March 29, 2023


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Discovered the exoplanet “ Lepus AF star b ”, the lightest planet discovered by topical astronomy | sorae Portal site to space

The orbital motion of a celestial body is interpreted as “a celestial body revolving around another celestial body,” like the moon orbiting the earth and the earth revolving around the sun. However, this is not strictlyThe actual orbital motion is ‘moving around a common center of gravity’.He is. In most cases, the mass of the companion star is very small compared to the main star, the center of mass is located inside the main star, and the main star itself hardly moves.

On the flip side, the star is also moving, albeit slightly, and this motion can be measured if you have a way to accurately measure the star’s position. If the motion of the primary star is known, it is possible to determine the mass and orbital period of the invisible companion star orbiting the center of gravity of the primary star, based on Kepler’s law. Such a way to know indirectly the existence of the orbital parameters of the companion star, which are too dim to be directly observed, through the motion of the main star is “Positional astronomyThe field of astronomy that uses positional astronomy is called “positional astronomy”.

In order to use positional astronomy for stars farthest from the Sun, it is necessary to accurately measure the star’s position. Changes in the position of the Earth due to its revolution and fluctuations in the image of the stars due to the atmosphere are major noises that hinder astronomy, and you can reduce the noise by optimizing. Therefore, the accuracy of positional astronomy continues to improve year after year.

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In this study, a research team led by Dr. Mesa at the Padua Observatory and a research team led by Kyle Franson at the University of Texas at Austin independently analyzed the same star, AF Lepus. AF Lepus is a star slightly more massive than the Sun, about 88 light-years away in the constellation of Lepus as seen from Earth.

AF Lepus is the European Space Agency (ESA)Hipparchus“And the”JayaIt is one of the stars he noticed. Hipparchus and Gaia are observational satellites that aim to accurately measure the position of stars from space, and data from the two satellites showed that AF Lepus changed its position periodically. This indicates the presence of a previously undiscovered companion star.

Therefore, the research team from Mesa et al.Paranal Observatory’s Very Large Telescope (VLT) monitoring devicesphereFrancon and his research teamThe Keck II telescope at the W.M. Keck Observatorymonitoring deviceNIRC2, we tried to directly observe the companion star of AF Lepus. Each instrument is not only highly sensitive, but also has a central mask (star vertebrae) that blocks light. By using this mask to block out very bright starlight, it becomes possible to capture the accompanying fainter starlight.

【▲ Fig. 1: AF Lepus b (bright spot on the left) imaged by the Very Large Telescope (VLT). Two photos indicate that they were taken at different times. The asterisk in the center indicates the location of the star, and the black circle is the part hidden by an astral vertebra, which blocks the star’s light (Credit: ESO/Mesa, De Rosa et al.)]

[الشكل 2: AF Lepus b (نقطة مضيئة على اليسار) مأخوذة بواسطة تلسكوب Keck.  تشير صورتان إلى أنهما تم التقاطهما في أوقات مختلفة. تشير الصلبان الموجودة في المركز إلى مواقع النجوم المخفية بواسطة فقرة نجمية.  (رصيد الصورة: فرانسون وآخرون)]

[الشكل 2: AF Lepus b (نقطة مضيئة على اليسار) مأخوذة بواسطة تلسكوب Keck. تشير صورتان إلى أنهما تم التقاطهما في أوقات مختلفة. يشير الصليب المركزي إلى موضع النجم الذي تحجبه الفقرة التاجية النجمية (Credit: Franson،]

As a result of the observation, each research team found a companion star.Lepus star AF bIt has been successfully observed directly. The companion star’s parameters vary slightly due to different observational instruments and analytical methods, but its mass is estimated to be approximately 2 to 5 times the mass of Jupiter. This is well below the minimum mass required for nuclear fusion at its core (about 13 times the mass of Jupiter). Jupiter).AF Lepus b is a direct observed exoplanetThat’s what it means. Also, the estimated mass of AF Lepus b isDiscover the smallest planet on record using astronomyHe is.

【▲ Figure 3: Lepus AF parameters b.  There are differences in values ​​between the two research teams due to differences in analytical methods.  (Image credit: Riri Ayae)]

【▲ Figure 3: Lepus AF parameters b. Image copyright Riri Saie Image caption There are differences in values ​​between the two research teams due to differences in analysis methods]

The two studies also derive different estimates for other information about AF Lepus b, such as its orbit. Long-term observations are required due to the long orbital period estimated at about 20 years, but this gap will be filled in the future.

Another feature of AF Lepus is that it is very young at 24 million years old. Because AF Lepus is a star roughly the same size as the Sun, detailed observations of AF Lepus will provide useful data for estimating the early solar system.


  • De Mesa and others. “AF Lep b: Least Mass Planet Discovered in conjunction with direct and astrophotography data”. (arXiv)
  • Kyle Francon, and others. “Astronomical accelerations as dynamic beacons: a giant planet imaged within the debris disk of the young star AF Lep”. (arXiv)
  • ESO/Mesa, De Rosa et al. Discovery of a hidden exoplanet. (European Space Agency)

Text: Rare Aya