OH/IR star

OH / IR stars are hidden behind a dust shell red giants, the radiation predominantly in the infrared and sub-mm range emit.

Observation

OH / IR stars have been only discovered in the late '60s with the help of the radio and infrared astronomy. In the far-infrared light, a cyclic change with periods of 2 to 5 years and amplitudes shows similar to those of Mira stars. In the optical sources are barely detectable, although they are among the brightest infrared sources in the sky. In the far-infrared absorption lines of the star show at 10 and 20 microns, which are associated with silicate dust in the envelope of the late giant

In addition to non-thermal of the OH / IR star radiation are detected by some molecular lines. It involves OH, water and silicon oxide. The molecular lines show a typical U-shape in the spectrum and are interpreted as grain.

Natural Maser

Usually only one maser radiation at 1612 MHz from the hydroxyl radical (OH ) is demonstrated. The spacing of the lines in the U-profile corresponds to a speed of 5 to 25 km / sec A component comes from the front of the dust shell and the other the backside. The composition of the upper energy level by absorption of infrared radiation from the hot dust. Must be constant in order to achieve a sufficient reinforcement of the line speed of the flowing gas over long distances. Therefore, the maser radiation comes only from a small line of sight to Earth, while the other areas of the shell are not sufficiently reinforced radiated in our direction. The maser radiation follows with a delay of weeks the brightness variations in the infrared.

Development Status

OH / IR stars represent a 105 years period of intense mass ejection at the end of the AGB phase of massive stars, which is referred to as a super wind. The mass loss rate reaches some 10-5 solar masses per year and is triggered by the pulsations as in the Mira stars. The outflowing gas is condensed after a few stellar radii to dust and absorbs the visible radiation completely. The dust heats up and radiates heat in the infrared. The red giant initially have this mass 3-8 solar masses. In contrast, the Mira stars have masses of 1-2 solar masses and this is not enough to suffice for training optically thick envelopes.

Non- variable OH / IR stars

For the non - variable stars OH / IR stars no long periodic change in brightness in the infrared is more detectable. You have an already separate from the star dust shell, which is no longer fed by the post-AGB star. The water masers are already weak or undetectable, while the OH masers are still active. This short phase with a duration of about 1000 years is interpreted as the transition phase to the planetary nebula.

Example

The best known and best studied OH / IR star IRC 10216 is = CW Leo with a luminosity of the more than 10,000 times the sun. From lunar occultations a diameter determination could be made at several wavelengths in the infrared. The core of the dust cover is a temperature of 650 K at a radius of 60 AU and the halo of the dust cover at a temperature of about 375 K with a radius of 300 AE.