On the determination of stellar rotation and differential rotation from chromospheric activity data

1985 ◽  
Vol 97 ◽  
pp. 285 ◽  
Author(s):  
R. L. Gilliland ◽  
R. Fisher
Keyword(s):  
Differential Rotation ◽  
Stellar Rotation ◽  
Activity Data ◽  
Chromospheric Activity

scholarly journals Gravity darkening in stars with surface differential rotation

2017 ◽  
Vol 606 ◽  
pp. A32 ◽  
Author(s):  
J. Zorec ◽  
M. Rieutord ◽  
F. Espinosa Lara ◽  
Y. Frémat ◽  
A. Domiciano de Souza ◽  
...  
Keyword(s):  
Differential Rotation ◽  
Effective Temperature ◽  
Rotational Velocity ◽  
Viewing Angle ◽  
Rotating Stars ◽  
Stellar Rotation ◽  
Fundamental Parameters ◽  
Effective Gravity ◽  
Unique Interpretation

Context. The interpretation of stellar apparent fundamental parameters (viewing-angle dependent) requires that they be treated consistently with the characteristics of their surface rotation law. Aims. We aim to develop a model to determine the distribution of the effective temperature and gravity, which explicitly depend on the surface differential rotation law and on the concomitant stellar external geometry. Methods. The basic assumptions in this model are: a) the external stellar layers are in radiative equilibrium; b) the emergent bolometric flux is anti-parallel with the effective gravity; c) the angular velocity in the surface obeys relations like Ω(θ) = Ωo [ 1 + αΥ(θ,k) ] where Υ(θ,k) = coskθ or sinkθ, and where (α,k) are free parameters. Results. The effective temperature varies with co-latitude θ, with amplitudes that depend on the differential-rotation law through the surface effective gravity and the gravity-darkening function (GDF). Although the derived expressions can be treated numerically, for some low integer values of k, analytical forms of the integral of characteristic curves, on which the determination of the GDF relies, are obtained. The effects of the quantities (η,α,k) (η = ratio between centrifugal and gravitational accelerations at the equator) on the determination of the Vsini parameter and on the gravity-darkening exponent are studied. Depending on the values of (η,α,k) the velocity V in the derived Vsini may strongly deviate from the equatorial rotational velocity. It is shown that the von Zeipel’s-like gravity-darkening exponent β1 depends on all parameters (η,α,k) and that its value also depends on the viewing-angle i. Hence, there no unique interpretation of this exponent determined empirically in terms of (i,α). Conclusions. We stress that the data on rotating stars should be analyzed by taking into account the rotational effects through the GDF, by assuming k = 2 as a first approximation. Instead of the classic pair (η,β1), it would be more useful to determine the quantities (η,α,i) to characterize stellar rotation.

scholarly journals Quantifying Mold Biomass on Gypsum Board: Comparison of Ergosterol and Beta-N-Acetylhexosaminidase as Mold Biomass Parameters

2003 ◽  
Vol 69 (7) ◽  
pp. 3996-3998 ◽  
Author(s):  
M. Reeslev ◽  
M. Miller ◽  
K. F. Nielsen
Keyword(s):  
Stationary Phase ◽  
Linear Correlation ◽  
Stachybotrys Chartarum ◽  
Gypsum Board ◽  
Biomass Density ◽  
Activity Data ◽  
Good Linear ◽  
Ergosterol Content ◽  
Good Linear Correlation

ABSTRACT Two mold species, Stachybotrys chartarum and Aspergillus versicolor, were inoculated onto agar overlaid with cellophane, allowing determination of a direct measurement of biomass density by weighing. Biomass density, ergosterol content, and beta-N-acetylhexosaminidase (3.2.1.52) activity were monitored from inoculation to stationary phase. Regression analysis showed a good linear correlation to biomass density for both ergosterol content and beta-N-acetylhexosaminidase activity. The same two mold species were inoculated onto wallpapered gypsum board, from which a direct biomass measurement was not possible. Growth was measured as an increase in ergosterol content and beta-N-acetylhexosaminidase activity. A good linear correlation was seen between ergosterol content and beta-N-acetylhexosaminidase activity. From the experiments performed on agar medium, conversion factors (CFs) for estimating biomass density from ergosterol content and beta-N-acetylhexosaminidase activity were determined. The CFs were used to estimate the biomass density of the molds grown on gypsum board. The biomass densities estimated from ergosterol content and beta-N-acetylhexosaminidase activity data gave similar results, showing significantly slower growth and lower stationary-phase biomass density on gypsum board than on agar.

scholarly journals Interferometric studies of rapid rotators

2010 ◽  
Vol 6 (S272) ◽  
pp. 44-55 ◽  
Author(s):  
Ming Zhao ◽  
John D. Monnier ◽  
Xiao Che
Keyword(s):  
Fundamental Property ◽  
Optical Interferometry ◽  
Rotating Stars ◽  
Stellar Rotation ◽  
Rapid Rotation ◽  
Long Baseline ◽  
Imaging Results ◽  
Basic Physics ◽  
Stellar Photosphere

