I'm working on an observing project of pairs visible in my 20-inch where change in their orbital position might be noticed in the next ~30 years. I maintain a list of "Short Period" pairs generated from SkyTools 3 Pro on my laptop, and observe from that list when seeing permits. The search criteria are multiple systems with periods of less than 60 years and separations of between 0.2" and 15". Since I do not have the ability to take accurate measures, I simply make a sketch of what I see in relation to other field stars. In the years hence, I hope to notice the change by comparing my sketches.
Iota Virginis was included in the list generated by SkyTools, showing it is 4.09/+8, PA 80*, sep. 0.45", and I made an observation the night of 25 May 2020:
20-inch, 1067x & apodizing mask: "!! Blue and red! Overlapping disks. The blue brighter star is in front, red is behind it. Clear notching, some diffraction but clear. No other stars in view. Color not so vivid, pale blue/red. Notched elongation. Check spectra."
My sketches (at the bottom of this post) show a clear snowman, and it really jumped out at me as being an obvious and colorful pair, which made me make the excited !! note.
When it came time over the following week to write up my observations, I found Iota Vir was not in the WDS. I went to SIMBAD and was confused by the papers (I'm not a scientist), but did note it was spoken of as an astrometric binary (meaning only the primary has been observed and it binarity is inferred by it's movement in the sky), and that the B star had never been detected.
I emailed a friend who is better at interpreting scientific papers, and he provided a link to a 2018 study which said in part:
"Based on a direct combination of the Hipparcos data with astrometric ground-based observational catalogues having epochs between 1938 and 1999 the preliminary orbits and component masses are calculated for 6 binaries with no previous orbit calculation: ι Vir (HIP 69701) with period of 55 years, photocentric semi-major axis of 200 mas, relative semi-major axis of 830 mas and a dwarf secondary of 0.6 solar masses."
My friend pointed out the major axis would be 400 mas or 0.4”, which is close to the SkyTools value. Also the B star's magnitude is estimated but thought to be >8th magnitude.
I was out again the night of 2 June 2020, and under worse seeing and transparency conditions, recorded the following:
8-inch 667x: swimming in seeing but can see a red bump emerging behind the blue-white orb in the diffraction. Disks bloated due to seeing
8-inch 1067x: stars bloated but it's clear, blue in front of a red orb. Red seems only about one or two delta mag
20-inch 533x: seeing too poor to get good focus
20-inch 533x + apodizing mask: yellow, seems elongated in the same direction as what I saw in 8-inch
20-inch 667x + ap mask: deeper yellow-orange peanut in diffraction
20-inch 1067x + ap mask: blue star + red as peanut in diffraction.
I used similar magnitude Mu Vir as a standard star to compare at all powers with the masks, and I only saw it as round (bloated, but round) and without a discoloration effect such as red bumps etc.
When I disengaged the servo motors and let Iota Vir drift, I estimated a PA of the red star, B, being between SSE and due south of the blue-white A, which is in the northern quadrant.
Have I observed the apparently never before seen B star? I would greatly appreciate observations by others, particularly those able to make measurements, as some way of confirmation.
Edited by mccarthymark, 03 June 2020 - 09:08 PM.