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.

scholarly journals An ultra-short period rocky super-Earth orbiting the G2-star HD 80653

2020 ◽  
Vol 633 ◽  
pp. A133 ◽  
Author(s):  
G. Frustagli ◽  
E. Poretti ◽  
T. Milbourne ◽  
L. Malavolta ◽  
A. Mortier ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Thermal Emission ◽  
Earth Planet ◽  
Period Orbit ◽  
Short Period ◽  
Orbital Phase ◽  
Solar Type ◽  
Radial Velocity Data

Ultra-short period (USP) planets are a class of exoplanets with periods shorter than one day. The origin of this sub-population of planets is still unclear, with different formation scenarios highly dependent on the composition of the USP planets. A better understanding of this class of exoplanets will, therefore, require an increase in the sample of such planets that have accurate and precise masses and radii, which also includes estimates of the level of irradiation and information about possible companions. Here we report a detailed characterization of a USP planet around the solar-type star HD 80653 ≡EP 251279430 using the K2 light curve and 108 precise radial velocities obtained with the HARPS-N spectrograph, installed on the Telescopio Nazionale Galileo. From the K2 C16 data, we found one super-Earth planet (Rb = 1.613 ± 0.071 R⊕) transiting the star on a short-period orbit (Pb = 0.719573 ± 0.000021 d). From our radial velocity measurements, we constrained the mass of HD 80653 b to Mb = 5.60 ± 0.43 M⊕. We also detected a clear long-term trend in the radial velocity data. We derived the fundamental stellar parameters and determined a radius of R⋆ = 1.22 ± 0.01 R⊙ and mass of M⋆ = 1.18 ± 0.04 M⊙, suggesting that HD 80653 has an age of 2.7 ± 1.2 Gyr. The bulk density (ρb = 7.4 ± 1.1 g cm−3) of the planet is consistent with an Earth-like composition of rock and iron with no thick atmosphere. Our analysis of the K2 photometry also suggests hints of a shallow secondary eclipse with a depth of 8.1 ± 3.7 ppm. Flux variations along the orbital phase are consistent with zero. The most important contribution might come from the day-side thermal emission from the surface of the planet at T ~ 3480 K.

scholarly journals An application of a solar-type dynamo model for ε Eridani

2020 ◽  
Vol 497 (3) ◽  
pp. 3968-3975
Author(s):  
A P Buccino ◽  
L Sraibman ◽  
P M Olivar ◽  
F O Minotti
Keyword(s):  
Activity Cycle ◽  
Maunder Minimum ◽  
Dynamo Model ◽  
Dynamo Theory ◽  
Great Opportunity ◽  
Non Linear ◽  
Solar Type ◽  
Short And Long Term ◽  
Activity Cycles

ABSTRACT During the last decade, the relation between activity cycle periods and stellar parameters has received special attention. The construction of reliable registries of activity reveals that solar-type stars exhibit activity cycles with periods from few years to decades and, in some cases, long and short activity cycles coexist suggesting that two dynamos could operate in these stars. In particular, ε Eridani is an active young K2V star (0.8 Gyr), which exhibits short and long-term chromospheric cycles of ∼3 and ∼13-yr periods. Additionally, between 1985 and 1992, the star went through a broad activity minimum, similar to the solar Maunder Minimum state. Motivated by these results, we found in ε Eridani a great opportunity to test the dynamo theory. Based on the model developed in Sraibman & Minotti, in this work we built a non-linear axisymmetric dynamo for ε Eridani. The time series of the simulated magnetic field components near the surface integrated in all the stellar disc exhibits both the long and short activity cycles with periods similar to the ones detected from observations and also time intervals of low activity that could be associated with the broad Minimum. The short activity cycle associated with the magnetic reversal could be explained by the differential rotation, while the long cycle is associated with the meridional mass flows induced by the Lorentz force. In this way, we show that a single non-linear dynamo model derived from first principles with accurate stellar parameters could reproduce coexisting activity cycles.

scholarly journals High-amplitude, long-term X-ray variability in the solar-type star HD 81809: The beginning of an X-ray activity cycle?

