Sun as a star: Rotation rates from the Ca K-index

I review the advantages, techniques, and results of measurement of magnetic fields on cool stars in the infrared (IR). These measurements have generated several important results, including the following: the first data on the magnetic parameters of dMe and RS CVn variables; evidence for field strength confinement by photospheric gas pressure; support for the correlation between magnetic flux and rotation, with possible saturation at high rotation rates; indications of horizontal and/or vertical magnetic field structure; and evidence of spatial variations in B over a stellar surface. I discuss these results in detail, and suggest future directions for IR magnetic field research.

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An Empirical Study of the Relationship between Seasonal Precipitation and Thermodynamic Environment in Puerto Rico

Weather and Forecasting ◽

10.1175/waf-d-18-0127.1 ◽

2019 ◽

Vol 34 (2) ◽

pp. 277-288 ◽

Cited By ~ 2

Author(s):

Paul W. Miller ◽

Thomas L. Mote ◽

Craig A. Ramseyer

Keyword(s):

Puerto Rico ◽

Annual Rainfall ◽

Seasonal Precipitation ◽

Surface Precipitation ◽

Precipitation Forecasting ◽

Caribbean Islands ◽

K Index ◽

Groundwater Reserves ◽

The Tropics ◽

The Relationship

Abstract With limited groundwater reserves and few reservoirs, Caribbean islands such as Puerto Rico are largely dependent on regular rainfall to meet societal and ecological water needs. Thus, the ability to anticipate seasonal rainfall shortages, such as the 2015 drought, is particularly important, yet few reliable tools exist for this purpose. Consequently, interpolated surface precipitation observations from the Daymet archive are summarized on daily, annual, and seasonal time scales and compared to the host thermodynamic environment as characterized by the Gálvez–Davison index (GDI), a convective potential parameter designed specifically for the tropics. Complementing the Daymet precipitation totals, ≥1.1 million WSR-88D volume scans between 2002 and 2016 were analyzed for echo tops ≥ 10 000 ft (~3 km) to establish a radar-inferred precipitation activity database for Puerto Rico. The 15-yr record reveals that the GDI outperforms several midlatitude-centric thermodynamic indices, explaining roughly 25% of daily 3-km echo top (ET) activity during each of Puerto Rico’s primary seasons. In contrast, neither mean-layer CAPE, the K index, nor total totals explain more than 11% during any season. When aggregated to the seasonal level, the GDI strongly relates to 3-km ET (R2 = 0.65) and Daymet precipitation totals (R2 = 0.82) during the early rainfall season (ERS; April–July), with correlations weaker outside of this period. The 4-month ERS explains 51% (41%) of the variability to Puerto Rico’s annual rainfall during exceptionally wet (dry) years. These findings are valuable for climate downscaling studies predicting Puerto Rico’s hydroclimate in future atmospheric states, and they could potentially be adapted for operational seasonal precipitation forecasting.

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The Rotation Rates of White Dwarfs and Pulsars

The Astrophysical Journal ◽

10.1086/306153 ◽

1998 ◽

Vol 505 (1) ◽

pp. 339-343 ◽

Cited By ~ 42

Author(s):

Mario Livio ◽

J. E. Pringle

Keyword(s):

White Dwarfs ◽

Rotation Rates

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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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