NCAR: Star’s sound waves reveal cycle similar to the Sun's

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NCAR: Star’s sound waves reveal cycle similar to the Sun's

Post by bystander » Thu Aug 26, 2010 9:16 pm

Distant star’s sound waves reveal cycle similar to the Sun’s
National Center for Atmospheric Research | 26 Aug 2010
In a bid to unlock longstanding mysteries of the Sun, including the impacts on Earth of its 11-year cycle, an international team of scientists has successfully probed a distant star. By monitoring the star’s sound waves, the team has observed a magnetic cycle analogous to the Sun’s solar cycle.

The study, conducted by scientists at the National Center for Atmospheric Research (NCAR) and colleagues in France and Spain, is being published this week as a “Brevia” in Science.

The scientists studied a star known as HD49933, which is located 100 light years from Earth in the constellation Monoceros, the Unicorn, just east of Orion. The team examined the star’s acoustic fluctuations, using a technique called “stellar seismology.” They detected the signature of “starspots,” areas of intense magnetic activity on the surface that are similar to sunspots. While scientists have previously observed these magnetic cycles in other stars, this was the first time they have discovered such a cycle using stellar seismology.
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Studying many stars with stellar seismology could help scientists better understand how magnetic activity cycles can differ from star to star, as well as the processes behind such cycles. The work could especially shed light on the magnetic processes that go on within the Sun, furthering our understanding of its influence on Earth’s climate. It may also lead to better predictions of the solar cycle and resulting geomagnetic storms that can cause major disruption to power grids and communication networks.
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The scientists examined 187 days of data captured by the international Convection Rotation and Planetary Transits (CoRoT) space mission.
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The study authors found that HD49933 is much bigger and hotter than the Sun, and its magnetic cycle is much shorter. Whereas past surveys of stars have found cycles similar to the 11-year cycle of the Sun, this star has a cycle of less than a year.

This short cycle is important to scientists because it may enable them to observe an entire cycle more quickly, thereby gleaning more information about magnetic patterns than if they could only observe part of a longer cycle.

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CoRoT reveals a magnetic activity cycle in a Sun-like star - RA Garcia et al

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ScienceShot: Distant Sun Boasts Shortest Starspot Cycle

Post by bystander » Fri Oct 15, 2010 9:14 pm

Distant Sun Boasts Shortest Starspot Cycle
Science NOW | Science Shot | Astronomy | 15 Oct 2010
The planets orbiting Iota Horologii (inset) enjoy only brief respites from their tempestuous sun. The star, located 56 light-years away in the southern constellation Horologium, boasts the shortest starspot cycle ever seen: 1.6 years. The sunspot cycle of our own sun (main image), by contrast, waxes and wanes every 11 years. When sunspot numbers peak, the sun can hurl satellite-frying flares toward Earth. So any residents of the Iota Horologii system—which bears at least one giant planet—presumably experience more frequent outbursts, astronomers will report in an upcoming issue of The Astrophysical Journal Letters. Similar conditions may have confronted Earth as life was struggling to establish itself. At that time, the sun likely resembled Iota Horologii, because the star is young: it's thought to have escaped from the Hyades star cluster, which is just 600 million years old, or about one-eighth our sun's present age.
Discovery of a 1.6-year Magnetic Activity Cycle in the Exoplanet Host Star iota Horologii - TS Metcalfe et al
  • arXiv.org > astro-ph > arXiv:1009.5399 > 27 Sep 2010 (v1), 01 Oct 2010 (v2)

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Re: NCAR: Star’s sound waves reveal cycle similar to the Sun

Post by Ann » Sat Oct 16, 2010 6:07 am

The study authors found that HD49933 is much bigger and hotter than the Sun, and its magnetic cycle is much shorter. Whereas past surveys of stars have found cycles similar to the 11-year cycle of the Sun, this star has a cycle of less than a year.
I wouldn't say that HD49933 is much bigger and hotter than the Sun. It is a F2V star with a color index definitely bluer than the Sun's and a V luminosity 3.62 times greater than the Sun's. That is considerable, in view of the fact that stars are rarer the more luminous they are. But of the 25 brightest-looking naked-eye stars in the sky, only Alpha Centauri (and the Sun, of course) have absolute V luminosities fainter than this. Iota Horologii is less remarkable still. This star is sometimes classified as G3 subgiant and sometimes as a G0 dwarf, but in any case it is just a bit hotter and bluer than the Sun, and its luminosity is 1.71 times that of the Sun.

Yet these two stars, HD49933 and Iota Horilogii, which are not that much hotter and brighter than the Sun, have much shorter magnetic cycles than the Sun. Is that common or is it unusual? More interestingly, is the Sun's 11-year magnetic cycle common or unusual? I'm sure I have read an article in Sky & Telescope (or possibly Astronomy) which claimed that astronomers have had a hard time finding a star that is really similar to the Sun. While there is no shortage of G2V stars, my impression of the article was that almost all G2V stars observed have shorter magnetic cycles than the Sun. Anyway, if decade-long magnetic cycles are common, wouldn't it be more interesting to observe a Sun-like star with a Sun-like magnetic cycle than a Sun-like star with a much shorter magnetic cycle? So...
Whereas past surveys of stars have found cycles similar to the 11-year cycle of the Sun
I'd really like to hear more about the stars that were found to have magnetic cycles similar to the Sun's!
26 Aug 2010: The study authors found that HD49933 is much bigger and hotter than the Sun, and its magnetic cycle is much shorter. Whereas past surveys of stars have found cycles similar to the 11-year cycle of the Sun, this star has a cycle of less than a year.
15 Oct 2010: The planets orbiting Iota Horologii (inset) enjoy only brief respites from their tempestuous sun. The star, located 56 light-years away in the southern constellation Horologium, boasts the shortest starspot cycle ever seen: 1.6 years.
Isn't that a contradiction?

Ann
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