The Metallicity Dependence of the Stellar Luminosity and Initial Mass Function: HST Observations of Open and Globular Clusters

Hippel, Ted von; Gilmore, G.; Tanvir, N. R.; Robinson, D. K.; Jones, D. H. P.

doi:10.1086/118000

Cited by 38 publications

(37 citation statements)

References 27 publications

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“…We note that von Hippel et al (1996), based on deep V and I HST and WFPC2 photometry of the central parts of NGC 2477, described a break in the MF, but occurring at a lower mass value, m ≈ 0.27 M (Sect. 5).…”

Section: Mass Functionsmentioning

confidence: 85%

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Detailed analysis of open clusters: A mass function break and evidence of a fundamental plane

Bonatto¹,

Bica²

2005

A&A

122

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Abstract. We derive photometric, structural and dynamical evolution-related parameters of 11 nearby open clusters with ages in the range 70 Myr to 7 Gyr and masses in the range ≈400 M to ≈5300 M . The clusters are homogeneously analysed by means of J, H and K S 2MASS photometry, which provides spatial coverage wide enough to properly take into account the contamination of the cluster field by Galaxy stars. Structural parameters such as core and limiting radii are derived from the background-subtracted radial density profiles. Luminosity and mass functions (MFs) are built for stars later than the turnoff and brighter than the 2MASS PSC 99.9% completeness limit. The total mass locked up in stars in the core and the whole cluster, as well as the corresponding mass densities, are calculated by taking into account the observed stars (evolved and main sequence) and extrapolating the MFs down to the H-burning mass limit, 0.08 M . We illustrate the methods by analysing for the first time in the near-infrared the populous open clusters NGC 2477 and NGC 2516. For NGC 2477 we derive an age of 1.1 ± 0.1 Gyr, distance from the Sun d = 1.2 ± 0.1 kpc, core radius R core = 1.4 ± 0.1 pc, limiting radius R lim = 11.6 ± 0.7 pc and total mass m tot ≈ (5.3 ± 1.6) × 10 3 M . Large-scale mass segregation in NGC 2477 is reflected in the significant variation of the MF slopes in different spatial regions of the cluster, and in the large number-density of giant stars in the core with respect to the cluster as a whole. For NGC 2516 we derive an age of 160 ± 10 Myr, d = 0.44 ± 0.02 kpc, R core = 0.6 ± 0.1 pc, R lim = 6.2 ± 0.2 pc and m tot ≈ (1.3 ± 0.2) × 10 3 M . Mass-segregation in NGC 2516 shows up in the MFs. Six of the 11 clusters present a slope break in the MF occurring at essentially the same mass as that found for the field stars in Kroupa's universal IMF. The MF break is not associated to cluster mass, at least in the clusters in this paper. In two clusters the low-mass end of the MF occurs above the MF break. However, in three clusters the MF break does not occur, at least for the mass range m ≥ 0.7 M . One possibility is dynamical evolution affecting the MF slope distribution. We also search for relations of structural and evolutionary parameters with age and Galactocentric distance. The main results for the present sample are: (i) cluster size correlates both with age and Galactocentric distance; (ii) because of size and mass scaling, core and limiting radii, and core and overall mass correlate; (iii) massive (m ≥ 1000 M ) and less-massive clusters follow separate correlation paths on the plane core radius and overall mass; (iv) MF slopes of massive clusters are restricted to a narrow range, while those of the less-massive ones distribute over a wider range. Core and overall MF flattening is related to the ratio (τ) of age to relaxation time. For large values of τ the effects of large-scale mass segregation and low-mass stars evaporation can be observed in the MFs. In this sense, τ appears to characterize the evolutionary stat...

