scholarly journals Time series Doppler imaging using STELLA

2008 ◽  
Vol 4 (S259) ◽  
pp. 427-428
Author(s):  
Michael Weber ◽  
Klaus G. Strassmeier ◽  
Thomas Granzer
Keyword(s):  
Time Series ◽  
Differential Rotation ◽  
Stellar Surface ◽  
Doppler Imaging ◽  
Stellar Activity ◽  
Giant Star ◽  
Preliminary Results ◽  
The Core

AbstractOne of the core programs of the STELLA robotic observatory is to monitor the stellar activity on a sample of stars using Doppler imaging. We present first preliminary results of the rapidly rotating, single giant star HD 31993 from the first two years of operation. We confirm the presence and orientation of differential rotation on the stellar surface.

scholarly journals Stellar activity, differential rotation, and exoplanets

2010 ◽  
Vol 6 (S273) ◽  
pp. 89-95 ◽  
Author(s):  
A. F. Lanza
Keyword(s):  
Time Series ◽  
Differential Rotation ◽  
Solar Irradiance ◽  
Giant Planet ◽  
Total Solar Irradiance ◽  
Short Term ◽  
Stellar Activity ◽  
Transiting Planets ◽  
Spot Model ◽  
Spot Activity

AbstractThe photospheric spot activity of some of the stars with transiting planets discovered by the CoRoT space experiment is reviewed. Their out-of-transit light modulations are fitted by a spot model previously tested with the total solar irradiance variations. This approach allows us to study the longitude distribution of the spotted area and its variations versus time during the five months of a typical CoRoT time series. The migration of the spots in longitude provides a lower limit for the surface differential rotation, while the variation of the total spotted area can be used to search for short-term cycles akin the solar Rieger cycles. The possible impact of a close-in giant planet on stellar activity is also discussed.

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 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.

scholarly journals Starspots properties and stellar activity from planetary transits

2016 ◽  
Vol 12 (S328) ◽  
pp. 69-76
Author(s):  
Adriana Valio
Keyword(s):  
Magnetic Field ◽  
Time Series ◽  
Light Curve ◽  
Physical Properties ◽  
Differential Rotation ◽  
Magnetic Activity ◽  
Stellar Surface ◽  
Stellar Rotation ◽  
Long Time ◽  
Magnetic Cycles

AbstractMagnetic activity of stars manifests itself in the form of dark spots on the stellar surface. This in turn will cause variations of a few percent in the star light curve as it rotates. When an orbiting planet eclipses its host a star, it may cross in front of one of these spots. In this case, a “bump” will be detected in the transit lightcurve. By fitting these spot signatures with a model, it is possible to determine the spots physical properties such as size, temperature, location, magnetic field, and lifetime. Moreover, the monitoring of the spots longitude provides estimates of the stellar rotation and differential rotation. For long time series of transits during multiple years, magnetic cycles can also be determined. This model has been applied successfully to CoRoT-2, CoRoT-4, CoRot-5, CoRoT-6, CoRoT-8, CoRoT-18, Kepler-17, and Kepler-63.

scholarly journals Spectral Line-Profile Variability as a Probe for ℓ and m

1998 ◽  
Vol 185 ◽  
pp. 393-394
Author(s):  
C. Schrijvers ◽  
J.H. Telting
Keyword(s):  
Time Series ◽  
Spectral Line ◽  
Line Profile ◽  
Stellar Surface ◽  
Doppler Imaging ◽  
Radial Pulsation ◽  
Rotation Rates ◽  
Spectroscopic Characteristics ◽  
Spectral Line Profile

We investigate the observable spectroscopic characteristics of non-radial pulsation for stars with rotation rates large enough to resolve the stellar surface by Doppler imaging. We show that the intensity variations in time series of theoretical spectra, at each position in the line profile, cannot be described by a single sinusoid: at least one harmonic sinusoid needs to be included to describe the data. Across the line profile the relative amplitudes and phases of both these sinusoids vary independently.

scholarly journals Surface differential rotation of IL Hya from time-series Doppler images

2013 ◽  
Vol 9 (S302) ◽  
pp. 379-380 ◽  
Author(s):  
Zsolt Kővári ◽  
Levente Kriskovics ◽  
Katalin Oláh ◽  
Krisztián Vida ◽  
János Bartus ◽  
...  
Keyword(s):  
Time Series ◽  
Differential Rotation ◽  
Cross Correlation ◽  
Meridional Circulation ◽  
Imaging Study ◽  
Doppler Imaging ◽  
Surface Pattern ◽  
Cross Correlation Analysis ◽  
Solar Type