AbstractStellar rotation, like stellar mass and metallicity, is a fundamental property of stars. Rapid rotation distorts the stellar photosphere and affects a star's luminosity, abundances and evolution. It is also linked to stellar wind and mass loss. The distortion of the stellar photosphere due to rapid rotation causes the stellar surface brightness and effective temperature to vary with latitude, leading to a bright pole and a dark equator - a phenomenon known as ‘Gravity Darkening’. Thanks to the development of long baseline optical interferometry in recent years, optical interferometers have resolved the elongation of rapidly rotating stars, and have even imaged a few systems for the first time, directly confirming the gravity darkening effect. In this paper, we review the recent interferometric studies of rapid rotators, particularly the imaging results from CHARA-MIRC. These sub-milliarcsecond resolution observations permit the determination of the inclination, the polar and equatorial radius and temperature, as well as the fractional rotation speed of several rapid rotators with unprecedented precision. The modeling also allows the determination of the true effective temperatures and luminosities of these stars, permitting the investigation of their true locations on the HR diagram. Discrepancies from standard models were also found in some measurements, suggesting the requirement of more sophisticated mechanisms such as non-uniform rotation in the model. These observations have demonstrated that optical interferometry is now sufficiently mature to provide valuable constraints and even model-independent images to shed light on the basic physics of stars.

scholarly journals Differential Rotation and the v sin i Parameter

2004 ◽  
Vol 215 ◽  
pp. 21-22 ◽  
Author(s):  
J. Zorec ◽  
A. Domiciano de Souza ◽  
Y. Frémat
Keyword(s):  
Kinetic Energy ◽  
Potential Energy ◽  
Line Width ◽  
Differential Rotation ◽  
Rotation Velocity ◽  
Rigid Rotation ◽  
Gravitational Potential Energy ◽  
Aspect Angle ◽  
Energy Ratios

We study the effects of a differential rotation upon the determination of the v sin i parameter. The effects are studied for several values of the ratio t = kinetic energy/gravitational potential energy, which include energy ratios higher than permitted for critical rigid rotation and using an internal conservative rotation law that allows for a latitudinal differential rotation in the stellar surface. Two effects are outstanding: when differential rotation is dependent on the stellar latitude the v sin i parameter does not necessarily correspond to the equatorial rotation velocity; the line width is a double valued function of v sin i and it is dependent on t and the aspect angle i.

Searching for the cycle period in chromospherically active stars

2019 ◽  
Vol 15 (S354) ◽  
pp. 120-122
Author(s):  
F. Villegas ◽  
R. E. Mennickent ◽  
J. Garcés
Keyword(s):  
Cycle Length ◽  
Variable Star ◽  
Line Emission ◽  
Cycle Period ◽  
Stellar Rotation ◽  
Convective Flows ◽  
Chromospheric Activity ◽  
Magnetic Cycles ◽  
First Time

AbstractThe detection and analysis of line emission of the CaII, H(396.8nm) and K(393.3nm) have confirmed the chromospheric activity of some single and binaries stars. This activity is associated to the presence of magnetic fields which in turn are produced by internal convective flows along with stellar rotation producing a long-term photometric cycle length related to the apparition and vanishing of superficial stellar spots. We present a photometric study of stars of the type RS CVn, Rotationally variable Star and BY Dra, that have shown evidence of chromospheric activity. The analysis of these measurements has allowed us to delimit periods of rotation. In addition, we have detected and measured the cycle length in some cases. It allows us to complement previous investigations and in some cases to determine for the first time the presence of a long photometric cycle, contributing to complement the link between rotation and magnetic cycles.

scholarly journals Rotation & differential rotation of the active Kepler stars

2013 ◽  
Vol 9 (S302) ◽  
pp. 216-219
Author(s):  
Timo Reinhold ◽  
Ansgar Reiners ◽  
Gibor Basri
Keyword(s):  
Temperature Dependence ◽  
Differential Rotation ◽  
Large Scatter ◽  
Stellar Rotation ◽  
Rotation Periods ◽  
Active Stars ◽  
Magnetic Braking ◽  
The Absolute ◽  
First Time ◽  
Second Period

AbstractStellar rotation is a well-known quantity for tens of thousands of stars. In contrast, differential rotation (DR) is only known for a handful of stars because DR cannot be measured directly. We present rotation periods for more than 24,000 active stars in the Kepler field. Thereof, more than 18,000 stars show a second period, which we attribute to surface differential rotation. Our rotation periods are consistent with previous measurements and the theory of magnetic braking. Our results on DR paint a rather different picture: The temperature dependence of the absolute shear δΩ is split into two groups separated around 6000 K. For the cooler stars δΩ only slightly increases with temperature, whereas stars hotter than 6000 K show large scatter. This is the first time that DR has been measured for such a large number of stars.

