3 research outputs found
Stellar Populations and the Local Group Membership of the Dwarf Galaxy DDO 210
We present deep BVI CCD photometry of the stars in the dwarf galaxy DDO 210.
The color-magnitude diagrams of DDO 210 show a well-defined red giant branch
(RGB) and a blue plume. The tip of the RGB is found to be at I_TRGB = 20.95 +/-
0.10 mag. From this the distance to DDO 210 is estimated to be d = 950 +/- 50
kpc. The corresponding distance of DDO 210 to the center of the Local Group is
870 kpc, showing that it is a member of the Local Group. The mean metallicity
of the red giant branch stars is estimated to be [Fe/H] = -1.9 +/- 0.1 dex.
Integrated magnitudes of DDO 210 within the Holmberg radius (r_H=110 arcsec =
505 pc) are derived to be M_B=-10.6 +/- 0.1 mag and M_V=-10.9 +/- 0.1 mag. B
and V surface brightness profiles of DDO 210 are approximately consistent with
an exponential law with scale lengths r_s(B) = 161 pc and r_s(V) = 175 pc. The
brightest blue and red stars in DDO 210 (BSG and RSG) are found to be among the
faintest in the nearby galaxies with young stellar populations: _{BSG}
= -3.41 +/- 0.11 mag and _{RSG} = -4.69 +/- 0.13 mag. An enhancement of
the star formation rate in the recent past (several hundred Myrs) is observed
in the central region of DDO 210. The opposite trend is observed in the outer
region of the galaxy, suggesting a possible two-component structure of the kind
disk/halo found in spiral galaxies. The real nature of this two-component
structure must, however, be confirmed with more detailed observations.Comment: Latex file, 17 pages with 9 figures, uses emulateapj.sty To appear in
the AJ (in August 1999