| Date/epoch | Band | 
|
PA | Ref.a |
| (%) | ( )
|
|||
| 1973-1975 | V | 2.2 (0.1) | 99.3 | 1 |
| 1980 Mar. | U | 0.8 (0.1) | 99.0 | 2 |
| B | 1.6 (0.1) | 99.0 | 2 | |
| V | 1.65 (0.4) | 95.0 | 2 | |
| 1989 May | U | 1.6 (0.1) | 100 | 3 |
| B | 2.5 (0.1) | 100 | 3 | |
| V | 2.1 (0.1) | 100 | 3 | |
| R | 1.9 (0.1) | 100 | 3 |
Errors in parenthesis. a (1) Klare & Neckel (1977), mean of two measurements. It is not clear which broadband filter was used. We assumed optical V broadband for simplicity; (2) Barbier & Swings (1982), mean of five measurements and after taking into account an interstellar contribution; (3) Gnedin et al. (1992). The PA quoted is the mean value including all filters as reference.
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