Discovery of a Sub-Megagauss Magnetic White Dwarf through Spectropolarimetry
Abstract
A circular polarization survey for weakly magnetized (about 10 kG-1 MG) white dwarfs has been initiated using a newly developed CCD imaging/spectropolarimeter. Among the first two-dozen stars studied, WD 0637 + 477 revealed strong polarization reversals across both H-alpha and H-beta, indicating a mean longitudinal ('effective') field of Be = +349 +/- 19 kG. Corresponding estimates of the mean surface field and dipolar field values are Bs = 950 +/- 100 kG and Bp = 1.2 +/- 0.2 MG. WD 0637 + 477 portrays the weakest field yet found on a magnetic white dwarf by a factor of 2. Given the small survey sample observed to date, statistics on the incidence of magnetic fields in the range 100 kG-1 MG permit a distribution which either increases smoothly with decreasing field strength, or is bimodal, wherein a small percentage of stars possess fields above about 1 MG and the vast majority are essentially nonmagnetized.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- October 1992
- DOI:
- 10.1086/186576
- Bibcode:
- 1992ApJ...398L..57S
- Keywords:
-
- Astronomical Polarimetry;
- Magnetic Stars;
- Stellar Spectrophotometry;
- White Dwarf Stars;
- Charge Coupled Devices;
- Circular Polarization;
- Photosphere;
- Astrophysics;
- STARS: FUNDAMENTAL PARAMETERS;
- STARS: INDIVIDUAL ALPHANUMERIC: WD 0637;
- 477;
- STARS: MAGNETIC FIELDS;
- STARS: WHITE DWARFS