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Astron. Astrophys. 317, 694-700 (1997)

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3. Matter injection and removal

3.1. Injection

Significant mass loss only occurs after a star has evolved off the main-sequence. After this time, the star rapidly goes through a number of evolutionary states to end up as a white dwarf. The rate at which matter is injected into a cluster will thus depend solely on the rate at which stars evolve off the main-sequence and the amount of mass each star loses before it becomes a white dwarf.

3.2. Removal

Mechanisms proposed for the removal of intracluster matter from a GC may be intrinsic or extrinsic to the cluster. Several mechanisms have been proposed (see e.g. LR90, Smith et al. 1995 and references therein), although in the majority of cases the timescale for the mechanism to operate exceeds the time since the last crossing of the Galactic plane. We will re-assess these mechanisms in a later paper and for the present summarize the various mechanisms below.

3.2.1. Internal mechanisms

Mechanisms which are independent of the cluster environment include:

(i) removal by photoionized isothermal cluster winds;

(ii) heating by faint X-ray sources;

(iii) classical novae ejection. However recent observations of the remnant of the nova T Sco in the GC M80 (Shara & Drissen 1995) suggest that there may be fewer cataclysmic variables in GCs than had previously been estimated;

(iv) radiation pressure from the stars;

(v) kinetic ejection by hot and cold stellar and pulsar winds;

(vi) high speed of matter ejected from stars.

(vii) erosion of grains by X-rays from the X-ray sources in the clusters.

3.2.2. External mechanisms

Mechanisms proposed for the removal of matter which are dependent on the cluster environment include:

(i) ram-pressure stripping by halo gas;

(ii) ejection by the integrated radiation pressure of Galactic stars;

(iii) erosion of grains by the hot x-ray emitting gas in the Galactic halo, either by sputtering by the atoms or by the X-rays from the gas.

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© European Southern Observatory (ESO) 1997

Online publication: July 8, 1998
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