Object of the Week, August 18th, 2024 - NGC 6765

[obrazell]

For this OOTW I am choosing the other NGC planetary nebula in Lyra in NGC 6765.
I am surprised that it has not been included as an OOTW before. NGC 6765 was first
discovered by Albert Marth using William Lassell’s 48” speculum metal mirror
telescope in 1864 and then independently rediscovered by Truman Safford in 1870
and then again by Stephan in 1888. It was not recognised as a planetary nebula until
1946 when Minkowski observed that it had an emission line spectra from plates taken
with an objective prism on the 10” Bruce Astrograph at Mt Wilson, although this
maybe questionable as the 10” Bruce went back to Yerkes after Barnard had finished
with it and never came back to Mount Wilson. Mt Wilson did have a similar telescope
which I thought was a Cooke astrograph. Perhaps surprisingly there does not seem
to have been much research done on the nebula itself, although it is suggested that it
is in the early stages of an interaction with the local ISM. The classification given here
is WZO1. There has been a certain amount of research done on the central star as it is
a rare type of star known as a PG 1159 star. These are hydrogen deficient stars in the
transition between CSPN and white dwarfs. The central star currently has a temperature
of around 93000K. They are also very short period variables. NGC 6765 is thought to lie
at a distance of perhaps 9400 light years, GAIA gives 3476 pc. It is also suggested that
the nebula is about 8000 years old, but with large error bars. The nebula itself has a
bipolar structure looking like a much fainter version of M76 with a bar and then handles.
A fine amateur image can be found at http://www.astrophoton.com/NGC6765.htm.
There is also an outer loop in this image which maybe part of the interaction with the ISM.


ngc6765pan.jpg

I was surprised that it had not made it into the venerable WSDSH Vol. 2
My initial observations of this nebula using my old 20” Obsession showed only the faint
streak but the use of an OIII filter brought out some of the handles and that fact that
the bar was not uniform. It is another nebula where what you see is very dependent on
the sky conditions at the time. For various reasons I have not tried it yet wit the 15".

Anyway as always give it a go and let us know what you find.

[lamperti]

Back in 1991 with a 13" at 130x + UHC: "Once I got to the area (too many stars to hop easily) it was easy. Elongated fuzzy, no brightening."
In 2006 with a 20" at 272x + UHC: "Brightening towards the center. Fairly small with the UHC brightening it up a bit. Maybe more to it if used an O-III filter."

[Uwe Glahn]

Interesting story behind this object. Does not know, that this is such an unique PN with a special CS.
I got three different observations with larger aperture. My rough notes says:

16", 360x, NELM 7m0+
40" long, 1:5 NE-SW elongated main body; relative small but with higher surface brightness; NE end seems to be somewhat brighter, towards the SW end I could pick up some mottling; knot to the SE not visible

20", 400x, NELM 6m5+
central bar divided into three parts - NE tip is a faint star, in the middle is a longish part and at the SW end another smaller knot with similar brightness is visible; detached knot to the SE indicated

27", 586x, NELM 7m0+, Seeing III
see sketch; best view without any filter; faint CS is steadily visible with averted vision
NGC6765.jpg
home

[Raul Leon]

Hi, here's my observation from 10/16/2009: Ngc 6765 is a planetary nebula in Lyra ; mag:13.1 ; size: 38" ; small, fairly faint and elongated; no central star observed. I used a 7mm Nagler with my 14.5 StarStructure f/4.3
ngc 6765.jpg

[Clear Skies]

Nice one, Owen!

2 Observation in my log. The first in September 2009 in the French Alps using my 12" SCT @ 191x / 26'. Nothing knotty observed but I did note something "stellar":

16mm Nagler T5: Resembles a galaxy, slightly elongated NE to SW, slightly brighter in the middle. Using AV a central star or a superimposed star is visible, approximately mag. 14.

To the SW are two mag. 13 stars aligned NNE to SSW (not a double in WDS), three times that distance to the WNW are a mag. 12 (SE) and a mag. 13 (NW) star aligned NW to SE.

16mm Nagler T5, Lumicon OIII: Clearer with use of this filter and it's clear that the brighter central part is elongated in the same direction.

The second one in September 2022 from the French Ardennes, 14" SCT @ 259x / 19' & 407x / 12', with a bit more use of filters. A hint of a detached knot to the southeast using 11mm + UHC, but nothing definitive. Using 7mm I did notice something "stellar", again, on the southwest edge of the brightest northeastern part of the nebula:

11mm Nagler T6: A clearly NW-SE elongated glow, much brighter in the NE part, tapering towards the SW. The knots to the ESE and WNW are not visible.

11mm Nagler T6, Lumicon OIII: Using this filter, without AV, the nebula is slightly larger and is more even in brightness in the NE part, with AV the nebula is slightly irregular in the NE part. The knot to the SE is not visible.

11mm Nagler T6, Lumicon UHC: Using this magnification the SE knot sometimes jumps into view but can not be held. With this filter the SW part of the nebula is slightly wider causing the nebula overall to somewhat have a "waist", which makes for a nice view.

11mm Nagler T6, Lumicon Hydrogen-Beta: Using this filter the nebula is not visible.

7mm Nagler T6: Using this magnification the nebula is more even in brightness and it is clear that to the NE, in line with the nebula, there is a mag. 14 star.

7mm Nagler T6, Lumicon OIII: Using this magnification and this filter the nebula is clearly brighter and irregular in the NE part. The knot to the SE is not visible.

7mm Nagler T6, Lumicon UHC: Using this magnification and this filter a stellar knot is subtly discernible on the SW edge of the brighter NE part. The knot to the SE is not visible.

Here's the guide.

DSF OotW 2024-33 - NGC6765 Lyr_1.jpeg DSF OotW 2024-33 - NGC6765 Lyr_2.jpeg

[akarsh]

I'm away from my original logbooks and only have access to low-quality scans, but I observed this object with my 18" f/4.5 on 2022 June 26 using a DGM NPB filter. It responded well to the filter, and my rough sketch shows a horizontal line (NE-SW) with a gap in-between, and a bright spot on top (SE) of the line.