Modeling the Infrared Bow Shock at delta Velorum: Implications for Studies of Debris Disks and lambda Bootis Stars

TL;DR

This study reveals a bow shock around delta Velorum caused by star-ISM interaction, challenging previous debris disk classification and providing insights into lambda Bootis star phenomena.

Contribution

It models the star-ISM interaction producing observed infrared features, questioning debris disk classification and testing the ISM accretion theory for lambda Bootis stars.

Findings

Bow shock detected at 24 and 70 microns.

Modeled ISM density is 15 times the local average.

Delta Velorum does not belong to the lambda Bootis class.

Abstract

We have discovered a bow shock shaped mid-infrared excess region in front of delta Velorum using 24 micron observations obtained with the Multiband Imaging Photometer for Spitzer (MIPS). The excess has been classified as a debris disk from previous infrared observations. Although the bow shock morphology was only detected in the 24 micron observations, its excess was also resolved at 70 micron. We show that the stellar heating of an ambient interstellar medium (ISM) cloud can produce the measured flux. Since delta Velorum was classified as a debris disk star previously, our discovery may call into question the same classification of other stars. We model the interaction of the star and ISM, producing images that show the same geometry and surface brightness as is observed. The modeled ISM is 15 times overdense relative to the average Local Bubble value, which is surprising considering the close proximity (24 pc) of delta Velorum. The abundance anomalies of lambda Bootis stars have been previously explained as arising from the same type of interaction of stars with the ISM. Low resolution optical spectra of delta Velorum show that it does not belong to this stellar class. The star therefore is an interesting testbed for the ISM accretion theory of the lambda Bootis phenomenon.