scholarly journals Starspot evolution, differential rotation, and correlation between chromospheric and photospheric activities on Kepler-411

2020 ◽  
Vol 501 (2) ◽  
pp. 1878-1890
Author(s):  
Fukun Xu ◽  
Shenghong Gu ◽  
Panogiotis Ioannidis
Keyword(s):  
Differential Rotation ◽  
Spectroscopic Data ◽  
Rotation Period ◽  
Periodic Variation ◽  
Strongly Correlated ◽  
Chromospheric Activity ◽  
Large Dispersion ◽  
Chromospheric Emission ◽  
Efficient Program ◽  
Basis Vectors

ABSTRACT We present an analysis of the starspot evolution, the surface differential rotation (SDR), the correlation between chromospheric activity indicators and the spatial connection between chromospheric and photospheric activities on the active star Kepler-411, using time-series photometry over four years from Kepler, and spectroscopic data from Keck I 10-m and Lijiang 2.4-m telescopes. We constructed the light curve (LC) by re-performing photometry and reduction from the Target Pixel Files and Cotrending Basis Vectors with a manually redefined aperture using the software pyke3. An efficient program, gemc_lcm, was developed to apply a two-spots model to chosen LC segments with three spot groups at fixed latitudes (30○, 45○), (30○, 60○) and (45○, 60○). We found a periodic variation of the starspots at the period of about 660 d which independs on spot latitudes, and estimated the lower limit of SDR rate α = 0.1016(0.0023) and equatoral rotation period Peq = 9.7810(0.0169) d. Simultaneously, the relative variations of chromospheric activity indicators were derived by subtracting the overall mean spectrum from individual spectrum. It is found that Ca ii H and K emissions are strongly correlated with each other, and there also exists a correlation between Hα and Ca ii H & K emissions, with large dispersion, in accordance with previous results. Furthermore, we find the correlation between Ca ii H and K emissions is different in 2011 and 2012. The chromospheric emission variation shows a highly spatial anticorrelation with the LC, suggesting a spatial connection between the chromospheric active region and spot region.

scholarly journals Learning about Stellar Dynamos from Long–term Photometry of Starspots

1991 ◽  
Vol 130 ◽  
pp. 353-369 ◽  
Author(s):  
Douglas S. Hall
Keyword(s):  
Differential Rotation ◽  
Rotation Period ◽  
Turnover Time ◽  
Rotating Stars ◽  
Photometric Variability ◽  
Solar Type ◽  
Magnetic Cycles ◽  
The Many ◽  
Rapidly Rotating Stars

AbstractSpottedness, as evidenced by photometric variability in 277 late-type binary and single stars, is found to occur when the Rossby number is less than about 2/3. This holds true when the convective turnover time versus B–V relation of Gilliland is used for dwarfs and also for subgiants and giants if their turnover times are twice and four times longer, respectively, than for dwarfs. Differential rotation is found correlated with rotation period (rapidly rotating stars approaching solid-body rotation) and also with lobe-filling factor (the differential rotation coefficient k is 2.5 times larger for F = 0 than F = 1). Also reviewed are latitude extent of spottedness, latitude drift during a solar-type cycle, sector structure and preferential longitudes, starspot lifetimes, and the many observational manifestations of magnetic cycles.

scholarly journals Surface magnetic activity of the fast-rotating G5 giant IN Comae, central star of the faint planetary nebula LoTr 5

2019 ◽  
Vol 624 ◽  
pp. A83 ◽  
Author(s):  
Zs. Kővári ◽  
K. G. Strassmeier ◽  
K. Oláh ◽  
L. Kriskovics ◽  
K. Vida ◽  
...  
Keyword(s):  
Time Series ◽  
Differential Rotation ◽  
Planetary Nebula ◽  
Spectral Synthesis ◽  
Binary Star ◽  
Rotation Period ◽  
Planetary Nebulae ◽  
Asymptotic Giant Branch ◽  
Stellar Surface ◽  
Average Lifetime

