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Estimating the obstructed portion of the night sky using digital image processing
(IK Press) Silva, Felipe Alexandre da; Castro, Vinicius Daniel dos Reis de; Oliveira, Marcos William da Silva; Caritá, Lucas Antonio; Rodrigues, Irapuan; Fernandes, Francisco Carlos Rocha
Determining the portion obscured by clouds in the night sky recorded in an image from a meteor monitoring station can be useful to help in the discussion and analysis of studies in this area. Thereby, this work presents a proposal to quantitatively measure the proportion of the night sky covered by clouds from images of meteor records. The images used are from EXOSS database, particularly from the UVP1 and UVP2 stations. Two approaches were elaborated: the first one computes the proportion of pixels in clouds over the total number of pixels, the second approach calculates another percentage value by using image processing techniques and applying an equalization method. An application was created to perform the calculations in an automated way. The program displays an enhanced image and the two calculated percentages and can be used for specialists as a tool to guide their choice of coverage values. The results showed that the second approach proves to be better for “many” and “few” clouds; furthermore, the first approach proves to be better in low cloud density images.
Enhancing learning of the Grad-Shafranov equation through scientific literature: part 2 of a physics education series
(Sociedade Brasileira de Física) Santos, Lenadro Nunes dos; Ojeda-González, Arian; La Luz, Victor Hugo de; Klausner, Virgínia; Pilling, Sergio; Prestes, Alan; Sousa, Antonio Nilson Laurindo; Oliveira, Matheus Felipe Cristaldo de
In part 1 of our physics education series, we introduced a novel solution based on Yoon-Lui’s solutions 1 and 2. Building upon that, this follow-up presents a new solution obtained by combining the generating functions of Yoon-Lui-1 and Yoon-Lui-3, resulting in a new and simplified general solution. We also calculate the singular points and determine their coordinates for various parameter values. A graphical representation of the solution is presented, showing the magnetic field lines and current density distribution. The behavior of the magnetic field and the effect of varying the parameter are discussed. The observed magnetic islands and singular points are relevant in the fields of Plasma Physics and Space Physics, providing insights into magnetic structures in plasmas and their impact on confinement and stability. Furthermore, this study encourages innovation and equips researchers and students with the necessary tools to make meaningful contributions to the field, emphasizing the integration of scientific literature into physics education to promote a comprehensive understanding of physical concepts and their practical applications.
Enhancing learning of the Grad-Shafranov Equation through scientific literature: part 1 of a physics education series
(Sociedade Brasileira de Física) Ojeda-González, Arian; Santos, Lenadro Nunes dos; La Luz, Victor Hugo de; Oliveira, Matheus Felipe Cristaldo de; Sousa, Antonio Nilson Laurindo; Prestes, Alan; Klausner, Virgínia; Pilling, Sergio
This article provides a comprehensive review of relevant studies in the fields of plasma physics, electromagnetism, and space physics. The aim is to demonstrate how the study of the scientific literature can be used to enhance problem-solving abilities and develop innovative solutions in physics. In this paper, we focus on the study of solutions of the specific Grad-Shafranov equation. Two of the new solutions proposed by Yoon and Lui (2005) are used as a basis for the development of a new solution. The new solution presented has singular points similar to the Yoon-Lui-2 solution, but with an inverted configuration, and also presents less rounded double islands compared to the Yoon-Lui-2 solution. Additionally, the new solution does not exhibit the formation of a current ring, a characteristic of the Yoon-Lui-1 solution, and varying its parameters may lead to higher plasma confinement efficiency. In summary, we illustrate how a thorough analysis of literature can serve as a powerful means for generating innovative approaches to resolving theoretical issues in physics.
