Stellar Variability and Distance Indicators in the Near-infrared in Nearby Galaxies. I. RR Lyrae and Anomalous Cepheids in Draco dwarf spheroidal
Anupam Bhardwaj, Marina Rejkuba, Chow-Choong Ngeow, Marcella Marconi, Vincenzo Ripepi, Abhinna Sundar Samantaray, Harinder P. Singh
arXiv:2404.01394v1 Announce Type: new
Abstract: Draco dwarf Spheroidal galaxy (dSph) is one of the nearest and the most dark matter dominated satellites of the Milky Way. We obtained multi-epoch near-infrared (NIR, $JHK_s$) observations of the central region of Draco dSph covering a sky area of $sim 21’times21’$ using the WIRCam instrument at the 3.6-m Canada-France-Hawaii Telescope. Homogeneous $JHK_s$ time-series photometry for 212 RR Lyrae (173 fundamental-mode, 24 first-overtone, and 15 mixed-mode variables) and 5 Anomalous Cepheids in Draco dSph is presented and used to derive their period-luminosity relations at NIR wavelengths for the first-time. The small scatter of $sim 0.05$~mag in these empirical relations for RR Lyrae stars is consistent with those in globular clusters and suggests a very small metallicity spread, up to $sim0.2$~dex, among these centrally located variables. Based on empirically calibrated NIR period-luminosity-metallicity relations for RR Lyrae in globular clusters, we determined a distance modulus to Draco dSph of $mu_textrm{RRL} = 19.557 pm 0.026$ mag. The calibrated $K_s$-band period-luminosity relations for Anomalous Cepheids in the Draco dSph and the Large Magellanic Cloud exhibit statistically consistent slopes but systematically different zero-points, hinting at possible metallicity dependence of $sim-0.3$ mag~dex$^{-1}$. Finally, the apparent magnitudes of the tip of the red giant branch in $I$ and $J$ bands also agree well with their absolute calibrations with the adopted RR Lyrae distance to Draco. Our recommended $sim1.5%$ precise RR Lyrae distance, $D_textrm{Draco} = 81.55 pm 0.98 textrm{(statistical)} pm 1.17 textrm{(systematic)}$~kpc, is the most accurate and precise distance to Draco dSph galaxy.arXiv:2404.01394v1 Announce Type: new
Abstract: Draco dwarf Spheroidal galaxy (dSph) is one of the nearest and the most dark matter dominated satellites of the Milky Way. We obtained multi-epoch near-infrared (NIR, $JHK_s$) observations of the central region of Draco dSph covering a sky area of $sim 21’times21’$ using the WIRCam instrument at the 3.6-m Canada-France-Hawaii Telescope. Homogeneous $JHK_s$ time-series photometry for 212 RR Lyrae (173 fundamental-mode, 24 first-overtone, and 15 mixed-mode variables) and 5 Anomalous Cepheids in Draco dSph is presented and used to derive their period-luminosity relations at NIR wavelengths for the first-time. The small scatter of $sim 0.05$~mag in these empirical relations for RR Lyrae stars is consistent with those in globular clusters and suggests a very small metallicity spread, up to $sim0.2$~dex, among these centrally located variables. Based on empirically calibrated NIR period-luminosity-metallicity relations for RR Lyrae in globular clusters, we determined a distance modulus to Draco dSph of $mu_textrm{RRL} = 19.557 pm 0.026$ mag. The calibrated $K_s$-band period-luminosity relations for Anomalous Cepheids in the Draco dSph and the Large Magellanic Cloud exhibit statistically consistent slopes but systematically different zero-points, hinting at possible metallicity dependence of $sim-0.3$ mag~dex$^{-1}$. Finally, the apparent magnitudes of the tip of the red giant branch in $I$ and $J$ bands also agree well with their absolute calibrations with the adopted RR Lyrae distance to Draco. Our recommended $sim1.5%$ precise RR Lyrae distance, $D_textrm{Draco} = 81.55 pm 0.98 textrm{(statistical)} pm 1.17 textrm{(systematic)}$~kpc, is the most accurate and precise distance to Draco dSph galaxy.