NASA Lab Astrophysics Workshop: pre-registration & abstract

[Karly Pitman <kpitman@levee.wustl.edu>]

To whom it may concern:

Please accept the attached LaTeX format conference abstract and
pre-registration form for the NASA Laboratory Astrophysics Workshop to be
hosted by UNLV (Feb. 14-16 2006).  A check payment of $125 for the
workshop registration fee is en route via FedEx and should arrive at the
UNLV physics department c/o Cara Loomis tomorrow afternoon.

Thank you --

Karly M. Pitman, Ph.D.
kpitman@levee.wustl.edu



Registration form
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Last name:  Pitman
First name:  Karly
Middle name/initial:  M.
Affiliation: Washington University - St. Louis
Street Address: Washington University
                Department of Earth & Planetary Sciences
                Campus Box 1169
City: St. Louis
State: Missouri
Postal Code: 63130-4862
Country: USA
Tel: 314-935-5021
Fax: 314-935-7361
E mail: kpitman@levee.wustl.edu
Citizenship*:  US
Abstract title: Challenging the Identification of Silicon Nitride Dust
in Extreme Carbon Stars
co-authors not attending: Anne M. Hofmeister (Washington Univ. - St.
Louis), Angela K. Speck (Univ. Missouri - Columbia)
Special requirements: n/a -- poster session preferred
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\begin{document}

\title{Challenging the Identification of Silicon Nitride Dust 
in Extreme Carbon Stars}

\author{Karly M. Pitman (Washington University - St. Louis)
       \and Anne M. Hofmeister (Washington University - St. Louis)
       \and Angela K. Speck (University of Missouri - Columbia)}

\date{3 January 2006}

\maketitle

\begin{abstract}

It has been well established that SiC is a dominant
mineral in the condensation sequence of carbon-rich stars (or C-stars).  
The presence of other mineral species in interstellar dust surrounding 
C-stars may be indicative of exotic formation conditions for these 
objects.  Observers have long held out hope for detecting the compound 
silicon nitride (Si$_{3}$N$_{4}$) in stellar spectra;
however, previous attempts to identify Si$_{3}$N$_{4}$ in dust material 
around novae, planetary nebulae, and 
late-type binary and C-stars have proved to be unsuccessful 
(Cl\'{e}ment et al. 2005, ApJ, 821, 985 and references therein).  
Cl\'{e}ment et al. (2005) suggested that a broad, double-peaked 9-11 
$\mu$m absorption feature in the ISO SWS spectra of two extreme C-stars 
(AFGL 2477 and AFGL 5625) is due to Si$_{3}$N$_{4}$.  This assignment 
was based on the correlation of several weak observational 
spectral features with laboratory spectral features of 
$\alpha$-Si$_{3}$N$_{4}$ in the 15-30 $\mu$m range.  The broad 9-11
$\mu$m feature had been previously attributed to a mixture of SiC and
interstellar silicate (Speck et al. 1997, MNRAS, 20, 431), and more
recently to amorphous SiC (Speck et al. 2005, ApJ, 634, 426).  We dispute
the Si$_{3}$N$_{4}$ assignment on the basis of expected interstellar 
abundances, Si$_{3}$N$_{4}$ meteoritic isotope studies, blackbody correction 
methods, and spectral peak assignment as compared to noise.  Speck et al. 
(2005) discovered another extreme carbon star (IRAS 00210$+$6221) that 
exhibits a 9-11 $\mu$m absorption feature identical to those found in AFGL 
2477 and AFGL 5625.  A preliminary re-analysis of the spectra of these three
extreme carbon star spectra has revealed that neither AFGL 2477 nor IRAS
00210$+$6221 display any of the 15-30 $\mu$m features.  For AFGL 5625,
any features present in this range are at $>$ 2$\sigma$ level, and therefore
may just be noise.  We compare the observational spectra to independently
acquired laboratory spectra for Si$_{3}$N$_{4}$, as well as other nitride
minerals consistent with recently published condensation sequences (e.g., 
AlN, TiN), carbides, and silicides.  Our thin film laboratory 
absorbance spectra of $\alpha$- and $\beta$-Si$_{3}$N$_{4}$ appear to 
give good agreement with the KBr pellet method transmission spectra of 
Cl\'{e}ment et al. (2005).  Based on these analyses, we conclude that 
a unique identification of Si$_{3}$N$_{4}$ has not yet been made and 
calculate an upper limit to the abundance based on a non-detection.

This work is supported through NASA APRA04-000-0041. 


\end{abstract}

\end{document}