The method combining near IR and IRAS photometric data to separate carbon-rich against oxygen-rich stars has been shown to be very efficient to identify new IRCS and to study their properties. We have used this method to study the space distribution of IRCS. At the opposite of OH/IR stars, no cut-off in the anticenter direction was necessary to fit their number counts. 2 solutions that could reproduce IRCS counts and the variation of their percentage with l are discussed: i) an exponential decrease of the density with the galactocentric distance (R) with no IRCS in the few kpc around the GC, ii) a density independent of R. For lack of statistics, it is difficult to choose one of them. Toward directions close to the Galactic Center, the later seems to be better and toward directions near the anticenter, it is the opposite. The lack of IRCS toward longitudes of around the Galactic Center and beyond about 4 kpc from the Sun previously noticed might be due to a selection effect.
To conclude definitely on these points, data of the ongoing near infrared surveys (DENIS, 2MASS) combined with mid infrared data (IRAS, ISOGAL, MSX) are barely needed. In addition, complete samples of IRCS will be extremely helpful to study the structure and evolution of the galactic disk by estimating parameters such as the disk radius, the replenishment of the interstellar medium, etc.
© European Southern Observatory (ESO) 1998
Online publication: May 15, 1998