scholarly journals An X-ray activity cycle on the young solar-like star ɛ Eridani

2020 ◽  
Vol 636 ◽  
pp. A49 ◽  
Author(s):  
M. Coffaro ◽  
B. Stelzer ◽  
S. Orlando ◽  
J. Hall ◽  
T. S. Metcalfe ◽  
...  
Keyword(s):  
Emission Measure ◽  
Active Regions ◽  
Activity Cycle ◽  
Activity Level ◽  
Coronal Emission ◽  
X Ray ◽  
Magnetic Structures ◽  
Activity Cycles ◽  
Measure Distribution

Chromospheric Ca II activity cycles are frequently found in late-type stars, but no systematic programs have been created to search for their coronal X-ray counterparts. The typical time scale of Ca II activity cycles ranges from years to decades. Therefore, long-lasting missions are needed to detect the coronal counterparts. The XMM-Newton satellite has so far detected X-ray cycles in five stars. A particularly intriguing question is at what age (and at what activity level) X-ray cycles set in. To this end, in 2015 we started the X-ray monitoring of the young solar-like star ɛ Eridani, previously observed on two occasions: in 2003 and in early 2015, both by XMM-Newton. With an age of 440 Myr, it is one of the youngest solar-like stars with a known chromospheric Ca II cycle. We collected the most recent Mount Wilson S-index data available for ɛ Eridani, starting from 2002, including previously unpublished data. We found that the Ca II cycle lasts 2.92 ± 0.02 yr, in agreement with past results. From the long-term XMM-Newton lightcurve, we find clear and systematic X-ray variability of our target, consistent with the chromospheric Ca II cycle. The average X-ray luminosity is 2 × 1028erg s−1, with an amplitude that is only a factor of 2 throughout the cycle. We apply a new method to describe the evolution of the coronal emission measure distribution of ɛ Eridani in terms of solar magnetic structures: active regions, cores of active regions, and flares covering the stellar surface at varying filling fractions. Combinations of these three types of magnetic structures can only describe the observed X-ray emission measure of ɛ Eridani if the solar flare emission measure distribution is restricted to events in the decay phase. The interpretation is that flares in the corona of ɛ Eridani last longer than their solar counterparts. We ascribe this to the lower metallicity of ɛ Eridani. Our analysis also revealed that the X-ray cycle of ɛ Eridani is strongly dominated by cores of active regions. The coverage fraction of cores throughout the cycle changes by the same factor as the X-ray luminosity. The maxima of the cycle are characterized by a high percentage of covering fraction of the flares, consistent with the fact that flaring events are seen in the corresponding short-term X-ray lightcurves predominately at the cycle maxima. The high X-ray emission throughout the cycle of ɛ Eridani is thus explained by the high percentage of magnetic structures on its surface.

scholarly journals Relations between photospheric structure and X-ray emission

1996 ◽  
Vol 176 ◽  
pp. 477-484
Author(s):  
M. Kürster
Keyword(s):  
Active Regions ◽  
Light Curves ◽  
Coronal Emission ◽  
Term Trend ◽  
X Ray ◽  
V Band ◽  
Subsequent Rise ◽  
Long Term Trend ◽  
Rise Phase

The relation between photospheric and coronal active regions in late–type stars is studied from two different points of departure. First, I report on 5 years of ROSAT X–ray monitoring of the active young K–star AB Dor. I compare the X–ray data with 16 years of V–band brightness monitoring showing a 10–year decline between 1978 and 1989 and a subsequent rise phase. Quite differently, the X–ray flux of AB Dor (while exhibiting strong variability on time scales of minutes to weeks) reveals no pronounced long–term trend over the 5 years of the program. This supports the concept of a saturated corona. Second, I present rotationally modulated ROSAT X–ray light curves of three active stars (AB Dor, CF Tuc, YY Men) and compare them with contemporaneous Doppler images. I demonstrate that it is possible to explain the X–ray light curves by coronal emission regions that are spatially related with photospheric active regions. I discuss the concept of X–ray bright loops connecting the major star spot complexes.

scholarly journals Coronal Activity on Rapidly-Rotating Solar-Like Stars: Chandra Observations of ER Vul

