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N Bastian - One of the best experts on this subject based on the ideXlab platform.
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the e mosaics project simulating the formation and co evolution of galaxies and their Star Cluster populations
Monthly Notices of the Royal Astronomical Society, 2018Co-Authors: Joel Pfeffer, J Diederik M Kruijssen, Robert A Crain, N BastianAbstract:We introduce the MOdelling Star Cluster population Assembly In Cosmological Simulations within EAGLE (E-MOSAICS) project. E-MOSAICS incorporates models describing the formation, evolution, and disruption of Star Clusters into the EAGLE galaxy formation simulations, enabling the examination of the co-evolution of Star Clusters and their host galaxies in a fully cosmological context. A fraction of the Star formation rate of dense gas is assumed to yield a Cluster population; this fraction and the population’s initial properties are governed by the physical properties of the natal gas. The subsequent evolution and disruption of the entire Cluster population are followed accounting for two-body relaxation, stellar evolution, and gravitational shocks induced by the local tidal field. This introductory paper presents a detailed description of the model and initial results from a suite of 10 simulations of ∼L galaxies with disc-like morphologies atz = 0. The simulations broadly reproduce key observed characteristics of young Star Clusters and globular Clusters (GCs), without invoking separate formation mechanisms for each population. The simulated GCs are the surviving population of massive Clusters formed at early epochs (z 1–2), when the characteristic pressures and surface densities of Star-forming gas were significantly higher than observed in local galaxies. We examine the influence of the Star formation and assembly histories of galaxies on their Cluster populations, finding that (at similar present-day mass) earlier-forming galaxies foster a more massive and disruption-resilient Cluster population, while galaxies with late mergers are capable of forming massive Clusters even at late cosmic epochs. We find that the phenomenological treatment of interstellar gas in EAGLE precludes the accurate modelling of Cluster disruption in low-density environments, but infer that simulations incorporating an explicitly modelled cold interstellar gas phase will overcome this shortcoming.
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the search for multiple populations in magellanic cloud Clusters iv coeval multiple stellar populations in the young Star Cluster ngc 1978
Monthly Notices of the Royal Astronomical Society, 2018Co-Authors: S Martocchia, N Bastian, F Niederhofer, E Dalessandro, N Kacharov, Christopher Usher, I Cabreraziri, C Lardo, S Cassisi, D GeislerAbstract:We have recently shown that the $\sim2$ Gyr old Large Magellanic Cloud Star Cluster NGC 1978 hosts multiple populations in terms of Star-to-Star abundance variations in [N/Fe]. These can be seen as a splitting or spread in the sub-giant and red giant branches (SGB and RGB) when certain photometric filter combinations are used. Due to its relative youth, NGC 1978 can be used to place stringent limits on whether multiple bursts of Star-formation have taken place within the Cluster, as predicted by some models for the origin of multiple populations. We carry out two distinct analyses to test whether multiple Star-formation epochs have occurred within NGC 1978. First, we use UV CMDs to select Stars from the first and second population along the SGB, and then compare their positions in optical CMDs, where the morphology is dominantly controlled by age as opposed to multiple population effects. We find that the two populations are indistinguishable, with age differences of $1\pm20$ Myr between them. This is in tension with predictions from the AGB scenario for the origin of multiple populations. Second, we estimate the broadness of the main sequence turnoff (MSTO) of NGC 1978 and we report that it is consistent with the observational errors. We find an upper limit of $\sim$65 Myr on the age spread in the MSTO of NGC 1978. This finding is in conflict with the age spread scenario as origin of the extended MSTO in intermediate age Clusters, while it fully supports predictions from the stellar rotation model.
