Object of the Week April 07, 2013 - A whiff of a Planetary: Longmore-Tritton 5

[reiner]

Longmore-Tritton 5, LoTr 5, PN G339.9+88.4

Coma Berenices

RA
12 55 33
Dek
+25 53 30

Planetary Nebula



Longmore-Tritton 5 has a diameter of about 9' and is therefore one of the very large PN. However, compared with most of the other members of that illustrious list, it is an "easy" object with OIII filter (it's only very faint instead of extremely faint :-)).

DSS images of LoTr 5 (color and blue inverted).

563

564

LoTr 5 was discovered by A.J. Longmore and S.B. Britton in 1980 by visual inspection of blue plates of the ESO/SRC Southern Sky Survey taken with the UK 1.2m Schmidt telescope. LoTr 5's galactic coordinates are 339° +88°, the PN is therefore at a (for a PN) very unusual position close to one of the galactic poles: A single PN amidst thousand of galaxies at the Coma/Virgo border. At the time of its discovery, it was the PN with the highest galactic latitude. Its central star IN Com is a binary formed by a relatively bright (8m7 vis) G5 star and an extremely hot (150 000 K) white dwarf. Further, a third M5 companion to the G5 star had been suggested.

LoTr 5 is a bipolar PN, even if it doesn't look like it at the eyepiece (http://adsabs.harvard.edu/abs/1980MNRAS.193..521L). Its bipolar axis deviates only 17° from our line of sight, such that we are viewing this PN "head-on". Good images of this PN were obtained by Stefan Binnewies and Josef Poepsel http://www.capella-observatory.com/ImageHTMLs/PNs/LoTr5.htm and by Stefane Zoll http://www.astrosurf.com/zoll/images/LOTR5_LORGB_1280.jpg. On these deep images, the bipolarity becomes evident and the PN appears as two slightly excentric rings.


I have observed this PN already several times under various conditions with both my 14" and 22" Dobs:

Under fair skies, it is difficult to separate the diffuse glow of this PN from stray light of its mag 8.7 central star, even with OIII filter.

Under excellent conditions, the PN reveals a faint disk with well defined edge towards S, coinciding with the weak star in between the central star and the bright star S of it. Under such conditions, it is also visible using the UHC filter, albeit with somewhat lower contrast. Due to the relatively bright CS, it is very difficult to nail down any internal structure.


So when you're hunting in the Virgo Cluster, don't forget to switch to your OIII filter and take a look at this unusual PN. Can you see evidence of the bipolarity and the two slightly excentric rings?


"GIVE IT A GO AND LET US KNOW"

GOOD LUCK AND GREAT VIEWING!

[Uwe Glahn]

Hi Reiner,

fine object that I have to revisit, thanks for the idea.

Under good transparency it was never a problem to see the PN as a very faint glow around the bright CS. I was also of the opinion to see differences within the glow. For me the eastern part was always a bit brighter. But it does not fit perfectly with the pictures.

I remember a lecture of Bernd Gährken about CS in PN for small aperture. Funny, but this CS is one of the few which is visible in binoculars :)

16", 51x, [OIII], NELM 6m8
567

[reiner]

I remember a lecture of Bernd Gährken about CS in PN for small aperture. Funny, but this CS is one of the few which is visible in binoculars :)

That's the point and this is actually the main difficulty in observing this PN under less than optimal conditions: Separating it from the glow of the CS (not the true progenitor star, which is now a White Dwarf, but its bright G5 companion).

[reiner]

I just noticed that I used the wrong link in my first post. The link goes to the discovery paper by Longmore and Tritton.

The paper about the bipolarity (shown by a spectroscopic analysis of the shells) is here
http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?2004MNRAS.347.1370G

Here's a figure from the paper showing the two excentric rings due to the bipolar character of the PN.

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[Jimi Lowrey]

Reiner,

I had Steve Gottlieb and Howard Banich observing at my place last week and we took a look at this large faint PN last Friday night. The conditions here were not the best we were having an air glow event from the solar maximum and the seeing was below average that night. The best view was with a OIII filter at low power with a 24MM Brandon eyepiece @ 203X. I could not make out a solid ring I could only make out what looked like a little wider that a half moon shape object. Unfiltered it almost disappears from view with only a small brighting barley detectable on one small edge. I hope Steve and Howard will jump in and add there observations here.

[FaintFuzzies]

Jimi and I took a look at my last time I was observing with his 48"...it was pretty much what Jimi described it to be.

[reiner]

Hi Jimi and Alvin,

"half moon shaped" - does this mean you saw only one half of the PN disk? This is interesting, as I also found the side where there is that small star superimposed on the rim of the disk is more distinct with better defined rims. Was your observation on the same side?

