Biological Role of Vitamin K—With Particular Emphasis on Cardiovascular and Renal Aspects

Stępień, Anna; Koziarska-Rościszewska, Małgorzata; Rysz, Jacek; Stępień, Mariusz

doi:10.3390/nu14020262

Cited by 27 publications

(17 citation statements)

References 64 publications

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“…Abt & Morrell 1995). As proposed by Stȩpień (2000), the slow rotation of Ap/Bp stars can be explained by angular momentum loss at the pre-main sequence phase, taking into account accretion of matter along the magnetic field lines, the stellar field-disc interaction and a magnetised stellar wind.…”

Section: Introductionmentioning

confidence: 87%

“…As discussed earlier, magnetic A and B type stars on the main sequence rotate significantly more slowly than non-magnetic stars of the same spectral type. This suggests that the magnetic field plays an important role in the shedding of rotational angular momentum in the magnetic stars, probably at the pre-main sequence stage (e.g., see Stȩpień 2000). Alecian et al (in prep) explore this aspect in some detail, first by using their measured v sin is, and more accurately by using their directly-inferred rotational periods and radii.…”

Section: Activity Magnetospheric Accretion Chemical Peculiarity and R...mentioning

confidence: 99%

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T Tauri and Herbig Ae/Be stars

Bastien¹,

Kolokolova²,

Hough³

et al. 2015

Polarimetry of Stars and Planetary Systems

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Observations of magnetic fields of stars at the pre-main sequence phase can provide important new insights into the complex physics of the late stages of star formation. This is especially true at intermediate stellar masses, where magnetic fields are strong and globally organised, and therefore most amenable to direct study. Recent circularly-polarised spectroscopic observations of pre-main sequence Herbig Ae/Be stars have revealed the presence of organised magnetic fields in the photospheres of a small fraction of these objects. To date, 9 magnetic HAeBe stars have been detected, and those detections confirmed by repeated observations. The morphology and variability of their Stokes V signatures indicates that their magnetic fields have important dipole components of ∼kG strength, and that the dipole is stable on timescales ofat least years. These magnetic stars exhibit a large range of stellar mass, from ∼ 2 − 13 M ⊙ , and diverse rotational properties, with v sin i from a few km/s to ∼ 200 km/s. Most magnetic HAeBe stars show approximately solar abundances; they clearly do not generally exhibit the strong and systematic peculiarities of the magnetic main sequence A and B type stars (the Ap/Bp stars). The observed fractional bulk incidence of magnetic HAeBe stars is about 7%, a value compatible with the incidence of magnetic intermediate-mass stars on the main sequence. This low incidence is at odds with formation scenarios generally involving magneticallymediated accretion. The similarily between the magnetic properties of the premain sequence and main sequence intermediate-mass stars appears compatible with the hypothesis of a fossil origin of magnetism in these objects.

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Section: Introductionmentioning

confidence: 87%

Section: Activity Magnetospheric Accretion Chemical Peculiarity and R...mentioning

confidence: 99%

T Tauri and Herbig Ae/Be stars

Bastien¹,

Kolokolova²,

Hough³

et al. 2015

Polarimetry of Stars and Planetary Systems

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“…The fossil field hypothesis relies on the long-term stability of magnetic fields and assumes that these fields were generated during the star formation process or at the latest during the pre-main sequence evolution of the star (Donati & Landstreet 2009). In lower-mass Ap and Herbig Ae/Be stars, pre-main sequence magnetic braking is indeed evidenced (Stȩpień 2000;Alecian et al 2013). This could also be the case for O and B stars (where the pre-main sequence phase and the magnetic fields are not practically observable due to these stars being embedded in dust).…”

Section: Rotational Evolution Of Known Magnetic B-type Starsmentioning

confidence: 99%

The effects of surface fossil magnetic fields on massive star evolution – II. Implementation of magnetic braking in mesa and implications for the evolution of surface rotation in OB stars