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the ngc 404 nucleus Star Cluster and possible intermediate mass black hole
The Astrophysical Journal, 2010Co-Authors: Anil C. Seth, Nelson Caldwell, Victor P. Debattista, Michele Cappellari, Nadine Neumayer, N Bastian, Knut Olsen, R D Blum, Richard M Mcdermid, Thomas H PuziaAbstract:We examine the nuclear morphology, kinematics, and stellar populations in nearby S0 galaxy NGC 404 using a combination of adaptive optics assisted near-IR integral-field spectroscopy, optical spectroscopy, and Hubble Space Telescope imaging. These observations enable study of the NGC 404 nucleus at a level of detail possible only in the nearest galaxies. The surface brightness profile suggests the presence of three components: a bulge, a nuclear Star Cluster (NSC), and a central light excess within the Cluster at radii < 3 pc. These components have distinct kinematics with modest rotation seen in the NSC and counter-rotation seen in the central excess. Molecular hydrogen emission traces a disk with rotation nearly orthogonal to that of the Stars. The stellar populations of the three components are also distinct, with half of the mass of the NSC having ages of ~1 Gyr (perhaps resulting from a galaxy merger), while the bulge is dominated by much older Stars. Dynamical modeling of the stellar kinematics gives a total NSC mass of 1.1 × 107 M ☉. Dynamical detection of a possible intermediate-mass black hole (BH) is hindered by uncertainties in the central stellar mass profile. Assuming a constant mass-to-light ratio, the stellar dynamical modeling suggests a BH mass of <1 × 105 M ☉, while the molecular hydrogen gas kinematics are best fitted by a BH with a mass of 4.5+3.5 –2.0 × 105 M ☉. Unresolved and possibly variable dust emission in the near-infrared and active galactic nucleus-like molecular hydrogen emission-line ratios do suggest the presence of an accreting BH in this nearby LINER galaxy.
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the ngc 404 nucleus Star Cluster and possible intermediate mass black hole
arXiv: Cosmology and Nongalactic Astrophysics, 2010Co-Authors: Anil C. Seth, Nelson Caldwell, Victor P. Debattista, Michele Cappellari, Nadine Neumayer, N Bastian, Knut Olsen, R D Blum, Richard M Mcdermid, Thomas H PuziaAbstract:We examine the nuclear morphology, kinematics, and stellar populations in nearby S0 galaxy NGC 404 using a combination of adaptive optics assisted near-IR integral-field spectroscopy, optical spectroscopy, and HST imaging. These observations enable study of the NGC 404 nucleus at a level of detail possible only in the nearest galaxies. The surface brightness profile suggests the presence of three components, a bulge, a nuclear Star Cluster, and a central light excess within the Cluster at radii <3 pc. These components have distinct kinematics with modest rotation seen in the nuclear Star Cluster and counter-rotation seen in the central excess. Molecular hydrogen emission traces a disk with rotation nearly orthogonal to that of the Stars. The stellar populations of the three components are also distinct, with half of the mass of the nuclear Star Cluster having ages of ~1 Gyr (perhaps resulting from a galaxy merger), while the bulge is dominated by much older Stars. Dynamical modeling of the stellar kinematics gives a total nuclear Star Cluster mass of 1.1x10^7 Msol. Dynamical detection of a possible intermediate mass black hole is hindered by uncertainties in the central stellar mass profile. Assuming a constant mass-to-light ratio, the stellar dynamical modeling suggests a black hole mass of <1x10^5 Msol, while the molecular hydrogen gas kinematics are best fit by a black hole with mass of 4.5x10^5 Msol. Unresolved and possibly variable dust emission in the near-infrared and AGN-like molecular hydrogen emission line ratios do suggest the presence of an accreting black hole in this nearby LINER galaxy.
