scholarly journals Long-term spot monitoring of the young solar analogue V889 Herculis

2019 ◽  
Vol 622 ◽  
pp. A170 ◽  
Author(s):  
T. Willamo ◽  
T. Hackman ◽  
J. J. Lehtinen ◽  
M. J. Käpylä ◽  
I. Ilyin ◽  
...  
Keyword(s):  
Magnetic Activity ◽  
Doppler Imaging ◽  
Mean Temperature ◽  
Photometric Observations ◽  
Crucial Information ◽  
The Mean ◽  
Magnetic Cycles ◽  
Temperature Maps ◽  
Weak Tendency

Context. Starspots are important manifestations of stellar magnetic activity. By studying their behaviour in young solar analogues, we can unravel the properties of their magnetic cycles. This gives crucial information of the underlying dynamo process. Comparisons with the solar cycle enable us to infer knowledge about how the solar dynamo has evolved during the Sun’s lifetime. Aims. Here we study the correlation between photometric brightness variations, spottedness, and mean temperature in V889 Her, a young solar analogue. Our data covers 18 years of spectroscopic and 25 years of photometric observations. Methods. We use Doppler imaging to derive temperature maps from high-resolution spectra. We use the Continuous Period Search method to retrieve mean V-magnitudes from photometric data. Results. Our Doppler imaging maps show a persistent polar spot structure varying in strength. This structure is centred slightly off the rotational pole. The mean temperature derived from the maps shows an overall decreasing trend, as does the photometric mean brightness, until it reaches its minimum around 2017. The filling factor of cool spots, however, shows only a weak tendency to anti-correlate with the decreasing mean brightness. Conclusions. We interpret V889 Her to have entered into a grand maximum in its activity. The clear relation between the mean temperature of the Doppler imaging surface maps and the mean magnitude supports the reliability of the Doppler images. The lack of correlation between the mean magnitude and the spottedness may indicate that bright features in the Doppler images are real.

scholarly journals Magnetic Cycles and Rotation in Active Late–Type Stars

2004 ◽  
Vol 215 ◽  
pp. 289-291
Author(s):  
Ilkka Tuominen ◽  
Svetlana V. Berdyugina ◽  
Maarit J. Korpi
Keyword(s):  
Mean Field ◽  
Point Of View ◽  
Doppler Imaging ◽  
Late Type ◽  
Dynamo Theory ◽  
Flip Flop ◽  
Cyclic Behaviour ◽  
Magnetic Cycles ◽  
Mean Field Dynamo

Observational evidence, based both on spectroscopic Doppler imaging and long-term photometry, of strongly nonaxisymmetric spot distributions in magnetically very active late-type stars, with a special cyclic behaviour (the “flip-flop” effect), is presented. Theoretical implications of these results are discussed from the point of view of nonlinear mean-field dynamo theory.

scholarly journals Seismic signatures of magnetic activity in solar-type stars observed by Kepler

2018 ◽  
Vol 13 (S340) ◽  
pp. 225-228
Author(s):  
A. R. G. Santos ◽  
T. L. Campante ◽  
W. J. Chaplin ◽  
M. S. Cunha ◽  
M. N. Lund ◽  
...  
Keyword(s):  
Seismic Data ◽  
Magnetic Activity ◽  
Acoustic Properties ◽  
Acoustic Modes ◽  
Solar Type ◽  
Magnetic Cycles

AbstractThe properties of the acoustic modes are sensitive to magnetic activity. The unprecedented long-term Kepler photometry, thus, allows stellar magnetic cycles to be studied through asteroseismology. We search for signatures of magnetic cycles in the seismic data of Kepler solar-type stars. We find evidence for periodic variations in the acoustic properties of about half of the 87 analysed stars. In these proceedings, we highlight the results obtained for two such stars, namely KIC 8006161 and KIC 5184732.

scholarly journals How the planetary research helps to the stellar dynamo understanding