Context. On the asymptotic giant branch, low to intermediate mass stars blow away their outer envelopes, forming planetary nebulae. Dynamic interaction between the planetary nebula and its central progenitor is poorly understood. The interaction is even more complex when the central object is a binary star with a magnetically active component, as is the case for the target in this paper. Aims. We aim to quantify the stellar surface activity of the cool binary component of IN Com and aim to explain its origin. In general, we need a better understanding of how central binary stars in planetary nebulae evolve and how this evolution could develop such magnetically active stars as IN Com. Methods. We present a time series of 13 consecutive Doppler images covering six months in 2017 that we used to measure the surface differential rotation with a cross-correlation method. Hitherto unpublished high-precision photometric data from 1989 to 2017 are presented. We applied Fourier-transformation-based frequency analysis to both photometry and spectra. Very high resolution (R ≈ 200 000) spectra were used to update IN Com’s astrophysical parameters by means of spectral synthesis. Results. Our time-series Doppler images show cool and warm spots coexisting with an average surface temperature contrast of −1000 K and +300 K with respect to the effective temperature. Approximately 8% of the stellar surface is covered with cool spots and ∼3% with warm spots. A consistent cool polar spot is seen in all images. The average lifetime of the cool spots is not much more than a few stellar rotations (one month), while the warm spots appear to live longer (three months) and are mostly confined to high latitudes. We found anti-solar surface differential rotation with a shear coefficient of α = −0.026 ± 0.005 suggesting an equatorial rotation period of 5.973 ± 0.008 d. We reconfirm the 5.9 day rotation period of the cool star from photometry, radial velocities, and Hα line-profile variations. A long-term V-brightness variation with a likely period of 7.2 yr is also found. It appears in phase with the orbital radial velocity of the binary system in the sense that it is brightest at highest velocity and faintest at lowest velocity, that is, at the two phases of quadrature. We redetermine [Ba/Fe], [Y/Fe], and [Sr/Fe] ratios and confirm the overabundance of these s-process elements in the atmosphere of IN Com.

scholarly journals X Sources in δ Scuti Stars: an Ultraviolet Study of 71 Tau

1993 ◽  
Vol 139 ◽  
pp. 396-396
Author(s):  
L.E. Pasinetti Fracassini ◽  
L. Pastori ◽  
F. De Nile ◽  
E. Poretti ◽  
E. Antonello
Keyword(s):  
Mass Loss ◽  
Spectroscopic Data ◽  
Pulsation Period ◽  
X Ray ◽  
Chromospheric Activity ◽  
Hyades Cluster ◽  
Photometric Observations ◽  
Scuti Stars ◽  
Einstein Observatory ◽  
Δ Scuti Stars

IUE observations of δ Scuti variables were planned to study the correlations between chromospheric activity and dynamics of pulsations, convection, rotation and to search for evidence of mass loss. So far we observed the following stars: ρ Pup, β Cas, o1 Eri, K2 Boo, τ Peg, 69 Tau, 71 Tau and τ Cyg. Results and discussions on our survey may be found in Pasinetti Fracassini et al. (1990) and Fracassini et al. (1991).Ultraviolet spectroscopic data (6 LWP and 3 SWP spectra) of 71 Tau were obtained with IUE in the year 1990, spanning an interval of 5h35rn and covering about 1.5 cycles of the pulsation period. The period, derived from new photometric observations, is 4h32m with an cimplitude of 0m.028. This variable is the most intense X-ray source in the Hyades cluster according to the results of Einstein Observatory.