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the Star Cluster population of m 51 ii age distribution and relations among the derived parameters
Astronomy and Astrophysics, 2005Co-Authors: N Bastian, M Gieles, H J G L M Lamers, R A Scheepmaker, R De GrijsAbstract:We use archival Hubble Space Telescope observations of broad-band images from the ultraviolet (F255W- filter) through the near infrared (NICMOS F160W-filter) to study the Star Cluster population of the interacting spiral galaxy M51. We obtain age, mass, extinction, and effective radius estimates for 1152 Star Clusters in a region of � 7.3 × 8.1 kpc centered on the nucleus and extending into the outer spiral arms. In this paper we present the data set and exploit it to determine the age distribution and relationships among the fundamental parameters (i.e. age, mass, effective radius). We show the critical dependence of the age distribution on the sample selection, and confirm that using a constant mass cut-off, above which the sample is complete for the entire age range of interest, is essential. In particular, in this sample we are complete only for masses above 5×10 4 M⊙ for the last 1 Gyr. Using this dataset we find: i) that the Cluster formation rate seems to have had a large increase � 50-70 Myr ago, which is coincident with the suggested second passage of its companion, NGC 5195, ii) a large number of extremely young (< 10 Myr) Star Clusters, which we interpret as a population of unbound Clusters of which a large majority will disrupt within the next �10 Myr, and iii) that the distribution of Cluster sizes can be well approximated by a power-law with exponent, � = 2.2 ± 0.2, which is very similar to that of Galactic globular Clusters, indicating that Cluster disruption is largely independent of Cluster radius. In addition, we have used this dataset to search for correlations among the derived parameters. In particular, we do not find any strong trends between the age and mass, mass and effective radius, nor between the galactocentric distance and effective radius. There is, however, a strong correlation between the age of a Cluster and its extinction, with younger Clusters being more heavily reddened than older Clusters.
Matthew R. Bate - One of the best experts on this subject based on the ideXlab platform.
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stellar brown dwarf and multiple Star properties from a radiation hydrodynamical simulation of Star Cluster formation
arXiv: Solar and Stellar Astrophysics, 2011Co-Authors: Matthew R. BateAbstract:We report the statistical properties of Stars, brown dwarfs and multiple systems obtained from the largest radiation hydrodynamical simulation of Star Cluster formation to date that resolves masses down to the opacity limit for fragmentation (a few Jupiter masses). The initial conditions are identical to those of previous barotropic calculations published by Bate, but this time the calculation is performed using a realistic equation of state and radiation hydrodynamics. The calculation uses sink particles to model 183 Stars and brown dwarfs, including 28 binaries and 12 higher-order multiple systems, the properties of which are compared the results from observational surveys. We find that the radiation hydrodynamical/sink particle simulation reproduces many observed stellar properties very well. In particular, whereas using a barotropic equation of state produces more brown dwarfs than Stars, the inclusion of radiative feedback results in a stellar mass function and a ratio of brown dwarfs to Stars in good agreement with observations of Galactic Star-forming regions. In addition, many of the other statistical properties of the Stars and brown dwarfs are in reasonable agreement with observations, including multiplicity as a function of primary mass, the frequency of very-low-mass binaries, and general trends for the mass ratio and separation distributions of binaries. We also examine the velocity dispersion of the Stars, the distributions of disc truncation radii due to dynamical interactions, and coplanarity of orbits and sink particle spins in multiple systems. Overall, the calculation produces a Cluster of Stars whose statistical properties are difficult to distinguish from observed systems, implying that gravity, hydrodynamics, and radiative feedback are the primary ingredients for determining the origin of the statistical properties of low-mass Stars.
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on the evolution of a Star Cluster and its multiple stellar systems following gas dispersal
Monthly Notices of the Royal Astronomical Society, 2010Co-Authors: Nickolas Moeckel, Matthew R. BateAbstract:We investigate the evolution, following gas dispersal, of a Star Cluster produced from a hydrodynamical calculation of the collapse and fragmentation of a turbulent molecular cloud. We find that when the gas, initially comprising ≈60 per cent of the mass, is removed, the system settles into a bound Cluster containing ≈30–40 per cent of the stellar mass surrounding by an expanding halo of ejected Stars. The bound Cluster expands from an initial radius of <0.05 to 1–2 pc over ≈4–10 Myr, depending on how quickly the gas is removed, implying that stellar Clusters may begin with far higher stellar densities than usually assumed. With rapid gas dispersal, the most massive Stars are found to be mass segregated for the first ∼ 1M yr of evolution, but classical mass segregation only develops for cases with long gas removal time-scales. Eventually, many of the most massive Stars are expelled from the bound Cluster. Despite the high initial stellar density and the extensive dynamical evolution of the system, we find that the stellar multiplicity is almost constant during the 10 Myr of evolution. This is because the primordial multiple systems are formed in a Clustered environment and, thus, by their nature are already resistant to further evolution. The majority of multiple system evolution is confined to the decay of high-order systems (particularly quadruple systems) and the formation of a significant population of very wide (10 4 –10 5 au) multiple systems in the expanding halo. This formation mechanism for wide binaries potentially solves the problem of how most Stars apparently form in Clusters and yet a substantial population of wide binaries exist in the field. We also find that many of these wide binaries and the binaries produced by the decay of high-order multiple systems have unequal mass components, potentially solving the problem that hydrodynamical simulations of Star formation are found to underproduce unequal mass solar-type binaries.
