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

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