Can you see individual stars in other galaxies?

[Steve Gottlieb]

If you observe from the southern hemisphere, like Dan Smiley did a couple of weeks ago, the answer is easy.  Of course, you can, silly.

The LMC (and SMC) are highly resolved into a multitude of faint stars and many are visible in even a small scope.  The brightest individual star in the LMC is S Doradus (variable), which sits in the center of the open cluster NGC 1910 (the LMC contains nearly 300 NGC clusters!!).  S Doradus is one of the massive known stars and generally shines between 9th and 10th mag — it was a bit brighter than 10th mag the last time I observed it.  Of course, that’s an outlier but once you reach 12th mag or so, loads of young, energetic O- and B-type stars are resolved in open clusters or just scanning along the bar of the LMC.  Once again, the southern hemisphere observers have most of the best goodies!

But what about us poor northerners?  Can you throw us a few crumbs? Well, there are some opportunities, but you’ll probably need a 12” at minimum, dark skies, and good seeing.  The easiest extragalactic star to observe is known as B324, which is the brightest individual V-mag star in M33  It lies just 6' from the center of M33 in the star association IC 142.  It was originally considered an A5-type star and possible LBV (luminous blue variable), but is now considered a warm yellow supergiant, which are among the most massive and luminous known stars.  If you observed M33 closely, IC 142 is in the northern spiral arm that also contains IC 143 and ends at NGC 604.  I first noted this star in 1997 using my old 17.5” Sky Designs scope at the north edge of IC 142, but didn't realize at the time that the star was extragalactic!  So, how bright is this star?  Compared to the LMC/SMC stars it’s quite dim — 14.9V — and you’ll have to look carefully as it’s nearly lost in the glow of IC 142.  But this star is 2.8-3.0 million light-years away, so I think it’s certainly worth trying to track down!

Perhaps a bit surprisingly, M31 has NO stars this bright.  The brightest confirmed star is a yellow supergiant (type F2 Ia) with the ungainly designation LGGS J004406.32+420131.3, which is basically its coordinates (00 44 06.3 +42 01 31).  I mentioned observing this star from Lake Sonoma with my 24-inch in an OR in October 2021, but it doesn’t take this large of a scope.  Bob King wrote a column in the December ’21 issue of Sky & Telescope about viewing this star with his 15-inch.  I identified the star immediately at 260x just 1.5' SW of a mag 9.3 star (SAO 36612) and nearly on a line with a mag 14.2 star 1' NNE of the bright star.  The star was surprisingly easy to view at 375x as my visual limit this night was at least 16.5. But you’ll need a good finder chart to make sure you’re seen the correct star!  I’ve observed several additional 16th mag stars in M31, including a couple that were tracked down at CalStar four years ago named MAC 2-203 and MAC 2-123.

A week and a half ago (Sept. 13th), I added another galaxy with visible extragalactic stars — Barnard’s Galaxy (NGC 6822)!  These were the two brightest spectroscopically confirmed stellar members, which lie at the south end of the galaxy at a distance of about 1.7 million light years.  [K67] C84 at V = 16.0 and [K67] C74 at V = 16.5.  Both are B-type supergiants and they lie within 0.7' of each other.  C84 has a fainter (perhaps foreground) star just 4" W, which was not seen separately.  Using the DSS2 photo as a finder chart, C84 was easily identified (perhaps enhanced slightly by its close companion) at 375x. It forms a pair with a mag 15.7 star just 14" W.  C74 is 43" WSW of C84 and was quite dim but repeatedly glimpsed and confirmed at the same position.  A mag 12.8 field star is 1.1' to its WNW.

The final extragalactic star I’ve observed is [SK76] A 43 in the Local Group dwarf irregular galaxy IC 1613 in Cetus (distance 2.4 to 2.5 million light years).  This star is located in the northeast portion of the diffuse galaxy and shines weakly at 16.4V. I’ve only had a chance to observe it through Jimi Lowrey’s 48-inch, but it’s on my observing list in the coming months.  These are the 6 galaxies outside the Milky Way with the best shot (including the two trivial ones to the south) of glimpsing an individual star visually.

[Lumpy Darkness]

On Saturday, September 23, 2023 at 12:48:40 PM UTC-7 Steve Gottlieb wrote:

Perhaps a bit surprisingly, M31 has NO stars this bright.  

Hi Steve,

I seem to recall from many years ago being aware of a cluster of blue giants in an outside arm on M31, past M32 along the major axis.  No?  Perhaps since they are not resolved (just a bright glow) so don't count?  Or am I just mistaken? 

[Steve Gottlieb]

You’re probably thinking about NGC 206, the large association/star cloud towards the SW end of M31. 

Back in 1987, Stephen Odewahn (an astronomer at McDonald - it’s possible we met him there) wrote a paper titled "A photometric survey of the rich OB association NGC 206 in M31”.  It included a table of stars in NGC 206 as bright as 16th magnitude.  A number of amateurs have looked at NGC 206 with this paper in mind, seen a few (or several) superimposed stars and reported they observed individual stars in NGC 206.  The problem is the the table in Odewahn’s paper include superimposed Milky Way stars that were not spectroscopically confirmed as members of M31.  But even if you throw out those stars, there are other problems.

It was later shown (using the HST) that Odewahn #12 (the one that’s mag 16.0) is not a single star but actually a luminous star cluster.  In addition, #112 (listed at V = 16.8) is a clump of stars or a cluster. Same with #40 (V = 17.0). Visually these all LOOK like stars, though — even in a 48-inch telescope!  So, the end result is NGC 206 isn’t a reliable place to go searching for M31 stars.

I included the M31 stars MAC 2-203 and 2-123 (with positions and a finder chart) in this Calstar OR from a few years back.

Steve

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[Steve Gottlieb]

I forgot to add that Adventures in Deep Space (hosted by Mark) has an article by Scott Harrington titled “The Stars of NGC 206”.  It’s a deep dive into this whole topic about the brightest stars in M31.

Steve

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[Lumpy Darkness]

Yes, NGC 206, Steve.  I didn't want to guess after a lunchtime margarita.  Great info on it, although I haven't looked at Scott Harrington's ADS inclusion yet, I will.

I do remember Odewahn - McDonald's chief astronomer,  Among other highlights on that trip was the private tour he gave of the HET, and the *great* visit to the optics lab where we were inspecting the segmented mirror cells.  What a blast!  In fact, I liked that tour way more than the observing on Jimi's 48 ;-)  Who arranged that visit, you or Jimi?

[Matthew Buynoski]

This is sort of “cheating,” but in almost any galaxy except those so far distant as to be invisible to amateur aperture ’scopes, a supernova (caused by just one star, albeit blown to bits by the time you see it :-) is very visible, often shining brighter than the rest of the host galaxy.

[Ted Hauter]

Amazing info and answers.

Southern sky is my comfort food if I have to miss an opportunity or get aperture fever, knowing I'm not even in the right hemisphere!

On Sat, Sep 23, 2023, 5:44 PM Matthew Buynoski <buyn...@batnet.com> wrote:

This is sort of “cheating,” but in almost any galaxy except those so far distant as to be invisible to amateur aperture ’scopes, a supernova (caused by just one star, albeit blown to bits by the time you see it :-) is very visible, often shining brighter than the rest of the host galaxy.

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