2012 ◽  
Vol 8 (S294) ◽  
pp. 471-475
Author(s):  
I. Boisse ◽  
M. Oshagh ◽  
C. Lovis ◽  
N. C. Santos ◽  
X. Dumusque ◽  
...  
Keyword(s):  
Planetary System ◽  
Magnetic Activity ◽  
Doppler Imaging ◽  
Habitable Zone ◽  
Stellar Activity ◽  
Term Variation ◽  
Solar Type ◽  
Low Mass ◽  
Stellar Dynamo

AbstractMost of the exoplanet science is dependent on the stellar knowledge. One of them that has to be understood is the magnetic activity when we search for planets with radial velocity or photometry measurements. The main shape of stellar activity and spots properties have to be understood, for example, to choose the best targets to search for low-mass planets in the habitable zone or to derive the accurate parameters of a planetary system. With that aim, we show in this presentation how these studies lead to give clues on spots latitudes and on the long term variation of stellar activity. The properties of magnetic activity on the low rotators solar-type stars are not easily reachable by other techniques (spectropolarimetry or Doppler imaging) and these studies should be used to constrain theories of stellar dynamo.

scholarly journals RS CVn binary IM Peg – investigation of stellar activity and surface flows

2009 ◽  
Vol 5 (S264) ◽  
pp. 267-269
Author(s):  
Heidi Korhonen ◽  
Michael Weber ◽  
Markus Wittkowski ◽  
Thomas Granzer ◽  
Klaus G. Strassmeier
Keyword(s):  
Surface Temperature ◽  
Differential Rotation ◽  
Imaging Techniques ◽  
Input Parameter ◽  
Magnetic Activity ◽  
Stellar Surface ◽  
Doppler Imaging ◽  
Time Period ◽  
Rotation Pattern ◽  
Temperature Maps

AbstractWe have obtained high resolution, high S/N spectra of the RS CVn binary IM Peg using UVES spectrograph at Kueyen 8.2m telescope of ESO VLT. We use Doppler imaging techniques to obtain stellar surface temperature maps from the UVES data. The TempMap code allows us to use surface differential rotation as an input parameter and thus to try to construct the rotation pattern on the stellar surface as part of the inversion process. The UVES observations are combined with spectroscopic observations from another time period obtained at the STELLA observatory. We obtain stellar surface temperature maps also from these spectra. These Doppler images are used to study the magnetic activity and surface differential rotation on IM Peg.

Photometric results of the long-term monitoring of the active asteroid (596) Scheila

2020 ◽  
Author(s):  
Zhong-Yi Lin ◽  
Chen-Yen Hsu
Keyword(s):  
Light Curve ◽  
Rotation Period ◽  
Impact Event ◽  
Mean Values ◽  
Photometric Observations ◽  
The Mean ◽  
The Difference ◽  
The Impact ◽  
Term Monitoring

<p>(596) Scheila was observed to have an active appearance as a result of impact event in late 2010. In additional the coma feature, the shape of light curve had been found the difference probably fresh material or surface properties changed around the impact site. In this study, we present the results of our monitoring observations obtained in 2014 and 2019-2020. The mean values of the color indices (B−V = (0.75 ± 0.08)<sup>m</sup>, V−R = (0.45 ± 0.04)<sup>m</sup>, and R−I = (0.44 ± 0.09)<sup>m</sup>) agree well with the values for asteroids of the D-types. The rotation period of the asteroid estimated from photometric observations in 2014 is 15.8 ± 0.1 h. The shape of the light curve is similar as that found after impact event. Furthermore, we did not find any rotational color variability in B-V, V-R and R-I diagrams, meaning the observed surface in this observing period of 2019-2020 is homogeneous.</p>

scholarly journals Magnetic field and chromospheric activity evolution of HD 75332: a rapid magnetic cycle in an F star without a hot Jupiter

2020 ◽  
Author(s):  
E L Brown ◽  
S C Marsden ◽  
M W Mengel ◽  
S V Jeffers ◽  
I Millburn ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Magnetic Activity ◽  
Doppler Imaging ◽  
Shallow Convection ◽  
Magnetic Cycle ◽  
Field Polarity ◽  
Chromospheric Activity ◽  
Magnetic Cycles ◽  
Hot Jupiter

