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Astron. Astrophys. 352, 363-370 (1999)

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4. Radial density profile and integrated photometry

The radial density profile of SagDIG has been obtained by counting stars in circular concentric annuli from the apparent optical center of the galaxy. Fig. 8 shows the results. It is apparent from this figure that the galaxy vanishes at [FORMULA], the background level corresponding to about 0.016 stars arcsec-2. From the nearby companion field that we have taken, a similar but slightly lower value of 0.013 stars arcsec-2 is obtained.

[FIGURE] Fig. 8. Radial density profile of SagDIG. Circular apertures have been used. The adopted background level is marked by the horizontal line in the lower righthand corner.

Subtracting the former value of the background to the density profile, an exponential law has been fitted to the region [FORMULA], which results in a scale length of [FORMULA] or 140 pc.

Total integrated magnitudes and colours have also been obtained. To reduce the effects of foreground contamination, we have first remove all the stars with [FORMULA] and [FORMULA]. The sky level has been approximated by a 2-dimension polynomial, using regions with few stars near the edges of the images. Then, integrated photometry of SagDIG has been performed with increasing circular apertures. The galaxy magnitude in each band has then been measured as the asymptotic value of the derived growth curve. The [FORMULA] colour has been determined as the difference of total magnitudes in each band. The results are [FORMULA] and [FORMULA].

Fig. 9 shows the CMDs for 2 circular regions centered in the galaxy center and radii 60" and 120", respectively. It visualizes the relative contribution of SagDIG and foreground stars for increasing radial distances.

[FIGURE] Fig. 9. Reddening and distance-corrected CMDs for the stars inside two circular regions centered in the galaxy center and radii 60" and 120".

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© European Southern Observatory (ESO) 1999

Online publication: December 2, 1999
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