Discovery | |
---|---|
Discovered by | Currie et al. [1] |
Discovery site | Subaru Telescope, Hubble Space Telescope |
Discovery date | April 4, 2022 |
Direct imaging | |
Orbital characteristics | |
44.6–143.2 [1] AU | |
Eccentricity | 0.19–0.60 [1] |
Inclination | 27.1–58.2 [1] |
Physical characteristics | |
Mean radius | 2.75 [2] RJ |
Mass | 9–12 [1] MJ |
Temperature | 2,000–2,500 K [1] |
AB Aurigae b (or AB Aur b) [1] is a directly imaged protoplanet embedded within the protoplanetary disk of the young, Herbig AeBe star AB Aurigae. The system is about 508 light-years away: AB Aur b is located at a projected separation of about 93 AU from its host star. AB Aur b is the first confirmed directly imaged exoplanet still embedded in the natal gas and dust from which planets form. It may also provide evidence for the formation of gas giant planets by disk instability.
AB Aur b was discovered by a team led by Thayne Currie, Kellen Lawson, and Glenn Schneider using the Subaru Telescope on Mauna Kea, Hawaii and the Hubble Space Telescope (HST). The Subaru data utilized the observatory's extreme adaptive optics system, SCExAO, to correct for atmospheric blurring and the CHARIS integral field spectrograph to record AB Aur b's brightness measurements at different near-infrared wavelengths. AB Aur b's position coincides with the predicted location of a massive protoplanet required to explained CO gas spirals detected with ALMA and lies interior to the ring of pebble-sized dust seen in ALMA continuum data. [3] The companion was initially detected in 2016: the team initially believed that the signal identified a piece of AB Aurigae's protoplanetary disk, not a newly forming planet. [4] However, subsequent SCExAO/CHARIS data obtained with Subaru over the next four years showed that AB Aur b's spectrum is dissimilar to that of the protoplanetary disk, with a temperature similar to predicted values for a newly born planet. A new detection with HST using the STIS instrument and an archival detection with the now-decommissioned NICMOS instrument from 2007 confirmed evidence from Subaru data that AB Aur b orbits the star and is not a static feature.
AB Aur b is detected in near-infrared wavelengths between 1.1 and 2.4 microns with SCExAO/CHARIS, at 1.1 microns with HST/NICMOS, and in unfiltered optical data with HST/STIS. The CHARIS and NICMOS data are consistent with interpreting AB Aur b as a 9 to 12 Jupiter-mass object with a radius of about 2.75 times that of Jupiter. It is also detected in H-alpha with the VAMPIRES instrument behind SCExAO, although it is unclear whether this detection originates from the protoplanet itself or surrounding scattered light.
The emission sources responsible for AB Aur b are subject of active investigation. Its H-alpha detection could be due to active accretion or scattered light. The discovery paper matches the protoplanet's emission using a composite model consisting of a 2000–2500 K thermal component responsible for the CHARIS and NICMOS detections and magnetospheric accretion that also contributes to its detection with STIS. AB Aur b is also detected in multiple other narrow UV-optical passbands. Analysis of these data suggests that at least its optical emission is also consistent with scattered light. [5]
The companion appears as a bright, spatially-extended source approximately 0.6 arcseconds (about 93 AU) away from the star, which contrasts with the point source nature of all other directly imaged planets. This morphology is likely due to light from AB Aur b being intercepted and reprocessed by the star's protoplanetary disk. It is not clearly detected as a concentrated source in polarized light. Because of its very large distance from the star, AB Aur b's orbit is not well constrained. Modeling thus far suggests that the companion's orbit is inclined about 43 degrees from our line-of-sight, possibly coplanar with the star's protoplanetary disk.
The canonical model for gas giant planet formation – core accretion – has significant difficulty forming massive gas giant planets at AB Aur b's very large distance from its host star. Instead, AB Aur b may be forming by disk (gravitational) instability, [6] where as a massive disk around a star cools, gravity causes the disk to rapidly break up into one or more planet-mass fragments. [7] The numerous spiral arms in AB Aur's protoplanetary disk are consistent with models of planet formation by disk instability.
The system AB Aurigae made a brief appearance in the 2021 film "Don't Look Up" during depicted Subaru observations, although the companion is not visible on the displayed image.
The nebular hypothesis is the most widely accepted model in the field of cosmogony to explain the formation and evolution of the Solar System. It suggests the Solar System is formed from gas and dust orbiting the Sun which clumped up together to form the planets. The theory was developed by Immanuel Kant and published in his Universal Natural History and Theory of the Heavens (1755) and then modified in 1796 by Pierre Laplace. Originally applied to the Solar System, the process of planetary system formation is now thought to be at work throughout the universe. The widely accepted modern variant of the nebular theory is the solar nebular disk model (SNDM) or solar nebular model. It offered explanations for a variety of properties of the Solar System, including the nearly circular and coplanar orbits of the planets, and their motion in the same direction as the Sun's rotation. Some elements of the original nebular theory are echoed in modern theories of planetary formation, but most elements have been superseded.
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HD 100546, also known as KR Muscae, is a pre-main sequence star of spectral type B8 to A0 located 353 light-years from Earth in the southern constellation of Musca. The star is surrounded by a circumstellar disk from a distance of 0.2 to 4 AU, and again from 13 AU out to a few hundred AU, with evidence for a protoplanet forming at a distance of around 47 AU.
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HR 8799 b is an extrasolar planet located approximately 129 light-years away in the constellation of Pegasus, orbiting the 6th magnitude Lambda Boötis star HR 8799. It has a mass between 4 and 7 Jupiter masses and a radius from 10 to 30% larger than Jupiter's. It orbits at 68 AU from HR 8799 with an unknown eccentricity and a period of 460 years, and is the outermost known planet in the HR 8799 system. Along with two other planets orbiting HR 8799, the planet was discovered on November 13, 2008 by Marois et al., using the Keck and Gemini observatories in Hawaii. These planets were discovered using the direct imaging technique.
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