EXOSAT observations of variable coronal X-ray emission from the young K dwarf AB Doradus (= HD 36705)

Cameron, A. Collier; Bedford, D. K.; Ruciński, S. M.; Vilhu, O.; White, N. E.

doi:10.1093/mnras/231.1.131

Cited by 52 publications

(30 citation statements)

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“…The first X-ray detection of AB Dor A was obtained with the Einstein Observatory (Pakull 1981;Vilhu & Linsky 1987), and ever since then AB Dor A has been observed repeatedly by almost all X-ray observatories (Collier Cameron et al 1988;Vilhu et al 1993;Mewe et al 1996;Maggio et al 2000;Güdel et al 2001;Sanz-Forcada et al 2003;Hussain et al 2007;Lalitha et al 2013). The long-term X-ray behaviour of the X-ray emission from the AB Dor system is dominated by AB Dor A (Güdel et al 2001;Sanz-Forcada et al 2003).…”

Section: Our Target Starmentioning

confidence: 99%

X-ray activity cycle on the active ultra-fast rotator AB Doradus A?

Lalitha

Schmitt

2013

A&A

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Context. Although chromospheric activity cycles have been studied in a larger number of late-type stars for quite some time, very little is known about coronal activity-cycles in other stars and their similarities or dissimilarities with the solar activity cycle. Aims. While it is usually assumed that cyclic activity is present only in stars of low to moderate activity, we investigate whether the ultra-fast rotator AB Dor, a K dwarf exhibiting signs of substantial magnetic activity in essentially all wavelength bands, exhibits an X-ray activity cycle in analogy to its photospheric activity cycle of about 17 years and possible correlations between these bands. Methods. We analysed the combined optical photometric data of AB Dor A, which span ∼35 years. Additionally, we used ROSAT and XMM-Newton X-ray observations of AB Dor A to study the long-term evolution of magnetic activity in this active K dwarf over nearly three decades and searched for X-ray activity cycles and related photometric brightness changes. Results. AB Dor A exhibits photometric brightness variations ranging between 6.75 < V mag ≤ 7.15 while the X-ray luminosities range between 29.8 < log L X [erg/s] ≤ 30.2 in the 0.3-2.5 keV. As a very active star, AB Dor A shows frequent X-ray flaring, but in the long XMM-Newton observations a kind of basal state is attained very often. This basal state probably varies with the photospheric activity-cycle of AB Dor A, which has a period of ∼17 years, but the X-ray variability amounts at most to a factor of ∼2, which is, much lower than the typical cycle amplitudes found on the Sun.

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Section: Our Target Starmentioning

confidence: 99%

X-ray activity cycle on the active ultra-fast rotator AB Doradus A?

Lalitha

Schmitt

2013

A&A

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“…Since then it has been extensively observed in the ultraviolet (Rucinski et al 1995;Moos et al 2000;Vilhu et al 2001) and X-rays (Vilhu et al 1987;Collier Cameron et al 1988;Mewe et al 1996;Kuerster et al 1997;Maggio et al 2000;Güdel et al 2001). Kuerster et al (1997) found variability on short timescales but no long-term trend or cyclical variability of the X-ray emission.…”

Section: Ab Dormentioning

confidence: 99%

The Coronae of AB Doradus and V471 Tauri: Primordial Angular Momentum versus Tidal Spin‐up

García-Álvarez

Drake

Lin

et al. 2005

ApJ

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The zero-age main-sequence star AB Dor and the K dwarf component of the V471 Tau close binary have essentially identical rotation rates and spectral types. An analysis of their high-resolution Chandra X-ray spectra reveals remarkably similar coronal characteristics in terms of both temperature structure and element abundances. Both stars show depletions of low first ionization potential (FIP) elements by factors of $3, with higher FIP elements showing more mild depletions. No evidence for enhancements of very low FIP (<7 eV) elements, such as Na, Al, and Ca, as compared to other low-FIP elements, was found. The abundance anomaly pattern for AB Dor and V471 Tau is similar to, although less extreme than, the abundance anomalies exhibited by active RS CVn-type binaries. While we find statistically significant structure in the underlying differential emission measure distributions of these stars over narrow temperature intervals, this structure is strongly dependent on the lines used in the analysis and is probably spurious. On the basis of their X-ray similarities, we conclude that the exact evolutionary state of a star has little effect on coronal characteristics and that the parameters that dominate coronal structure and composition are simply the rotation rate and spectral type.

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“…This suggests that the star may exhibit longlived active longitudes in the photosphere, chromosphere and corona. Long rise-times of X-ray flares suggest that they occur in loop structures with lengths of several stellar radii (Collier Cameron et al 1988). AB Dor has been extensively studied with Doppler imaging techniques (Kürster et al 1994;Collier Cameron & Unruh 1994;Collier Cameron 1995;Donati & Collier Cameron 1997;Donati et al 1999Donati et al , 2003Hussain et al 2002).…”

Section: Introductionmentioning

confidence: 99%

Magnetic activity in the young solar analog AB Dor

Järvinen

Berdyugina

Tuominen³

et al. 2005

A&A

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Abstract. We analyse photometric observations of the young active dwarf AB Dor, spanning more than 20 years. Similar to the young solar analog LQ Hya, AB Dor shows long-lived, nonaxisymmetric spot distribution -active longitudes in opposite hemispheres. The active longitudes migrate nonlinearly in the fixed reference frame, because of the differential rotation and changes of the mean spot latitudes. At least two activity cycles are found in the data. One cycle originates from repeating switches of the activity between the two active longitudes in about (2-3)-year intervals. This results in the flip-flop cycle of about 5.5 years, which includes two consecutive switches. The 5.5-yr cycle also modulates variations of the minimum stellar brightness and the peak-to-peak amplitude, that suggests a periodic redistribution of the spot area between the opposite longitudes and supports the reality of the flip-flop cycle. The other cycle is clearly seen in variations of the mean and maximum stellar brightness on the time-scale of 20 years and is reminiscent of the 11-year sunspot cycle.

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EXOSAT observations of variable coronal X-ray emission from the young K dwarf AB Doradus (= HD 36705)

Cited by 52 publications

References 0 publications

X-ray activity cycle on the active ultra-fast rotator AB Doradus A?

X-ray activity cycle on the active ultra-fast rotator AB Doradus A?

The Coronae of AB Doradus and V471 Tauri: Primordial Angular Momentum versus Tidal Spin‐up

Magnetic activity in the young solar analog AB Dor

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