The benchmark cluster reddening project. II. A reddening value for M67

Since 1954, 70 reddening determinations have been published for M67. Those results are of very diverse quality, and they imply only that the value of E(B - V) for the cluster lies between -0.02 and +0.14 mag. In addition, this uncertainty is habitually concealed by long-standing citation practices. In response, a reformed reddening protocol called alternative scholarship is applied, with tenets including (1) rigorous published foundations for reddening values, (2) accountability for all extant reddening results for M67, (3) explicit quality control of reddening techniques, (4) use of techniques with limited metallicity sensitivity, (5) explicit zero-point control of input data (when possible), (6) a reddening zero point based ultimately on the dust-free solar neighborhood, and (7) adherence to statistical norms. Results from reddening maps are then set aside pending further examination of their zero points and accidental errors. In addition, reddening values derived from color-magnitude analysis and from averages of published reddening results are likewise set aside. Five techniques that satisfy the adopted protocol are then selected and applied. By averaging results from cluster A and F stars and K giants, one finds that the mean value of E(B - V) for M67 is 41 +/- 4 mmag. It is also found that extant results from additional techniques are consistent with this result or else can be set aside for plausible reasons. The analysis yields a collateral value of [Fe/H], and this is consistent with the derived reddening value. Using published high-dispersion data, it is found that the mean cluster value of [Fe/H] is -0:009 +/- 0: 009 dex. For M67 and the Hyades combined, no mean metallicity difference between giants and stars near the main sequence is found that is >= 0.036 dex at 95% confidence.