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on the evolution of a Star Cluster and its multiple stellar systems following gas dispersal
arXiv: Solar and Stellar Astrophysics, 2010Co-Authors: Nickolas Moeckel, Matthew R. BateAbstract:We investigate the evolution, following gas dispersal, of a Star Cluster produced from a hydrodynamical calculation. We find that when the gas, initially comprising 60% of the mass, is removed, the system settles into a bound Cluster containing 30-40% of the stellar mass surrounding by an expanding halo of ejected Stars. The bound Cluster expands from an initial radius of <0.05 pc to 1-2 pc over 4-10 Myr, depending on how quickly the gas is removed, implying that stellar Clusters may begin with far higher stellar densities than usually assumed. With rapid gas dispersal the most massive Stars are found to be mass segregated for the first ~1 Myr of evolution, but classical mass segregation only develops for cases with long gas removal timescales. Eventually, many of the most massive Stars are expelled from the bound Cluster. Despite the high initial stellar density and the extensive dynamical evolution of the system, we find that the stellar multiplicity is almost constant during the 10 Myr of evolution. This is because the primordial multiple systems are formed in a Clustered environment and, thus, by their nature are already resistant to further evolution. The majority of multiple system evolution is confined to the decay of high-order systems and the formation of a significant population of very wide (10^4-10^5 AU) multiple systems in the expanding halo. This formation mechanism for wide binaries potentially solves the problem of how most Stars apparently form in Clusters and yet a substantial population of wide binaries exist in the field. Many of these wide binaries and the binaries produced by the decay of high-order multiple systems have unequal mass components, potentially solving the problem that hydrodynamical simulations of Star formation are found to under-produce unequal-mass solar-type binaries.
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stellar brown dwarf and multiple Star properties from hydrodynamical simulations of Star Cluster formation
Monthly Notices of the Royal Astronomical Society, 2009Co-Authors: Matthew R. BateAbstract:We report the statistical properties of Stars, brown dwarfs and multiple systems obtained from the largest hydrodynamical simulation of Star Cluster formation to date that resolves masses down to the opacity limit for fragmentation (a few Jupiter masses). The simulation is essentially identical to that of Bate, Bonnell & Bromm except that the initial molecular cloud is larger and more massive. It produces more than 1250 Stars and brown dwarfs, providing unprecedented statistical information that can be compared with observational surveys. The calculation uses sink particles to model the Stars and brown dwarfs. Part of the calculation is rerun with smaller sink particle accretion radii and gravitational softening to investigate the effect of these approximations on the results. We find that hydrodynamical/sink particle simulations can reproduce many of the observed stellar properties very well. Multiplicity as a function of the primary mass, the frequency of very low mass (VLM) binaries, general trends for the separation and mass ratio distributions of binaries and the relative orbital orientations of triples systems are all in reasonable agreement with observations. We also examine the radial variations of binarity, velocity dispersion and mass function in the resulting stellar Cluster and the distributions of disc truncation radii due to dynamical interactions. For VLM binaries, because their separations are typically close, we find that their frequency is sensitive to the sink particle accretion radii and gravitational softening used in the calculations. Using small accretion radii and gravitational softening results in a frequency of VLM binaries similar to that expected from observational surveys (≈20 per cent). We also find that VLM binaries evolve from wide, unequal-mass systems towards close equal-mass systems as they form. The two main deficiencies of the calculations are that they overproduce brown dwarfs relative to Stars and that there are too few unequalmass binaries with K- and G-dwarf primaries. The former of these is likely due to the absence of radiative feedback and/or magnetic fields.
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Physics and modes of Star Cluster formation
Proceedings of the International Astronomical Union, 2009Co-Authors: Matthew R. BateAbstract:I review the progress made in understanding the physics and modes of Star Cluster formation through the use of direct self-gravitating hydrodynamical simulations, including those that have recently been performed incorporating radiative transfer and magnetic fields.
