Compact planetary nebulae MaC 2-1 and Sp 4-1: Photoionization models and
  dust characteristics
  We study the characteristics of planetary nebulae (PNe), MaC 2-1 and Sp 4-1.
We use our optical spectra taken at 2 m Himalayan Chandra Telescope, Spitzer
mid-infrared (mid-IR) spectra, HST images, and IR photometric data. These PNe
have not been individually studied in details earlier. Both the PNe are in the
low- to moderate-excitation class. MaC 2-1 shows the presence of silicon
carbide (SiC) and magnesium sulphide (MgS) dust. Sp 4-1 hosts polycyclic
aromatic hydrocarbon (PAH) molecules. We obtain plasma properties of the PNe
from the optical and mid-IR emission line fluxes. We compute photoionization
models of the PNe for self-consistent estimation of physical parameters
associated with the central star and the nebula, including nebular abundances.
From the modelling of the IR data, we obtain the characteristics of dust and
molecules formed in the nebulae. From our study, we estimate that the
progenitors of MaC 2-1 and Sp 4-1 had masses of 1.2 and 1.55 $M_{\sun}$,
respectively, and both of them seem to have born in metal poor environment.
Both are distant PNe, with the estimated distances of 16 and 18 kpc for MaC 2-1
and Sp 4-1, respectively.
