104 research outputs found
Scaling and Evolution of Stellar Magnetic Activity
No full textAbstract Magnetic activity is a ubiquitous feature of stars with convective outer layers, with implications from stellar evolution to planetary atmospheres. Investigating the mechanisms responsible for the observed stellar activity signals from days to billions of years is important in deepening our understanding of the spatial configurations and temporal patterns of stellar dynamos, including that of the Sun. In this paper, we focus on three problems and their possible solutions. We start with direct field measurements and show how they probe the dependence of magnetic flux and its density on stellar properties and activity indicators. Next, we review the current state-of-the-art in physics-based models of photospheric activity patterns and their variation from rotational to activity-cycle timescales. We then outline the current state of understanding in the long-term evolution of stellar dynamos, first by using chromospheric and coronal activity diagnostics, then with model-based implications on magnetic braking, which is the key mechanism by which stars spin down and become inactive as they age. We conclude by discussing possible directions to improve the modeling and analysis of stellar magnetic fields
Stellar Stalling: the view from asteroseismology
No full textAsteroseismology, the study of intrinsic oscillations in stars, can reveal fundamental properties of cool stars critical in our understanding of stellar rotational evolution. Through space missions such as Kepler and TESS, asteroseismology has seen a surge of new data and research in the past decade. These data have contributed to important results in the field of stellar braking particularly for F, G and K stars, thanks to estimates of stellar age for rotating field stars, and the measurement of stellar rotation through oscillation spectra as important comparisons for estimates from star-spots.
In this talk, I will provide an introduction to asteroseismology how it can provide important results for your research. This will be followed by a breakdown of how asteroseismologists have used these techniques to establish the presence of weakened magnetic braking on the main sequence using asteroseismic data, and what we should be looking forward to from these techniques with the TESS mission
Further Evidence of Modified Spin-down in Sun-like Stars: Pileups in the Temperature-Period Distribution
No full textWe combine stellar surface rotation periods determined from NASA's Kepler
mission with spectroscopic temperatures to demonstrate the existence of pileups
at the long-period and short-period edges of the temperature-period
distribution for main-sequence stars with temperatures exceeding K.
The long-period pileup is well-described by a curve of constant Rossby number,
with a critical value of . The long-period
pileup was predicted by van Saders et al. (2019) as a consequence of weakened
magnetic braking, in which wind-driven angular momentum losses cease once stars
reach a critical Rossby number. Stars in the long-period pileup are found to
have a wide range of ages (Gyr), meaning that, along the pileup,
rotation period is strongly predictive of a star's surface temperature but
weakly predictive of its age. The short-period pileup, which is also
well-described by a curve of constant Rossby number, is not a prediction of the
weakened magnetic braking hypothesis but may instead be related to a phase of
slowed surface spin-down due to core-envelope coupling. The same mechanism was
proposed by Curtis et al. (2020) to explain the overlapping rotation sequences
of low-mass members of differently aged open clusters. The relative dearth of
stars with intermediate rotation periods between the short- and long-period
pileups is also well-described by a curve of constant Rossby number, which
aligns with the period gap initially discovered by McQuillan et al. (2013a) in
M-type stars. These observations provide further support for the hypothesis
that the period gap is due to stellar astrophysics, rather than a non-uniform
star-formation history in the Kepler field.Comment: Accepted to ApJ. 29 pages, 21 figures. The data and code required to
reproduce this work is available at
http://github.com/trevordavid/rossby-ridg
The Structure and Evolution of Stars: Introductory Remarks
No full textIn this introductory chapter of the Special Issue entitled ‘The Structure and Evolution of Stars’, we highlight the recent major progress made in our understanding of the physics that governs stellar interiors. In so doing, we combine insight from observations, 1D evolutionary modelling and 2D + 3D rotating (magneto)hydrodynamical simulations. Therefore, a complete and compelling picture of the necessary ingredients in state-of-the-art stellar structure theory and areas in which improvementsstillneedtobemadearecontextualised. Additionally, the over-arching perspective linking all the themes of subsequent chapters is presented
MOA-2010-BLG-311: A planetary candidate below the threshold of reliable detection
No full textpeer reviewedWe analyze MOA-2010-BLG-311, a high magnification (A_max>600) microlensing event with complete data coverage over the peak, making it very sensitive to planetary signals. We fit this event with both a point lens and a 2-body lens model and find that the 2-body lens model is a better fit but with only Delta chi^2~140. The preferred mass ratio between the lens star and its companion is $q=10^(-3.7+/-0.1), placing the candidate companion in the planetary regime. Despite the formal significance of the planet, we show that because of systematics in the data the evidence for a planetary companion to the lens is too tenuous to claim a secure detection. When combined with analyses of other high-magnification events, this event helps empirically define the threshold for reliable planet detection in high-magnification events, which remains an open question
GOODS 850-5 -- A z>4 Galaxy Doscovered in the Submillimeter?
No full text[[sponsorship]]天文及天文物理研究所[[note]]已出版;[SCI];有審查制度;具代表性[[note]]http://gateway.isiknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=Drexel&SrcApp=hagerty_opac&KeyRecord=0004-637X&DestApp=JCR&RQ=IF_CAT_BOXPLO
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