scholarly journals The evolution of ‘the moment of inertia’ of stars

2008 ◽  
Vol 4 (S252) ◽  
pp. 117-118 ◽  
Author(s):  
Y.-C. Kim ◽  
S. Barnes
Keyword(s):  
Stellar Evolution ◽  
Convection Zone ◽  
Open Cluster ◽  
Rotation Period ◽  
Stellar Mass ◽  
Turnover Time ◽  
Moment Of Inertia ◽  
The Core ◽  
Rotation Periods ◽  
The Moment

AbstractObservations of the rotation periods of cool open cluster stars display a distinctive dichotomy when plotted against stellar mass/color. Other measures of stellar activity are also known to be dependent on stellar mass and structure, especially the onset and characteristics of convection zones. One proposal for understanding the observed rotation period dichotomy suggested dependencies on the moment of inertia of either the whole star or that of only the outer convection zone (Barnes 2003).The moment of inertia of stars with the mass between 0.1Msun and 3.0Msun have been calculated using a version of Yale Stellar evolution code (aka YREC). Each star has been evolved from stellar birthline to the onset of the core He burning. For easy comparison to observations, we have calculated the isochrones of these quantities as well as the convective turnover time, of interest to the activity community.

scholarly journals NGTS clusters survey – I. Rotation in the young benchmark open cluster Blanco 1

2020 ◽  
Vol 492 (1) ◽  
pp. 1008-1024 ◽  
Author(s):  
Edward Gillen ◽  
Joshua T Briegal ◽  
Simon T Hodgkin ◽  
Daniel Foreman-Mackey ◽  
Floor Van Leeuwen ◽  
...  
Keyword(s):  
Angular Momentum ◽  
Open Cluster ◽  
Rotation Period ◽  
High Mass ◽  
Single Star ◽  
Multiple Systems ◽  
Rotation Periods ◽  
M Stars ◽  
Photometric Monitoring ◽  
Rotation Sequence

ABSTRACT We determine rotation periods for 127 stars in the ∼115-Myr-old Blanco 1 open cluster using ∼200 d of photometric monitoring with the Next Generation Transit Survey. These stars span F5–M3 spectral types (1.2 M⊙ ≳ M ≳ 0.3 M⊙) and increase the number of known rotation periods in Blanco 1 by a factor of four. We determine rotation periods using three methods: Gaussian process (GP) regression, generalized autocorrelation function (G-ACF), and Lomb–Scargle (LS) periodogram, and find that the GP and G-ACF methods are more applicable to evolving spot modulation patterns. Between mid-F and mid-K spectral types, single stars follow a well-defined rotation sequence from ∼2 to 10 d, whereas stars in photometric multiple systems typically rotate faster. This may suggest that the presence of a moderate-to-high mass ratio companion inhibits angular momentum loss mechanisms during the early pre-main sequence, and this signature has not been erased at ∼100 Myr. The majority of mid-F to mid-K stars display evolving modulation patterns, whereas most M stars show stable modulation signals. This morphological change coincides with the shift from a well-defined rotation sequence (mid-F to mid-K stars) to a broad rotation period distribution (late-K and M stars). Finally, we compare our rotation results for Blanco 1 to the similarly aged Pleiades: the single-star populations in both clusters possess consistent rotation period distributions, which suggests that the angular momentum evolution of stars follows a well-defined pathway that is, at least for mid-F to mid-K stars, strongly imprinted by ∼100 Myr.

scholarly journals Revisiting the connection between magnetic activity, rotation period, and convective turnover time for main-sequence stars

2018 ◽  
Vol 618 ◽  
pp. A48 ◽  
Author(s):  
M. Mittag ◽  
J. H. M. M. Schmitt ◽  
K.-P. Schröder
Keyword(s):  
Main Sequence ◽  
Rotation Period ◽  
Magnetic Activity ◽  
Turnover Time ◽  
Rossby Number ◽  
Stellar Rotation ◽  
Main Sequence Stars ◽  
Rotation Periods ◽  
Period Distribution ◽  
Cool Stars