The Impact of Dust/Gas Ratios on Chromospheric Activity in Red Giant and Supergiant Stars

2018 ◽  
Vol 14 (S343) ◽  
pp. 365-367
Author(s):  
Kenneth G. Carpenter ◽  
Gioia Rau
Keyword(s):  
Surface Fluxes ◽  
Emission Lines ◽  
Chromospheric Activity ◽  
Cool Stars ◽  
Chromospheric Emission ◽  
Activity Temperature ◽  
Wind Characteristics ◽  
Red Giant ◽  
The Impact ◽  
Reduced Activity

AbstractStencel et al. (1986) analyzed IUE spectra of a modest set of cool stars and found that they continue to produce chromospheres even in the presence of high dust levels in their outer atmospheres. This reversed the previous results of Jennings (1973) and Jennings & Dyck (1972). We describe an on-going extension of these studies to a sample of stars representing a broader range in dust/gas ratios, using archival IUE and archival and new HST data on both RGB and AGB stars. Surface fluxes in emission lines will be analyzed to assess the chromospheric activity and obscuration by dust in each star, as those fluxes will follow a different pattern for reduced activity (temperature/density dependent) vs. dust obscuration (wavelength dependent). Wind characteristics will be measured by modeling of wind-reversed chromospheric emission lines.

scholarly journals Stellar activity analysis of Barnard’s Star: Very slow rotation and evidence for long-term activity cycle

2019 ◽  
Author(s):  
B Toledo-Padrón ◽  
J I González Hernández ◽  
C Rodríguez-López ◽  
A Suárez Mascareño ◽  
R Rebolo ◽  
...  
Keyword(s):  
Time Series ◽  
Spectroscopic Data ◽  
Rotation Period ◽  
Photometric Data ◽  
Activity Level ◽  
Slow Rotation ◽  
Activity Levels ◽  
Stellar Activity

Abstract The search for Earth-like planets around late-type stars using ultra-stable spectrographs requires a very precise characterization of the stellar activity and the magnetic cycle of the star, since these phenomena induce radial velocity (RV) signals that can be misinterpreted as planetary signals. Among the nearby stars, we have selected Barnard’s Star (Gl 699) to carry out a characterization of these phenomena using a set of spectroscopic data that covers about 14.5 years and comes from seven different spectrographs: HARPS, HARPS-N, CARMENES, HIRES, UVES, APF, and PFS; and a set of photometric data that covers about 15.1 years and comes from four different photometric sources: ASAS, FCAPT-RCT, AAVSO, and SNO. We have measured different chromospheric activity indicators (Hα, Ca II HK and Na I D), as well as the FWHM of the cross-correlation function computed for a sub-set of the spectroscopic data. The analysis of Generalized Lomb-Scargle periodograms of the time series of different activity indicators reveals that the rotation period of the star is 145 ± 15 days, consistent with the expected rotation period according to the low activity level of the star and previous claims. The upper limit of the predicted activity-induced RV signal corresponding to this rotation period is about 1 m/s. We also find evidence of a long-term cycle of 10 ± 2 years that is consistent with previous estimates of magnetic cycles from photometric time series in other M stars of similar activity levels. The available photometric data of the star also support the detection of both the long-term and the rotation signals.

scholarly journals Soft X-ray emission as diagnostics for Maunder minimum stars

2011 ◽  
Vol 7 (S286) ◽  
pp. 346-349
Author(s):  
Katja Poppenhaeger ◽  
Jürgen H. M. M. Schmitt
Keyword(s):  
Low Temperature ◽  
Main Sequence ◽  
Coronal Holes ◽  
Maunder Minimum ◽  
Coronal Plasma ◽  
X Ray ◽  
Chromospheric Activity ◽  
Chromospheric Emission ◽  
Solar Coronal

AbstractThe identification of stars in a Maunder minimum state purely from their chromospheric emission (for example in Ca II lines) has proven to be difficult. Photospheric contributions, metallicities and possible deviations from the main sequence stage may lead to very low values of the traditional chromospheric activity indicators, while no Maunder minimum state may be present. X-ray observations can be a key tool for identifying possible Maunder minimum stars: We have detected very soft X-ray emission from low-temperature coronal plasma, similar to emission from solar coronal holes, in several stars with very low chromospheric activity indicators. The coronal properties inferred from X-ray observations can therefore yield a crucial piece of information to verify Maunder minimum states in stars.

scholarly journals Differential rotation in convective envelopes: constraints from eclipsing binaries

