Distances to the Galaxies M81 and NGC 2403 from CCD I Band Photometry of Cepheids
Abstract
I band CCD photometry has been obtained for the only two known Cepheids in M81 and for eight of the known Cepheids in NGC 2403 using prime focus CCD cameras on the CFHT 3.6 m and on the KPNO 4 m. For M81, an apparent I band distance modulus and formal fitting error of (m - M)_I_ = 27.64 +/- 0.09 mag are derived; while for NGC 2403 (m - M)_I_ = 27.57 +/- 0.14 mag. Taking a true distance modulus of 18.50 mag for the Large Magellanic Cloud Cepheids used in the comparative fit, and by examining the accumulated random errors, a true modulus of 27.59 mag +/- 0.31 is obtained for M81, and 27.51 mag +/- 0.24 for NGC 2403 (foreground reddenings of A_I_ = 0.05 and 0.06 mag being adopted for M81 and NGC 2403, respectively.) These moduli correspond to distances of 3.3 +/- 0.5 and 3.2 +/- 0.4 Mpc, respectively, but they are still upper limits since we have not yet independently determined the reddening internal to the parent galaxies. Although separated by more than 10^deg^ on the sky, M81 and NGC 2403 appear to be at very similar distances along the line of sight, as was first suggested by Holmberg.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- September 1988
- DOI:
- 10.1086/185267
- Bibcode:
- 1988ApJ...332L..63F
- Keywords:
-
- Astronomical Photometry;
- Cepheid Variables;
- Spiral Galaxies;
- Charge Coupled Devices;
- Error Analysis;
- Magellanic Clouds;
- Northern Hemisphere;
- Astronomy;
- GALAXIES: INDIVIDUAL MESSIER NUMBER: M81;
- GALAXIES: INDIVIDUAL NGC NUMBER: NGC 2403;
- GALAXIES: PHOTOMETRY;
- STARS: CEPHEIDS