The connection between stellar rotation, stellar activity, and convective turnover time is revisited with a focus on the sole contribution of magnetic activity to the Ca II H&K emission, the so-called excess flux, and its dimensionless indicator R+HK in relation to other stellar parameters and activity indicators. Our study is based on a sample of 169 main-sequence stars with directly measured Mount Wilson S-indices and rotation periods. The R+HK values are derived from the respective S-indices and related to the rotation periods in various B–V-colour intervals. First, we show that stars with vanishing magnetic activity, i.e. stars whose excess flux index R+HK approaches zero, have a well-defined, colour-dependent rotation period distribution; we also show that this rotation period distribution applies to large samples of cool stars for which rotation periods have recently become available. Second, we use empirical arguments to equate this rotation period distribution with the global convective turnover time, which is an approach that allows us to obtain clear relations between the magnetic activity related excess flux index R+HK, rotation periods, and Rossby numbers. Third, we show that the activity versus Rossby number relations are very similar in the different activity indicators. As a consequence of our study, we emphasize that our Rossby number based on the global convective turnover time approaches but does not exceed unity even for entirely inactive stars. Furthermore, the rotation-activity relations might be universal for different activity indicators once the proper scalings are used.

scholarly journals ON THE MAXIMUM MASS OF GENERAL RELATIVISTIC UNIFORMLY ROTATING WHITE DWARFS

2011 ◽  
Vol 20 (supp01) ◽  
pp. 136-140 ◽  
Author(s):  
KUANTAY BOSHKAYEV ◽  
JORGE RUEDA ◽  
REMO RUFFINI
Keyword(s):  
General Relativity ◽  
Quadrupole Moment ◽  
White Dwarfs ◽  
Rotation Period ◽  
Moment Of Inertia ◽  
Einstein Equations ◽  
Central Density ◽  
Maximum Mass ◽  
General Relativistic ◽  
The Moment

The properties of uniformly rotating white dwarfs are analyzed within the framework of general relativity. Hartle's formalism is applied to construct self-consistently the internal and external solutions to the Einstein equations. The mass, the radius, the moment of inertia and quadrupole moment of rotating white dwarfs have been calculated as a function of both the central density and rotation period of the star. The maximum mass of rotating white dwarfs for stable configurations has been obtained.

scholarly journals K2 observations of the pulsating subdwarf B stars UY Sex and V1405 Ori

2020 ◽  
Vol 492 (4) ◽  
pp. 5202-5217
Author(s):  
M D Reed ◽  
M Yeager ◽  
J Vos ◽  
J H Telting ◽  
R H Østensen ◽  
...  
Keyword(s):  
Rotation Period ◽  
B Stars ◽  
Subdwarf B Stars ◽  
Fundamental Properties ◽  
The Core ◽  
Rotation Periods ◽  
Short Period ◽  
Marginal Detection

ABSTRACT We processed and analysed K2 observations of the pulsating subdwarf-B (sdBV) stars UY Sex and V1405 Ori. We detect 97 p-mode pulsations in UY Sex while we discover V1405 Ori to be a rare rich hybrid pulsator with over 100 p-mode pulsations and 19 g-mode pulsations. We detect frequency multiplets, which we use to identify pulsation modes as well as determine rotation periods. For UY Sex, we find a rotation period of the envelope of 24.6 ± 3.5 d and for V1405 Ori, we find a rotation period of 0.555 ± 0.029 d for the p modes and a marginal detection of 4.2 ± 0.4 d for the g modes. We discover that V1405 Ori is unique among sdBV stars observed to date. It is a rich hybrid pulsator, allowing us to simultaneously probe the envelope and interior; its frequency multiplets indicate V1405 Ori to be rotating differentially with the core rotating more slowly than the envelope, and it is also in a short-period binary (0.398 d) with an envelope that is nearly but not quite tidally locked. For both stars, we have obtained spectroscopic follow-up observations and examine combining them with Gaia parallaxes and archival photometry to determine fundamental properties. Our derived masses are inconsistent with spectroscopy and previous determinations and indicate problems with the methodology.

scholarly journals Rotation periods for cool stars in the open cluster Ruprecht 147 (NGC 6774)

2020 ◽  
Vol 644 ◽  
pp. A16
Author(s):  
D. Gruner ◽  
S. A. Barnes
Keyword(s):  
Open Cluster ◽  
Rotation Period ◽  
Principal Component ◽  
Mass Region ◽  
Open Clusters ◽  
Light Curves ◽  
Rotating Stars ◽  
Rotation Periods ◽  
Periodicity Analysis ◽  
Cool Stars