Effects of the terdiurnal tide on the sporadic E (Es) layer development at low latitudes over the Brazilian sector
(European Geosciences Union) Fontes, Pedro Alves; Muella, Marcio Tadeu De Assis Honorato; Resende, Laysa Cristina Araújo; Andrioli, Vânia Fátima; Fagundes, Paulo Roberto; Pillat, Valdir Gil; Batista, Paulo Prado; Carrasco, Alexander Jose
Sporadic E (Es) layers are patches of high ionization observed at around 100–140 km height in the E region. Their formation at low latitudes is primarily associated with the diurnal and semidiurnal components of the tidal winds via the ion convergence driven by the wind shear mechanism. However, recent studies have shown the influence of other tidal modes, such as the terdiurnal tide. Therefore, this work investigates the effect of terdiurnal tide-like oscillations on the occurrence and formation of the Es layers observed over Palmas (10.17∘ S, 48.33∘ W; dip lat. −7.31∘), a low-latitude station in Brazil. The analysis was conducted from December 2008 to November 2009 by using data collected from CADI (Canadian Advanced Digital Ionosonde). Additionally, the E Region Ionospheric Model (MIRE) was used to simulate the terdiurnal tidal component in the Es layer development. The results show modulations of 8 h periods on the occurrence rates of the Es layers during all seasonal periods. In general, we see three well-defined peaks in a superimposed summation of the Es layer types per hour in summer and autumn. We also observed that the amplitude modulation of the terdiurnal tide on the Es occurrence rates minimizes in December in comparison to the other months of the summer season. Other relevant aspects of the observations, with complementary statistical and periodogram analysis, are highlighted and discussed.
Cosmic metallicity evolution of Active Galactic Nuclei: implications for optical diagnostic diagrams
(Royal Astronomical Society) Dors Junior, Oli Luiz; Cardaci, Mónica Viviana; Hägele, Guilhermo F.; Ilha, Gabriele da Silva; Oliveira Junior, Celso Benedito de; Riffel, Rogemar A.; Riffel, Rogério; Krabbe, Angela Cristina
We analyse the validity of optical diagnostic diagrams relying on emission-lines ratios and in the context of classifying Active Galactic Nuclei (AGNs) according to the cosmic metallicity evolution in the redshift range⁠. In this regard, we fit the results of chemical evolution models (CEMs) to the radial gradients of the N/O abundances ratio derived through direct estimates of electron temperatures (Te-method) in a sample of four local spiral galaxies. This approach allows us to select representative CEMs and extrapolate the radial gradients to the nuclear regions of the galaxies in our sample, inferring in this way the central N/O and O/H abundances. The nuclear abundance predictions for theoretical galaxies from the selected CEMs, at distinct evolutionary stages, are used as input parameters in AGN photoionization models built with the Cloudy code. We found that standard BPT diagnostic diagrams are able to classify AGNs with oxygen abundances at redshift. On the other hand, the He iiλ4685/Hβ versus [N ii]λ6584/Hα diagram produces a reliable AGN classification independent of the evolutionary stage of these objects.
