The exoplanet too big for his star


Hot Jupiter

I Tau B is a paradoxical planet, but new research on Jupiter's mass, brightness, and hot carbon monoxide begins to answer the question of how such a large planet could have formed around a star two million years.

For decades, most astronomers have believed that giant planets such as Jupiter and Saturn were formed far from their stars over periods of 10 million years or more. But the discovery of dozens of "hot Jupiters" has led to new theoretical models describing the eventual formation of such planets.

At today's meeting of the American Astronomical Society, astronomers Christopher Johns-Krull of Rice University and Lisa Prato of Lowell Observatory presented the results of a spectroscopic analysis in the near infrared over four years of light from CI Tau b, a giant orbiting orbiting "Jupiter hot", orbiting a nine-day orbit around its parent star about 450 light-years from Earth in the constellation of Taurus.

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"What's exciting is that we are able to detect light directly from the planet. This is the first time that this is a close planet around such a young star, "said Johns-Krull, professor of physics and astronomy and co-author of a study whose publication is planned in Astrophysical Journal Letters of AAS. "The most valuable way to learn how planets are formed is to study planets in formation or in training, such as that of Tau b."

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Johns-Krull stated that the age of CI Tau b made it the ideal candidate for observation with the immersive array infrared spectrograph (IGRINS), a unique high-resolution instrument used in CI Tau observations b from the 2.7 meter Harlan J. of McDonald Observatory. Smith Telescope and the 4.3-meter Discovery Channel telescope at the Lowell Observatory.

Since each atomic element and molecule of a star emits light from a single set of wavelengths, astronomers can search for specific signatures, or spectral lines, to determine whether an element is present in a particular set of wavelengths. a star or a distant planet. Spectral lines can also reveal the temperature and density of a star, as well as its speed.

Prato said the research team had used the spectral lines of carbon monoxide to distinguish the light emitted by the planet from the light emitted by the nearby star.

"Many of the planet's spectral lines are also in the star," Prato said. "If the planet and the star were motionless, their spectral lines would blend, and we would not be able to say what belonged to the star and what was on the planet. But because the planet is spinning fast around the star, its lines change dramatically. We can subtract the lines of the star and see only the lines of the planet. And from these, we can determine the brilliance of the planet, relative to the star, which tells us something about its formation. "

This is because the brightness of a star or a planet depends on both its size and its temperature.

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"The evidence of direct observation of the mass and brightness of the IC Tau B is particularly useful because we also know that it revolves around a very young star," he said. Rice, Ph.D. student Laura Flagg, the main author of the next study. "Most of the hot Jupiters we found are middle-aged stars in orbit. The age of CI Tau imposes a strict constraint on the testing of models: can they produce such a brilliant and massive planet in such a short time?

Flagg's analysis of carbon monoxide spectral lines showed that CI Tau b had a mass of 11.6 Jupiters and was about 134 times weaker than its parent star. According to Prato, this clearly shows that he was formed via a "hot start", a theoretical model describing how gravitational instabilities could form giant planets faster than traditional models.

Prato said the new study provides a unique empirical criterion for measuring competing theories. "At around 2 million years ago, CI Tau B is by far the youngest hot Jupiter detected directly," she said. "We now have a mass and brightness for it – the only mass and brightness measured directly for a hot young Jupiter – and this provides very powerful tests for planet-forming models."

IGRINS, designed by co-author of the study, Daniel Jaffe of the University of Texas at Austin, uses a silicon-based diffraction grating to improve both the resolution and the number of spectral bands near infrared that can be observed from distant objects such as CI Tau. b and his star-mother. IGRINS was transferred from McDonald's to Lowell midway through the study.

The Daily Galaxy via Rice University

Image at the top of the page: ATG MEDIALAB, ESA


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