EVIDENCE FOR MAGNETIC FLUX SATURATION IN RAPIDLY ROTATING M STARS

By A. Reiners, G. Basri, M. Browning. 2008

158 citations recorded by the source corpus.

We present magnetic flux measurements in seven rapidly rotating M dwarfs. Our sample stars have X-ray and Hα emission indicative of saturated emission, i.e., emission at a high level, independent of rotation rate. Our measurements are made using near-infrared FeH molecular spectra observed with the High Resolution Echelle Spectrometer at Keck. Because of their large convective overturn times, the rotation velocity of M stars with small Rossby numbers is relatively slow and does not hamper the measurement of Zeeman splitting. The Rossby numbers of our sample stars are as small as 0.01. All our sample stars exhibit magnetic flux of kG strength. We find that the magnetic flux saturates in the same regime as saturation of coronal and chromospheric emission, at a critical Rossby number of around 0.1. The filling factors of both field and emission are near unity by then. We conclude that the strength of surface magnetic fields remains independent of rotation rate below that; making the Rossby number yet smaller by a factor of 10 has little effect. These saturated M-star dynamos generate an integrated magnetic flux of roughly 3 kG, with a scatter of about 1 kG. The relation between emission and flux also has substantial scatter.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/6d0308f4ac2445d9e1ba0e94254d8fd540eaf532

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

1. A. Reiners
2. M. Browning
3. G. Basri
4. D. Charbonneau
5. A. Brun
6. J. Bouvier
7. Mark S. Miesch
8. J. Toomre

Citations in the corpus

• THE Hα EMISSION OF NEARBY M DWARFS AND ITS RELATION TO STELLAR ROTATION (2016, background): “…seen in a wide variety of tracers of magnetic activity, including xray flux (Stauffer et al. 1994; James et al. 2000; Wright et al. 2011), Ca H&K, (Browning et al. 2010), Hα emission (Delfosse et al. 1998; Mohanty & Basri 2003; Reiners et al. 2012), and global magnetic flux (Reiners et al. 2009).”
• Observations of Cool-Star Magnetic Fields (2012, methodology): “However, in contrast to pre-main sequence stars, and in contrast to older brown dwarfs, none of the young brown dwarfs investigated by Reiners et al. (2009b) exhibited a field above the detection threshold that in all cases lay below the fields typically found among the other groups.”
• The FIP and Inverse FIP Effects in Solar and Stellar Coronae (2015, background): “While the magnetic fields measured in these stars are similar to those in the Sun, the filling factor is higher (e.g., Donati and Landstreet, 2009; Reiners et al., 2009), allowing less volume for expansion with increasing altitude.”
• Large-scale magnetic topologies of late M dwarfs★: Magnetic topologies of late M dwarfs (2010, methodology): “We use v sin i = 5.0 km s−1 (Reiners et al. 2009) which accounts for Zeeman broadening and results in better agreement with our Stokes I and V LSD profiles than the previous value of v sin i = 7.7 kms−1 inferred from correlation profiles (Delfosse et al. 1998).”
• The Transit Light Source Effect: False Spectral Features and Incorrect Densities for M-dwarf Transiting Planets (2017, background): “…there is direct observational evidence for widespread, multi-kilogauss magnetic fields outside of spots in active M dwarfs (i.e., dMe stars) at high filling factors in excess of 50% based on the analysis of magnetically sensitive photospheric features (Saar & Linsky 1985; Reiners et al. 2009).”
• THE MASS-DEPENDENCE OF ANGULAR MOMENTUM EVOLUTION IN SUN-LIKE STARS (2014, background): “Observations of various indicators of magnetic activity (Noyes et al. 1984a; Reiners et al. 2009; Pizzolato et al. 2003; Mamajek & Hillenbrand 2008; Wright et al. 2011; Vidotto et al. 2014), as well as theoretical models for magnetic field generation (Durney & Latour 1978; Noyes et al. 1984b;…”
• THE STELLAR-ACTIVITY–ROTATION RELATIONSHIP AND THE EVOLUTION OF STELLAR DYNAMOS (2011, background): “…dynamo has been argued by some to suggest that coronal saturation is caused by saturation of the dynamo itself (e.g. Gilman 1983; Vilhu & Walter 1987), a theory supported by recent observations of magnetic flux saturation in rapidly rotating M dwarfs at Rossby numbers of ∼0.1 (Reiners et al. 2009).”
• A BCool magnetic snapshot survey of solar-type stars (2013, background): “Observations of Stokes I and V have shown that typical values for the ratio between the full average field (from Stokes I) and the large scale field (Stokes V) are on the order of 10% or lower (Reiners 2012; Reiners et al. 2009).”
• PERSISTENT MAGNETIC WREATHS IN A RAPIDLY ROTATING SUN (2010, result): “Similar correspondence is observed between rotation rate and estimates of the unsigned surface magnetic flux (Saar 1996, 2001; Reiners et al. 2009).”
• MAGNETIC BRAKING FORMULATION FOR SUN-LIKE STARS: DEPENDENCE ON DIPOLE FIELD STRENGTH AND ROTATION RATE (2012, background): “…2010; Mamajek & Hillenbrand 2008; Meibom et al. 2011; Epstein & Pinsonneault 2012); and the correlation of stellar activity with rotation, as well as the “saturation” of this activity in fast rotators (e.g., Saar & Brandenburg 1999; Pizzolato et al. 2003; Reiners et al. 2009; Wright et al. 2011).”
• TESTING A PREDICTIVE THEORETICAL MODEL FOR THE MASS LOSS RATES OF COOL STARS (2011, methodology): “We did not use the M dwarf data presented by Reiners et al. (2009) because these stars all tended to sit in the saturated region of Figure 7 (i.e., Ro/ ⊙ < 0.1), and thus do not contribute to improving our knowledge of the rotation dependence off∗.”
• A VOLUME-LIMITED SAMPLE OF 63 M7–M9.5 DWARFS. II. ACTIVITY, MAGNETISM, AND THE FADE OF THE ROTATION-DOMINATED DYNAMO (2009, methodology): “The Connection between Rotation, Activity, and Magnetic Flux Solar-type stars as well as early-M stars show a well-documented relation between rotation and magnetic activity (e.g., Pizzolato et al. 2003; Reiners 2007; Reiners et al. 2009a).”
• Improved angular momentum evolution model for solar-like stars (2013, unknown): “0.1 − 0.13 (see Reiners et al. 2009, Fig.”
• RADIUS-DEPENDENT ANGULAR MOMENTUM EVOLUTION IN LOW-MASS STARS. I (2011, background): “(2) This form of the field scaling is motivated by theory as well as observations of sun-like stars and M stars (Reiners et al. 2009).”