scrutiny, that we can exclude both of these scenarios from the multiwavelength transit photometry, thus validating TOI 620 b as a low-density exoplanet transiting the central star in this system. The low density of TOI 620 b makes it one of the most amenable exoplanets for atmospheric characterization, such as with the James Webb Space Telescope and Ariel, validated or confirmed by the TESS mission to date
TOI 560 : Two Transiting Planets Orbiting a K Dwarf Validated with iSHELL, PFS and HIRES RVs
We validate the presence of a two-planet system orbiting the 0.2--1.4 Gyr K4
dwarf TOI 560 (HD 73583). The system consists of an inner moderately eccentric
transiting mini-Neptune (TOI 560 b, days,
) initially discovered in the Sector 8 \tess\ mission
observations, and a transiting mini-Neptune (TOI 560 c, days) discovered in the Sector 34 observations, in a rare 1:3 orbital
resonance. We utilize photometric data from \tess\, \textit{Spitzer}, and
ground-based follow-up observations to confirm the ephemerides and period of
the transiting planets and vet false positive scenarios. We obtain follow-up
spectroscopy and corresponding precise radial velocities (RVs) with the iSHELL
spectrograph at the NASA Infrared Telescope Facility and the HIRES Spectrograph
at Keck Observatory to validate the planetary nature of these signals, which we
combine with published PFS RVs from Magellan Observatory. We place upper limits
on the masses of both planets of 2.1 and 4.1 M for b and c,
respectively. We apply a Gaussian Processes (GP) model to the \tess\ light
curves to place priors on a chromatic radial velocity GP model to constrain the
stellar activity of the TOI 560 host star. TOI 560 is a nearby moderately young
multi-planet system with two planets suitable for atmospheric characterization
with James Webb Space Telescope (JWST) and other upcoming missions. In
particular, it will undergo six transit pairs separated by 6 hours before
June 2027.Comment: AAS Journals, submitte