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Met 9 (12547+2206)

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#1 mccarthymark


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Posted 19 June 2019 - 12:55 PM

I was out last night using my 20" in my back yard (SQML 18.5), going through some pairs in CDSA.  Seeing and transparency were both mediocre, so I was mostly using an 8" off axis mask (effective f/13).  I came upon Met 9 in Coma Berenices and had this observation:


Met 9: 8" mask @ 205x, do not see any double.  8" mask @ 410x suspect elongation.  8" mask @  667x see a fleeting, bluish point just outside of first diffraction ring.  A star is light yellow orange and bright; 2 delta mag. to B.  A feels elongated / egg shaped.  At 20" and 667x the seeing is too messy though there is a knot in the diffraction where I had noticed the point with 8".  Strong feeling A is elongated.


WDS: 12h 54m 39.98s +22° 06' 28.8" P.A. 51 sep 1.7 mag 5.70,7.77 Sp F8V+M2-3V dist. 33.85 pc (110.42 l.y.)


Stelle Doppie shows first measure in 2002 and slightly widening through the last measure in 2013 (due for a new measure -- hope Nucleophile sees this!)


Since there is no other than an AB pair shown I checked Aladin Lite.  SIMBAD gives only one green box, HD 112196.  But Gaia layer gives 2 green boxes which call out different coordinates.  I don't know if this means there are two stars here?  Also it seems there are two closely separated stars; may be there is a AC pair?  It could just be the elongation I sensed was due to the seeing...


Appreciate those who can to observe and perhaps measure it.  And I appreciate the help to interpret Aladin Lite.

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Edited by mccarthymark, 19 June 2019 - 12:56 PM.

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#2 Nucleophile


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Posted 19 June 2019 - 03:51 PM

Hi Mark,


According to the calculator I am developing you should easily split this with an 8" objective IF the mags are as listed.  But those are not visual--they are in the IR as hinted at in Stelle Doppie (see screenshot).  Going to the WDS 4th Catalog, we see those mags come from a study at 2145nm (see screenshot).


On to your question about Gaia DR2.  Yes, the two boxes mean two stars.  I analyzed them and found the following:

g mean mag (supposed to mimic visual mag):  6.86 and 10.45

rho:  1.670"

theta:  51.0 degrees


So, I think you most certainly detected the B component of Met 9--congrats!

I am keen to look at and measure this one, but it may be until next year as it is heading out of view for me.  I usually skip over K band doubles when I come across them, but I have learned from this experience there may be more than meets the eye.  lol.gif






PS  I am quite surprised this pair wasn't discovered prior to 2002--seems like something Burnham or Couteau would have found.  Perhaps there is more to the story with this one....

Edited by Nucleophile, 19 June 2019 - 04:45 PM.

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#3 fred1871



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Posted 20 June 2019 - 01:00 AM

The WDS historic data has a K in the notes column, which indicates IR observing, and the magnitudes will reflect this, as MarkM notes. The G magnitudes from Gaia, roughly similar to V (visual) magnitudes, are often a bit brighter than the V magnitudes. 


So we have a pair with fairly close separation and on the G-magnitudes a brightness difference of 3.6 magnitudes, with fairly dim secondary. On the numbers, the pair is widening, noticeably over 11 years (2002-2013). 


Just as Paul Couteau discovered the widening pair Theta CrB in 1971, visible by then with a 30cm scope, but likely too close to notice back in the beginning of the 20th century when Aitken was doing his great survey, various recent discoveries reflect change in the doubles. Burnham, mostly working in the period before Aitken, did not systematically survey the whole northern sky; he used different search methods.


Looking at the Gaia DR2 data, the parallaxes are somewhat different at 28.4 and 31.2 mas, and the formal errors are small enough to prevent overlap. Proper Motion (PM) numbers are similar for RA at 52 and 56 mas/year, but in Declination quite different, 32 and 16.7 mas/year. That leaves us wondering if it's a binary with parallaxes that should be better measured, and odd PM differences, or going with the first impression that it's an optical pair, with change due to PM differences.


Either way, it's widening, so would presumably have been tighter as we go back in time.


If we take the Gaia parallax for the brighter star, that gives a distance from us of only some 35 parsecs (114 ly), so the separation in line of sight at discovery, 1.5", is ~52 AU. That's not a tiny separation. Difficult to guess the likely period, as the widening is not especially slow, so it could be a longish way from maximum separation (near maximum, change is slowest). Even on an assumption of maximum being not too many decades off, the orbital period could be several centuries, taking into account approximate likely masses based on spectral types. It will be of some interest to watch. Does it begin to close again? (binary) - does it keep widening in linear fashion long-term (optical).


And so we have another addition to the fairly-difficult-doubles-for-amateurs category.

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