Spitzer Space Telescope - General Observer Proposal #40896


The dust disk of HR 4049

Principal Investigator: Jan Cami
           Institution: SETI Institute

     Technical Contact: Jan Cami, SETI Institute

Science Category: evolved stars/pn/sne 
 Observing Modes: IrsStare 
  Hours Approved: 0.4 

Abstract:
HR 4049 is the prototype of a class of binary post-AGB stars with very peculiar
properties. One of those surprising properties is the presence in the IR
spectrum of gas species typically found in O-rich environments (carbon dioxide,
water, OH) at the same time as species typical for C-rich environments (HCN,
Polycyclic Aromatic Hydrocarbons, nanodiamonds). Moreover, the carbon dioxide
bands require an extreme enrichment in 17O and 18O isotopes of nearly 3 orders
of magnitude. Previous IR observations have indicated the presence of a massive
and vertically extended disk surrounding the entire binary system. This disk is
important to explain the peculiar abundance pattern in the stellar photosphere,
but may be equally important for understanding the simultaneous occurence of
O-rich and C-rich species in this object. Crucial in this context is the nature
(O-rich vs C-rich) of the dust disk at the inner rim. Currently available IR
observations do not allow to establish the nature of the dust. Here, we propose
to observe HR 4049 with Spitzer-IRS using the LH module in order to study the
composition of the dust in the circumbinary disk by searching for dust features
at wavelengths between 19.3 and 36 micron.