Astronomy and Astrophysics – Astronomy
Scientific paper
Jul 1990
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990stin...9422412w&link_type=abstract
M.S. Thesis Saint Mary's Univ., Halifax (Nova Scotia). Dept. of Astronomy.
Astronomy and Astrophysics
Astronomy
Astronomical Photometry, Elliptical Galaxies, Brightness Distribution, Color, Data Reduction, Isophotes
Scientific paper
Independently calibrated charge coupled device surface photometry data were derived from 12 images of the shell galaxy NGC 2865 in the B, V, and R passbands. Short exposures were used to permit accurate sky subtraction. Mean isophotes were derived for each passband over the 3-60 second radial distance range. The isophotes are presented in the form of their best-fit ellipse parameters. The parameters for the best-fit de Vaucouleurs surface brightness law were determined for the mean profile in each passband, and deviations of the actual surface brightness profile from the r to the 1/4 power law are discussed in terms of the galaxy's shell structure. From the best-fit ellipse parameters, the amplitudes of the cosine(4 theta) component of the isophotes could be measured. It was found that they do not show the boxiness often observed in a galaxy which had experienced a recent merger. On the contrary, a peak amplitude of about +1 percent (2 sigma) over the 25-40 second interval suggests only the presence of a weak disk. If the disk is real it indicates NGC 2865 is an S0 galaxy. Both (B-V) and (B-R) color gradients were measured and show the galaxy becomes bluer with increasing radius. This may be explained in terms of a radial metallicity gradient in the sense that the metallicity decreases by about a factor of two per decade increase in distance.
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