The Carina Project. I. Bright Variable Stars

Abstract

We present new BV time series data of the Carina dwarf spheroidal galaxy (dSph). Current data cover an area of %0.3 deg 2 around the center of the galaxy and allow us to identify 92 variables. Among them 75 are RR Lyrae stars, 15 are bona fide anomalous Cepheids, one might be a Galactic field RR Lyrae star, and one is located along the Carina red giant branch. Expanding upon the seminal photographic investigation by Saha, Monet, & Seitzer we supply, for the first time, accurate estimates of their pulsation parameters (periods, amplitudes, mean magnitudes, and colors) on the basis of CCD photometry. Approximately 50% of both RR Lyrae stars and anomalous Cepheids are new identifications. Among the RR Lyrae sample, six objects are new candidate double-mode (RRd ) variables. On the basis of their pulsation properties we estimate that two variables (V158, V182) are about 50% more massive than typical RR Lyrae stars, while the bulk of the anomalous Cepheids are roughly a factor of 2 more massive than fundamental-mode (RRab) RR Lyrae stars. This finding supports the evidence that these objects are intermediate-mass stars during central He-burning phases. We adopted three different approaches to estimate the Carina distance modulus, namely, the first-overtone blue edge method, the period-luminosity-amplitude relation, and the periodluminosity-color relation. We found DM ¼ 20:19 AE 0:12, a result that agrees quite well with similar estimates based on different distance indicators. The data for Carina, together with data available in the literature, strongly support the conclusion that dSph's can barely be classified into the classical Oosterhoff dichotomy. The mean period of RRab's in Carina resembles that found for Oosterhoff type II clusters, whereas the ratio between first-overtone (RRc) pulsators and the total number of RR Lyrae stars is quite similar to that found in Oosterhoff type I clusters.

The episodic star formation history of the Carina dwarf spheroidal galaxy

“…The distance to Carina has been determined using several optical and near-infrared distance indicators, including RR Lyrae stars, the tip of the red giant branch (RGB) and the horizontal branch (HB) level, resulting in a distance of 106 ± 2 kpc or (m − M) V = 20.13 ± 0.04 (Dall'Ora et al 2003;Smecker-Hane et al 1994;Pietrzyński et al 2009). Furthermore, Carina has a core radius of 0.15 degrees (277 pc) and tidal radius of 0.48 degrees (888 pc), as determined from A&A 572, A10 (2014) King-profile stellar density fitting and an estimated extinction of E(B−V) = 0.061, as measured from dust extinction maps (Irwin & Hatzidimitriou 1995;Schlegel et al 1998).…”

The Araucaria Project: The Distance to the Carina Dwarf Galaxy From Infrared Photometry of Rr Lyrae Stars

“…The dates and coordinates of target fields are given in Table 2. The location of six target fields in the Carina dSph galaxy was purposely chosen to overlap the Wide Field Imager (WFI) field from Dall'Ora et al (2003), as shown in Figure 1. The HAWK-I field of view of four 2048 × 2048 pixel detectors was about 7 ′ .…”

“…The list of variables from Dall'Ora et al (2003) served as a reference to cross-identify 33 RRL (29 RRab + 4 RRc) stars in our fields. Although our six HAWK-I fields overlapped the WFI field only 30% of the time (see Figure 1), the sample of identified RRL stars constitutes 61% of the sample of Dall'Ora.…”

“…This error is extensively reduced by taking a large sample of stars. The J-and K-band random-phased magnitudes of the final RRL sample together with formal photometry errors from DAOPHOT and pulsational periods from the reference list (Dall'Ora et al 2003) are presented in Table 4. In the case of nine RRL stars observed more than once, individual observations were put in separate rows.…”

“…7 The above equations also account for first-overtone pulsators, once their period has been "fundamentalized" by adding a value of 0.127 to the logarithm of their periods. We calculated K-and J-band photometric zero points and slopes for our sample of 33 RRLs using photometric magnitudes derived from our data and pulsational periods excerpted from Dall'Ora et al (2003), as given in Table 4. The linear least squares fitting to our data yielded the following slopes: −1.79 ± 0.13 and −2.35 ± 0.08 in the J and K bands, respectively.…”