6,960 research outputs found
The Effect of Combined Magnetic Geometries on Thermally Driven Winds I: Interaction of Dipolar and Quadrupolar Fields
Cool stars with outer convective envelopes are observed to have magnetic
fields with a variety of geometries, which on large scales are dominated by a
combination of the lowest order fields such as the dipole, quadrupole and
octupole modes. Magnetised stellar wind outflows are primarily responsible for
the loss of angular momentum from these objects during the main sequence.
Previous works have shown the reduced effectiveness of the stellar wind braking
mechanism with increasingly complex, but singular, magnetic field geometries.
In this paper, we quantify the impact of mixed dipolar and quadrupolar fields
on the spin-down torque using 50 MHD simulations with mixed field, along with
10 of each pure geometries. The simulated winds include a wide range of
magnetic field strength and reside in the slow-rotator regime. We find that the
stellar wind braking torque from our combined geometry cases are well described
by a broken power law behaviour, where the torque scaling with field strength
can be predicted by the dipole component alone or the quadrupolar scaling
utilising the total field strength. The simulation results can be scaled and
apply to all main-sequence cool stars. For Solar parameters, the lowest order
component of the field (dipole in this paper) is the most significant in
determining the angular momentum loss.Comment: 15 pages + 9 figures (main), 3 pages + 1 figure (appendix), accepted
for publication to Ap
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Digital Systems Teaching and Research (DSTR) Robot: A Flexible Platform for Education and Applied Research
The DSTR (pronounced “Disaster”) robot has a strong history of being adaptable to different user’s needs, and there are many opportunities ahead that indicate that the sky, quite literally, is not the limit for this robust platform. This paper provides a historical perspective on the development of the DSTR robot as a collaborative design developed by the Mobile Integrated Solutions Laboratory (MISL) at Texas A&M University and ASEP 4X4 Inc. Texas Instruments has been a major partner in the integration of the control electronics, and Texas Space Technology Applications and Research (T STAR) LLC has played a significant role in the propagation of the DSTR robot as an adaptable applied research/education/STEM outreach platform. The paper will present examples of the strong industry-academic relationships that allow the DSTR robot to be utilized in a multitude of experiential learning environments. In addition to a number of STEM outreach activities, the DSTR robots are being used in the Introduction to Engineering course at Blinn College and in the Freshman Engineering curriculum at Texas A&M University. DSTRs have also been selected by NASA scientists as a low-cost lunar sample collector. The paper will also discuss the newly developed DSTR-E (DSTR Engineering) unit which requires students to perform several engineering tasks during the build process. The paper will also include the lessons learned from initial design through its transfer to the private sector for commercialization and future plans.Cockrell School of Engineerin
The Effect of Magnetic Variability on Stellar Angular Momentum Loss II: The Sun, 61 Cygni A, Eridani, Bootis A and Bootis A
The magnetic fields of low-mass stars are observed to be variable on decadal
timescales, ranging in behaviour from cyclic to stochastic. The changing
strength and geometry of the magnetic field should modify the efficiency of
angular momentum loss by stellar winds, but this has not been well quantified.
In Finley et al. (2018) we investigated the variability of the Sun, and
calculated the time-varying angular momentum loss rate in the solar wind. In
this work, we focus on four low-mass stars that have all had their surface
magnetic fields mapped for multiple epochs. Using mass loss rates determined
from astrospheric Lyman- absorption, in conjunction with scaling
relations from the MHD simulations of Finley & Matt (2018), we calculate the
torque applied to each star by their magnetised stellar winds. The variability
of the braking torque can be significant. For example, the largest torque for
Eri is twice its decadal averaged value. This variation is
comparable to that observed in the solar wind, when sparsely sampled. On
average, the torques in our sample range from 0.5-1.5 times their average
value. We compare these results to the torques of Matt et al. (2015), which use
observed stellar rotation rates to infer the long-time averaged torque on
stars. We find that our stellar wind torques are systematically lower than the
long-time average values, by a factor of ~3-30. Stellar wind variability
appears unable to resolve this discrepancy, implying that there remain some
problems with observed wind parameters, stellar wind models, or the long-term
evolution models, which have yet to be understood.Comment: 15 pages + 8 figures, accepted for publication to Ap
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