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MODEST-18: Dense Stellar Systems in the Era of Gaia, LIGO and LISA June 25 - 29, 2018 | Santorini, Greece

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MODEST-18: Dense Stellar Systems in the Era of Gaia, LIGO and LISA June 25 - 29, 2018 | Santorini, Greece MODEST-18: Dense Stellar Systems in the Era of Gaia, LIGO and LISA June 25 - 29, 2018 | Santorini, Greece POSTER Federico Abbate (Milano-Bicocca): Ionized Gas in 47 Tuc – A Detailed Study with Millisecond Pulsars Globular clusters are known to be very poor in gas despite predictions telling us otherwise. The presence of ionized gas can be investigated through its dispersive effects on the radiation of the millisecond pulsars inside the clusters. This effect led to the first detection of any kind of gas in a globular cluster in the form of ionized gas in 47 Tucanae. With new timing results of these pulsars over longer periods of time we can improve the precision of this measurement and test different distribution models. We first use the parameters measured through timing to measure the dynamical properties of the cluster and the line of sight position of the pulsars. Then we test for gas distribution models. We detect ionized gas distributed with a constant density of n = (0.22 ± 0.05) cm−3. Models predicting a decreasing density or following the stellar distribution are highly disfavoured. Thanks to the quality of the data we are also able to test for the presence of an intermediate mass black hole in the center of the cluster and we derive an upper limit for the mass at ∼ 4000 M_sun. 1 MODEST-18: Dense Stellar Systems in the Era of Gaia, LIGO and LISA June 25 - 29, 2018 | Santorini, Greece POSTER Javier Alonso-García (Antofagasta): VVV and VVV-X Surveys – Unveiling the Innermost Galaxy We find the densest concentrations of field stars in our Galaxy when we look towards its central regions. But our knowledge of the innermost Milky Way is seriously hampered by the dust and gas present at low latitude lines of sight. The VVV and the VVV-X surveys can beat these difficulties by observing the Galactic Bulge and inner Disk at near-infrared wavelengths were extinction is highly diminished. Using the 4m VISTA telescope located in Cerro Paranal, the VVV and VVV-X surveys provide wide-field high-resolution images of the highly reddened inner Galaxy in the Z, Y, J, H and Ks near infrared filters. In my talk I will present a new photometric catalog that we have built with nearly one billion sources from the inner Galactic regions surveyed by the VVV. Using the color-magnitude diagrams we build, we are able to disentangle and provide a detailed description of the inner Galactic stellar populations. I will also report on the proper characterization of the extinction law towards the inner Milky Way that we have obtained. Finally, I will describe VVV-X, the extended VVV survey, that we are currently running over a much bigger area in the inner Galaxy, and talk about possible synergies with Gaia and other Galactic surveys. 2 MODEST-18: Dense Stellar Systems in the Era of Gaia, LIGO and LISA June 25 - 29, 2018 | Santorini, Greece POSTER Jeff J. Andrews (Crete/FORTH): Double Neutron Star Formation: Supernova Dynamics and Orbital Decay due to Gravitational Wave Radiation The formation and evolution of double neutron stars (DNS) has traditionally been studied using binary population synthesis in which one randomly generates a set of stellar binaries from initial conditions and evolves them forward using our best understanding of the physics involved. Here, I take an alternative approach by focusing only on the second supernova (SN) forming the DNS and the subsequent orbital decay and merger due to gravitational wave radiation. Since we have decoupled the effects of uncertainties in prior binary evolution, our results are quite general. Using analytic and numerical methods, we explore how different kick velocity distributions, pre-SN orbital separations, and progenitor He-star masses affect the derived delay time distributions, systemic velocities, and distances traveled before the DNS mergers. We find that DNSs typically have a systemic velocity of order the pre-SN orbital velocity, but often much less depending on the kick velocity. Furthermore, we provide realistic travel distances for systems that escape the gravitational potential of their host galaxies. Only relatively tight systems can leave host galaxies with escape velocities above a ~100 km/s. However, those that do escape may travel as far as ~Mpc before merging, possibly explaining the so-called host-less short gamma ray bursts that are found far from any galaxy. 