scholarly journals Sorption isotherms of ingredients and diets for poultry

2020 ◽  
Vol 9 (9) ◽  
pp. e828997729
Author(s):  
Carina Sordi ◽  
Fernando de Castro Tavernari ◽  
Diego Surek ◽  
Laudete Maria Sartoretto ◽  
Tiago Goulart Petrolli ◽  
...  
Keyword(s):  
Water Activity ◽  
Dry Matter ◽  
Choline Chloride ◽  
Sorption Isotherms ◽  
Vitamin Supplement ◽  
Mineral Supplement ◽  
Activity Data ◽  
Nutritional Values ◽  
Hygroscopic Behavior

This study aimed to determine sorption isotherms of ingredient and poultry diet. The samples were encapsulated in capsules and dehydrated by oven-drying in a desiccator for more than 24 hours. The samples were transferred to desiccator containing water in the base and placed in the oven, with one sample of each material being removed at incremental intervals. The sample was weighed and for determination of water activity and for dry matter. The moisture and water activity data were evaluated by eight mathematical models. The GAB mathematical model fitted the experimental data to constitute the isotherm for each material. Type II sorption isotherms were found, except for BHT: demonstrated values that did not fit the isotherm determination. The hygroscopic behavior of the ingredients in ascending order were: L- threonine, limestone, BHT, DL- methionine, L-valine, L- tryptophan, phosphate, kaolin, vitamin supplement, salt, mycotoxin deactivator, pelleted rooster diet, mash rooster diet, mash layer diet, pelleted layer diet, corn, bacitracin zinc, vitamin mineral supplement, phytase, rice bran, wheat bran, mineral supplement, soybean meal, coccidiostat, L- Lysine HCl and choline chloride. Ingredients and diets have different hygroscopic behavior: can lead to deterioration and low accuracy in nutritional values of diet, since formulation is based on as-is fed basis.

scholarly journals Analytical Quality Assessment, Microbial Activity and Shelf Life Determination of Commercial Butter Samples in India

2019 ◽  
pp. 275-278
Author(s):  
Parankusham Chandana Narayan ◽  
Barika Anam ◽  
Khairunnisa Amreen
Keyword(s):  
Quality Assessment ◽  
Microbial Activity ◽  
Room Temperature ◽  
Research Work ◽  
Storage Period ◽  
Project Based Learning ◽  
Activity Data ◽  
Different Temperatures ◽  
Master Level

This study aimed to train the master level students for carrying out the research work as a part of minor research project based learning. In this the quality assessment of butter samples obtained from the local super market in India was performed. Thirty different butter samples (commercially available) were analyzed. Quality assessment was carried out by calculation of the Reichert-Meissl (RM) value. Microbiological activity was also tested by storing the samples in two different temperatures: room temperature and refrigerated conditions. Based on the RM value and microbial activity data taken for a period of six consecutive months, self life of the butter samples were calculated to estimate the appropriate storage period and conditions suitable for consumption.

scholarly journals Stellar Chromospheric Variability

Universe ◽  
2021 ◽  
Vol 7 (11) ◽  
pp. 440
Author(s):  
Richard de de Grijs ◽  
Devika Kamath
Keyword(s):  
Large Scale ◽  
Binary Systems ◽  
Magnetic Activity ◽  
Close Binary ◽  
Physical Parameters ◽  
Stellar Rotation ◽  
Chromospheric Activity ◽  
Recent Developments ◽  
Hα Emission ◽  
Activity Cycles

Cool stars with convective envelopes of spectral types F and later tend to exhibit magnetic activity throughout their atmospheres. The presence of strong and variable magnetic fields is evidenced by photospheric starspots, chromospheric plages and coronal flares, as well as by strong Ca ii H+K and Hα emission, combined with the presence of ultraviolet resonance lines. We review the drivers of stellar chromospheric activity and the resulting physical parameters implied by the observational diagnostics. At a basic level, we explore the importance of stellar dynamos and their activity cycles for a range of stellar types across the Hertzsprung–Russell diagram. We focus, in particular, on recent developments pertaining to stellar rotation properties, including the putative Vaughan–Preston gap. We also pay specific attention to magnetic variability associated with close binary systems, including RS Canum Venaticorum, BY Draconis, W Ursae Majoris and Algol binaries. At the present time, large-scale photometric and spectroscopic surveys are becoming generally available, thus leading to a resurgence of research into chromospheric activity. This opens up promising prospects to gain a much improved understanding of chromospheric physics and its wide-ranging impact.

scholarly journals Angular Velocity Distribution in Rotating Massive Stars

1967 ◽  
Vol 20 (6) ◽  
pp. 651
Author(s):  
MPC Legg
Keyword(s):  
Angular Velocity ◽  
Velocity Distribution ◽  
Radiation Pressure ◽  
Electron Scattering ◽  
Differential Rotation ◽  
Meridional Circulation ◽  
Massive Stars ◽  
Effects Of Radiation ◽  
Uniform Composition

The angular velocity distribution in rotating massive stars with uniform composition and opacity due to electron scattering is calculated on the assumption that meridional circulation is neglible. The effects of radiation pressure are taken into account in the determination of the differential rotation and the angularvelocity is assumed to be ndependent of latitude.

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