Planetary Nebula Central Stars


Kent Blackwell
 

Last night I tried my hand at seeing a central stars in a few planetary nebulae. The most challenging is the central star in M 57, The Ring Nebula. I could count the times in one hand I've seen it in 50 years. Using my 25" I was not able to see it with a 16mm Nagler (200x), nor could I see it bumping the power up to 635x with a Pentax 5mm. Finally using a 7mm Pentax at 435x I saw it for one fleeting second, then again; quickly disappearing as fast as it appeared.
Almost as challenging is the central star in NGC 7009, The Saturn Nebula. This time it popped into view using a 3.5mm Pentax, at a whopping 907x.
Lastly was the very blue central star in NGC 6891 in Sagittarius. It's small so I had to once again use the 3.5mm Pentax at 907x. It reminds me of the above Saturn Nebula, being slightly flattened.


Ted Forte
 

Great observation Kent. 

 

Conventional wisdom has it that seeing is the limiting factor in detecting the central stars of certain PNe and I have no reason to suspect otherwise.  When the central star is similar in brightness to the central area of the PN, it takes steady seeing to detect it. I know from ample literature that is the case with the Ring Nebula.  There are far fewer scholarly discussions on the visibility of the central stars in the Saturn Nebula and NGC 6891 but I strongly suspect that the situation is similar.  Surface brightness values can be misleading as they are an average over the entire body and they do not account for variations across the body.  I believe the brightness of M57’s central star is only about .1 or .2 magnitudes brighter than the surrounding nebulosity.

 

Anyway, I can also attest to the difficulty in detecting the central stars of all three PNe that Kent mentions here. My logs contain 17 descriptions of NGC 6891 and 6 of them report detecting the central star. I’ve described NGC 7009 in my logs 62 times and mention the central star being  visible in only 5 of them.  Suffice it to say, that I’ve seen the central star in M57 a small number of times in relation to the 382 descriptions I’ve recorded – I’m just not going to read through them all to count!

 

It is unfortunate however, that like many observers, I don’t always mention negative attempts to see the CSPN, so I can only guess at whether I actually considered the visibility of the central star for any particular instance where it is not specified. That is sometimes I’ve specifically said that the central star was not visible and other times, its just not mentioned in my notes.

 

Ted

 

From: BackBayAstro@groups.io <BackBayAstro@groups.io> On Behalf Of Kent Blackwell
Sent: Saturday, September 4, 2021 5:09 AM
To: BackBayAstro@groups.io
Subject: [BackBayAstro] Planetary Nebula Central Stars

 

Last night I tried my hand at seeing a central stars in a few planetary nebulae. The most challenging is the central star in M 57, The Ring Nebula. I could count the times in one hand I've seen it in 50 years. Using my 25" I was not able to see it with a 16mm Nagler (200x), nor could I see it bumping the power up to 635x with a Pentax 5mm. Finally using a 7mm Pentax at 435x I saw it for one fleeting second, then again; quickly disappearing as fast as it appeared.

Almost as challenging is the central star in NGC 7009, The Saturn Nebula. This time it popped into view using a 3.5mm Pentax, at a whopping 907x.

Lastly was the very blue central star in NGC 6891 in Sagittarius. It's small so I had to once again use the 3.5mm Pentax at 907x. It reminds me of the above Saturn Nebula, being slightly flattened.


Kent Blackwell
 

It's interesting that atmospheric seeing makes a huge difference is detecting the central stars in PnE. Probably because the magnification can be pushed to the absolute limit. 


jimcoble2000
 

That and the general hazy interiors of PNs require good definition to be able to separate the star from the background in so many of them. Maybe like the moons of Saturn. All you need to do is smear the light the tiniest bit and it is gone.

On Saturday, September 4, 2021, 12:10:31 PM EDT, Kent Blackwell <kent@...> wrote:


It's interesting that atmospheric seeing makes a huge difference is detecting the central stars in PnE. Probably because the magnification can be pushed to the absolute limit.