Nonthermal Radio Emission from the Precataclysmic Binary System V471 Tauri

Nicholls, Jennifer; Storey, Michelle C.

doi:10.1086/307372

Cited by 8 publications

(11 citation statements)

References 30 publications

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“…The new e-EVN data suggest that there is a correlation between the observed radio flux and the AM Her orbital phase. Moreover, the radio light curve is similar to observed in V471 Tau (Nicholls & Storey 1999), a pre-CV eclipsing binary with orbital period 12.51 hr . Nicholls & Storey (1999) proposed that the emission mechanism similar to RS CVn binary systems could explain observed radio properties of V471 Tau, where the gyrosynchrotron emission originates from ∼ 400 keV electrons near the surface of the secondary component.…”

Section: Properties Of the Observed Radio Emissionsupporting

confidence: 71%

Another look at AM Herculis – radio-astrometric campaign with the e-EVN at 6 cm

Gawroński

Goździewski

Rycyk

2018

Monthly Notices of the Royal Astronomical Society

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We conducted radio-interferometric observations of the well known binary cataclysmic system AM Herculis. This particular system is formed by the magnetic white dwarf (primary) and the red dwarf (secondary), and is the prototype of so-called polars. Our observations were conducted with the European VLBI Network (EVN) in the e-EVN mode at 5 GHz. We obtained six astrometric measurements spanning one year, which make it possible to update the annual parallax for this system with the best precision to date (π = 11.29 ± 0.08 mas), equivalent to the distance of 88.6 ± 0.6 pc. The system was observed mostly in the quiescent phase (visual magnitude m v ∼ 15.3), when the radio emission was at the level of about 300 µJy. Our analysis suggests that the radio flux of AM Herculis is modulated with the orbital motion. Such specific properties of the radiation can be explained using the emission mechanism similar to the scenario proposed for V471 Tau and, in general, for RS CVn type stars. In this scenario the radio emission arises near the surface of the red dwarf, where the global magnetic field strength may reach a few kG. We argue that the quiescent radio emission distinguishes AM Herculis together with AR Ursae Majoris (the second known persistent radio polar) from other polars, as the systems with a magnetized secondary star.

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Section: Properties Of the Observed Radio Emissionsupporting

confidence: 71%

Another look at AM Herculis – radio-astrometric campaign with the e-EVN at 6 cm

Gawroński

Goździewski

Rycyk

2018

Monthly Notices of the Royal Astronomical Society

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“…At a distance of 47.6 pc (de Bruijne et al 2001), the flux density scales to levels consistent with the measured flux densities of AM Her and AR UMa. An emission mechanism similar to that proposed for the RS CVn binaries has been suggested for V471 Tau ( Lim et al 1996;Nicholls & Storey 1999), with the argument that electrons are accelerated close to the white dwarf. This is where the magnetic fields of the two stars interact, since reconnection takes place owing to the difference between the rotational period of the white dwarf of 9.25 minutes ( Robinson et al 1988) and the binary period of 12.5 hr.…”

Section: Precataclysmic Variablesmentioning

confidence: 53%

“…Radio emission has been detected from V471 Tau, an eclipsing pre-CV and member of the Hyades star cluster with an orbital period of 12.5 hr. The secondary is a K2 dwarf that is only minimally distorted by the Roche potential (Nicholls & Storey 1999). Quiescent, nonflaring, radio emission of up to 1 mJy clearly modulates as a function of orbital phase.…”

Section: Precataclysmic Variablesmentioning

confidence: 99%

AR Ursae Majoris Discovered to Be a Persistent Radio Polar: Results from a VLA Survey of Magnetic Cataclysmic Variables

Mason

Gray

2007

ApJ

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We conducted a VLA survey of nine magnetic cataclysmic variable stars (MCVs) at 8.436 GHz in 2003 October, to constrain models of radio emission. A follow-up study was conducted in 2004 September. We obtained the first radio detections of AR UMa, the MCV with the highest known magnetic field (230 MG), at flux densities of 0.422 AE 0.060 mJy (2003 October 16) and 0.734 AE 0.095 mJy (2004 September 4). We have completed the sample of radio observations of MCVs out to 100 pc. Surprisingly, the only radio-selected CV, FIRST J1023þ0038, was not detected. An upper limit of 0.20 mJy (4 ) was obtained. The original radio MCV, AM Her, was detected with a flux density of 0.586 AE 0.074 mJy (2003 October 17), consistent with previous observations. Typical (4 ) upper limits of 0.12 mJy were obtained for other targets. The lack of radio emission from isolated magnetic white dwarfs, as well as from nonmagnetic CVs (outside of outburst), places constraints on radio emission mechanisms for CVs. We suggest that accretion disks may preclude radio emission. Also, since we detect radio emission from AM Her in a low state and the pre-CV V471 Tau is a persistent radio source, accretion is not a necessary condition. A secondary with a kilogauss magnetic field might be necessary. We argue that the emission from AR UMa originates near the secondary. AR UMa joins AM Her and AE Aqr as the only confirmed persistent radio MCVs, and we suggest avenues of further study.

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“…Other chromospheric lines, such as the Ca ii H and K lines and the Ca ii infrared triplet, show similar behavior, confirming that the activity is coming from the chromosphere of the K dwarf. Different authors have presented evidence for magnetically induced activity on the K dwarf based on optical and photometric flares (Young et al 1991), X-ray flares (Young et al 1983), and radio flaring activity (Patterson et al 1993;Nicholls & Storey 1999). Jensen et al (1986) and Sion et al (1998) found a periodic 9.25 minute modulation in the soft X-ray and EUV bands of V471 Tau, which was subsequently found in the optical band by Robinson et al (1988).…”

Section: V471 Taumentioning

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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Nonthermal Radio Emission from the Precataclysmic Binary System V471 Tauri

Cited by 8 publications

References 30 publications

Another look at AM Herculis – radio-astrometric campaign with the e-EVN at 6 cm

Another look at AM Herculis – radio-astrometric campaign with the e-EVN at 6 cm

AR Ursae Majoris Discovered to Be a Persistent Radio Polar: Results from a VLA Survey of Magnetic Cataclysmic Variables

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

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