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

van Belle, Gerard T. and von Braun, Kaspar and Ciardi, David R. and Pilyavsky, Genady and Buckingham, Ryan S. and Boden, Andrew F. and Clark, Catherine A. and Hartman, Zachary and van Belle, Gerald and Bucknew, William and Cole, Gary (2021) Direct Measurements of Giant Star Effective Temperatures and Linear Radii: Calibration against Spectral Types and V − K Color. Astrophysical Journal, 922 (2). Art. No. 163. ISSN 0004-637X. doi:10.3847/1538-4357/ac1687.

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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 V₀ − K₀ 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, V₀ − K₀ from 1.9 to 8.5. For the V₀ − K₀ = {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.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
van Belle, Gerard T.0000-0002-8552-158X
von Braun, Kaspar0000-0002-5823-4630
Ciardi, David R.0000-0002-5741-3047
Clark, Catherine A.0000-0002-2361-5812
Hartman, Zachary0000-0003-4236-6927
van Belle, Gerald0000-0001-7421-7526
Cole, Gary0000-0002-8041-5649
Additional Information:© 2021. The American Astronomical Society. Received 2021 April 17; revised 2021 July 14; accepted 2021 July 15; published 2021 November 29. We would like to graciously acknowledge productive discussions and helpful suggestions from Chengjie Xiong (Washington University); we also acknowledge and appreciate the helpful feedback from an anonymous referee. We have made extensive use of the SIMBAD database and the VizieR catalog access tool, operated by the CDS in Strasbourg, France (Ochsenbein et al. 2000). This research has made use of the AFOEV database, operated at CDS, France, and the GCPD database at the University of Lausanne, Switzerland (Mermilliod et al. 1997). This research has made use of NASA's Astrophysics Data System. Portions of this work were performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. As always, we caution users of the Palomar site to watch out for giant bumblebees in the sky. This work has made use of data from the European Space Agency (ESA) mission Gaia (, processed by the Gaia Data Processing and Analysis Consortium (DPAC; Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. Funding for this research has been generously provided in part by Lowell Observatory. This material is based upon work supported by the National Science Foundation (NSF) under grant No. AST-1212203 and NASA grant No. NNX13AF01G. This work was supported in part through a NASA grant awarded to the Arizona/NASA Space Grant Consortium and by the NSF Research Experiences for Undergraduates (REU) program. Facilities: PO:PTI - Palomar Testbed Interferometer, LO:0.8m. -
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Gaia Multilateral AgreementUNSPECIFIED
Arizona Space Grant ConsortiumUNSPECIFIED
Subject Keywords:Fundamental parameters of stars; Red giant stars; Stellar properties; Stellar radii; Calibration; Long baseline interferometers; Optical interferometry; Stellar masses; Interferometry; High angular resolution; Stellar effective temperatures; Flux calibration
Issue or Number:2
Classification Code:Unified Astronomy Thesaurus concepts: Fundamental parameters of stars (555); Red giant stars (1372); Stellar properties (1624); Stellar radii (1626); Calibration (2179); Long baseline interferometers (931); Optical interferometry (1168); Stellar masses
Record Number:CaltechAUTHORS:20211204-000110519
Persistent URL:
Official Citation:Gerard T. van Belle et al 2021 ApJ 922 163
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:112225
Deposited By: George Porter
Deposited On:06 Dec 2021 18:30
Last Modified:06 Dec 2021 18:30

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