Norikazu Mizuno - One of the best experts on this subject based on the ideXlab platform.
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the two molecular clouds in rcw 38 evidence for the formation of the youngest super Star Cluster in the milky way triggered by cloud cloud collision
The Astrophysical Journal, 2016Co-Authors: Y Fukui, Akio Ohama, K Torii, K Hasegawa, Hidetoshi Sano, Yusuke Hattori, Satoshi Ohashi, K Fujii, Sho Kuwahara, Norikazu MizunoAbstract:We present distributions of two molecular clouds having velocities of 2 and 14 km s{sup −1} toward RCW 38, the youngest super Star Cluster in the Milky Way, in the {sup 12}CO J = 1–0 and 3–2 and {sup 13}CO J = 1–0 transitions. The two clouds are likely physically associated with the Cluster as verified by the high intensity ratio of the J = 3–2 emission to the J = 1–0 emission, the bridging feature connecting the two clouds in velocity, and their morphological correspondence with the infrared dust emission. The velocity difference is too large for the clouds to be gravitationally bound. We frame a hypothesis that the two clouds are colliding with each other by chance to trigger formation of the ∼20 O Stars that are localized within ∼0.5 pc of the Cluster center in the 2 km s{sup −1} cloud. We suggest that the collision is currently continuing toward part of the 2 km s{sup −1} cloud where the bridging feature is localized. This is the third super Star Cluster alongside Westerlund 2 and NGC 3603 where cloud–cloud collision has triggered the Cluster formation. RCW 38 is the youngest super Star Cluster in the Milky Way,more » holding a possible sign of on-going O Star formation, and is a promising site where we may be able to witness the moment of O Star formation.« less
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the two molecular clouds in rcw 38 evidence for formation of the youngest super Star Cluster in the milky way triggered by cloud cloud collision
arXiv: Solar and Stellar Astrophysics, 2015Co-Authors: Y Fukui, Akio Ohama, K Torii, K Hasegawa, Hidetoshi Sano, Yusuke Hattori, Satoshi Ohashi, K Fujii, Sho Kuwahara, Norikazu MizunoAbstract:We present distributions of two molecular clouds having velocities of 2 km s$^{-1}$ and 14 km s$^{-1}$ toward RCW 38, the youngest super Star Cluster in the Milky Way, in the $^{12}$CO ($J=$1--0 and 3--2) and $^{13}$CO ($J=$1--0) transitions. The two clouds are likely physically associated with the Cluster as verified by the high intensity ratio of the $J$=3--2 emission to the $J$=1--0 emission, the bridging feature connecting the two clouds in velocity and their morphological correspondence with the infrared dust emission. The total mass of the clouds and the Cluster is too small to gravitationally bind the velocity difference. We frame a hypothesis that the two clouds are colliding with each other by chance to trigger formation of the $\sim$20 candidate O Stars which are localized within $\sim$0.3 pc of the Cluster center in the 2 km s$^{-1}$ cloud. We suggest that the collision is currently continuing toward part of the 2 km s$^{-1}$ cloud where the bridging feature is localized. This is the third super Star Cluster alongside of Westerlund2 and NGC3603 where cloud-cloud collision triggered the Cluster formation. RCW38 is the most remarkable and youngest Cluster, holding a possible sign of on-going O Star formation, and is the most promising site where we may be able to witness the moment of O-Star formation.
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molecular clouds toward the super Star Cluster ngc 3603 possible evidence for a cloud cloud collision in triggering the Cluster formation
The Astrophysical Journal, 2013Co-Authors: Y Fukui, Akio Ohama, Naoki Hanaoka, N Furukawa, K Torii, J R Dawson, Norikazu Mizuno, K Hasegawa, T FukudaAbstract:We present new large field observations of molecular clouds with NANTEN2 toward the super Star Cluster NGC 3603 in the transitions {sup 12}CO(J = 2-1, J = 1-0) and {sup 13}CO(J = 2-1, J = 1-0). We suggest that two molecular clouds at 13 km s{sup –1} and 28 km s{sup –1} are associated with NGC 3603 as evidenced by higher temperatures toward the H II region, as well as morphological correspondence. The mass of the clouds is too small to gravitationally bind them, given their relative motion of ∼20 km s{sup –1}. We suggest that the two clouds collided with each other 1 Myr ago to trigger the formation of the super Star Cluster. This scenario is able to explain the origin of the highest mass stellar population in the Cluster, which is as young as 1 Myr and is segregated within the central sub-pc of the Cluster. This is the second super Star Cluster along with Westerlund 2 where formation may have been triggered by a cloud-cloud collision.
