Dwarf spheroidal satellites of M31: I. Variable stars and stellar populations in Andromeda XIX

Abstract

We present B,V time-series photometry of Andromeda XIX (And XIX), the most extended (half-light radius of 6.2') of Andromeda's dwarf spheroidal companions, that we observed with the Large Binocular Cameras at the Large Binocular Telescope. We surveyed a 23'x 23' area centered on And XIX and present the deepest color magnitude diagram (CMD) ever obtained for this galaxy, reaching, at V~26.3 mag, about one magnitude below the horizontal branch (HB). The CMD shows a prominent and slightly widened red giant branch, along with a predominantly red HB, which, however, extends to the blue to significantly populate the classical instability strip. We have identified 39 pulsating variable stars, of which 31 are of RR Lyrae type and 8 are Anomalous Cepheids (ACs). Twelve of the RR Lyrae variables and 3 of the ACs are located within And XIX's half light radius. The average period of the fundamental mode RR Lyrae stars (<Pab> = 0.62 d, σ= 0.03 d) and the period-amplitude diagram qualify And XIX as an Oosterhoff-Intermediate system. From the average luminosity of the RR Lyrae stars (<V (RR)> = 25.34 mag, σ= 0.10 mag) we determine a distance modulus of (m-M)${}_0$=$24.52\pm 0.23$ mag in a scale where the distance to the Large Magellanic Cloud (LMC) is $18.5\pm 0.1$ mag. The ACs follow a well defined Period-Wesenheit (PW) relation that appears to be in very good agreement with the PW relationship defined by the ACs in the LMC.

accepted for publication in ApJ

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• Toward an internally consistent astronomical distance scale
• Variable stars and stellar populations in Andromeda XXV: III. A central cluster or the galaxy nucleus?
• RR Lyrae-based Distances for 39 Nearby Dwarf Galaxies Calibrated to Gaia eDR3
• Variable Stars in Local Group Galaxies. IV. RR Lyrae stars in the central regions of the low-density galaxy Crater II
• A stellar population synthesis approach to the Oosterhoff dichotomy
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• Variable Stars and Stellar Populations in Andromeda XXVII: IV. An off-centered, disrupted galaxy
• Variability search in M 31 using Principal Component Analysis and the Hubble Source Catalog
• Predicting light curves of RR Lyrae variables using artificial neural network based interpolation of a grid of pulsation models