Instantaneous and average tidal radii of globular clusters

Brosche, P.; Odenkirchen, M.; Geffert, M.

doi:10.1016/s1384-1076(99)00014-7

Cited by 16 publications

(38 citation statements)

References 17 publications

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“…It is found that a stability region exists for both the global and the local criterion and, in addition, the instability first occurs at the perigalacticon, as expected in connection with instantaneous tidal radius. A powerlaw dependence of tidal radius from cluster mass and galactocentric distance, a *0 , is shown to be consistent with data from a sample of 16 objects investigated by Brosche et al (1999). No significant correlation is found between the ratio of cluster radius to tidal radius and the orbital ratio of apogalacticon to perigalacticon, similar to averaged tidal radii defined by Brosche et al (1999).…”

supporting

confidence: 75%

A global and a local criterion in defining the tidal radius

Caimmi

Secco

2003

Astron Nachr

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The basic theory of potential-energy tensors related to heterogeneous spheres is reviewed, and the special case of truncated, singular, isothermal spheres is examined in detail. Special effort is devoted to a system made of two isothermal spheres, one completely lying within the other, the mass and the radius of the embedded sphere being negligible with respect to the mass and radius of the embedding sphere, and the radius of the embedded sphere being negligible with respect to the distance between the centres. The potential-energy tensors related to the potential induced by the embedding sphere on the mass distribution of the embedded sphere, are expressed as the sum of two contributions: one, coming from the embedded sphere after collapse towards its centre, and one other, related to the actual mass distribution of the embedded sphere. Using the latter, both a global and a local criterion in defining the tidal radius of the embedded sphere, are formulated in connection with either the binding-energy tensor or the virial-energy tensor. In doing this, the tensor components along the axis joining the centre of the embedding and the embedded sphere, are considered. The global criterion is related to the whole, embedded sphere, while the local criterion is related to an infinitesimal mass element placed at the boundary of the embedded sphere, where the distance from the centre of the embedding sphere attains a maximum. The virial theorem in tensor form is splitted into two distinct expressions, related to orbital and intrinsic motions of the embedded sphere. Alternative criterions in defining the tidal radius of the embedded sphere, are formulated taking into consideration the centrifugal tensor potential and the tensor potential induced by orbital motions. With regard to a selected criterion, the tidal radius calculated with and without the inclusion of the centrifugal potential, exhibits a maximum variation by a factor of about two, related to circular orbits. An application is made, where the embedding and the embedded sphere are taken as representative of the Galaxy and a globular cluster, respectively. It is found that a stability region exists for both the global and the local criterion and, in addition, the instability first occurs at the perigalacticon, as expected in connection with instantaneous tidal radius. A power-law dependence of tidal radius from cluster mass and galactocentric distance, aC* ∝ MC1/3R02/3, is shown to be consistent with data from a sample of 16 objects investigated by te{bra99} (1999). No significant correlation is found between the ratio of cluster radius to tidal radius and the orbital ratio of apogalacticon to perigalacticon, similar to averaged tidal radii defined by te{bra99} (1999). An additional object, Pal 5, which is experiencing progressive disruption via tidal shocks during disk passages, is shown to be among the less bound (or more unbound) clusters, within the framework of the model. If the representation of globular clusters as isothermal spheres introduces only systemat...

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supporting

confidence: 75%

A global and a local criterion in defining the tidal radius

Caimmi

Secco

2003

Astron Nachr

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“…The correct formula to use for the purpose of comparing the theoretical tidal radii with the observed limiting radii is a matter of some controversy (Brosche et al 1999 and references therein). We are well aware of the fact that a ''tidal radius'' is only a very coarse approximation to the dynamical processes occurring in a cluster.…”

Section: Tidal Radiimentioning

confidence: 99%

The Orbits of 48 Globular Clusters in a Milky Way–like Barred Galaxy

Allen

Moreno

Pichardo

2006

ApJ

122

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The effect of a barred potential (such as the one of the Milky Way) on the Galactic orbits of 48 globular clusters for which absolute proper motions are known is studied. The orbital characteristics are compared with those obtained for the case of an axisymmetric Galactic potential. Tidal radii are computed and discussed for both the better known axisymmetric case and that including a bar. The destruction rates due to bulge and disk shocking are calculated and compared in both Galactic potentials.

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“…Galactic orbits of globular clusters computed in an axisymmetric Galactic potential have been studied by many authors (e.g., Allen & Martos 1988;Allen 1990;Brosche et al 1991;Dauphole et al 1996;Dinescu et al 1999, hereafter D99;Brosche et al 1999). Properties of the computed orbits (e.g., eccentricity, peri-and apogalactic distances, maximum distance from the Galactic plane, energy, z-component of the angular momentum) have usually been related to the metallicity of the cluster, inferring from this how the Galactic halo and disk were formed.…”

Section: Orbits Of Some Globular Clustersmentioning

confidence: 99%

Models for the Gravitational Field of the Galactic Bar: An Application to Stellar Orbits in the Galactic Plane and Orbits of Some Globular Clusters

Pichardo

Martos

Moreno

2004

ApJ

118

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We built three models for the gravitational field of the Galactic bar. These models are an inhomogeneous ellipsoid, an inhomogeneous prolate spheroid, and a superposition of four inhomogeneous ellipsoids. Among the three models, the superposition provides our best approximation to the observed boxy mass distribution of the Galactic bar. Adding the bar component to an axisymmetric Galactic model, we have calculated stellar midplane orbits and orbits of some globular clusters with known kinematical data. For all models we find a secular dispersion effect on the orbital energy and angular momentum, as measured in the Galactic inertial frame. This effect might be relevant to explain the orbital prograde-retrograde distribution of globular clusters. For the stellar kinematics, we study the connection between the sense of orbital motion in the midplane and the onset of chaos in the presence of the bar. In the inner region of the bar, chaos is induced by an axisymmetric central component (bulge), and it arises in orbits that change its orbital sense from prograde to retrograde and vice versa as seen from an inertial reference frame. Outside the bar region, chaos appears only in prograde orbits. Our results concerning such a connection are consistent and extend those obtained for midplane orbits in the presence of only a spiral pattern in the axisymmetric Galactic model.

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Instantaneous and average tidal radii of globular clusters

Cited by 16 publications

References 17 publications

A global and a local criterion in defining the tidal radius

A global and a local criterion in defining the tidal radius

The Orbits of 48 Globular Clusters in a Milky Way–like Barred Galaxy

Models for the Gravitational Field of the Galactic Bar: An Application to Stellar Orbits in the Galactic Plane and Orbits of Some Globular Clusters

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