Keszthelyi

Meynet

Shultz

et al. 2020

Monthly Notices of the Royal Astronomical Society

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The time evolution of angular momentum and surface rotation of massive stars is strongly influenced by fossil magnetic fields via magnetic braking. We present a new module containing a simple, comprehensive implementation of such a field at the surface of a massive star within the Modules for Experiments in Stellar Astrophysics (mesa) software instrument. We test two limiting scenarios for magnetic braking: distributing the angular momentum loss throughout the star in the first case, and restricting the angular momentum loss to a surface reservoir in the second case. We perform a systematic investigation of the rotational evolution using a grid of OB star models with surface magnetic fields (M = 5 − 60 M , Ω/Ω crit = 0.2 − 1.0, B p = 1 − 20 kG). We then employ a representative grid of B-type star models (M = 5, 10, 15 M , Ω/Ω crit = 0.2, 0.5, 0.8, B p = 1, 3, 10, 30 kG) to compare to the results of a recent selfconsistent analysis of the sample of known magnetic B-type stars. We infer that magnetic massive stars arrive at the zero age main sequence with a range of rotation rates, rather than with one common value. In particular, some stars are required to have close-to-critical rotation at the ZAMS. However, magnetic braking yields surface rotation rates converging to a common low value, making it difficult to infer the initial rotation rates of evolved, slowly-rotating stars.

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“…The model atmospheres feature a photosphere in radiative + convective equilibrium for the stellar parameters using the current production version of PHOENIX (version 18.05). Consequently, none of the Stepien (1994).…”

Section: Phoenix Model Atmospheresmentioning

confidence: 99%

EMISSA -- Exploring Millimeter Indicators of Solar-Stellar Activity I. The Initial mm-cm Main Sequence Star Sample

Mohan,

Wedemeyer,

Pandit

et al. 2021

Preprint

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Context. Due to their wide wavelength coverage across the millimeter to centimeter (mm -cm) range and their increased sensitivity, modern interferometric arrays facilitate observations of the thermal and non-thermal radiation that is emitted from different layers in the outer atmospheres of stars. Aims. We study the spectral energy distribution (S obs (ν)) of main-sequence stars based on archival observations in the mm -cm range with the aim to study their atmospheric stratification as a function of stellar type. Methods. The main-sequence stars with significant detection in mm bands were identified in the ALMA Science Archive. These data were then complemented with spectral flux data in the extreme ultraviolet (EUV) to cm range as compiled from various catalogues and observatory archives. We compared the resultant S obs (ν) of each star with a photospheric emission model (S mod (ν)) calculated with the PHOENIX code. The departures of S obs (ν) from S mod (ν) were quantified in terms of a spectral flux excess parameter (∆S /S mod ) and studied as a function of stellar type.Results. The initial sample consists of 12 main-sequence stars across a broad range of spectral types from A1 to M3.5 and the Sunas-a-star as reference. The stars with T eff = 3000 − 7000 K (F -M type) showed a systematically higher S obs (ν) than S mod (ν) in the mm -cm range. Their ∆S /S mod exhibits a monotonic rise with decreasing frequency. The steepness of this rise is higher for cooler stars in the T eff = 3000 -7000 K range, although the single fully convective star (T eff ∼ 3000 K) in the sample deviates from this trend. Meanwhile, S obs (ν) of the A-type stars agrees with S mod (ν) within errors. Conclusions. The systematically high ∆S /S mod in F -M stars indicates hotter upper atmospheric layers, that is, a chromosphere and corona, in these stars like for the Sun. The mm -cm ∆S /S mod spectrum offers a way to estimate the efficiency of the heating mechanisms across various outer atmospheric layers in main-sequence stars, and thereby to understand their structure and activity. We emphasise the need for dedicated surveys of main-sequence stars in the mm -cm range.

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Biological Role of Vitamin K—With Particular Emphasis on Cardiovascular and Renal Aspects

Cited by 27 publications

References 64 publications

T Tauri and Herbig Ae/Be stars

T Tauri and Herbig Ae/Be stars

The effects of surface fossil magnetic fields on massive star evolution – II. Implementation of magnetic braking in mesa and implications for the evolution of surface rotation in OB stars

EMISSA -- Exploring Millimeter Indicators of Solar-Stellar Activity I. The Initial mm-cm Main Sequence Star Sample

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