Frequencies Comparison - Task 2

2005©MJM | 2007-01-08

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Task 2

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In this task we aim at testing, comparing and optimising the seismic codes used to calculate the oscillations of models for different types of stars. In order to do so we consider steps in the comparison by addressing some of the most relevant items that must be compared regarding the seismic characterisation of the models:

• Step 1: comparison of the frequencies from different seismic codes for the same model.
• Step 2: comparison of the frequencies from different seismic codes for different models of the same stellar case.
• Step 3: comparison of the frequencies for specific pulsators.

The details and data for each step is given below. Please send us your results.

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Step 1: Frequencies for a specific model

In this task a stellar model is made available in several file formats in order to allow all seismic codes to be able calculate the frequencies. The compressed model files are available for download in the following formats: OSC, FGONG, SROX, FAMDL.

The assumptions to be used in the calculation are:

• to consider linear adiabatic oscillations,
• at the outermost mesh point the lagrangian perturbation of pressure is zero,
• no changes to the model mesh are introduced for calculating the frequencies.

A small report on each code being used would also be very useful if it is not yet available in our list.

The comparisons being organized are the following:

1a) Frequency comparison for a single model  -  done!

The participants with access to a seismic code are asked to calculate, before the 23^rd of November 2005, the full spectrum for frequencies from 100μHz to 4000μHz and mode degree l = 0, 1, 2 and 3. Some of the results of this exercise are available as:

• Data produced by the participants for this comparison,
• presentations and posters shown at the CoRoT Week 9.

1b) Frequency comparison for different meshes
The participants with access to a seismic code are asked to calculate the full spectrum for frequencies from 20μHz to 2500μHz and mode degree l = 0, 1, 2 and 3 (g and p modes). For this exercise please see the following directories for the
• models and frequencies,
• results.

Please send an email to Andy Moya and Mário Monteiro (please replace * by @ in the addresses) with your contributions to these exercices.

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Step 2: Frequencies for the same stellar case

Under this step models, as calculated by different evolution codes, for the same stellar cases will be used in order to evaluate by how much the frequencies of oscillations may differ. For this step of the frequency comparison the models used in model comparison for each stellar case will be used.

Preliminary results have been presented at the CoRoT Week 9.

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Step 3: Frequencies for specific pulsators

Under this task a few specific, fully identified, stellar pulsators are proposed as the items to be compared. The goal is to quantify the uncertainty on the predicted oscillations for each particular case.

The proposed procedure is to calculate stellar models using different codes and to determine the seismic characteristics of these models using the available oscillations codes. Several combinations, as obtained by the options for evolution + seismic codes, can provide an estimation on the theoretical uncertainties for the oscillations of the pulsators being considered.

The stars to be modelled, and the frequency range to be calculated, have been identified by Andy Moya and are listed below.

Case	log (L/Lsun)	Teff	log g	Frequencies (μHz)	Models	Frequencies
γ Doradus	0.845	7200	4.24	[ 11, 22 ]
δ Scuti (FG Vir.)	1.109	7345	4.00	[ 70, 410 ]
SPB (HD 215573)	2.453	12 960	4.09	[ 5, 12 ]
β Ceph. (EN Lac.)	3.877	21 756	3.842	[ 55, 95 ]

 

The physical assumptions proposed as the reference for the calculation of the internal structure are the same as used for Task 1.