Abstract Studying cool star magnetic activity gives an important insight into the stellar dynamo and its relationship with stellar properties, as well as allowing us to place the Sun’s magnetism in the context of other stars. Only 61 Cyg A (K5V) and τ Boo (F8V) are currently known to have magnetic cycles like the Sun’s, where the large-scale magnetic field polarity reverses in phase with the star’s chromospheric activity cycles. τ Boo has a rapid ∼240 d magnetic cycle, and it is not yet clear whether this is related to the star’s thin convection zone or if the dynamo is accelerated by interactions between τ Boo and its hot Jupiter. To shed light on this, we studied the magnetic activity of HD 75332 (F7V) which has similar physical properties to τ Boo and does not appear to host a hot Jupiter. We characterized its long term chromospheric activity variability over 53 yrs and used Zeeman Doppler Imaging to reconstruct the large-scale surface magnetic field for 12 epochs between 2007 and 2019. Although we observe only one reversal of the large-scale magnetic dipole, our results suggest that HD 75332 has a rapid ∼1.06 yr solar-like magnetic cycle where the magnetic field evolves in phase with its chromospheric activity. If a solar-like cycle is present, reversals of the large-scale radial field polarity are expected to occur at around activity cycle maxima. This would be similar to the rapid magnetic cycle observed for τ Boo, suggesting that rapid magnetic cycles may be intrinsic to late-F stars and related to their shallow convection zones.

scholarly journals Activity on a Li-rich giant: DI Psc revisited

2013 ◽  
Vol 9 (S302) ◽  
pp. 383-384
Author(s):  
Levente Kriskovics ◽  
Zsolt Kővári ◽  
Krisztián Vida ◽  
Katalin Oláh
Keyword(s):  
Surface Temperature ◽  
Time Evolution ◽  
Differential Rotation ◽  
Imaging Study ◽  
Magnetic Activity ◽  
Doppler Imaging ◽  
Rotation Pattern ◽  
Evolutionary Phase ◽  
Temperature Maps

AbstractWe present a new Doppler imaging study for the Li-rich single K-giant DI Psc. Surface temperature maps are reconstructed for two subsequent rotation cycles. From the time evolution of the spot distribution antisolar-type differential rotation pattern is revealed. We show marks of non-uniform Li-abundance as well. The possible connection between the current evolutionary phase of the star and its magnetic activity is briefly discussed.

scholarly journals Spot evolution on LQ Hya from 2006–2017: temperature maps based on SOFIN and FIES data

2019 ◽  
Vol 629 ◽  
pp. A120 ◽  
Author(s):  
Elizabeth M. Cole-Kodikara ◽  
Maarit J. Käpylä ◽  
Jyri J. Lehtinen ◽  
Thomas Hackman ◽  
Ilya V. Ilyin ◽  
...  
Keyword(s):  
Surface Temperature ◽  
High Latitude ◽  
Phase Behaviour ◽  
Doppler Imaging ◽  
Chaotic State ◽  
Rapid Phase ◽  
Latitude Range ◽  
Spot Activity ◽  
Temperature Maps

