A STUDY OF CEPHEIDS IN M81 WITH THE LARGE BINOCULAR TELESCOPE (EFFICIENTLY CALIBRATED WITH HUBBLE SPACE TELESCOPE)
- Department of Astronomy, Ohio State University, 140 West 18th Avenue, Columbus, OH 43210 (United States)
- Carnegie Observatories, Pasadena, CA 91101 (United States)
- George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy, Department of Physics and Astronomy, Texas A and M University, 4242 TAMU, College Station, TX 77843-4242 (United States)
We identify and phase a sample of 107 Cepheids with 10 days < P < 100 days in M81 using the Large Binocular Telescope and calibrate their B, V, and I mean magnitudes with archival Hubble Space Telescope (HST) data. The use of a ground-based telescope to identify and phase the Cepheids and HST only for the final calibration reduces the demand on this highly oversubscribed spacecraft by nearly an order of magnitude and yields period-luminosity (PL) relations with dispersions comparable to the best LMC samples. We fit the sample using the OGLE-II LMC PL relations and are unable to find a self-consistent distance for different band combinations or radial locations within M81. We can do so after adding a radial dependence to the PL zero point that corresponds to a luminosity dependence on metallicity of {gamma}{sub {mu}} = -0.56 {+-} 0.36 mag dex{sup -1}. We find marginal evidence for a shift in color as a function of metallicity, distinguishable from the effects of extinction, of {gamma}{sub 2} = +0.07 {+-} 0.03 mag dex{sup -1}. We find a distance modulus for M81, relative to the LMC, of {mu}{sub M81} - {mu}{sub LMC} = 9.39 {+-} 0.14 mag, including uncertainties due to the metallicity corrections. This corresponds to a distance to M81 of 3.6 {+-} 0.2 Mpc, assuming an LMC distance modulus of 18.41 mag. We carry out a joint analysis of M81 and NGC 4258 Cepheids and simultaneously solve for the distance of M81 relative to NGC 4258 and the metallicity corrections. Given the current data, the uncertainties of such joint fits are dominated by the relative metallicities and the abundance gradients rather than by measurement errors of the Cepheid magnitudes or colors. We find {mu}{sub M81} - {mu}{sub LMC} = 9.40{sup +0.15}{sub -0.11} mag, {mu}{sub N4258} - {mu}{sub LMC} = 11.08{sup +0.21}{sub -0.17} mag, and {mu}{sub N4258} - {mu}{sub M81} = 1.68 {+-} 0.08 mag and metallicity effects on luminosity and color of {gamma}{sub {mu}} = -0.62{sup +0.31}{sub -0.35} mag dex{sup -1} and {gamma}{sub 2} = 0.01 {+-} 0.01 mag dex{sup -1}. Quantitative analyses of Cepheid distances must take into account both the metallicity dependencies of the Cepheids and the uncertainties in the abundance estimates.
- OSTI ID:
- 22004420
- Journal Information:
- Astrophysical Journal, Vol. 743, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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