Stellar Variability and Distance Indicators in the Near-infrared in Nearby Galaxies. II. Pulsating Stars in the Carina Dwarf Spheroidal

Abstract

We present homogeneous, near-infrared ($JHK_s$ bands) time-series observations of the classical Carina dwarf Spheroidal (dSph) galaxy to determine accurate and precise distances using the pulsating stars as standard candles. These observations cover two Carina dSph fields ($\sim10.8'\times10.8'$) obtained with the FourStar infrared camera mounted on the 6.5-m Magellan Telescope. We collected precise photometric measurements of 43 RR Lyrae, 11 anomalous Cepheids (ACep), and 102 dwarf Cepheids (DCep) in Carina dSph. Using RR Lyrae, we obtained a distance modulus of $20.079\pm0.028\mathrm{(statistical)}\pm0.045\mathrm{(systematic)}$~mag, or a distance to Carina of $103.7\pm1.3\mathrm{(statistical)}\pm2.2\mathrm{(systematic)}$~kpc. The literature calibrations based on SX Phoenicis or delta-Scuti stars were used to anchor the $JHK_s$ period-luminosity relations for DCep. This resulted in a distance modulus that is in excellent agreement with RR Lyrae based determination. Finally, the distance moduli estimates using the ACep were found to be systematically smaller than the RR Lyrae-based distance modulus, suggesting a metallicity dependence on the ACep period-luminosity relation.

Figures (10)

• Figure 1: Seeing as a function of airmass for the Magellan/FourStar observations.
• Figure 2: Spatial distribution of two fields of Carina dSph, observed by Magellan/FourStar, overlaid on the Digitized Sky Survey (DSS) red plates image (with a size of $40\arcmin \times 40\arcmin$). The blue ellipse represents the contour with semimajor axis twice of the half-light radius ($r_h$) of Carina dSph, using the following parameters adopted from munoz2018: $r_h = 10.1\arcmin$, ellipticity of 0.36, and position angle of $60^\circ$. The diamonds, squares and triangles are the locations of fundamental mode RR Lyrae (RRab), first-overtone and double mode RR Lyrae (RRcd), and ACep, respectively. For clarity, locations of DCep were omitted.
• Figure 3: Extinction corrected CMD in the NIR for the combined sources (light grey dots) in the two Carina fields. The dark grey circles represent the sources with membership probability greater than 0.5, as determined by battaglia2022. Foreground contamination can be clearly seen in the CMD as a vertical stripe of sources around $(J-K_S)\sim 0.8$ that are mostly the late-type dwarf stars in the Milky Way. Variable stars studied in this work are overplotted with their mean magnitudes and colors; clear outliers (V182 and DC85) are explained in the text. The theoretically predicted instability strip boundaries - fundamental red edge (solid red line) and first-overtone blue edge (dashed blue line) are taken from marconi2015, shifted using a distance modulus of $\sim 20.07$ mag karczmarek2015. The inset figure represents the CMD in the Gaia filters for sources cross-matched to the battaglia2022 catalog. On the right the representative $\pm3\sigma$ error bars are shown as a function of magnitude and color.
• Figure 4: Examples of the phased light curves in the $JHK_S$ bands for RR Lyrae. Left: RRab stars. Right: RRc/RRd stars. For a better visualisation, the $J$- and $K_S$-band light curves have been shifted by $+0.2$ mag and $-0.3$ mag, respectively. The dashed lines represent the best-fit templates. The variable star ID, subtype, and the pulsation period are included at the top of each panel. The first-overtone mode periods were used to phase light curves of RRd stars.
• Figure 5: Same as Figure \ref{['fig_rr']}, but for the three representative ACep pulsating stars.