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Post Info TOPIC: Alpha Virginis


L

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HD 116658
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Handheld photo of Jupiter (top) and the blue star Alpha Virginis (Spica)

Picture 819



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L

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Spica
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The Alpha Virginis (Spica) Nebula

An extensive ultra-violet nebula surrounding Spica has been reported by Kupperian, Boggess, and Milligan. Their rocket-borne photon counters yielded an isophotal map of roughly circular extent 22 in diameter, increasing in brightness from the outside towards Spica but reaching the instrumental saturation-level for the central area. If the nebula were due to Lyman-Alpha radiation it would be reasonable to assume that Ha should also be detectable, but no nebula has ever been detected by conventional photographic means. This may have been due to the fact that the strong image of Spica drowns the faint nebula close to the star. On the red plates of the Palomar Sky Survey, the over-exposed image of Spica covers more than 10 min. of arc, while on the blue plates it is nearly three times larger in diameter. The spectrum of Spica itself does not show Ha in emission.
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RE: Alpha Virginis
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Spica (Alpha Virginis) is the brightest star in the constellation Virgo, and the 15th brightest star in the nighttime sky.
The Sun passes a little more than 2 north of Spica around October 16 every year, and the star's heliacal rising occurs about two weeks later.

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Title: Line-profile variability from tidal flows in Alpha Virginis (Spica)
Authors: D.M. Harrington, G. Koenigsberger, E. Moreno, J.R. Kuhn
(Version v2)

We present the results of high precision, high resolution (R~68000) optical observations of the short-period (4d) eccentric binary system Alpha Virginis (Spica) showing the photospheric line-profile variability that in this system can be attributed to non-radial pulsations driven by tidal effects. Although scant in orbital phase coverage, the data provide S/N>2000 line profiles at full spectral resolution in the wavelength range delta-lambda = 4000--8500 Angstroms, allowing a detailed study of the night-to-night variability as well as changes that occur on ~2 hr timescale. Using an ab initio theoretical calculation, we show that the line-profile variability can arise as a natural consequence of surface flows that are induced by the tidal interaction.

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