THE THIRD SIGNATURE OF GRANULATION IN BRIGHT-GIANT AND SUPERGIANT STARS

Journal Article · Sun Apr 15 04:00:00 EDT 2012 · Astronomical Journal (New York, N.Y. Online)

DOI:https://doi.org/10.1088/0004-6256/143/4/92· OSTI ID:22034660

Gray, David F; Pugh, Teznie ^[1]

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1. Department of Physics and Astronomy, University of Western Ontario, London, Ontario (Canada)

We investigated third-signature granulation plots for 18 bright giants and supergiants and one giant of spectral classes G0 to M3. These plots reveal the net granulation velocities, averaged over the stellar disk, as a function of depth. Supergiants show significant differences from the 'standard' shape seen for lower-luminosity stars. Most notable is a striking reversal of slope seen for three of the nine supergiants, i.e., stronger lines are more blueshifted than weaker lines, opposite the solar case. Changes in the third-signature plot of {alpha} Sco (M1.5 Iab) with time imply granulation cells that penetrate only the lower portion of the photosphere. For those stars showing the standard shape, we derive scaling factors relative to the Sun that serve as a first-order measure of the strength of the granulation relative to the Sun. For G-type stars, the third-signature scale of the bright giants and supergiants is approximately 1.5 times as strong as in dwarfs, but for K stars, there in no discernible difference between higher-luminosity stars and dwarfs. Classical macroturbulence, a measure of the velocity dispersion of the granulation, increases with the third-signature-plot scale factors, but at different rates for different luminosity classes.

• OSTI ID: 22034660
• Journal Information: Astronomical Journal (New York, N.Y. Online), Journal Name: Astronomical Journal (New York, N.Y. Online) Journal Issue: 4 Vol. 143; ISSN 1538-3881
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ASTRONOMY
ASTROPHYSICS
CONVECTION
GRANULATION
LUMINOSITY
PHOTOSPHERE
SUN
SUPERGIANT STARS
VELOCITY