[yt-users] Tipsy Stellar Ages

B.W. Keller kellerbw at mcmaster.ca
Mon Mar 30 11:38:35 PDT 2015


I created that dataset, and yes, the stars have ages that are in the future
(gasoline uses stellar ages to determine feedback rates, so stars with ages
in the future will not do any feedback, which I needed for the experiment
that dataset came from). Sorry for the confusion.
On Mar 30, 2015 2:33 PM, "Desika Narayanan" <dnarayan at haverford.edu> wrote:

> Hey Nathan,
>
> This is great - thanks!
>
> -d
>
>
> On Mon, Mar 30, 2015 at 2:24 PM, Nathan Goldbaum <nathan12343 at gmail.com>
> wrote:
>
>>
>> On Mon, Mar 30, 2015 at 11:10 AM, Desika Narayanan <
>> dnarayan at haverford.edu> wrote:
>>
>>> Hi All,
>>>
>>> I'm trying to understand some of the stellar ages that the Tipsy example
>>> data (the isolated galaxy) at:
>>>
>>> http://yt-project.org/data/
>>>
>>> When I examine the formation time with the super-simple script:
>>>
>>> http://paste.yt-project.org/show/5501/
>>>
>>> I get:
>>>
>>> max star age:  100.000499852 Gyr
>>>
>>> I thought normally the formation time was the current simulation time
>>> minus the stellar age for Tipsy outputs - am I interpreting this wrongly?
>>>
>>>
>>>
>> Hi Desika,
>>
>> I encountered this before.  Take a look at the following section of the
>> docs, which makes use of this dataset:
>>
>>
>> http://yt-project.org/docs/dev/analyzing/filtering.html#filtering-particle-fields
>>
>> I don't have a copy of gasoline to confirm this, but the conclusion I
>> came to is that the stars in the initial conditions for this simulation
>> were given a creation time arbitrarily far in the future, generating
>> spurious stellar ages.
>>
>> If you instead define particle filters for formed stars like so:
>>
>> def young_stars(pfilter, data):
>>     age = data.ds.current_time - data[pfilter.filtered_type,
>> "creation_time"]
>>     filter = np.logical_and(age.in_units('Myr') <= 5, age >= 0)
>>     return filter
>>
>> def old_stars(pfilter, data):
>>     age = data.ds.current_time - data[pfilter.filtered_type,
>> "creation_time"]
>>     filter = np.logical_or(age.in_units('Myr') >= 5, age < 0)
>>     return filter
>>
>> where I've arbitrarily chosen 5 Myr as the cutoff for old stars and young
>> stars, you'll find that your results make more sense.
>>
>> HTH,
>>
>> Nathan
>>
>>> Thanks,
>>> desika
>>>
>>>
>>>
>>>
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