2004 ◽  
Vol 418 (1) ◽  
pp. L13-L16 ◽  
Author(s):  
F. Favata ◽  
G. Micela ◽  
S. L. Baliunas ◽  
J. H. M. M. Schmitt ◽  
M. Güdel ◽  
...  
Keyword(s):  
Activity Cycle ◽  
High Amplitude ◽  
Type Star ◽  
X Ray ◽  
Solar Type ◽  
Solar Type Star

scholarly journals Activity–rotation in the dM4 star Gl 729

2020 ◽  
Vol 644 ◽  
pp. A2
Author(s):  
R. V. Ibañez Bustos ◽  
A. P. Buccino ◽  
S. Messina ◽  
A. F. Lanza ◽  
P. J. D. Mauas
Keyword(s):  
Differential Rotation ◽  
Activity Cycle ◽  
Magnetic Activity ◽  
Power Law Distribution ◽  
Dynamo Theory ◽  
Strong Shear ◽  
Solar Type ◽  
Activity Cycles ◽  
The One

Aims. Recently, new debates about the role of layers of strong shear have emerged in stellar dynamo theory. Further information on the long-term magnetic activity of fully convective stars could help determine whether their underlying dynamo could sustain activity cycles similar to the solar one. Methods. We performed a thorough study of the short- and long-term magnetic activity of the young active dM4 star Gl 729. First, we analyzed long-cadence K2 photometry to characterize its transient events (e.g., flares) and global and surface differential rotation. Then, from the Mount Wilson S-indexes derived from CASLEO spectra and other public observations, we analyzed its long-term activity between 1998 and 2020 with four different time-domain techniques to detect cyclic patterns. Finally, we explored the chromospheric activity at different heights with simultaneous measurements of the Hα and the Na I D indexes, and we analyzed their relations with the S-Index. Results. We found that the cumulative flare frequency follows a power-law distribution with slope ~−0.73 for the range 1032–1034 erg. We obtained Prot = (2.848 ± 0.001) days, and we found no evidence of differential rotation. We also found that this young active star presents a long-term activity cycle with a length of about 4 yr; there is less significant evidence of a shorter cycle of 0.8 yr. The star also shows a broad activity minimum between 1998 and 2004. We found a correlation between the S index, on the one hand, and the Hα the Na I D indexes, on the other hand, although the saturation level of these last two indexes is not observed in the Ca lines. Conclusions. Because the maximum-entropy spot model does not reflect migration between active longitudes, this activity cycle cannot be explained by a solar-type dynamo. It is probably caused by an α2-dynamo.

scholarly journals Discovery of short-term activity cycles in F-type stars

2019 ◽  
Vol 621 ◽  
pp. A136 ◽  
Author(s):  
M. Mittag ◽  
J. H. M. M. Schmitt ◽  
A. Hempelmann ◽  
K.-P. Schröder
Keyword(s):  
Activity Cycle ◽  
Total Activity ◽  
Short Term ◽  
Cyclic Activity ◽  
Solar Type ◽  
Cyclic Variations ◽  
Activity Cycles ◽  
F Stars ◽  
One Year ◽  
Index Time Series

Previous studies have revealed a 120 day activity cycle in the F-type star τ Boo, which represents the shortest activity cycle discovered until now. The question arises as to whether or not short-term activity cycles are a common phenomenon in F-type stars. To address this question, we analyse S-index time series of F-type stars taken with the TIGRE telescope to search for periodic variations with a maximal length of 2 years using the generalised Lomb-Scargle periodogram method. In our sample, we find four F-type stars showing periodic variations shorter than one year. However, the amplitude of these variations in our sample of F-star type stars appears to be smaller than that of solar-type stars with well-developed cyclic activity, and apparently represents only a part of the total activity. We conclude that among F-stars, the time-behaviour of activity differs from that of the Sun and cooler main sequence stars, as short-term cyclic variations with shallow amplitude of the cycle seem to prevail, rather than cycles with 10+ years periods and a larger cycle amplitude.

