Astronomers measure an elusive 'Rossiter-McLaughlin effect' during the last Venus Transit

Dec 11, 2012

A team of Italian astronomers performed a very difficult measurement for which it was necessary to use the most advanced instrumentation in combination with an unusual technique, so as to involve even the Moon as a natural astronomical mirror. The challenge was the observation of effect occurred during the transit of Venus across the Sun on June 6th, dubbed "Rossiter-McLaughlin effect". This is a phenomenon that occurs when a celestial body passes in front of a star, hiding a part of its rotating surface and that produces a temporary distortion in the profiles of the spectral lines of light coming from the eclipsed star. Astronomers led by Paolo Molaro, from INAF Astronomical Observatory of Trieste succeeded in this ambitious task, observing and measurirng the magnitude of this tiny effect. Their findings are published online today in a paper of the journal Monthly Notices of the Royal Astronomical Society.

The Rossiter-McLaughlin effect has already been observed in systems composed of two stars that eclipse each other, but it becomes more and more difficult to observe when the is the size of a planet, and moreover not so great as Jupiter but rather similar in size to the Earth, just as it is during the . Measuring the extent of this weak effect on the light from other planetary systems through telescopes of the next generation such as E-ELT (the European Extremely Large Telescope) will be a useful tool for the search and study of exoplanets. Astronomers will be able to learn important orbital parameters in these systems and thus improve our understanding of the history of their formation.

"Critical to the success of this mission was the use of the HARPS at ESO that now, along with his 'twin brother' installed at the Telescopio Nazionale Galileo (TNG) operated by INAF on Canary Islands, represents the state of the art for measuring of and the best hunter of planetary systems around other stars. The measured magnitude of the effect is comparable to being able to track the speed of a person walking at a slow pace at a distance of 150 million kilometers, the space that separates us from the Sun. Nowadays there is no other instrument capable of recording so tiny changes, especially if you only have a few hours to measure them" said Lorenzo Monaco, an Italian astronomer working at ESO.

But the mere use of HARPS would not be sufficient to achieve this result. The observations of the integrated light of the sun at high resolution are in fact extremely difficult to conduct and to overcome this problem, astronomers pointed their instruments to the Moon to capture the sunlight reflected from it. For this reason, the transit was observed by astronomers in Chile when in fact it would be impossible to do so, since in that region of the world it was night. This unusual strategy has imposed special calculations to achieve the desired results. "The transit of Venus seen from the Moon has a slightly different schedule than what has been observed on Earth," said Simone Zaggia from INAF of Padua, who participated in the mission. "The Moon was in fact 8 degrees ahead of the Earth and Venus reaches alignment with the Sun and the Moon about two hours later. The transit was also slightly longer than that observed on Earth because the Moon was above the plane of rotation of the Earth around the Sun".

Observations show that the partial eclipse on the solar disc produced by the transit of Venus has generated a modulation in the radial velocity of the Sun of less than one meter per second, which is just 3 km/h. "The agreement with the theoretical models is around a few centimetres per second and is an amazing result ever reached before" says Mauro Barbieri, from University of Padua, who is also a member of the team. "Among other things, this change in velocity is comparable with that due to the natural expansion and contraction of our star. However, our observations have allowed us to clearly see the Rossiter-McLaughlin effect during transit".

The results obtained from these observations - the only ones with purely scientific purposes that have been carried out on the Earth during the last transit of Venus - will be of great help to astronomers, who in the next decade will be able measure this phenomenon in extrasolar systems, unleashing the full potential of new generation of telescopes such as the E-ELT. "This measurement - says Paolo Molaro - foretells the sensational results that in a few years will be able to get thanks to the advent of the 40-meter class telescopes equipped with high-resolution spectrographs. This mammoth astronomical instruments will open for sure a new horizon in the study of orbital properties of other Earth-like planets that are found around other stars in our galaxy".

Explore further: The changing laws that determine how dust affects the light that reaches us from the stars

add to favorites email to friend print save as pdf

Related Stories

Hubble to use moon as mirror to see Venus transit

May 04, 2012

This mottled landscape showing the impact crater Tycho is among the most violent-looking places on our moon. Astronomers didn't aim NASA's Hubble Space Telescope to study Tycho, however. The image was taken ...

Venus to appear in once-in-a-lifetime event

May 01, 2012

On 5 and 6 June this year, millions of people around the world will be able to see Venus pass across the face of the Sun in what will be a once-in-a-lifetime experience.

ND expert: The science behind the transit of Venus

May 30, 2012

University of Notre Dame professor of physics Peter Garnavich has research interests that cover a wide range of topics in observational astrophysics. In preparation for the Tuesday (June 5) Transit of Venus, he offers an ...

Get ready for the transit of Venus

May 25, 2012

Scientists and amateur astronomers around the world are preparing to observe the rare occurrence of Venus crossing the face of the Sun on 5-6 June, an event that will not be seen again for over a hundred years.

Recommended for you

ESO image: A study in scarlet

21 hours ago

This new image from ESO's La Silla Observatory in Chile reveals a cloud of hydrogen called Gum 41. In the middle of this little-known nebula, brilliant hot young stars are giving off energetic radiation that ...

Astronomers: 'Tilt-a-worlds' could harbor life

Apr 15, 2014

A fluctuating tilt in a planet's orbit does not preclude the possibility of life, according to new research by astronomers at the University of Washington, Utah's Weber State University and NASA. In fact, ...

Pushy neighbors force stellar twins to diverge

Apr 15, 2014

(Phys.org) —Much like an environment influences people, so too do cosmic communities affect even giant dazzling stars: Peering deep into the Milky Way galaxy's center from a high-flying observatory, Cornell ...

Image: Multiple protostars within IRAS 20324+4057

Apr 14, 2014

(Phys.org) —A bright blue tadpole appears to swim through the inky blackness of space. Known as IRAS 20324+4057 but dubbed "the Tadpole", this clump of gas and dust has given birth to a bright protostar, ...

User comments : 0

More news stories

Meteorites yield clues to Martian early atmosphere

(Phys.org) —Geologists who analyzed 40 meteorites that fell to Earth from Mars unlocked secrets of the Martian atmosphere hidden in the chemical signatures of these ancient rocks. Their study, published ...

Let's put a sailboat on Titan

The large moons orbiting the gas giants in our solar system have been getting increasing attention in recent years. Titan, Saturn's largest moon, is the only natural satellite known to house a thick atmosphere. ...

New clinical trial launched for advance lung cancer

Cancer Research UK is partnering with pharmaceutical companies AstraZeneca and Pfizer to create a pioneering clinical trial for patients with advanced lung cancer – marking a new era of research into personalised medicines ...

'Chief Yahoo' David Filo returns to board

Yahoo announced the nomination of three new board members, including company co-founder David Filo, who earned the nickname and formal job title of "Chief Yahoo."