An ALMA view of CS and SiS around oxygen-rich AGB stars. (arXiv:1901.00070v1 [astro-ph.SR])

An ALMA view of CS and SiS around oxygen-rich AGB stars. (arXiv:1901.00070v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Danilovich_T/0/1/0/all/0/1">T. Danilovich</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Richards_A/0/1/0/all/0/1">A. M. S. Richards</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Karakas_A/0/1/0/all/0/1">A. I. Karakas</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Sande_M/0/1/0/all/0/1">M. Van de Sande</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Decin_L/0/1/0/all/0/1">L. Decin</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ceuster_F/0/1/0/all/0/1">F. De Ceuster</a>

We aim to determine the distributions of molecular SiS and CS in the
circumstellar envelopes of oxygen-rich asymptotic giant branch stars and how
these distributions differ between stars that lose mass at different rates. In
this study we analyse ALMA observations of SiS and CS emission lines for three
oxygen-rich galactic AGB stars: IK Tau, with a moderately high mass-loss rate
of $5times10^{-6}$M$_odot$ yr$^{-1}$, and W Hya and R Dor with low mass loss
rates of $sim1times10^{-7}$M$_odot$ yr$^{-1}$. These molecules are usually
more abundant in carbon stars but the high sensitivity of ALMA allows us to
detect their faint emission in the low mass-loss rate AGB stars. The high
spatial resolution of ALMA also allows us to precisely determine the spatial
distribution of these molecules in the circumstellar envelopes. We run
radiative transfer models to calculate the molecular abundances and abundance
distributions for each star. We find a spread of peak SiS abundances with
$sim10^{-8}$ for R Dor, $sim10^{-7}$ for W Hya, and $sim3times10^{-6}$ for
IK Tau relative to H$_2$. We find lower peak CS abundances of
$sim7times10^{-9}$ for R Dor, $sim7times10^{-8}$ for W Hya and
$sim4times10^{-7}$ for IK Tau, with some stratifications in the abundance
distributions. For IK Tau we also calculate abundances for the detected
isotopologues: C$^{34}$S, $^{29}$SiS, $^{30}$SiS, Si$^{33}$S, Si$^{34}$S,
$^{29}$Si$^{34}$S, and $^{30}$Si$^{34}$S. Overall the isotopic ratios we derive
for IK Tau suggest a lower metallicity than solar.

We aim to determine the distributions of molecular SiS and CS in the
circumstellar envelopes of oxygen-rich asymptotic giant branch stars and how
these distributions differ between stars that lose mass at different rates. In
this study we analyse ALMA observations of SiS and CS emission lines for three
oxygen-rich galactic AGB stars: IK Tau, with a moderately high mass-loss rate
of $5times10^{-6}$M$_odot$ yr$^{-1}$, and W Hya and R Dor with low mass loss
rates of $sim1times10^{-7}$M$_odot$ yr$^{-1}$. These molecules are usually
more abundant in carbon stars but the high sensitivity of ALMA allows us to
detect their faint emission in the low mass-loss rate AGB stars. The high
spatial resolution of ALMA also allows us to precisely determine the spatial
distribution of these molecules in the circumstellar envelopes. We run
radiative transfer models to calculate the molecular abundances and abundance
distributions for each star. We find a spread of peak SiS abundances with
$sim10^{-8}$ for R Dor, $sim10^{-7}$ for W Hya, and $sim3times10^{-6}$ for
IK Tau relative to H$_2$. We find lower peak CS abundances of
$sim7times10^{-9}$ for R Dor, $sim7times10^{-8}$ for W Hya and
$sim4times10^{-7}$ for IK Tau, with some stratifications in the abundance
distributions. For IK Tau we also calculate abundances for the detected
isotopologues: C$^{34}$S, $^{29}$SiS, $^{30}$SiS, Si$^{33}$S, Si$^{34}$S,
$^{29}$Si$^{34}$S, and $^{30}$Si$^{34}$S. Overall the isotopic ratios we derive
for IK Tau suggest a lower metallicity than solar.

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