scholarly journals Magnetic activity evolution on Sun-like stars

2018 ◽  
Vol 616 ◽  
pp. A154 ◽  
Author(s):  
P. Gondoin
Keyword(s):  
Magnetic Activity ◽  
Open Clusters ◽  
Rotating Stars ◽  
Coronal Emission ◽  
Solar Mass ◽  
X Ray ◽  
Bolometric Luminosity ◽  
Rotation Periods ◽  
Pms Stars ◽  
Activity Indices

Context. Characterising the time evolution of magnetic activity on Sun-like stars is important not only for stellar physics but also for determining the environment in which planets evolve. Aims. In recent decades, many surveys of open clusters have produced extensive rotation periods measurements on Sun-like stars of different ages. The present study uses this information with the aim to improve the description of their magnetic activity evolution. Methods. I present a method that infers the long-term evolution of Ca II chromospheric (R′HK) and X-ray coronal (LX) emission on solar mass stars by combining a best fit parametric model of their rotation evolution with empirical rotation-activity relationships. Results. The inferred scenario reproduces the high chromospheric and coronal emission levels around R′HK ≈ 10−4 and LX ≈ 1030 erg s−1 that are observed on pre-main sequence (PMS) stars. At the end of the PMS contraction phase around the age of ~30 Myr, the slowest rotating stars experience a rapid transition of their magnetic activity to more moderate levels around R′HK ≈ 4 × 10−5 and L5 ≈ 1029 erg s−1. This transition occurs later on more rapidly rotating stars, up to an age of ~600 Myr for the fastest rotators. After this brief episode of large magnetic activity decay, the average chromospheric and coronal emission levels of solar-mass stars decrease steadily converging towards similar values (R′HK ≈ 10−5 and LX ≈ 1027 erg s−1) by the age of the Sun. Conclusion. The study suggests that solar mass stars in open clusters with ages between ~30 and ~600 Myr exhibit bimodal distributions of their R′HK chromospheric activity indices and coronal X-ray to bolometric luminosity ratios that can be traced back to their rotation evolution. This conclusion is consistent with available measurements of activity indices from Sun-like stars in nearby open clusters.

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 Stellar Magnetic Dynamos and Activity Cycles

2013 ◽  
Vol 9 (S302) ◽  
pp. 190-193
Author(s):  
Nicholas J. Wright
Keyword(s):  
Coronal Emission ◽  
X Ray ◽  
Rotation Periods ◽  
Early Results ◽  
Uniform Sample ◽  
Activity Cycles ◽  
Blind Search ◽  
The Relationship ◽  
Interface Type ◽  
Stellar Dynamo

AbstractUsing a new uniform sample of 824 solar and late-type stars with measured X-ray luminosities and rotation periods we have studied the relationship between rotation and stellar activity that is believed to be a probe of the underlying stellar dynamo. Using an unbiased subset of the sample we calculate the power law slope of the unsaturated regime of the activity – rotation relationship as LX / Lbol ∝ Roβ, where β = − 2.70 ± 0.13. This is inconsistent with the canonical β = − 2 slope to a confidence of 5σ and argues for an interface-type dynamo. We map out three regimes of coronal emission as a function of stellar mass and age, using the empirical saturation threshold and theoretical super-saturation thresholds. We find that the empirical saturation timescale is well correlated with the time at which stars transition from the rapidly rotating convective sequence to the slowly rotating interface sequence in stellar spin-down models. This may be hinting at fundamental changes in the underlying stellar dynamo or internal structure. We also present the first discovery of an X-ray unsaturated, fully convective M star, which may be hinting at an underlying rotation - activity relationship in fully convective stars hitherto not observed. Finally we present early results from a blind search for stellar X-ray cycles that can place valuable constraints on the underlying ubiquity of solar-like activity cycles.

scholarly journals Age, Activity and Rotation in Mid and Late-Type M Dwarfs from MEarth

2013 ◽  
Vol 9 (S302) ◽  
pp. 176-179
Author(s):  
Andrew A. West ◽  
Kolby L. Weisenburger ◽  
Jonathan Irwin ◽  
David Charbonneau ◽  
Jason Dittmann ◽  
...  
Keyword(s):  
Dimensional Space ◽  
Large Fraction ◽  
Rotation Period ◽  
Magnetic Activity ◽  
Rotating Stars ◽  
Late Type ◽  
M Dwarfs ◽  
Magnetic Field Generation ◽  
Rotation Periods ◽  
Wide Range

