arXiv subjects

O. Caliskan

Publications and source records attributed to O. Caliskan.

3 recordsLinked to original sources

arXiv2026

Kinematic and Dynamical Properties of Solar Neighborhood White Dwarfs from SDSS DR19 and Gaia DR3

We present a comprehensive kinematic and dynamical analysis of 5,837 DA white dwarfs with SDSS DR19 spectroscopy and Gaia DR3 astrometry. Using complementary spatial distributions, kinematic properties, and orbital parameters, we show that the sample is overwhelmingly dominated by the thin disk, with only minor contributions from the thick disk and the halo. Velocity dispersions and orbital eccentricities increase systematically from the thin disk to the halo, reflecting progressively hotter Galactic populations. Total stellar ages available for 4,829 white dwarfs reveal a clear age-velocity dispersion relation with power-law indices of 0.06-0.17, confirming that white dwarfs preserve the secular dynamical heating history of the Galactic disk. We derive a thin-disk scale-height of 123-229 pc and radial scale-length of 3.2-3.5 kpc, while the thick disk has a scale height of 865 pc and contributes approximately 6-7 % of the local stellar density. Reconstructed birth radii indicate that changes in the guiding radii represent an important component of the present-day radial redistribution of nearby white dwarfs, although the relative contributions of radial migration and orbital blurring cannot be uniquely separated from these displacement measures. These results establish white dwarfs as powerful tracers of the kinematic, dynamical, and structural evolution of the Milky Way.

astro-ph.SR↗

arXiv2025

Asteroseismology of WD J004917.14-252556.81, the Most Massive Pulsating White Dwarf

We present extensive follow-up time-series photometry of WD J0049$-$2525, the most massive pulsating white dwarf currently known with $T_{\rm eff} = 13\, 020\,{\rm K}$ and $\log{\it g} = 9.34$ cm s$^{-2}$. The discovery observations detected only two significant pulsation modes. Here, we report the detection of 13 significant pulsation modes ranging from 170 to 258 s based on 11 nights of observations with the New Technology Telescope, Gemini, and Apache Point Observatory telescopes. We use these 13 modes to perform asteroseismology and find that the best-fitting models (under the assumption of an ONe core composition) have $M_{\star} \approx 1.29~M_\odot$, surface hydrogen layer mass of $\log(M_{\rm H}/M_{\star}) \lesssim -7.5$, and a crystallized core fraction of $>99\%$. An analysis of the period spacing also strongly suggests a very high mass. The asteroseismic distance derived is in good agreement with the distance provided by Gaia. We also find tentative evidence of a rotation period of 0.3 or 0.67 d. This analysis provides the first look at the interior of a $\sim 1.3~M_{\odot}$ white dwarf.

astro-ph.SR↗

arXiv2025

Investigating the Colour-Magnitude Relations for White Dwarf Stars in SDSS Photometry

In this study, colour-magnitude relations (CMRs) for DA-type white dwarfs in the Sloan Digital Sky Survey (SDSS) photometric system were investigated. For this purpose, the SDSS data for 20,247 white dwarf stars, as provided in the study by Anguiano et al. (2017), were matched with the Gaia third data release (Gaia DR3) catalogue to obtain trigonometric parallax ($\varpi$) data. The SDSS $ugriz$ magnitudes of the stars were corrected for interstellar extinction using dust maps provided for the Milky Way, and distances from the Sun to the stars were calculated. The SDSS magnitudes were thus corrected for the effects of interstellar extinction. For the calibration of the stars, 5,516 white dwarf stars were selected, with apparent magnitudes brighter than $g_0=21$ mag and relative parallax errors measured to better than $σ_\varpi/\varpi=0.1$. Subsequently, three separate CMRs were derived for the absolute magnitudes $M_{\rm g}$, $M_{\rm r}$, and $M_{\rm i}$, each calibrated to two-colour indices. The coefficient of determination ($R^2$) of the obtained CMRs are highly reliable in the bf range of 0.86 to 0.95. Moreover, the standard deviations of the differences between the absolute magnitudes obtained from the relations and the original ones of the calibration stars range from 0.26 to 0.37 mag.

astro-ph.SR↗