Variable stars in the NIR in nearby galaxies. I.

We obtained multiepoch near-infrared (NIR, JHKs) observations of the central region of Draco dSph covering a sky area of ~21x21' using the WIRCam instrument at the 3.6m Canada-France-Hawaii Telescope. Homogeneous JHKs time-series photometry for 212 RR Lyrae (173 fundamental-mode, 24 first-overtone, and 15 mixed-mode variables) and five Anomalous Cepheids in Draco dSph are presented and used to derive their period-luminosity relations at NIR wavelengths for the first- time.

The small scatter of ~0.05mag in these empirical relations for RR Lyrae stars is consistent with those in globular clusters and suggests a very small metallicity spread, up to ~0.2dex, 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}RRL=19.557{+/-}0.026mag. The calibrated Ks-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 ~-0.3mag/dex.