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molecular clouds toward the super Star Cluster ngc3603 possible evidence for a cloud cloud collision in triggering the Cluster formation
arXiv: Astrophysics of Galaxies, 2013Co-Authors: Y Fukui, Akio Ohama, Naoki Hanaoka, N Furukawa, K Torii, J R Dawson, Norikazu Mizuno, K Hasegawa, T Fukuda, Sho SogaAbstract:We present new large field observations of molecular clouds with NANTEN2 toward the super Star Cluster NGC3603 in the transitions 12CO(J=2-1, J=1-0) and 13CO(J=2-1, J=1-0). We suggest that two molecular clouds at 13 km s-1 and 28 km s-1 are associated with NGC3603 as evidenced by higher temperatures toward the H II region as well as morphological correspondence. The mass of the clouds is too small to gravitationally bind them, given their relative motion of ~20 km s-1. We suggest that the two clouds collided with each other a Myr ago to trigger the formation of the super Star Cluster. This scenario is able to explain the origin of the highest mass stellar population in the Cluster which is as young as a Myr and is segregated within the central sub-pc of the Cluster. This is the second super Star Cluster along side Westerlund2 where formation may have been triggered by a cloud-cloud collision.
Mark Morris - One of the best experts on this subject based on the ideXlab platform.
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an ultradeep chandra catalog of x ray point sources in the galactic center Star Cluster
Astrophysical Journal Supplement Series, 2018Co-Authors: Zhiyuan Li, Mark MorrisAbstract:We present an updated catalog of X-ray point sources in the inner 500$\arcsec$ ($\sim$20 parsec) of the Galactic Center (GC), where the {\it nuclear Star Cluster} (NSC) stands, based on a total of $\sim$4.5 Ms of {\it Chandra} observations taken from September 1999 to April 2013. This ultra-deep dataset offers unprecedented sensitivity for detecting X-ray sources in the GC, down to an intrinsic 2--10 keV luminosity of $1.0\times10^{31}{\rm~erg~s^{-1}}$. A total of 3619 sources are detected in the 2--8 keV band, among which $\sim$3500 are probable GC sources and $\sim$1300 are new identifications. The GC sources collectively account for $\sim$20\% of the total 2--8 keV flux from the inner 250$\arcsec$ region where detection sensitivity is the greatest. Taking advantage of this unprecedented sample of faint X-ray sources that primarily traces the old stellar populations in the NSC, we revisit global source properties, including long-term variability, cumulative spectra, luminosity function and spatial distribution. Based on the equivalent width and relative strength of the iron lines, we suggest that in addition to the arguably predominant population of magnetic cataclysmic variables (CVs), non-magnetic CVs contribute substantially to the detected sources, especially in the lower-luminosity group. On the other hand, the X-ray sources have a radial distribution closely following the stellar mass distribution in the NSC, but much flatter than that of the known X-ray transients, which are presumably low-mass X-ray binaries (LMXBs) caught in outburst. This, together with the very modest long-term variability of the detected sources, strongly suggests that quiescent LMXBs are a minor ($\lesssim$ a few percent) population.