Context. Gyrochronology allows the derivation of ages for cool main sequence stars based on their observed rotation periods and masses, or a suitable proxy thereof. It is increasingly well-explored for FGK stars, but requires further measurements for older ages and K – M-type stars. Aims. We study the 2.7 Gyr-old open cluster Ruprecht 147 to compare it with the previously-studied, but far more distant, NGC 6819 cluster, and especially to measure cooler stars than was previously possible there. Methods. We constructed an inclusive list of 102 cluster members from prior work, including Gaia DR2, and for which light curves were also obtained during Campaign 7 of the Kepler/K2 space mission. We placed them in the cluster color-magnitude diagram and checked the related information against appropriate isochrones. The light curves were then corrected for data systematics using Principal Component Analysis on all observed K2 C07 stars and subsequently subjected to periodicity analysis. Results. Periodic signals are found for 32 stars, 21 of which are considered to be both highly reliable and to represent single, or effectively single, Ru 147 stars. These stars cover the spectral types from late-F to mid-M stars, and they have periods ranging from 6 d – 33 d, allowing for a comparison of Ruprecht 147 to both other open clusters and to models of rotational spindown. The derived rotation periods connect reasonably to, overlap with, and extend to lower masses the known rotation period distribution of the 2.5 Gyr-old cluster NGC 6819. Conclusions. The data confirm that cool stars lie on a single surface in rotation period-mass-age space, and they simultaneously challenge its commonly assumed shape. The shape at the low mass region of the color-period diagram at the age of Ru 147 favors a recently-proposed model which requires a third mass-dependent timescale in addition to the two timescales required by a former model, suggesting that a third physical process is required to model rotating stars effectively.

scholarly journals Seismic Solar Models and the Neutrino Problem

1998 ◽  
Vol 185 ◽  
pp. 21-24
Author(s):  
M. Takata ◽  
H. Shibahashi
Keyword(s):  
Stellar Evolution ◽  
Sound Speed ◽  
Convection Zone ◽  
Solar Model ◽  
The Sun ◽  
Solar Neutrino Problem ◽  
Sound Speed Profile ◽  
The Core ◽  
Neutrino Fluxes ◽  
Capture Rates

We determine the structure of the solar radiative zone with the imposition of the sound speed profile and the depth of the convection zone obtained from helioseismic analysis. We discuss the neutrino fluxes and capture rates using the resultant seismic solar model. We find that the seismic solar model cannot resolve the solar neutrino problem. The hydrogen and helium profiles of the Sun are obtained as a part of the solutions. We find that hydrogen is reduced in the core as expected in the theory of stellar evolution.

scholarly journals A Formalism for Differential Rotation

1980 ◽  
Vol 5 ◽  
pp. 121-127
Author(s):  
B. R. Durney ◽  
H. C. Spruit
Keyword(s):  
Differential Rotation ◽  
Convection Zone ◽  
Meridional Circulation ◽  
Rotation Axis ◽  
Turbulent Viscosity ◽  
Turbulent Transport ◽  
Rotation Period ◽  
Turnover Time ◽  
Viscous Force ◽  
Preferred Direction

One of the approaches for dealing with the differential rotation of the Sun is to separate the flow in the convection zone into an axisymmetric steady part (differential rotation plus meridional circulation) and a “turbulent” part comprising all smaller scales of motion. In the equations of motion and energy the effect of the small scales is then represented by a turbulent viscosity and conductivity. Theories of this type at present belong to either of two categories:a)Theories stressing the role of an anisotropic turbulent viscosity. Due to the presence of gravity as a preferred direction the velocity distribution in the turbulent flow is different in the horizontal and vertical directions. This implies that the turbulent viscosity is also anisotropic. Biermann (1951) showed that as a result, the convection zone cannot rotate as a solid body. Theories based on this idea were developed by Kippenhahn (1963) and Köhler (1970).b)Theories using a latitude dependence of the efficiency of turbulent transport of heat. In the deeper layers of the convection zone the influence of rotation on convection is strong because the convective turnover time is comparable to the rotation period. Since the angle between gravity and the rotation axis varies with latitude, this influence must also vary with latitude. This produces a temperature variation between the pole and the equator which drives a meridional circulation. Since the Coriolis force dominates over the viscous force in most of the convection zone, there is a strong differential rotation associated with this circulation (quasi geostrophic flow). This type of theory has been developed by Weiss (1965), Durney and Roxburgh (1971) and Belvedere and Paterno (1977).

