337 research outputs found
Discovering the colliding wind binary HD 93129A
No full textHD 93129A is a binary system including an O2 If+ and probably an O3.5 V-star orbiting at a distance of about 140 AU (55 mas given the distance of 2.5 kpc), which potentially makes the system the most massive one in the Galaxy, ahead of eta-Carina. Its non-thermal radio emission was proposed to be originated by the collision between the winds of both stars. HST/FGS data have been reanalyzed to derive an accurate absolute position of the stars to compare them with the radio emission. The analysis of ATCA radio observations along several years reveals a power-lawspectrum with an increase on the radio flux density along time. We conducted an observation with the Australian Long Baseline Array (LBA) at 2.3 GHz in 2008 to resolve the radio source and its location within the stellar system. These radio data revealed a bow-shape extended emissionlocated between both stars, as expected in a wind collision region. The observed structure allows us to roughly estimate the mass-loss rate ratio for the two stars in the system, concluding that dM_b/dt = 0.7 dM_a/dt. The multiwavelength analysis points out that the detected radio emission is likely to be originated by one of the most massive collision wind binary in the Galaxy.Fil: Marcote, B.. Universidad de Barcelona; EspañaFil: Benaglia, Paula. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; ArgentinaFil: Moldon, J.. Netherlands Institute for Radio Astronomy; Países BajosFil: Nelan, E.. Space Telescope Science Institute; Estados UnidosFil: De Becker, M.. Université de Liège; BélgicaFil: Dougherty, S, M.. NRC Herzberg Astronomy And Astrophysics; CanadáFil: Koribalski, Bärbel. Australia Telescope National Facility; Australia12th European VLBI Network Symposium and Users MeetingCagliariItaliaIstituto di Radioastronomi
Zooming-in on the sources of fast radio transients
No full textSince the 1960s, Galactic neutron stars have been known to emit short duration radio transients. More recently, a population of higher luminosity short-duration radio transients originating from extragalactic distances were discovered. The nature of these fast radio bursts (FRBs) still remains a mystery, but it is clear that they reflect an extreme astrophysical process, too extreme to be replicated on Earth. Additionally, these transients carry valuable clues about otherwise invisible material that they pass through on their journey to Earth. Currently FRBs are divided into two groups observationally: those which repeat and those which have been seen only a single time. In this thesis, we probe FRB burst properties and their local environments at the highest possible resolutions, to address the following open science questions: what types of astrophysical objects are capable of producing FRB emission?; do repeating and non-repeating FRBs have the same physical origin?; are all repeating FRBs the same type of object?; and what is the physical mechanism creating these luminous radio transients? We show that FRBs come in a variety of “shapes and sizes” in their timescales, luminosities and local environments. This diversity must be accommodated for in the progenitor and emission models of fast radio transients: either a single FRB progenitor exists that can live in a large variety of surroundings, or FRBs can originate from multiple astrophysical sources
The k-restricted edge-connectivity of a product of graphs
No full textAbstractThis work deals with a generalization of the Cartesian product of graphs, the product graph Gm∗Gp introduced by Bermond et al. [J.C. Bermond, C. Delorme, G. Farhi, Large graphs with given degree and diameter II, J. Combin. Theory, Series B 36 (1984), 32–48]. The connectivity of these product graphs is approached by studying the k-restricted edge-connectivity, which is defined as the minimum number of edges of a graph whose deletion yields a disconnected graph with all its components having at least k vertices. To be more precise, we present lower and upper bounds for the k-restricted edge-connectivity of Gm∗Gp, and provide sufficient conditions that ensure an optimal value for this parameter. When both Gm and Gp are regular graphs, conditions for guaranteeing that Gm∗Gp is super-λ(k) are also presented, and the particular case where both Gm and Gp are complete graphs is considered
Phosphorylation and Activation of Human Cdc25-C by Cdc2 Cyclin-B and its Involvement in the Self-Amplification of Mpf At Mitosis
No full textWe have investigated the mechanisms responsible for the sudden activation of the cdc2-cyclin B protein kinase before mitosis. It has been found previously that cdc25 is the tyrosine phosphatase responsible for dephosphorylating and activating cdc2-cyclin B. In Xenopus eggs and early embryos a cdc25 homologue undergoes periodic phosphorylation and activation. Here we show that the catalytic activity of human cdc25-C phosphatase is also activated directly by phosphorylation in mitotic cells. Phosphorylation of cdc25-C in mitotic HeLa extracts or by cdc2-cyclin B increases its catalytic activity. cdc25-C is not a substrate of the cyclin A-associated kinases. cdc25-C is able to activate cdc2-cyclin B1 in Xenopus egg extracts and to induce Xenopus oocyte maturation, but only after stable thiophosphorylation. This demonstrates that phosphorylation of cdc25-C is required for the activation of cdc2-cyclin B and entry into M-phase. Together, these studies offer a plausible explanation for the rapid activation of cdc2-cyclin B at the onset of mitosis and the self-amplification of MPF observed in vivo.</p
On the size of immune sets in the k-PULL infection model
No full text© 2025 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).This paper addresses immune sets in graphs, which are subsets of nodes that remain unaffected during the spread of influence, failure, or infection. The specific propagation model examined is the -PULL infection rule, also referred to as bootstrap percolation. Studying immune sets offers important insights into the structural vulnerabilities and defensive capabilities of networks. In particular, we establish upper bounds for the size of minimal -immune sets in graphs with a given maximum degree. Additionally, we focus on the -immune number of a graph, defined as the minimum number of vertices in a -immune set, and we derive bounds for this parameter. Lastly, we investigate the -immune number of the Cartesian product of two graphs.Partially supported by the Ministerio de Ciencia e Innovación/Agencia Estatal de Investigación, Spain, and the European Regional Development
Fund under project PGC2018-095471-B-I00; and by AGAUR from the Catalan Government under projects 2017SGR–1087 and 2021SGR–00595.Peer ReviewedPostprint (published version
First EVN measurements of the transient FIRST J141918.9+394036 on milliarcsecond scales
No full textFIRST J141918.9+394036 has been reported as a slowly-evolving extragalactic radio transient (Law et al. 2018, arXiv:1808.08964), consistent with a fading orphan long gamma-ray burst (LGRB)
Informe de resultados de la Campaña Calibración Platuxa 2001 en la Zona de Regulación de la NAFO
No full textEl objetivo de la Campaña "Calibración Platuxa 2001", realizada con el B/O Vizconde de Eza y el B/C Playa de Menduiña, fue obtener los factores para la conversión de los índices de la serie Platuxa 1995-2001 en nuevos índices Vizconde de Eza. La serie de Campañas Platuxa estuvo dirigida a obtener índices de abundancia y conocer la estructura de las poblaciones de especies comerciales en el área de Regulación de la NAFO, Divisiones 3N y 3O
Radio modelling of the brightest and most luminous non-thermal colliding-wind binary Apep
No full textStars and planetary system
First EVN measurements of the transient FIRST J141918.9+394036 on milliarcsecond scales
No full textFIRST J141918.9+394036 has been reported as a slowly-evolving extragalactic radio transient (Law et al. 2018, arXiv:1808.08964), consistent with a fading orphan long gamma-ray burst (LGRB)
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