2019 ◽  
Vol 491 (1) ◽  
pp. 690-707 ◽  
Author(s):  
Adam S Jermyn ◽  
Jamie Tayar ◽  
Jim Fuller
Keyword(s):  
Differential Rotation ◽  
Orbital Period ◽  
Binary Systems ◽  
Rotation Period ◽  
Eclipsing Binaries ◽  
Rotation Periods ◽  
Short Period ◽  
Orbital Periods ◽  
The Difference ◽  
Surface Convection

ABSTRACT Over time, tides synchronize the rotation periods of stars in a binary system to the orbital period. However, if the star exhibits differential rotation, then only a portion of it can rotate at the orbital period, so the rotation period at the surface may not match the orbital period. The difference between the rotation and orbital periods can therefore be used to infer the extent of the differential rotation. We use a simple parametrization of differential rotation in stars with convective envelopes in circular orbits to predict the difference between the surface rotation period and the orbital period. Comparing this parametrization to observed eclipsing binary systems, we find that in the surface convection zones of stars in short-period binaries there is very little radial differential rotation, with |r∂rln Ω| < 0.02. This holds even for longer orbital periods, though it is harder to say which systems are synchronized at long periods, and larger differential rotation is degenerate with asynchronous rotation.

scholarly journals Solar activity and differential rotation

2010 ◽  
Vol 6 (S273) ◽  
pp. 298-302
Author(s):  
Hari Om Vats ◽  
Satish Chandra
Keyword(s):  
Solar Activity ◽  
Differential Rotation ◽  
Rotation Rate ◽  
Rotation Period ◽  
Activity Cycle ◽  
Solar Activity Cycle ◽  
X Ray ◽  
Sunspot Numbers ◽  
Sidereal Rotation

AbstractThe coronal sidereal rotation rate as a function of latitude for each year, extending from 1992 to 2001 for soft X-ray images and from 1998 - 2005 for radio images are obtained. The present analysis reveals that the equatorial rotation rate of the corona is comparable to the photosphere and the chromosphere, However, at the higher latitudes, the corona rotation quite differently than the photosphere and chromosphere. The latitude differential obtained by both radio and X-ray images is quite variable throughout the period of the study. The equatorial rotation period seems to vary almost systematically with sunspot numbers which indicates its dependence on the phases of the solar activity cycle.

Magnetic activity based on LAMOST medium-resolution spectra and the Kepler survey

2020 ◽  
Vol 495 (1) ◽  
pp. 1252-1270 ◽  
Author(s):  
Li-yun Zhang ◽  
Liu Long ◽  
Jianrong Shi ◽  
Hong-peng Lu ◽  
Qi Gao ◽  
...  
Keyword(s):  
Rotation Period ◽  
Magnetic Activity ◽  
Physical Parameters ◽  
Late Type ◽  
Data Bases ◽  
Interesting Phenomenon ◽  
Chromospheric Activity ◽  
Medium Resolution ◽  
Hα Emission ◽  
Relationship Of

ABSTRACT Stellar magnetic activity is an interesting phenomenon in late-type stars. We use the medium-resolution spectroscopic observations of 406 069 late-type stars from LAMOST to explore their properties. We perform a statistical analysis on the magnetic activity of the stars and their associated physical parameters. Our samples are cross-matched with other data bases (LAMOST DR5, VSX, and SDSS DR12) to obtain additional observational properties. The equivalent widths (EWs) of Hα lines, an indicator of chromospheric activity, are calculated. According to the EWs of the Hα line, we detect 8816 spectra with apparent Hα emission for a total of 2115 stars among the 2 108 565 spectra analysed. Furthermore, 1521 of these stars show variability in their Hα lines. In addition, we detect 2132 flare events associated with 41 542 stars from the catalogue by cross-matching our LAMOST medium-resolution samples and the Kepler and K2 data bases. We also confirm a weak relationship of the flare amplitude with increasing Rossby number. There is a clear decease in the strength of chromospheric activity (LHα/Lbol) with increasing rotation period. Moreover, the ratio of the flare energy and stellar luminosity is found to decrease with the stellar mass.

Sign in / Sign up

Export Citation Format

Share Document