AbstractUsing spectroscopic observations and photometric light curves of 280 nearby M dwarfs from the MEarth exoplanet transit survey, we examine the relationships between magnetic activity (quantified by Hα emission), rotation period, and stellar age (derived from three-dimensional space velocities). Although we have known for decades that a large fraction of mid-late-type M dwarfs are magnetically active, it was not clear what role rotation played in the magnetic field generation (and subsequent chromospheric heating). Previous attempts to investigate the relationship between magnetic activity and rotation in mid-late-type M dwarfs were hampered by the limited number of M dwarfs with measured rotation periods (and the fact that vsini measurements only probe rapid rotation). However, the photometric data from the MEarth survey allows us to probe a wide range of rotation periods for hundreds of M dwarf stars (from less than one to over 100 days). Over all M spectral types we find that magnetic activity decreases with longer rotation periods, including late-type, fully convective M dwarfs. We find that the most magnetically active (and hence, most rapidly rotating) stars are consistent with a kinematically young population, while slow-rotators are less active or inactive and appear to belong to an older, dynamically heated stellar population.

scholarly journals Stellar flares and the dark energy of CMEs

2015 ◽  
Vol 11 (S320) ◽  
pp. 196-201 ◽  
Author(s):  
Jeremy J. Drake ◽  
Ofer Cohen ◽  
Cecilia Garraffo ◽  
V. Kashyap
Keyword(s):  
Large Scale ◽  
Magnetic Activity ◽  
Radiative Energy ◽  
Flare Activity ◽  
X Rays ◽  
Active Region Noaa ◽  
Coronal Emission ◽  
X Ray ◽  
Stellar Flares ◽  
Active Stars

AbstractFlares we observe on stars in white light, UV or soft X-rays are probably harbingers of coronal mass ejections (CMEs). If we use the Sun as a guide, large stellar flares will dissipate two orders of magnitude less X-ray radiative energy than the kinetic energy in the associated CME. Since coronal emission on active stars appears to be dominated by flare activity, CMEs pose a quandary for understanding the fraction of their energy budget stars can spend on magnetic activity. One answer is magnetic suppression of CMEs, in which the strong large-scale fields of active stars entrap and prevent CMEs unless their free energy exceeds a critical value. The CME-less flaring active region NOAA 2192 presents a possible solar analogue of this. Monster CMEs will still exist, and have the potential to ravage planetary atmospheres.

scholarly journals The Sun Through Time

2020 ◽  
Vol 216 (8) ◽  
Author(s):  
Manuel Güdel
Keyword(s):  
Stellar Wind ◽  
Rotation Period ◽  
High Energy ◽  
Magnetic Activity ◽  
Energy Output ◽  
The Sun ◽  
Stellar Rotation ◽  
Solar Mass ◽  
Rotation Periods ◽  
Rotational Evolution

AbstractMagnetic activity of stars like the Sun evolves in time because of spin-down owing to angular momentum removal by a magnetized stellar wind. These magnetic fields are generated by an internal dynamo driven by convection and differential rotation. Spin-down therefore converges at an age of about 700 Myr for solar-mass stars to values uniquely determined by the stellar mass and age. Before that time, however, rotation periods and their evolution depend on the initial rotation period of a star after it has lost its protostellar/protoplanetary disk. This non-unique rotational evolution implies similar non-unique evolutions for stellar winds and for the stellar high-energy output. I present a summary of evolutionary trends for stellar rotation, stellar wind mass loss and stellar high-energy output based on observations and models.

X-ray bright points and the solar cycle

1980 ◽  
Vol 297 (1433) ◽  
pp. 595-604 ◽  
Keyword(s):  
Solar Cycle ◽  
Magnetic Flux ◽  
Active Regions ◽  
Coronal Emission ◽  
X Ray ◽  
Large Numbers ◽  
Activity Spectrum ◽  
Long Lifetime ◽  
Traditional Activity ◽  
Activity Indices

Soft X-ray filtergrams show the presence on the Sun of large numbers of small, closed regions of coronal emission. These features, called 'X-ray bright points' correspond to small, short-lived regions of emerging magnetic flux. As a function of size or lifetime they form a broad spectrum of activity which is continuous with the active regions. The shape of the Sun’s activity spectrum is such that most of all magnetic flux emerging at the surface comes in the form of bright points. From this viewpoint, active regions may be viewed as the long lifetime tail end of the bright point spectrum. Examination of soft X-ray data obtained from 1970 to 1978 shows that the number of bright points appears to be anticorrelated with traditional activity indices such as sunspot number; the anticorrelation persists after corrections are made for obscuration by active regions. Comparison of X-ray data with KPNO magnetograms shows that to within a factor of 2, the average total amount of magnetic flux emerging over the full Sun is constant through the entire period of observation. The solar cycle therefore appears to be more an oscillation in the wavenumber distribution of emerging flux than of the total quantity of magnetic flux produced.

