scholarly journals How accurately can we age-date solar-type dwarfs using activity/rotation diagnostics?

2008 ◽  
Vol 4 (S258) ◽  
pp. 375-382 ◽  
Author(s):  
Eric E. Mamajek
Keyword(s):  
Main Sequence ◽  
Structural Evolution ◽  
Planetary Systems ◽  
Age Dating ◽  
Rossby Number ◽  
Main Sequence Stars ◽  
Primary Motivation ◽  
X Ray ◽  
Recent Interest ◽  
Solar Type

AbstractIt is well established that activity and rotation diminishes during the life of sun-like main sequence (~F7-K2V) stars. Indeed, the evolution of rotation and activity among these stars appears to be so deterministic that their rotation/activity diagnostics are often utilized as estimators of stellar age. A primary motivation for the recent interest in improving the ages of solar-type field dwarfs is in understanding the evolution of debris disks and planetary systems. Reliable isochronal age-dating for field, solar-type main sequence stars is very difficult given the observational uncertainties and multi-Gyr timescales for significant structural evolution. Observationally, significant databases of activity/rotation diagnostics exist for field solar-type field dwarfs (mainly from chromospheric and X-ray activity surveys).But how well can we empirically age-date solar-type field stars using activity/rotation diagnostics?Here I summarize some recent results for F7-K2 dwarfs from an analysis by Mamajek & Hillenbrand (2008), including an improved “gyrochronology” [Period(color, age)] calibration, improved chromospheric (R′HK) and X-ray (log(LX/Lbol)) activity vs. rotation (via Rossby number) relations, and a chromospheric vs. X-ray activity relation that spans four orders of magnitude in log(LX/Lbol). Combining these relations, one can produce predicted chromospheric and X-ray activity isochrones as a function of color and age for solar type dwarfs.

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.

scholarly journals Activity and rotation of the X-ray emitting Kepler stars

2019 ◽  
Vol 628 ◽  
pp. A41 ◽  
Author(s):  
D. Pizzocaro ◽  
B. Stelzer ◽  
E. Poretti ◽  
S. Raetz ◽  
G. Micela ◽  
...  
Keyword(s):  
White Light ◽  
Main Sequence ◽  
Magnetic Activity ◽  
Light Curves ◽  
Late Type ◽  
Main Sequence Stars ◽  
Photometric Variability ◽  
X Ray ◽  
Rotation Periods ◽  
Flare Frequency

The relation between magnetic activity and rotation in late-type stars provides fundamental information on stellar dynamos and angular momentum evolution. Rotation-activity studies found in the literature suffer from inhomogeneity in the measurement of activity indexes and rotation periods. We overcome this limitation with a study of the X-ray emitting, late-type main-sequence stars observed by XMM-Newton and Kepler. We measured rotation periods from photometric variability in Kepler light curves. As activity indicators, we adopted the X-ray luminosity, the number frequency of white-light flares, the amplitude of the rotational photometric modulation, and the standard deviation in the Kepler light curves. The search for X-ray flares in the light curves provided by the EXTraS (Exploring the X-ray Transient and variable Sky) FP-7 project allows us to identify simultaneous X-ray and white-light flares. A careful selection of the X-ray sources in the Kepler field yields 102 main-sequence stars with spectral types from A to M. We find rotation periods for 74 X-ray emitting main-sequence stars, 20 of which do not have period reported in the previous literature. In the X-ray activity-rotation relation, we see evidence for the traditional distinction of a saturated and a correlated part, the latter presenting a continuous decrease in activity towards slower rotators. For the optical activity indicators the transition is abrupt and located at a period of ~10 d but it can be probed only marginally with this sample, which is biased towards fast rotators due to the X-ray selection. We observe seven bona-fide X-ray flares with evidence for a white-light counterpart in simultaneous Kepler data. We derive an X-ray flare frequency of ~0.15 d−1, consistent with the optical flare frequency obtained from the much longer Kepler time-series.

scholarly journals Age-related observations of low mass pre-main and young main sequence stars

2008 ◽  
Vol 4 (S258) ◽  
pp. 81-94 ◽  
Author(s):  
Lynne A. Hillenbrand
Keyword(s):  
Main Sequence ◽  
Rotation Period ◽  
Age Dating ◽  
Main Sequence Stars ◽  
Solar Mass ◽  
Age Related ◽  
Stellar Ages ◽  
Dating Methods ◽  
Low Mass ◽  
Lithium Depletion

AbstractThis overview summarizes the age dating methods available for young sub-solar mass stars. Pre-main sequence age diagnostics include the Hertzsprung-Russell (HR) diagram, spectroscopic surface gravity indicators, and lithium depletion; asteroseismology is also showing recent promise. Near and beyond the zero-age main sequence, rotation period or vsiniand activity (coronal and chromospheric) diagnostics along with lithium depletion serve as age proxies. Other authors in this volume present more detail in each of the aforementioned areas. Herein, I focus on pre-main sequence HR diagrams and address the questions: Do empirical young cluster isochrones match theoretical isochrones? Do isochrones predict stellar ages consistent with those derived via other independent techniques? Do the observed apparent luminosity spreads at constant effective temperature correspond to true age spreads? While definitive answers to these questions are not provided, some methods of progression are outlined.

