Nice work Albert. Excellent explanation. Is Sherlock your middle name? I
told you recently that a guy like me could learn a thing or two about
astronomy from a guy like you. I'll have to expand that list to include Bob
Czerwinski and Steve Gottlieb. I think congratulations are in order. Casey
----- Original Message -----
From: "Albert Highe" <ahighe@No-Spam>
To: "TAC" <sf-bay-tac@No-Spam>
Sent: Thursday, September 04, 2003 7:14 PM
Subject: [TAC] 130 year old puzzle solved: Location of NGC 6138
> There are a few reasons I'd like to inform TAC of a group effort to locate
> NGC 6138.
>
> 1) We are among the first to know the answer to this 130 year old puzzle.
> 2) The story provides some insight into what the NGC/IC Project Team does.
> 3) I learned some new information that might be helpful to others.
>
> Bob Czerwinski and I recently have been hunting down objects in the galaxy
> cluster Abell 2197. On TAC, Bob had mentioned his difficulty finding NGC
> 6138. "The Sky" says it doesn't exist, as well as gives a location for it
2'
> from where the sources below say it is. Uranometria and the NASA/IPAC
> Extragalactic Database (NED) place NGC 6138 at RA 16h 24m 54.1s, DEC +41d
> 03m 03s. The Digitized Sky Survey also shows a galaxy at that location.
Sure
> enough, I was able to see it. For me, that would have been the end of the
> story.
>
> However, thinking that NGC 6138 was one of those NGC objects incorrectly
> identified, Bob consulted the NGC/IC Project page. Bob posted on TAC that
> the NGC/IC Project identified NGC 6138 as NGC 6263. This puzzled me, since
I
> had seen a galaxy at the "correct" location. In addition, NGC 6263 is
nearly
> 15 degrees away!
>
> So, I consulted the ultimate source - Steve Gottlieb. Steve is an amazing
> resource who seems to have endless knowledge about amateur astronomy. He
> impressed me by taking the time to immediately respond with the following
> detailed information.
>
> "Stephan's discovery was "announced" in his list II, which was published
in
> Monthly Notices of the Royal Society (November 1871). He gave a position
> for 1870 as 16h 18m 28.76s +41d 14' 18.5" which precesses to 16h 22m 50.9s
> +40d 56' 04" (2000). This position was micrometrically computed using an
> offset star which was identified in the Monthly Notices paper as "2,821
Arg.
> Z +41d". The actual micrometric offset is not given in the paper but the
> position of the star is listed at 16h 17m 7.32s +41d 10m 39.7s (1870) or
16h
> 21m 30.1s +40d 52' 11" (2000) with a magnitude of 9.2. If you subtract
the
> RA and Dec positions for the offset star and NGC 6138 we can infer
Javelle's
> offsets as 1 minute 21 seconds in RA and a bit under 4' in declination.
Fair
> enough. But if you look up the position of 16h 21m 30.1s +40d 52' 11"
> (2000) on sky charting software, there is no 9th magnitude star there!
So,
> clearly Javelle gave the wrong position for his offset star but I don't
know
> where the star he mentioned is located -- and even then it's possible he
> misidentified the offset star. Corwin claims the modern designation for
> this star is BD +41 deg 2821. If you can track down the 2000 coordinates
> for this star, we could go from there."
>
> Well, I did as Steve suggested and found BD +41 2821 in the Bonner
> Durchmusterung catalog.
> BD +41 2821
> RA 17 16 38.5, DEC +41 11.6 (1855), mag 9.2
>
> Stephan reported his discovery was near 2821 Arg. Z +41d.
> RA 16 17 7.31, DEC +41 10 39.7 (1870)
> It appears that the 16 and 17 for RA degrees and minutes were transposed
in
> Stephan's report. Fortunately, he named the star so it was possible to
look
> up the correct coordinates for it.
>
> The 1855 coordinates for BD +41 2821 translate to:
> RA 17 21 17.7, DEC +41 03.0 (2000).
>
> There is a star very near these coordinates at RA 17 21 18.5, DEC +41 02
> 13.9. "The Sky" says it is a mag 10. The Guide Star Catalogue says it is a
> 9.88. It looks like a match to Stephan's reference star.
>
> That puts NGC 6363 (not NGC 6263) at exactly the right offset. Stephan
> apparently made a mistake and transposed the numbers for RA degrees and
> minutes for his reference star. He actually discovered NGC 6363 and
> calculated its position using the transposed numbers. That is why no
object
> appears at his coordinates. So, the galaxy cited as NGC 6138 in
Uranometria
> and NED is mislabeled. It should have one of its other designations, such
as
> MCG+7-34-20.
>
> Apparently someone has figured this out before, but incorrectly wrote down
> NGC 6263 instead of NGC 6363. Steve confirmed that this is true. The
> correction will eventually make its way into the appropriate professional
> and amateur databases.
>
> This was a nice exercise since I learned quite a lot from it. Here are
some
> of the lessons learned.
> 1) TAC is a great tool for sharing observations. Bob's posts of his
> observations set the ball rolling.
>
> 2) Steve is a wonderful resource. If he hadn't already done the background
> research, hadn't the info at his fingertips, or hadn't been so responsive,
> the ball would have stopped. He also directed me where to look.
>
> 3) The information readily available through the Internet continues to
amaze
> me. Steve probably gave me more credit than I deserved. I know very little
> about star designations and had no idea what BD +41 deg 2821 meant. But a
> search of "stellar databases" quickly gave me a review of various systems
> for naming stars. I learned that BD stands for "Bonner Durchmusterung."
>
> 4) From my research on galaxy clusters, I was aware of various catalogues
> and a variety of search methods for finding galaxies. I was very surprised
> to learn that the Bonner Durchmusterung catalog
> (http://vizier.u-strasbg.fr/viz-bin/Cat?I/122) of stars, first assembled
in
> 1859-62, is available and searchable on-line. The updates in years 1903,
> 1951, and 1968 are also included. It was straightforward to search the
> database using VizieR (http://vizier.u-strasbg.fr/viz-bin/VizieR-3).
VizieR
> can also be used to translate the older stated coordinates into modern
Epoch
> 2000 coordinates.
>
> As amateurs, we use the published databases extensively to select and/or
> identify objects. Many errors still exist among objects readily observable
> by us. We shouldn't hesitate to question the accuracy of what we read when
> we discover discrepancies between our observations and the published data.
> Doing so may allow us to make a small, yet satisfying contribution to
> astronomy.
>
> Albert
>
>