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Title: On the Relation of Silicates and SiO Maser in Evolved Stars

Abstract

The SiO molecule is one of the candidates for the seed of silicate dust in the circumstellar envelope of evolved stars, but this opinion is challenged. In this work we investigate the relation of the SiO maser emission power and the silicate dust emission power. With both our own observation by using the PMO/Delingha 13.7 m telescope and archive data, a sample is assembled of 21 SiO v  = 1, J  = 2 − 1 sources and 28 SiO v  = 1, J  = 1 − 0 sources that exhibit silicate emission features in the ISO /SWS spectrum as well. The analysis of their SiO maser and silicate emission power indicates a clear correlation, which is not against the hypothesis that the SiO molecules are the seed nuclei of silicate dust. On the other hand, no correlation is found between SiO maser and silicate crystallinity, which may imply that silicate crystallinity does not correlate with mass-loss rate.

Authors:
;  [1]
  1. Department of Astronomy, Beijing Normal University, Beijing 100875 (China)
Publication Date:
OSTI Identifier:
22663724
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astronomical Journal (Online); Journal Volume: 153; Journal Issue: 4; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; CORRELATIONS; COSMIC DUST; EMISSION; MASERS; MASS TRANSFER; MOLECULES; SILICON OXIDES; STAR EVOLUTION; STARS; STELLAR WINDS; TELESCOPES

Citation Formats

Liu, Jiaming, and Jiang, Biwei, E-mail: bjiang@bnu.edu.cn. On the Relation of Silicates and SiO Maser in Evolved Stars. United States: N. p., 2017. Web. doi:10.3847/1538-3881/AA6334.
Liu, Jiaming, & Jiang, Biwei, E-mail: bjiang@bnu.edu.cn. On the Relation of Silicates and SiO Maser in Evolved Stars. United States. doi:10.3847/1538-3881/AA6334.
Liu, Jiaming, and Jiang, Biwei, E-mail: bjiang@bnu.edu.cn. Sat . "On the Relation of Silicates and SiO Maser in Evolved Stars". United States. doi:10.3847/1538-3881/AA6334.
@article{osti_22663724,
title = {On the Relation of Silicates and SiO Maser in Evolved Stars},
author = {Liu, Jiaming and Jiang, Biwei, E-mail: bjiang@bnu.edu.cn},
abstractNote = {The SiO molecule is one of the candidates for the seed of silicate dust in the circumstellar envelope of evolved stars, but this opinion is challenged. In this work we investigate the relation of the SiO maser emission power and the silicate dust emission power. With both our own observation by using the PMO/Delingha 13.7 m telescope and archive data, a sample is assembled of 21 SiO v  = 1, J  = 2 − 1 sources and 28 SiO v  = 1, J  = 1 − 0 sources that exhibit silicate emission features in the ISO /SWS spectrum as well. The analysis of their SiO maser and silicate emission power indicates a clear correlation, which is not against the hypothesis that the SiO molecules are the seed nuclei of silicate dust. On the other hand, no correlation is found between SiO maser and silicate crystallinity, which may imply that silicate crystallinity does not correlate with mass-loss rate.},
doi = {10.3847/1538-3881/AA6334},
journal = {Astronomical Journal (Online)},
number = 4,
volume = 153,
place = {United States},
year = {Sat Apr 01 00:00:00 EDT 2017},
month = {Sat Apr 01 00:00:00 EDT 2017}
}
  • Based on the simultaneous observational results of SiO and H{sub 2}O masers toward 401 evolved stars, we have performed statistical analyses. We find that the peak and integrated intensities of SiO masers are stronger than those of H{sub 2}O masers in both Mira variables and OH/IR stars at most optical phases. However, the relative intensity ratios of H{sub 2}O to SiO masers in OH/IR stars are larger than those in Mira variables. Moreover, the intensity ratios of H{sub 2}O to SiO masers are found to be increased around the optical phases from 0-0.4. The H{sub 2}O photon luminosities also tendmore » to be more dependent on the optical phase compared with those of SiO masers. These facts suggest that H{sub 2}O masers are more sensitive to expanding the motion of circumstellar envelopes and also shock waves arising from the pulsations of the central star compared with SiO masers. This result may also be related to the differences in the maser location and pumping mechanism between H{sub 2}O and SiO masers. The full width at zero power of SiO masers in Mira variables shows similar values to those of OH/IR stars, while those of H{sub 2}O masers in OH/IR stars show larger values than those of Mira variables. These differences may originate from the different mass-loss rates and the different location of the two masers. The mean velocity shift of SiO and H{sub 2}O masers with respect to the stellar velocity was investigated as a function of optical phase. The velocity shift of the H{sub 2}O masers shows that the redshifted emission dominates during the phases from 0.3-0.6, while the blueshifted emission appears at phase 0.6 and coexists with the redshifted emission during other phases. These features show an associated pattern with the CO ΔV = 3 radial velocity curve, which exhibits a typical pulsation motion. On the other hand, the velocity shift of the SiO v = 2 maser shows slightly similar features to the H{sub 2}O maser, while that of SiO v = 1 does not show these similar features. Finally, the distributions of all 401 observed sources are investigated in the IRAS two-color diagram in relation to the late evolutionary processes of asymptotic giant branch stars.« less
  • The equations of photodissociation and radiative transfer are solved for the photochemical chain H/sub 2/O yields OH + H yields O + H + H in the circumstellar envelopes produced by steady mass loss from cool evolved stars. The solution is performed for a large range of mass-loss rates, outflow velocities, and interstellar UV radiation field densities. Comparison with observations shows that, over a wide range of mass-loss rates, the radius at which the OH density peaks coincides with the radius defined by maser emission in the 1612 MHz line. This allows the use of these models, together with observationsmore » of OH maser shell radii and wind outflow velocities, to measure mass-loss rates. A simple power-law function relating mass-loss rate to OH shell radius and wind outflow velocity is developed from these models and is applied to the existing measurements of OH shell radii to derive mass-loss rates for 42 stars. 34 references.« less
  • We report the Spitzer Infrared Spectrograph (IRS) observations of three evolved stars: IRAS 16456-3542, 18354-0638, and 23239+5754. The 9.9-37.2 {mu}m Spitzer/IRS high-resolution spectra of these three sources exhibit rich sets of enstatite-dominated crystalline silicate emission features. IRAS 16456-3542 is extremely rich in crystalline silicates, with >90% of its silicate mass in crystalline form, the highest to date ever reported for crystalline silicate sources.
  • Calculations were performed for the coupled radiative transfer and statistical equilibrium of CO in spherically symmetric, expanding stellar envelopes. The results were used to determine intensities of the rotational lines and the shapes of the emergent line profiles as measured by a telescope which, in general, partially resolves the expanding envelopes. The profiles and intensities are presented for a large range of mass loss rates, CO abundances, and infrared radiation fields.
  • The presently reported detection of SiO maser lines from highly excited rotational states in R Leo constitutes the highest rotational transition detected to date. The detection of v = 1, J = 6-5 transition emission may be sensitivity-limited, although the photon flux in this transition is significantly diminished relative to the power energy transitions. While emission from the v = 2 and v = 3 states is rare in the high rotational transitions, SiO maser emission is mostly confined to states with v no higher than 3 and J no higher than 6. 17 references.