Distance determination to PNe using the extinction-distance method

Abstract

Abstract. We present individual distances to three PNe: NGC 6537, NGC 6781 and NGC 7027, determined by the extinction-distance method. These objects are part of a larger sample (35) of PNe that we observed at ORM. In order to apply this method, and to obtain accurate distances, we determined the spectral type of 40 to 60 stars in the line of sight of each PNe. This implied the necessity of classifying few thousands of stellar spectra with S/N ratio between 10 and 60. To solve such need we developed an ANN system to perform automatic spectral classification which could classify spectra with S/N ratio as low as 20 with an accuracy better than 2 spectral subtypes. In this poster we compare the accuracy of such distances with previous distance determinations using other methods. We conclude that it is possible to use this method to obtain the distance of a large number of PNe with better precision.

The H surface brightness-radius relation: a robust statistical distance indicator for planetary nebulae

“…However, extinction distances to compact PNe might be overestimated if internal dust is significant (e.g. Ciardullo & Jacoby 1999;Giammanco et al 2011), and the effect has been seen in young PNe like NGC 7027 (Navarro et al 2012). Nevertheless, most PNe seem to show little or no internal extinction due to intrinsic dust (F08), verified from the observed blue colours of the CSPNe in evolved objects at high latitudes, such as NGC 246 and NGC 7293 (see Landolt & Uomoto 2007;F08;De Marco et al 2013).…”