Late-type stars and extinction from infrared photometry
Maria Messineo (Università di Bologna)
Tuesday 17/12/2024 @ 14:00, Sala Antonio Sollima (IV piano Battiferro)
I will illustrate some of the science issues I have worked on to, then, focus on infrared extinction measurements. Red supergiants (RSGs) and asymptotic giant branch stars (AGBs) are the brightest stars at infrared wavelengths, easily detectable at a distance of a few megaparsecs. With their winds and mass-loss, they enrich and shape the interstellar medium. Even though the Milky Way is the closest laboratory of resolved stellar populations, dust obscuration and poor knowledge of distances hamper a clear separation of the RSG and AGB populations, limiting our capacity of reconstructing the Galactic history of star formation. Currently, about 700 bonafide spectroscopic Galactic RSGs are detected in Gaia DR3 and 1,720,588 long-period variables. When working with cold stars, a primary issue is the decomposition of the interstellar extinction in interstellar and envelope components. For example, Mira AGBs may suffer from very high circumstellar obscuration (Ak> 3 mag), and stars located at the Galactic Center may suffer a similar amount of interstellar extinction. To properly estimate the stellar luminosity of cold stars, one must estimate the two components of extinction, and mid-infrared observations are essential. I will show you a small exercise on Near- and Mid-infrared photometry of Mira stars to estimate the interstellar and circumstellar extinction of individual stars independently of their surrounding. The exercise is based on the "Jolly equation", i.e., on the definition of extinction free colours.