[Mesa-users] Question about RSP and equilibrium quantities

Tue Jan 21 15:51:53 EST 2020

Thanks Radek,

That's very useful! Would you say that the average that I calculated by
averaging over the data points is a good representation of the "equilibrium
radius" or is such a quantity not meaningful?

I ask because papers purport to have measured this radius using other means
e.g. V-K calibrations but it is not clear to me what such a quantity
corresponds to if the radius is varying by 4 solar radii.

On Tue, Jan 21, 2020 at 10:44 AM Radek Smolec <smolec at camk.edu.pl> wrote:

> Such procedure would work provided light/radius curve is very densely
> sampled. Here it is not the case.  RSP time steps are distributed
> regularly, but not synchronised with pulsation phase (i.e. we don't have
> time stamps at the same pulsation phases of the consecutive pulsation
> cycles). It is  visible in your plots with colored points. If I see it
> correctly in the (strong) zoom, black point overlap with blue. Hence you
> have two representations for consecutive pulsation cycles with differently
> distributed time stamps. It may be enough to produce small, alternating
> difference in the average.
> Radek
>
>
> wt., 21 sty 2020 o 21:11 Jeremy Sakstein <sakstein at hawaii.edu> napisał(a):
>
>> To average I just pick a pulsation cycle, add up the radius over that
>> cycle and divide by the number of data points.
>>
>> On Tue, Jan 21, 2020 at 10:09 AM Radek Smolec <smolec at camk.edu.pl> wrote:
>>
>>> So I'm confused; you wrote:
>>>
>>>> I am taking a single pulsation cycle and averaging over the radius
>>>> throughout the cycle
>>>>
>>> how do you average? It seems the pulsations nicely  repeat and problem
>>> is in the averaging procedure.
>>> If you are not averaging, but want to look at radius at some specific
>>> pulsation phase, then you need to interpolate, as RSP time steps are not
>>> synchronised with pulsation phase.
>>> Radek
>>>
>>>
>>> wt., 21 sty 2020 o 21:01 Jeremy Sakstein <sakstein at hawaii.edu>
>>> napisał(a):
>>>
>>>> I think it does alternate. Here is a zoom in over 20 cycles:
>>>>
>>>> [image: image.png]
>>>>
>>>> Here is a plot with 3 alternating cycles:
>>>>
>>>> [image: image.png]
>>>>
>>>> The three colours correspond to the different cycles so with the
>>>> exception of the number/position of data points it appears the plots are
>>>> identical. Here's the radius, which also looks identical:
>>>>
>>>> [image: image.png]
>>>>
>>>> I'm not using the time-steps at all. I made these points by picking out
>>>> the data points where the pulsation cycle (rsp_num_periods) is fixed to
>>>> some value.
>>>>
>>>>
>>>> On Tue, Jan 21, 2020 at 9:47 AM Radek Smolec <smolec at camk.edu.pl>
>>>> wrote:
>>>>
>>>>> So does it alterante between two values?
>>>>> Can you attach a plot of a few consecutive pulsation cycles, maybe
>>>>> with zoom at radii maxima or minima?
>>>>> If you get alteranating values of average radius the consecutive
>>>>> pulsation cycles must differ.
>>>>>
>>>>> One other idea, do you interpolate for start of the pulsation cycle?
>>>>> If you use the time steps as used by rsp, without interpolation, then some
>>>>> scatter in the averaged radius is possible (but likely not alternations).
>>>>> Radek
>>>>>
>>>>>
>>>>> wt., 21 sty 2020 o 20:39 Jeremy Sakstein <sakstein at hawaii.edu>
>>>>> napisał(a):
>>>>>
>>>>>> Hi Both,
>>>>>>
>>>>>> I don't think it's periodu doubling because I just see a single
>>>>>> harmonic when I plot the light curves.
>>>>>>
>>>>>> Sorry to be unclear. I am plotting the average stellar (surface)
>>>>>> radius for each pulsation cycle.
>>>>>>
>>>>>> On Tue, Jan 21, 2020 at 9:37 AM Radek Smolec via Mesa-users <
>>>>>> mesa-users at lists.mesastar.org> wrote:
>>>>>>
>>>>>>> Hi Jeremy,
>>>>>>>
>>>>>>> It is difficult to guess what is happening without more detailed
>>>>>>> information. The effect you describe may be physical: for example
>>>>>>> low-amplitude period doubling phenomenon may be present in your model and
>>>>>>> then averages for even and odd pulsation cycles will differ.
>>>>>>> With such large difference you should be able to figure it out
>>>>>>> simply looking at the light or radius variation curve.
>>>>>>>
>>>>>>> For the general point; what you consider as "true equilibriu model"?
>>>>>>> RSP starts from equilibrium model, but it doesn't mean that the linear
>>>>>>> properties of the model, such as pulsation period, will not change when
>>>>>>> model pulsates at full amplitude.
>>>>>>> It is best to develop own procedures for computing such quantities
>>>>>>> as mean magnitude, radius, etc.
>>>>>>> Cheers,
>>>>>>> Radek
>>>>>>>
>>>>>>>
>>>>>>> wt., 21 sty 2020 o 20:20 Jeremy Sakstein <sakstein at sas.upenn.edu>
>>>>>>> napisał(a):
>>>>>>>
>>>>>>>> Hi Everyone,
>>>>>>>>
>>>>>>>> I have a quick question about finding the equilibrium values of the
>>>>>>>> stellar parameters when using RSP Cepheid.
>>>>>>>>
>>>>>>>> At the moment, I am taking a single pulsation cycle and averaging
>>>>>>>> over the radius throughout the cycle but this seems to give me two (very
>>>>>>>> closely separated values).
>>>>>>>>
>>>>>>>> Below I am plotting radius vs pulsation number. As you can see, I
>>>>>>>> end up with two very closely separated values for the average. Is this
>>>>>>>> because the model is changing ever so slightly between pulsations? If so,
>>>>>>>> why does it converge to two values and not a small scatter about the mean?
>>>>>>>>
>>>>>>>> [image: image.png]
>>>>>>>>
>>>>>>>> On a more general point, is it possible to extract the true
>>>>>>>> equilibrium model from the output rather than taking an average?
>>>>>>>>
>>>>>>>> Cheers,
>>>>>>>>
>>>>>>>> Jeremy
>>>>>>>> _______________________________________________
>>>>>>>> mesa-users at lists.mesastar.org
>>>>>>>> https://lists.mesastar.org/mailman/listinfo/mesa-users
>>>>>>>>
>>>>>>>> _______________________________________________
>>>>>>> mesa-users at lists.mesastar.org
>>>>>>> https://lists.mesastar.org/mailman/listinfo/mesa-users
>>>>>>>
>>>>>>>
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