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Issue A&A
Volume 395, Number 3, December I 2002
Page(s) 929 - 941
Section Diffuse matter in space
DOI http://dx.doi.org/10.1051/0004-6361:20021315



A&A 395, 929-941 (2002)
DOI: 10.1051/0004-6361:20021315

The $\alpha$-element abundances in the most oxygen-poor planetary nebula PNG 135.9+55.9

M. G. Richer1, G. Tovmassian1, G. Stasinska2, R. F. Jameson3, P. D. Dobbie3, C. Veillet4, C. Gutierrez5 and F. Prada6

1  Observatorio Astronómico Nacional, Instituto de Astronomía, UNAM, PO Box 439027, San Diego, CA 92143-9027, USA
    e-mail: {richer, gag}@astrosen.unam.mx
2  LUTH, Observatoire de Meudon, 5 place Jules Janssen, 92195 Meudon Cedex, France
    e-mail: grazyna.stasinska@obspm.fr
3  University of Leicester, University Road, Leicester LE1 7RH, UK
    e-mail: {rfj, pdd}@star.le.ac.uk
4  Canada-France-Hawaii Telescope Corp., PO Box 1597, Kamuela, HI 96743, USA
    e-mail: veillet@cfht.hawaii.edu
5  Instituto de Astrofísica de Canarias, C/Vía Láctea s/n, 38200, La Laguna, Tenerife, Spain
    e-mail: cgc@ll.iac.es
6  Centro Astronómico Hispano Alemán, C/Jesús Durbán Remón 2-2, 04004, Almería, Spain
    e-mail: prada@caha.es

(Received 26 June 2002 / Accepted 9 September 2002 )

Abstract
We present extensive new spectroscopy and imaging of PNG 135.9+55.9. We use these data as constraints to photoionization models to derive limits on the oxygen abundance. We find that PNG 135.9+55.9 has an oxygen abundance less than 1/50 of the solar value. Our models favour a value of $12 + \log {\rm O}/{\rm H}$ between 5.8 and 6.5 dex, confirming that PNG 135.9+55.9 is the most oxygen-poor planetary nebula known (Tovmassian et al. 2001). We also derive ${\rm Ne}/{\rm O} = 0.5 \pm 0.3$, ${\rm S}/{\rm O} < 0.094$, and ${\rm Ar}/{\rm O} < 0.23$. Although the value of Ne/O is nominally high, it need not imply that the progenitor of PNG 135.9+55.9 converted any of its initial oxygen abundance to neon. The helium abundance appears to be very low, ${\rm He}/{\rm H}\sim 0.08$, but a precise determination will require a much more detailed study. We find that ${\rm H}\alpha/{\rm H}\beta$ is lower than expected and perhaps variable, a finding for which we have no clear explanation.


Key words: planetary nebulae: individual: PNG 135.9+55.9

Offprint request: M. Richer, richer@astrosen.unam.mx

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