3 MODEST-18: Dense Stellar Systems in the Era of Gaia, LIGO and LISA June 25 - 29, 2018 | Santorini, Greece POSTER Francisco Aros (MPIA/ESO): Axisymmetric Dynamical Models for Stellar Systems: an Application to Local Dwarf Spheroidal Galaxies In the search to understand the nature of dark matter, the dynamical analysis of dark matter dominated galaxies is expected to be of special interest. In this sense, the local dwarf spheroidal galaxies are the ideal objects for this kind of studies. Up to now, most approaches have assumed spherical symmetry and explored dynamical models based on the Jeans equations. However, we know that the stellar component of these galaxies are not spherical, and thus their mass determination may have been biased. Dynamical models based on the Jeans Equations have been successful on determining global properties of these systems under the assumption of spherical symmetry; yet we do not know if these would also apply to axisymmetric models. Here we present a thorough analysis on the constraints for the intrinsic flattening of the dark matter halo and its degeneracy with the velocity anisotropy. 4 MODEST-18: Dense Stellar Systems in the Era of Gaia, LIGO and LISA June 25 - 29, 2018 | Santorini, Greece POSTER Alessandro Ballone (INAF Padova): Weighing the IMBH candidate CO-0.40-0.22* in the Galactic Centre The high velocity gradient observed in the compact cloud CO-0.40-0.22, at a projected distance of 60 pc from the centre of the Milky Way, has led its discoverers to identify the closeby mm continuum emitter, CO-0.40-0.22*, with an intermediate mass black hole (IMBH) candidate. We describe the interaction between CO-0.40-0.22 and the IMBH, by means of a simple analytical model and of hydrodynamical simulations. Through such calculation, we obtain a lower limit to the mass of CO-0.40-0.22* of few 10^4 × M_sun. This result tends to exclude the formation of such massive black hole in the proximity of the Galactic Centre. On the other hand, CO-0.40-0.22* might have been brought to such distances in cosmological timescales, if it was born in a dark matter halo or globular cluster around the Milky Way. 5 MODEST-18: Dense Stellar Systems in the Era of Gaia, LIGO and LISA June 25 - 29, 2018 | Santorini, Greece POSTER Matteo Bonetti (Insubria): Gravitational Waves from Massive Black Hole Triplets Massive black-hole binaries (MBHBs) are thought to be the main source of gravitational waves (GWs) in the low-frequency domain surveyed by ongoing and forthcoming Pulsar Timing Array (PTA) campaigns and future space-borne missions (LISA). However, MBHBs in realistic astrophysical environments may not always reach separations small enough to allow significant GW emission. This “final-parsec problem” can be eased by the appearance of a third massive black hole (MBH) whose action can force, under certain conditions, the former MBHB on a very eccentric orbit, hence allowing intense GW emission eventually leading to coalescence. A detailed assessment of the process requires a general relativistic treatment and the inclusion of environmental effects. In order to tackle the problem, we developed a three-body Post-Newtonian (PN) code framed in a spherical galactic potential, including GR corrections up to 2.5PN order as well as the effects of orbital hardening and dynamical friction. I will present the results of an extensive set of simulations aimed at characterize the dynamics of such triple systems in a cosmological context. Finally, I will analyze the implications on the emitted GW signal. 6 MODEST-18: Dense Stellar Systems in the Era of Gaia, LIGO and LISA June 25 - 29, 2018 | Santorini, Greece POSTER Phil Breen (Edinburgh): Light Element Variations in Globular Clusters via Nucleosynthesis in Black Hole Accretion Discs Ancient globular clusters contain multiple stellar populations identified by variations in light elements (e.g., C, N, O, Na). Although many scenarios have been suggested to explain this phenomenon, all are faced with challenges when compared with all the observational evidence. In this Letter, we propose a new scenario in which light element variations are determined by nucleosynthesis in accretion discs around black holes. Since the black holes form after a few Myrs, the cluster is expected to still be embedded in a gas rich environment. By using a simplified accretion model which assumes virial temperatures, we show that the correct light element anti-correlations could be produced in accretion flows around stellar-mass black holes. Assuming a Kroupa IMF, each black hole would only have to process 300Msun of material in order to produce multiple populations; over a period of 3Myr this corresponds to 10^-4 Msun/yr, which is within the range of values typically assumed for the formation of massive stars. 7 MODEST-18: Dense Stellar Systems in the Era of Gaia, LIGO and LISA June 25 - 29, 2018 | Santorini, Greece POSTER Katelyn Breivik (CIERA): Revealing Black Holes in Binaries with Gaia We estimate the population of black holes with luminous stellar companions (BH-LCs) in the Milky Way (MW) observable by Gaia. We evolve a realistic distribution of BH-LC progenitors from zero-age to the current epoch taking into account relevant physics, including binary stellar evolution, BH-formation physics, and star formation rate, in order to estimate the BH-LC population in the MW today.
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