Understanding the astrophysical-ice nanostructures formation through classical molecular dynamics
(Universidade do Vale do Paraíba) Silva, Priscila Alves da; Pilling, Sergio; Amarim, Rodrigo Garcia
Astrophysical ices (formed by water, among other molecules) act as a catalyst and a reservoir of carbonaceous species, both of which have major implications for astrobiology. In this work, we studied the formation of astrophysical ice nanostructures found in the interstellar medium, having a sheet of graphene as a catalyst substrate, using the classical molecular dynamics technique to model these astrophysical environments. For this, two systems were designed: the first composed of graphene and H2Oand the second composed of graphene, H2Oand CO2. Initially, a simulation box was built where the area was delimited by graphene whose height varied from 4, 6, 8 and 10 nm. The molecules were evenly distributed throughout the box. The molecular dynamics technique proved to be a promising tool to understand the phenomenon of adsorption of molecules on the substrate, allowing us to realize that the random distribution of molecules in the system interferes with the geometric structure formed by an ice nanostructure. This study allows us to understand, from the nanometric point of view, the influence of some physical-chemical parameters, regarding the formation of nanostructures of astrophysical ices, such as the number of hydrogen bonds, the initial size of the simulation box, and its density during the freezing process
Chemical evolution of electron-bombarded crystalline water ices at different temperatures using the procoda code
(Royal Astronomical Society) Pilling, Sergio; Silveira, Carolina Hahn da; Ojeda-González, Arian
Water ices are a common component of cold space environments, including molecular and protostellar clouds, and the frozen surfaces of moons, planets, and comets. When exposed to ionizing and/or thermal processing, they become a nursery for new molecular species and are also responsible for their desorption to the gas-phase. Crystalline water ice, produced by the deposition of gaseous water at warm (80–150 K) surfaces or by the heating of cold amorphous water ice (up to ∼150 K), is also regularly detected by astronomical observations. Here, we employed the procoda code to map the chemical evolution of 5 keV electron-bombarded crystalline water-ices at different temperatures (12, 40, 60 and 90 K). The chemical network considered a total of 61 coupled reactions involving nine different chemical species within the ice. Among the results, we observe that the average calculated effective rate constants for radiation-induced dissociation decrease as the ice´s temperature increases. The abundance of molecular species in the ice at chemical equilibrium and its desorption to gas-phase depend on both the temperature of the ice. H2O molecules are the dominant desorbed species, with a desorption yield of about 1 molecule per 100 electrons, which seems to be enhanced for warmer crystalline ices. The obtained results can be employed in astrochemical models to simulate the chemical evolution of interstellar and planetary environments. These findings have implications for astrochemistry and astrobiology, providing insight into crucial chemical processes and helping us understand the chemistry in cold regions in space.
Chemical abundances in Seyfert galaxies – X. Sulphur abundance estimates
(Royal Astronomical Society) Dors Junior, Oli Luiz; Valerdi, Mabel; Riffel, Rogemar A.; Riffel, Rogério; Cardaci, Mónica Viviana; Hägele, Guilhermo F.; Armah, Mark; Revalski, Mitchell; Flury, Sophia; Lemes, Priscila Freitas; Amôres, Eduardo; Krabbe, Angela Cristina; Binette, Luc; Feltre, Anna; Bergmann, Thaisa Storchi
For the first time, the sulphur abundance relative to hydrogen (S/H) in the narrow-line regions of a sample of Seyfert 2 nuclei (Sy 2s) has been derived via direct estimation of the electron temperature. Narrow emission-line intensities from the Sloan Digital Sky Survey (SDSS) Data Release 17 (DR17) [in the wavelength range 3000 < λ(Å) < 9100] and from the literature for a sample of 45 nearby (z < 0.08) Sy 2s were considered. Our direct estimates indicate that Sy 2s have similar temperatures in the gas region where most of the S+ ions are located in comparison with that of star-forming regions (SFs). However, Sy 2s present higher temperature values (∼10 000 K) in the region where most of the S2+ ions are located relative to that of SFs. We derive the total sulphur abundance in the range of 6.2 􏰀 12 + log(S/H) 􏰀 7.5, corresponding to 0.1–1.8 times the solar value. These sulphur abundance values are lower by ∼0.4 dex than those derived in SFs with similar metallicity, indicating a distinct chemical enrichment of the interstellar medium (ISM) for these object classes. The sulphur abundance relative to oxygen (S/O) values for our Sy 2 sample present an abrupt (∼0.5 dex) decrease with increasing oxygen abundance relative to hydrogen (O/H) for the high-metallicity regime [12 + log(O/H) 􏰁 8.7)], what is not seen for the SFs. However, when our Sy 2 estimates are combined with those from a large sample of SFs, we did not find any dependence between S/O and O/H.
