J/A+A/581/A83 Metal enriched X-ray bursting neutron star atmos. (Nattila+, 2015)
Models of neutron star atmospheres enriched with nuclear burning ashes.
Nattila J., Suleimanov V.F., Kajava J.J.E, Poutanen J.
<Astron. Astrophys. 581, A83 (2015)>
=2015A&A...581A..83N 2015A&A...581A..83N (SIMBAD/NED BibCode)
ADC_Keywords: Models, atmosphere ; Binaries, X-ray
Keywords: radiative transfer - methods: numerical - stars: neutron -
stars - atmospheres - X-rays: stars - X-rays: bursts
Abstract:
Low-mass X-ray binaries hosting neutron stars (NS) exhibit
thermonuclear (type-I) X-ray bursts, which are powered by unstable
nuclear burning of helium and/or hydrogen into heavier elements deep
in the NS "ocean". In some cases the burning ashes may rise from
the burning depths up to the NS photosphere by convection, leading to
the appearance of the metal absorption edges in the spectra, which
then force the emergent X-ray burst spectra to shift toward lower
energies.
These effects may have a substantial impact on the color correction
factor fc and the dilution factor w, the parameters of the diluted
blackbody model FE=wBE(fcTeff) that is commonly used to
describe the emergent spectra from NSs. The aim of this paper is to
quantify how much the metal enrichment can change these factors.
We have developed a new NS atmosphere modeling code, which has a few
important improvements compared to our previous code required by
inclusion of the metals. The opacities and the internal partition
functions (used in the ionization fraction calculations) are now taken
into account for all atomic species. In addition, the code is now
parallelized to counter the increased computational load.
Description:
Data includes 12 sets of atmosphere models for 4 different chemical
compositions (solar mix of hydrogen and helium with various enhanced
heavy metal abundances Z=1, 20 and 40Z☉; In addition we present
atmospheres consisting of pure iron) and three surface gravities,
logg=14.0, 14.3, and 14.6 (g in units cm/s2). Each of these 12 sets
is also characterized by the Eddington temperature at the surface,
neutron star radius (computed for the assumed mass M=1.4M☉), and
redshift, as detailed in set.dat file.
In tableb.dat, for each of the 12 sets there are 28-30 lines of data
(for various values of relative luminosity and corresponding effective
temperature) containing the color corrections fc of the blackbody
fits to the emergent model spectra. In addition, the file contains the
corresponding dilution factors for each atmosphere. The product of
dilution factor and fc4 are also given.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
set.dat 44 12 Atmosphere parameters
tableb.dat 38 336 Color correction and dilution factors
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See also:
J/A+A/527/A139 : Xray bursting neutron star atmos. models (Suleimanov+, 2011)
J/A+A/545/A120 : Xray bursting neutron star atmos. models II (Suleimanov+ 2012)
Byte-by-byte Description of file: set.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- Set [1/12] Set number
4- 8 F5.3 --- X X abundance (0.738, 0.550, 0.352, 0.0)
10- 14 F5.3 --- Y Y abundance
(0.249, 0.185, 0.118, 0.0)
16- 20 F5.3 --- Z Z abundance
(0.013, 0.265, 0.530, 1.0)
22- 25 F4.1 [cm/s2] logg Logarithm of surface gravity
(14.0, 14.3, 14.6)
27- 30 F4.2 keV TEdd Eddington temperature (12 values)
32- 36 F5.2 km R Neutron star radius (8.16, 10.88, 14.80)
38- 41 F4.2 --- z Redshift (0.18, 0.27, 0.42)
43- 44 I2 --- Lum Number of luminosities for a given set
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Byte-by-byte Description of file: tableb.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- Set [1/12] Set number
4- 8 F5.3 --- l Relative luminosity L/L_Edd (1)
10- 14 F5.3 --- grad/g Ratio of the radiation acceleration to gravity
16- 20 F5.3 keV Teff Effective temperature
22- 26 F5.3 --- fc1 Color correction factor fc (2)
28- 32 F5.3 --- w Dilution factor w
34- 38 F5.3 --- w*fc+4 Product of dilution factor and (fc)4
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Note (1): Lum values (28-30) of relative luminosity from 0.001 to 1.06-1.10.
Note (2): fc=Tbb/Teff, where Tbb is the fitted color temperature.
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Acknowledgements:
Joonas Nattila, joonas.a.nattila(at)utu.fi, University of Turku
(End) Joonas Nattila [Turku Univ], Patricia Vannier [CDS] 20-Jul-2015