HARPS tunes in on 'noisy' planets

Aug 10, 2011 by Tammy Plotner, Universe Today
Montage of the HARPS spectrograph and the 3.6m telescope at La Silla. The upper left shows the dome of the telescope, while the upper right illustrates the telescope itself. The HARPS spectrograph is shown in the lower image during laboratory tests. The vacuum tank is open so that some of the high-precision components inside can be seen. Credit: European Southern Observatory

Able to achieve an astounding precision of 0.97 m/s (3.5 km/h), with an effective precision of the order of 30 cms-1, the High Accuracy Radial velocity Planet Searcher (HARPS) echelle spectrograph has already discovered 16 planetary objects in the southern hemisphere and has now logged four more. And that’s only the beginning...

“A long-period companion, probably a second planet, is also found orbiting HD7449. around HD137388, HD204941, and HD7199 have rather low eccentricities (less than 0.4) relative to the 0.82 eccentricity of HD7449b. All these planets were discovered even though their hosting stars have clear signs of activity.” says X. Dumusque (et al). “Solar-like magnetic cycles, characterized by long-term activity variations, can be seen for HD137388, HD204941 and HD7199, whereas the measurements of HD7449 reveal a short-term activity variation, most probably induced by magnetic features on the stellar surface.”

Using radial velocity is currently the preferred method for detecting new planets. But, despite the quality of the equipment, low mass planets placed at a great distance from the host star become problematic because of the star’s own “noise”. RV is an indirect method which utilizes the presence of star wobble to spot orbiting bodies. Unfortunately, normal star activity such as magnetic cycles, spots and plagues can produce similar signals, but now long term variables like these are being fine tuned into the equation.

“The planets announced in this paper for the first time have been discovered even though their host stars display clear signs of activity. We have found that HD7449 exhibits signs of short term activity, whereas HD7199, HD137388, and HD204941 have solar-like magnetic cycles.” says Dumusque. “When examining the RVs and the fitted planets for HD7199, HD137388, and HD204941, it is clear that magnetic cycles induce RV variations that could be misinterpreted as long-period planetary signature. Therefore, the long-term variations in the activity index have to be studied properly to distinguish between the real signature of a planet and long-term activity noise.”

The paper then goes on to explain our Sun should show RV variations of 10ms?1 over its cycle and that it is typical behavior for solar-like stars. Perhaps all stars which display magnetic cycles also have long-term RV variations? “The high precision HARPS sample, composed of 451 , provides a good set of measurements to search for this activity-RV correlation.” says Lovis (et al). “A more complete study is in progress and will be soon published.”

Factual Information Courtesy of Wikipedia. Further Reading: The HARPS search for southern extra-solar planets. XXX. Planetary systems around stars with solar-like magnetic cycles and short-term activity variation.

Explore further: Finding hints of gravitational waves in the stars

More information: The HARPS search for southern extra-solar planets. XXX. Planetary systems around stars with solar-like magnetic cycles and short-term activity variation, arxiv.org/abs/1107.1748

add to favorites email to friend print save as pdf

Related Stories

Coming to a solar system near you… super-Earth!

Aug 08, 2011

It is our general understanding of solar system composition that planets fall into two categories: gas giants like Jupiter, Saturn, Neptune and Uranus… and rocky bodies that support some type of atmosphere ...

Doubt cast on existence of habitable alien world

Oct 13, 2010

Last month, astronomers announced the discovery of the first potentially habitable extrasolar planet. But this week at an International Astronomical Union meeting, doubts were raised about the existence o ...

Exomoons could be excellent incubators

Jun 20, 2011

With the arrival of the Cassini–Huygens mission in 2004 to Saturn’s satellite Titan, we terrestrials became acutely aware that similar moons could be orbiting similarly large planets in other solar ...

Richest planetary system discovered (w/ Video)

Aug 24, 2010

(PhysOrg.com) -- Astronomers using ESO's world-leading HARPS instrument have discovered a planetary system containing at least five planets, orbiting the Sun-like star HD 10180. The researchers also have tantalising ...

Exoplanets Clue to Sun's Curious Chemistry

Nov 11, 2009

(PhysOrg.com) -- A ground-breaking census of 500 stars, 70 of which are known to host planets, has successfully linked the long-standing "lithium mystery" observed in the Sun to the presence of planetary systems. ...

Recommended for you

Finding hints of gravitational waves in the stars

5 hours ago

Scientists have shown how gravitational waves—invisible ripples in the fabric of space and time that propagate through the universe—might be "seen" by looking at the stars. The new model proposes that ...

How gamma ray telescopes work

6 hours ago

Yesterday I talked about the detection of gamma ray bursts, intense blasts of gamma rays that occasionally appear in distant galaxies. Gamma ray bursts were only detected when gamma ray satellites were put ...

The frequency of high-energy gamma ray bursts

8 hours ago

In the 1960s a series of satellites were built as part of Project Vela.  Project Vela was intended to detect violations of the 1963 ban on above ground testing of nuclear weapons.  The Vela satellites were ...

What causes the diffraction spikes in images of stars?

8 hours ago

When stars are portrayed in media, they are often shown with long spikes emanating from them. Perhaps the most common example is that of the "star of Bethlehem" which, according to the story, led the wise ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

omatumr
1 / 5 (4) Aug 10, 2011
Congratulations!

Please keep in mind that the first extra-solar planets found were rocky, Earth-like planets orbiting a pulsar.

www2.astro.psu.ed...ext.html

That is also the way planets formed here.

www.omatumr.com/a...enon.pdf

With kind regards,
Oliver K. Manuel
Former NASA Principal
Investigator for Apollo