Characterization of acetonitrile ice irradiated by X-rays employing the procoda code – II. Desorption processes
(Royal Astronomical Society) Carvalho, Geanderson Araújo; Pilling, Sergio; Gerasimenko, Svitlana
In this work, we focus on the study of radiation-induced desorption processes that occurred in acetonitrile ice irradiated by broad-band X-rays (6 eV to 2 keV) monitored by Fourier transform infrared spectroscopy at different radiation fluences. In a previous work, we used the procoda code to derive the chemical evolution of the ice. Here, we have observed that the acetonitrile desorbed column density is at least two orders of magnitude larger than the desorbed column densities of daughter or granddaughter molecular species at chemical equilibrium stage. This indicates that total desorption column density is mainly governed by the father molecule, as also previously hypothesized in experimental studies. This occurs basically because the acetonitrile column density is larger than the other ones. In particular, at chemical equilibrium acetonitrile desorption column density represents almost 98 per cent of the total, while it is close to 1 per cent for H, CN, and CH2, the species with larger molecular desorption percentages at chemical equilibrium. Another derived quantity is what we called intrinsic desorption rate, which is a number per second for individual species. Some of the larger intrinsic desorption rates were 6.2 × 10−6 (CH3CN), 6.2 × 10−6 (CN), 5.7 × 10−6 (H), 5.7 × 10−6 (CH2), and 4.4 × 10−6 (C2N2). These results help to put constraints in astrochemical models and can also be useful to clarify some astronomical radio observations.
Assessing the effects of a minor CIR‐HSS geomagnetic storm on the brazilian low‐latitude ionosphere: ground and space‐based observations
(Advancing Earth and Space Sciences) Chingarandi, Frank Simbarashe; Candido, Claúdia Maria Nicoli; Guedes, Fabio Becker; Jonah, Olusegun Folarin; Santos, Stella Pires Moraes; Klausner, Virgínia; Osanyin, Taiwo Olusayo
This paper investigates the effects of a minor G1 Co-rotating Interaction Region (CIR)/High-Speed Stream (HSS)-driven geomagnetic storm that occurred on (13–14 October 2018), during deep solar minimum. We used simultaneous observations from multiple instruments, namely; ground-based Global Navigation Satellite Systems (GNSS) receivers, a Digisonde, ground magnetometers, and space-based observations from the National Aeronautics and Space Administration Global-scale Observations of Limb and Disk (GOLD) and SWARM missions. This study presents a detailed picture of the low-latitude ionosphere response over the Brazilian sector during a minor storm. Our results showed that the minor CIR/HSS-driven storm caused a positive ionospheric storm of over ∼20 TECU in magnitude. For the first time, periodic post-sunset irregularities and Equatorial Plasma Bubbles, equatorial plasma bubbles, were analyzed using GOLD FUV OI 135.6 nm emission, Total Electron Content (TEC) maps, Rate of TEC index, ROTI, and TEC gradients. Fluctuations in the interplanetary magnetic field Bz and changes in the thermospheric column density ratio (∑O/N2) are discussed as the main sources of ionospheric changes during the storm. This paper highlights the importance of monitoring and understanding the impact of Sun-Earth interactions and provides insight into the behavior of the low-latitude ionosphere during minor geomagnetic storms.
