TY - JOUR

T1 - Inhomogeneous planetary nebulae

T2 - Carbon and oxygen abundances

AU - Kholtygin, A. F.

PY - 1998/1/20

Y1 - 1998/1/20

N2 - We reconsider the problem of the difference between the abundances of carbon and oxygen in galactic planetary nebulae (PN) derived from the intensities of the recombination and collisionally excited lines. This discrepancy can be explained by an inhomogeneity of the PNe and an overestimation of the weak line intensities. The formulae for calculation of the nebular line P intensities in presence of both temperature and density fluctuations are given. The intensities of the forbidden [OIII] lines, the CII, CIII and CIV recombination lines and the CIII] λ 1909 UV intercombination doublet for different values of the mean electron temperature T0 in PNe and the rms temperature variation t2, are calculated. Results of these calculations are used to find F the values of T0 and t2 which allow to provide the best fit of the observed and calculated line intensities (taking into account the observational errors). In most cases, the obtained values of T0 appear to be significantly smaller than ordinarily used for I the abundance determinations Te([OIII]), while t2 < 0.16. The carbon and oxygen abundances for more than 70 PNe are calculated. For these PNe average chemical abundances are evaluated separately for nebulae of type I, II and III. For the first, we found C/H=6.67·10-4 cm-3 and O/H=5.74·10-44 cm-3. For the second they are C/H=8.94·10-4 cm-3 and O/H=6.36·10-4 cm-3. For the third we obtained C/H=3.94·10-4 cm-3 and O/H=4.79· 10-4 cm-3. Results of the fitting of the line intensities for the NIII λ4640 and NIV] λ1486 lines are also given.

AB - We reconsider the problem of the difference between the abundances of carbon and oxygen in galactic planetary nebulae (PN) derived from the intensities of the recombination and collisionally excited lines. This discrepancy can be explained by an inhomogeneity of the PNe and an overestimation of the weak line intensities. The formulae for calculation of the nebular line P intensities in presence of both temperature and density fluctuations are given. The intensities of the forbidden [OIII] lines, the CII, CIII and CIV recombination lines and the CIII] λ 1909 UV intercombination doublet for different values of the mean electron temperature T0 in PNe and the rms temperature variation t2, are calculated. Results of these calculations are used to find F the values of T0 and t2 which allow to provide the best fit of the observed and calculated line intensities (taking into account the observational errors). In most cases, the obtained values of T0 appear to be significantly smaller than ordinarily used for I the abundance determinations Te([OIII]), while t2 < 0.16. The carbon and oxygen abundances for more than 70 PNe are calculated. For these PNe average chemical abundances are evaluated separately for nebulae of type I, II and III. For the first, we found C/H=6.67·10-4 cm-3 and O/H=5.74·10-44 cm-3. For the second they are C/H=8.94·10-4 cm-3 and O/H=6.36·10-4 cm-3. For the third we obtained C/H=3.94·10-4 cm-3 and O/H=4.79· 10-4 cm-3. Results of the fitting of the line intensities for the NIII λ4640 and NIV] λ1486 lines are also given.

KW - Planetary nebulae: general ISM: Abundances

UR - http://www.scopus.com/inward/record.url?scp=0007186905&partnerID=8YFLogxK

M3 - Article

AN - SCOPUS:0007186905

VL - 329

SP - 691

EP - 703

JO - ASTRONOMY & ASTROPHYSICS

JF - ASTRONOMY & ASTROPHYSICS

SN - 0004-6361

IS - 2

ER -