skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: RADIUS-DEPENDENT ANGULAR MOMENTUM EVOLUTION IN LOW-MASS STARS. I

Abstract

Angular momentum evolution in low-mass stars is determined by initial conditions during star formation, stellar structure evolution, and the behavior of stellar magnetic fields. Here we show that the empirical picture of angular momentum evolution arises naturally if rotation is related to magnetic field strength instead of to magnetic flux and formulate a corrected braking law based on this. Angular momentum evolution then becomes a strong function of stellar radius, explaining the main trends observed in open clusters and field stars at a few Gyr: the steep transition in rotation at the boundary to full convection arises primarily from the large change in radius across this boundary and does not require changes in dynamo mode or field topology. Additionally, the data suggest transient core-envelope decoupling among solar-type stars and field saturation at longer periods in very low mass stars. For solar-type stars, our model is also in good agreement with the empirical Skumanich law. Finally, in further support of the theory, we show that the predicted age at which low-mass stars spin down from the saturated to unsaturated field regimes in our model corresponds remarkably well to the observed lifetime of magnetic activity in these stars.

Authors:
 [1];  [2]
  1. Institut fuer Astrophysik, Georg-August-Universitaet, Friedrich-Hund-Platz 1, 37077 Goettingen (Germany)
  2. Imperial College London, 1010 Blackett Laboratory, Prince Consort Road, London SW7 2AZ (United Kingdom)
Publication Date:
OSTI Identifier:
22011837
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 746; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; CONVECTION; MAGNETIC FIELDS; MAGNETIC FLUX; MASS; ROTATION; STAR EVOLUTION; STARS

Citation Formats

Reiners, Ansgar, and Mohanty, Subhanjoy, E-mail: Ansgar.Reiners@phys.uni-goettingen.de. RADIUS-DEPENDENT ANGULAR MOMENTUM EVOLUTION IN LOW-MASS STARS. I. United States: N. p., 2012. Web. doi:10.1088/0004-637X/746/1/43.
Reiners, Ansgar, & Mohanty, Subhanjoy, E-mail: Ansgar.Reiners@phys.uni-goettingen.de. RADIUS-DEPENDENT ANGULAR MOMENTUM EVOLUTION IN LOW-MASS STARS. I. United States. doi:10.1088/0004-637X/746/1/43.
Reiners, Ansgar, and Mohanty, Subhanjoy, E-mail: Ansgar.Reiners@phys.uni-goettingen.de. Fri . "RADIUS-DEPENDENT ANGULAR MOMENTUM EVOLUTION IN LOW-MASS STARS. I". United States. doi:10.1088/0004-637X/746/1/43.
@article{osti_22011837,
title = {RADIUS-DEPENDENT ANGULAR MOMENTUM EVOLUTION IN LOW-MASS STARS. I},
author = {Reiners, Ansgar and Mohanty, Subhanjoy, E-mail: Ansgar.Reiners@phys.uni-goettingen.de},
abstractNote = {Angular momentum evolution in low-mass stars is determined by initial conditions during star formation, stellar structure evolution, and the behavior of stellar magnetic fields. Here we show that the empirical picture of angular momentum evolution arises naturally if rotation is related to magnetic field strength instead of to magnetic flux and formulate a corrected braking law based on this. Angular momentum evolution then becomes a strong function of stellar radius, explaining the main trends observed in open clusters and field stars at a few Gyr: the steep transition in rotation at the boundary to full convection arises primarily from the large change in radius across this boundary and does not require changes in dynamo mode or field topology. Additionally, the data suggest transient core-envelope decoupling among solar-type stars and field saturation at longer periods in very low mass stars. For solar-type stars, our model is also in good agreement with the empirical Skumanich law. Finally, in further support of the theory, we show that the predicted age at which low-mass stars spin down from the saturated to unsaturated field regimes in our model corresponds remarkably well to the observed lifetime of magnetic activity in these stars.},
doi = {10.1088/0004-637X/746/1/43},
journal = {Astrophysical Journal},
number = 1,
volume = 746,
place = {United States},
year = {Fri Feb 10 00:00:00 EST 2012},
month = {Fri Feb 10 00:00:00 EST 2012}
}