Star & Protostars

Stars emit X-rays through a variety of mechanisms. Massive, early-type, stars eject strong winds that build shocks that radiate X-ray light. Late-type stars radiate in X-rays through coronal activity. Stars that have exhausted their supply of fussionable material, namely white dwarfs and neutron stars, can emit X-rays through the slow cooling of their once hot surfaces. The X-ray astronomy group at MSFC has studied numerous aspects of cooling neutron stars and investigated the X-ray properties of an isolated white dwarf, GD 356

One of the fundamental discoveries unveiled by the Chandra X-ray Observatory's superb angular resolution is X-ray emission from protostars embedded in their nascent cold gas clouds. Such emission may have several origins including coronal activity. Arguably the most interesting is emission that arises from the coupling between protostars and circumstellar disks from which they are forming. One such object we have studied in detail is the Herbig Ae star HD 163296.

Another legacy of the Chandra X-ray Observatory is its rich archive of high spectral resolution grating observations of stars and other objects. An important spectral diagnostic in stellar studies is fluorescence from photospheres caused by photoionization within the photosphere by energetic photons emitted in coronal activity above the surface of the star. In collaboration with colleagues at the Smithsonian Astrophysical Observatory, we have investigated the possibility of using characteristic fluorescent lines of iron from stellar photospheres as a diagnostic of the stellar geometry and metallicities.