2004 ◽  
Vol 215 ◽  
pp. 334-335
Author(s):  
Alexander Brown ◽  
Joanna M. Brown ◽  
Rachel A. Osten ◽  
Thomas R. Ayres ◽  
Edward Guinan
Keyword(s):  
Emission Measure ◽  
The Sun ◽  
Coronal Emission ◽  
Dwarf Stars ◽  
X Ray ◽  
Rotation Rates ◽  
Elemental Abundances ◽  
Long Duration ◽  
Short Period ◽  
Measure Distribution

We investigate the coronal structure of rapidly-rotating, solar-like stars using Chandra HETGS spectra of the short-period binary ER Vul, and by comparison with X-ray observations of the Sun and other dwarf stars. ER Vul consists of two solar-like (G0 + G5) dwarfs with rotation rates ~ 40 times that of the Sun. This binary is not interacting and these stars are the fastest rotating G dwarfs suitable for high resolution X-ray spectroscopy. X-ray (1.8-40 Å) spectra were obtained on 2001 March 29-30 along with 10.5 hours of simultaneous VLA monitoring at 3.6 and 20 cm. These spectra show hot, multi-temperature coronal emission with emission lines ranging in temperature from O VII (2 MK) to Fe XXIV (30 MK). ER Vul showed only low-level variability during the X-ray observation. Unlike the behaviour of longer period active binaries, no large, long-duration flares were detected, consistent with previous X-ray observations of this binary. No evidence for eclipses is seen in either the X-ray or radio emission. The coronal emission measure distribution and elemental abundances were derived for ER Vul.

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 Goals for the Application of High-Resolution X-ray Spectroscopy to the Diagnosis of Stellar Coronal Plasmas

1990 ◽  
Vol 115 ◽  
pp. 94-109 ◽  
Author(s):  
Jeffrey L. Linsky
Keyword(s):  
High Resolution ◽  
Spectral Resolution ◽  
Transient Flow ◽  
Emission Measure ◽  
Active Regions ◽  
High Sensitivity ◽  
High Spectral Resolution ◽  
Spectral Features ◽  
Signal To Noise ◽  
X Ray

AbstractI provide examples of how high-resolution x-ray spectra may be used to determine the temperature and emission measure distributions, electron densities, steady and transient flow velocities, and location of active regions in stellar coronae. For each type of measurement I estimate the minimum spectral resolution required to resolve the most useful spectral features. In general, high sensitivity is required to obtain sufficient signal-to-noise to exploit the high spectral resolution. Although difficult, each measurement should be achievable with the instrumentation proposed for AXAF.

scholarly journals First Determinations of Differential Emission Measure Distribution from RESIK X-ray Spectra

2004 ◽  
Vol 2004 (IAUS223) ◽  
pp. 461-462 ◽  
Author(s):  
A. K[ecedilla]pa ◽  
J. Sylwester ◽  
B. Sylwester ◽  
M. Siarkowski
Keyword(s):  
Emission Measure ◽  
Differential Emission Measure ◽  
X Ray ◽  
Measure Distribution

scholarly journals A Model of Solar X-ray Bright Points and Ephemeral Active Regions

1979 ◽  
Vol 32 (6) ◽  
pp. 671 ◽  
Author(s):  
JH Piddington
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Large Scale ◽  
Flux Rope ◽  
Active Regions ◽  
Activity Cycle ◽  
Solar Magnetic Fields ◽  
Flux Tubes ◽  
X Ray ◽  
Field System

Solar ephemeral active regions may provide a larger amount of emerging magnetic flux than the active regions themselves, and the origin and disposal of this flux pose problems. The related X-ray bright points are a major feature of coronal dynamics, and the two phenomena may entail a revision of our ideas of the activity cycle. A new large-scale subsurface magnetic field system has been suggested, but it is shown that such a system is neither plausible nor necessary. The emerging magnetic bipoles merely represent loops in pre-existing vertical flux tubes which are parts of active regions or the remnants of active regions. These loops result from the kink (or helical) instability in a twisted flux tube. Their observed properties are explained in terms of the flux-rope theory of solar fields. The model is extended to some dynamical effects in emerging loops. Further observations of ephemeral active regions may provide important tests between the traditional and flux-rope theories of solar magnetic fields.

scholarly journals Multi-wavelength variability of the young solar analog ι Horologii

2019 ◽  
Vol 631 ◽  
pp. A45 ◽  
Author(s):  
J. Sanz-Forcada ◽  
B. Stelzer ◽  
M. Coffaro ◽  
S. Raetz ◽  
J. D. Alvarado-Gómez
Keyword(s):  
Light Curve ◽  
Thermal Structure ◽  
Rotation Period ◽  
Activity Cycle ◽  
X Rays ◽  
X Ray ◽  
Multi Wavelength ◽  
Activity Cycles ◽  
Irregular Behavior

