The effect of extremely rapid rotation on stellar activity: The case of gliese 890

AbstractStellar activity has a particularly strong influence on planets at small orbital distances, such as close-in exoplanets. For such planets, we present two extreme cases of stellar variability, namely stellar coronal mass ejections and stellar wind, which both result in the planetary environment being variable on a timescale of billions of years. For both cases, direct interaction of the streaming plasma with the planetary atmosphere would entail servere consequences. In certain cases, however, the planetary atmosphere can be effectively shielded by a strong planetary magnetic field. The efficiency of this shielding is determined by the planetary magnetic dipole moment, which is difficult to constrain by either models or observations. We present different factors which influence the strength of the planetary magnetic dipole moment. Implications are discussed, including nonthermal atmospheric loss, atmospheric biomarkers, and planetary habitability.

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The most massive white dwarfs in the solar neighbourhood

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab767 ◽

2021 ◽

Vol 503 (4) ◽

pp. 5397-5408

Author(s):

Mukremin Kilic ◽

P Bergeron ◽

Simon Blouin ◽

A Bédard

Keyword(s):

White Dwarf ◽

White Dwarfs ◽

Transverse Velocity ◽

Maximum Mass ◽

Model Calculations ◽

Rapid Rotation ◽

Rotation Rates ◽

Binary Mergers ◽

Chandrasekhar Limit

ABSTRACT We present an analysis of the most massive white dwarf candidates in the Montreal White Dwarf Database 100 pc sample. We identify 25 objects that would be more massive than $1.3\, {\rm M}_{\odot }$ if they had pure H atmospheres and CO cores, including two outliers with unusually high photometric mass estimates near the Chandrasekhar limit. We provide follow-up spectroscopy of these two white dwarfs and show that they are indeed significantly below this limit. We expand our model calculations for CO core white dwarfs up to M = 1.334 M⊙, which corresponds to the high-density limit of our equation-of-state tables, ρ = 109 g cm−3. We find many objects close to this maximum mass of our CO core models. A significant fraction of ultramassive white dwarfs are predicted to form through binary mergers. Merger populations can reveal themselves through their kinematics, magnetism, or rapid rotation rates. We identify four outliers in transverse velocity, four likely magnetic white dwarfs (one of which is also an outlier in transverse velocity), and one with rapid rotation, indicating that at least 8 of the 25 ultramassive white dwarfs in our sample are likely merger products.

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ROSAT observations of V471 Tauri, showing that stellar activity is determined by rotation, not age

Monthly Notices of the Royal Astronomical Society ◽

10.1046/j.1365-8711.1998.01607.x ◽

1998 ◽

Vol 297 (4) ◽

pp. 1145-1150 ◽

Cited By ~ 16

Author(s):

P. J. Wheatley

Keyword(s):

Stellar Activity

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Stellar activity, differential rotation, and exoplanets

Proceedings of the International Astronomical Union ◽

10.1017/s1743921311015067 ◽

2010 ◽

Vol 6 (S273) ◽

pp. 89-95 ◽

Cited By ~ 1

Author(s):

A. F. Lanza

Keyword(s):

Time Series ◽

Differential Rotation ◽

Solar Irradiance ◽

Giant Planet ◽

Total Solar Irradiance ◽

Short Term ◽

Stellar Activity ◽

Transiting Planets ◽

Spot Model ◽

Spot Activity

AbstractThe photospheric spot activity of some of the stars with transiting planets discovered by the CoRoT space experiment is reviewed. Their out-of-transit light modulations are fitted by a spot model previously tested with the total solar irradiance variations. This approach allows us to study the longitude distribution of the spotted area and its variations versus time during the five months of a typical CoRoT time series. The migration of the spots in longitude provides a lower limit for the surface differential rotation, while the variation of the total spotted area can be used to search for short-term cycles akin the solar Rieger cycles. The possible impact of a close-in giant planet on stellar activity is also discussed.

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Origin of the Continuous Component of the Variation in the Solar and Stellar Activity Spectra

Geomagnetism and Aeronomy ◽

10.1134/s0016793221070185 ◽

2021 ◽

Vol 61 (7) ◽

pp. 911-916

Author(s):

D. D. Sokoloff ◽

P. G. Frick

Keyword(s):

Continuous Component ◽

Stellar Activity

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Investigating the Magnetospheres of Rapidly Rotating B-type Stars

Proceedings of the International Astronomical Union ◽

10.1017/s1743921317002812 ◽

2016 ◽

Vol 12 (S329) ◽

pp. 369-372

Author(s):

C. L. Fletcher ◽

V. Petit ◽

Y. Nazé ◽

G. A. Wade ◽

R. H. Townsend ◽

...

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Centrifugal Force ◽

Point Of View ◽

Closed Field ◽

Theoretical Point ◽

X Rays ◽

Rapid Rotation ◽

X Ray ◽

Surface Magnetic Field

AbstractRecent spectropolarimetric surveys of bright, hot stars have found that ~10% of OB-type stars contain strong (mostly dipolar) surface magnetic fields (~kG). The prominent paradigm describing the interaction between the stellar winds and the surface magnetic field is the magnetically confined wind shock (MCWS) model. In this model, the stellar wind plasma is forced to move along the closed field loops of the magnetic field, colliding at the magnetic equator, and creating a shock. As the shocked material cools radiatively it will emit X-rays. Therefore, X-ray spectroscopy is a key tool in detecting and characterizing the hot wind material confined by the magnetic fields of these stars. Some B-type stars are found to have very short rotational periods. The effects of the rapid rotation on the X-ray production within the magnetosphere have yet to be explored in detail. The added centrifugal force due to rapid rotation is predicted to cause faster wind outflows along the field lines, leading to higher shock temperatures and harder X-rays. However, this is not observed in all rapidly rotating magnetic B-type stars. In order to address this from a theoretical point of view, we use the X-ray Analytical Dynamical Magnetosphere (XADM) model, originally developed for slow rotators, with an implementation of new rapid rotational physics. Using X-ray spectroscopy from ESA’s XMM-Newton space telescope, we observed 5 rapidly rotating B-types stars to add to the previous list of observations. Comparing the observed X-ray luminosity and hardness ratio to that predicted by the XADM allows us to determine the role the added centrifugal force plays in the magnetospheric X-ray emission of these stars.

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