arXiv subjects

Kayla Owens

Publications and source records attributed to Kayla Owens.

4 recordsLinked to original sources

arXiv2026

I-Band Asymptotic Giant Branch (IAGB) Stars: I. Exploring a New Standard Candle for the Extragalactic Distance Scale

In the I-band color-magnitude diagrams (CMD) of resolved nearby galaxies, the reddest asymptotic giant branch (AGB) stars form a previously unremarked-upon, but nevertheless distinct and easily-identified population of high-luminosity stars. Hereafter we refer to this population as being comprised of I-Band AGB (IAGB) stars. Identifying these stars in the Large Magellanic Cloud (LMC), the Small Magellanic Cloud (SMC) and in NGC4258 (for all three of which there are published geometric distances) we find that the marginalized luminosity functions are each well approximated by single-peaked Gaussians, having one-sigma dispersions of +/- 0.22 mag, +/- 0.25 mag and +/- 0.24 mag, respectively. The zero points for the modal I-band absolute magnitudes of IAGB stars are found to be M_I = -4.49 +/- 0.003 mag (stat) in the LMC (4204 stars), M_I = -4.67 +/- 0.008 mag (stat), for the SMC sample (916 stars), and M_I = -4.78 +/- 0.030 mag (stat) for NGC4258 (62 stars). A global average over these three independent calibrations of the IAGB zero point (weighted inversely by squares of their systematic errors) gives = -4.65 +/- 0.119 mag (stat) +/- 0.025 (sys). In Paper II we will show the results of applying the IAGB Method to 92 galaxies additional galaxies resolved by HST, reaching out to distances just short of 10 Mpc.

astro-ph.SR↗

arXiv2025

Chicago-Carnegie Hubble Program (CCHP) A Multi-Wavelength Search for the Effects of Metallicity on the Cepheid Distance Scale. Part II: Theoretical Models and Synthetic Spectra

This is the second of two papers exploring the effects of metallicity on the multi-wavelength properties of Cepheids in terms of their multi-wavelength period-luminosity (PL) relations, impacting their use as extragalactic distance indicators, underpinning one of the most popular paths to estimating of the expansion rate of the Universe, Ho. In Paper I (Madore & Freedman 2024) we presented five tests for the influence of metallicity on galactic and extragalactic Cepheid PL relations, spanning nearly 2 dex in metallicity, and inspecting PL relations from the optical (BVI), through the near-infrared (JHK) and into mid-infrared (at 3.4 and 4.5 microns). And,in no case were any statistically significant results forthcoming. Here we interrogate published spectral energy distributions constructed from theoretical (static) stellar atmospheres, covering the surface gravity and temperature ranges attributed to classical (supergiant, F and K spectral type) Cepheid variables, and explore the differential effects of changing the atmospheric metallicity, down by 2 dex from solar (a factor of 100 below the average Milky Way value) and then up from solar by 0.5 dex (i.e., factor of 3x above the Milky Way value). The theoretical models clearly show that metallicity systematically impacts each of the bandpasses differentially: the level of this effect is largest in the ultraviolet (where line blanketing is most intense), reversing sign in the optical (due to flux redistribution from the UV), and then asymptotically falling back to zero from the red to the far infrared. The discovered effects of metallicity are systematic, but they are small; and as such they do not contradict the findings of Paper I, but they do explain why the problem has been so hard to resolve given the low level of precision of the photometry for all but the very nearest and apparently brightest Cepheids.

astro-ph.GA↗

arXiv2023

Astrophysical Distance Scale VII: A Self-Consistent, Multi-Wavelength Calibration of the Slopes and Relative Zero Points for the Run of Luminosity with Color of Stars Defining the Tip of the Red Giant Branch

Given the recent successful launch of the James Webb Space Telescope, determining robust calibrations of the slopes and absolute magnitudes of the near- to mid-infrared Tip of the Red Giant Branch (TRGB) will be essential to measuring precise extragalactic distances via this method. Using ground-based data of the Large Magellanic Cloud from the Magellanic Clouds Photometric Survey along with near-infrared (NIR) data from 2MASS and mid-infrared (MIR) data collected as a part of the SAGE survey using the Spitzer Space Telescope, we present slopes and zero-points for the TRGB in the optical (VI), NIR (JHK) and MIR ([3.6] & [4.5]) bandpasses. These calibrations utilize stars +0.3 +/- 0.1 mag below the tip, providing a substantial statistical improvement over previous calibrations which only used the sample of stars narrowly encompassing the tip.

astro-ph.GA↗

arXiv2022

Milky Way Zero-Point Calibration of the JAGB Method: Using Thermally Pulsing AGB Stars in Galactic Open Clusters

We present a new calibration of the J-band absolute magnitude of the JAGB method based on thermally pulsing AGB stars that are members of Milky Way open clusters, having distances and reddenings, independently compiled and published by Marigo et al (2022). 17 of these photometrically-selected J-Branch AGB stars give M_J = -6.40 mag with a scatter of +/-0.40 mag, and a sigma on the mean of +/-0.10 mag. Combining the Milky Way field carbon star calibration of Lee et al. (2021) with this determination gives a weighted average of M_J(MW) = -6.19 +/- 0.04 mag (error on the mean). This value is statistically indistinguishable from the value determined for this population of distance indicators in the LMC and SMC, giving further evidence that JAGB stars are extremely reliable distance indicators of high luminosity and universal applicability. Combining the zero points for JAGB stars in these three systems, a value of M_J = -6.20 +/- 0.01 (stat) +/- 0.04 (sys) mag becomes our best current estimate of the JAGB zero point and its associated errors. Finally, we note that no evidence is found for any statistically significant dependence of this zero point on metallicity.

astro-ph.GA↗