AGN feedback and star formation in the peculiar galaxy NGC 232: insights from VLT-MUSE observations
(Royal Astronomical Society) Souza, José Henrique Costa; Riffel, Rogemar A.; Dors Junior, Oli Luiz; Riffel, Rogério; Poppe, Paulo César da Rocha
We use VLT-MUSE integral field unit data to study the ionized gas physical properties and kinematics as well as the stellar populations of the Seyfert 2 galaxy NGC 232 as an opportunity to understand the role of AGN feedback on star formation. The data cover a field of view of 60 × 60 arcsec2 at a spatial resolution of ∼850 pc. The emission-line profiles have been fitted with two Gaussian components, one associated to the emission of the gas in the disc and the other due to a bi-conical outflow. The spectral synthesis suggests a predominantly old stellar population with ages exceeding 2 Gyr, with the largest contributions seen at the nucleus and decreasing outwards. Meanwhile, the young and intermediate age stellar populations exhibit a positive gradient with increasing radius and a circum-nuclear star-forming ring with radius of ∼0.5 kpc traced by stars younger than 20 Myr, is observed. This, along with the fact that AGN and SF dominated regions present similar gaseous oxygen abundances, suggests a shared reservoir feeding both star formation and the AGN. We have estimated a maximum outflow rate in ionized gas of ∼1.26 M yr−1 observed at a distance of ∼560 pc from the nucleus. The corresponding maximum kinetic power of the outflow is ∼3.4 × 1041 erg s−1. This released energy could be sufficient to suppress star formation within the ionization cone, as evidenced by the lower star formation rates observed in this region.
Modeling the chemical evolution and kinetics of pure H2O Ices under various types of radiation employing the PROCODA code
(Elsevier) Silveira, Carolina Hahn da; Pilling, Sergio
Water is one of the most abundant molecules in space, especially in cold environments, where it is the main constituting of astrophysical ices. The space ionizing radiation affects these ices and induces chemical changes, including desorption to gas-phase, which increase the complexity of the interstellar medium. In this work, we employed the PROCODA code to investigate the behavior of several pure water ices under different type of ionizing radiation such as UV, X-rays, electrons and cosmic rays analogues. Here, we employ molecular column densities from laboratory and solved a set of coupled chemical reactions to calculated effective reaction rates (ERCs) and characterize the chemical equilibrium of water ices under high radiation fluences. Briefly, we monitored the evolution of nine species (including the observed ones H2O, H2O2, and O3, and the predicted ones H, O, H2, OH, O2, and HO2). A discussion on the branching ratio for the considered reactions with the type of ionizing radiation is provided. Among the results, we observed that approximately 63% of the modeled molecules quantified at chemical equilibrium were non-observed species in the X-rays experiment, highlighting the importance of this work in providing insights into the processes that occur on the surface of icy interstellar grains exposed to cosmic radiation, including the formation and destruction of water ice. Accurate modeling of these processes can lead to a better understanding of the chemical evolution of interstellar and circumstellar environments, as well as offer insight into the formation and composition of celestial objects such as comets.
Deuteration of molecular clumps induced by cosmic rays
(Elsevier) Pilling, Sergio; Pazianotto, Maurício Tizziani; Molina, Jose Manuel Quesada
The D/H ratio in astrophysical environments has instigated the scientists for at least 50 years. The wide range of values in the interstellar medium (ISM) from 10e to 7 to 10e-1 have usually been claimed to be due to small zero-point energy differences between reactants and products involving D and H (mainly at low temperatures). Here, we present a new source of deuteration processes in the ISM clouds as a result of cosmic ray irradiation. As a study object, we consider a typical molecular clump under the presence of incoming cosmic rays simulated computationally. The calculations were performed employing the Monte Carlo toolkit GEANT4 code (considering hadronic physics) and considering mainly the proton and alpha component of the incoming cosmic rays from the ISM (the dominant ones for the production of secondary protons and deuterons). The results suggest an increasing D/H ratio as function of time in the central part of molecular clumps (<200 AU) with the largest deuteration in the central region of the cloud, and a bump in the D/H ratio around 2–10 AU (which becomes more pronounced for clouds with larger timescales; > 10 Myrs). The results also show that for timescales between 10 and 100 Myrs the central part of the cloud has D/H around 6-16e-3, a value compatible with the observed D/H in some interstellar clouds. This work adds a new piece to the D/H puzzle of the ISM and might also help to explain the D/H ratio measured in different objects inside the Solar system.
