Detection of an extraordinarily large
 magnetic field  in the unique ultra-cool Ap star HD 154708

Hubrig, S.; Nesvacil, N.; Schöller, M.; North, P.; Mathys, G.; Kurtz, D. W.; Wolff, B.; Szeifert, T.; Cunha, M. S.; Elkin, V. G.

doi:10.1051/0004-6361:200500164

Cited by 83 publications

(81 citation statements)

References 27 publications

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“…15 it is obvious that stronger magnetic fields appear in very young Herbig Ae stars, and the magnetic fields become very weak at the end of their PMS life. These results clearly confirm the conclusions of Hubrig et al (2000Hubrig et al ( , 2005Hubrig et al ( , 2007a) that magnetic fields in stars with masses less than 3 M are rarely found close to the ZAMS and that kG magnetic fields appear in A stars already evolved from the ZAMS. In contrast, magnetic Bp stars with masses M > 3 M seem to be concentrated closer to the ZAMS.…”

Section: Agesupporting

confidence: 90%

Searching for a link between the magnetic nature and other observed properties of Herbig Ae/Be stars and stars with debris disks

Hubrig

Stelzer

Schöller

et al. 2009

A&A

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149

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Context. Recently, evidence for the presence of weak magnetic fields in Herbig Ae/Be stars has been found in several studies. Aims. We seek to expand the sample of intermediate-mass pre-main sequence stars with circular polarization data to measure their magnetic fields, and to determine whether magnetic field properties in these stars are correlated with mass-accretion rate, disk inclination, companions, silicates, PAHs, or show a correlation with age and X-ray emission as expected for the decay of a remnant dynamo. Methods. Spectropolarimetric observations of 21 Herbig Ae/Be stars and six debris disk stars have been obtained at the European Southern Observatory with FORS 1 mounted on the 8 m Kueyen telescope of the VLT. With the GRISM 600B in the wavelength range 3250-6215 Å we were able to cover all hydrogen Balmer lines from Hβ to the Balmer jump. In all observations a slit width of 0. 4 was used to obtain a spectral resolving power of R ≈ 2000. Results. Among the 21 Herbig Ae/Be stars studied, new detections of a magnetic field were achieved in six stars. For three Herbig Ae/Be stars, we confirm previous magnetic field detections. The largest longitudinal magnetic field, B z = −454 ± 42 G, was detected in the Herbig Ae/Be star HD 101412 using hydrogen lines. No field detection at a significance level of 3σ was achieved in stars with debris disks. Our study does not indicate any correlation of the strength of the longitudinal magnetic field with disk orientation, disk geometry, or the presence of a companion. We also do not see any simple dependence on the mass-accretion rate. However, it is likely that the range of observed field values qualitatively supports the expectations from magnetospheric accretion models giving support for dipole-like field geometries. Both the magnetic field strength and the X-ray emission show hints of a decline with age in the range of ∼2-14 Myr probed by our sample, supporting a dynamo mechanism that decays with age. However, our study of rotation does not show any obvious trend of the strength of the longitudinal magnetic field with rotation period. Furthermore, the stars seem to obey the universal power-law relation between magnetic flux and X-ray luminosity established for the Sun and main-sequence active dwarf stars.

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Section: Agesupporting

confidence: 90%

Searching for a link between the magnetic nature and other observed properties of Herbig Ae/Be stars and stars with debris disks

Hubrig

Stelzer

Schöller

et al. 2009

A&A

Self Cite

149

View full text Add to dashboard Cite

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“…1 In the sample of Ap and Bp stars (Table A1), six roAp stars show magnetic fields well above the 3 σ level, strongly underlying the close observational connection between magnetic field and pulsation: HD 42659, HD 60435, HD 80316, HD 84041, HD 86181 and HD 154708. The star HD 154708 is likely one of the coolest and least massive among the Ap stars and exhibits the second-largest mean magnetic field modulus, 24.5 kG, ever measured in an Ap star (Hubrig et al 2005a). Low-amplitude pulsations in HD 154708 have recently been discovered by Kurtz et al (2006, in preparation).…”

Section: Resultsmentioning

confidence: 98%

Evolution of magnetic fields in stars across the upper main sequence: I. Catalogue of magnetic field measurements with FORS 1 at the VLT