Context. LQ Hya is one of the most frequently studied young solar analogue stars. Recently, it has been observed to show intriguing behaviour when analysing long-term photometry. For instance, from 2003–2009, a coherent spot structure migrating in the rotational frame was reported by various authors. However, ever since, the star has entered a chaotic state where coherent structures seem to have disappeared and rapid phase jumps of the photometric minima occur irregularly over time. Aims. LQ Hya is one of the stars included in the SOFIN/FIES long-term monitoring campaign extending over 25 yr. Here, we publish new temperature maps for the star during 2006–2017, covering the chaotic state of the star. Methods. We used a Doppler imaging technique to derive surface temperature maps from high-resolution spectra. Results. From the mean temperatures of the Doppler maps, we see a weak but systematic increase in the surface temperature of the star. This is consistent with the simultaneously increasing photometric magnitude. During nearly all observing seasons, we see a high-latitude spot structure which is clearly non-axisymmetric. The phase behaviour of this structure is very chaotic but agrees reasonably well with the photometry. Equatorial spots are also frequently seen, but we interpret many of them to be artefacts due to the poor to moderate phase coverage. Conclusions. Even during the chaotic phase of the star, the spot topology has remained very similar to the higher activity epochs with more coherent and long-lived spot structures. In particular, we see high-latitude and equatorial spot activity, the mid latitude range still being most often void of spots. We interpret the erratic jumps and drifts in phase of the photometric minima to be caused by changes in the high-latitude spot structure rather than the equatorial spots.

A model of vegetative flush development and its potential use managing macadamia (Macadamia integrifolia) tree canopies

2009 ◽  
Vol 60 (5) ◽  
pp. 420 ◽  
Author(s):  
J. D. Wilkie ◽  
M. Sedgley ◽  
T. Olesen
Keyword(s):  
Solar Radiation ◽  
Stem Elongation ◽  
Stem Length ◽  
Weather Data ◽  
Macadamia Integrifolia ◽  
Mean Temperature ◽  
Tree Canopies ◽  
The Mean ◽  
The Relationship

We examined the relationship between shoot growth and temperature and solar radiation in macadamia (Macadamia integrifolia Maiden and Betche, M. integrifolia × tetraphylla Johnson) as an aid to developing pruning strategies for this crop. Trees growing at Alstonville (28.9°S) in northern NSW, Australia, were pruned at various times to promote vegetative flushing under a range of environmental conditions. Flush development in macadamia is cyclic: bud release and stem elongation followed by a period of dormancy, before bud release of the subsequent flush. The rate of bud release after pruning was best correlated with the product of the mean temperature and solar radiation (r2 = 0.75, P < 0.0001), whereas the rate of flush development was best correlated with the mean temperature (r2 = 0.76, P < 0.0001). The number of buds released per pruned stem was greater under higher temperatures and solar radiation (r2 = 0.37, P < 0.001), but the length of the flush after pruning decreased with increasing temperatures (r2 = 0.32, P < 0.01). The descriptive models were combined with long-term weather data to predict the duration and characteristics of flushes following pruning at various times of the year along Australia’s eastern seaboard, from Mareeba (17.0°S) to Coffs Harbour (30.3°S). Flush duration and stem length following June pruning were predicted to be greater than following early autumn or September pruning and to vary from year to year, and with location (latitude). We discuss the implications of the model predictions for productivity and propose pruning times intended to optimise flowering and yield. Further research is required to test these proposed pruning strategies.

scholarly journals Using planetary transits to estimate magnetic cycles lengths in Kepler stars

2016 ◽  
Vol 12 (S328) ◽  
pp. 152-158 ◽  
Author(s):  
Raissa Estrela ◽  
Adriana Valio
Keyword(s):  
Cycle Length ◽  
Rotation Period ◽  
Activity Cycle ◽  
Magnetic Activity ◽  
Activity Level ◽  
Light Curves ◽  
Cycle Period ◽  
Solar Type ◽  
Magnetic Cycles

AbstractObservations of various solar-type stars along decades showed that they could have magnetic cycles, just like our Sun. These observations yield a relation between the rotation period Prot and the cycle length Pcycle of these stars. Two distinct branches for the cycling stars were identified: active and inactive, classified according to stellar activity level and rotation rate. In this work, we determined the magnetic activity cycle for 6 active stars observed by the Kepler telescope. The method adopted here estimates the activity from the excess in the residuals of the transit light curves. This excess is obtained by subtracting a spotless model transit from the light curve, and then integrating over all the residuals during the transit. The presence of long term periodicity is estimated from the analysis of a Lomb-Scargle periodogram of the complete time series. Finally, we investigate the rotation-cycle period relation for the stars analysed here.

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