We present deep wide field VI CCD photometry of the Sextans dwarf spheroidal galaxy ( dSph ) in the Local Group , covering a field of 42 ^ { \prime } \times 28 ^ { \prime } located at the center of the galaxy ( supplemented by short B photometry ) .
The limiting magnitudes with 50 % completeness are V = 24.4 mag and I = 23.6 mag .
Color-magnitude diagrams of the Sextans dSph show well-defined red giant branch ( RGB ) , blue horizontal branch ( BHB ) , prominent red horizontal branch ( RHB ) , asymptotic giant branch ( AGB ) , \sim 120 variable star candidates including RR Lyraes and anomalous Cepheids , \sim 230 blue stragglers ( BSs ) , and main sequence ( MS ) stars .
The main sequence turn-off ( MSTO ) of old population is found to be located at V \approx 23.7 mag and ( V - I ) \approx 0.56 .
The distance to the galaxy is derived using the I -band magnitude of the tip of the RGB at I ( TRGB ) = 15.95 \pm 0.04 : ( m - M ) _ { 0 } = 19.90 \pm 0.06 for an adopted reddening of E ( B - V ) = 0.01 .
This estimate agrees well with the distance estimate based on the mean V -band magnitude of the HB at V ( HB ) = 20.37 \pm 0.04 .
The mean metallicity of the RGB is estimated from the ( V - I ) color : [ Fe/H ] = -2.1 \pm 0.1 ( statistical error ) \pm 0.2 ( standard calibration error ) dex , with a dispersion of \sigma [ Fe/H ] =0.2 dex .
The age of the MSTO of the main old population is estimated to be similar to that of the metal-poor Galactic globular cluster M92 , and there are seen some stellar populations with younger age .
There is found to be one RGB bump at V = 19.95 \pm 0.05 mag ( M _ { V } = 0.03 mag ) , and a weak brighter bump at V = 19.35 \pm 0.05 mag ( M _ { V } = -0.58 mag ) which is probably an AGB bump .
The V -band luminosity function of the RGB and MS stars is in general similar to that of the globular cluster M92 , with a slight excess of stars in the magnitude range brighter than the MSTO with respect to that of M92 .
The bright BSs are more centrally concentrated than the faint BSs .
The V -band luminosity function of the BSs in the inner region is found to extend to a brighter magnitude and to have a flatter slope compared with that of the BSs in the outer region .
Significant radial gradients are seen for several kinds of populations : the RHB , the red RGB , the red subgiant branch ( SGB ) , and the bright BSs are more centrally concentrated toward the center of the galaxy , compared with the BHB , the blue RGB , the blue SGB , and the faint BSs , respectively .