Observation of IRAS 17436+5003 / PN G0.77.1+30.8, a post-AGB (PPNe) object

[sudhashn]

Hello all,

In my recent visit to Hanle (a Bortle 1 location in Ladakh, North India), a cold dry dessert at an elevation of 4300m, (32°47'N 78°58'E ), I tried to observe this Proto Planetary Nebulae in the constellation Hercules (about 1.8° of Eltanin in Draco).

From my voice notes
Located it in the 17mm Baader Hyperion (~90x) eyepiece, looked like a bluish star. Flanked by 2 stars of similar brightness forming an almost equilateral triangle with the object. Needed to go much higher in magnification.
Properly observed with 6.5mm ES eyepiece + 2x Barlow (460x). Did try with 10mm Super Plossl (150x), 6.5mm EP (230x). 230x started showing some nebulosity.
A definite bigger halo, almost circular in shape, was observed. Compared to the halo of nearby two (pretty close to each other) stars, this halo was larger & definitive. Nearby dimmer stars resolved into pinpoint sources too.

As it was a manual scope (with no tracking), I had great difficulty in maintaining the object in the FoV. After 15-20min of struggle, could keep for 20-30s in the FoV to observe properly.

Two accompanying friends (visual observers) confirmed elongation between 1-7O clock positions (in the FoV). However I couldn't observe elongation consistently.

Equipment used : 12" Skywatcher Dobsonian 300mm Flextube Collapsible, manual.
Conditions: Bortle 1 (pristine conditions I have ever observed).
Observation on 30th Sept 2024, 8pm - 10pm.

Other designations: V814 Her, HD 161796 Simbad (https://simbad.cds.unistra.fr/simbad/sim-id?Ident=Hd+161796&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id)query here.

P.S. As I was browsing through Stellarium for objects, usual grid search of 1.5° x 1.5° in Stellarium, found this & noted it down for observation (months before). Interestingly enough, did remember to observe it on the trip too.

Would love to hear from the community on your observations on the same object. Upon research, understood that this is an unique class of object that I have gotten to observe & conditions/friends helped.

Regards
Sudhash

[Clear Skies]

Hi Sudhash,

I took a look at the information you sent and I can not identify an extended, non-stellar object at the position of V814 Herculis. I am quite confident you observed a halo brought upon your optics by that mag. 7.3 star.

Cheers,


Victor

[Steve Gottlieb]

Here's an HST image (https://fox.ncac.torun.pl/postagb2?lang=en&branch=postagb2world&id=2&l=77.133&b=30.87&ctx=hstp), which shows an irregular dust shell elongated N-S, though scattered light from the bright post-AGB star does seem the most likely cause.

The Torun catalogue of Galactic post-AGB and related objects (https://fox.ncac.torun.pl/camkweb/postagb2.php) has a page on this star here (https://fox.ncac.torun.pl/postagb2?lang=en&branch=postagb2world&id=2&l=77.133&b=30.87) with photometric data and bibliography.

[Clear Skies]

The problem with this "observation" is unfamiliarity with angular size and the true field of view in an eyepiece. In (visual) astronomy this is as basic a thing as understanding right ascension & declination and cardinal directions.

As the Hubble images show, the object is a mere 4"x2" in size. In speak, that is four by two seconds of arc. We call planetaries of that size 'stellar'. Also, the image was taken at a wavelength of 100 micrometer: that's near-infrared.

The image below is a POSS2 Blue DSS image, 1/4 degree = 15' in size (fifteen minuten of arc) = 900" (nine hundred seconds of arc).

5559

The size of the object, per near-infrared Hubble image, translated to the DSS image scale is therefor 4/900 x 2/900.

Please note the little red speck centered on V814 Herculis; I drew an ellipse but on an image scale of 900 pixels, a 4 x 2 pixel ellipse becomes a rectangle. Anyway: that's the angular size of the object "observed". Is that an object that can be observed with a mag. 7 star smack in the middle of it..?

Finally, please compare this image (https://www.cloudynights.com/uploads/monthly_10_2024/post-200402-0-90289000-1729289224.jpg) posted on Cloudy Nights. The arc drawn onto that image is > 1' = > 60" (greater than one minute of arc = greater than 60 seconds of arc) which is well over fifteen times the (long side's) size of the object imaged by Hubble.

