ABSTRACT. We present mid-IR observations of the Galactic Luminous Blue Variable (LBV) HR Car and its associated nebula carried out with the Spitzer Space Telescope using both Infrared Array Camera and Infrared Spectrograph, as part of a GTO program aimed to study stellar ejecta from evolved stars. Our observations reveal a rich mid-IR spectrum of the inner nebula showing both solid state and atomic gas signatures. Strong low-excitation atomic fine structure lines such as 26.0 μm [Fe II] and 34.8 μm [Si II], indicate, for the first time, the presence of a PDR in this object class. While the physics and chemistry of the low-excitation gas appears to be dominated by photodissociation, a possible contribution due to shocks can be inferred from the evidence of gas phase Fe abundance enhancement. The presence of amorphous silicates, inferred from the observed characteristic broad feature at 10 μm located in the inner nebula, suggests that dust has formed during the LBV outburst. This is in contrast with the detection of crystalline dust in other probably more evolved Galactic LBVs, which is similar to the crystalline dust observed in red supergiants. This has been considered to be evidence of dust production during evolutionary phases prior to the outburst.

Key words: circumstellar matter; infrared: stars; stars: early-type; stars: individual (HR CAR); stars: winds, outflows

Print publication: Issue 1 (2009 March 20)
Received 2008 September 19, accepted for publication 2009 January 2
Published 2009 March 17