The Arches Cluster Mass Function

Kim, Sungsoo S.; Figer, Donald F.; Kudritzki, R. P.; Najarro, F.

doi:10.1086/510529

Cited by 108 publications

(169 citation statements)

References 18 publications

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“…>200 d & >40 d for 30 Dor and R136 proper; Schnurr et al 2008aSchnurr et al , 2009b) and the additional X-ray selected candidates. This is consistent with other surveys which find similarly high percentages for OB and Wolf-Rayet stars, albeit for different samples of stars comprising either lower (Clark et al 2008;Ritchie et al 2009) or a wider range of masses (Kobulnicky & Fryer 2007;Sana et al 2008;Bosch et al 2009). Such a binary fraction potentially presents important constraints on the formation mechanisms for very massive stars such as CXO J1745-28 and the Arches population.…”

Section: Discussion and Concluding Remarkssupporting

confidence: 92%

“…Spitzer IRAC photometry is not available, although the theoretical model suggests (Reid 1993). These correspond to absolute F205W magnitudes of -6.4 to -7.2 mag for a uniform K-band extinction of A K s = 3.1 mag (Kim et al 2006) and (identical) distance of 8 kpc. As such, one would expect that CXO J1745-28 to be amongst the most luminous of the WN9h stars in the Galactic Centre region.…”

Section: Irtf/spex Spectroscopymentioning

confidence: 93%

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The binary nature of the Galactic centre X-ray source CXOGC J174536.1-285638

Clark

Crowther

Mikles

2009

A&A

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Context. The combination of X-ray and near-IR surveys of the central 2 o × 0.8 o of the Galactic centre have revealed a population of X-ray bright massive stars. However, the nature of the X-ray emission, originating in wind collision zones or via accretion onto compact objects, is uncertain. Aims. In order to address this we investigated the nature of one of the most luminous X-ray sources − CXOGC J174536.1-285638. Methods. This was accomplished by an analysis of the near-IR spectrum with a non-LTE model atmosphere code to determine the physical parameters of the primary.Results. This was found to be an highly luminous WN9h star, which is remarkably similar to the most massive stars found in the Arches cluster, for which comparison to evolutionary tracks suggest an age of 2-2.5 Myr and an initial mass of ∼110 M . The X-ray properties of CXOGC J174536.1-285638 also resemble those of 3 of the 4 X-ray detected WN9h stars within the Arches and in turn other very massive WNLh colliding wind binaries, of which WR25 forms an almost identical "twin". Simple analytical arguments demonstrate consistency between the X-ray emission and a putative WN9h+mid O V-III binary, causing us to favour such a scenario over an accreting binary. However, we may not exclude a high mass X-ray binary interpretation, which, if correct, would provide a unique insight into the (post-SN) evolution of extremely massive stars. Irrespective of the nature of the secondary, CXOGC J174536.1-285638 adds to the growing list of known and candidate WNLh binaries. Of the subset of WNLh stars subject to a radial velocity survey, we find a lower limit to the binary fraction of ∼45%; of interest for studies of massive stellar formation, given that they currently possess the highest dynamically determined masses of any type of star.

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Section: Discussion and Concluding Remarkssupporting

confidence: 92%

Section: Irtf/spex Spectroscopymentioning

confidence: 93%

The binary nature of the Galactic centre X-ray source CXOGC J174536.1-285638

Clark

Crowther

Mikles

2009

A&A

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“…While they basically confirmed the strong flattening of the slope in the central regions, they also found evidence of a sharp turnover in the mass function around 6−7 M that they interpreted as a low-mass truncation in the cluster IMF. A new investigation of Arches by Kim et al (2006b) using the AO camera of the Keck telescope confirmed a flatter slope and revealed the ∼6 M feature as a local maximum in the cluster mass function. With appropiate parameters as input, this bump was also reproduced later by the coalescence-collapse model of Dib et al (2007).…”

Section: Introductionmentioning

confidence: 92%

“…Although previous investigations have noted these large star-to-star extinction variations towards the Arches, they have chosen to apply an average extinction correction (Kim et al 2006b), or to subtract a radial term for radii >0.2 pc, assuming the reddening in the cluster core to be uniform (SGB02; SBG05). Our data show that the radial trend results from the area of high extinction located SW of the cluster center.…”

