Spectroscopy of giants in LMC clusters. II. Kinematics of the cluster sample

Robert A. Schommer, Edward W. Olszewski, Nicholas B. Suntzeff, Hugh C. Harris

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Abstract

We analyze velocities for 83 star clusters in the LMC, based on individual stellar velocities measured at the Calcium triplet. One-half of the clusters are objects in the outer parts of the LMC (radius≥5°), which had no previous velocity determinations. Published velocities for intermediate and old clusters are shown to have had systematic errors. We compare our new velocities with various rotation curve analyses of the LMC, and test aspects of the twisted disk model proposed by Freeman et al. [AJ, 272, 488 (1983) ]. Our outer cluster sample and the intermediate age inner clusters form a disk which agrees with the parameters of the optical isophotes and inner H I rotation curve. The oldest clusters still present an enigma; they do not have the kinematics of an isothermal, or slowly rotating, pressure-supported halo. These oldest objects rotate with an amplitude comparable to that of the younger disk and have a small velocity dispersion, although the parameters are poorly determined in this small sample. When the transverse motion of the LMC is taken into account, a single rotating disk solution fits the old and intermediate-aged clusters and other tracers (i.e., there is no need for an additional "tilted disk" system). In the inner 2° the old clusters still exhibit peculiar velocities, as do the CH stars and the old long-period variables. The rotation curve of the LMC does not show signs of a Keplerian falloff out to at least 5-6 disk scale lengths, implying the existence of dark matter associated with the LMC. The mass of the LMC is larger than 1.5×1010 script M sign . The integrated mass-to-light ratio of the LMC is ∼10.

Original languageEnglish (US)
Pages (from-to)447-459
Number of pages13
JournalAstronomical Journal
Volume103
Issue number2
StatePublished - Feb 1 1992

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ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Schommer, R. A., Olszewski, E. W., Suntzeff, N. B., & Harris, H. C. (1992). Spectroscopy of giants in LMC clusters. II. Kinematics of the cluster sample. Astronomical Journal, 103(2), 447-459.