2017A&A...607A..92L


Query : 2017A&A...607A..92L

2017A&A...607A..92L - Astronomy and Astrophysics, volume 607A, 92-92 (2017/11-1)

Monitoring and modelling of white dwarfs with extremely weak magnetic fields. WD 2047+372 and WD 2359-434.

LANDSTREET J.D., BAGNULO S., VALYAVIN G. and VALEEV A.F.

Abstract (from CDS):

Magnetic fields are detected in a few percent of white dwarfs. The number of such magnetic white dwarfs known is now some hundreds. Fields range in strength from a few kG to several hundred MG. Almost all the known magnetic white dwarfs have a mean field modulus ≥1MG. We are trying to fill a major gap in observational knowledge at the low field limit (≤200kG) using circular spectro-polarimetry. In this paper we report the discovery and monitoring of strong, periodic magnetic variability in two previously discovered "super-weak field" magnetic white dwarfs, WD 2047+372 and WD 2359-434. WD 2047+372 has a mean longitudinal field that reverses between about -12 and +15kG, with a period of 0.243d, while its mean field modulus appears nearly constant at 60kG. The observations can be interpreted in terms of a dipolar field tilted with respect to the stellar rotation axis. WD 2359-434 always shows a weak positive longitudinal field with values between about 0 and +12kG, varying only weakly with stellar rotation, while the mean field modulus varies between about 50 and 100kG. The rotation period is found to be 0.112 d using the variable shape of the Hα line core, consistent with available photometry. The field of this star appears to be much more complex than a dipole, and is probably not axisymmetric. Available photometry shows that WD 2359-434 is a light variable with an amplitude of only 0.005mag; our own photometry shows that if WD 2047+372 is photometrically variable, the amplitude is below about 0.01mag. These are the first models for magnetic white dwarfs with fields below about 100kG based on magnetic measurements through the full stellar rotation. They reveal two very different magnetic surface configurations, and that, contrary to simple ohmic decay theory, WD 2359-434 has a much more complex surface field than the much younger WD 2047+372.

Abstract Copyright: © ESO, 2017

Journal keyword(s): white dwarfs - stars: magnetic field - stars: individual: WD 2047+372 - stars: individual: WD 2359-434 - stars: individual: WD 2359-434

Simbad objects: 18

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Number of rows : 18
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2023
#notes
1 LAWD 96 WD* 00 02 10.7241976499 -43 09 55.390578662   13.12 13.05     DAP5.8 109 0
2 EGGR 381 WD* 00 12 14.7449947981 +50 25 20.736275736   14.6   14.2   DA7.6 90 0
3 Feige 7 WD* 00 43 45.9806246832 -10 00 25.016051736   14.49       DBAP3 95 0
4 HE 0241-0155 WD* 02 44 22.1904832488 -01 42 42.402801204   16.2   16.8   DAH 15 0
5 EGGR 476 WD* 02 59 59.1463320316 +08 11 56.433119456   16.33 15.90 15.3   DA7.8 47 0
6 V* CL Oct WD* 03 17 15.8468594712 -85 32 25.558244556   13.78 13.66 15.19   DAP 158 1
7 EGGR 566 WD* 03 25 11.0474878302 -01 49 15.047041848   16.8 16.22     DZA9 74 0
8 WG 47 WD* 04 43 46.4273702112 -78 51 50.182236864 12.36 13.304 13.418 13.764   DA2.1 42 1
9 EGGR 904 WD* 08 56 18.9476777928 +16 11 03.744751560   15.544 15.595 15.885   DB2 49 1
10 PG 1015+014 WD* 10 18 05.0427157728 +01 11 23.527902156   16.33 16.3     DAH 68 0
11 Ton 527 WD* 10 33 49.1967544416 +23 09 16.254781992   15.3 15.73     DAP2 108 0
12 HE 1045-0908 WD* 10 47 36.1228977120 -09 24 32.628359808   16.78 16.74     DA 24 0
13 LP 852-7 WD* 12 05 26.6739103248 -23 33 12.139045488   13.04 12.90 12.66 12.52 DA5.7 49 0
14 BD-07 3632 WD* 13 30 13.6370112733 -08 34 29.468140653 11.803 12.398 12.340 12.39 12.436 DA3.5 180 0
15 LP 276-33 WD* 16 54 45.6926039157 +38 29 36.628370427   17.1 15.86 16.5   DZA 49 0
16 LAWD 79 WD* 19 56 29.2263375910 -01 02 32.671070269   13.89 13.56 13.73   DA6.4 133 0
17 EGGR 261 WD* 20 49 06.6996392736 +37 28 14.050387020   13.40   13.2   DA3.4 70 0
18 LAWD 83 WD* 21 13 16.8549349741 -81 49 12.878285501 13.28 13.82 13.59 13.6   DA4.8 96 0

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2023.02.09-11:00:26

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