Section: Magnitude Limit Effectmentioning

confidence: 99%

The massive star initial mass function of the Arches cluster

Espinoza

Selman

Melnick

2009

A&A

149

228

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The massive Arches cluster near the Galactic center should be an ideal laboratory for investigating massive star formation under extreme conditions. But it comes at a high price: the cluster is hidden behind several tens of magnitudes of visual extinction. Severe crowding requires space or AO-assisted instruments to resolve the stellar populations, and even with the best instruments interpreting the data is far from direct. Several investigations using NICMOS and the most advanced AO imagers on the ground revealed an overall top-heavy IMF for the cluster, with a very flat IMF near the center. There are several effects, however, that could potentially bias these results, in particular the strong differential extinction and the problem of transforming the observations into a standard photometric system in the presence of strong reddening. We present new observations obtained with the NAOS-Conica (NACO) AO-imager on the VLT. The problem of photometric transformation is avoided by working in the natural photometric system of NACO, and we use a Bayesian approach to determine masses and reddenings from the broad-band IR colors. A global value of Γ = −1.1 ± 0.2 for the high-mass end (M > 10 M ) of the IMF is obtained, and we conclude that a power law of Salpeter slope cannot be discarded for the Arches cluster. The flattening of the IMF towards the center is confirmed, but is less severe than previously thought. We find Γ = −0.88 ± 0.20, which is incompatible with previous determinations. Within 0.4 pc we derive a total mass of ∼2.0(±0.6) × 10 4 M for the cluster and a central mass density ρ = 2(±0.4) × 10 5 M pc −3 that confirms Arches as the densest known young massive cluster in the Milky Way.

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“…Observations of the Arches cluster initially showed a shallow IMF (Figer et al 1999;Stolte et al 2002) and a turnover mass, hence a typical mass, at a few solar masses (6−7 M , Stolte et al 2005). However, Kim et al (2006) do detect low-mass stars with their deep photometry and merely find a local bump at ∼6.3 M and a somewhat shallower IMF (Γ = −1.0 to −1.1). Dib et al (2007) confirm these results and claim a top-heavy IMF.…”

Section: Introductionmentioning

confidence: 99%

The thermodynamics of molecular cloud fragmentation

Hocuk

Spaans

2010

A&A

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Context. Properties of candidate stars, forming out of molecular clouds, depend on the ambient conditions of the parent cloud. We present a series of 2D and 3D simulations of fragmentation of molecular clouds in starburst regions, as well as of clouds under conditions in dwarf galaxies, leading to the formation of protostellar cores. Aims. We explore in particular the metallicity dependence of molecular cloud fragmentation and the possible variations in the dense core mass function, as the expression of a multi-phase ISM, due to dynamic and thermodynamic effects in starburst and metal-poor environments. Methods.The adaptive mesh refinement code FLASH is used to study the level of fragmentation during the collapse. With this code, including self-gravity, thermal balance, turbulence, and shocks, collapse is simulated with four different metallicity-dependent cooling functions. Turbulent and rotational energies are considered as well. During the simulations, number densities of 10 8 −10 9 cm −3 are reached. The influences of dust and cosmic ray heating are investigated and compared to isothermal cases. Results. The results indicate that fragmentation increases with metallicity, while cosmic ray and gas-grain collisional heating counteract this. We also find that modest rotation and turbulence can affect the cloud evolution as far as fragmentation is concerned. In this light, we conclude that radiative feedback in starburst regions will inhibit fragmentation, while low-metallicity dwarfs should also enjoy a star formation mode in which fragmentation is suppressed.

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The Arches Cluster Mass Function

Cited by 108 publications

References 18 publications

The binary nature of the Galactic centre X-ray source CXOGC J174536.1-285638

The binary nature of the Galactic centre X-ray source CXOGC J174536.1-285638

The massive star initial mass function of the Arches cluster

The thermodynamics of molecular cloud fragmentation

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