Lithosphere atmosphere ionosphere coupling during the September 2015 Coquimbo earthquake
(Springer Nature Link) Adhikari, Bhoj Raj; Klausner, Virgínia; Cândido, Claudia Maria Nicoli; Poudel, Prakash; Macedo, Humberto Gimenes; Silwal, Ashok; Gautam, Sujan Prasad; Calabia, Andrés; Shah, Munawar
This study explores temporal variations in seismic data, interplanetary parameters, and geomagnetic indices during the 2015 Coquimbo earthquake. We employ wavelet transform techniques to investigate potential coupling mechanisms between the lithosphere, atmosphere, and ionosphere (LAI), even during geomagnetically disturbed periods. Our analysis is strengthened by evaluating geomagnetic data and all- sky images within a 2000–3000 km radius of the epicenter. We explore the post-Chilean earthquake seismogenic perturbations in the upper atmosphere on September 16–17, 2015. Coseismic and post- seismic events emerge in the Brazilian region 1–3 hrs after the earthquake onset. The co-occurrence and subsequent response of these disturbances to seismic events suggest their seismogenic nature. Addi- tionally, we utilize geomagnetic storm and interplanetary magnetic Beld (IMF) indices to differentiate magnetic Cuctuations arising from solar storms during seismic events. While our study detects magnetic disturbances associated with seismic activity, distinguishing them from the eAects of solar storms in the geomagnetic records or all-sky images remains challenging. These observations prompt further investigation into the intricate interplay between geomagnetic and ionospheric disturbances and their connection to seismic and geomagnetic storm activity.
Evidence of anti-correlation between sporadic (Es) layers occurrence and solar activity observed at low latitudes over the Brazilian sector
(Elsevier) Fontes Neto, Pedro Alves; Muella, Marcio Tadeu de Assis Honorato; Resende, Laysa Cristina Araújo; Fagundes, Paulo Roberto
Sporadic E-layers (Es) are thin and denser layers with high ionization observed at about 100–140 km altitude in the E region. Their formation is mainly associated with the tidal components of the diurnal and semidiurnal winds with the convergence of ions driven by the wind shear mechanism. This present work shows evidence of the relationship between the occurrence of Es layers and the solar activity at two observatories located in the Brazilian sector, the near-equatorial site of Palmas (PAL, 10.17 S; 48.33 W; dip lat. 7.31 ) and the low latitude station of Sa ̃o Jose ́ dos Campos (SJC, 23.18 S; 45.89 W; dip lat. 19.35 ). The analysis was performed from Decem- ber/2008 to November/2009 (a period of low solar activity) and from December/2013 to November/2014 (a period of high solar activity) using data collected from two digital ionosondes. Our results show an anti-correlation of the Es layer occurrence concerning the solar activity over both stations studied here. A more clearly observed anti-correlation at the SJC station can be attributed to a greater tidal amplitude at low latitudes. Other relevant aspects of the observations associated with the formation of the Es layers are highlighted and discussed.
Effects of the Northern Hemisphere sudden stratospheric warmings on the Sporadic-E layers in the Brazilian sector
(Elsevier) Fontes Neto, Pedro Alves; Muella, Tadeu de Assis Honorato; Resende, Laysa Cristina Araújo; Jesus, Rodolfo de; Fagundes, Paulo Roberto; Batista, Paulo Prado; Pillat, Valdir Gil; Tardelli, Alexandre; Andrioli, Vania F.
