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Tuesday, September 27, 2011

FGK stars

So before I go running after observing time to measure rotation periods for FG and K type stars, I first need to do a more thorough check of the literature. Also, some rotation periods quoted in the literature are photometrically determined, while others are calculated from the activity levels (Noyes 84). I can also extend my code from Mamajek & Hillenbrand 2008  - originally I only translated the portion that related to rotation periods, but you can calculate these from Rhk, Rhk', Lx/Lbol, etc. So if I can gather those parameters for stars, I can a) determine ages for stars with no quoted rotation period in the literature and b) check the agreement between photometrically determined rotation periods and those calculated from activity level markers. This time, I'm keeping more careful track of my references so that I can look them up later and find the method of Prot determination used.

So far, I've got:

Baliunas 1996 - calculated Prot from activity (Rossby #) AND photometrically determined Prot from periodic fluxuations in CaII. How accurate are these calculations? might be worth making a Prot vs Prot graph to compare these methods.

Soderblom 1985 - calculated Prot from Rhk'. He used a model from 1980 to determine the best-fit convective turnover timescale tau(c), which is used in the calculation of Prot. Therefore, I'm not sure how much I trust his values for Prot. However, his values of Rhk' were measured directly from the spectra, so I'd rather plug those into the Mamajek code and come up with my own calculations for Prot. Again, it might be worth it to make a Prot (Soderblom) vs Prot (mamajek) plot to see if the newly calculated values of Prot agree with the old calculations. The mamajek code itself provides several references for this calculation (R'hk-->age): Soderblom91, Donahue93, Lachaume99, and finally a calculation from Mamajek08 itself.

Wright 2011 - calculated Prot collected from the literature in which Prot was photometrically determined. The sources he lists are:
      Hartman 2010, Irwin 2007, Irwin 2008, Delorme 2011, Scholtz 2011, Hartman 2011, Kiraga + Stepien 2007, Xing 2007, Bouvier 1997, Mamajek & Hillenbrand 2008, FEPS program

Wright actually uses gyrochronology data to determine tau(c) as a function of stellar mass. Since this paper is from 2011, the Mamajek code does not take into account this calculation for tau, but I can add it to the code and compare the resulting ages with those using Mamajek's calculated value for tau(c).



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