Context. Chromospheric activity cycles are common in late-type stars; however, only a handful of coronal activity cycles have been discovered. ι Hor is the most active and youngest star with known coronal cycles. It is also a young solar analog, and we are likely facing the earliest cycles in the evolution of solar-like stars, at an age (~600 Myr) when life appeared on Earth. Aims. Our aim is to confirm the ~1.6 yr coronal cycle and characterize its stability over time. We use X-ray observations of ι Hor to study the corona of a star representing the solar past through variability, thermal structure, and coronal abundances. Methods. We analyzed multi-wavelength observations of ι Hor using XMM-Newton, TESS, and HST data. We monitored ι Hor throughout almost seven years in X-rays and in two UV bands. The summed RGS and STIS spectra were used for a detailed thermal structure model, and the determination of coronal abundances. We studied rotation and flares in the TESS light curve. Results. We find a stable coronal cycle along four complete periods, more than covered in the Sun. There is no evidence for a second longer X-ray cycle. Coronal abundances are consistent with photospheric values, discarding any effects related to the first ionization potential. From the TESS light curve we derived the first photometric measurement of the rotation period (8.2 d). No flares were detected in the TESS light curve of ι Hor. We estimate the probability of having detected zero flares with TESS to be ~2%. Conclusions. We corroborate the presence of an activity cycle of ~1.6 yr in ι Hor in X-rays, more regular than its Ca II H&K counterpart. A decoupling of the activity between the northern and southern hemispheres of the star might explain the disagreement. The inclination of the system would result in an irregular behavior in the chromospheric indicators. The more extended coronal material would be less sensitive to this effect.

Coronal magnetic structures observing campaign. I - Simultaneous microwave and soft X-ray observations of active regions at the solar limb

1991 ◽  
Vol 374 ◽  
pp. 374 ◽  
Author(s):  
N. Nitta ◽  
S. M. White ◽  
M. R. Kundu ◽  
N. Gopalswamy ◽  
G. D. Holman ◽  
...  
Keyword(s):  
Solar Limb ◽  
Active Regions ◽  
X Ray ◽  
Magnetic Structures

scholarly journals HD 38858: a solar-type star with an activity cycle of ∼10.8 yr

2018 ◽  
Vol 620 ◽  
pp. A34 ◽  
Author(s):  
M. Flores ◽  
J. F. González ◽  
M. Jaque Arancibia ◽  
C. Saffe ◽  
A. Buccino ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Activity Cycle ◽  
Earth Planet ◽  
Stellar Activity ◽  
Balmer Lines ◽  
Solar Type ◽  
Activity Cycles ◽  
Novel Strategy ◽  
Solar Type Star

Context. The detection of chromospheric activity cycles in solar-analogue and twin stars can be used to place the solar cycle in a wider context. However, relatively few of these stars with activity cycles have been detected. It is well known that the cores of the Ca II H&K lines are modulated by stellar activity. The behaviour of the Balmer and other optical lines with stellar activity is not yet completely understood. Aims. We search for variations in the Ca II H&K, Balmer, and Fe II lines modulated by stellar activity. In particular, we apply a novel strategy to detect possible shape variations in the Hα line. Methods. We analysed activity signatures in HD 38858 using HARPS and CASLEO spectra obtained between 2003 and 2017. We calculated the Mount Wilson index (SMW), log(R′HK), and the statistical moments of the Ca II H&K, Balmer, and other optical lines. We searched for periodicities using the generalized Lomb-Scargle periodogram. Results. We detect a long-term activity cycle of 10.8 yr in Ca II H&K and Hα in the solar-analogue star HD 38858. In contrast, this cycle is marginally detected in the Fe II lines. We also detect a noticeable variation in radial velocity that seems to be produced by stellar activity. Conclusions. HD 38858 is the second solar-analogue star where we find a clear activity cycle that is replicated in the Balmer lines. Spectral indexes based on the shape of Hα line seem to be more reliable than the fluxes in the same line for detecting activity variations. The cyclic modulation we detected gives place to a variation in radial velocity that previously has been associated with a super-Earth planet. Finally, due to the similarity of HD 38858 with the Sun, we recommend to continue monitoring this star.

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