Astrometric Detection of a Low‐Mass Companion Orbiting the Star AB Doradus

Guirado, J. C.; Reynolds, J. E.; Lestrade, J. F.; Preston, R. A.; Jauncey, D. L.; Jones, Dayton L.; Tzioumis, A. K.; Ferris, R. H.; King, E. A.; Lovell, J. E. J.; McCulloch, P. M.; Johnston, K. J.; Kingham, K. A.; Martin, Jim; White, Graeme L.; Jones, Peter N.; Arenou, Frédéric; Frœschlé, M.; Kovalevsky, J.; Märtin, Christian; Lindegren, L.; Söderhjelm, S.

doi:10.1086/304920

Cited by 62 publications

(62 citation statements)

References 20 publications

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“…However, the binarity of AB Dor B itself with a separation of only 0.7 (called AB Dor Ba and AB Dor Bb) was detected only after the advent of adaptive optics. Yet another low-mass companion to AB Dor A is AB Dor C Guirado et al (1997), located about 0.16 away from AB Dor A.…”

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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“…Its age is estimated to be 20-30 Myr (Guirado et al 1997;Collier Cameron & Foing 1997), and Innis et al (1986) suggested that AB Dor is member of the Pleiades based on its space velocity. The main physical parameters of AB Dor are shown in Table 1.…”

Section: Ab Dormentioning

confidence: 99%

“…Our final DEMs are corrected for the distances of the stars: we have adopted D ¼ 14:9 pc (Guirado et al 1997) and D ¼ 48 pc (de Bruijne et al 2001) for AB Dor and V471 Tau, respectively.…”

Section: Algg Orithm and Line Selectionmentioning

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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“…Precise astrometry of the orbital motion of stars in binary systems allows us to obtain accurate, model-independent estimates of the masses of the individual components, relevant to provide tests of stellar evolution models (Guirado et al 1997;Torres et al 2012;Reid & Honma 2014). In the case of low-and very-lowmass stars, only a handful of stellar systems with dynamicallydetermined masses have been reported (Hillenbrand & White 2004;Stassun et al 2004;Mathieu et al 2007).…”

Section: Introductionmentioning

confidence: 99%

“…Given its high-level of radio emission, during the early 90's AB Dor A was monitored astrometrically with VLBI as part of a program to link the optical reference frame, defined by the positions of the stars observed by the ESA's astrometric satellite Hipparcos (Lindegren & Kovalevsky 1995;Lestrade et al 1995), and the celestial reference frame, defined by VLBI positions (Lestrade et al 1995). The VLBI-Hipparcos combined data revealed the presence of a low-mass companion, 0.090 M , AB Dor C (Guirado et al 1997), orbiting AB Dor A at an average angular distance of 0.2 . Imaging this new low-mass companion was difficult and it had to wait until the VLT near-infrared observations carried out by Close et al (2005Close et al ( , 2007 using commissioning time of the Simultaneous Differential Imager (SDI) at the VLT, which allowed independent photometry of AB Dor C, free from contamination of the much brighter AB Dor A.…”

Section: Introductionmentioning

confidence: 99%

The AB Doradus system revisited: The dynamical mass of AB Dor A/C

Azulay

Guirado

Marcaide

et al. 2017

A&A

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Context. The study of pre-main-sequence (PMS) stars with model-independent measurements of their masses is essential to check the validity of theoretical models of stellar evolution. The well-known PMS binary AB Dor A/C is an important benchmark for this task, since it displays intense and compact radio emission, which makes possible the application of high-precision astrometric techniques to this system. Aims. We aim to revisit the dynamical masses of the components of AB Dor A/C to refine earlier comparisons between the measurements of stellar parameters and the predictions of stellar models. Methods. We observed in phase-reference mode the binary AB Dor A/C, 0.2 separation, with the Australian Long Baseline Array at 8.4 GHz. The astrometric information resulting from our observations was analyzed along with previously reported VLBI, optical (Hipparcos), and infrared measurements. Results. The main star AB Dor A is clearly detected in all the VLBI observations, which allowed us to analyze the orbital motion of the system and to obtain model-independent dynamical masses of 0.90 ± 0.08 M and 0.090 ± 0.008 M , for AB Dor A and AB Dor C, respectively. Comparisons with PMS stellar evolution models favor and age of 40−50 Myr for AB Dor A and of 25−120 Myr for AB Dor C. Conclusions. We show that the orbital motion of the AB Dor A/C system is remarkably well determined, leading to precise estimates of the dynamical masses. Comparison of our results with the prediction of evolutionary models support the observational evidence that theoretical models tend to slightly underestimate the mass of the low-mass stars.

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Astrometric Detection of a Low‐Mass Companion Orbiting the Star AB Doradus

Cited by 62 publications

References 20 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

The AB Doradus system revisited: The dynamical mass of AB Dor A/C

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