Browsing by Author "Cuadra, J."
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- ItemAT 2021hdr: A candidate tidal disruption of a gas cloud by a binary super massive black hole system(EDP Sciences, 2024) Hernández-García, L.; Muñoz-Arancibia, A. M.; Lira, P.; Bruni, G.; Cuadra, J.; Arévalo, P.; Sánchez-Sáez, P.; Bernal, S.; Bauer, Franz Erik; Catelan, Márcio; Panessa, F.; Pávez-Herrera, M.; Ricci, C.; Reyes-Jainaga, I.; Ailawadhi, B.; Chavushyan, V.; Dastidar, R.; Deconto-Machado, A.; Forster, F.; Gangopadhyay, A.; García-Pérez, A.; Márquez, I.; Masegosa, J.; Misra, K.; Patiño-Alvarez, V. M.; Puig-Subira, M.; Rodi, J.; Singh, M.With a growing number of facilities able to monitor the entire sky and produce light curves with a cadence of days, in recent years there has been an increased rate of detection of sources whose variability deviates from standard behavior, revealing a variety of exotic nuclear transients. The aim of the present study is to disentangle the nature of the transient AT 2021hdr, whose optical light curve used to be consistent with a classic Seyfert 1 nucleus, which was also confirmed by its optical spectrum and high-energy properties. From late 2021, AT 2021hdr started to present sudden brightening episodes in the form of oscillating peaks in the Zwicky Transient Facility (ZTF) alert stream, and the same shape is observed in X-rays and UV from Swift data. The oscillations occur every ≈60-90 days with amplitudes of ≈0.2 mag in the g and r bands. Very Long Baseline Array (VLBA) observations show no radio emission at milliarcseconds scale. It is argued that these findings are inconsistent with a standard tidal disruption event (TDE), a binary supermassive black hole (BSMBH), or a changing-look active galactic nucleus (AGN); neither does this object resemble previous observed AGN flares, and disk or jet instabilities are an unlikely scenario. Here, we propose that the behavior of AT 2021hdr might be due to the tidal disruption of a gas cloud by a BSMBH. In this scenario, we estimate that the putative binary has a separation of ≈0.83 mpc and would merge in ≈7 × 104 years. This galaxy is located at 9 kpc from a companion galaxy, and in this work we report this merger for the first time. The oscillations are not related to the companion galaxy.
- ItemDusty spirals triggered by shadows in transition discs(2019) Cuello, N.; Montesinos, M.; Stammler, S. M.; Louvet, F.; Cuadra, J.Context. Despite the recent discovery of spiral-shaped features in protoplanetary discs in the near-infrared and millimetre wavelengths, there is still an active discussion to understand how they formed. In fact, the spiral waves observed in discs around young stars can be due to different physical mechanisms: planet/companion torques, gravitational perturbations, or illumination effects.
- ItemEvolution of binary black holes in self gravitating discs Dissecting the torques(2012) Roedig, C.; Sesana, A.; Dotti, M.; Cuadra, J.; Amaro-Seoane, P.; Haardt, F.Context. Massive black hole binaries, formed in galaxy mergers, are expected to evolve in dense circumbinary discs. Understanding of the disc-binary coupled dynamics is vital to assess both the final fate of the system and its potentially observable features.
- ItemEvolution of massive stars with new hydrodynamic wind models(2022) Gormaz-Matamala, A. C.; Cure, M.; Meynet, G.; Cuadra, J.; Groh, J. H.; Murphy, L. J.Context. Mass loss through radiatively line-driven winds is central to our understanding of the evolution of massive stars in both single and multiple systems. This mass loss plays a key role in modulating massive star evolution at different metallicities, especially in the case of very massive stars (M* >= 25 M-circle dot).
