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the dsphs in the local group offer a unique opportunity for testing our understanding of galaxy evolution .
new cmds obtained for dsphs show that most have undergone complex evolution .
they formed stars over _ many gyr _ rather than on a dynamical timescale ( few @xmath2 yr ) despite the fact that they are now devoid of gas and their low total masses ( @xmath3 to @xmath4 ) make them highly susceptible to supernova - driven galactic winds .
( for a recent review , see smecker - hane 1997 . )
we have undertaken as series of studies involving photometry and spectroscopy of stars in the carina and fornax dsphs to determine their star - formation and chemical evolution histories .
here we report on our spectroscopy of carina dsphs stars and their derived metallicities .
we used our photometric survey of bright stars centered on the carina dsph ( smecker - hane , et al .
1994 ) to identify red giants that were probable members of the galaxy . at a galactic latitude of @xmath5 ,
the carina fields are contaminated with a significant number of galactic foreground stars .
although members can not be positively identified by their location in the cmd , they are easily identified by their large radial velocities ( 223 km / sec ) . for our spectroscopic sample , we randomly chose stars from the cmd that had magnitudes within 1.5 mag of the tip of the red giant branch ( rgb ) , ( b - i ) colors within @xmath6 of the mean color of the rgb , and distances @xmath7 arcmin ( 1 core radius ) from the center of the galaxy .
we obtained spectra of these stars with the cerro tololo inter - american observatory 4.0-meter telescope and the argus multi - fiber system in november , 1997 .
the argus system allows simultaneous observation of 24 stars and 24 sky positions .
total exposure times were 3.5 to 5 hours .
images were reduced using the standard ccd reduction package in the image reduction and analysis facility ( iraf ) , and the spectra were extracted and calibrated with the argus package .
the most difficult part of the data reduction was the sky subtraction because the ca ii lines fall among bright night sky emission lines .
the fluxes in the sky lines were typically 5 times higher than the stellar continuum fluxes in the region of the the ca ii lines .
the final stellar spectra have a dispersion of 0.83  / pix , and a typical signal - to - noise ratio of 17 per pixel .
examples are shown in figure  1 .
we derived metallicities , [ fe / h ] , from the reduced equivalent width , @xmath8 , of the ca ii infrared triplet lines in each spectrum .
this technique has been empirically calibrated by rutledge , et al .
( 1997 ) using observations of numerous galactic globular cluster stars , and interested readers are referred to it for details . in brief , the sum of the equivalent widths of the two strongest lines of the ca ii triplet at 8542 and 8662  , @xmath9 , shows a linear dependence with [ fe / h ] when the effect of effective temperature and gravity are removed to first order .
the later is effectively done by forming the reduced equivalent width for each star , @xmath10 , where @xmath11 is the magnitude of the star and @xmath12 is the magnitude of the horizontal branch . the equivalent width for each ca
ii line was determined by fitting a linear continuum plus gaussian - shaped absorption feature in the standard wavelength regions defined by armandroff & da costa ( 1991 ) . the adopted calibration equation , [ fe / h ] @xmath13 , from rutledge , et al .
( 1997 ) gives metallicities based on the scale defined by the high - dispersion spectroscopic work of carretta & gratton ( 1997 ) .
figure 2 shows a histogram of the derived metallicities for 52 radial velocity members of carina and a gaussian fit to the histogram .
the average metallicity is [ fe / h ] @xmath14 ( including the calibration zeropoint error in the uncertainty ) and the observed dispersion is @xmath15 dex .
the error in each derived metallicity is set primarily by the sky flux and random fiber - star positioning errors .
thus the [ fe / h ] measurement errors are , to first order , independent of the magnitude and metallicity of the stars in the limited magnitude range over which we are observing .
subtracting in quadrature the average measurement error of 0.15 dex and 0.02 dex uncertainty in the slope of the calibration from the observed dispersion reveals an intrinsic metallicity dispersion of @xmath16 dex ( 1.0 dex full width ) for the carina dsph .
two notable calibration issues deserve discussion .
first , the @xmath8[fe / h ] calibration is strictly valid for old stars although armandroff & da costa ( 1991 ) note no strong age dependence .
second , the calibrating galactic globular clusters exhibit a relatively well - defined relationship in [ ca / fe ] versus [ fe / h ] that reflects the history of enrichment from type  ia and type  ii supernovae in the galaxy .
however dwarf galaxies may have entirely different star - formation histories and may not share the same [ ca / fe]-[fe / h ] relationship ( see smecker - hane & mcwilliam in these proceedings for a discussion of abundance ratios in the sagittarius dsph ) .
therefore , we are embarking on a series of observations to calibrate @xmath8 to yield [ ca / h ] and to explore its sensitivity to age .
the derived mean metallicity and intrinsic metallicity dispersion roughly agree with our initial analysis of the carina cmd ( smecker - hane 1997 ) although the metallicity dispersion derived from spectroscopy is larger .
a full analysis of the cmd is underway to determine carina s star - formation history .
carina s rgb is very narrow in color because of the degeneracy of age and metallicity .
a wide range in age ( @xmath17 2 to 14 gyr ) counteracts a 1.0 dex spread in metallicity in such a way that the younger rgb stars are more metal rich and hence have approximately the same colors as the older , more metal - poor , rgb stars .
thus a galaxy with a narrow rgb may indeed have a complex stellar population .
an interesting contrast to the carina dsph is the leo i dsph . from analysis of its cmd ,
gallart , et al .
( 1999 ) conclude that its wide rgb may be a result of its wide range in age ( @xmath17 1 to 10  15 gyr ) and its internal metallicity dispersion may be very small . in conclusion ,
the dsphs exhibit a very wide variety of star - formation and chemical evolution histories , and we can learn much about the physical mechanisms that control their evolution by studying them in detail .
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we report on the chemical abundances of stars in the carina dwarf spheroidal galaxy ( dsph ) derived from low - resolution spectra . we have determined values of [ fe / h ] for 52 stars from the reduced equivalent width of the ca ii infrared triplet lines . 
 the carina dsph has a mean metallicity of [ fe / h]@xmath0 and an intrinsic metallicity dispersion 0.25 dex ( 1@xmath1 ) . by directly determining the chemical abundances of carina stars through spectroscopy 
 , we can overcome the age  
 metallicity degeneracy inherent in color - magnitude diagrams ( cmds ) and determine its star - formation history with unprecedented accuracy .