The Mass Distribution of the Milky Way Deduced from Globular Cluster Dynamics

Dauphole, B.; Colin, J.; Geffert, M.; Odenkirchen, M.; Tucholke, H. J.

doi:10.1007/978-94-009-1687-6_115

Cited by 21 publications

(35 citation statements)

References 4 publications

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“…In fact, the space motion parameters used by the authors above for NGC 6218 are not consistent with the latest determination of its absolute proper motion based on the Hipparcos reference system. The proper motion measured by Brosche et al (1991), combined with the radial velocity measurements of Pryor & Meylan (1993), allowed Dauphole et al (1996) to put some constraints on the space motion parameters of this cluster. Their findings were confirmed by an independent analysis of the orbit, based on improved absolute proper motions (Scholz et al 1996), which indicated that NGC 6218 should have a short orbital period (0.17 Gyr) but also that it never ventures closer than ∼3 kpc from the Galactic centre, with less than 15% of its orbit lying within 1 kpc of the Galactic plane.…”

Section: Discussionmentioning

confidence: 99%

“…This has been made possible by an in-depth analysis of the mechanisms responsible for cluster disruption (Aguilar et al 1988;Gnedin & Ostriker 1997) and by the availability of more accurate space motion parameters for the clusters (Dauphole et al 1996;Odenkirchen et al 1997). Models that make use of GC proper motion information (Dinescu et al 1999;Baumgardt & Makino 2003) should, in principle, provide a more reliable description of the clusters' past dynamical history than those purely based on radial velocity data (Gnedin & Ostriker 1997).…”

Section: Introductionmentioning

confidence: 99%

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Why is the mass function of NGC 6218 flat?

Marchi¹,

Pulone²,

Paresce³

2006

A&A

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We have used the FORS-1 camera on the VLT to study the main sequence (MS) of the globular cluster NGC 6218 in the V and R bands. The observations cover an area of 3. 4 × 3. 4 around the cluster centre and probe the stellar population out to the cluster's half-mass radius (r h 2. 2). The colour-magnitude diagram (CMD) that we derive in this way reveals a narrow and well defined MS extending down to the 5 σ detection limit at V 25, or about 6 magnitudes below the turn-off, corresponding to stars of ∼0.25 M . The luminosity function (LF) obtained with these data shows a marked radial gradient, in that the ratio of lower-and higher-mass stars increases monotonically with radius. The mass function (MF) measured at the half-mass radius, and as such representative of the cluster's global properties, is surprisingly flat. Over the range 0.4−0.8 M , the number of stars per unit mass follows a power-law distribution of the type dN/dm ∝ m 0 , where, for comparison, Salpeter's IMF would be dN/dm ∝ m −2.35 . We expect that such a flat MF does not represent the cluster's IMF but is the result of severe tidal stripping of the stars from the cluster due to its interaction with the Galaxy's gravitational field. Our results cannot be reconciled with the predictions of recent theoretical models that imply a relatively insignificant loss of stars from NGC 6218 as measured by its expected very long time to disruption. They are more consistent with the orbital parameters based on the Hipparcos reference system that imply a much higher degree of interaction of this cluster with the Galaxy than assumed by those models. Our results indicate that, if the orbit of a cluster is known, the slope of its MF could be useful in discriminating between the various models of the Galactic potential.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Why is the mass function of NGC 6218 flat?

Marchi¹,

Pulone²,

Paresce³

2006

A&A

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“…Although the inclination of the cluster's orbit determines the rate at which the MF exponent decreases, all orbits with perigalacticon within a few kpc of the Galactic centre are exposed to this erosion. For clusters such as NGC 6712, whose orbit is mostly contained within the disk (Dauphole et al 1996), the heating due to disk and bulge shocking is diluted over a long time, comparable with the dynamical relaxation time of the cluster itself 1 . It is, thus, not unreasonable that two-body relaxation can proceed almost undisturbed, and it does so on a continuously varying mass spectrum.…”

Section: Discussionmentioning

confidence: 99%

“…With a perigalactic distance smaller than 300 pc, this cluster ventures so frequently and so deeply into the Galactic bulge (Dauphole et al 1996) that it is likely to have undergone severe tidal shocking during the numerous encounters with both the disk and the bulge during its life-time. The latest Galactic plane crossing could have happened as recently as 4 × 10 6 year ago (Cudworth 1988), which is much smaller than its half-mass relaxation time of 1 Gyr (Harris 1996).…”

