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We have been doing a sample survey in UBV photometry and proper motions as part of an investigation of galactic structure and evolution. The 3 fields in the direction of galactic anticentre (l = 167°, b = 47°), centre (l = 3°, b = 47°) and antirotation (l = 278°, b = 47°) have been surveyed. The high astrometric quality of the MAMA machine (CAI, Paris) gives access to micronic accuracy (leading to < 2 mas per year) on proper motions with a 35 years time base. The kinematical distribution of F and G–type stars have been probed to distances up to 2.5 kpc above the galactic plane. We have derived the constrain on the structural parameters of the thin and thick disk components of the Galaxy (Ojha et al. 1994abc):
• The scale lengths of the thin and thick disks are found to be 2.6±0.1 and 3.3±0.5 kpc, respectively. The density laws for stars with 3.5≤MV≤5 as a function of distance above the plane follow a single exponential with scale height of ∼ 260 pc (thin disk) and a second exponential with scale height of ∼ 800 pc (thick disk) with a local normalization of 5–6% of the disk.
• The thin disk population was found with (〈 U+W〉, 〈V〉) = (1±4, −14±2) km/s and velocity dispersions (σU+W, σV) = (35±2, 30±1) km/s. The thick disk population was found to have a rotational velocity of Vrot = 177 km/s and velocity dispersions (σU, σV, σW) = (67,51,42) km/s. No dependence with r and z distances was found in the asymmetric drift measurements of the thick disk population.
We investigate the kinematics of the thick disk population using photometric and astrometric sample surveys towards two opposite directions at intermediate latitude. A multivariate discriminant analysis (MDA) is used to distinguish the ‘Thick Disk’ from other populations with the help of the Besançon model of population synthesis. The data constrain the asymmetric drift of the thick disk population, which is found to be 40±10 km/s and does not depend on the galactic radius.
We have conducted deep near-infrared surveys of the Sh-2 255, W3 Main and NGC 7538 massive star forming regions using simultaneous observations of the JHKs-band with the near-infrared camera SIRIUS on the UH 88-inch telescope and with SUBARU. The near-infrared surveys cover a total area of ~ 72 arcmin2 of three regions with 10-σ limiting magnitudes of ~ 19.5, 18.4 and 17.3 in J, H and Ks-band, respectively. Based on the color-color and color-magnitude diagrams and their clustering properties, the candidate young stellar objects are identified and their luminosity functions are constructed in Sh-2 255, W3 Main and NGC 7538 star forming regions. A large number of previously unreported red sources (H-K > 2) have also been detected around these regions. We argue that these red stars are most probably pre-main-sequence stars with intrinsic color excesses. The detected young stellar objects show a clear clustering pattern in each region: the Class I-like sources are mostly clustered in molecular cloud region, while the Class II-like sources are in or around more evolved optical HII regions. We find that the slopes of the Ks-band luminosity functions of Sh-2 255, W3 Main and NGC 7538 are lower than the typical values reported for the young embedded clusters, and their stellar populations are primarily composed of low mass pre-main-sequence stars. From the slopes of the Ks-band luminosity functions, we infer that Sh-2 255, W3 Main and NGC 7538 star forming regions are rather young (age ≤ 1 Myr).
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