- ItemEvolution of rotating massive stars adopting a newer, self-consistent wind prescription at Small Magellanic Cloud metallicity(2024) Gormaz-Matamala, A. C.; Cuadra, J.; Ekstrom, S.; Meynet, G.; Cure, M.; Belczynski, K.Aims. We aim to measure the impact of our mass-loss recipe in the evolution of massive stars at the metallicity of the Small Magellanic Cloud (SMC). Methods. We used the Geneva-evolution code (GENEC) to run evolutionary tracks for stellar masses ranging from 20 to 85 M-circle dot at SMC metallicity (Z(SMC) = 0.002). We upgraded the recipe for stellar winds by replacing Vink's formula with our self-consistent m-CAK prescription, which reduces the value of the mass-loss rate, (M) over dot, by a factor of between two and six depending on the mass range. Results. The impact of our new [weaker] winds is wide, and it can be divided between direct and indirect impact. For the most massive models (60 and 85 M-circle dot) with (M) over dot greater than or similar to 2 x 10(-7) M-circle dot yr(-1), the impact is direct because lower mass loss make stars remove less envelope, and therefore they remain more massive and less chemically enriched at their surface at the end of their main sequence (MS) phase. For the less massive models (20 and 25 M-circle dot) with (M) over dot less than or similar to 2 x 10(-8) M-circle dot yr(-1), the impact is indirect because lower mass loss means the stars keep high rotational velocities for a longer period of time, thus extending the H-core burning lifetime and subsequently reaching the end of the MS with higher surface enrichment. In either case, given that the conditions at the end of the H-core burning change, the stars will lose more mass during their He-core burning stages anyway. For the case of M-zams = 20-40 M-circle dot, our models predict stars will evolve through the Hertzsprung gap, from O-type supergiants to blue supergiants (BSGs), and finally red supergiants (RSGs), with larger mass fractions of helium compared to old evolution models. New models also sets the minimal initial mass required for a single star to become a Wolf-Rayet (WR) at metallicity Z = 0.002 at M-zams = 85 M-circle dot. Conclusions. These results reinforce the importance of upgrading mass-loss prescriptions in evolution models, in particular for the earlier stages of stellar lifetime, even for Z << Z(circle dot). New values for (M) over dot need to be complemented with upgrades in additional features such as convective-core overshooting and distribution of rotational velocities, besides more detailed spectroscopical observations from projects such as XShootU, in order to provide a robust framework for the study of massive stars at low-metallicity environments.
- ItemEvolution of rotating massive stars with new hydrodynamic wind models(2023) Gormaz-Matamala, A. C.; Cuadra, J.; Meynet, G.; Cure, M.Context. Mass loss due to radiatively line-driven winds is central to our understanding of the evolution of massive stars in both single and multiple systems. This mass loss plays a key role in modulating the stellar evolution at different metallicities, particularly in the case of massive stars with M-* >= 25 M-circle dot.
- ItemFeedback-limited accretion: variable luminosity from growing planets(2021) Garate, M.; Cuadra, J.; Montesinos, M.; Arevalo, P.Planets form in discs of gas and dust around stars, and continue to grow by accretion of disc material while available. Massive planets clear a gap in their protoplanetary disc, but can still accrete gas through a circumplanetary disc. For high enough accretion rates, the planet should be detectable at infrared wavelengths. As the energy of the gas accreted on to the planet is released, the planet surroundings heat up in a feedback process. We aim to test how this planet feedback affects the gas in the coorbital region and the accretion rate itself. We modified the 2D code FARGO-AD to include a prescription for the accretion and feedback luminosity of the planet and use it to model giant planets on 10 au circular and eccentric orbits around a solar mass star. We find that this feedback reduces but does not halt the accretion on to the planet, although this result might depend on the near-coincident radial ranges where both recipes are implemented. Our simulations also show that the planet heating gives the accretion rate a stochastic variability with an amplitude Delta(M)over dot(p) similar to 0.1 (M)over dot(p). A planet on an eccentric orbit (e = 0.1) presents a similar variability amplitude, but concentrated on a well-defined periodicity of half the orbital period and weaker broad-band noise, potentially allowing observations to discriminate between both cases. Finally, we find that the heating of the co-orbital region by the planet feedback alters the gas dynamics, reducing the difference between its orbital velocity and the Keplerian motion at the edge of the gap, which can have important consequences for the formation of dust rings.