Section: Introductionmentioning

confidence: 99%

VLT observations of the peculiar globular cluster NGC 6712

Andreuzzi

Marchi

Ferraro

et al. 2001

A&A

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Abstract.We have carried out extensive VLT-FORS1 observations covering a fair fraction of the intermediate metallicity globular cluster NGC 6712 in the V and R bands. We derive accurate colour-magnitude diagrammes (CMD) and luminosity functions (LFs) of the cluster main sequence (MS) for four overlapping fields extending from the centre of the cluster out to a radius of ∼10 , well beyond the nominal tidal radius, and for a control field at ∼42 distance. The LFs extend from the cluster turn-off (TO) at MR 4 to the point at which the incompleteness drops below 50% (corresponding to R 23 or MR 7.5) for most fields studied. Cluster stars become indistinguishable from field stars at r 5 . The shape of the cluster's LF and its variation with distance from the centre in these ranges are well described by a standard multi-mass static model having the following parameters: core radius rc = 1 , half-light radius r hl = 1. 8, tidal radius rt = 5. 2, concentration ratio c = 0.7, and a power-law global mass function (MF) with index α 0.9 for masses smaller than 0.8 M , i.e. for all detected MS stars, and α −2.35 for evolved objects. The MF obtained in this way is consistent with that found in a preliminary investigation of this cluster with the VLT Test Camera and confirms that this is the only globular cluster known so far for which the global MF drops with decreasing mass below the TO. Possible reasons for this unique characteristic are discussed with the most likely associated with its extreme vulnerability to tidal disruption.

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“…Thus suggesting that the clumping in the radial gradient might be associated to azimuthal variations across the body of the cluster. It is worth noting that the main over-density of bMS stars is pointing towards the Galactic center (GC) (Dauphole et al 1996;Leon et al 2000, see the arrows plotted in the left panel of Fig. 14).…”

Section: Star Counts Across the Body Of The Clustermentioning

confidence: 99%

The Not So Simple Globular Cluster ω Cen. I. Spatial Distribution of the Multiple Stellar Populations^∗

Calamida

Rest

Bono

et al. 2017

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We present a multi-band photometric catalog of ≈ 1.7 million cluster members for a field of view of ≈ 2×2• across ω Cen. Photometry is based on images collected with the Dark Energy Camera on the 4m Blanco telescope and the Advanced Camera for Surveys on the Hubble Space Telescope. The unprecedented photometric accuracy and field coverage allowed us for the first time to investigate the spatial distribution of ω Cen multiple populations from the core to the tidal radius, confirming its very complex structure. We found that the frequency of blue main-sequence stars is increasing compared to red main-sequence stars starting from a distance of ≈ 25' from the cluster center. Blue main-sequence stars also show a clumpy spatial distribution, with an excess in the North-East quadrant of the cluster pointing towards the direction of the Galactic center. Stars belonging to the reddest and faintest redgiant branch also show a more extended spatial distribution in the outskirts of ω Cen, a region never explored before. Both these stellar sub-populations, according to spectroscopic measurements, are more metal-rich compared to the cluster main stellar population. These findings, once confirmed, make ω Cen the only stellar system currently known where metal-rich stars have a more extended spatial distribution compared to metal-poor stars. Kinematic and chemical abundance measurements are now needed for stars in the external regions of ω Cen to better characterize the properties of these sub-populations.

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The Mass Distribution of the Milky Way Deduced from Globular Cluster Dynamics

Cited by 21 publications

References 4 publications

Why is the mass function of NGC 6218 flat?

Why is the mass function of NGC 6218 flat?

VLT observations of the peculiar globular cluster NGC 6712

The Not So Simple Globular Cluster ω Cen. I. Spatial Distribution of the Multiple Stellar Populations^∗

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The Mass Distribution of the Milky Way Deduced from Globular Cluster Dynamics

Cited by 21 publications

References 4 publications

Why is the mass function of NGC 6218 flat?

Why is the mass function of NGC 6218 flat?

VLT observations of the peculiar globular cluster NGC 6712

The Not So Simple Globular Cluster ω Cen. I. Spatial Distribution of the Multiple Stellar Populations∗

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Product

Resources

About

The Not So Simple Globular Cluster ω Cen. I. Spatial Distribution of the Multiple Stellar Populations^∗