Spica (Alpha Virginis) is the fifteenth brightest star in the night sky, a spectroscopic double, and the brightest member of a class of stars known as ellipsoidal variables. The primary (Spica A) consists of two stars (Aa and Ab) that orbit so closely together that they are distorted into ellipsoids whose cross-section area and thus brightness varies as they present different aspects of their shapes to the observer. However, this variation may only be by 0.03 magnitudes and thus impossible to detect visually. It also seems that Spica A is a beta Cephei variable with a short 4 hour period that is superimposed on the changes caused by the rotation of the primaries (although one source claims that the beta Cephei pulses stopped around 1970).
As of 1985 and according to the paper "The Ellipsoidal Variable Stars" as published in the Astrophysical Journal there are only twenty documented ellipsoidal variable stars. Thus, Spica is indeed a rare type of star.
In addition to the closely spaced primaries (Aa and Ab), this system has two additional, fainter, and widely separated members that were first cataloged by astronomer S. W. Burnham in 1879. These other two stars are known as Spica AB and AC and are listed in the Washington Double Star Catalog (WDS) as "uncertain" members of the Spica system. The magnitudes, separations from Spica A, and position angles of these two stars are shown below (as taken from the Stelle Doppie web site):
AB 12.00 151.9" 33°
AC 10.50 367.3" 61°
Oddly, there is a fifth entry in the WDS for another star of magnitude 7.5 that is separated from Spica A by just 0.5 arc seconds. I suspect this is in error as it was first reported in 1975 and apparently (?) never observed since. That said, a star of that magnitude so close to a first magnitude star would undoubtedly be very difficult to see (perhaps a task best confirmed by the Hubble Space Telescope).
Okay, so enough with the preliminaries and on to my contribution.
I'm currently "testing" a Laida Optics 50mm aperture finder/guide scope with an inexpensive Astromania 2X barlow to see whether that combination can be used to create a compact, long-focus guide scope for increased image scale. Thus, a few days ago while under a bright gibbous moon I decided to take some images using that combination as a 50mm, f/7.8 "astrograph" 
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Below is the result, an RGB image of the multiple star system Spica showing components AB and AC.
The limiting reach on this image is somewhat beyond the 14th magnitude and the brightest field star has a magnitude of 10.8 (TYC 5547-1507-1, as labeled in my image). Spica AC looks slightly fainter than this and AC's visual magnitude as reported by SkySafari when calculated from the GAIA data is 11.3.
Although I refocused at each filter change you can see that there is still a good amount of blue and red bloat. However, the green-filtered image wasn't too bad, as witness this link to an image of the moon that I took that same night ( __Gibbous Moon with Laida Guide Scope__ ).
The red diffraction spikes are apparently an interaction between the poor color correction of this inexpensive achromat and the micro-lensing of the ASI178MM camera (the latter not usually visible except when a bright star is grossly overexposed).
C&C welcomed and thanks for looking.
Attached Thumbnails
Edited by james7ca, 17 March 2022 - 03:04 PM.