Please, fellow stargazers, do not use Hubble images to plan observations and please, do take the effort to familiarize yourself with the very basics of celestial mechanics, star charts and the gear you use. 'Cause if you skip the basics, you will be forever stuck in them.

[wvreeven]

The Hubble image shows that there is a shell so there is a possibility that it can be observed visually. In that sense the Hubble pic can very well be used for planning observations.

A shell of 4" x 2" is tiny but not impossible. 4" is comparable to the size of the disk of Uranus. 2" is comparable to the size of the disk of Neptune. It is possible to discern the disks of Ganymede and other Jovian moons visually and those are even smaller.

Having said that, discerning a faint tiny disk surrounding a magnitude 7 star is challenging, to put it mildly. But given the right sky conditions and optical elements, I don't think it is impossible, especially if filters can be used that dim the star but not the disk.


Clear skies, Wouter

[Clear Skies]

.
The Hubble image shows that there is a shell so there is a possibility that it can be observed visually. In that sense the Hubble pic can very well be used for planning observations.

A shell of 4" x 2" is tiny but not impossible. 4" is comparable to the size of the disk of Uranus. 2" is comparable to the size of the disk of Neptune. It is possible to discern the disks of Ganymede and other Jovian moons visually and those are even smaller.

Having said that, discerning a faint tiny disk surrounding a magnitude 7 star is challenging, to put it mildly. But given the right sky conditions and optical elements, I don't think it is impossible, especially if filters can be used that dim the star but not the disk.


Clear skies, Wouter


Yeah, no.

[wvreeven]

.


Yeah, no.
Can you give a more constructive reply?

With my 12" I have observed the disks of several stellar planetary nebulae so I know it is possible. Also TS states that two other observers confirmed their observations.

[sudhashn]

Thanks Steve Gottlieb, for the HST image & an amazing list of post AGB objects. I will try & add as many as I can for the 12" scope.

Thanks Victor, for the response. Hopefully you didn't struggle like me at higher magnifications. Upto which magnication did you go? There was a 2-star system nearby & this halo was slightly larger than their combined halo.

I had no prior knowledge on the type of object. 'PN G' (which is the original catalogue that I had) meant that I was looking for a planetary nebulae & went in for observation blindly without giving much thought. Once I encountered something peculiar, asked two other friends who were observing together, to take a look at it. I have observed Neptune in Jan 2024, as a tiny non-stellar disk with greenish/bluish hues. My original expectations of this PNG object prior to observation was "12inch: Try….no size info given…." (from Stellarium).

Thanks wvreeven, for the response. Appreciate the inputs on the dimensions. Once the other observers did suspect orientation, we did cross check in the HST images & found some elongation. Other observers were pretty young (atleast 15 & 20 years younger). It took a while to locate this object in the internet (that's when the IRAS designation was found). After spending 2hrs on the object, on that night, I felt strongly about it. I couldn't observe any orientation per se, it looked circular to me (aged 50yrs). I hope to repeat the observation next Sept/Oct. Lets see. In the meanwhile, hope some of you will try & observe the beauty...and report here.

In the meanwhile, clear skies to you all. Thank you for reading. Hopefully it inspired some of you to take a relook at post-AGB stars.

[akarsh]

I was one of the observers who saw the halo around the star. There was definitely a brighter halo around V814 Her than other stars that "appeared" roughly similar in brightness. I put appeared in quotes because the reference star we used for comparison was about a magnitude fainter when I checked later – so it is plausible that we were misled.

I also noted the inner halo with an elongation. Soon after we observed it, I independently found the HST paper and noticed that the elongation was north-south. The elongation we observed was not a north-south elongation, so I imagine this inner halo must be attributed to optics. We were observing at 333× with a 12-arcminute field-of-view. Both me and the other observer (Mihir) who studied the inner "halo" agreed on the orientation, so it was something "real" except it may be (and is very likely) due to optics. The "outer" circular halo, though, seemed more real to me – but as I said our comparison star was fainter as I checked later. I would like to follow it up with my 28" when I get a chance.