Space motions of globular clusters NGC 362 and NGC 6218 (M12)

Brosche, P.; Tucholke, H. J.; Klemola, A. R.; Ninković, S.; Geffert, M.; Doerenkamp, P.

doi:10.1086/116024

Cited by 30 publications

(19 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…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: 97%

Why is the mass function of NGC 6218 flat?

Marchi¹,

Pulone²,

Paresce³

2006

A&A

View full text Add to dashboard Cite

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.

show abstract

Section: Discussionmentioning

confidence: 97%

Why is the mass function of NGC 6218 flat?

Marchi¹,

Pulone²,

Paresce³

2006

A&A

View full text Add to dashboard Cite

show abstract

“…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

View full text Add to dashboard Cite

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.

show abstract

“…To put our current results into perspective, cluster shocking during passage through the Galactic disk has long been considered a main threat to the longterm survivability of globular clusters (Ostriker et al 1972) but the reaction of the disk to that passage was not studied or even mentioned until much later. In a little-known paper, Brosche et al (1991) stated that "Every transit of a globular cluster through the interstellar matter in the galactic plane will, in principle, affect this material. There is slight hope that such perturbing effects may be noticeable even today."…”

Section: Our Results In Contextmentioning

confidence: 99%

Gravitational interactions between globular and open clusters: an introduction

Marcos

Reilly

2013

Astrophys Space Sci

View full text Add to dashboard Cite

Historically, it has been assumed that globular and open clusters never interact. However, recent evidence suggests that: globular clusters passing through the disk may be able to perturb giant molecular clouds (GMCs) triggering formation of open clusters and some old open clusters may be linked to accreted globulars. Here, we further explore the existence of possible dynamical connections between globular and open clusters, and realize that the most obvious link must be in the form of gravitational interactions. If open clusters are born out of GMCs, they have to move in similar orbits. If we accept that globulars can interact with GMCs, triggering star formation, it follows that globular and open clusters must also interact. Consistently, theoretical arguments as well as observational evidence, show that globular and open clusters certainly are interacting populations and their interactions are far more common than usually thought, especially for objects part of the bulge/disk. Monte Carlo calculations confirm that conclusion. Globular clusters seem capable of not only inducing formation of open clusters but, more often, their demise. Relatively frequent high speed cluster encounters or cluster harassment may also cause, on the long-term, slow erosion and tidal truncation on the globulars involved. The disputed object FSR 1767 (2MASS-GC04) may be, statistically speaking, the best example of an ongoing interaction.

show abstract

Space motions of globular clusters NGC 362 and NGC 6218 (M12)

Cited by 30 publications

References 0 publications

Why is the mass function of NGC 6218 flat?

Why is the mass function of NGC 6218 flat?

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

Gravitational interactions between globular and open clusters: an introduction

Contact Info

Product

Resources

About