J/A+A/701/A297 Microturbulence across the HR Diagram (Markova+, 2025)
Microturbulence across the Hertzsprung-Russell Diagram Setting observational
constraints on Milky Way stars.
Markova N., Cantiello M., Grassitelli L.
<Astron. Astrophys. 701, A297 (2025)>
=2025A&A...701A.297M 2025A&A...701A.297M (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Stars, atmospheres ; Effective temperatures ;
MK spectral classification
Keywords: stars: abundances - stars: atmospheres - stars: fundamental parameters
Abstract:
Despite its critical importance for determining stellar properties and
evolution, the origin and physical nature of microturbulence remains
poorly understood. Most of the existing works are focussed on specific
spectral types and luminosity classes. However, a comprehensive,
unified view has yet to emerge.
Our main goal is to investigate the behaviour of photospheric
micro-turbulence across the Hertzsprung-Russell diagram (HRD) and to
bridge theory with observations.
We assembled a homogeneous database of precise and consistent
determinations of effective temperature, surface gravity, projected
rotational rate (vsini), and macro- and micro-turbulent velocities
(vmac & vmic) for over 1800 Galactic stars spanning spectral types O
to K and luminosity classes I to V. By carefully minimising biases due
to target selection, data quality, and disparate analysis techniques,
we performed statistical tests and comparative analyses to probe
potential dependencies between these parameters and vmic.
Our findings indicate that photospheric micro-turbulence is a genuine
physical phenomenon, rather than a modelling artefact. A direct
comparison between observed vmic velocities and corresponding
theoretical predictions for the turbulent pressure fraction strongly
suggests that this phenomenon most likely arises from photospheric
motions driven (directly or indirectly) by envelope convection zones,
with an additional pulsational component likely operating in main
sequence B stars. We show that neglecting micro-turbulence in Fourier
transform analyses can partly (but not solely) explain the dearth of
slow rotators and the scarcity of stars with extremely low vmac. We
argue that including micro-turbulent pressure in atmospheric modelling
can significantly mitigate (and even resolve) the mass discrepancy for
less massive O stars.
We provide new observational insights into the nature and origin of
micro-turbulence across the HRD. Our database offers a valuable
resource for testing and refining theoretical scenarios, particularly
those addressing a range of puzzling phenomena in hot, massive stars.
Description:
We present a homogeneous database of precise and consistent
determinations of effective temperature (Teff), surface equatorial
gravity (logg) and photospheric micro-turbulent velocity (Vmic) for
over 1800 presumably single (pulsating and non-pulsating) stars with
diverse properties in the MW.
Based on these data, we studied the behaviour of Vmic as a function of
Teff and logg within each spectral type, luminosity class, and
pulsation type, and provide the first comprehensive and statistically
significant overview of this phenomenon in Galactic stars. As a first
application, we place observational constraints and evaluate several
scenarios proposed to explain specific pheno- mena in hot, massive
stars whose nature and origin remain poorly understood.
By carefully minimising biases due to target selection, data
quality, and disparate analysis techniques, we have compiled an
empirical database of literature determinations of Teff, logg and
Vmic (complemented with corresponding spectroscopic luminosity
calculated by us) for a huge number of Galactic stars with various SpT
and LC. Non-pulsating and pulsating stars are both involved with the
later constituting about 20% of the total sample, and including four
categories of non-radial pulsators (slowly pulsating B-stars (SPBs),
beta Cephei, gamma Doradus, and delta Scuti variables) and one type of
radial pulsators (classical Cepheids).
Although not statistically complete, our database is sufficiently
extensive and with comprehensive coverage of the Hertzsprung-Russell
diagram, and can there- fore serve as a platform to investigate the
nature and the origin of micro- turbulent broadening of stars in the
MW.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablee1.dat 41 1455 Effective temperature, surface equatorial gravity,
micro-turbulent velocity and spectroscopic
luminosity of non-pulsating Galactic stars
tablee2.dat 36 368 Effective temperature, surface equatorial gravity,
micro-turbulent velocity, and spectroscopic
luminosity of pulsating Galactic stars
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Byte-by-byte Description of file: tablee1.dat
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Bytes Format Units Label Explanations
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1- 11 A11 --- ID Star name/Star identifier
14- 18 F5.2 kK Teff Effective temperature (1)
21- 24 F4.2 [cm/s2] logg Logarithm of surface equatorial gravity
27- 31 F5.2 km/s Vmic Micro-turbulent velocity (2)
34- 38 F5.2 --- logLsp Logarithm of spectroscopic luminosity (G1)
40- 41 A2 --- SpType Spectral type (4)
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Note (1): Teff from spectroscopic and photometric techniques
Note (2): Vmic determined by means of the classical approach (i.e., by
eliminating trends between derived abundances and equivalent widths of metal
lines from a particular ion).
Note (4): Spectral type from O to K plus red giants/supergiants (rg).
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Byte-by-byte Description of file: tablee2.dat
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Bytes Format Units Label Explanations
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1- 6 A6 --- ID Star name/Star identifier
9- 13 F5.2 kK Teff Effective temperature
16- 19 F4.2 [cm/s2] logg Logarithm of surface equatorial gravity
22- 26 F5.2 km/s Vmic Micro-turbulent velocity
29- 32 F4.2 --- logLsp Logarithm of spectroscopic luminosity (G1)
34- 36 A3 --- PulsType Type of pulsation (1)
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Note (1): Type of pulsation as follows:
bc = beta Cephei variables
spb = genuin slowly pulsating B stars
bsp = suspected slowly pulsating B stars
gd = gamma Doradus variables
ds = delta Scuty variables
cp = classical Cepheids
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Global notes:
Note (G1): Spectroscopic luminosity (= Teff^4/g), a quantity used to construct
the spectroscopic Hertzsprung-Russell diagram (for more information see
Langer and Kudritzki, 2014A&A...564...A52).
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Acknowledgements:
Nevena Markova, nmarkova(at)astro.bas.bg
(End) Patricia Vannier [CDS] 03-Dec-2025