- ItemInfrared variability of young solar analogues in the Lagoon Nebula(2022) Ordenes-Huanca, C.; Zoccali, M.; Bayo, A.; Cuadra, J.; Ramos, R. Contreras; Hillenbrand, L. A.; Lacerna, I; Abarzua, S.; Avendano, C.; Diaz, P.; Fernandez, I; Lara, G.T Tauri stars are low-mass pre-main sequence stars that are intrinsically variable. Due to the intense magnetic fields they possess, they develop dark spots on their surface that, because of rotation, introduce a periodic variation of brightness. In addition, the presence of surrounding discs could generate flux variations by variable extinction or accretion. Both can lead to a brightness decrease or increase, respectively. Here, we have compiled a catalogue of light curves for 379 T Tauri stars in the Lagoon Nebula (M8) region, using VVVX survey data in the K-s-band. All these stars were already classified as pre-MS stars based on other indicators. The data presented here are spread over a period of about eight years, which gives us a unique follow-up time for these sources at this wavelength. The light curves were classified according to their degree of periodicity and asymmetry, to constrain the physical processes responsible for their variation. Periods were compared with the ones found in literature, on a much shorter baseline. This allowed us to prove that for 126 stars, the magnetically active regions remain stable for several years. Besides, our near-IR data were compared with the optical Kepler/K2 light curves, when available, giving us a better understanding of the mechanisms responsible for the brightness variations observed and how they manifest at different bands. We found that the periodicity in both bands is in fairly good agreement, but the asymmetry will depend on the amplitude of the bursts or dips events and the observation cadence.
- ItemThe effect of cooling on the accretion of circumprimary discs in merging supermassive black hole binaries(2020) Fontecilla Suárez, Camilo José; Lodato, G.; Cuadra, J.
- ItemTIDAL DISRUPTIONS IN CIRCUMBINARY DISKS. II. OBSERVATIONAL SIGNATURES IN THE REVERBERATION SPECTRA(2014) Brem, P.; Cuadra, J.; Amaro-Seoane, P.; Komossa, S.Supermassive binary black holes (SMBBHs) with sub-pc separations form in the course of galaxy mergers, if both galaxies harbor massive black holes. Clear observational evidence for them however still eludes us. We propose a novel method of identifying these systems by means of reverberation mapping their circumbinary disk after a tidal disruption event has ionized it. The tidal disruption of a star at the secondary leads to strong asymmetries in the disk response. We model the shape of the velocity-delay maps for various toy disk models and more realistic gas distributions obtained by smoothed particle hydrodynamics simulations. The emissivity of the ionized disk is calculated with Cloudy. We find peculiar asymmetries in the maps for off center ionizing sources that may help us constrain geometrical parameters of a circumbinary disk such as semimajor axis and orbital phase of the secondary, as well as help strengthen the observational evidence for sub-parsec SMBBHs as such.
- ItemUnveiling the structural content of NGC 6357 via kinematics and NIR variability(2024) Ordenes-Huanca, C.; Zoccali, M.; Bayo, A.; Cuadra, J.; Contreras Ramos, R.; Rojas-Arriagada, A.NGC 6357, a star-forming complex at similar to 1.7 kpc from the Sun, contains giant molecular clouds and three prominent star clusters alongside with HII regions, very massive stars and thousands of young stellar objects in different evolutionary stages. We present a combined infrared kinematic and time domain study of the line of sight towards this region enabled by the VVVX survey. In terms of kinematics, a novel discovery emerges: an asymmetrical distribution in the vector point diagram. Some stars in the sample exhibit spatial proximity to dusty regions, with their proper motions aligned with filament projections, hinting at a younger population linked to triggered star formation. However, this distribution could also stem from an asymmetric stellar expansion event within NGC 6357, warranting further investigation. Comparing this data with Gaia revealed inconsistencies likely due to high extinction levels in the region. Additionally, owing to accretion episodes and surface cool spots, young stars display high variability. Using the K-s-band time series data, we overcome the extreme levels of extinction towards the region, and compile a catalogue of 774 infrared light curves of young stars. Each light curve has been characterized in terms of asymmetry and periodicity, to infer the dominant underlying physical mechanism. These findings are then correlated with evolutionary stages, aiming to uncover potential age disparities among the observed stars. This study contributes to our understanding the intricate dynamics and evolutionary processes within NGC 6357, offering valuable insights into the formation and development of stellar populations within such complex environments