scholarly journals High dispersion spectroscopy of solar-type superflare stars. II. Stellar rotation, starspots, and chromospheric activities

2015 ◽  
Vol 67 (3) ◽  
pp. 33 ◽  
Author(s):  
Yuta Notsu ◽  
Satoshi Honda ◽  
Hiroyuki Maehara ◽  
Shota Notsu ◽  
Takuya Shibayama ◽  
...  
Keyword(s):  
High Dispersion ◽  
Stellar Rotation ◽  
Solar Type

scholarly journals High dispersion spectroscopy of solar-type superflare stars. III. Lithium abundances

2015 ◽  
Vol 67 (5) ◽  
pp. 85 ◽  
Author(s):  
Satoshi Honda ◽  
Yuta Notsu ◽  
Hiroyuki Maehara ◽  
Shota Notsu ◽  
Takuya Shibayama ◽  
...  
Keyword(s):  
High Dispersion ◽  
Solar Type

scholarly journals SUPERFLARES ON SOLAR-TYPE STARS OBSERVED WITHKEPLERII. PHOTOMETRIC VARIABILITY OF SUPERFLARE-GENERATING STARS: A SIGNATURE OF STELLAR ROTATION AND STARSPOTS

2013 ◽  
Vol 771 (2) ◽  
pp. 127 ◽  
Author(s):  
Yuta Notsu ◽  
Takuya Shibayama ◽  
Hiroyuki Maehara ◽  
Shota Notsu ◽  
Takashi Nagao ◽  
...  
Keyword(s):  
Stellar Rotation ◽  
Photometric Variability ◽  
Solar Type

scholarly journals Effects of Stellar Rotation on Spectral Classification

1979 ◽  
Vol 47 ◽  
pp. 87-94
Author(s):  
Arne Slettebak ◽  
Thomas J. Kuzma
Keyword(s):  
Systematic Errors ◽  
Stellar Atmospheres ◽  
High Dispersion ◽  
Rotational Line ◽  
Spectral Classification ◽  
Line Broadening ◽  
Stellar Rotation ◽  
First Case ◽  
Balmer Lines ◽  
Physical Changes

AbstractStellar rotation may affect the strengths of lines used in spectral classification because of effects of plate resolution and also because of physical changes in the rotating stellar atmospheres. In the first case, the importance of using standard stars with appropriate rotational line broadening in classifying spectra of relatively high dispersion (resolution) is emphasized. Rotational effects on weak lines in general and on the Balmer lines may cause systematic errors in the assignment of spectral types and luminosity classes unless the standard stars are chosen with line broadening similar to that of the star to be classified. With regard to physical changes in the rotating atmospheres, we have extended the earlier work of Collins to include the Balmer lines plus additional lines of He I and Si II which are important in spectral classification over a wider range of spectral types.

scholarly journals 29. Stellar Spectra

1970 ◽  
Vol 14 (1) ◽  
pp. 319-329
Author(s):  
M. W. Feast ◽  
Y. Fujita ◽  
M. K. V. Bappu ◽  
G. Herbig ◽  
L. Houziaux ◽  
...  
Keyword(s):  
Mass Loss ◽  
Working Group ◽  
White Dwarfs ◽  
Vice President ◽  
Stellar Atmospheres ◽  
High Dispersion ◽  
Stellar Rotation ◽  
Stellar Spectra ◽  
Working Groups ◽  
Main Activity

Material for this report was collected by the President, Vice-President and Members of the Organizing Committee. The President is, however, responsible for the form in which the report now appears. A number of special abbreviations in the references are explained in the report of Committee 27a. In addition, 3rd Harvard = 3rd Harvard-Smithsonian Conference on Stellar Atmospheres (1968). The field of Commission 29 overlaps particularly with those of 9, 27a, 36, 44 and 45 whose reports should be consulted. Since the last IAU meeting 29 has co-sponsored the following meetings: IAU Colloquium No. 4 on Stellar Rotation (Columbus, Ohio, September 1969); IAU Symposium No. 36, Ultraviolet Stellar Spectra and Related Ground-Based Observations (Lunteren, June, 1969); Second Trieste Colloquium, Mass Loss from Stars (September, 1968). We are also co-sponsoring IAU Symposium No. 42 on White Dwarfs to be held in Scotland (August, 1970). The thanks of the commission are due to their representatives on the organizing committees of these meetings. Reports from some working groups are appended. The working group with Commission 44 has not felt it necessary to submit a report (its main activity was the organization of Symposium No. 36). Miss Underhill (Chairman) recommends that the working group on Tracings of High Dispersion Stellar Spectra be dissolved.