Tidal and Planetary Wave (PWs) amplitudes are strongly influenced by Sudden Stratospheric Warming (SSW) events. A nonlinear interaction between the tidal winds and planetary waves during the SSW may contribute to the intensification of sporadic-E (Es) layers in the lower thermosphere. This work investigated the relationship between SSW events in the Northern Hemisphere and the Es layer occurrence at low latitudes in the Brazilian sector. We used data from digital ionosondes installed in the observatories of Araguatins (ARA, 5.65◦ S; 48.12◦ W; dip lat. − 5.44◦) and S ̃ao Jos ́e dos Campos (SJC, 23.18◦ S; 45.89◦ W; dip lat. − 21.37◦) to analyze the Es layers. Additionally, we used the temperature, zonal wind, and PWs data at high latitudes in the Northern Hemisphere during the major SSW event that occurred in February/2018 and during the events of Dec/2018–Jan/2019 and Dec/2020–Jan/2021. The results showed a maximum frequency peak of 20 MHz (~5 × 106 electrons.cm− 3) at ARA and SJC during these SSW events. The large values of ftEs, fbEs, and electronic densities were observed between 100 and 115 km height in the Esf/l type layers during daytime or nighttime periods. The results also showed that the number of large values of ftEs, fbEs, and electronic density of the Es layer was much higher in ARA than in SJC, in general. The wavelet power spectrum analyses of the ftEs and fbEs showed a periodicity of 2- days before and after the central day of the SSWs events at the station of ARA, with three prominent peaks in the 2018/2019 event. At the SJC station the quasi-2-day periodicity in the wavelet analyses of the ftEs was observed after the central day in all three SSW events, with a peak before the central day during the 2020/2021 event.
Enhancing learning of the Grad-Shafranov equation through scientific literature: Part 3 of a physics education series
(Sociedade Brasileira de Física) Ojeda-González, Arian; Oliveira, Matheus Felipe Cristaldo de; Santos, Leandro Nunes dos; Sousa, Antonio Nilson Laurindo; Pilling, Sergio
The Grad-Shafranov (GS) equation is a fundamental tool extensively used in plasma physics, particularly in the context of magnetic confinement, notably in tokamaks for fusion energy research. This equation plays a crucial role in reconstructing magnetic field topology in plasma regions like the magnetopause and magnetotail, leading to the development of the GS reconstruction technique. In this third installment of our series, we explore the merger of the Yoon-Lui-2 and Yoon-Lui-3 generating functions, allowing for a deeper understanding of the core equation in Plasma Physics. Furthermore, this article provides a comprehensive summary of solutions previously presented in Parts 1 and 2. We investigate the behavior of magnetic islands positioned above either the X-axis or the Z-axis for specific parameter values and their impact on plasma confinement. The article concludes that the derived model offers a simpler, more stable, and easily analyzable solution for magnetic morphology. However, it is worth noting that the model’s inflexibility in singularity positions may limit its adaptability to different scenarios. This article marks the conclusion of our physics education series dedicated to studying new specific solutions of the GS equation.
Exploring patterns in dendrochronological data through cluster analysis
(Universidade Federal do Paraná) Muraja, Daniela Oliveira Silva; Leite, Cecília Lemes; Klausner, Virginia; Prestes, Alan; Silva, Iuri Rojahn da
This study employed the dendrogram methodology to analyze time series data obtained from measuring tree growth rings. A total of 64 samples were collected from 21 individual trees. Polynomials were applied to filter the natural growth pattern of the trees and enhance the impact of external factors, such as climate influences. Cluster analysis using Ward's minimum variance and Euclidean squared distance was utilized to group the data based on similarity. Three dendrograms were constructed, consisting of 10, 47, and 64 samples, respectively. The analysis revealed that the samples with the highest correlations, encompassing over 95% of the total samples, formed homogeneous groups. Pearson correlation was also employed to confirm the results obtained from the dendrograms. Consequently, it can be affirmed that the most suitable samples were utilized in constructing the average chronology from the available data.
