27 research outputs found
Gaia archive
The Gaia archive is being designed and implemented by the DPAC Consortium.
The purpose of the archive is to maximize the scientific exploitation of the
Gaia data by the astronomical community. Thus, it is crucial to gather and
discuss with the community the features of the Gaia archive as much as
possible. It is especially important from the point of view of the GENIUS
project to gather the feedback and potential use cases for the archive. This
paper presents very briefly the general ideas behind the Gaia archive and
presents which tools are already provided to the community.Comment: Proceedings of the XXXVII Meeting of the Polish Astronomical Societ
Cataclysmic variables in Globular clusters: First results on the analysis of the MOCCA simulations database
In this first investigation of the MOCCA database with respect to cataclysmic
variables, we found that for models with Kroupa initial distributions,
considering the standard value of the efficiency of the common-envelope phase
adopted in BSE, no single cataclysmic variable was formed only via binary
stellar evolution, i. e., in order to form them, strong dynamical interactions
have to take place. Our results also indicate that the population of
cataclysmic variables in globular clusters are, mainly, in the last stage of
their evolution and observational selection effects can change drastically the
expected number and properties of observed cataclysmic variables.Comment: 4 pages, 3 figures. Presented at the MODEST 16/Cosmic Lab conference
in Bologna, Italy, April 18-22 2016. To be pusblished in Mem. S. A. It.
Conference Serie
MOCCA Survey Database I: Dissolution of tidally filling star clusters harbouring BH subsystems
We investigate the dissolution process for dynamically evolving star clusters
embedded in an external tidal field by exploring the MOCCA Survey Database I,
with focus on the presence and evolution of a stellar-mass black hole
subsystem. We argue that the presence of a black hole subsystem can lead to the
dissolution of tidally filling star clusters and this can be regarded as a
third type of cluster dissolution mechanism (in addition to well-known
mechanisms connected with strong mass loss due to stellar evolution and mass
loss connected with the relaxation process). This third process is
characterized by abrupt cluster dissolution connected with the loss of
dynamical equilibrium. The abrupt dissolution is powered by strong energy
generation from a stellar-mass black hole subsystem accompanied by tidal
stripping. Additionally, we argue that such a mechanism should also work for
even tidally under-filling clusters with top-heavy initial mass function.
Observationally, star clusters which undergo dissolution powered by the third
mechanism would look as a 'dark cluster' i.e. composed of stellar mass black
holes surrounded by an expanding halo of luminous stars (Banerjee & Kroupa
2011), and they should be different from 'dark clusters' harbouring
intermediate mass black holes as discussed by Askar et al. (2017a). An
additional observational consequence of an operation of the third dissolution
mechanism should be a larger than expected abundance of free floating black
holes in the Galactic halo.Comment: 14 pages, 14 figures, accepted to MNRA
MOCCA SURVEY Database I: Binary Black Hole Mergers from Globular Clusters with Intermediate Mass Black Holes
The dynamical formation of black hole binaries in globular clusters that
merge due to gravitational waves occurs more frequently in higher stellar
density. Meanwhile, the probability to form intermediate mass black holes
(IMBHs) also increases with the density. To explore the impact of the formation
and growth of IMBHs on the population of stellar mass black hole binaries from
globular clusters, we analyze the existing large survey of Monte-Carlo globular
cluster simulation data (MOCCA SURVEY Database I). We show that the number of
binary black hole mergers agrees with the prediction based on clusters' initial
properties when the IMBH mass is not massive enough or the IMBH seed forms at a
later time. However, binary black hole formation and subsequent merger events
are significantly reduced compared to the prediction when the present-day IMBH
mass is more massive than or the present-day IMBH mass
exceeds about 1 per cent of cluster's initial total mass. By examining the
maximum black hole mass in the system at the moment of black hole binary
escaping, we find that 90 per cent of the merging binary black holes
escape before the formation and growth of the IMBH. Furthermore, large fraction
of stellar mass black holes are merged into the IMBH or escape as single black
holes from globular clusters in cases of massive IMBHs, which can lead to the
significant under-population of binary black holes merging with gravitational
waves by a factor of 2 depending on the clusters' initial distributions.Comment: 9 pages, 8 figures, Accepted for publication in MNRA