scholarly journals Seismic probing of the first dredge-up event through the eccentric red-giant and red-giant spectroscopic binary KIC 9163796

2018 ◽  
Vol 612 ◽  
pp. A22 ◽  
Author(s):  
P. G. Beck ◽  
T. Kallinger ◽  
K. Pavlovski ◽  
A. Palacios ◽  
A. Tkachenko ◽  
...  
Keyword(s):  
Stellar Evolution ◽  
Binary Systems ◽  
Rotation Period ◽  
Stellar Mass ◽  
Strong Impact ◽  
Mass Ratio ◽  
Lithium Abundance ◽  
Convective Envelope ◽  
Surface Rotation ◽  
Red Giant

Context. Binaries in double-lined spectroscopic systems (SB2) provide a homogeneous set of stars. Differences of parameters, such as age or initial conditions, which otherwise would have strong impact on the stellar evolution, can be neglected. The observed differences are determined by the difference in stellar mass between the two components. The mass ratio can be determined with much higher accuracy than the actual stellar mass. Aim. In this work, we aim to study the eccentric binary system KIC 9163796, whose two components are very close in mass and both are low-luminosity red-giant stars. Methods. We analysed four years of Kepler space photometry and we obtained high-resolution spectroscopy with the Hermes instrument. The orbital elements and the spectra of both components were determined using spectral disentangling methods. The effective temperatures, and metallicities were extracted from disentangled spectra of the two stars. Mass and radius of the primary were determined through asteroseismology. The surface rotation period of the primary is determined from the Kepler light curve. From representative theoretical models of the star, we derived the internal rotational gradient, while for a grid of models, the measured lithium abundance is compared with theoretical predictions. Results. From seismology the primary of KIC 9163796 is a star of 1.39 ± 0.06M⊙, while the spectroscopic mass ratio between both components can be determined with much higher precision by spectral disentangling to be 1.015 ± 0.005. With such mass and a difference in effective temperature of 600 K from spectroscopy, the secondary and primary are, respectively, in the early and advanced stage of the first dredge-up event on the red-giant branch. The period of the primary’s surface rotation resembles the orbital period within ten days. The radial rotational gradient between the surface and core in KIC 9163796 is found to be 6.9−1.0+2.0. This is a low value but not exceptional if compared to the sample of typical single field stars. The seismic average of the envelope’s rotation agrees with the surface rotation rate. The lithium’abundance is in agreement with quasi rigidly rotating models. Conclusions. The agreement between the surface rotation with the seismic result indicates that the full convective envelope is rotating quasi-rigidly. The models of the lithium abundance are compatible with a rigid rotation in the radiative zone during the main sequence. Because of the many constraints offered by oscillating stars in binary systems, such objects are important test beds of stellar evolution.

scholarly journals Rossby Number or Rotation Period?

1993 ◽  
Vol 157 ◽  
pp. 141-145
Author(s):  
K. Stȩpień
Keyword(s):  
Main Sequence ◽  
Rotation Period ◽  
Turnover Time ◽  
Activity Period ◽  
Rossby Number ◽  
Main Sequence Stars ◽  
Rotation Periods ◽  
Dependent Parameter ◽  
Solar Type ◽  
Activity Indices

It is shown that the scaling of rotation periods by a color-dependent parameter (turnover time) improves substantially the observed activity-period relations only for single, main sequence, solar type stars with 0.5 ≲ B – V ≲ 0.8. For other single main sequence stars and for single giants activity indices correlate equally well with rotation period and the Rossby number, or show no correlation with either parameter.

Perception of the moment of inertia of hand tools

1982 ◽  
Author(s):  
Carol Zahner ◽  
M. Stephen Kaminaka
Keyword(s):  
Moment Of Inertia ◽  
Hand Tools ◽  
The Moment
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