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 The Mount Wilson Program for Stellar Activity Cycles

1983 ◽  
Vol 102 ◽  
pp. 113-132
Author(s):  
Arthur H. Vaughan
Keyword(s):  
Stellar Mass ◽  
Present Review ◽  
Current Evidence ◽  
Stellar Activity ◽  
Activity Cycles

The present review will focus upon the incidence, form, and characteristic timescale of long-term chromospheric variations that, from the work of O.C. Wilson and his successors, can be descerned in records of CaII H and K emission now extending over 16 years, and the relation, if any, between properties of activity cycles and stellar mass, age, and rate of rotation, in the light of current evidence.

scholarly journals Transition from spot to faculae domination

2018 ◽  
Vol 621 ◽  
pp. A21 ◽  
Author(s):  
Timo Reinhold ◽  
Keaton J. Bell ◽  
James Kuszlewicz ◽  
Saskia Hekker ◽  
Alexander I. Shapiro
Keyword(s):  
Time Series ◽  
Phase Difference ◽  
Process Model ◽  
Activity Cycle ◽  
Magnetic Activity ◽  
Cycle Period ◽  
Stellar Activity ◽  
Rotation Periods ◽  
Active Stars ◽  
Activity Cycles

Context. The study of stellar activity cycles is crucial to understand the underlying dynamo and how it causes magnetic activity signatures such as dark spots and bright faculae. Having knowledge about the dominant source of surface activity might allow us to draw conclusions about the stellar age and magnetic field topology, and to put the solar cycle in context. Aims. We investigate the underlying process that causes magnetic activity by studying the appearance of activity signatures in contemporaneous photometric and chromospheric time series. Methods. Lomb-Scargle periodograms are used to search for cycle periods present in the photometric and chromospheric time series. To emphasize the signature of the activity cycle we account for rotation-induced scatter in both data sets by fitting a quasi-periodic Gaussian process model to each observing season. After subtracting the rotational variability, cycle amplitudes and the phase difference between the two time series are obtained by fitting both time series simultaneously using the same cycle period. Results. We find cycle periods in 27 of the 30 stars in our sample. The phase difference between the two time series reveals that the variability in fast-rotating active stars is usually in anti-phase, while the variability of slowly rotating inactive stars is in phase. The photometric cycle amplitudes are on average six times larger for the active stars. The phase and amplitude information demonstrates that active stars are dominated by dark spots, whereas less-active stars are dominated by bright faculae. We find the transition from spot to faculae domination to be at the Vaughan–Preston gap, and around a Rossby number equal to one. Conclusions. We conclude that faculae are the dominant ingredient of stellar activity cycles at ages ≳2.55 Gyr. The data further suggest that the Vaughan–Preston gap cannot explain the previously detected dearth of Kepler rotation periods between 15 and 25 days. Nevertheless, our results led us to propose an explanation for the lack of rotation periods to be due to the non-detection of periodicity caused by the cancelation of dark spots and bright faculae at ∼800 Myr.

scholarly journals Stellar Activity and Calcium Emission Variability

1983 ◽  
Vol 71 ◽  
pp. 195-199
Author(s):  
Sallie L. Baliunas
Keyword(s):  
Solar Activity ◽  
Magnetic Fields ◽  
Magnetic Activity ◽  
Small Scale ◽  
Physical Parameters ◽  
Stellar Activity ◽  
Ongoing Work ◽  
Chromospheric Emission ◽  
Activity Cycles

ABSTRACT.Time series analysis of fluctuations of Ca II H and K chromospheric emission has provided us with much information concerning stellar activity. On all timescales, events which parallel solar behavior can be observed: activity cycles, on timescales of years; rotation of stars and evolution of active areas on timescales of days to weeks; flare-like phenomena on timescales as short as minutes.We expect that the analogues of solar activity exist on other stars . By studying stellar counterparts to solar activity, we can hope to investigate the physical parameters which are thought to influence chromospheric and coronal activity. The stellar surfaces are usually spatially unresolvable; it is thus difficult to measure directly either small-scale surface inhomogeneities or the associated magnetic fields expected from spatially restricted areas.On the Sun, however, areas with strong surface magnetic fields show intense chromospheric Ca II H and K emission (Babcock and Babcock 1955; Skumanich et al 1975). Although indirect, the Ca II H and K features are good indicators of stellar magnetic activity. A major advantage of the Ca II features is their accessibility to ground-based observatories. Long-term synoptic programs are in progress to monitor stellar chromospheric activity, and this paper will highlight ongoing work at Mt. Wilson. Monitoring variations of Ca II H and K chromospheric emission over different timescales can reveal different physical phenomena: (1) Long-term (years) variations corresponding to stellar activity cycles; (2) intermediate term (days-months) variations indicating rotation or evolution of stellar active areas; (3) short-term (minutes-hours) variations resulting from impulsive and flare-like phenomena.

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