scholarly journals Rotational evolution of solar-type protostars during the star-disk interaction phase

2019 ◽  
Vol 632 ◽  
pp. A6 ◽  
Author(s):  
F. Gallet ◽  
C. Zanni ◽  
L. Amard
Keyword(s):  
Stellar Wind ◽  
Main Sequence ◽  
Stellar Winds ◽  
Stellar Rotation ◽  
Solar Mass ◽  
Stellar Envelope ◽  
Spin Evolution ◽  
Rotational Evolution ◽  
Solar Type ◽  
The Impact

Context. The early pre-main sequence phase during which solar-mass stars are still likely surrounded by an accretion disk represents a puzzling stage of their rotational evolution. While solar-mass stars are accreting and contracting, they do not seem to spin up substantially. Aims. It is usually assumed that the magnetospheric star-disk interaction tends to maintain the stellar rotation period constant (“disk-locking”), but this hypothesis has never been thoroughly verified. Our aim is to investigate the impact of the star-disk interaction mechanism on the stellar spin evolution during the accreting pre-main sequence phases. Methods. We devised a model for the torques acting on the stellar envelope based on studies of stellar winds, and we developed a new prescription for the star-disk coupling founded on numerical simulations of star-disk interaction and magnetospheric ejections. We then used this torque model to follow the long-term evolution of the stellar rotation. Results. Strong dipolar magnetic field components up to a few kG are required to extract enough angular momentum so as to keep the surface rotation rate of solar-type stars approximately constant for a few Myr. Furthermore an efficient enough spin-down torque can be provided by either one of the following: a stellar wind with a mass outflow rate corresponding to ≈10% of the accretion rate, or a lighter stellar wind combined with a disk that is truncated around the corotation radius entering a propeller regime. Conclusions. Magnetospheric ejections and accretion powered stellar winds play an important role in the spin evolution of solar-type stars. However, kG dipolar magnetic fields are neither uncommon or ubiquitous. Besides, it is unclear how massive stellar winds can be powered while numerical models of the propeller regime display a strong variability that has no observational confirmation. Better observational statistics and more realistic models could contribute to help lessen our calculations’ requirements.

scholarly journals Magnetic Activity and Rotation in Brown Dwarfs and Low Mass Stars

2003 ◽  
Vol 211 ◽  
pp. 427-435 ◽  
Author(s):  
Gibor Basri ◽  
Subanjoy Mohanty
Keyword(s):  
Theoretical Work ◽  
Magnetic Activity ◽  
Stellar Rotation ◽  
Low Mass Stars ◽  
Strong Activity ◽  
Substellar Objects ◽  
Substantial Progress ◽  
Solar Type ◽  
Low Mass ◽  
M Stars

One of the triumphs of the last 2 decades has been the establishment of the relation between stellar rotation and magnetic activity in solar-type stars. Rapid rotation produces strong activity, which in turn provides magnetic braking to reduce rotation. A solar-type dynamo cannot operate in fully convective stars, so it is of interest to study mid and late M stars. Hints that a dramatic change occurs in very low-mass stars and substellar objects appeared in 1995. The past 7 years have seen substantial progress on this question, with the conclusion that the rotation-activity connection indeed breaks down. As one goes to the bottom of the main sequence and below, the amount of magnetic activity takes a sudden fall, with a concomitant increase in the spindown times of the objects. We summarize these results, and some theoretical work which helps explain them. We also present some remaining mysteries, such as why very young objects seem excessively active, and flaring in objects with no other signs of magnetic activity.

scholarly journals Coronal Mass Ejections and Angular Momentum Loss in Young Stars

2013 ◽  
Vol 8 (S300) ◽  
pp. 318-321
Author(s):  
Alicia N. Aarnio ◽  
Keivan G. Stassun ◽  
Sean P. Matt
Keyword(s):  
Angular Momentum ◽  
Coronal Mass Ejections ◽  
Necessary Conditions ◽  
Central Star ◽  
Young Stars ◽  
Activity Levels ◽  
Stellar Rotation ◽  
Momentum Loss ◽  
Angular Momentum Loss ◽  
Solar Type

