J/A+A/567/A133 Habitable zone code (Valle+, 2014)
Evolution of the habitable zone of low-mass stars.
Detailed stellar models and analytical relationships for different mass and
chemical compositions.
Valle G., Dell'Omodarme M., Prada Moroni P.G., Degl'Innocenti S.
<Astron. Astrophys. 567, A133 (2014)>
=2014A&A...567A.133V 2014A&A...567A.133V
ADC_Keywords: Models, evolutionary ; Stars, double and multiple ; Planets
Keywords: stars: evolution - stars: low-mass - methods: statistical -
astrobiology - planet - star interactions -
planets and satellites: physical evolution
Abstract:
The habitability of an exoplanet is assessed by determining the times
at which its orbit lies in the circumstellar habitable zone (HZ). This
zone evolves with time following the stellar luminosity variation,
which means that the time spent in the HZ depends on the evolution of
the host star. We study the temporal evolution of the HZ of low-mass
stars -- only due to stellar evolution -- and evaluate the related
uncertainties. These uncertainties are then compared with those due to
the adoption of different climate models. We computed stellar
evolutionary tracks from the pre-main sequence phase to the helium
flash at the red-giant branch tip for stars with masses in the range
[0.70-1.10]M☉, metallicity Z in the range [0.005-0.04], and
various initial helium contents. By adopting a reference scenario for
the HZ computations, we evaluated several characteristics of the HZ,
such as the distance from the host star at which the habitability is
longest, the duration of this habitability, the width of the zone for
which the habitability lasts one half of the maximum, and the
boundaries of the continuously habitable zone (CHZ) for which the
habitability lasts at least 4Gyr. We developed analytical models,
accurate to the percent level or lower, which allowed to obtain these
characteristics in dependence on the mass and the chemical composition
of the host star. The metallicity of the host star plays a relevant
role in determining the HZ. The importance of the initial helium
content is evaluated here for the first time; it accounts for a
variation of the CHZ boundaries as large as 30% and 10% in the inner
and outer border. The computed analytical models allow the first
systematic study of the variability of the CHZ boundaries that is
caused by the uncertainty in the estimated values of mass and
metallicity of the host star. An uncertainty range of about 30% in the
inner boundary and 15% in the outer one were found. We also verified
that these uncertainties are larger than that due to relying on
recently revised climatic models, which leads to a CHZ boundaries
shift within ±5% with respect to those of our reference scenario. We
made an on-line tool available that provides both HZ characteristics
and interpolated stellar tracks.
Description:
A C computation code that provide in output the distance dm (in AU)
for which the duration of habitability is longest, the corresponding
duration tm (in Gyr), the width W (in AU) of the zone for which the
habitability lasts tm/2, the inner (Ri) and outer (Ro)
boundaries of the 4Gyr continuously habitable zone.
The code read the input file HZ-input.dat, containing in each row the
mass of the host star (range: 0.70-1.10M☉), its metallicity
(either Z (range: 0.005-0.004) or [Fe/H]), the helium-to-metal
enrichment ratio (range: 1-3, standard value = 2), the equilibrium
temperature for habitable zone outer boundary computation (range:
169-203K) and the planet Bond Albedo (range: 0.0-1.0, Earth = 0.3).
The output is printed on-screen.
Compilation: just use your favorite C compiler: gcc hz.c -lm -o HZ
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
hz.c 78 151 C habitable zone computation code
HZ-input.dat 25 2 Example of input file for the computation code
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See also:
http://astro.df.unipi.it/stellar-models/HZ :
on-line HZ calculator and track interpolator
Byte-by-byte Description of file: HZ-input.dat
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Bytes Format Units Label Explanations
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1- 4 F4.2 Msun M Mass of the star
6- 10 F5.3 --- Z Metallicity of the star
12- 16 F5.3 --- DYDZ Helium-to-metal enrichment ratio
18- 20 I3 K To Equilibrium temperature for the HZ outer boundary
22- 25 F4.2 --- A Planet Bond albedo
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Acknowledgements:
Giada Valle, valle(at)df.unipi.it
(End) Giada Valle [Dip. Fisica, Univ. Pisa], Patricia Vannier [CDS] 11-Jun-2014