16 replies to this topic

[Redbetter]

I haven't seen this one posted and considering recent discussions of Mirach's Ghost, etc. it seemed a good topic.  Last night while star hopping to Hickson Compact Group 21, my first hop was to Tau 1 Eridani.  Now don't ask me why there is a long string of Tau Eridani stars with sequential numerals...that is something that baffles me, obviously some cartographer didn't get the memo about constellation star nomenclature.  But I was sure of my visual hop to the one of many Eridani Tau, and when I turned to the eyepiece there was something wrong:  there was a galaxy preceding the star and it wasn't in Uranometria (or Wikisky)  Rechecking...yes, that is the right star.  Must be a reflection/optical ghost.  Changing eyepieces, position in the field etc. didn't move it at all...it was real rather than an artifact.

 

And it was small but bright!  I pegged it at likely 14 to no dimmer than 14.5 mag visual, with high surface brightness.  It was easier to see than two MCG galaxies to the southeast in Uranometria (MCG-3-8-22/23) despite the glare of a bright star in the same field with the anonymous galaxy.  But when I got home it was not ID'ed in Wikisky or Stellarium, although visible in Wikisky.   A position search in NED yields a designation of LEDA 2816331 or IRAS F02426-1847 and no useful photometry. 

 

I figure this galaxy has some better commonly known name, because it is relatively easy and hundreds or more must have stumbled onto it the same way before.  I didn't have super steady skies last night, and the transparency was only fair.

[StanH]

Wow!  Quite a catch so close to a bright star.

 

VizieR has data from several catalogs, but no useful magnitude data.

 

However, in Aladin pulling up the Gaia DR1 it shows it at 18.574G.  That seems a bit faint.  However, for MCG-3-8-23 it has it at 18.474G.  No data for MCG-3-8-22.

 

In the Imperial IRAS-FSC redshift catalogue (IIFSCz) (Wang+, 2009) has a redshift of 0.0153.

[sgottlieb]

Great find!  HyperLeda references a magnitude of 15.79 in the blue band, though shows no magnitude on the main page for the galaxy.

 

This is just the kind of galaxy that Sherburne Wesley Burnham would have picked up with the Lick 36-inch refractor in the early 1890's while he was surveying the sky (brighter stars) looking for close doubles.

[Redbetter]

Wow, I'll take any comparison to Burnham as high praise. 

 

I am kicking myself for not spending more time on a description including estimate of size and PA orientation.  I didn't even look to see if the core was stellar although I have the recollection of central brightening--which I suspected was evidence of a reflection/ghost from the star until I watched the drift, moved it around the field, and tried another eyepiece.   The initial power used was only 156x and confirmation was at 357x.  It was so easily seen that I expected it would be a common sub-100,000 PGC with various MCG or CGCG catalog names that just slipped through the cracks.  

 

The HyperLeda 15.79 for blue would correspond to something more like 14.8 for visual.  That could be about right, but it seemed to have higher surface brightness than that would have resulted in.  Hmmm, using the Wikisky image and correcting left right spread for chromatic dispersion I estimate dimensions of about 0.57x0.33 arc minutes.  This combined with 14.8 mag yields a surface brightness of about 21.6 MPSAS.  That is relatively bright and consistent with the visual impression I had.

 

I just roughed out the figures for NGC 404 and arrive at identical surface brightness:  10.27 visual, 3.5x3.5 arc minutes, 21.6 MPSAS.  This seems to explain the visibility well.  The surprise to me is that this one next to Tau 1 Eridani has not been catalogued earlier.  Perhaps too small or past a magnitude cut off in earlier sweeps of the survey images?

 

Hopefully, I will get a chance to target it again next month to try to better characterize it.  However, I will likely be stuck at a low altitude site with more haze and a city light dome in that direction.  (Prompting me to kick myself again for not spending more time on this one when I had the chance.)

 

I look forward to visual confirmations and descriptions by others as well.  I think a 15 or 16" in suitably dark skies will find it manageable for experienced observers.  I don't know how much below that is reasonable. 

