| 1 | Whether a dwarf spheroidal galaxy is in equilibrium or being tidally
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| 2 | disrupted by the Milky Way is an important question for the study of its
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| 3 | dark matter content and distribution. This question is investigated using
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| 4 | 328 recent observations on velocity and position of stars from the dwarf
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| 5 | spheroidal Leo I. For Leo I, tidal disruption is detected, at least for
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| 6 | stars sufficiently far from the center, but the effect appears to be
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| 7 | quite modest.
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| 8 |
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| 9 | A complicating feature of the data is that not all stars in the
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| 10 | sample are really members of the galaxy. Some are foreground stars,
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| 11 | located along our line of sight toward Leo I. We develop an algorithm for
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| 12 | estimating parameters of a distribution sampled with contamination. We
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| 13 | employ a statistical technique known as "expectation maximization" (EM).
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