AbstractWe present a time-series Doppler imaging study of the K-subgiant component in the RS CVn-type binary system IL Hya (Porb=12.905 d). From re-processing the unique long-term spectroscopic dataset of 70 days taken in 1996/97, we perform a thorough cross-correlation analysis to derive surface differential rotation. As a result we get solar-type differential rotation with a shear value α of 0.05, in agreement with preliminary suggestions from previous attempts. A possible surface pattern of meridional circulation is also detected.

scholarly journals Geomagnetic Virtual Observatories: monitoring geomagnetic secular variation with the Swarm satellites

2021 ◽  
Vol 73 (1) ◽  
Author(s):  
Magnus D. Hammer ◽  
Grace A. Cox ◽  
William J. Brown ◽  
Ciarán D. Beggan ◽  
Christopher C. Finlay
Keyword(s):  
Time Series ◽  
Secular Variation ◽  
Geomagnetic Field ◽  
Time Windows ◽  
Low Earth Orbit ◽  
Data Selection ◽  
Spherical Harmonic Analysis ◽  
Core Field ◽  
The Core ◽  
Swarm Satellites

AbstractWe present geomagnetic main field and secular variation time series, at 300 equal-area distributed locations and at 490 km altitude, derived from magnetic field measurements collected by the three Swarm satellites. These Geomagnetic Virtual Observatory (GVO) series provide a convenient means to globally monitor and analyze long-term variations of the geomagnetic field from low-Earth orbit. The series are obtained by robust fits of local Cartesian potential field models to along-track and East–West sums and differences of Swarm satellite data collected within a radius of 700 km of the GVO locations during either 1-monthly or 4-monthly time windows. We describe two GVO data products: (1) ‘Observed Field’ GVO time series, where all observed sources contribute to the estimated values, without any data selection or correction, and (2) ‘Core Field’ GVO time series, where additional data selection is carried out, then de-noising schemes and epoch-by-epoch spherical harmonic analysis are applied to reduce contamination by magnetospheric and ionospheric signals. Secular variation series are provided as annual differences of the Core Field GVOs. We present examples of the resulting Swarm GVO series, assessing their quality through comparisons with ground observatories and geomagnetic field models. In benchmark comparisons with six high-quality mid-to-low latitude ground observatories we find the secular variation of the Core Field GVO field intensities, calculated using annual differences, agrees to an rms of 1.8 nT/yr and 1.2 nT/yr for the 1-monthly and 4-monthly versions, respectively. Regular sampling in space and time, and the availability of data error estimates, makes the GVO series well suited for users wishing to perform data assimilation studies of core dynamics, or to study long-period magnetospheric and ionospheric signals and their induced counterparts. The Swarm GVO time series will be regularly updated, approximately every four months, allowing ready access to the latest secular variation data from the Swarm satellites.

scholarly journals Doppler imaging of stellar surface structure

2003 ◽  
Vol 411 (3) ◽  
pp. 595-604 ◽  
Author(s):  
K. G. Strassmeier ◽  
T. Pichler ◽  
M. Weber ◽  
T. Granzer
Keyword(s):  
Surface Structure ◽  
Stellar Surface ◽  
Doppler Imaging

scholarly journals Time-series Doppler imaging of the red giant HD 208472

2016 ◽  
Vol 593 ◽  
pp. A123 ◽  
Author(s):  
O. Özdarcan ◽  
T. A. Carroll ◽  
A. Künstler ◽  
K. G. Strassmeier ◽  
S. Evren ◽  
...  
Keyword(s):  
Time Series ◽  
Doppler Imaging ◽  
Red Giant

scholarly journals PRELIMINARY STUDIES ON SEDIMENT CORE FROM THE TYRO BASIN

2017 ◽  
Vol 50 (1) ◽  
pp. 324
Author(s):  
M. Geraga ◽  
Ch. Anagnostou ◽  
I. Iliopoulos ◽  
M. Kontali
Keyword(s):  
Mediterranean Sea ◽  
Sediment Core ◽  
Eastern Mediterranean ◽  
Planktonic Foraminifera ◽  
Mineralogical Composition ◽  
Eastern Mediterranean Sea ◽  
Sediment Samples ◽  
Preliminary Results ◽  
The Core ◽  
Mineral Constituents

The present paper summarizes the preliminary results of the mineralogical and micropaleontological analysis conducted on sediment samples from core TYR05 retrieved from the anoxic and hypersaline Tyro basin in the eastern Mediterranean Sea. The core comprises a complex lithostratigraphic sequence attributed to the strong geodynamic regime of the area. The planktonic foraminifera associations present fluctuations which coincide with changes in the lithology of the core. The mineralogical composition of the sediments shows influence from the evaporites developed on the bottom of the basin. The mineral constituents in association to the microfauna assemblages suggest that the sediments include sapropelic layers. Further analyses are needed in order to determine safely the sapropelic deposits.

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