The linear dispersion properties of proton temperature anisotropy instabilities in a homogeneous infinite Vlasov plasma are studied by using a configuration appropriate to the solar wind at 1 AU. The proton distribution is taken to consist of two components, a cooler T⊥>T∥ 'core' and a hotter T∥>T⊥ 'halo'. For the parameters considered the k∥B0 fire hose and ion cyclotron instabilities are the most important modes. Resonant proton effects enhance both instabilities, and the presence of the cooler component can substantially reduce the threshold anisotropy of the halo-driven fire hose.