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super solar metallicity Stars in the galactic center nuclear Star Cluster unusual sc v and y abundances
The Astrophysical Journal, 2018Co-Authors: Tuan Do, Andrea M. Ghez, Jessica R Lu, Wolfgang Kerzendorf, Quinn Konopacky, Joseph M Marcinik, Mark MorrisAbstract:We present adaptive-optics assisted near-infrared high-spectral resolution observations of late-type giants in the nuclear Star Cluster of the Milky Way. The metallicity and elemental abundance measurements of these Stars offer us an opportunity to understand the formation and evolution of the nuclear Star Cluster. In addition, their proximity to the supermassive black hole ($\sim 0.5$ pc) offers a unique probe of the Star formation and chemical enrichment in this extreme environment. We observed two Stars identified by medium spectral-resolution observations as potentially having very high metallicities. We use spectral-template fitting with the PHOENIX grid and Bayesian inference to simultaneously constrain the overall metallicity, [M/H], alpha-element abundance [$\alpha$/Fe], effective temperature, and surface gravity of these Stars. We find that one of the Stars has very high metallicity ([M/H] $> 0.6$) and the other is slightly above solar metallicity. Both Galactic center Stars have lines from scandium (Sc), vanadium (V), and yttrium (Y) that are much stronger than allowed by the PHOENIX grid. We find, using the spectral synthesis code Spectroscopy Made Easy, that [Sc/Fe] may be an order of magnitude above solar. For comparison, we also observed an empirical calibrator in NGC6791, the highest metallicity Cluster known ([M/H] $\sim 0.4$). Most lines are well matched between the calibrator and the Galactic center Stars, except for Sc, V, and Y, which confirms that their abundances must be anomalously high in these Stars. These unusual abundances, which may be a unique signature of nuclear Star Clusters, offer an opportunity to test models of chemical enrichment in this region.
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Measuring the stellar luminosity function and spatial density profile of the inner 0.5 pc of the Milky Way nuclear Star Cluster
Journal of Physics: Conference Series, 2012Co-Authors: Tuan Do, Sylvana Yelda, Shelley A. Wright, Andrea M. Ghez, Jessica R Lu, James S Bullock, Annika H G Peter, Mark Morris, G Martinez, Manoj KaplinghatAbstract:We report on measurements of the luminosity function of early (young) and late-type (old) Stars in the central 0.5 pc of the Milky Way nuclear Star Cluster as well as the density profiles of both components. The young (~ 6 Myr) and old Stars (> 1 Gyr) in this region provide different physical probes of the environment around a supermassive black hole; the luminosity function of the young Stars offers us a way to measure the initial mass function from Star formation in an extreme environment, while the density profile of the old Stars offers us a probe of the dynamical interaction of a Star Cluster with a massive black hole. The two stellar populations are separated through a near-infrared spectroscopic survey using the integral-field spectrograph OSIRIS on Keck II behind the laser guide Star adaptive optics system. This spectroscopic survey is able to separate early-type (young) and late-type (old) Stars with a completeness of 50% at K' = 15.5. We describe our method of completeness correction using a combination of Star planting simulations and Bayesian inference. The completeness corrected luminosity function of the early-type Stars contains significantly more young Stars at faint magnitudes compared to previous surveys with similar depth. In addition, by using proper motion and radial velocity measurements along with anisotropic spherical Jeans modeling of the Cluster, it is possible to measure the spatial density profile of the old Stars, which has been difficult to constrain with number counts alone. The most probable model shows that the spatial density profile, n(r) ∝ r−γ, to be shallow with γ = 0.4 ± 0.2, which is much flatter than the dynamically relaxed case of γ = 3/2 to 7/4, but does rule out a 'hole' in the distribution of old Stars. We show, for the first time, that the spatial density profile, the black hole mass, and velocity anisotropy can be fit simultaneously to obtain a black hole mass that is consistent with that derived from individual orbits of Stars at distances < 1000 AU from the Galactic center.
Konstantin V Getman - One of the best experts on this subject based on the ideXlab platform.
