Stellar rotation in lower main-sequence stars measured from time variations in H and K emission-line fluxes. I - Initial results

1981 ◽  
Vol 250 ◽  
pp. 276 ◽  
Author(s):  
A. H. Vaughan ◽  
G. W. Preston ◽  
S. L. Baliunas ◽  
L. W. Hartmann ◽  
R. W. Noyes ◽  
...  
Keyword(s):  
Emission Line ◽  
Main Sequence ◽  
Stellar Rotation ◽  
Main Sequence Stars ◽  
Time Variations ◽  
Initial Results

Stellar rotation in lower main-sequence stars measured from time variations in H and K emission-line fluxes. II - Detailed analysis of the 1980 observing season data

1983 ◽  
Vol 275 ◽  
pp. 752 ◽  
Author(s):  
S. L. Baliunas ◽  
L. Hartmann ◽  
R. W. Noyes ◽  
H. Vaughan ◽  
G. W. Preston ◽  
...  
Keyword(s):  
Emission Line ◽  
Detailed Analysis ◽  
Main Sequence ◽  
Stellar Rotation ◽  
Main Sequence Stars ◽  
Time Variations

A search for weak H-alpha emission line pre-main-sequence stars

1983 ◽  
Vol 88 ◽  
pp. 431 ◽  
Author(s):  
E. D. Feigelson ◽  
G. A. Kriss
Keyword(s):  
Emission Line ◽  
Main Sequence ◽  
Main Sequence Stars ◽  
Alpha Emission

scholarly journals Long rotation period main-sequence stars from Kepler SAP light curves

2019 ◽  
Vol 489 (4) ◽  
pp. 5513-5529 ◽  
Author(s):  
Kaiming Cui ◽  
Jifeng Liu ◽  
Shuhong Yang ◽  
Qing Gao ◽  
Huiqin Yang ◽  
...  
Keyword(s):  
Light Curve ◽  
Main Sequence ◽  
Rotation Period ◽  
Light Curves ◽  
Stellar Rotation ◽  
Main Sequence Stars ◽  
Found Objects ◽  
Period Detection ◽  
Search Data

ABSTRACT Stellar rotation plays a key role in stellar activity. The rotation period could be detected through light curve variations caused by star-spots. Kepler provides two types of light curves: one is the Pre-search Data Conditioning (PDC) light curves, and the other is the Simple Aperture Photometer (SAP) light curves. Compared with the PDC light curves, the SAP light curves keep the long-term trend, relatively suitable for searches of long-period signals. However, SAP data are inflicted by some artefacts such as quarterly rolls and instrumental errors, making it difficult to find the physical periods in the SAP light curves. We explore a systematic approach based on the light curve pre-processing, period detection, and candidate selection. We also develop a simulated light curve test to estimate our detection limits for the SAP-like LCs. After applying our method to the raw SAP light curves, we found more than 1000 main-sequence stars with periods longer than 30 d; 165 are newly discovered. Considering the potential flaw of the SAP, we also inspect the newly found objects with photometry methods, and most of our periodical signals are confirmed.

Absolute Fluxes of K Chromospheric Emission on the H-R Diagram

1976 ◽  
Vol 71 ◽  
pp. 473-473
Author(s):  
C. Blanco ◽  
S. Catalano ◽  
E. Marilli
Keyword(s):  
Emission Line ◽  
Main Sequence ◽  
Previous Analysis ◽  
Main Sequence Stars ◽  
Chromospheric Emission

Continuing our previous analysis of the chromospheric emission (Blanco et al., 1974), absolute fluxes of the K emission line have been evaluated from 10 Å mm−1 spectrograms of the O. C. Wilson collection for 31 F5-K7 main sequence stars and 172 G2-M5 giants.

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 The Rotation of Low-Mass Pre-Main-Sequence Stars

2004 ◽  
Vol 215 ◽  
pp. 113-122 ◽  
Author(s):  
Robert D. Mathieu
Keyword(s):  
Angular Momentum ◽  
Main Sequence ◽  
Rotation Period ◽  
Rotating Stars ◽  
Stellar Rotation ◽  
Main Sequence Stars ◽  
Star Forming ◽  
Rotation Periods ◽  
Order Of Magnitude ◽  
Critical Velocities

