view Abstract Citations (21) References (13) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Type I supernovae as cosmological clocks. de Vaucouleurs, G. ; Pence, W. D. Abstract The use of supernovae as cosmological clocks requires that proper allowance be made for absolute luminosity and color effects. The existence of two luminosity groups of Type I supernovae and, within each group, of a correlation between decay rate and absolute luminosity at maximum has been documented. It is shown that the proper form of the relationship is logarithmic, that regression effects must be taken into account for a correct reduction to standard conditions, and that it is essential to apply to the apparent decay rates another correction allowing for the second-order or differential K-effect arising from the rapid color evolution of Type I supernovae during the first month past maximum. Calculations of K-corrections are presented for photographic light curves using a realistic approximation of the U-B, B-V color evolution for durations not exceeding 33 days and z not exceeding 0.15, from which are derived the rate of change dK/dt and the corresponding correction factor to the time scale for decay. An application to data for 36 supernovae (z less than 0.06) shows that these corrections reduce the scatter in the (t, z)-diagram and yield a better-defined slope in the decay time-redshift relation. Publication: The Astrophysical Journal Pub Date: November 1976 DOI: 10.1086/154768 Bibcode: 1976ApJ...209..687D Keywords: Cosmology; Decay Rates; Supernovae; Time Measurement; Astronomical Catalogs; Color; Stellar Luminosity; Time Constant; Astrophysics full text sources ADS | data products NED (71) SIMBAD (36)