"Molecules of Life" around galactic hypergiant

Sub-millimetre observations of one of the most luminous red giant stars have recently revealed several simple molecules such as HCN, NaCl, and a phosphorus-containing radical PN. Similar molecules are known to exist in large quantities in molecular clouds such as the Orion nebula where they are protected from ultraviolet starlight by copious quantities of dust. An analogous shielding mechanism seems to occur in the atmosphere of evolved, red giant and supergiant stars, which have cool extended atmospheres at temperatures of a few thousand Kelvin.

The star VY Canis Majoris is an extreme example of the red supergiant family, with a luminosity of 500,000 times the Sun's and an estimated mass of 25 times that of the Sun. For comparison, the well-known red supergiant Betelgeuse has a luminosity of 15,000 times the Sun's and a mass of perhaps 10 solar masses.

Seventeen species have been found in the oxygen-rich environment, including CS, HCO+ and HNC as well as the sulphur-containing compounds SO and SO2. The shapes of the lines suggest that SiO dominates in a roughly spherical wind-like outflow, while SO and SO2 are abundant in the collimated jet-like outflows. VY CMa has a strong stellar wind, losing an entire solar mass of material every 5000 years.

The discovery was made with a new detector destined for the Atacama Large Millimetre Array (ALMA), an array of telescopes built in the Atacama desert in Chile for observing short-wave radio and sub-mm wavebands. It was fitted to the 10-metre dish at Arizona Radio Observatory for these measurements, and contains a superconducting-isolating-superconducting (SIS) receiver to achieve quantum-limited sensitivity levels. ALMA will operate in the range 30 to 1000 GHz (0.3 to 9.6 millimetres) and will be ideal for observing star formation and interstellar chemistry.

Links

AAVSO article on VY Canis Majoris