NASAのウェッブ望遠鏡、最も小さい自由浮動褐色矮星を発見(NASA’s Webb identifies tiniest free-floating brown dwarf)

2023-12-142024-02-03

2023-12-13 ペンシルベニア州立大学(PennState)

◆NASAのJames Webb Space Telescopeを使用して、天文学者たちは新しい最小の星のように形成される天体の記録保持者を特定しました。その天体は、わずか3〜4倍の木星の質量しかない小さな自由浮遊褐色矮星です。この新発見は、星と惑星の境界をまたぐ物体である褐色矮星についての興味深い情報を提供します。
◆これらの褐色矮星は星のように形成され、自らの重力の下で崩壊するほど密度が増しますが、水素の融合が始まり、星に変わるほどには十分に密度が高くなりません。それらはまた、惑星と同様に、星を取り囲むガスと塵のディスクで形成されるものと異なります。

＜関連情報＞

JWSTによるIC 348の惑星質量褐色矮星の探査 A JWST Survey for Planetary Mass Brown Dwarfs in IC 348

K. L. Luhman, C. Alves de Oliveira, I. Baraffe, G. Chabrier, T. R. Geballe, R. J. Parker, Y. J. Pendleton, and P. Tremblin
The Astronomical Journal Published 2023 December 13
DOI:10.3847/1538-3881/ad00b7

Abstract

We have obtained images of the center of the star-forming cluster IC 348 with the James Webb Space Telescope and have identified brown dwarf candidates based on their photometry and point-like flux profiles. Low-resolution spectroscopy has been performed on four promising candidates, three of which have molecular absorption bands that indicate late spectral types. Among those late-type objects, the brightest is similar to known young L dwarfs while the other two show the so-called 3.4 μm feature that has been previously observed in the diffuse interstellar medium and in the atmospheres of Saturn and Titan, which has been attributed to an unidentified aliphatic hydrocarbon. Those two objects also exhibit features between 1.1 and 2.6 μm that we identify as the overtone and combination bands for that hydrocarbon. After accounting for the hydrocarbon bands, the remaining spectral features are consistent with youth and inconsistent with field dwarfs. Based on the low extinctions of those objects and the strengths of the overtone and combination bands, we conclude that the hydrocarbon resides in their atmospheres rather than in foreground material. Thus, our detections of the 3.4 μm feature are the first in atmospheres outside of the solar system. The presence of this hydrocarbon is not predicted by any atmospheric models of young brown dwarfs. Based on its luminosity and evolutionary models, the faintest new member of IC 348 has an estimated mass of 3–4 M_Jup, making it a strong contender for the least massive free-floating brown dwarf that has been directly imaged to date.