Formation of Transition Alumina Dust around Asymptotic Giant Branch Stars: Condensation Experiments using Induction Thermal Plasma Systems

Aki Takigawa, Tae Hee Kim, Yohei Igami, Tatsuki Umemoto, Akira Tsuchiyama, Chiyoe Koike, Junya Matsuno, Takayuki Watanabe

Research output: Contribution to journalArticle

Abstract

Mid-infrared spectroscopic observations of oxygen-rich asymptotic giant branch (AGB) stars show the common presence of dust species that have a broad feature at ∼11-12 μm. Chemically synthesized amorphous alumina (Al2O3) is widely accepted as the source of this emission, although it is not obvious that amorphous alumina can condense in circumstellar conditions. We performed condensation experiments of Al-Si-Mg-O and Mg-Al-O gases using induction thermal plasma systems, in which small particles condense from vapors with a steep temperature gradient. The condensates were analyzed using X-ray diffraction and Fourier transform infrared spectroscopy, and observed with a transmission electron microscope. The condensed nanoparticles from the Al and O gases were transition aluminas based on face-centered cubic (fcc) packed oxygen (δ- and λ-alumina, and an unknown phase). The fcc oxygen frameworks were maintained in the condensed alumina containing small amounts of Mg and Si. Condensates from the gases of Al:Mg = 99:1 and 95:5 had δ- and γ-alumina structures. Particles with λ- and γ-alumina structures formed from starting materials of Al:Si = 9:1 and Al:Si:Mg = 8:1:1, respectively. Amorphous silica-rich particles condensed from gases of Al/(Si+Al) < 0.75. The condensed transition alumina containing ∼10% Si showed similar spectral shapes to the observed dust emission from the alumina-rich AGB star T Cep. Based on the present results, it is reasonable that the source of 11-12 μm broad emission of alumina-rich stars is not amorphous alumina, but is transition alumina containing ∼10% Si.

Original languageEnglish
Article numberL7
JournalAstrophysical Journal Letters
Volume878
Issue number1
DOIs
Publication statusPublished - Jun 10 2019

Fingerprint

thermal plasmas
asymptotic giant branch stars
aluminum oxide
condensation
induction
aluminum oxides
dust
plasma
experiment
condensate
gases
gas
oxygen
condensates
FTIR spectroscopy
temperature gradient
temperature gradients
silica
electron microscopes
infrared spectroscopy

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Formation of Transition Alumina Dust around Asymptotic Giant Branch Stars : Condensation Experiments using Induction Thermal Plasma Systems. / Takigawa, Aki; Kim, Tae Hee; Igami, Yohei; Umemoto, Tatsuki; Tsuchiyama, Akira; Koike, Chiyoe; Matsuno, Junya; Watanabe, Takayuki.

In: Astrophysical Journal Letters, Vol. 878, No. 1, L7, 10.06.2019.

Research output: Contribution to journalArticle

Takigawa, Aki ; Kim, Tae Hee ; Igami, Yohei ; Umemoto, Tatsuki ; Tsuchiyama, Akira ; Koike, Chiyoe ; Matsuno, Junya ; Watanabe, Takayuki. / Formation of Transition Alumina Dust around Asymptotic Giant Branch Stars : Condensation Experiments using Induction Thermal Plasma Systems. In: Astrophysical Journal Letters. 2019 ; Vol. 878, No. 1.
@article{b13549a1a43342eb973042e911a046d1,
title = "Formation of Transition Alumina Dust around Asymptotic Giant Branch Stars: Condensation Experiments using Induction Thermal Plasma Systems",
abstract = "Mid-infrared spectroscopic observations of oxygen-rich asymptotic giant branch (AGB) stars show the common presence of dust species that have a broad feature at ∼11-12 μm. Chemically synthesized amorphous alumina (Al2O3) is widely accepted as the source of this emission, although it is not obvious that amorphous alumina can condense in circumstellar conditions. We performed condensation experiments of Al-Si-Mg-O and Mg-Al-O gases using induction thermal plasma systems, in which small particles condense from vapors with a steep temperature gradient. The condensates were analyzed using X-ray diffraction and Fourier transform infrared spectroscopy, and observed with a transmission electron microscope. The condensed nanoparticles from the Al and O gases were transition aluminas based on face-centered cubic (fcc) packed oxygen (δ- and λ-alumina, and an unknown phase). The fcc oxygen frameworks were maintained in the condensed alumina containing small amounts of Mg and Si. Condensates from the gases of Al:Mg = 99:1 and 95:5 had δ- and γ-alumina structures. Particles with λ- and γ-alumina structures formed from starting materials of Al:Si = 9:1 and Al:Si:Mg = 8:1:1, respectively. Amorphous silica-rich particles condensed from gases of Al/(Si+Al) < 0.75. The condensed transition alumina containing ∼10{\%} Si showed similar spectral shapes to the observed dust emission from the alumina-rich AGB star T Cep. Based on the present results, it is reasonable that the source of 11-12 μm broad emission of alumina-rich stars is not amorphous alumina, but is transition alumina containing ∼10{\%} Si.",
author = "Aki Takigawa and Kim, {Tae Hee} and Yohei Igami and Tatsuki Umemoto and Akira Tsuchiyama and Chiyoe Koike and Junya Matsuno and Takayuki Watanabe",
year = "2019",
month = "6",
day = "10",
doi = "10.3847/2041-8213/ab1f80",
language = "English",
volume = "878",
journal = "Astrophysical Journal Letters",
issn = "2041-8205",
publisher = "IOP Publishing Ltd.",
number = "1",