AbstractIn our own solar system, the necessity of understanding space weather is readily evident. Fortunately for Earth, our nearest stellar neighbor is relatively quiet, exhibiting activity levels several orders of magnitude lower than young, solar-type stars. In protoplanetary systems, stellar magnetic phenomena observed are analogous to the solar case, but dramatically enhanced on all physical scales: bigger, more energetic, more frequent. While coronal mass ejections (CMEs) could play a significant role in the evolution of protoplanets, they could also affect the evolution of the central star itself. To assess the consequences of prominence eruption/CMEs, we have invoked the solar-stellar connection to estimate, for young, solar-type stars, how frequently stellar CMEs may occur and their attendant mass and angular momentum loss rates. We will demonstrate the necessary conditions under which CMEs could slow stellar rotation.

scholarly journals High dispersion spectroscopy of solar-type superflare stars. I. Temperature, surface gravity, metallicity, andvsin i

2015 ◽  
Vol 67 (3) ◽  
pp. 32 ◽  
Author(s):  
Yuta Notsu ◽  
Satoshi Honda ◽  
Hiroyuki Maehara ◽  
Shota Notsu ◽  
Takuya Shibayama ◽  
...  
Keyword(s):  
Surface Gravity ◽  
High Dispersion ◽  
Solar Type ◽  
Temperature Surface

scholarly journals Probing rotation in pulsating stars from space

2004 ◽  
Vol 215 ◽  
pp. 189-198
Author(s):  
Jaymie M. Matthews
Keyword(s):  
Real Data ◽  
Stellar Rotation ◽  
Instability Strip ◽  
Optical Telescope ◽  
Pulsating Stars ◽  
Rotation Periods ◽  
Diagnostic Potential ◽  
Solar Type ◽  
Ap Stars ◽  
Scuti Stars

At the time of the last Stellar Rotation symposium in 1969, the map of known pulsators in the H-R Diagram covered a lot less territory, being confined mainly to the classical instability strip. Among the new classes of pulsators are the strongly magnetic roAp (rapidly oscillating Ap) stars whose pulsation amplitudes and phases are modulated with their rotation periods. Among the classical pulsators, the δ Scuti stars are now known to show many more eigenmodes and frequency splitting than was ever recognised three decades ago. Both are examples of the diagnostic potential and severe challenges to detect and interpret correctly rotational fine structure in the pulsational frequency spectrum. In a pulsating star, rotation can perturb the structure or dynamics, and it can split degeneracies to serve as a diagnostic of pulsational modes. One tool which should help us exploit the potential and overcome the challenges of studying the interaction between rotation and pulsation is Canada's MOST (Microvariability & Oscillations of STars) microsatellite. MOST is a small optical telescope and ultraprecise CCD photometer designed to detect and characterise acoustic (p-mode) oscillations with periods of minutes and amplitudes as low as 1 micromagnitude in bright stars. While customised to conduct asteroseismology of solar-type stars, the MOST mission will also include roAp stars as prime targets and eventuallly δ Scutis as secondary targets. I present here simulations of MOST observations of such targets with different rotation periods, in advance of the real data expected in the months after the scheduled 30 June 2003 launch.

scholarly journals Stellar rotation and mixing

1997 ◽  
Vol 181 ◽  
pp. 175-188
Author(s):  
Jean-Paul Zahn
Keyword(s):  
Chemical Elements ◽  
Transport Mechanisms ◽  
Stellar Rotation ◽  
Uniform Rotation ◽  
Mixing Processes ◽  
Convective Envelope ◽  
Stellar Radiation ◽  
Nuclear Burning ◽  
Solar Type ◽  
Meridian Circulation

Many observations indicate that some mixing occurs in stellar radiation zones: in massive stars, chemical elements resulting from nuclear burning in the core are detected at the surface, and in solar-type stars lithium is depleted with age. Since all mixing processes transport also momentum, the depletion of lithium should be linked with the loss of angular momentum through the stellar wind, and there are indeed signs of such a correlation in the behavior of tidally-locked binaries. Moreover, any transport process leaves its signature in the internal rotation profile, and this can help greatly in its identification. After reviewing the main transport mechanisms which have been considered so far, our present conclusion is that the uniform rotation observed in the radiative interior of the Sun is probably achieved by the action of internal waves emitted at the base of the convective envelope. It remains to be verified whether these waves contribute directly to the mixing, or whether they act only through the shaping of the rotation profile, which in turn determines the mixing through meridian circulation and turbulent diffusivity.

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