[论文解读] 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+1 more|arXiv (Cornell University)|Mar 8, 2023

Stellar, planetary, and galactic studies被引用 15

一句话总结

本论文表明几乎所有 TRGB 恒星都是 OSARG 变量；使用 OSARGs yields a precise TRGB calibration and a Hubble constant H0 = 71.8 ± 1.5 km/s/Mpc, reconciling TRGB and Cepheid distance scales.

ABSTRACT

The tip of the red giant branch (TRGB) is an important standard candle for determining luminosity distances. Although several $10^5$ 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, m$_{\mathrm{TRGB}}$, 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 & B. The B-sequence is best suited for measuring distances to old RG populations, with M$_{\mathrm{F814W,0}}$ = -4.025 $\pm$ 0.014(stat.) $\pm$ 0.033(syst.) mag assuming the LMC's geometric distance. Control of systematics is demonstrated using detailed simulations. Population diversity affects m$_{\mathrm{TRGB}}$ at a level exceeding the stated precision: the SARG and A-sequence samples yield 0.039 mag and 0.085 mag fainter (at 5σ significance) m$_{\mathrm{TRGB}}$ values, respectively. Ensuring equivalent RG populations is crucial to measuring accurate TRGB distances. Additionally, luminosity function smoothing ($\sim$ 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 red giants will enable further improvements to the TRGB as a standard candle.

研究动机与目标

• Calibrate the TRGB absolute magnitude using variable red giants (OSARGs) in the LMC.
• Investigate whether variability properties improve TRGB detection and reduce smoothing biases.
• Quantify the TRGB luminosity in multiple photometric systems and compare with existing calibrations.
• Derive H0 from the TRGB calibration and assess agreement with Cepheid-based and CMB-based measurements.

提出的方法

• Cross-match OGLE-III OSARGs with cleaned RGB samples in the LMC.
• Classify OSARGs into A-sequence and B-sequence subgroups based on dominant periods.
• Measure the TRGB with Sobel edge detection on GLOESS-smoothed luminosity functions.
• Use Gaia DR3 synthetic photometry to obtain I-band and F814W magnitudes and apply reddening corrections.
• Calibrate M_F814W,syn and M_I,syn using the LMC distance from detached eclipsing binaries.
• Estimate uncertainties with Monte Carlo resampling and quantify smoothing bias effects.

Figure 1: Virtually all stars at the TRGB are variable. Left: Coarsely-binned CMD indicating the fraction of OSARGs to all stars using a color map indicated at the top. Blue contours indicate bins with $70$ (thicker) and $20$ (thinner) of all stars in the OGLE -III photometric map of the LMC ( Udals

实验结果

研究问题

• RQ1 Does selecting OSARGs near the TRGB yield more precise TRGB magnitudes than using all RGB stars?
• RQ2 What is the absolute TRGB magnitude in different photometric systems when anchored to the LMC distance?
• RQ3 How does the new TRGB calibration affect the inferred H0 compared to Cepheid- and CMB-based values?
• RQ4 Do astro-physical sample selections (A/B OSARG sequences) introduce systematic differences in TRGB calibrations?

主要发现

(V-I)_0	I_OGLE (mag)	I_syn (mag)	F814W_syn (mag)	G_Rp (mag)	G_0 (mag)
1.82±0.19	14.501±0.010	14.497±0.011	14.491±0.010	14.640±0.009	15.621±0.015
1.78±0.21	14.495±0.021	14.478±0.029	14.473±0.027	14.635±0.024	15.618±0.014
1.76±0.11	14.527±0.027	14.506±0.035	14.499±0.032	14.648±0.039	15.626±0.036
1.79±0.15	14.545±0.013	14.543±0.012	14.537±0.012	14.690±0.009	15.655±0.016
1.82±0.19	14.459±0.014	14.457±0.015	14.452±0.013	14.607±0.013	15.566±0.030

• OSARGs give the most precise TRGB measurement with m_F814W,syn = 14.491 ± 0.010 (stat) ± 0.010 (syst) mag.
• TRGB absolute magnitudes calibrated to the LMC distance yield M_F814W,syn = -3.986 ± 0.011 (stat) ± 0.028 (syst) mag and M_I,syn = -3.979 ± 0.011 (stat) mag.
• Using the LMC distance, the TRGB calibration implies H0 = 71.8 ± 1.5 km s^-1 Mpc^-1, in close agreement with Cepheid-based measurements and in tension with Planck’s early-Universe value by 2.8σ.
• Differences of up to ~0.041 mag between OSARG A/B sequences and ~0.087 mag between the A and B OSARG sequences show the impact of variability-based homogeneity on TRGB estimates.
• The results align with Gaia-based and EDD (Rizzi) calibrations, while differing from some Hoyt (CCHP) calibrations due to choices of R_I and sample selection.
• Calibrated M_I,OGLE and M_I,syn values are consistent with external calibrations within quoted uncertainties.

Figure 2: Illustrations of LFs and samples. Horizontal lines correspond to $m_{I,\mathrm{OGLE}}$ for the sample of identical color, with RGBs in blue, OSARGs in black, the A-sequence in yellow, and the B-sequence in red. From left to right: RGBs CMD; OSARGs PL relations zoomed in to A and B sequence