Spitzer Space Telescope - General Observer Proposal #20100


Infrared studies of the Helium nova V445 Puppis.

Principal Investigator: Dipankar Banerjee
           Institution: Physical Research Laboratory

Co-Investigators: 
K. Y. L. Su, Steward Observatory, Arizona                             
N.M. Ashok, Physical. Research Lab., India                            
R.D. Gehrz, University of Minnesota                                   
A. Henden, US Naval Obs'tory, Flagstaff                               
D.K. Lynch, The Aerospace Corporation, LA                             
K Misselt, Steward Observatory, Arizona                               
E.F Polomski, University of Minnesota                                 
R.J. Rudy, The Aerospace Corporation, LA                              
S. Starrfield, Arizona State University                               
W.P Varricatt, Joint Astronomy Centre, Hawaii                         
R.M. Wagner, Large Binocular Telescope Observatory                    
C.E. Woodward, University of Minnesota                                

Science Category: evolved stars/pn/sne 
 Observing Modes: IracMap IrsStare MipsPhot 
  Hours Approved: 2.7 

Abstract:
V445 Puppis, which erupted in a nova-like outburst in Dec.  2000,
could well be the first, observed example of a "Helium nova".  A
classical nova eruption occurs on the surface of white-dwarf (WD) due
to a thermo-nuclear runaway in the matter accreted by the WD from its
companion main sequence star.  Since this material is H rich, the
outburst spectrum is expected to be rich in H lines in the optical and
near-IR regions.  Such H lines are invariably observed in novae
spectra.  However, V445 Puppis showed no sign of any H lines in the
optical or near-IR spectra obtained after outburst and also in spectra
obtained very recently.  Instead it shows an unusual enrichment of
Helium and Carbon spectral features.  The object defies classification
in known categories of eruptive variables and appears to be a
potential Helium nova candidate.  A "Helium nova" outburst had been
predicted to occur when the accreted matter on the WD was Helium rich
and appropriate physical conditions prevailed.  But such a theoretical
prediction had no observable counterpart till the outburst of V445
Puppis.  Now, several theoretical studies, which have modelled the low
outburst-amplitude observed in V445 Pup and also its slowly-declining
light curve, indicate that it has strong potential as a genuine He
nova candidate.  Our proposed Spitzer observations will (i) study the
properties of the thick dust shell that enshrouds V445 Pup.  A
significant part of the object's emission is in the infrared (ii)
explore its spectra in the mid-IR and compare it with spectra of
classical novae to see the differences between them.  Such spectra,
given the nature of V445 Pup, will have the potential to yield
new/unanticipated results (iii) estimate physical properties like
temperature, electron density etc.  of the object's environment based
on its spectra and (iv) try to detect the expanding nova shell from
the 2000  outburst whose detection in the optical has been reported
recently.