Yu.V.Lunyova, A.F.Kholtygin . Chemical evolution of the system of galactic planetrary nebulae , Astrophysics , 45 , 451-463 (2002) . Chemical evolution of the system of galactic planetary nebulae beginning from the early age of the Galaxy is investigated. We calculate radial and vertical abundance gradients of C, N, O, Ne, Ar, Cl and S depending of different ages of the central star of the nebula. It have been founded statistically significant dependence of abundance gradients with the age of central star.

... We also analyze Chandra X-ray archive data for the Mon R2 region and find IRS 3 A and IRS 3 C to be sources of hard (3 - 10 keV) and variable X-ray emission , suggesting plasma temperatures of at least 50 в 106 K. The similarity of the X-ray properties to those of Class I protostars suggests magnetic interaction between the protostars and their circumstellar disks to be the origin of the X-ray ... 2002). ... Upper Upper Lower Lower K-band Images of Mon R2 IRS 3. ... X-ray results. ...