The physics and kinematics of the evolved, interacting planetary nebula PN G342.0-01.7

¹ Astronomy Dept, Faculty of Science, King Abdulaziz University, 22254 Jeddah, Saudi Arabia
e-mail: afmali@kau.edu.sa
² Department of Astronomy, Faculty of Science, Cairo University, Giza, Egypt
³ Research School of Astronomy and Astrophysics, Australian National University, Cotter Rd., Weston ACT 2611, Australia

Received: 30 March 2015
Accepted: 5 August 2015

Abstract

Integral field spectroscopy has been obtained for very few evolved planetary nebulae (PNe). Here we aim to study the physical and kinematical characteristics of the unstudied old planetary nebula PN G342.0-01.7, which shows evidence of interaction with its surrounding interstellar medium. We used integral field spectra from the Wide Field Spectrograph on the ANU 2.3 m telescope to provide spectroscopy across the whole object covering the spectral range 3400−7000 Å. We formed narrow-band images to investigate the excitation structure. The spectral analysis shows that the object is a distant Peimbert Type I planetary nebula (PN) of low excitation, formally of excitation class of 0.5. The low electron density, high dynamical age, and low surface brightness of the object confirm that it is observed fairly late in its evolution. It shows clear evidence for dredge-up of CN-processed material characteristic of its class. In addition, the low peculiar velocity of 7 km s^-1 shows it to be a member of the young disk component of our Galaxy. We further determined an average expansion velocity of V_exp = 20.2 ± 1.3 km s^-1, a local standard of rest radial velocity RV_LSR = −27.7 ± 1.7 km s^-1, and a distance of 2.06 ± 0.6 kpc for the object. We built a self-consistent photoionisation model for the PN matching the observed spectrum, the Hβ luminosity, and the diameter. On the basis of this we derive an effective temperature log T_eff ~ 5.05 and luminosity 1.85 < log L< 2.25. The temperature is much higher than might have been expected using the excitation class, proving that this can be misleading in classifying evolved PNe. PN G342.0-01.7 is in interaction with its surrounding interstellar medium through which the object is moving in the south-west direction. This interaction drives a slow shock into the outer PN ejecta. A shock model suggests that it only accounts for about 10% of the total luminosity, but has an important effect on the global spectrum of the PN.