The araucaria project: First cepheid distance to the sculptor group galaxy ngc 7793 from variables discovered in a wide-field imaging survey

Grzegorz Pietrzyński, Wolfgang Gieren, Mario Hamuy, Giuliano Pignata, Igor Soszyński, Andrzej Udalski, Alistair Walker, Pascal Fouqué, Fabio Bresolin, Rolf Peter Kudritzki, Alejandro Garcia-Varela, Olaf Szewczyk, Michał Szymański, Marcin Kubiak, Łukasz Wyrzykowski

Research output: Contribution to journalArticlepeer-review

10 Citations (Scopus)


For the first time, we have detected Cepheid variables in the Sculptor Group spiral galaxy NGC 7793. From widefield images obtained in the optical V and I bands on 56 nights in 2003-2005, we have discovered 17 long-period (24-62 days) Cepheids whose periods and mean magnitudes define tight period-luminosity relations. We use the (V-I) Wesenheit index to determine a reddening-free true distance modulus to NGC 7793 of 27.68 ± 0.05 mag (internal error) ± 0.08 mag (systematic error). The comparison of the reddened distance moduli in V and I with the one derived from the Wesenheit magnitude indicates that the Cepheids in NGC 7793 are affected by an average total reddening of E(B - V) = 0.08 mag, 0.06 of which is produced inside the host galaxy. As in the earlier Cepheid studies of the Araucaria Project, the reported distance is tied to an assumed LMC distance modulus of 18.50. The quoted systematic uncertainty takes into account effects like blending and possible inhomogeneous filling of the Cepheid instability strip on the derived distance. The reported distance value does not depend on the (unknown) metallicity of the Cepheids according to recent theoretical and empirical results. Our Cepheid distance is shorter, but within the errors consistent with the distance to NGC 7793 determined earlier with the TRGB and Tully-Fisher methods. The NGC 7793 distance of 3.4 Mpc is almost identical to the one our project had found for NGC 247, another spiral member of the Sculptor Group located close to NGC 7793 on the sky. Two other conspicuous spiral galaxies in the Sculptor Group, NGC 55 and NGC 300, are much nearer (1.9 Mpc), confirming the picture of a very elongated structure of the Sculptor Group in the line of sight put forward by Jerjen et al. and others.

Original languageEnglish
Pages (from-to)1472-1485
Number of pages14
JournalAstronomical Journal
Issue number5
Publication statusPublished - Nov 2010


  • Cepheids
  • Distance scale - Galaxies
  • Distances and redshifts - Galaxies
  • Individual (ngc 7793) - Galaxies
  • Stellar content - Stars
  • Variables

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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