Direct Measurements of Giant Star Effective Temperatures and Linear Radii: Calibration against Spectral Types and V − K Color

Abstract

We calculate directly determined values for effective temperature (T eff) and radius (R) for 191 giant stars based upon high-resolution angular size measurements from optical interferometry at the Palomar Testbed Interferometer. Narrow- to wideband photometry data for the giants are used to establish bolometric fluxes and luminosities through spectral energy distribution fitting, which allows for homogeneously establishing an assessment of spectral type and dereddened V 0 − K 0 color; these two parameters are used as calibration indices for establishing trends in T eff and R. Spectral types range from G0III to M7.75III, V 0 − K 0 from 1.9 to 8.5. For the V 0 − K 0 = {1.9, 6.5} range, median T eff uncertainties in the fit of effective temperature versus color are found to be less than 50 K; over this range, T eff drops from 5050 to 3225 K. Linear sizes are found to be largely constant at 11 R ⊙ from G0III to K0III, increasing linearly with subtype to 50 R ⊙ at K5III, and then further increasing linearly to 150 R ⊙ by M8III. Three examples of the utility of this data set are presented: first, a fully empirical Hertzsprung–Russell diagram is constructed and examined against stellar evolution models; second, values for stellar mass are inferred based on measures of R and literature values for log g ; finally, an improved calibration of an angular size prediction tool, based upon V and K values for a star, is presented.

Simultaneous Six-way Observations from the Navy Precision Optical Interferometer

“…In order to determine each star's luminosity (L) and T eff , we generated SED fits using photometric values published in Johnson et al (1966), Golay (1972), Johnson & Mitchell (1975), Oja (1984), Mermilliod (1987), Helou & Walker (1988), Beichman et al (1988), Mermilliod & Nitschelm (1989), Mermilliod (2006), Gezari et al (1993), Oja (1993), Gezari et al (1999), Høg et al (2000), Ducati (2002), Cutri et al (2003), Smith et al (2004), andvan Leeuwen (2007). The assigned uncertainties for the 2MASS infrared measurements are as reported in Cutri et al (2003), and an uncertainty of 0.05 mag was assigned to the optical measurements.…”

The recurrent nova V3890 Sgr: a near-infrared and optical study of the red giant component and its environment

“…The secondary star in V3890 Sgr has been variously classified as M8 III (Williams et al 1991) andM5 III (Harrison, Johnson &Spyromilio 1993;Anupama & Miko lajewska 1999); the observations on which these classifications were based were carried out before (Williams et al 1991) and after (Harrison et al 1993;Anupama & Miko lajewska 1999) the 1990 eruption. The effective temperature corresponding to these classifications ranges from T eff ∼ 3100 K to ∼ 3400 K (see, e.g., van Belle et al 2021).…”

Gaia FGK benchmark stars: Fundamental Teff and log g of the third version

“…We took advantage of recent interferometric studies that provided new measurements of angular diameters for large samples of stars (e.g. Ligi et al 2016;Baines et al 2018Baines et al , 2021van Belle et al 2021) and for metal-poor stars (e.g. Creevey et al 2015;Karovicova et al 2018Karovicova et al , 2020.…”