Doppler Imaging: Results

Rotationally-phased Ca maps for five independent subsets of data.

Aitoff projection (Fe line).	Polar projection (Fe line).	Aitoff projection (Ca line).
Animated GIF files of 28 temperature maps.

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We reconstruct a time series of 28 surface temperature maps (Doppler-images) of the spotted single K2-dwarf LQ Hya from 35 consecutive stellar rotations in Nov.-Dec. 1996. Two more maps are obtained from data in late April and early May 2000, just two weeks apart. All maps show spot activity preferably at low latitudes between -20° and +50°, with a concentration in a band centered at around +30°, and with only occasional evidence for a higher-latitude spot extension. No trace of a polar spot is found at any of above epochs. Most of this morphology can be reproduced by our flux-tube emergence model, except for the equatorial activity where the strong Coriolis force due to the rapid rotation always deflects flux tubes to higher latitudes. We also present the detection of weak differential surface rotation from a number of cross-correlation maps of the time-series images in late 1996. A solar-type differential rotation law, i.e. the equator rotating faster than the poles, with ΔΩ=+0.022 (lap time of ~280 days) is in agreement with the data. Using the available photoelectric observations from 21 years we refine the rotation period to 1.60066±0.00013 days and find a remarkable phase coherence over the course of 21 years, supporting the recent finding of active longitudes by Berdyugina et al.. Furthermore, our photometry shows a complex multi-cyclic long-term brightness variability with three periods of 13.8±2.8 years, its harmonic 6.9±0.8 and 3.7±0.3 years, respectively. The 3.7-year period would be in good agreement with the fundamental-mode oscillation period predicted by Kitchatinov et al. from a distributed-dynamo model, but remains yet to be confirmed.

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Kővári, Strassmeier, Granzer, Weber, Oláh and Rice, 2003, A&A, submitted

Average temperature map.	Temperature sigma map.

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We present the first Doppler image of the single G0-dwarf HD 171488. As a 30-Myr young field star with a lithium abundance of ~140-times that of the Sun and a rotation 20 times faster, it is hardly a "solar analog" but could be coined an "infant Sun". Its position in the H-R diagram suggests it to be in the rapid-braking phase just prior to arrival on the ZAMS. Our Doppler images from four spectral lines show a cool polar spot and various high-latitude spot features with a temperature contrast of 500-1600 K relative to the effective (photospheric) temperature. Low-to-medium latitude features may be present but appear to be biased by the uneven phase coverage of our spectra and are too weak to be conclusively judged significant. We determine the rotational period to be 1.3371±0.0002 days and find a long-term, possibly cyclic variation of the mean V brightness of ~7 years. A constant radial velocity of -23.6±1.5 km/s suggests that HD 171488 is indeed a single star. Rising flux-tube models indicate preferred surfacing latitudes between 25°-60° for HD 171488 while our Doppler images reveal mostly high-latitude spots in excess of 60°. We emphasize that this discrepancy exists for all rapidly rotating single G dwarfs observed so far.

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Strassmeier, Pichler, Weber, Granzer, 2003, A&A, submitted

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We present two Doppler images from two consecutive stellar rotations of the single K2-giant HD 31993. Each Doppler image is reconstructed from spectra obtained within a single stellar rotation. With its 25-day rotational period and a radius of ~18 solar radii, HD 31993 is considered a very rapidly rotating star and thus allows the application of the Doppler-imaging technique, despite the unusually long period. All maps reveal 7 isolated, predominantly low-latitude spots with a temperature difference, photosphere minus spot, of just ~200 K. No polar spot or high-latitude activity above, say, +60° is seen. A large warm feature is detected at high latitude and is believed to be real. These spots act as tracers for a cross correlation analysis and yield a clear signature of anti-solar differential surface rotation, i.e. the polar regions rotating faster than the equator, with α=0.125±0.05 corresponding to a lap time of ~200 days. A detailed parameter study is carried out to verify the reality of the HD 31993 maps.

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Strassmeier, Kratzwald and Weber, 2003, A&A, 408, 1103

LQ Hya (mpeg) by J. Rice (340 kB)

V410 Tau (1992, mpeg) by J. Rice (340 kB)

V410 Tau (1993, mpeg) by J. Rice (340 kB)

Pseudo three-dimensional view of the σ² CrB binary system. The maps are those from the full-spectrum inversion. Note that the obtained ratio of the stellar radii of the two components is 0.955 but that they are shown at different size during the two conjunction phases (90° and 270° , respectively) for better 3-D viewing.

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Strassmeier & Rice 2003, A&A, 399, 315

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We present eight Doppler images of UZ Librae from the years 1994, 1996, 1997, 1998 and 2000. These maps indicate a preferred temperature distribution from one year to the other and suggest preferred spot locations for at least the seven years of our observations. Two equatorial active regions appear facing towards and opposite the (unseen) companion star. A large and cool polar spot, with two or maybe three appendages extending down to a latitude of 40°-50°, is present and causes the long-term light variability of UZ Lib. The appendages appear at longitudes very similar to the two equatorial active regions and sometimes are possibly even attached to them. No coherent sign of differential rotation is found for the equatorial regions up to a latitude of approximately +50°, but the polar appendages may indicate a general acceleration of the polar regions. If interpreted due to differential rotation, if real at all, then UZ Lib clearly exhibits a non-solar flow pattern.

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Oláh, Strassmeier, Weber 2002, A&A 389, 202

We present the first Doppler image of a solar-type G dwarf in the Pleiades open cluster obtaine from high-resolution Gecko CFHT spectra. The star represents the Sun at an age of approximately 100 Myr and could be an important target for further progress in magnetic-braking and angular-momentum-transport theories. Our image reconstructions were done from a full spectrum inversion with a total of 38 spectral lines simultaneously but we also present single-line inversions using the prominent Li I 6707 Å line and the nearby Ca I 6717 Å line. The maps reveal cool spots at or near the pole and within the equatorial regions, in contradiction to our predictions from flux-tube modelling that only medium-latitude spots should be seen. The maps also show several warm spots near the equatorial regions but their reality needs to be confirmed. A polar spot is recovered but likely consists of several smaller spots at very high latitudes touching the visible pole instead of a big cap-like spot as seen on some RS CVn binaries.

	Fig.1: Doppler image of the Pleiades G-dwarf HII 314 (left). The surface grid is shown in the right image.
	Fig.2: Doppler image of HII 314 from a 20-Å piece of spectrum including the Li I 6707 Å and the Ca I 6717 Å lines. Maps are plotted in a spherical projection at eight equidistant rotational phases. The temperature scale is indicated and is the same for all projections.

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Strassmeier & Rice 2001, A&A 377, 264

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We present a simultaneous photometric and spectroscopic imaging analysis of the long-period RS CVn binary sigma Gem, covering 3.6 consecutive rotation cycles with high time resolution. From six overlapping but consecutive Doppler maps we trace the evolution of individual spots throughout the time range covered. All spots group either along a band at approximately +45° latitude and a width of 30°, or appear centered at the equator. No polar spot is detected. We did not find a conclusive migration pattern from the cross-correlation maps from one rotation to the next and attribute this to a masking effect of short-term spot changes.

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Kővári, Strassmeier, Bartus, Washuettl, Weber, Rice 2001, A&A 373, 199

Single Doppler Image

Doppler Images at four rotation phases

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Animated Pictures:

Animated GIF of HR 1099 by J. Bartus (365 kB) - big version (1255 kB)