J/A+A/630/A143 Magnesium and silicon K-edges cross sections (Rogantini+, 2019)
Interstellar dust along the line of sight of GX 3+1.
Rogantini D., Costantini E., Zeegers S.T., de Vries C.P., Mehdipour M.,
de Groot F., Mutschke H., Psaradaki I., Waters L.B.F.M.
<Astron. Astrophys. 630, A143 (2019)>
=2019A&A...630A.143R 2019A&A...630A.143R (SIMBAD/NED BibCode)
ADC_Keywords: Interstellar medium ; Atomic physics
Keywords: dust, extinction - X-rays: ISM - X-rays: individuals: GX 3+1 -
astrochemistry - X-rays: binaries - ISM: abundances
Abstract:
Studying absorption and scattering of X-ray radiation by interstellar
dust grains allows us to access the physical and chemical properties
of cosmic grains even in the densest regions of the Galaxy. We aim at
characterising the dust silicate population which presents clear
absorption features in the energy band covered by the Chandra X-ray
Observatory. Through these absorption features, in principle, it is
possible to infer the size distribution, composition, and structure of
silicate in the interstellar medium. In particular, in this work we
investigate magnesium and silicon K-edges. We built X-ray extinction
models for 15 dust candidates using newly acquired synchrotron
measurements. These models were adapted for astrophysical analysis and
implemented in the Spex spectral fitting program. We used the models
to reproduce the dust absorption features observed in the spectrum of
the bright low mass X-ray binary GX 3+1, which is used as a background
source. With the simultaneous analysis of the two edges we test two
different size distributions of dust: one corresponding to the
standard Mathis-Rumpl-Nordsieck model and one considering larger
grains (n(a)∝ai-3.5 with 0.005µm<a1<0.25µm and
0.05µm<a2<0.5µm, respectively, with a the grain size). These
distributions may be representative of the complex Galactic region
towards this source. We find that up to 70% of dust is constituted by
amorphous olivine. We discuss the crystallinity of the cosmic dust
found along this line of sight. Both magnesium and silicon are highly
depleted into dust (δZ=0.89 and 0.94, respectively), while
their total abundance does not depart from solar values.
Description:
In our sample set we considered pyroxenes and olivine with varying
Mg-to-Fe ratios. Olivine can be pure Mg2SiO4 (forsterite),
Fe2SiO4 (fayalite), or some combination of the two, written as .
Pyroxene can be Mg-pure MgSiO3 (enstatite), Fe-pure FeSiO3
(ferrosilite), or a combination of the two. The nomenclature
En(x)Fs(1-x) indicates the fraction of iron (or magnesium) included in
the compound. "En" stands for enstatite and "Fs" for
ferrosilite. These silicate compounds are present in both crystalline
and amorphous forms. We completed our sample set adding spinel, which
is a Mg-bearing compound which crystallises in the cubic crystal
system formed by oxygens, whereas Mg and Al atoms sit in tetrahedral
and octahedral sites in the lattice (Mutschke et al.,
1998A&A...333..188M 1998A&A...333..188M). Spinel has been observed in chondritic meteorite
with pre-solar composition and has been produced by gas outflows of
red giant stars (Zinner et al. 2005, Geochim. Cosmochim. Acta, 69,
4149).
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
oliv-am.dat 61 4500 *Extinction, scattering and absorption cross
sections of olivine amorphous [MgFeSiO4]
oliv-cr.dat 61 4500 *Extinction, scattering and absorption cross
sections of olivine crystalline
[Mg1.56Fe0.4Si0.91O4 ]
fors-cr.dat 61 4500 *Extinction, scattering and absorption cross
sections of forsterite crystalline [Mg2FeSiO4]
enst-cr.dat 61 4500 *Extinction, scattering and absorption cross
sections of enstatite crystalline [MgFeSiO3]
enst-am.dat 61 4500 *Extinction, scattering and absorption cross
sections of enstatite amorphous [MgFeSiO3]
e60f40am.dat 61 4500 *Extinction, scattering and absorption cross
sections of En60Fs40 amorphous [Mg0.6Fe0.4SiO3]
e60f40cr.dat 61 4500 *Extinction, scattering and absorption cross
sections of En60fs40 crystalline [Mg0.6Fe0.4SiO3]
e75f25am.dat 61 4500 *Extinction, scattering and absorption cross
sections of En75Fs25 amorphous [Mg0.75Fe0.25SiO3]
hype-cr.dat 61 4500 *Extinction, scattering and absorption cross
sections of Hypersthene crystalline
[Mg1.502Fe0.498Si2O6 ]
e90f10am.dat 61 4500 *Extinction, scattering and absorption cross
sections of En90Fs10 amorphous [Mg0.9Fe0.1SiO3]
e90f10cr.dat 61 4500 *Extinction, scattering and absorption cross
sections of En90Fs10 crystalline [Mg0.9Fe0.1SiO3]
spin-cr.dat 61 4000 *Extinction, scattering and absorption cross
sections of Spinel crystalline [MgAl2O4]
--------------------------------------------------------------------------------
Note on *.dat: Header included 3 rows:
- Compound name, form and chemical formula
- Units
- Column labels
--------------------------------------------------------------------------------
See also:
J/A+A/627/A16 : Silicon K-edge dust absorption cross sections (Zeegers+, 2019)
Byte-by-byte Description of file (#): *.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
7- 13 F7.5 keV E Energy in the Mg K-edge region
17- 29 E13.7 cm+2/H Ext Extinction cross section
33- 45 E13.7 cm+2/H Sca Scattering cross section
49- 61 E13.7 cm+2/H Abs Absorption cross section
--------------------------------------------------------------------------------
Acknowledgements:
Daniele Rogantini, d.rogantini(at)sron.nl
(End) Patricia Vannier [CDS] 17-Sep-2019