arXiv subjects

Huajian Wang

Publications and source records attributed to Huajian Wang.

4 recordsLinked to original sources

arXiv2026

The Dependence of the Extinction Coefficient on Reddening for Galactic Cepheids

Cepheids are fundamental distance indicators, playing a crucial role not only in the cosmic distance ladder but also in mapping the structure, kinematics, and extinction properties of the Milky Way. Using high-precision photometry and parallaxes from $Gaia$ Data Release 3, we identify a significant anti-correlation between the $G$-band extinction coefficient and reddening for Galactic Cepheids, quantified as $R_G = 1.918 \pm 0.060 - (0.106 \pm 0.022)\,E(G_{\mathrm{BP}} - G_{\mathrm{RP}})$. We propose that this anti-correlation arises from the combination of the non-linear effects inherent to the broad $Gaia$ bands and the $R_V$ variations caused by diverse interstellar medium. Adopting a fixed $R_G$ would not only lead to an overestimation of the metallicity dependence of Cepheid luminosities, but also systematically underestimate the distances to highly reddened Cepheids. Moreover, the strong reddening dependence of $R_G$ makes Wesenheit function based on it unsuitable for highly reddened Cepheids, since the definition of Wesenheit magnitudes requires a fixed extinction coefficient. In contrast, infrared-based distances, being less affected by non-linear effects and insensitive to $R_V$, provide the most reliable Cepheid distances at present. This work emphasizes the importance of accurately determining $R_V$ for Galactic Cepheids and accounting for non-linear effects in distance measurements, particularly in the optical bands.

astro-ph.GA↗

arXiv2025

Milky Way Classical Cepheids Distances from Calibrated Infrared Period-Luminosity-Metallicity Relations

Classical Cepheids (DCEPs) serve as fundamental standard candles for measuring cosmic distances and investigating the structure and evolution of the Milky Way disc. However, accurate distance estimation faces challenges due to severe extinction, particularly toward the Galactic center. Although the $Gaia$ Wesenheit magnitude reduces extinction effects, its reliance on a constant optical extinction law introduces significant uncertainties in regions of heavy obscuration. Infrared Period-Luminosity relations, combined with 3D extinction maps, offer an alternative, but these maps become unreliable beyond approximately 5 kpc. In this work, we calibrate the Period-Luminosity-Metallicity (PLZ) relations for DCEPs across three near-infrared bands ($J, H, K_S$) and four mid-infrared bands ($W1, W2, [3.6]$, and $[4.5]$). This includes the first calibration of the $W1$ and $W2$ bands. To correct for extinction, we employ the infrared multi-passband optimal distance method and the BP-RP method, which complement and validate each other. These homogeneous PLZ relations, combined with reliable extinction corrections, yield the most accurate Galactic DCEP distances to date, covering 3,452 DCEPs with an average relative distance error of 3.1%.

astro-ph.GA↗

arXiv2024

Search for Classical Cepheids in Galactic Open Clusters and Calibration of the Period Wesenheit Metallicity Relation in the Gaia Bands

It is beneficial to calibrate the period Wesenheit metallicity relation (PWZR) of Delta Cephei stars (DCEPs), i.e., classical Cepheids, using accurate parallaxes of associated open clusters (OCs) from Gaia data release 3 (DR3). To this aim, we obtain a total of 43 OC-DCEPs (including 33 fundamental mode, 9 first overtone mode, and 1 multimode DCEPs.) and calibrate the PWZR as $W_G=(-3.356 \,\pm\, 0.033) \,(\log{P-1})+(-5.947 \,\pm\, 0.025)+(-0.285 \,\pm\, 0.064)[\textrm{Fe/H}]$. The concurrently obtained residual parallax offset in OC, $zp = -4\pm5\,μ\textrm{as}$, demonstrate the adequacy of the parallax corrections within the magnitude range of OC member stars. By comparing the field DCEPs' DR3 parallaxes with their photometric parallaxes derived by our PWZR, we estimated the residual parallax offset in field DCEPs as $zp = -15\pm3\,μ\textrm{as}$. Using our PWZR, we estimate the distance modulus of the Large Magellanic Cloud to be $18.482 \,\pm\, 0.040$ mag, which aligns well with the most accurate published value obtained through geometric methods.

astro-ph.SR↗

arXiv2013

Reducing Poisson noise and baseline drift in X-ray spectral images with bootstrap Poisson regression and robust nonparametric regression

X-ray spectral imaging provides quantitative imaging of trace elements in biological sample with high sensitivity. We propose a novel algorithm to promote the signal-to-noise ratio (SNR) of X-ray spectral images that have low photon counts. Firstly, we estimate the image data area that belongs to the homogeneous parts through confidence interval testing. Then, we apply the Poisson regression through its maximum likelihood estimation on this area to estimate the true photon counts from the Poisson noise corrupted data. Unlike other denoising methods based on regression analysis, we use the bootstrap resampling method to ensure the accuracy of regression estimation. Finally, we use a robust local nonparametric regression method to estimate the baseline and subsequently subtract it from the X-ray spectral data to further improve the SNR of the data. Experiments on several real samples show that the proposed method performs better than some state-of-the-art approaches to ensure accuracy and precision for quantitative analysis of the different trace elements in standard reference biological sample.

physics.med-ph↗