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Register a new userThe absolute proper motions of the Arches and Quintuplet clusters
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Arches and Quintuplet are two young, massive clusters projected near the Galactic Center. To date, studies focused on understanding their origin have been based on proper motions (PMs) derived in the clusters reference frames and required some assumptions about their 3D motion. In this paper, we combine public PM catalogs of these clusters with the Gaia DR2 catalog and, for the first time, transform the relative PMs of the Arches and Quintuplet clusters onto an absolute reference system. We find that the absolute PM of the Arches is $(mu_alpha cosdelta,mu_delta)$ $=$ $(-1.45 pm 0.23,-2.68 pm 0.14)$ mas yr$^{-1}$, and that of the Quintuplet is $(mu_alpha cosdelta,mu_delta)$ $=$ $(-1.19 pm 0.09,-2.66 pm 0.18)$ mas yr$^{-1}$. These values suggest that these systems are moving almost parallel to the Galactic plane. A measurement of the clusters distances is still required to meaningfully constrain the clusters orbits and shed light on the origin of the Arches and Quintuplet.
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Proper motions (PMs) are crucial to fully understand the internal dynamics of globular clusters (GCs). To that end, the Hubble Space Telescope (HST) Proper Motion (HSTPROMO) collaboration has constructed large, high-quality PM catalogues for 22 Galactic GCs. We highlight some of our exciting recent results: the first directly-measured radial anisotropy profiles for a large sample of GCs; the first dynamical distance and mass-to-light (M/L) ratio estimates for a large sample of GCs; and the first dynamically-determined masses for hundreds of blue-straggler stars (BSSs) across a large GC sample.
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Recently, more than 100 Wolf-Rayet and OB stars were identified in the Galactic center. About a third of these sources are not spatially associated with any of the known star clusters in this region. We probe the distribution of drifted sources in numerical models of the massive clusters in the Galactic center and compare it to the observed distribution of isolated massive sources in this region. We find that stars as massive as 100 Msun drift away from the center of each cluster by up to ~60 pc using the cluster models. Our best model reproduces ~60% of the known isolated massive stars out to 80 pc from the center of the Arches cluster. This number increases to 70%-80% when we only consider the region of ~20 pc from the Arches cluster.
In this paper we report a new estimate of the absolute proper motion (PM) of the globular cluster NGC 5139 ($omega$ Cen) as part of the HST large program GO-14118+14662. We analyzed a field 17 arcmin South-West of the center of $omega$ Cen and computed PMs with an epoch span of $sim$15.1 years. We employed 45 background galaxies to link our relative PMs to an absolute reference-frame system. The absolute PM of the cluster in our field is: $(mu_alpha cosdelta , mu_delta) = (-3.341 pm 0.028 , -6.557 pm 0.043)$ mas yr$^{-1}$. Upon correction for the effects of viewing perspective and the known cluster rotation, this implies that for the cluster center of mass $(mu_alpha cosdelta , mu_delta) = (-3.238 pm 0.028, -6.716 pm 0.043)$ mas yr$^{-1}$. This measurement is direct and independent, has the highest random and systematic accuracy to date, and will provide an external verification for the upcoming Gaia Data Release 2. It also differs from most reported PMs for $omega$ Cen in the literature by more than 5$sigma$, but consistency checks compared to other recent catalogs yield excellent agreement. We computed the corresponding Galactocentric velocity, calculated the implied orbit of $omega$ Cen in two different Galactic potentials, and compared these orbits to the orbits implied by one of the PM measurements available in the literature. We find a larger (by about 500 pc) perigalactic distance for $omega$ Cen with our new PM measurement, suggesting a larger survival expectancy for the cluster in the Galaxy.
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