[Jimi Lowrey]

Hi Reiner,

I think you are right. I will do a quick drawing of LoTr 5 and post it here next time I am at the telescope to show you the orientation and star field . I should be able to do it tonight as the weather looks good. I did not see it as a full disk as in Uwe drawing above the other night.

[Howard B]

Jimi's description matches what I saw too, only one side of the planetary was seen and it was really faint. Oddly, it didn't seem centered on the "central" star but rather centered between it and the nearby field star of similar brightness. As soon as I scan my notes I'll post my sketch.

[i_sairanen]

I had a chance to observe this planetary nebula two nights ago. Conditions were fairly good; SQM 21.55, NELM 6.8. I found the right place easily and observed it about one hour with different eyepieces and filters. Despite of that I cannot be sure if I saw it or not. 21 mm and 17 mm Hyperions with an O-III filter showed very occasionally something with sweeping and optimal averted vision. This might be also a glow of central star... I cannot certainly say how large the glow was and was there any brighter areas like others have been reported. I must try again on the next time. Sadly observing season is over here in Finland and next good skies will be on August. Weather forecast promises cloudy and rain and after that the Moon is too big for deepsky observing...and after the Moon bright summer nights starts.

[Jimi Lowrey]

Here is my rough eyepiece drawing that I did last night . The best view was with a 17MM Ethos @ 287X and O III filter. The PN is much dimmer that the drawing suggest :-)

573

[RolandosCY]

Hi guys, we attempted this planetary on Friday night. Unfortunately, it was after we had someone light up truck headlamps right in the middle of our observing site (Grrrr!). Anyway, after waiting for about 30 to 40 minutes we attempted it with my 18". I could see nothing with the Nagler 31 and Lumicon OIII, but I sort of suspected something around the correct star when I increased the magnification with my 13mm Ethos and OIII. I would not call it a positive observation, but I would not consider it a failure - at least we found the field! NicosCY was also with me at the time. Sky conditions were quite good with good transparency and above average seeing, SQM reading 21.04 at the time towards Coma. Maybe we should try it from a darker, mountaineous location, or before our dark adaptation gets ruined!

[Uwe Glahn]

Yesterday we - Christian Rausch and myself tried the PN again with 12" and 27".

With 27", 113x, AP 6,1mm + [OIII] we saw the PN as a complete circle around the bright CS. There was definitely structure within the PN glow, but a could not hold any differences. But we both suspected brightest parts in the W to NW.

With 12", 49x, AP 6,1mm + [OIII] the PN was easier to see than in the 27"! No problem to detect the glow around the CS while the other similar bright stars has nothing around. We both saw the glow fully around the CS again. Brightest side was to the N.

[reiner]

Thanks to you all for your reports, in particular to you Uwe!

Once again, a puzzling object, in particular in regard of the quite different observing results. Like Uwe, I never considered this PN to be extremely hard (like PuWe 1 or similar ones), in particular as it has a very good filter response. It certainly needs good transparency, but I would not consider my usual observing location at 1200 m as a place with outstanding atmospheric properties (in particular not as compared with the excellent dry sites of some of you as for instance in western Texas).

Jimi, Howard, and Steve, you said that you had pronounced airglow during your observation. Could this have interefered in particular with the OIII lines during your observation?

[RolandosCY]

Yesterday we - Christian Rausch and myself tried the PN again with 12" and 27"... With 12", 49x, AP 6,1mm + [OIII] the PN was easier to see than in the 27"! No problem to detect the glow around the CS while the other similar bright stars has nothing around....

Hmmmm! Interesting! One of the rare cases of TOO MUCH aperture it seems! It has happened before to me, on one particular evening I could see more detail in IC342 with my 80mm refractor than with the 12" dob I used to have before the 18"...

[Atlas]

I observed LoTr 5 two days ago through my 25“ f 4 Dobsonian at 950 m altitude. Transparency was good, seeing was mediocre. I saw the nebula as a circular disc around the bright star with the star offset from the middle to the west. I had studied the halo of “Frosty Leo” and CW Leonis before turning to LoTr 5, and in comparison to these objects the planetary was not difficult to see. Magnification of 230x with UHC filter yielded the best result, even slightly better than OIII. The photos that Reiner linked show a curved dark wedge intruding into the rim of the nebula from the south and west. I assume that this is the central congestion separating the two lobes. The streak of nebulosity beyond that wedge to the west would then be the rim of the far side lobe. I searched for that dark wedge and finally came to suspect its location. But when I looked up the photos back home it turned out to be at a different place. So my suspicion was wrong. Apparently it is very hard to pin down the internal structure of this object.

Johannes