by Staff Writers
Munich, Germany (SPX) Nov 20, 2012
An infrared imaging search with the Subaru telescope has captured a rare image of a "Super-Jupiter" around the massive star Kappa Andromedae (K And). The gas giant has a mass about 13 times that of Jupiter, while the host star has a mass 2.5 times that of the Sun.
There are strong indications that this planet formed in a manner similar to ordinary, lower-mass exoplanets: in a "protoplanetary disk" of gas and dust that surrounded the newborn star.
This makes the planet an important test case for current models of planet formation and their predictions about planets around massive stars.
Of the nearly 850 exoplanets - planets orbiting stars other than the Sun - currently known, only a minute fraction have been captured in actual astronomical images. The vast majority of detections rely on indirect methods.
The reason for this discrepancy: stars are much brighter than their planets (typically by a factor of a billion or more); using traditional observational techniques, the planet will be hidden in the glare of its host star.
Now, a research team led by Joseph Carson (College of Charleston and Max Planck Institute for Astronomy) has managed to obtain an image of a large "Super-Jupiter" around the massive star K And ("kappa Andromedae"). Their discovery makes use of the Subaru 8-meter telescope on the summit of Mauna Kea in Hawai'i, operated by the National Astronomical Observatory of Japan.
K And is a very young star, with an estimated age of 30 million years (our Sun, for comparison, is around 5 billion years old). Obtaining an image of its companion K And b required advanced techniques both for observation and for image analysis.
A particular challenge was that the orbit of the newly detected object is only somewhat larger than that of Neptune - most planetary images have been obtained for planets in significantly larger orbits.
With a mass of about 13 times that of Jupiter, the object, called K And b ("Kappa Andromedae b"), could be either a planet or a very lightweight "brown dwarf", an object that is intermediate between planets and stars. Circumstantial evidence indicates that it is likely to be a planet.
An interesting aspect of the new Super-Jupiter is that it orbits a fairly young star, and at a distance comparable to planetary orbits within our own Solar System.
Taken together, this is a strong indication that the planet formed in a manner similar to that of lower mass planets: within a primordial, "protoplanetary" disk of gas and dusk which surrounded the star during its earliest stages.
In recent years, observers and theoreticians have argued that large, massive stars like this are more likely to have large planets than smaller stars such as our Sun.
Yet there have also been concerns: massive young stars emit enormous amounts of high-energy radiation. This radiation could dissipate parts of the protoplanetary disk, which would in turn disrupt planet formation.
The discovery of the Super-Jupiter K And b suggests that stars as massive as 2.5 solar masses are still fully capable of producing planets within their primordial circumstellar disks - key information for researchers working on models of planet formation.
A key advantage of direct exoplanet detection is the target's immediate accessibility for follow-up examination by traditional astronomical techniques, such as an in-depth analysis of its light by spectroscopy. This is the aim of ongoing observations of the light emitted by K And b across a broad range of wavelengths.
The ongoing observations will lead to a better understanding of the gas giant's atmospheric chemistry, and yield more precise information about the object's orbit and the possible presence of additional planets.
In the end, the astronomers should have a better picture of the Super-Jupiter's genesis, and about planet formation around massive stars in general.
The discovery was made in the context of the SEEDS project ("Strategic Explorations of Exoplanets and Disks with Subaru").
The observational data was obtained using the HiCIAO high-contrast imaging instrument and the IRCS infrared camera at the Subaru telescope on Mauna Kea, Hawai'i, operated by the National Astronomical Observatory of Japan (NAOJ).
The SEEDS survey is led by principal investigator Dr. Motohide Tamura (NAOJ). The lead author of the discovery paper is Dr. Joseph Carson of College of Charleston (CofC) and the Max Planck Institute for Astronomy (MPIA) in Heidelberg, Germany. The local SEEDS Co-PI at the Max Planck Institute for Astronomy is Prof. Dr. Thomas Henning.
The work described here will be published as J. Carson et al., "Direct Imaging Discovery of a 'Super-Jupiter' Around the late B-Type Star Kappa Andromedae" in the Astrophysical Journal Letters.
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