Herschel PACS and SPIRE imaging of CW Leo

TL;DR

This study uses Herschel PACS and SPIRE imaging to analyze the structure and interaction of the carbon star CW Leo with the interstellar medium, revealing a bow shock and measuring its properties.

Contribution

First detailed Herschel imaging of CW Leo's interaction with the ISM, including bow shock structure and physical parameters derived from multi-band data.

Findings

Extended arc of interaction consistent with a bow shock.

Measured temperature of dust in the interaction region (~25 K).

Estimated star's relative velocity with respect to the ISM.

Abstract

Herschel PACS and SPIRE images have been obtained over a 30'x30' area around the well-known carbon star CW Leo (IRC +10 216). An extended structure is found in an incomplete arc of ~22' diameter, which is cospatial with the termination shock due to interaction with the interstellar medium (ISM) as defined by Sahai & Chronopoulos from ultraviolet GALEX images. Fluxes are derived in the 70, 160, 250, 350, and 550 um bands in the region where the interaction with the ISM takes place, and this can be fitted with a modified black body with a temperature of 25+-3 K. Using the published proper motion and radial velocity for the star, we derive a heliocentric space motion of 25.1 km/s. Using the PACS and SPIRE data and the analytical formula of the bow shock structure, we infer a de-projected standoff distance of the bow shock of R0 = (8.0+-0.3)x10^17 cm. We also derive a relative velocity of the star with respect to the ISM of (106.6+-8.7)/sqrt(n_ISM) km/s, where n_ISM is the number density of the local ISM.