1999ApJ...519..153K

A study of the stellar population of the M31 spiral arm around OB association A24 was carried out based on the photometric data obtained from deep V and JHK imaging. The luminosity function was obtained for -7≲M_bol≲-3.5 by applying the extinction correction corresponding to A_V=1 and the bolometric correction BC_K as an empirical function of (J-K)₀. In comparing the observed color-luminosity diagrams with semitheoretical isochrones modified for the dust-shell effects, we found the young population of t≲30 Myr with supergiants of M_bol≲-5, the bulk of the intermediate-age population of t∼0.2-2.5 Gyr with bright asymptotic giant branch (AGB) stars of -5≲M_bol≲-4, and old populations of t≳3 Gyr with AGB and red giant branch (RGB) stars of M_bol≳-4. The average star formation rate was estimated to be ∼1.8x10⁴ m_☉.Myr^–1 and ∼0.7x10⁴ m_☉.Myr^–1 per deprojected disk area of 1 kpc² from the number density of B0 V stars around M_V=-4.0 (age ∼10 Myr) and the number density of bright AGB stars around M_bol=-4.3 (age ∼1 Gyr), respectively. A study of the local variation in the V and the J and H luminosity functions revealed a kind of anticorrelation between the population of the young component and that of the intermediate-age component when subdomains of ∼100 pc scales were concerned. This finding suggests that the disk domain around the A24 area experienced a series of star formation episodes alternatively among different subdomains with a timescale of several spiral passage periods. Brief discussions are given about the interstellar extinction and about the lifetimes of bright AGB stars and the highly red objects in the same area.