17 research outputs found
Analysis of Magnetic field Geometry and Its Interaction with Circumstellar Environment of HD 57682 by the MiMeS Collaboration
Analysis of Magnetic field Geometry and Its Interaction with Circumstellar Environment of HD 57682 by the MiMeS Collaboration
Investigating the spectroscopic, magnetic and circumstellar variability of the O9 subgiant star HD 57682
Improvements in the determination of ISS Ca II K parameters
Measurements of the ionized Ca II K line are one of the major resources for
long-term studies of solar and stellar activity. They also play a critical role
in many studies related to solar irradiance variability, particularly as a
ground-based proxy to model the solar ultraviolet flux variation that may
influence the Earth's climate. Full disk images of the Sun in Ca II K have been
available from various observatories for more than 100 years and latter
synoptic Sun-as-a-star observations in Ca II K began in the early 1970s. One of
these instruments, the Integrated Sunlight Spectrometer (ISS) has been in
operation at Kitt Peak (Arizona) since late 2006. The ISS takes daily
observations of solar spectra in nine spectra bands, including the Ca II K and
H line s. We describe recent improvements in data reduction of Ca II K
observations, and present time variations of nine parameters derived from the
profile of this spectral line
Accretion, Outflows, and Winds of Magnetized Stars
Many types of stars have strong magnetic fields that can dynamically
influence the flow of circumstellar matter. In stars with accretion disks, the
stellar magnetic field can truncate the inner disk and determine the paths that
matter can take to flow onto the star. These paths are different in stars with
different magnetospheres and periods of rotation. External field lines of the
magnetosphere may inflate and produce favorable conditions for outflows from
the disk-magnetosphere boundary. Outflows can be particularly strong in the
propeller regime, wherein a star rotates more rapidly than the inner disk.
Outflows may also form at the disk-magnetosphere boundary of slowly rotating
stars, if the magnetosphere is compressed by the accreting matter. In isolated,
strongly magnetized stars, the magnetic field can influence formation and/or
propagation of stellar wind outflows. Winds from low-mass, solar-type stars may
be either thermally or magnetically driven, while winds from massive, luminous
O and B type stars are radiatively driven. In all of these cases, the magnetic
field influences matter flow from the stars and determines many observational
properties. In this chapter we review recent studies of accretion, outflows,
and winds of magnetized stars with a focus on three main topics: (1) accretion
onto magnetized stars; (2) outflows from the disk-magnetosphere boundary; and
(3) winds from isolated massive magnetized stars. We show results obtained from
global magnetohydrodynamic simulations and, in a number of cases compare global
simulations with observations.Comment: 60 pages, 44 figure
Magnetic Field Generation in Stars
Enormous progress has been made on observing stellar magnetism in stars from
the main sequence through to compact objects. Recent data have thrown into
sharper relief the vexed question of the origin of stellar magnetic fields,
which remains one of the main unanswered questions in astrophysics. In this
chapter we review recent work in this area of research. In particular, we look
at the fossil field hypothesis which links magnetism in compact stars to
magnetism in main sequence and pre-main sequence stars and we consider why its
feasibility has now been questioned particularly in the context of highly
magnetic white dwarfs. We also review the fossil versus dynamo debate in the
context of neutron stars and the roles played by key physical processes such as
buoyancy, helicity, and superfluid turbulence,in the generation and stability
of neutron star fields.
Independent information on the internal magnetic field of neutron stars will
come from future gravitational wave detections. Thus we maybe at the dawn of a
new era of exciting discoveries in compact star magnetism driven by the opening
of a new, non-electromagnetic observational window.
We also review recent advances in the theory and computation of
magnetohydrodynamic turbulence as it applies to stellar magnetism and dynamo
theory. These advances offer insight into the action of stellar dynamos as well
as processes whichcontrol the diffusive magnetic flux transport in stars.Comment: 41 pages, 7 figures. Invited review chapter on on magnetic field
generation in stars to appear in Space Science Reviews, Springe
Magnetism in massive early-type stars
In the last five years our knowledge of magnetism in early-type stars has significantly improved because of the new gen- eration of high-resolution spectropolarimeters (ESPaDOnS@CFHT, Narval@TBL, HARPSpol@ESO). The success of the Magnetism in Massive Stars (MiMeS) Project, for example, has greatly improved our understanding of the magnetic properties of massive early-type stars; however, it was mainly focused on single stars. Summarized here is our general understanding of stellar magnetism in early-type stars and the recent findings from the MiMeS project. As recent results suggest a significant fraction of early-type stars are in binaries, this implies that the interplay between magnetic fields and binarity has yet to be investigated in any significant detail. To this end, the current analysis of the recently discovered magnetic field in the rapidly-rotating secondary star of the close, massive binary system known as Plaskett’s star – a unique system that is testing our current theories of binarity and magnetism in early-type stars, and a target for investigation in the recently accepted Binarity and Magnetic Interactions in various classes of Stars (BinaMIcS) Large Programs at CFHT and TBL – is discussed