Norman Baker's research while affiliated with Columbia University and other places

Publications (3)

Article
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Article
The observational evidence leading to the classification, following Oosterhoff, of globular clusters containing RR Lyrae stars into two distinct groups, is summarized and discussed in the light of results of stellar evolution theory and pulsation theory. The dichotomy is caused, at least in part, by a dichotomy in the ‘transition period’ between th...

Citations

... As this is a rather tedious procedure and only a few stars are affected we did not include these in our final sample. This does not apply for those stars taken from literature which were measured using other fitting techniques, or in the case of SB 744, where the secondary continuum was subtracted (Unglaub & Bues 1990). The photometry (where the effect of the secondary can be seen in the B − V colours, see also Fig. 2.2) and proper motions of these stars (named sdB+x) are included in the according data tables, i.e. sdB stars may be the result of close binary evolution. ...
... However, a few metal-rich clusters (NGC 6441, NGC 6388, [Fe/H] >−0.7 dex) have a longer value for the mean-period of RRab (0.7 days) and are often called OoIII clusters. Initially, the dichotomy was attributed to a dichotomy in the "transition period" between RRab and RRc stars, which reflects a difference in the effective temperature at the transition point [83]. It was suggested that the temperature difference arising from the "hysteresis effect" [83] is responsible for the Oosterhoff dichotomy. ...
... To overcome possible observational biases in defining our list of variable stars and before cross-correlating Fornax external catalogs, we performed a blind variability search. This was done by using five different implementations of period search algorithms: i) the Welch-Stetson (WS, Welch & Stetson 1993;Stetson 1996) index; ii) The Lomb -Scargle Periodogram (LS, Scargle 1982); iii) the Generalized Lomb-Scargle Periodogram (GLS, Zechmeister & Kürster 2009); iv) The GATSPY package based on the Lomb-Scargle Periodogram (VanderPlas & Ivezić 2015) and v) the Phase-Dispersion Minimization (PDM, Stellingwerf 1978). We have visually inspected the light curves folded with the best-period estimates provided by the quoted algorithms applied on both the B-and V-band time series and selected the best one for each candidate variable. ...