[azure1961p]

Nice find Red. I enjoyed the thread .

 

Pete

[Redbetter]

Had some rain Sunday night and the sky cleared Monday so I went back up the mountain last night to try to squeeze in an observation with the 20", even though the moon would still be up.  Fortunately the small amount of snow above 5,000 feet was cleared.  Unfortunately the jet stream and winds absolutely wrecked the seeing...downright awful.  But at 12:30, before Tau 1 could slip behind a tree, I made an observation in 20.65 MPSAS conditions.  Tau 1 was swelled up like a beach ball by the seeing.  

 

Surprisingly, the galaxy was again seen immediately at 156x, despite the moon.  I again watched the galaxy and star track across the field to see if the orientation shifted, repositioned it in the field, etc. but the  position angle and separation remained constant.  I then repeated at 278x which made it even easier to see.   The poor seeing and bright sky limited my ability to measure the size of the galaxy, but I was able to measure the passage time between the galaxy reaching the edge of the field and the Tau 1 following.  The difference was about 9 secs, which, when I checked, turned out to be a fair match for their RA values.   The galaxy disk was elongated NW/SE and the core frequently flashed stellar despite the abysmal seeing. 

 

My conclusion is that this is not a difficult target for large aperture.  If I can still see it in terrible seeing with a moon at a little over half phase and still above the horizon, then it shouldn't pose too much difficulty for a 14, 15, or 16" scope in better conditions.  A 12" might be able to bring it in with dark, transparent skies. 

 

Edit:  I had hoped to do a comparison with NGC 404, Mirach's Ghost, but I had an enormous pine blocking the view.

Edited by Redbetter, 28 November 2017 - 11:43 AM.

[azure1961p]

It's an interesting thing, cold weather brings beautifully transparent dry-air skys but all this can be for naught when t y e seeing is in the lower values.  The first thing to vanish are the stellar or near stellar nuclei and as much stellar appearing HII regions. Glad though you got the timings and PA confirmed so that's good. Doubt I'll ever nail it with the 8 but your accounts were enjoyable nevertheless.

 

Pete

[Ptarmigan]

Interesting this galaxy has not been cataloged despite being next to a star.

 

This makes me wonder galaxies near stars that go undetected.

 

Should be interesting to use EAA. 

Edited by Ptarmigan, 03 December 2017 - 08:56 PM.

[Redbetter]

I took a look at some other Tau Eri galaxies last night that were similarly close, but dimmer.  Tau 2 and Tau 3 also have galaxies nearby that don't appear to have much visual coverage...Tau 3 had no less than three that I observed last night.  Also got a better look at the Tau 1 galaxy, I am more satisfied with my previous impressions of it now that I have sketched it and the others mentioned in this post.

[Redbetter]

My son was able to join me last night with his Z10 and we kicked things off by observing the Tau 1 Eri galaxy in the 20".  He didn't have any trouble seeing it or its stellar core at 227x.  We then took a look at Tau 2 and Tau 3.  He was able to see 3 of the 4 galaxies I had seen near these on 12/12/17.  I did not see the 4th with certainty this time either, but we didn't spend a lot of time looking for it.

 

We then tried for the Tau 1 galaxy with his Z10.  We had some difficulty when his finder batteries died and he had to do a finder swap.  The 4.7mm ES82 wasn't quite cutting it at 266x so I put in a 6mm KK ortho to try a power in between (208x) with a somewhat more generous exit pupil. This did the trick.  He actually spotted the galaxy before I did; I was looking too close in and was assuming less field rotation had occurred during the time between the initial sighting in the 20".  When I rechecked in the 20" it had moved in line with a diffraction spike at the 10:30 position.  Going back to the Z10 I found the galaxy in the same position without difficulty, although it was averted vision only.  The core was not visible in the 10" scope for either of us.       

