Tau Bootis: Searching Masers around exoplanets

In the past decade, a few things “real” scientists once poo poo’d as science fiction have been found happily taking place in our universe. For instance, just the other day I heard a colleague discussing how planets aren’t found in binary systems. Since he is a physicist, I didn’t laugh, but instead just passed him some references to some nice discoveries that proved his older thinking wrong. One of my favorite named stars is actually part of one of these binary star + planets systems. The stars are (say it out loud to get the full effect) tau Boo a (short for tau Bootis a) and tau Boo b (who said a PhD prevented potty humor). The planet is tau Boo c, and it orbits tau Boo a, which is an F6 main sequence star (a star a bit hotter than the Sun). Tau Boo b (go ahead and giggle again) is a red dwarf star with a highly elliptical orbit that generally keeps it roughly 245 AU from tau Boo a. If life could live on this planet, tau Boo b would appear as a faint red dot in the distance. (image credit: David Aguilar/ CfA)

This planet really doesn’t resemble anything we’re familiar with. It is at least 4.14 Jupiter masses and orbits tau Boo a at a distance of just 4.7 million miles. (For perspective, the moon is 240,000 miles from Earth and Mercury orbits 43,400,000 miles from the Sun.) This little alien world has a 3.31 day year length, and (thanks to an effect called tidal locking) also has a 3.31 day day length. This means the same side of the planet always faces tau Boo a, and the little planet is flying around its star at break neck speeds.

Astronomers here on Earth are still trying to figure out what to make of these giant planets that orbit smooshed up against their parent stars. We keep trying to find ways to compare them to things we understand, but so far they keep surprising us. For instance, astronomers Joseph Lazio (Naval Research Laboratory) and W.M. Farrell (Goddard SFC) recently looked for masers associated with tau Boo a’s not so little planet, and just couldn’t find any.

Masers are natures way of shooting lasers. Technically, laser beams emit photons (particles of light) in optical or infrared colors and masers emit photons in microwave and radio colors of light, although the terms get mixed and broadened depending on who is talking. Bottom line: You can shoot red laser beams at the floor to harmlessly amuse your cat, and space can shoot microwave and radio maser beams toward earth to harmlessly amuse astronomers. Within our own solar system, Jupiter is famous for putting on maser shows. What makes this natural light show possible is Jupiter’s magnetic field. This magnetic field is driven by the rotation of Jupiter’s superfluid interior and a lot of really scary physics. What matters is simple: If a planet is filled with the right stuff and it is rotating, a magnetic field will occur. Some of these magnetic fields produce masers.

Following this logic, Lazio and Farrell used the Very Large Array in New Mexico to look for masers in the tau Boo system. They took three sets of observations with the VLA spread out into its largest configuration, a setup that allows for the highest resolution
images. Unfortunately, within the sensitivity of their instruments, tau Boo a’s over heated world wasn’t interested in shooting masers. In a different study, by Shkolnik, no evidence was found for any planetary magnetic fields, but they did find the planet mucks up tau Boo a’s magnetic fields.

Jupiter rotates roughly every 10 hours. This high speed rotation is partially responsible for its magnetic field. Tau Boo a’s planet rotates significantly slower. Speculating (as only a scientist who openly admits this isn’t their field of research can do), I’d guess that this planet’s combination of always having the same side facing its star and interacting with its sun’s magnetic field are thoroughly preventing noticeable masing and measurable magnetic fields from being associated with this alien world.

Moral of the story: If you get to close to your star, nature takes away your masers.


  1. Margaret July 14, 2007 at 1:37 am #

    Boo hoo, there is no tau Boo h 😉

  2. Richard July 15, 2007 at 6:05 pm #

    I just love these strange exoplanets!

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