Major photometric monitoring campaigns of star-forming regions in the past decade have provided rich rotation period distributions of pre-main-sequence stars. The rotation periods span more than an order of magnitude in period, with most falling between 1 and 10 days. Thus the broad rotation period distributions found in 100 Myr clusters are already established by an age of 1 Myr. The most rapidly rotating stars are within a factor of 2-3 of their critical velocities; if angular momentum is conserved as they evolve to the ZAMS, these stars may come to exceed their critical velocities. Extensive efforts have been made to find connections between stellar rotation and the presence of protostellar disks; at best only a weak correlation has been found in the largest samples. Magnetic disk-locking is a theoretically attractive mechanism for angular momentum evolution of young stars, but the links between theoretical predictions and observational evidence remain ambiguous. Detailed observational and theoretical studies of the magnetospheric environments will provide better insight into the processes of pre-main-sequence stellar angular momentum evolution.

scholarly journals A random walk approach to the problem of turbulent diffusion and lithium destruction in main sequence stars

1984 ◽  
Vol 105 ◽  
pp. 533-535
Author(s):  
Roger Cayrel
Keyword(s):  
Random Walk ◽  
Turbulent Diffusion ◽  
Main Sequence ◽  
Meridional Circulation ◽  
Convective Zone ◽  
Lithium Content ◽  
Stellar Rotation ◽  
Main Sequence Stars ◽  
Consistent Description ◽  
Self Consistent

It has been suggested by Schatzman (1977) that the empirical lithium content/age relationship found by Herbig (1965) could be explained by exchange of matter between the convective zone and deeper layers, where the rate of lithium burning is higher, by turbulent diffusion. The claim by Tassoul and Tassoul (1983) that such a turbulence is necessary to obtain a self-consistent description of stellar rotation and meridional circulation has given some momentum to Schatzman's proposal, as well as other successes of the turbulent diffusion hypothesis (Schatzman et al. 1981).

scholarly journals The Remarkable Rotational Braking of G5 Giants

1983 ◽  
Vol 102 ◽  
pp. 461-466
Author(s):  
David F. Gray
Keyword(s):  
Magnetic Field ◽  
Main Sequence ◽  
Driving Forces ◽  
Stellar Winds ◽  
Main Sequence Stars ◽  
Dynamo Mechanism ◽  
Slow Progress ◽  
Time Variations ◽  
The Magnetic Field ◽  
Stellar Dynamo

The strong rotational braking seen in the G5 III stage of evolution may be the key to understanding how stellar dynamos work.We are all familiar with the leisurely spin-down seen in cool main-sequence stars like our Sun. The time scales here are ∼ 109 years and the accepted cause is the loss of high angular momentum mass in the form of stellar winds interacting with the stellar magnetic field. The magnetic field is believed to result from the interaction of envelope convection with the rotation of the star through a dynamo mechanism. Our understanding of how a dynamo actually operates, how that operation depends on the driving forces of rotation and convection, what kind of stochastic and secular time variations are to be expected, remains fragmentary even though many inventive minds have contributed. One reason for slow progress is simply that the Sun is almost the only example of a stellar dynamo we have had. But nature has given us another, much more powerful dynamo in the G5 giants, it just took us a little longer to discover it.

scholarly journals On Stellar Rotation: II. The Rotation of Lower Main Sequence Stars

1964 ◽  
Vol 128 (3) ◽  
pp. 237-248 ◽  
Author(s):  
I. W. Roxburgh
Keyword(s):  
Main Sequence ◽  
Stellar Rotation ◽  
Main Sequence Stars

scholarly journals Emission line spectropolarimetry and circumstellar structures

2014 ◽  
Vol 10 (S305) ◽  
pp. 288-292
Author(s):  
Jorick S. Vink
Keyword(s):  
Emission Line ◽  
Accretion Disks ◽  
Main Sequence ◽  
Gamma Ray ◽  
Young Stars ◽  
Main Sequence Stars ◽  
Current Sensitivity ◽  
Luminous Blue Variables ◽  
3D Monte Carlo

AbstractWe discuss the role of linear emission-line polarimetry in a wide set of stellar environments, involving the accretion disks around young pre-main sequence stars, to the aspherical outflows from O stars, luminous blue variables and Wolf-Rayet stars, just prior to explosion as a supernova or a gamma-ray burst. We predict subtle QU line signatures, such as single/double QU loops for un/disrupted disks. Whilst there is plenty of evidence for single QU loops, suggesting the presence of disrupted disks around young stars, current sensitivity (with S/N of order 1000) is typically not sufficient to allow for quantitative 3D Monte Carlo modeling. However, the detection of our predicted signatures is expected to become feasible with the massive improvement in sensitivity of extremely large mirrors.

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