REPOSITÓRIO INSTITUCIONAL DA UNIVERSIDADE DO VALE DO PARAÍBA
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Submissões Recentes
NGC 6845 Revisited: Stellar Kinematics on the Early Type Member Galaxies
(IOP science) Gimeno, German; Díaz, Ruben J.; Dottori, Horacio; Rodrigues, Irapuan; Mast, Damian
We observed the compact group of galaxies NGC 6845 with GMOS-S imaging and long-slit spectroscopy. The group itself is comprised of two spiral galaxies and two S0 galaxies, and shows signs of gravitational interaction among them. While the spiral galaxies have been already well studied, the two S0 galaxies have received little attention. We investigate the morphology and stellar kinematics of the two S0 galaxies in detail in order to derive the value for their mass and subsequently incorporate them into the mass model for the group. It was found that the internal kinematics of the largest S0 (NGC 6845 C) is mostly regular, while the smallest S0 (NGC 6845 D) shows some hint of interaction, most likely with NGC 6845 C and NGC 6845 A. The new determination of the dynamical mass of the group implies that the group mass has to be 10 times the combined mass of the individual members according to their internal kinematics. The results point to an early stage of the group interaction and also to the possibility that it has still not reached virial equilibrium. From the galaxy evolution viewpoint, this group represents an example of the case of the transformation of Spirals into S0 galaxies in dense environments.
New Findings of the Sporadic E (Es) Layer Development Around the Magnetic Equator During a High-Speed Solar (HSS) Wind Stream Event
(Advancing Earth and Space Sciences) Resende, Laysa Cristina Araújo; Zhu, Y.; Denardini, Clezio Marcos; Batista, Inez Staciarini; Shi, Jiankui; Moro, Juliano; Chen, Sony Su; Santos, Fredson Conceição; Silva, Ligia Alves da; Andrioli, Vania Fatima; Muella, Marcio Tadeu de Assis Honorato; Fagundes, Paulo Roberto; Carrasco, Alexander Jose; Pillat, Valdir Gil; Wang, Chi; Liu, Z.
The equatorial (Esq) and blanketing (Esb) sporadic (Es) layers occur due to the EquatorialElectrojet Current (EEJ) plasma instabilities and tidal wind components, respectively. Both Esq and Esb layers can appear concurrently over some Brazilian equatorial regions due to the peculiar geomagnetic field configuration in this sector. Previous works indicate that the inclination angle limit for the Esq occurrence in ionograms is 7°. However, we found evidence that regions more distant can also experience such equatorial dynamics during disturbed periods. In this context, we deeply investigated this EEJ influence expansion effect by analyzing the Esq layers in regions not so close to the magnetic equator during a high-speed solar wind stream event that occurred on May 05 and 06, 2018. To explain these atypical Esq layer occurrences, we considered the Es layer parameters obtained from digital ionosondes over the Brazilian regions, São Luís (dip: 9.5°), and Araguatins (dip: 10.5°). We use magnetometer data and a model named MIRE (E Region Ionospheric Model) to validate this mechanism. The results show that the eastward electric field of the Gradient Drift instability in the EEJ is effective during the magnetic storm main phase in the boundary equatorial magnetic sites, creating the Es q layers. Thus, the EEJ plasma irregularity superimposes the wind shear mechanism, changing the Es layer dynamics during disturbed periods over the magnetic equator boundary sites. Therefore, this work establishes new findings of the EEJ influence expansion dynamics in the Es layer formation over the Brazilian regions, which was considered in MIRE for the first time.
Modos de ondas magnetohidrodinámicas influenciados por la corriente de desplazamiento
(Sociedade Brasileira de Física) Ojeda-González, Arian; González-Avilés, José Juan; Luz, Victor Hugo de La; Santos, Lenadro Nunes dos
En este artículo trabajamos con la ecuación de velocidad de un fluido magneto-conductor utilizando dos aproximaciones: (i) la ley de Ampère y (ii) tomando en cuenta la corrección de Maxwell. Considerando una dirección arbitraria entre el vector de onda y el campo magnético se obtiene una expresión para la velocidad de fase de la onda. Existen tres modos de onda magnetohidrodinámicas (MHD) cuando la corriente de desplazamiento (Jd) no es considerada. Primero, se hace una comparación de los modos de onda entre sí, y después se comparan con los modos obtenidos con y sin la Jd. La comparación, permite discutir las variaciones entre estos modos MHD en los casos teóricos, cuando la velocidad de Alfvén aumenta hasta valores cercanos a la velocidad de la luz. El objetivo principal del art ́ıculo es mostrar la importancia del efecto de la Jd en los modos puro y ra ́pido de ondas MHD, en el caso particular en donde la velocidad de Alfvén es mayor que la velocidad adiaba ́tica de una onda acústica. Encontramos que para el modo lento, la Jd prácticamente no influye en el valor de la velocidad de fase de la onda cuando la velocidad de Alfv ́en aumenta.
Modeling dark matter halos with nonlinear field theories
(APS) Correa, Rafael Augusto Couceiro; Moraes, Henrique Ribeiro da Silva; Dutra, Alvaro de Souza; Dors Júnior, Oli Luiz; Paula, Wayne de; Frederico, Tobias
In the present work, we adopt a nonlinear scalar field theory coupled to the gravity sector to model galactic dark matter. We find analytical solutions for the scalar field considering the weak field gravity limit, which is usually done in galaxy rotation curves analysis and in order to do so we assume an isotropic spacetime and a field potential, with a position dependent form of the superpotential, which entails the nonlinear dynamics of the model with self-interactions. The model introduces a position dependent enhancement of the self-interaction of the scalar fields toward the galaxy center, and while going toward the galaxy border the interaction tends to vanish building a non–self-interacting DM scenario. The developed approach is able to provide a reasonable analytical description of the rotation curves in both dwarf and low surface brightness late-type galaxies, with parameters associated with the dynamics of the scalar field.
Ground and satellite-based observations of ionospheric plasma bubbles and blobs at 5.65° latitude in the Brazilian sector
(Elsevier) Agyei-Yeboah, Ebenezer; Fagundes, Paulo Roberto; Tardelli, Alexandre; Pillat, Valdir Gil; Pignalberi, Alessio; Kavutarapu, Venkatesh; Pezzopane, Michael; Vieira, Francisco
This investigation uses simultaneous observations from all-sky imager system and an ionosonde collocated at Araguatins (5.65° S, 48.07° W and dip-latitude of 4.17° S), a near-equatorial region in Brazil. These simultaneous observations were used to investigate the occurrence of plasma bubbles and blobs in the field of the imaging system and their association with atypical range Spread-F signature in ionograms. Also, in-situ observation of plasma density from Swarm satellites were used to support the ground-based observations. Using a few cases, a methodology will be established to identify in the plasma blobs (atypical ESF) in the ionograms when there is the simultaneous observation of plasma bubbles and blobs in the field of view of the ionosonde. For this purpose, simultaneous sequence of OI 630.0 nm nightglow images and ionograms are presented for different case studies; 1. when there is the absence of a plasma bubble or blob, 2. when there is only the occurrence of plasma bubbles and 3. when there is the occurrence of plasma bubbles and blobs, in order to compare traces in the ionogram in all these case studies. With these we can cover all kinds of signatures in the ionograms corresponding to no irregularities, plasma bubbles only and plasma bubbles-blobs. These OI 630.0 nm nightglow and ionograms recorded simultaneously make it possible to establish a novel methodology to recognize in ionograms cases when there is the occurrence of Spread-F signature associated with bubble-blob in the FOV of the ionosonde.