B037 is of interest because it is both the most luminous and the most highly reddened cluster known in M31 .
Images of deep observations and of highly spatial resolutions with the Advanced Camera for Surveys on the Hubble Space Telescope ( HST ) firstly show that this cluster is crossed by a dust lane .
Photometric data in the F606W and F814W filters obtained in this paper provide that , colors of ( F 606 W - F 814 W ) in the dust lane are redder \sim 0.4 mags than ones in the other regions of B037 .
The HST images show that , this dust lane seems to be contained in B037 , not from the M31 disk or the Milky Way .
As we know , the formation of dust requires gas with a rather high metallicity .
However , B037 has a low metallicity to be [ Fe / H ] = -1.07 \pm 0.20 .
So , it seems improbable that the observed dust lane is physically associated with B037 .
It is clear that the origin of this dust lane is worthy of future study .
In addition , based on these images , we present the precise variation of ellipticity and position angle , and of surface brightness profile , and determine the structural parameters of B037 by fitting a single-mass isotropic King model .
In the F606W filter , we derive the best-fitting scale radius , r _ { 0 } = 0.56 \pm 0.02 \arcsec~ { } ( = 2.16 \pm 0.08 ~ { } pc ) , a tidal radius , r _ { t } = 8.6 \pm 0.4 \arcsec~ { } ( = 33.1 \pm 1.5 ~ { } pc ) , and a concentration index c = \log ( r _ { t } / r _ { 0 } ) = 1.19 \pm 0.02 .
In the F814W filter , we derive r _ { 0 } = 0.56 \pm 0.01 \arcsec~ { } ( = 2.16 \pm 0.04 ~ { } pc ) , r _ { t } = 8.9 \pm 0.3 \arcsec~ { } ( = 34.3 \pm 1.2 ~ { } pc ) , and c = \log ( r _ { t } / r _ { 0 } ) = 1.20 \pm 0.01 .
The extinction-corrected central surface brightness is \mu _ { 0 } = 13.53 \pm 0.03 ~ { } { mag~ { } arcsec ^ { -2 } } in the F606W filter , and 12.85 \pm 0.03 ~ { } { mag~ { } arcsec ^ { -2 } } in the F814W filter , respectively .
We also calculate the half-light radius , at r _ { h } = 1.05 \pm 0.03 \arcsec ( = 4.04 \pm 0.12 ~ { } pc ) in the F606W filter and r _ { h } = 1.07 \pm 0.01 \arcsec ( = 4.12 \pm 0.04 ~ { } pc ) in the F814W filter , respectively .
In addition , we derived the whole magnitudes of B037 in V and I bands by transforming the magnitudes from the ACS system to the standard system , which are in very agreement with the previous ground-based broad-band photometry .