Multisite observations of surface structures on AB Doradus in 1994 November

Cameron, A. Collier; Walter, F. M.; Vilhu, O.; Böhm, T.; Catala, C.; Char, S.; Clarke, Fraser; Felenbok, P.; Foing, B. H.; Ghosh, K. K.; Hao, Jinxin; Huang, Lin; Jackson, David A.; Janot-Pacheco, E.; Jiang, Shi-Yang; Lagrange, A. M.; Suntzeff, Nicholas B.; Zhai, D. S.

doi:10.1046/j.1365-8711.1999.02771.x

Cited by 23 publications

(11 citation statements)

References 19 publications

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“…AB Dor, however, remains the most studied object to date. Prominences have consistently been reported (Collier Cameron & Robinson 1989a,b; Donati & Collier Cameron 1997; Collier Cameron et al 1999; Donati et al 1999) to lie at a range of distances from the stellar rotation axis from 2 to 8 R * , with a concentration at the corotation radius (2.7 R * on AB Dor).…”

Section: Introductionmentioning

confidence: 81%

The coronal structure of Speedy Mic -- I. A densely packed prominence system beyond corotation

Dunstone

Barnes

Cameron

et al. 2006

Monthly Notices of the Royal Astronomical Society

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We present new observations of the prominence system on the K3 dwarf Speedy Mic (BO Mic, HD 197890). Using an improved technique to track the absorption features in Hα we find a very active prominence system with approximately 10 prominences on the observable hemisphere per rotation. From a total of 25 prominences, we find an average axial distance of (2.85 ± 0.54) R* which is twice the corotation radius above the stellar surface. We discuss the consequences of these observations on the nature of the supporting magnetic structures. Two consecutive nights, with complete phase coverage, combined with a further night after a three‐night gap allow us to study the evolution of the prominence system on two different time‐scales. Several of the prominences have counterparts at similar phases on consecutive nights. During this interval, many prominences show evidence for evolution in their heights and phases of observation. Five nights (13 rotation cycles) later, we recover many prominences at approximately the same phases. Whilst individual prominences change axial distances or appear/reappear from night‐to‐night, the underlying prominence supporting structures appear to be stable over as many as 13 stellar rotations.

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Section: Introductionmentioning

confidence: 81%

The coronal structure of Speedy Mic -- I. A densely packed prominence system beyond corotation

Dunstone

Barnes

Cameron

et al. 2006

Monthly Notices of the Royal Astronomical Society

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“…The AB Dor prominence system remains the most studied to date. Prominences have consistently been reported (Collier Cameron & Robinson 1989a,b; Donati & Collier Cameron 1997; Collier Cameron, Walter & Vilhu 1999; Donati et al 1999) to lie at a range of distances from the stellar rotation axis from 2 to 8 R * , with a concentration at the co‐rotation radius (2.7 R * on AB Dor).…”

Section: Introductionmentioning

confidence: 84%

The coronal structure of Speedy Mic – II. Prominence masses and off-disc emission*

Dunstone

Cameron

Barnes

et al. 2006

Monthly Notices of the Royal Astronomical Society

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Observations of stellar prominences on young rapidly rotating stars provide unique probes of their magnetic fields out to many stellar radii. We compare two independently obtained data sets of the K3 dwarf Speedy Mic (BO Mic, HD 197890) using the Anglo‐Australian Telescope (AAT) and the European Southern Observatory (ESO) Very Large Telescope (VLT). Taken more than a fortnight apart, they provide the first insight into the evolution of the prominence system on such a young rapidly rotating star. The largest prominences observed transiting the stellar disc are found at very similar rotational phases between the epochs. This suggests that the magnetic structures supporting the prominences retain their identity on a two to three week time‐scale. By taking advantage of the high signal‐to‐noise ratio and large wavelength range of the VLT observations, we identify prominences as transient absorption features in all lines of the hydrogen Balmer series down to H10. We use the ratios of the prominence equivalent widths (EWs) in these lines to determine their column densities in the first excited state of hydrogen. We determine the optical depths, finding prominences to be rather optically thick (τ≈ 20) in the Hα line. The total hydrogen column density and thus the prominence masses are determined via observations of the Ca II H&K lines. We find typical masses for four of the largest prominences to be in the range 0.5–2.3 × 1014 kg, slightly larger than giant solar prominence masses. Rotationally modulated emission is seen outside of the Hα line. These loops of emission are shown to be caused by prominences seen off the stellar disc. We find that all of the large emission loops can be associated with prominences we see transiting the stellar disc. This, combined with the fact that many prominences appear to eclipse the off‐disc emission of others, strongly suggests that the prominence system is highly flattened and likely confined to low stellar latitudes.

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“…Strassmeier 1999;Collier-Cameron et al 1999;Berdyugina et al 1998;Barnes et al 1998), differential rotation both in the same sense and in the opposite sense than on the Sun (Vogt et al 1999;Donati & Collier-Cameron 1997;Hatzes 1998;Rice & Strassmeier 1996;Barnes et al 2001), possibly detected meridional flows toward the pole (Weber & Strassmeier 2001;Strassmeier & Bartus 2000), detected and mapped prominences (Collier-Cameron et al 1999) and warm spots (Piskunov 1996;Unruh et al 1998;Strassmeier 1999), observed active longitudes and related activity flip-flops (Berdyugina et al 1999), found spot evolution on very short-and on very long timescales (e.g. Washuettl et al 2000;Barnes et al 1998) and, finally, directly detected complex magnetic surface fields (Wade et al 2000;Piskunov & Kochukhov 2001).…”

Section: Surface Imaging Of Solar-type Stars and What Does It Tell Usmentioning

confidence: 99%

Doppler imaging of stellar surface structure

Strassmeier

Rice

2003

A&A

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Abstract. We present the first Doppler image for both stellar components of the F9+G0 ZAMS binary σ 2 CrB and found evidence for the coexistence of cool and warm spots on both stars. Cool spots appear mainly at polar or high latitudes while a confined equatorial warm belt appears on the trailing hemisphere of each of the two stars with respect to the orbital motion. We also present an update of the TempMap imaging code that allows us to solve the stellar surface temperature distribution on both binary components simultaneously, including photometric input. Several test reconstructions are performed to demonstrate its reliability and robustness. Our new orbital solution results in very precise masses for both components -good to 0.4% -and confirms the spectral classifications of F9 and G0 for the primary and secondary, respectively. The visual component, σ 1 CrB, seems to be G4 rather than G0. All three components are on or very close to the ZAMS which is also confirmed by the relatively high lithium abundance of about twenty times the solar abundance. Photometric light variations are detected with a period of 1.157 ± 0.002 days that we interpret to be the rotation period of both binary components. A 0. m 04 dimming in y together with a reddening of 0. m 01 in b − y during the year 2000 suggests a long-term spot variability compatible with a period of at least 260 days.

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Multisite observations of surface structures on AB Doradus in 1994 November

Cited by 23 publications

References 19 publications

The coronal structure of Speedy Mic -- I. A densely packed prominence system beyond corotation

The coronal structure of Speedy Mic -- I. A densely packed prominence system beyond corotation

The coronal structure of Speedy Mic – II. Prominence masses and off-disc emission*

Doppler imaging of stellar surface structure

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