The Araucaria Project: The Distance to the Sculptor Group Galaxy NGC 247 From Cepheid Variables Discovered in a Wide-Field Imaging Survey

Abstract

1 Based on observations obtained with the 1.3 m telescope at the Las Campanas Observatory, the 2.2 m ESO/MPI telescope at the European Southern Observatory for Large Programme 171.D-0004, and the 4.0 m Blanco telescope at the Cerro Tololo Inter-American Observatory. This work is part of the PhD thesis of AGV. ABSTRACTWe report on the discovery of a Cepheid population in the Sculptor Group spiral galaxy NGC 247 for the first time. On the basis of wide-field images collected in photometric surveys in V and I bands which were conducted with three different telescopes and cameras, 23 Cepheid variables were discovered with periods ranging from 17 to 131 days. We have constructed the period-luminosity relations from these data and obtain distance moduli to NGC 247 of 28.20 ± 0.05 mag (internal error) in V, 28.04 ± 0.06 mag in I, and 27.80 ± 0.09 mag in the reddening-independent Wesenheit index. From our optical data we have determined the total mean reddening of the Cepheids in NGC 247 as E(B-V)=0.13 mag, which brings the true distance modulus determinations from the V and I bands into excellent agreement with the distance determination in the Wesenheit index. The best estimate for the true distance modulus of NGC 247 from our optical Cepheid photometry is 27.80 ±0.09 (internal error) ± 0.09 mag (systematic error) which is in excellent agreement with other recent distance determinations for NGC 247 from the Tip of the Red Giant branch method, and from the Tully-Fisher relation. The distance for NGC 247 places this galaxy at twice the distance of two other Sculptor Group galaxies, NGC 300 and NGC 55, yielding supporting evidence for the filament-like structure of this group of galaxies. The reported distance value is tied to an assumed LMC distance modulus of 18.50 mag.

Progenitors of Core-Collapse Supernovae

“…The distance limit within which massive stars have been quantitatively studied is reduced by a factor of approximately 6 compared to HST campaigns. The Araucaria Project has studied Cepheids and massive blue supergiants in spirals between 2-4.4 Mpc (Kudritzki et al 2008, Garcia-Varela et al 2008. High signal-to-noise quantitative photometric and spectroscopic data allow application of model atmosphere and stellar wind models to determine fundamental parameters of massive stars, even out to distances of 6-7 Mpc (e.g.…”

The young stellar population in NGC 247

“…In this figure we overlapped the PARSEC version 1.2S evolutionary model (Tang et al 2014) corresponding to 10 7 years and metallicity Z = 0.0152, to make a comparison with a young stellar population. This isochrone was displaced adopting a distance modulus of (V 0 − M V ) = 27.78 (García-Varela et al 2008), a normal reddening law (R = A V /E(B − V) = 3.1) and a value for E(B − V) = 0.015, corresponding to the foreground reddening toward NGC 247 (Schlafly & Finkbeiner 2011). The following coefficients were used to transform these values to the HST system: A F475W /A V = 1.192, A F606W /A V = 0.923, and A F814W /A V = 0.605 7 (O'Donnell 1994).…”

“…In this work we present a study of the young stellar population in the Sculptor group spiral galaxy NGC 247. This galaxy is catalogued as a SAB(s) d D (Konstantopoulos et al 2013), is located near the south Galactic pole (l = 113.95 • ; b = −83.56 • ), has a high inclination angle (i = 74 • ; Schaap et al 2000), and an estimated distance of 3.6 Mpc (García-Varela et al 2008).…”

New Blue and Red Variable Stars in NGC 247

“…The area observed with GMOS contains a modest number of previously identified variable stars. Two Cepheids (cep011 and cep022) discovered by Garcia-Varela et al (2008) were recovered using the procedure described above. There is an offset with respect to the Garcia-Varela et al ( 2008) co-ordinates of 2 arcsec in declination, and 1 sec (∼ 14 arcsec) in right ascension.…”

“…The variable star content of NGC 247 has not been extensively explored, and past studies have targeted only certain types of objects. The Aracauria project (Gieren et al 2005) detected 23 Cepheids in NGC 247 that span a range of periods (Garcia-Varela et al 2008). There are hints that the distribution of Cepheids throughout the galaxy may not be uniform, as only six Cepheids were found in the southern part of NGC 247, while Cepheids with periods < 30 days were found exclusively in the northern part of the disk.…”