A broadband X-ray study of the dwarf nova SS Cyg during quiescence and outburst

We present a broadband X-ray study ($\sim$\,0.3-50 keV) of the dwarf nova SS Cyg highlighting the changes in the accretion during two phases, the quiescence and the outburst states. The investigation was based on simultaneous observations carried out with the XMM-Newton and NuSTAR telescopes in two epochs, involving medium and high-resolution spectroscopy. Spectra were harder during quiescence ($kT_{\rm high}\sim22.8$ keV) than outburst ($kT_{\rm high}\sim8.4$ keV), while the mass accretion rate increased by $\sim35$ times in outburst ($1.7\times10^{16} \rm g\;s^{-1}$) than quiescence. The bolometric luminosity (0.01-100.0 keV) during the outburst was dominated by a blackbody emission ($kT_{\rm BB}\sim28$ eV) from the optically thick boundary layer, and the inner edge of the accretion disk resides very close to the WD surface. X-rays from the accretion disk boundary layer are consistent with the white dwarf having mass $1.18_{-0.01}^{+0.02} \rm M_{\odot}$. Our study conclusively confirms the presence of the reflection hump in the 10-30 keV range for both phases, which arises when X-ray photons hit colder material and undergo Compton scattering. We estimated a similarly strong reflection amplitude during quiescence ($\sim1.25$) and outburst ($\sim1.31$), indicating both the WD surface and disk are contributing to reflection. The neutral Fe K$_{\alpha}$ line, which is correlated with Compton reflection, also showed similar strength ($\sim80$ eV) in both phases. Finally, X-rays also revealed the presence of a partial intrinsic absorber during the outburst, possibly due to an outflowing accretion disk wind.Comment: 14 pages, 5 figures, 4 tables, Accepted for publication in The Astrophysical Journal (ApJ

Revisiting the fossil group candidates UGC 842 and NGC 6034

We present a new insight on NGC 6034 and UGC 842, two groups of galaxies previously reported in the literature as being fossil groups. The study is based on optical photometry and spectroscopy obtained with the CTIO Blanco telescope and Sloan Digital Sky Survey archival data. We find that NGC 6034 is embedded in a large structure, dominated by three rich clusters and other small groups. Its first and next four ranked galaxies have magnitude differences in the r band and projected distances which violate the optical criteria to classify it as a fossil group. We confirm that the UGC 842 group is a fossil group, but with about half the velocity dispersion that is reported in previous works. The velocity distribution of its galaxies reveals the existence of two structures in its line of sight, one with sigmaV ~ 223 km/s and another with sigmaV ~ 235 km/s, with a difference in velocity of ~820 km/s. The main structure is dominated by passive galaxies, while these represent ~60% of the second structure. The X-ray temperature for the intragroup medium of a group with such a velocity dispersion is expected to be kT ~0.5-1 keV, against the observed value of kT ~1.9 keV reported in the literature. This result makes UGC 842 a special case among fossil groups because (1) it represents more likely the interaction between two small groups, which warms the intragroup medium and/or (2) it could constitute evidence that member galaxies lost energy in the process of spiraling toward the group center, and decreased the velocity dispersion of the system. As far as we know, UGC 842 is the first low-mass fossil group studied in detail.Comment: 18 pages, 8 figures, published in A

AS CIDADES MÉDIAS DO HINTERLAND AMAZÔNICO PARAENSE: URBANIZAÇÃO E DESENVOLVIMENTO EM PERÍODO RECENTE

Os franceses foram os pioneiros a apresentarem discussões sobre a temática das cidades médias, desde o fim da segunda Guerra Mundial, mas principalmente a partir dos anos 50. No entanto, é somente nos finais dos anos sessenta que surge um conceito sobre cidades médias, na França, o qual estava associado às políticas de desconcentração de população e atividades implementadas pelo VI Plano de Desenvolvimento Econômico e Social (1971-1975), período em que a preocupação dos planejadores era o desenvolvimento regional e a correção dos desequilíbrios regionais. A definição de cidades médias sempre esteve associada de imediato ao seu porte demográfico, porém, estudos recentes apontam a necessidade de identificar fatores qualitativos associados as suas funções e os papéis desempenhados por elas, além disso, ainda existe a dificuldade de encontrar um valor quantitativo que identifique cidade média, já que a escala populacional varia de acordo com a análise. A presente pesquisa tem como objetivo investigar se as cidades paraenses com população superior 100 mil habitantes, vivendo em áreas urbanas, não pertencentes à região metropolitana, desempenham papéis de cidades médias. Dessa forma, serão abordados estudos urbanos referentes à temática, com a apresentação dos conceitos e suas limitações, logo em seguida, será exposta uma breve contextualização do processo de urbanização na Amazônia brasileira, e por último será analisado se as cidades consideradas são capazes de desempenharem papéis de cidades médias

Exploring the population of Hα emitters in the Southern Photometric Local Universe Survey (S-PLUS)

En astronomía, el estudio de los objectos con líneas de emisión resulta ser de gran importancia porque ellos reflejan diferentes procesos físicos que dan cuenta de la fomación, la presencia de gas, choques, estallidos de formación estelar en galaxias, y la etapa final de las estrellas, entre otros procesos. En este contexto, hemos llevado a cabo una búsqueda de emisores de Ha compactos en los datos del relevamiento S-PLUS, el cual se encuentra mapeando el Hemisferio Sur Celeste en altas latitudes galácticas (|b| >30 deg). Para ello, utilizamos el diagrama color-color (r — J0660) versus (r — i) dado que, se cree, el exceso de emisión en el filtro J0660 que presentan algunos objetos se debe a la línea de emisión de Ha. Combinando los valores de color (r — i) y (g — z) con técnicas de aprendizaje automático no supervisado, hemos logrado distinguir entre fuentes de emisión con un continuo espectral más intenso en la región azul del espectro, y fuentes con un continuo más intenso en la región roja. Utilizamos los algoritmos de agrupamiento jerárquico y HDBSCAN y, mediante un enfoque de agrupamiento "suave", asignamos una probabilidad a cada emisor de pertenecer a la población azul o roja del espectro. La técnica descrita en esta contribución resulta eficiente para identificar nuevos objetos con líneas de emisión y clasificarlos, utilizando datos multibanda. Los objetos seleccionados incluyen nebulosas planetarias, regiones Η II, objetos estelares jóvenes, sistemas estelares simbióticos, variables cataclísmicas, galaxias Seyfert y cuásares.Emission lines are key tracers of a myriad of physical processes in Astrophysics, from planetary to supermassive extragalactic systems. We have carried out a search for Ha emitters in the ongoing S-PLUS survey, which is mapping the Southern hemisphere at high galactic latitudes (|b| >30 deg) in twelve photometric bands. Excess emission in such a line was evidenced by contrasting the magnitude from the narrow band filter J0660 and those of the broadband r and i filters through the colour-colour (r — J0660) versus (r — i) diagram. Furthermore, unsupervised machine learning (clustering) applied to the colours (r — i) and (g — z) allowed us to separate the Ha emitter candidates into two subgroups: one with bluer and another one with redder sources. By adopting a "soft" clustering approach, we assign probabilities for each source in our final sample to belong to either the blue or red population. The method, which utilizes multi-colour data, has proven to be an effective tool for detecting and classifying new Hα emitters, including planetary nebulae, Η II regions, young stellar objects, symbiotic star systems, cataclysmic variables, Seyfert galaxies, and quasars.Asociación Argentina de AstronomíaFacultad de Ciencias Astronómicas y Geofísica