Bibcode
Coppola, G.; Marconi, M.; Stetson, P. B.; Bono, G.; Braga, V. F.; Ripepi, V.; Dall’Ora, M.; Musella, I.; Buonanno, R.; Fabrizio, M.; Ferraro, I.; Fiorentino, G.; Iannicola, G.; Monelli, M.; Nonino, M.; Thévenin, F.; Walker, A. R.
Bibliographical reference
The Astrophysical Journal, Volume 814, Issue 1, article id. 71, 28 pp. (2015).
Advertised on:
11
2015
Journal
Citations
65
Refereed citations
55
Description
We present new multiband (UBVI) time-series data of helium burning
variables in the Carina dwarf spheroidal galaxy. The current sample
includes 92 RR Lyrae—six of them are new identifications—and
20 Anomalous Cepheids, one of which is new identification. The analysis
of the Bailey diagram shows that the luminosity amplitude of the first
overtone component in double-mode variables is located along the
long-period tail of regular first overtone variables, while the
fundamental component is located along the short-period tail of regular
fundamental variables. This evidence further supports the transitional
nature of these objects. Moreover, the distribution of Carina
double-mode variables in the Petersen diagram
(P1/P0 versus P0) is similar to
metal-poor globulars (M15, M68), to the dwarf spheroidal Draco, and to
the Galactic Halo. This suggests that the Carina old stellar population
is metal-poor and affected by a small spread in metallicity. We use
trigonometric parallaxes for five field RR Lyrae stars to provide an
independent estimate of the Carina distance using the observed reddening
free Period–Wesenheit [PW, (BV)] relation. Theory and observations
indicate that this diagnostic is independent of metallicity. We found a
true distance modulus of μ = 20.01 ± 0.02 (standard error of
the mean) ± 0.05 (standard deviation) mag. We also provided
independent estimates of the Carina true distance modulus using four
predicted PW relations (BV, BI, VI, BVI) and we found: μ = (20.08
± 0.007 ± 0.07) mag, μ = (20.06 ± 0.006 ±
0.06) mag, μ = (20.07 ± 0.008 ± 0.08) mag, and μ =
(20.06 ± 0.006 ± 0.06) mag. Finally, we identified more
than 100 new SX Phoenicis stars that together with those already known
in the literature (340) make Carina a fundamental laboratory for
constraining the evolutionary and pulsation properties of these
transitional variables.
Related projects
Galaxy Evolution in the Local Group
Galaxy formation and evolution is a fundamental Astrophysical problem. Its study requires “travelling back in time”, for which there are two complementary approaches. One is to analyse galaxy properties as a function of red-shift. Our team focuses on the other approach, called “Galactic Archaeology”. It is based on the determination of galaxy
Matteo
Monelli