Annu. Rev. Astron. Astrophys. 1981. 19: 77-113
Copyright © 1981 by . All rights reserved

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5.3. Dwarf Spheroidal Systems

The dwarf spheroidal systems are probably satellites of the Galaxy, but represent small elliptical galaxies (-13 leq Mv < -8) in their own right since the spheroidals are morphologically distinct, being much less concentrated than Galactic globular clusters, and the Fornax system has its own globular clusters - all of which are metal poor (van den Bergh 1969, Danziger 1973). The proximity of these galaxies allows resolution of individual stars, and Demers, Kunkel & Hardy (1979) deduce [Fe/H] ~ - 0.5 for Fornax from the mean height of the giant branch, although recalibration of metal-rich globulars may lower this to perhaps -1.0. A planetary nebula found in Fornax (Danziger et al. 1978) yields [O/H] = - 0.6, [N/H] = - 0.7 [assuming uniform temperature and using solar values of Lambert (1978)], which may be consistent with an overall metallicity near -1.0 since O generally varies less than metals and N may be affected by self-enrichment. Other results for dwarf spheroidal systems are listed in Table 3.

In summary these are all metal-poor systems, as might be expected from the general abundance versus absolute magnitude relationship for elliptical galaxies (cf. Figure 7), and indeed the most massive (Fornax) is also the least metal poor.

Table 3. Metallicities in dwarf spheroidal systems

System Mv a [Fe/H] Method Ref.


       
Draco -8.6: -1.8 DDO Hartwick & McClure 1974 b
    -2.3 ± 0.4 CMT1T2 Canterna & Schommer 1978
    -1.7 to -2.1 Scanner Zinn 1978
    -1.8 to -2.8 Spectra Kinman & Kraft 1980 c,
        Kinman et al. 1981
U Mi -8.8 -2.1 ± 0.3 CMT1T2 Canterna & Schommer 1978
Sculptor -11.7 -1.9 H-R diagram Kunkel & Demers 1977
    -1.5 to -2.2 Spectra Norris & Bessell 1978
Fornax -13.6 -0.5 d H-R diagram Demers et al. 1979

a van den Bergh (1980).
b Using calibration by Bell & Gustafsson (1975).
c Evidence for nuclear processing in red giants.
d See text.

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