Astron. Astrophys. 352, L36-L39 (1999) 2. Quantitative surface brightness photometryWe use the methods of two-dimensional image fitting as developed by MAG to model the surface brightness of NGC 1288 in a quantitative way. In Fig. 1 an I-band image is reproduced. The disk is fitted by an exponential density law, where R denotes the galactocentric radius in the plane of the disk. The bulge is modelled by a spherical density distribution of the form The surface brightness profile follows a similar law with the exponent lowered by 0.5. The resulting parameters are listed in Table 1. According to the radial velocity = 4405 km s^{-1} (RC3, de Vaucouleurs et al. 1991) of NGC 1288 we assume a distance of 60 Mpc. Thus 1" corresponds to 290 pc or 1 kpc to 3.44". Although we use a different bulge model than MAG, the quality of the fit is comparable to that of MAG.
Table 1. Photometric parameters of NGC 1288 As can be seen in Fig. 2 the residuals of the data with respect to the axisymmetric fit model show the positive and negative brightness modulation due to the spiral arms. These have been Fourier analyzed with respect to the azimuthal angle along galactocentric annuli, The Fourier coefficients to are shown in Fig. 3 as function of galactocentric radius for each filter band as a two-dimensional contour plot. These allow a quantitative measurement of the multiplicity of the spiral arms.
© European Southern Observatory (ESO) 1999 Online publication: November 23, 1999 |