 

So there you have it: this one is visible in scopes at least as small as a 10" in dark skies.  We had some transparency issues at the time and the galaxy was dipping low in the sky by the time we got to it with the 10".  I estimate the galaxy would have been no dimmer than about 14.5 mag to be visible in this scope in these conditions near a bright star.

[sgottlieb]

Thanks for all the reports on this galaxy.  I took a look last night from my "local" site (Lake Sonoma) with an SQM-L reading of 21.3.  As advertised this small galaxy has a high surface brightness and was immediately seen through my 24" at 94x.  Still, I was surprised how prominent it appeared at 375x when I planted Tau 1 just off the edge of the field (while tracking).  And I'd be further surprised if it was fainter than 14.0 mag (V).

[sgottlieb]

An interesting update on LEDA 2816331 found by Redbetter...

 

I made the comment that this "hidden" galaxy might have been picked up by famed double star observer Sherburne Burnham if he had examined Tau1 Eridani (he discovered other galaxies close to stars). I decided to follow up on that idea and scanned through Burnham's published papers.

 

Guess what?  I found he actually did discover the galaxy back in 1890 at Lick Observatory with the 36-inch refractor!  He even measured the separation and position angle from the star to the galaxy.  Unfortunately his results weren't published at that time and the galaxy failed to receive an IC number (the NGC had already been published).  Perhaps if he had LEDA 2816331 would be a better known challenge object today.

 

But Burnham later reexamined the star/galaxy pair in 1909 and 1910 and made additional measures (98.25" separation in PA 243.8°) using the 40-inch refractor at Yerkes .  This time he published the results, along with other double star measures, in the journal Astronomische Nachrichten and mentioned the earlier 1890 observation at Lick.  Burnham added that visually the nebula was "small, and has something of the planetary appearance; difficult with the 40-inch.”   The fact that it was "difficult with the 40-inch" tells you something about the poor condition of the skies or the seeing at Yerkes.

 

In any case, we now know LEDA 2816331 was discovered visually 129 years ago!

[Redbetter]

Steve, thanks for digging into this.  I can't say I am surprised that it had been observed before--my initial shock was that something so obvious in the eyepiece could have escaped visual detection near a bright star for so long.  Knowing that Burnham observed and recorded it all those years ago restores order to the visual universe.  Unfortunately, since it wasn't published originally, we don't get a handy IC designation; and it also escaped the UGC, MCG, & CGCG catalogs as well.  The LEDA number is impersonal and hard to remember, so I refer to it as the Tau 1 Eridani galaxy out of sheer practicality...and that seems fitting since it isn't too far off from Burnham's 1911 published journal listing as "Tau¹ Eridani and nebula."

[Roragi]

Hi,

 

I'm curious to watch this this fall, but my old sky safary doesn't know how to hit MCG-3-8-22 and sees Aries constellation going to galaxy UGC 2327.

When putting Tau 1 the nearest galaxies are PGC 1360090 and 12679, any light? Thank you.

 

Roberto.

[sgottlieb]

Here's an image of the galaxy and the star.  Tau¹ Eridani is a naked-eye star -- mag 4.5 -- and the galaxy is just 2' to its southwest, so you just have to point your scope to the star!

 

This reminds me of the situation with planetary nebula Abell 12, which is hidden by 4th-magnitude Mu Orionis -- just 1.2' from the planetary!  It missed detection until discovery on the Palomar Sky Survey in the 1960's.  Yet the planetary is probably as bright as 12th magnitude and would be easy if not for the distracting glare of the star.

Edited by sgottlieb, 14 August 2019 - 01:01 PM.

[Roragi]

Thanks Steve, I misunderstood the translator, now with the information I am already located, now we just have to wait until autumn winter arrives.

 

Roberto.

[Starman1]

It's easily seen in this image:

https://www.google.c...nkS7sCjP0YbdvM:

Hard to believe it has no NGC number given it's not that far south (about -18.5°)

Edited by Starman1, 14 August 2019 - 02:16 PM.