NGC 6905, also known as theBlue Flash Nebula, is aplanetary nebula in the constellationDelphinus. It was discovered byWilliam Herschel in 1784. The central star is 14.0 mag. The distance of the nebula, as with most planetary nebulae, is not well determined and estimates range between 1.7 and 2.6 kpc.[2]
The shape of NGC 6905 is characterised by an internal shell with angular dimensions 47" ×34" and roughly conical extensions, with ansae-type formations along the major axis. The nucleus of the nebula possesses one of the most broad emission of OVIemission lines among planetary nebulae.[5] Moreover, OVIII emission has been detected in NGC 6905.[6] The ansae were particularly intense in NII.[5] The total mass of gas in NGC 6905 falls between 0.31 M☉ and 0.47 M☉.[7]
The central star has a spectral type of [WO2], meaning it has a spectrum similar to those ofWolf–Rayet stars and is rich in oxygen;[7] it is estimated to have a surface temperature of 150,000 K.[2][8] The spectrum also shows signs ofneon emission lines.[7] Currently about 60% the mass of theSun, before becoming a planetary nebula it had a mass of about 1.07 M☉.[7] An analysis ofGaia data suggests that the central star may be abinary system.[9]
NGC 6905 can be detected under dark skies with a 4-inch telescope, but it is better observed with larger instruments.[4]
^abCuesta, L.; Phillips, J. P.; Mampaso, A. (1993). "Spectroscopy and shock modelling of the unusual bipolar outflow NGC 6905".Astronomy and Astrophysics.266 (1):199–212.Bibcode:1993A&A...267..199C.
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