Evidence for mass loss from IRAS observations of classical Cepheids

Abstract

Mass loss from classical Cepheid variables is suspected on two grounds. First, it may provide an explanation of the persistent discrepancy between estimates of Cepheid masses based on the theories of stellar pulsation and of stellar evolution¹. Second, theoretical models of pulsating atmospheres² suggest that a pulsation mechanism may be responsible for causing, or enhancing, mass loss from Cepheids. In order to test these hypotheses, evidence of anomalous mass loss was sought by making a comparison between the infrared emission of Cepheids and that of nonvariable supergiants in the same luminosity and effective temperature range. A search of the IRAS (Infrared Astronomy Satellite) catalogue³ found a number of Cepheids and stable supergiants which showed emission in at least one of the IRAS wavelength bands. Some long-period Cepheids showed infrared excesses with respect to their non-pulsating counterparts, while emission from Cepheids with periods of less than 10 days was comparable to the levels seen in the stable supergiants. Mass loss rates of up to 7 × 10⁻⁷ M⊙ yr⁻¹ were derived from the infrared excesses, which is sufficiently high to have a major effect on the evolution of these stars.