scholarly journals X-Ray Properties of Pre-Main-Sequence Stars in the Orion Nebula Cluster with Known Rotation Periods

2004 ◽  
Vol 127 (6) ◽  
pp. 3537-3552 ◽  
Author(s):  
Keivan G. Stassun ◽  
David R. Ardila ◽  
Mary Barsony ◽  
Gibor Basri ◽  
Robert D. Mathieu
Keyword(s):  
Main Sequence ◽  
Orion Nebula ◽  
Main Sequence Stars ◽  
X Ray ◽  
Rotation Periods

scholarly journals Characterizing planetesimal belts through the study of debris dust

2010 ◽  
Vol 6 (S276) ◽  
pp. 54-59
Author(s):  
Amaya Moro-Martín
Keyword(s):  
Solar System ◽  
Main Sequence ◽  
Planetary Systems ◽  
Dust Particles ◽  
Debris Disks ◽  
Main Sequence Stars ◽  
Wide Range ◽  
Robust Process

AbstractMain sequence stars are commonly surrounded by disks of dust. From lifetime arguments, it is inferred that the dust particles are not primordial but originate from the collision of planetesimals, similar to the asteroids, comets and KBOs in our Solar system. The presence of these debris disks around stars with a wide range of masses, luminosities, and metallicities, with and without binary companions, is evidence that planetesimal formation is a robust process that can take place under a wide range of conditions. Debris disks can help us learn about the formation, evolution and diversity of planetary systems.

scholarly journals Non thermal emission from T Tauri stars

2010 ◽  
Vol 6 (S275) ◽  
pp. 404-405
Author(s):  
María V. del Valle ◽  
Gustavo E. Romero
Keyword(s):  
Main Sequence ◽  
Thermal Emission ◽  
High Energy ◽  
Magnetic Activity ◽  
T Tauri Stars ◽  
Main Sequence Stars ◽  
High Energy Radiation ◽  
X Ray ◽  
T Tauri ◽  
Low Mass

AbstractT Tauri stars are low mass, pre-main sequence stars. These objects are surrounded by an accretion disk and present strong magnetic activity. T Tauri stars are copious emitters of X-ray emission which belong to powerful magnetic reconnection events. Strong magnetospheric shocks are likely outcome of massive reconnection. Such shocks can accelerate particles up to relativistic energies through Fermi mechanism. We present a model for the high-energy radiation produced in the environment of T Tauri stars. We aim at determining whether this emission is detectable. If so, the T Tauri stars should be very nearby.

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 Testing the companion hypothesis for the origin of the X-ray emission from intermediate-mass main-sequence stars

2006 ◽  
Vol 452 (3) ◽  
pp. 1001-1010 ◽  
Author(s):  
B. Stelzer ◽  
N. Huélamo ◽  
G. Micela ◽  
S. Hubrig
Keyword(s):  
Main Sequence ◽  
Main Sequence Stars ◽  
Intermediate Mass ◽  
X Ray

scholarly journals X-Ray Superflares from Pre-main-sequence Stars: Flare Energetics and Frequency

2021 ◽  
Vol 916 (1) ◽  
pp. 32
Author(s):  
Konstantin V. Getman ◽  
Eric D. Feigelson
Keyword(s):  
Main Sequence ◽  
Main Sequence Stars ◽  
X Ray ◽  
Stars Flare

scholarly journals Non-Local Convection Models for Stellar Atmospheres and Envelopes

2003 ◽  
Vol 210 ◽  
pp. 143-156
Author(s):  
F. Kupka
Keyword(s):  
Numerical Simulations ◽  
Main Sequence ◽  
Stellar Atmospheres ◽  
Surface Velocity ◽  
Line Profiles ◽  
Main Sequence Stars ◽  
Solar Type ◽  
Non Local ◽  
Stress Models ◽  
Do So

We present an overview of the concepts underlying advanced non-local Reynolds stress models of turbulent convection and review a comparison of this approach with a series of numerical simulations of fully compressible convection. We then discuss results from applications of the model to complete envelopes of A-type main sequence stars. The non-local model reproduces surface velocities in agreement with the lower limit of observed macro- and microturbulence velocities of A-star photospheres, the asymmetry of the surface velocity field as inferred from spectral line profiles, and the overall structure of the photospheric and subphotospheric convection zones, as predicted by the most recent numerical simulations available for these stars. Traditionally, local models of convection are unable to do so. We conclude with a brief survey of extensions of the model which are interesting for other applications such as atmospheres of solar type stars and overshooting below deep convective envelopes or above the core in massive stars.

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