scholarly journals Magnetic Activity of Pre-main Sequence Stars

2004 ◽  
Vol 219 ◽  
pp. 211-222
Author(s):  
Eric D. Feigelson
Keyword(s):  
Main Sequence ◽  
Magnetic Activity ◽  
T Tauri Stars ◽  
X Rays ◽  
Orion Nebula ◽  
Main Sequence Stars ◽  
Nearby Star ◽  
X Ray ◽  
T Tauri ◽  
Pms Stars

I review here recent advances in our understanding of magnetic activity in pre-main sequence (PMS) protostars and T Tauri stars. Results are based on recent imaging, spectroscopic and temporal studies of nearby star forming regions from the Chandra X — ray Observatory and XMM — Newton, including a first look at an ultradeep Chandra exposure of the Orion Nebula Cluster.Pre-main sequence stars exhibit a high level of X-ray emission dominated by a bewildering variety of magnetic reconnection flares. Activity is linked to bulk stellar properties — Lbol, mass, surface area or volume — rather than rotation. This suggests that dynamo processes in deeply convective PMS stars may fundamentally differ from the tachocline dynamo operating in main sequence stars.X-rays and MeV particles from magnetic flares will affect the circumstellar environment in PMS systems, particularly the protoplanetary disk. X-ray emission may influence: disk ionization, turbulence and viscosity; Jovian planet formation and migration; the production of meteoritic isotopes and melting of meteoritic chondrules; the heating and chemistry of the disk. X-ray surveys are also effective in locating post-T Tauri stars for disk evolution studies.

scholarly journals A Radio Survey of Older T Tauri Stars in the η Chamaeleontis Cluster

1999 ◽  
Vol 16 (3) ◽  
pp. 257-261 ◽  
Author(s):  
Eric E. Mamajek ◽  
Warrick A. Lawson ◽  
Eric D. Feigelson
Keyword(s):  
Radio Emission ◽  
Main Sequence ◽  
T Tauri Stars ◽  
Young Stars ◽  
Radio Continuum ◽  
Rotating Stars ◽  
Main Sequence Stars ◽  
X Ray ◽  
Rotation Periods ◽  
T Tauri

AbstractA radio continuum survey of X-ray-identified weak-lined T Tauri stars (WTTs) in the newly-discovered η Chamaeleontis cluster has been completed using the Australia Telescope Compact Array (ATCA). The 10 known WTTs in the cluster form a unique sample of codistant late-type pre-main-sequence stars with ages of ~8 Myr and masses ranging from 0·1–1·0 M⊙. Our survey detected none of the 10 X-ray-emitting WTTs with 3σ sensitivity limits at 4·8 and 8·6 GHz (6·2 and 3·5 cm) of typically 0·4 mJy, corresponding to a radio luminosity of 4·5 ×1015 erg Hz−1 s−1. Rotation periods for these stars indicate that they are not, as a group, fast-rotating stars. The non-detection in the radio bands supports the findings of other radio surveys of inhomogeneous samples of young stars, where radio emission is fairly common (10–30%) among very young T Tauri stars across all late spectral types, but confined to rapidly-rotating F-G-K stars amongst older zero-age main sequence stars. Rotation, more than youth, appears to be the key to radio emission in young stars.

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 X-ray Emission from Young Stars in Suburban Orion

2004 ◽  
Vol 219 ◽  
pp. 228-232
Author(s):  
K. Briggs ◽  
M. Güdel ◽  
M. Audard ◽  
K. Smith ◽  
R. Mewe ◽  
...  
Keyword(s):  
Main Sequence ◽  
Rotation Period ◽  
Magnetic Activity ◽  
Young Stars ◽  
Rossby Number ◽  
Low Mass Stars ◽  
X Ray ◽  
Star Forming ◽  
Low Mass ◽  
Pms Stars

X-ray emission from > 100 pre-main sequence (PMS) stars in the Orion star-forming complex is studied in a 20-ks observation by XMM-Newton. No relation between the ratio of X-ray and bolometric luminosities, LX/Lbol, and rotation period or Rossby number is exhibited, though the action of a solar-like dynamo is not excluded because all stars would appear to be in the “saturated regime” of such a dynamo. Low-mass stars showing a strong U — V excess have lower median X-ray luminosity, suggesting that accretion suppresses magnetic activity.

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