Hubrig¹,

et al. 2006

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To properly understand the physics of Ap and Bp stars it is particularly important to identify the origin of their magnetic fields. For that, an accurate knowledge of the evolutionary state of stars that have a measured magnetic field is an important diagnostic. Previous results based on a small and possibly biased sample suggest that the distribution of magnetic stars with mass below 3 M in the H-R diagram differs from that of normal stars in the same mass range (Hubrig et al. 2000). In contrast, higher mass magnetic Bp stars may well occupy the whole main-sequence width (Hubrig, Schöller & North 2005b). In order to rediscuss the evolutionary state of upper main sequence magnetic stars, we define a larger and bias-free sample of Ap and Bp stars with accurate Hipparcos parallaxes and reliably determined longitudinal magnetic fields. We used FORS 1 at the VLT in its spectropolarimetric mode to measure the magnetic field in chemically peculiar stars where it was unknown or poorly known as yet. In this first paper we present our results of the mean longitudinal magnetic field measurements in 136 stars. Our sample consists of 105 Ap and Bp stars, two PGa stars, 17 HgMn stars, three normal stars, and nine SPB stars. A magnetic field was for the first time detected in 57 Ap and Bp stars, in four HgMn stars, one PGa star, one normal B-type star and four SPB stars.

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“…We have now the mass and period of rotation for the star HD 154708, which has an extra-strong surface magnetic field of 2.6 -2.88 Tesla. The mass density is calculated to be only 563.4 kg/m 3 , and we group it within the NGC 6819 group [40] [41]. We list in Table 4 the mass M/M☉, radius R/R☉, period of rotation P(s) of 5 stars in M35 according to [42].…”

Section: Angular Momentum Study Of the Low-mass Stars In The Old Clusmentioning

confidence: 99%

On the Origin of Mass and Angular Momentum of Stellar Objects

Fung¹,

Wong²

2015

JMP

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The consequence of the 5D projection theory [1] is extended beyond the Gell-Mann Standard Model for hadrons to cover astronomical objects and galaxies. The proof of Poincare conjecture by Perelman's differential geometrical techniques led us to the consequence that charged massless spinors reside in a 5D void of a galactic core, represented by either an open 5D core or a closed, time frozen, 3D × 1D space structure, embedded in massive structural stellar objects such as stars and planets. The open galactic core is obtained from Ricci Flow mapping. There exist in phase, in plane rotating massless spinors within these void cores, and are responsible for 1) the outward spiral motion of stars in the galaxy in the open core, and 2) self rotations of the massive stellar objects. It is noted that another set of eigen states pertaining to the massless charged spinor pairs rotating out of phase in 1D (out of the 5D manifold) also exist and will generate a relatively weak magnetic field out of the void core. For stars and planets, it forms the intrinsic dipole field. Due to the existence of a homogeneous 5D manifold from which we believe the universe evolves, the angular momentum arising from the rotation of the in-phase spinor pairs is proposed to be counter-balanced by the rotation of the matter in the surrounding Lorentz domain, so as to conserve net zero angular momentum. Explicit expression for this total angular momentum in terms of a number of convergent series is derived for the totally enclosed void case/core, forming in general the structure of a star or a planet. It is shown that the variables/parameters in the Lorentz spacetime domain for these stellar objects involve the object's mass M, the object's Radius R, period of rotation P, and the 5D void radius Ro, together with the Fermi energy E f and temperature T of the massless charged spinors residing in the void. We discovered three laws governing the relationships between R o /R, T, E f and the angular momentum Iω of such astronomical object of interest, from which we established two distinct regions, which we define as the First and Second Laws for the evolution of the stellar object. The Fermi energy E f was found to be that of the electron mass, as it is the lightest massive elementary particle that could be created from pure energy in the core. In fact the mid-temperature of the transition region between the First and Second Law regions for this E f value is 5.3 × 10 9 K, just about that of the Bethe fusion temperature. We then apply our P. C. W. Fung, K. W. Wong 2304 theory to analyse observed data of magnetars, pulsars, pre-main-sequence stars, the NGC 6819 group, a number of low-to-mid mass main sequence stars, the M35 members, the NGC 2516 group, brown dwarfs, white dwarfs, magnetic white dwarfs, and members of the solar system. The ρ = (R o /R) versus T, and ρ versus P relations for each representative object are analysed, with reference to the general process of stellar evolution. Our analysis leads us to the following age sequence of stell...

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Detection of an extraordinarily large magnetic field in the unique ultra-cool Ap star HD 154708

Cited by 83 publications

References 27 publications

Searching for a link between the magnetic nature and other observed properties of Herbig Ae/Be stars and stars with debris disks

Searching for a link between the magnetic nature and other observed properties of Herbig Ae/Be stars and stars with debris disks

Evolution of magnetic fields in stars across the upper main sequence: I. Catalogue of magnetic field measurements with FORS 1 at the VLT

On the Origin of Mass and Angular Momentum of Stellar Objects

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