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a chandra acis study of the young Star Cluster trumpler 15 in carina and correlation with near infrared sources
Astrophysical Journal Supplement Series, 2011Co-Authors: Junfeng Wang, P S Broos, Eric D Feigelson, Konstantin V Getman, S J Wolk, Thomas Preibisch, Keivan G Stassun, Leisa K. Townsley, Anthony F J MoffatAbstract:Using the highest-resolution X-ray observation of the Trumpler 15 Star Cluster taken by the Chandra X-ray Observatory, we estimate the total size of its stellar population by comparing the X-ray luminosity function (XLF) of the detected sources to a calibrator Cluster and identify for the first time a significant fraction (~14%) of its individual members. The highest-resolution near-IR observation of Trumpler 15 (taken by the HAWK-I instrument on the Very Large Telescope) was found to detect most of our X-ray selected sample of Cluster members, with a K-excess disk frequency of 3.8% ± 0.7%. The near-IR data, XLF, and published spectral types of the brightest members support a Cluster age estimate (5-10 Myr) that is older than those for the nearby Trumpler 14 and Trumpler 16 Clusters, and suggest that high-mass members may have already exploded as supernovae. The morphology of the inner ~0.7 pc core of the Cluster is found to be spherical. However, the outer regions (beyond ~2 pc) are elongated, forming an "envelope" of Stars that, in projection, appears to connect Trumpler 15 to Trumpler 14; this morphology supports the view that these Clusters are physically associated. Clear evidence of mass segregation is seen. This study appears in this special issue devoted to the Chandra Carina Complex Project, a 1.42 deg2 Chandra X-ray survey of the Great Nebula in Carina.
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a chandra acis study of the young Star Cluster trumpler 15 in carina and correlation with near infrared sources
arXiv: Solar and Stellar Astrophysics, 2011Co-Authors: Junfeng Wang, P S Broos, Eric D Feigelson, Konstantin V Getman, S J Wolk, Thomas Preibisch, Keivan G Stassun, Leisa K. Townsley, Anthony F J MoffatAbstract:Using the highest-resolution X-ray observation of the Trumpler 15 Star Cluster taken by the Chandra X-ray Observatory, we estimate the total size of its stellar population by comparing the X-ray luminosity function of the detected sources to a calibrator Cluster, and identify for the first time a significant fraction (~14%) of its individual members. The highest-resolution near-IR observation of Trumpler 15 (taken by the HAWK-I instrument on the VLT) was found to detect most of our X-ray selected sample of Cluster members, with a K-excess disk frequency of 3.8+-0.7%. The near-IR data, X-ray luminosity function, and published spectral types of the brightest members support a Cluster age estimate (5-10 Myr) that is older than those for the nearby Trumpler 14 and Trumpler 16 Clusters, and suggest that high-mass members may have already exploded as supernovae. The morphology of the inner ~0.7 pc core of the Cluster is found to be spherical. However, the outer regions (beyond 2 pc) are elongated, forming an `envelope' of Stars that, in projection, appears to connect Trumpler 15 to Trumpler 14; this morphology supports the view that these Clusters are physically associated. Clear evidence of mass segregation is seen. This study appears in a Special Issue of the ApJS devoted to the Chandra Carina Complex Project (CCCP), a 1.42 square degree Chandra X-ray survey of the Great Nebula in Carina.
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a chandra acis study of 30 doradus ii x ray point sources in the massive Star Cluster r136 and beyond
The Astronomical Journal, 2006Co-Authors: Leisa K. Townsley, P S Broos, Eric D Feigelson, G P Garmire, Konstantin V GetmanAbstract:We have studied the X-ray point-source population of the 30?Doradus (30 Dor) Star-forming complex in the Large Magellanic Cloud using high spatial resolution X-ray images and spatially resolved spectra obtained with the Advanced CCD Imaging Spectrometer (ACIS) on board the Chandra X-Ray Observatory. Here we describe the X-ray sources in a 17' ? 17' field centered on R136, the massive Star Cluster at the center of the main 30?Dor nebula. We detect 20 of the 32 Wolf-Rayet Stars in the ACIS field. The Cluster R136 is resolved at the subarcsecond level into almost 100 X-ray sources, including many typical O3-O5 Stars, as well as a few bright X-ray sources previously reported. Over 2 orders of magnitude of scatter in LX is seen among R136 O Stars, suggesting that X-ray emission in the most massive Stars depends critically on the details of wind properties and the binarity of each system, rather than reflecting the widely reported characteristic value LX/Lbol 10-7. Such a canonical ratio may exist for single massive Stars in R136, but our data are too shallow to confirm this relationship. Through this and future X-ray studies of 30?Dor, the complete life cycle of a massive stellar Cluster can be revealed.
