Saturday, October 31, 2020

surprised by STF 2877 (Halifax)

I spotted clear skies moving in over Nova Scotia for Saturday night. Given the "rare micro blue puny full Hunter's aka Falling Leaves creepy Moon" was out, I thought I'd aim at a double star. Found STF 2877 in Haas's book, a pair in Pegasus, noting the interesting colour descriptors. Also known as SAO 107756.

double star STF 2877 in luminance

Luminance filter, 1 second subexposures, 12 stacked shots. FITS Liberator, GIMP. North is up; left is east.

The two brightest stars are A and B, what Sissy refers to as grapefruit-orange and powder-blue. I look forward to assembling this data in colour..

But there are some surprises in this image from the Burke-Gaffney robotic telescope.

There's a faint star on the left/east diffraction spike, close in. Is it another companion? Is this the C star? SkyTools 3 Pro does not list a C element.

ST3P has revealed that the next brightest star to the north-west of A is the D partner.

Compelling is the equally luminous star due west.

And then, perhaps most fun, is the faint, tight, equal, and obvious pair to the north-east. Cool! Two in the view! SkyTools has poor data for this, showing only a single star, GSC 01685-0559 at magnitude 9.7.


Data from Stella Doppie on Σ 2877:


First discovered in 1825. The prime star is magnitude 6.65.

AB, 25, 24.0, 9.23
AC, 44, 97.3, 12.42
AD, 309, 101.2, 11.31

A quadruple system with 4 visible stars in this system.

This means the C compatriot is to the north-east and well away, about the same distance as D. Yep, OK, spotted easily in the image. Beyond B, roughly on the same line. Dimmer than D.


Searched the WDS. Found the faint pair: 22146+1714 HDO 170. First discovered in 1867. PA is 241 and the last separation was 7.3. Mag 11.4 and 11.6 stars. Precise location is 221438.65+171333.5. Angle, separation, and brightness values all look good.


As usual, the more I look...


OK. Here's the full colour version.

Struve 2877 in colour

FITS Liberator, Photoshop.

The A star of STF 2877 is definitely intense orange. B is pale blue. So there ya go.

D looks a bit red!

C is a darker blue than B.

HDO 170 A and B are nearly equal. A is maybe white or white with a hint of blue. B seems a tiny bit warmer. Tricky.

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