Absolute spectrophotometry in M31 and M32
Abstract: For a number of places in the bulge of M31, and for two places in M32, photometric scans from lambda = 3300 A to lambda = 10,600 A have been obtained with the multichannel spectrometer on the 5-m Hale telescope. The scans show that in both objects the color temperature (particularly shortward of 5000 A) decreases toward the center, and that the strength of the CN bands increases toward the center in both objects, in agreement with other earlier observations. The new data can all be interpreted in terms of an increase of heavy-element abundance toward the center in both objects by a factor probably less than 2, and by an excess of heavy elements in M31 compared with M32 by a factor probably greater than 2, in qualitative agreement with earlier conclusions of other observers.
Summary (1 min read)
- Alt}iough the instrument has both a star and sky aperture separated by 40 `, this is not useful for sky subtraction in extended hence objects;/the instrument was used either without the starsky chopper running, or by reducing data i n the two apertures completely separately.
- There is some suggestion that changes in the CN band strengths are smaller than in the previous case.
- Indeed the color difference turns out to be 0.04 mag, hard at the margin of measurability with the present data.
- Altogether then, these observations give for the entire bulge of M31 a progressive reddening of the spectral gradient as one approaches the center, the spectral changes being minor in the outer portions of the bulge but increasing rapidly towards the center -quite parallel to the strength of the CN features (Spinrad et al. 1971 ).
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