By L. da Silva et al. (2006); T. S. Rodrigues et al. (2014, 2017)
What it does
PARAM compares the observed properties of a star with every point of a grid of stellar evolution models. The properties are the effective temperature and metallicity, optionally the large frequency separation and the frequency of maximum oscillation power, and magnitudes or parallax. Each point is weighted by its likelihood times a prior (an initial mass function and a flat star-formation history). The result is a probability distribution for mass, radius, surface gravity and age, and in later versions distance and extinction.
The method is by L. da Silva and colleagues (2006). T. S. Rodrigues and colleagues (2014, 2017) added the seismic and distance extensions and the use of model frequencies in place of scaling relations. A web interface is hosted by INAF, Osservatorio Astronomico di Padova.
How I used it
In my MSc thesis on the Ariel input catalogue (Chapters 5 and 6), I used PARAM for consistency tests on synthetic stars, those of a synthetic cluster and those along a single track, and to characterise 35 seismic Ariel targets. I compared the results with those of four other codes: BASTA, ASTFIT, AMP and YMCM. I assembled the model grid PARAM reads, from MESA tracks with GYRE oscillation frequencies, through a conversion toolkit (Sect. 5.2).
During my MSc research fellowship in the BreakStarS project (IA Porto, M. Cunha and team; FCT PTDC/FIS-AST/30389/2017), I implemented a routine that computes the small frequency separation from GYRE modes for the PARAM grid. The small separation is the spacing between neighbouring l = 0 and l = 2 modes, and it is sensitive to the stellar core and so to age.
The animation
The grid points come from a public grid of stellar isochrones computed with MESA. It stands in for the grid PARAM reads: PARSEC isochrones in the public web interface, and the MESA plus GYRE grid I assembled for my thesis. The comb is the real GYRE frequencies of one main-sequence model on the 1 solar-mass track behind Stellar Explorer (MESA and GYRE models run by R. Costa, IA Porto). The observed star is the Sun, with its measured temperature and seismic parameters.
The gold threads mark the small separation, the quantity my routine computed. The camera, the Gaussian envelope, the uncertainties, the prior and the model seismic parameters from scaling relations are drawn for display. The histograms show the method run on this display grid and are not PARAM output.