443 research outputs found
Diagnostic of stellar magnetic fields with cumulative circular polarisation profiles
Information about stellar magnetic field topologies is obtained primarily
from high-resolution circular polarisation (Stokes ) observations. Due to
their generally complex morphologies, the stellar Stokes profiles are
usually interpreted with elaborate inversion techniques such as Zeeman Doppler
imaging (ZDI). Here we further develop a new method of interpretation of
circular polarisation signatures in spectral lines using cumulative Stokes
profiles (anti-derivative of Stokes ). This method is complimentary to ZDI
and can be applied for validation of the inversion results or when the
available observational data are insufficient for an inversion. Based on the
rigorous treatment of polarised line formation in the weak-field regime, we
show that, for rapidly rotating stars, the cumulative Stokes profiles
contain information about the spatially resolved longitudinal magnetic field
density. Rotational modulation of these profiles can be employed for a simple,
qualitative characterisation of the stellar magnetic field topologies. We apply
this diagnostic method to the archival observations of the weak-line T Tauri
star V410 Tau and Bp He-strong star HD 37776. We show that the magnetic field
in V410 Tau is dominated by an azimuthal component, in agreement with the ZDI
map that we recover from the same data set. For HD 37776 the cumulative Stokes
profile variation indicates the presence of multiple regions of positive
and negative field polarity. This behaviour agrees with the ZDI results but
contradicts the popular hypothesis that the magnetic field of this star is
dominated by an axisymmetric quadrupolar component.Comment: 11 pages, 9 figures; accepted for publication in A&
Remarkable non-dipolar magnetic field of the Bp star HD 137509
The southern magnetic Bp star HD 137509 exhibits complex rotational
modulation of the longitudinal field and other magnetic observables.
Interpretation of this magnetic variability in the framework of the low-order
multipolar field models suggests a very strong quadrupolar component to
dominate the surface field topology of HD 137509. I have examined the
high-quality VLT/UVES spectra of HD 137509 and discovered resolved Zeeman split
components in some of the spectral lines. The inferred mean surface field
modulus, =29 kG, agrees with the multipolar model predictions. This confirms
the presence of an extremely strong non-dipolar magnetic field in HD 137509 and
establishes this star as the object with the second-largest field among
magnetic chemically peculiar stars.Comment: accepted by A&A; 6 pages, 4 figure
- …