Water in Stars

Pedro Valdés Sada

Water is abundant in cool stars and is a major molecular constituent at low temperatures in oxygen-rich stars, dominating all molecular sources other than CO and H2 in regions at temperatures below 2000 K. The spectrum of hot water is most commonly observed in the near infrared at wavelengths between 0.9 and 3.2 microns. However, water was recently detected in sunspots where the temperature can be as low as in M-type stars. Pure rotational lines of OH and H2O are found in the spectrum between 10 and 20 microns. At 3000 to 4000 K, sunspots provide a starting point in a search for hot water in stars cooler than the sun. Here we present observations of water spectral features detected in red giant stars such as Betelgeuse and Antares. They were obtained at 12.3 microns using Celeste, a Goddard-developed cryogenic echelle spectrometer, in conjunction with the McMath-Pierce Solar Telescope (NSO/NOAO) at Kitt Peak National Observatory and the Infrared Telescope Facility on top of Mt. Kea.