Influence of temperature on the chemical evolution and desorption of pure CO ices irradiated by cosmic-rays analogues
(Royal Astronomical Society) Pilling, Sergio; Mateus, Marcelo Silva; Ojeda-González, Arian; Ferrão, Luiz Fernando de Araujo; Galvão, Breno R. L.; Boduch, Philippe; Rothard, Hermann
Carbon monoxide (CO) plays a vital role in interstellar chemistry, existing abundantly in both gaseous and frozen environments. Understanding the radiation-driven chemistry of CO-rich ices is crucial for comprehending the formation and desorption of C-bearing molecules in the interstellar medium (ISM), particularly considering the potential impact of temperature on these processes. We report experimental data on irradiation processing of pure CO ice by cosmic ray analogues (95.2 MeV 136Xe23+ ions) at temperatures of 10, 15, and 20 K, in the IGLIAS set-up coupled to the IRRSUD beamline at GANIL (Caen, France). The evolution of the irradiated frozen samples was monitored by infrared spectroscopy. The computational PROCODA code allows us to quantify the chemical evolution of the samples, determining effective reaction rates coefficients (ERCs), molecular abundances at the chemical equilibrium (CE) phase, and desorption processes. The model integrated 18 chemical species – 8 observed (CO, CO2, C3, O3, C2O, C3O, C3O2, and C5O3) and 10 non-observed but predicted (C, O, C2, O2, CO3, C4O, C5O, C2O2, C2O3, C4O2) – linked via 156 reactions. Our findings reveal temperature-driven influences on molecular abundances at chemical equilibrium, desorption yields and rates, and ERC values. Certain reaction routes exhibit distinct thermochemical behaviours of gas- and ice-phase reactions which may be attributed to the presence of neighbouring molecules within the ice matrix. This study provides pivotal insights into the chemical evolution of CO-enriched ice under irradiation, impacting solid-state astrochemistry, clarifying molecular abundances, and advancing our understanding of ISM chemistry and temperature effects on ionized radiation-processed frozen ices.
Constraints on the densities and temperature of the Seyfert 2 narrow line region
(EDP Sciences) Binette, Luc; Martin, Montserrat Villar; Dors Junior, Oli Luiz; Krongold, Yair; Morisset, Christophe; Revalski, Mitchell; Alarie, Alexandre; Riffel, Rogemar A.; Dopita, Michael
Context. Different studies have reported the so-called temperature problem of the narrow line region (NLR) of active galactic nuclei (AGNs). Its origin is still an open issue. To properly address its cause, a trustworthy temperature indicator is required. Aims. To determine the temperature of an emission line plasma, the [O iii] (λ4363Å/λ5007Å) line ratio is typically used. However, in the case of the NLR of AGNs, this ratio is not reliable when the electron density extends much above 10 cm−3 as collisional deexcitation strongly affects this ratio independently of the temperature. To verify the density regime, we need a density diagnostic that applies to high excitation plasma. Methods. We propose that the weak [Ar iv] λλ4711,40Å doublet is the appropriate tool for evaluating the density of the high excitation plasma. We subsequently made use of the recent S7 survey sample to extract reliable measurements of the weak [Ar iv] doublet in 16 high excitation Seyfert 2s. As a result we could derive the plasma density of the NLR of our Seyfert 2 sample and compared the temperature inferred from the observed [O iii] (λ4363Å/λ5007Å) ratios. Results. It was found that 13 Seyfert 2s cluster near similar values as the [O iii] (λ4363Å/λ5007Å) ratio, at a mean value of 0.0146 ± 0.0020. Three objects labeled outliers stand out at markedly higher [O iii] values (>0.03). Conclusions. If for each object one assumes a single density, the values inferred from the [Ar iv] doublet for the 13 clustering objects all lie below 60 000 cm−3 , indicating that the [O iii] (λ4363Å/λ5007Å) ratios in these objects is a valid tracer of plasma temperature. Even when assuming a continuous power-law distribution of the density, the inferred cut-off density required to reproduce the observed 5.1 −3 [Ar iv] doublet is in all cases <10 cm. The average NLR temperature inferred for the 13 Seyfert 2s is 13 000 ± 703 K, which photoionization models have difficulty reproducing. Subsequently we considered different mechanisms to account for the observed [O iii] ratios. For the three outliers, a double-bump density distribution is likely required, with the densest component having a density >10 cm-3 .

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