[Joe Keller]

I found Barbarossa on a third archive plate. There is no longer any doubt of Barbarossa's reality nor of Barbarossa's position. Using the two most credible of these "disappearing dots" (1987 & 1997) Barbarossa's period, assuming circular orbit, matches the progression of the imperfect 5:2 Jupiter:Saturn resonance, to 3% accuracy. As in earlier estimates, Barbarossa aligns in longitude, with one of the five (mean, corrected for Jupiter & Saturn eccentricity) resonance points, to 0.4 or maybe 0.1 deg error.

Corrected for Earth parallax, the four points (there are two competing dots on the 1954 plate scan) lie nearly on a great circle. The change in angular speed corresponds to orbital eccentricity of at least 0.1, or at least 0.25, if one or the other of the 1954 points is used in addition to the 1987 & 1997 points. The Red comparison-based magnitudes of three of the objects are all +17.6 +/- 0.3; one of the 1954 objects is about Red +18.3.

The plates (from online 1.0"-resolution scanned versions) are:

1. POSS-I E (a.k.a. POSS-I Red)(exposures for this series varied from 2400 to 4200 sec) Plate XE671, February 25, 1954, epoch 1954.154.

First dot: RA 11h 03m 12.4s Decl -5deg 58' 09"

I determined the Red magnitude as +17.6 by comparison with the USNO-B Red1 magnitude (Red1 was chiefly determined from plates of this series) of a nearby star with stable magnitude. I found this dot, March 29. If it is Barbarossa, then Barbarossa's eccentricity must be at least 0.25, assuming the validity of the 1987 & 1997 dots.

Second dot: RA 11h 02m 25.16s Decl -5deg 56' 11.3"

By comparison with nearby stars, this dot's Red mag is about +18.3. I found this dot, March 28. It is the brightest of a "flying circus" of five disappearing dots spread over about 1'. Together with the 1987 & 1997 dots, it would imply an eccentricity of at least 0.1.


2. SERC-ER (a.k.a. SERC2 Red)(exposure 3600 sec), Plate 713, January 31, 1987, epoch 1987.08215.

RA 11h 18m 03.18s Decl -7deg 58' 46.1"

Because this sky survey was only one of three used to determine the USNO-B Red2 magnitudes, I determined the magnitude of Barbarossa on this plate, by comparison with both the R1 & R2 magnitudes of four nearby stars, finding +17.3. I saw Barbarossa on this plate, March 4, and realized on March 5 that what I saw, was Barbarossa.


3. SERC-I (a.k.a. Optical Infrared)(exposure 5400 sec), Plate IS713(A438), March 3, 1997, epoch 1997.16711.

RA 11h 22m 16.77s Decl -8deg 29' 30.9"

I determined Barbarossa's Infrared magnitude as +18.1 by comparison with two nearby stars. Though the authors of the USNO-B catalog warn that it is a relatively inaccurate source for magnitudes of bright stars, I used the USNO-B's I-R value for Capella, 0.2, to correct the sunlit Barbarossa's Red magnitude to +17.9. I found this dot March 31. I've found no other Optical Infrared plate online with which to prove the disappearance of this dot. Instead, I found that it is absent from both the SERC Red and MASS IR J,K,H plate scan series, indicating, if not disappearance, then an aberrantly narrow spectrum.


The 1987-1997 track implies a 2775 year period for circular orbit. Recent values of Jupiter's and Saturn's periods indicate that their 5:2 resonance progesses with a period of 2696 yr.

Corrected for April 1 Earth parallax, Barbarossa's geocentric coordinates tonight, assuming a circular orbit through the 1987 & 1997 objects, are:

RA 11h 26m 30.9s Decl -9deg 00' 11"

The position might be 7' W to 1.5' E of this, if one or the other of the 1954 dots is used for prediction instead of, or in addition to, the 1997 dot. Last night Steve Riley imaged an approx. mag. +17.3 dot which tonight will be 3' NW of these coordinates (only 1' above the predicted track), if Steve indeed imaged Barbarossa.

Barbarossa's estimated apparent diameter is 0.9". Barbarossa's estimated retrograde motion is 0.7"/hr.

Sincerely,
Joseph C. Keller, M. D.