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Apparent multiple star BD +00 2087 in Canis Minor

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#1 The Ardent

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Posted 14 March 2019 - 04:15 PM

Apparent multiple star BD +00 2087 in Canis Minor


Tuesday evening I continued my observing in Canis Minor. A constellation with no showpiece deep sky targets. Using a 10” f/4 NMT dob with Paracorr 2 and 17mm Ethos that gives 70x and fov 1.5 degrees. The transparency was below average with the crescent moon behind a sheet of cirrus in the west, with mostly clear to the east. Seeing was average to below average, so a night for low power observing only.


Uranometria shows tiny open cluster ADS 6366, which is curious as ADS is usually a double star label. Sky Safari and Interstellarum list this as Herschel 1. Its aka STF 1141 or HD 63035.

Based on visual appearance, it’s either a very multiple star or open cluster. If CMi has a showpiece, this is certainly a contender.


In the same low power field is the bright wide triple DD CMi or STTA 88.


In between these two obvious groups I saw what appeared to be a conspicuously “ large” star BD 00 +2087. I use Sky Safari on my iPad next to the scope as a quick reference. This is the only identifier it provides for this star.


At first glance this star was different from others in the field. It was like seeing a tiny planetary as “non stellar” It appeared to have some size.


On closer inspection companion star was faint but clearly seen. I kept seeing a second fainter glow appear and fade with the seeing. Not clearly seen as a star.

I increased magnification to 150x and was able to see this glow as a faint star, making a close triangle with the other two.


Neither Sky Safari or SkyTools 3 list this star as a multiple. The latest version of Sky Safari gives a Gaia catalog for these two companion stars.


The pic from Aladin clearly shows the triangle.


Finding this made for an interesting session and pleasant reward for viewing in the overlooked constellation.

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#2 fred1871



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Posted 14 March 2019 - 09:03 PM

Simbad gives the Visual magnitude of the brightest star in the triangle as 10.25; the other two stars are obviously less bright. Looking at the DSS image on AladinLite, separations are around 15" and 23" as rough measures. 


Given the dim magnitudes, separations of this large size don't lead to listings as double or multiple stars in most cases. The likelihood is that it's the result of line of sight proximity (optical doubles). If Gaia has parallax and proper motion data suggesting connection, then it could be listed as a new double or triple star in the WDS.


But there are thousands of these combinations that are rather wide and dim. Few of them will prove to be gravitationally bound.


Looking at the Gaia DR2 data, three stars are listed within a 1' radius of the position of BD 00 +2087 ; Gmags are 10th, 11th+, 12th+. The dimmest of the three has no parallax or Proper Motion data; the parallaxes for the other two are very different, and the PM numbers differ significantly as well. Conclusion is that the brighter two stars are an optical pairing. No data for C to evaluate its status.

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