赤色巨星のバリトン音で宇宙距離測定に迫る(The baritone of Red Giants refines cosmic distance measurements)

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2024-03-15 スイス連邦工科大学ローザンヌ校(EPFL)

宇宙の拡大速度を測定するHubble定数(H0)には、さまざまな天体からの測定結果による相違があり、基本的な宇宙物理学の理解が不完全である。しかし、赤色巨星からの音波信号を利用した新たな研究では、宇宙の距離測定を精密化する手法が提案された。この手法はH0の緊張に関する議論を理解するのに役立ち、宇宙の進化に関する新しい洞察をもたらす可能性がある。

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小振幅の赤色巨星が、標準的なろうそくとしての赤色巨星ブランチの先端の性質を解明する Small-amplitude Red Giants Elucidate the Nature of the Tip of the Red Giant Branch as a Standard Candle

Richard I. Anderson, Nolan W. Koblischke, and Laurent Eyer
The Astrophysical Journal Letters  Published:2024 March 7
DOI:10.3847/2041-8213/ad284d

赤色巨星のバリトン音で宇宙距離測定に迫る(The baritone of Red Giants refines cosmic distance measurements)

Abstract

The tip of the red giant branch (TRGB) is an important standard candle for determining luminosity distances. Although several 105 small-amplitude red giant stars (SARGs) have been discovered, variability was previously considered irrelevant for the TRGB as a standard candle. Here, we show that all stars near the TRGB are SARGs that follow several period–luminosity sequences, of which sequence A is younger than sequence B as predicted by stellar evolution. We measure apparent TRGB magnitudes, mTRGB, in the Large Magellanic Cloud (LMC) using Sobel filters applied to photometry from the Optical Gravitational Lensing Experiment and the ESA Gaia mission, and we identify several weaknesses in a recent LMC-based TRGB calibration used to measure the Hubble constant. We consider four samples: all red giants (RGs), SARGs, and sequences A and B. The B sequence is best suited for measuring distances to old RG populations, with MF814W,0 = −4.025 ± 0.014(stat.) ± 0.033(syst.) mag assuming the LMC’s geometric distance. Control of systematics is demonstrated using detailed simulations. Population diversity affects mTRGB at a level exceeding the stated precision: the SARG and A-sequence samples yield 0.039 and 0.085 mag fainter (at 5σ significance) mTRGB values, respectively. Ensuring equivalent RG populations is crucial to measuring accurate TRGB distances. Additionally, luminosity function smoothing (∼0.02 mag) and edge detection response weighting (as much as −0.06 mag) can further bias TRGB measurements, with the latter introducing a tip-contrast relation. We are optimistic that variable RGs will enable further improvements to the TRGB as a standard candle.

1701物理及び化学
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