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Hydrodynamical simulations of convection-related stellar micro-variability. I. Statistical relations for photometric and photocentric variability

Ludwig, Hans-Günter LU (2006) In Astronomy & Astrophysics 445(2). p.86-661
Abstract
Local-box hydrodynamical model atmospheres provide statistical information about the spatial dependence, as well as temporal evolution, of a star's emergent radiation field. Here, we consider late-type stellar atmospheres for which temporal changes of the radiative output are primarily related to convective (granular) surface flows. We derived relations for evaluating the granulation-induced, disk-integrated thus observable fluctuations of the stellar brightness and location of the photocenter from radiation intensities available from a local model. Apart from their application in the context of hydrodynamical stellar atmospheres, these formulae provide some broader insight into the nature of the fluctuations under consideration.... (More)
Local-box hydrodynamical model atmospheres provide statistical information about the spatial dependence, as well as temporal evolution, of a star's emergent radiation field. Here, we consider late-type stellar atmospheres for which temporal changes of the radiative output are primarily related to convective (granular) surface flows. We derived relations for evaluating the granulation-induced, disk-integrated thus observable fluctuations of the stellar brightness and location of the photocenter from radiation intensities available from a local model. Apart from their application in the context of hydrodynamical stellar atmospheres, these formulae provide some broader insight into the nature of the fluctuations under consideration. Brightness fluctuations scale inversely proportional to the square root of the number of convective cells (the statistically independently radiating surface elements) present on the stellar surface and increase with more pronounced limb-darkening. Fluctuations of the stellar photocentric position do not depend on the number of cells and are largely insensitive to the degree of limb-darkening. They amount to a small fraction of the typical cell size, and can become a limiting factor for high-precision astrometry in the case of extreme giants. The temporal brightness and positional fluctuations are statistically uncorrelated but closely related in magnitude. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
convection, hydrodynamics, methods : numerical, stars : late-type, stars : atmospheres, radiative transfer
in
Astronomy & Astrophysics
volume
445
issue
2
pages
86 - 661
publisher
EDP Sciences
external identifiers
  • wos:000233995800025
  • scopus:30144431859
ISSN
0004-6361
DOI
10.1051/0004-6361:20042102
language
English
LU publication?
yes
id
b68fcf1b-dc4a-453b-9c25-ae94214c8785 (old id 743861)
date added to LUP
2007-12-12 12:11:36
date last changed
2018-07-08 04:00:04
@article{b68fcf1b-dc4a-453b-9c25-ae94214c8785,
  abstract     = {Local-box hydrodynamical model atmospheres provide statistical information about the spatial dependence, as well as temporal evolution, of a star's emergent radiation field. Here, we consider late-type stellar atmospheres for which temporal changes of the radiative output are primarily related to convective (granular) surface flows. We derived relations for evaluating the granulation-induced, disk-integrated thus observable fluctuations of the stellar brightness and location of the photocenter from radiation intensities available from a local model. Apart from their application in the context of hydrodynamical stellar atmospheres, these formulae provide some broader insight into the nature of the fluctuations under consideration. Brightness fluctuations scale inversely proportional to the square root of the number of convective cells (the statistically independently radiating surface elements) present on the stellar surface and increase with more pronounced limb-darkening. Fluctuations of the stellar photocentric position do not depend on the number of cells and are largely insensitive to the degree of limb-darkening. They amount to a small fraction of the typical cell size, and can become a limiting factor for high-precision astrometry in the case of extreme giants. The temporal brightness and positional fluctuations are statistically uncorrelated but closely related in magnitude.},
  author       = {Ludwig, Hans-Günter},
  issn         = {0004-6361},
  keyword      = {convection,hydrodynamics,methods : numerical,stars : late-type,stars : atmospheres,radiative transfer},
  language     = {eng},
  number       = {2},
  pages        = {86--661},
  publisher    = {EDP Sciences},
  series       = {Astronomy & Astrophysics},
  title        = {Hydrodynamical simulations of convection-related stellar micro-variability. I. Statistical relations for photometric and photocentric variability},
  url          = {http://dx.doi.org/10.1051/0004-6361:20042102},
  volume       = {445},
  year         = {2006},
}