[Mesa-users] Question about RSP and equilibrium quantities

Tue Jan 21 15:53:13 EST 2020

Sorry, I meant using detached eclipsing binary methods not V-K.

On Tue, Jan 21, 2020 at 10:51 AM Jeremy Sakstein <sakstein at hawaii.edu>
wrote:

> 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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