Astronomy and Astrophysics – Astrophysics
Scientific paper
2005-09-09
Mon.Not.Roy.Astron.Soc.364:738-742,2005
Astronomy and Astrophysics
Astrophysics
Five pages, 2 figures, accepted by MNRAS
Scientific paper
10.1111/j.1365-2966.2005.09592.x
We present radio continuum observations of the planetary nebula (PN) IRAS 17347-3139 (one of the only two known to harbour water maser emission), made to derive its spectral index and the turnover frequency of the emission. The spectrum of the source rises in the whole frequency range sampled, from 2.4 to 24.9 GHz, although the spectral index seems to decrease at the highest frequencies (0.79+-0.04 between 4.3 and 8.9 GHz, and 0.64+-0.06 between 16.1 and 24.9 GHz). This suggests a turnover frequency around 20 GHz (which is unusual among PNe, whose radio emission usually becomes optically thin at frequencies < 10 GHz), and a relatively high emission measure (1.5 x 10^9 cm^{-6} pc). The radio continuum emission has increased by a factor of ~1.26 at 8.4 GHz in 13 years, which can be explained as expansion of the ionized region by a factor of ~1.12 in radius with a dynamical age of ~120 yr and at an expansion velocity of ~5-40 km/s. These radio continuum characteristics, together with the presence of water maser emission and a strong optical extinction suggest that IRAS 17347-3139 is one of the youngest PNe known, with a relatively massive progenitor star.
Anglada Guillem
Gomez Jose F.
Gomez Yolanda
Gregorio-Monsalvo Itziar de
Lovell James E. J.
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