lightkurve.seismology.Seismology.estimate_logg

Seismology.estimate_logg(teff=None, numax=None)

Calculates the log of the surface gravity using the asteroseismic scaling relations.

The two global observable seismic parameters, numax and deltanu, along with temperature, scale with fundamental stellar properties (Brown et al. 1991; Kjeldsen & Bedding 1995). These scaling relations can be rearranged to calculate a stellar surface gravity as

g = gsol * (numax/numax_sol)(Teff/Teffsol)^0.5

where g is the surface gravity and Teff is the effective temperature, and the suffix ‘sol’ indicates a solar value. In this method we use the solar values for numax as given in Huber et al. (2011) and for Teff as given in Prsa et al. (2016). The solar surface gravity is calcluated from the astropy constants for solar mass and radius and does not have an error.

The solar surface gravity is returned as log10(g) with units in dex, as is common in the astrophysics literature.

This code structure borrows from work done in Bellinger et al. (2019), which also functions as an accessible explanation of seismic scaling relations.

If no value of effective temperature is given, this function will check the meta data of the Periodogram object used to create the Seismology object. These data will often contain an effective tempearture from the Kepler Input Catalogue (KIC, https://ui.adsabs.harvard.edu/abs/2011AJ….142..112B/abstract), or from the EPIC or TIC for K2 and TESS respectively. The temperature values in these catalogues are estimated using photometry, and so have large associated uncertainties (roughly 200 K, see KIC). For more better results, spectroscopic measurements of temperature are often more precise.

NOTE: These scaling relations are scaled to the Sun, and therefore do not always produce an entirely accurate result for more evolved stars.

Parameters
numaxfloat

The frequency of maximum power of the seismic mode envelope. If not given an astropy unit, assumed to be in units of microhertz.

tefffloat

The effective temperature of the star. In units of Kelvin.

numax_errfloat

Error on numax. Assumed to be same units as numax

teff_errfloat

Error on teff. Assumed to be same units as teff.

Returns
loggSeismologyQuantity

Stellar surface gravity estimate.