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Section: Mass Functionsmentioning

confidence: 85%

“…They also estimate that the total mass locked up in stars more massive than ≈1 M must be larger than 5400 M . A break in the mass function in the lower main sequence at m ≈ 0.27 M was suggested by von Hippel et al (1996). Nilakshi et al (2002) derived R core ≈ 2.2 pc and R lim ≈ 9.1 pc.…”

Section: Webdamentioning

confidence: 87%

Detailed analysis of open clusters: A mass function break and evidence of a fundamental plane

Bonatto¹,

Bica²

2005

A&A

122

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“…Accurate knowledge of the compositions of metal-poor VLM subdwarf M (hereafter sdM) stars and their positions in the Hertzprung-Russell diagram is essential to a full understanding of the chemical history of our Galaxy. The reconstruction of the initial mass function in the old disk, halo, and globular clusters-founded on an accurate mass-luminosity relation that is a sensitive function of the stellar chemical composition (Chabrier et al 1996a, D'Antona & Mazzitelli 1996, von Hippel et al 1996-also depends upon it.…”

Section: The Metal-deficient Vlm Starsmentioning

confidence: 99%

Model Atmospheres of Very Low Mass Stars and Brown Dwarfs

Allard

Hauschildt

Alexander

et al. 1997

Annu. Rev. Astron. Astrophys.

353

343

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As progressively cooler stellar and substellar objects are discovered, the presence first of molecules and then of condensed particulates greatly complicates the understanding of their physical properties. Accurate model atmospheres that include these processes are the key to establishing their atmospheric parameters. They play a crucial role in determining structural characteristics by setting the surface conditions of model interiors and providing transformations to the various observational planes. They can reveal the spectroscopic properties of brown dwarfs and help establish their detectability. In this paper, we review the current state-of-the-art theory and modeling of the atmospheres of very low mass stars, including the coolest known M dwarfs, M subdwarfs, and brown dwarfs, i.e. T eff ≤ 4,000 K and −4.0 ≤ [M/H] ≤ +0.0. We discuss ongoing efforts to incorporate molecular and grain opacities in cool stellar spectra, as well as the latest progress in (a) deriving the effective temperature scale of M dwarfs, (b) reproducing the lower main sequences of metal-poor subdwarfs in the halo and globular clusters, and (c) results of the models related to the search for brown dwarfs.

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“…We have assumed that the change in magnitude between disk and spheroid is and the corresponding change *M v \ 2.5, in metallicity is *Z \ 1.5. Following the Ðndings of von Hippel et al (1996), we assume that the luminosity function for the range we are interested in is independent of metallicity.…”

Section: The Effect Of Color Gradientsmentioning

confidence: 99%

Star Counts and the Warped and Flaring Milky Way Disk

Gyuk¹,

Flynn²,

Evans³

1999

ApJ

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This paper reports the star count predictions of warped and Ñaring models of the outer Milky Way disk. These have been suggested as possible locations of the lenses responsible for the microlensing events toward the Large Magellanic Cloud (LMC). Three such models are investigated in detail, and the theoretical predictions are confronted with Hubble Space T elescope star count data in seven low-latitude Ðelds (30¡ \ o b o \ 40¡). If the warped and Ñaring disk population has the same characteristics as disk stars in the solar neighborhood, then the models can be unambiguously ruled out. Metallicity gradients are well known in disk galaxies and may cause the outer disk population to di †er in colors and luminosity from the local population. This e †ect is studied using a simple Ansatz for the variation in the color-magnitude relation with position, and while it is shown to lead to better agreement with the star counts, upper limits on the contribution of the warped and Ñaring disk to the optical depth are still below the value measured toward the LMC. Only if the warp is very asymmetric or if the luminosity function changes strongly with Galactocentric radius can the models be made consistent with the star counts.

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The Metallicity Dependence of the Stellar Luminosity and Initial Mass Function: HST Observations of Open and Globular Clusters

Cited by 38 publications

References 27 publications

Detailed analysis of open clusters: A mass function break and evidence of a fundamental plane

Detailed analysis of open clusters: A mass function break and evidence of a fundamental plane

Model Atmospheres of Very Low Mass Stars and Brown Dwarfs

Star Counts and the Warped and Flaring Milky Way Disk

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