Some orders were also discarded because their fits were mediocre or uninformative. (2015) evolutionary tracks were calculated using BT-Settl photospheric spectra (Allard, 2014), which may introduce minor uncertainties when compared to results from the PHOENIX models used here.. Predictions for the wind mass-loss rates are, on average, slightly lower than the observations, which suggests that disk winds or X-winds may also contribute to the measured outflows. Absolute ages are usually inferred from comparisons between observed stellar properties and pre-main sequence evolutionary models, which are sensitive to stellar birthlines and the input physics that controls the contraction and internal heating. To understand their influence, we study the heavily-spotted weak-lined T-Tauri star LkCa 4 by searching for spectral signatures of radiation originating from the starspot or starspot groups. We also discuss how such a large spot could be interpreted, and suggest that even though LkCa 4 appears extreme, other young sources have similar characteristics. 18 0 obj The intra-grid-point spectra are “emulated” in a process similar but superior to interpolation since it seamlessly quantifies the uncertainty attributable to the coarsely sampled stellar intrinsic parameters (see Appendix of C15). The B−V color excess leads to an extinction AV=0.28±0.15 mag relative to main sequence colors, or 0.62±0.15 mag relative to pre-main sequence colors. In other words, most of the variance in a spectrum is attributable to temperature, assuming near-solar metallicity.

Grankin, 1998; Venuti et al., 2015; Koen, 2016). The TiO indices are also combined into a single TiO index by calculating the number of standard deviations each point is from the median value of the index and then averaging the standard deviation. It is estimated that roughly 10 percent of the final stellar mass, The results of a survey of excess optical continuum emission (veiling) in a sample of 35 K7-M1 pre-main-sequence stars in Taurus-Auriga are reported. Sources with such discrepancies have been seen previously, for example in Figures 4 and 5 in Bouvier & Appenzeller (1992).


The spectrum of LkCa 4 is well reproduced by a cool component of 2750 K covering 80% of the surface and a 4100 K component covering 20% of the surface.
Since 1992 the V band photometry has been as bright as 12.3 mag, which corresponds to a cool component fill factor of 65%, and as faint as 13.2 mag, or a cool component fill factor of 87%. Cool sunspots are associated with locally heightened magnetic fields on the sun, so synthetic spectral models employing negligible magnetic fields will fail to fit magnetic sensitive features.

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