2017), and previous spectropolarimetric studies have revealed that the source is circularly unpolarized, which only implies an upper limit of 10 G (Sabin et al. Earlier attempts with current magnetic tracers have not provided strong constraint no continuum polarization has been detected (see Akras et al. The magnetic field in the 89 Her's primary has been unknown to date. The resulting absorption lines from the aligned atoms are polarized parallel or perpendicular to the magnetic field direction. The GSA probe is particularly suitable for the sub-Gauss magnetic field because the atoms have long lifetimes in their ground states. In the Ground-level Hanle regime, however, the atoms preferentially follow neither the magnetic or radiation field ( r A ∼ 1 Yan & Lazarian 2008). In the GSA regime, the atoms are aligned with radiation field or realigned by magnetic field depending on the ratio of the two rates ( r A ≡ ν Lar/ ν Rad). These radiative-aligned atoms are magnetically realigned by fast precession as long as the Larmor precession rate ν Lar is larger than the radiative pumping rate ν Rad (Yan & Lazarian 2006, 2007). The anisotropic radiation aligns the atoms in the ground state by optical pumping (Happer 1972 Varshalovich 1971 Landolfi & Landi Degl'Innocenti 1986).
1952 Hawkins & Dicke 1953 Hawkins 1955 Cohen-Tannoudji et al. Ground-state alignment (GSA) is an established physical phenomenon that has solid physical foundations and has been studied and supported by numerous experiments (Kastler 1950 Brossel et al. The alignment is in terms of the angular momentum of atoms and ions (hereafter "atoms" for simplicity). This observation indicates the existence of ground-state magnetic alignment, which was proposed theoretically as a magnetic tracer in Yan & Lazarian ( 2006). In this Letter, we report the discovery of two ground-state Fe i photosphere absorption line polarizations whose directions have not shown orbital synchronization, but rather are aligned through all orbital phases. They have excluded the origin of such a signal from either the depolarization of stellar continuum polarization (including pulsations and hot spots) or scattered polarization from a bipolar outflows, and found that it is a result of optical pumping in the stellar environment. ( 2018) found that linearly polarized photospheric absorption lines of 89 Her present Q/ I and U/ I signals that vary according to the secondary orbital period (hereafter "orbital synchronization"). The projection of stellar outflows on the picture plane is 45° compared to the east–west orientation (Bujarrabal et al. It exhibits a circumstellar environment consisting of two main components: an expanding hourglass structure and a circumbinary rotating disk (Waters et al. 89 Her has an orbital period P orb ∼ 288 days and inclination 12°. The radius of the secondary orbital track is r orb = 67 R ⊙. The primary star is an F-type supergiant with a radius R pri = 41 R ⊙ and an effective temperature T eff = 6500 K, while the secondary is an M-type main sequence with R sec = 0.6 R ⊙ and T eff = 4045 K. 2018).Ĩ9 Her is a post-asymptotic giant branch (post-AGB) binary system. The surprisingly high polarimetric signals shown by the prototypical star 89 Herculis (89 Her on average, more than 1%) give us a unique opportunity to study this system (Leone et al. 2014) facilitate the investigation of polarimetric properties of single spectral lines. 2011 the HARPS-North polarimeter (HANPO), Leone et al. 2008 the High Accuracy Radial velocity Planet Searcher (HARPS), Piskunov et al. Developments in high-resolution spectral facilities with polarimeters (e.g., the Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI), Strassmeier et al. Spectral polarimetry observations can provide extensive information on magnetic field and the topology of radiation structure.
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