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Post Info TOPIC: HD79158
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Title: The magnetic Bp star 36 Lyncis, II. A spectroscopic analysis of its co-rotating disk
Authors: M.A. Smith, G.A. Wade, D.A. Bohlender, C.T. Bolton

Researchers report on the physical properties of the disk-like structure of B8 IIIp star 36 Lyncis from line syntheses of phase-resolved, high resolution spectra obtained from the IUE archives and from newly obtained ground-based Halpha spectra. This disk is highly inclined to the rotational axis and betrays its existence every half rotation cycle as one of two opposing sectors pass in front of the star. Although the disk absorption spectrum is at least ten times too weak to be visible in optical iron lines during these occultations, its properties can be readily examined in a large number of UV "iron curtain" lines because of their higher opacities. The analysis of the variations of the UV resonance lines brings out some interesting details about the radiative properties of the disks:
(1) they are optically thick in the C IV and Si IV doublets,
(2) the range of excitation of the UV resonance lines is larger at the primary occultation (phi = 0.00) than at the secondary one, and
(3) the bf relative strengths of the absorption peaks for the two occultations varies substantially from line to line. We have modelled the absorptions of the UV C IV resonance and Halpha absorptions by means of a simulated disk with opaque and translucent components. Our simulations suggest that a gap separates the star and the inner edge of the disk. The disk extends radially out to geq10 R_*. The disk scale height perpendicular to the plane is approx1R_*. However, the sector causing the primary occultation is about four times thicker than the opposite sector. The C IV scattering region extends to a larger height than the Halpha region does, probably because it results from shock heating far from the cooler disk plane.

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Title: The magnetic Bp star 36 Lyncis, I. Magnetic and photospheric properties
Authors: G.A. Wade, M.A. Smith, D.A. Bohlender, T.A. Ryabchikova, C.T. Bolton, T. Lueftinger, J.D. Landstreet, P. Petit, S. Strasser, M. Blake, G.M. Hill

This paper reports the photospheric, magnetic and circumstellar gas characteristics of the magnetic B8p star 36 Lyncis (HD 79158). Using archival data and new polarised and unpolarised high-resolution spectra, researchers redetermine the basic physical properties, the rotational period and the geometry of the magnetic field, and the photospheric abundances of various elements. Based on magnetic and spectroscopic measurements, the researchers infer an improved rotational period of 3.83475 ± 0.00002 d. They determine a current epoch of the longitudinal magnetic field positive extremum (HJD 2452246.033), and provide constraints on the geometry of the dipole magnetic field (i\geq 56degr, 3210
m G\leq B_
m d\leq 3930 G, beta unconstrained). The researchers the effective temperature and surface gravity using the optical and UV energy distributions, optical photometry and Balmer line profiles (T_rm eff=13300 ±300$ K, log g=3.7-4.2), and based on the Hipparcos parallax they redetermine the luminosity, mass, radius and true rotational speed (L=2.54 ±0.16 L_odot, M=4.0 ± 0.2 M_odot, R=3.4 ± 0.7 R_odot, v_rm eq=45-61.5 kms).
The researchers measure photospheric abundances for 21 elements using optical and UV spectra, and constrain the presence of vertical stratification of these elements. they perform preliminary Doppler Imaging of the surface distribution of Fe, finding that Fe is distributed in a patchy belt near the rotational equator. Most remarkably, they confirm strong variations of the Halpha line core which they interpret as due to occultations of the star by magnetically-confined circumstellar gas.

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