}

TY - JOUR

T1 - Formation of Transition Alumina Dust around Asymptotic Giant Branch Stars

T2 - Condensation Experiments using Induction Thermal Plasma Systems

AU - Takigawa, Aki

AU - Kim, Tae Hee

AU - Igami, Yohei

AU - Umemoto, Tatsuki

AU - Tsuchiyama, Akira

AU - Koike, Chiyoe

AU - Matsuno, Junya

AU - Watanabe, Takayuki

PY - 2019/6/10

Y1 - 2019/6/10

N2 - Mid-infrared spectroscopic observations of oxygen-rich asymptotic giant branch (AGB) stars show the common presence of dust species that have a broad feature at ∼11-12 μm. Chemically synthesized amorphous alumina (Al2O3) is widely accepted as the source of this emission, although it is not obvious that amorphous alumina can condense in circumstellar conditions. We performed condensation experiments of Al-Si-Mg-O and Mg-Al-O gases using induction thermal plasma systems, in which small particles condense from vapors with a steep temperature gradient. The condensates were analyzed using X-ray diffraction and Fourier transform infrared spectroscopy, and observed with a transmission electron microscope. The condensed nanoparticles from the Al and O gases were transition aluminas based on face-centered cubic (fcc) packed oxygen (δ- and λ-alumina, and an unknown phase). The fcc oxygen frameworks were maintained in the condensed alumina containing small amounts of Mg and Si. Condensates from the gases of Al:Mg = 99:1 and 95:5 had δ- and γ-alumina structures. Particles with λ- and γ-alumina structures formed from starting materials of Al:Si = 9:1 and Al:Si:Mg = 8:1:1, respectively. Amorphous silica-rich particles condensed from gases of Al/(Si+Al) < 0.75. The condensed transition alumina containing ∼10% Si showed similar spectral shapes to the observed dust emission from the alumina-rich AGB star T Cep. Based on the present results, it is reasonable that the source of 11-12 μm broad emission of alumina-rich stars is not amorphous alumina, but is transition alumina containing ∼10% Si.

AB - Mid-infrared spectroscopic observations of oxygen-rich asymptotic giant branch (AGB) stars show the common presence of dust species that have a broad feature at ∼11-12 μm. Chemically synthesized amorphous alumina (Al2O3) is widely accepted as the source of this emission, although it is not obvious that amorphous alumina can condense in circumstellar conditions. We performed condensation experiments of Al-Si-Mg-O and Mg-Al-O gases using induction thermal plasma systems, in which small particles condense from vapors with a steep temperature gradient. The condensates were analyzed using X-ray diffraction and Fourier transform infrared spectroscopy, and observed with a transmission electron microscope. The condensed nanoparticles from the Al and O gases were transition aluminas based on face-centered cubic (fcc) packed oxygen (δ- and λ-alumina, and an unknown phase). The fcc oxygen frameworks were maintained in the condensed alumina containing small amounts of Mg and Si. Condensates from the gases of Al:Mg = 99:1 and 95:5 had δ- and γ-alumina structures. Particles with λ- and γ-alumina structures formed from starting materials of Al:Si = 9:1 and Al:Si:Mg = 8:1:1, respectively. Amorphous silica-rich particles condensed from gases of Al/(Si+Al) < 0.75. The condensed transition alumina containing ∼10% Si showed similar spectral shapes to the observed dust emission from the alumina-rich AGB star T Cep. Based on the present results, it is reasonable that the source of 11-12 μm broad emission of alumina-rich stars is not amorphous alumina, but is transition alumina containing ∼10% Si.

UR - http://www.scopus.com/inward/record.url?scp=85070090998&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=85070090998&partnerID=8YFLogxK

U2 - 10.3847/2041-8213/ab1f80

DO - 10.3847/2041-8213/ab1f80

M3 - Article

AN - SCOPUS:85070090998

VL - 878

JO - Astrophysical Journal Letters

JF - Astrophysical Journal Letters

SN - 2041-8205

IS - 1

M1 - L7

ER -