Spectroscopic Bolometric Corrections and Empirical Zero-point Constants of Gaia Magnitudes, 𝐺 𝐺 , and 𝐺 , from Gaia XP Spectra P P

The International Astronomical Union 2015 Resolution B2 (IAU2015GARB2) has resolved the long-standing problem of zeropoint constants for the absolute and apparent bolometric magnitude scales and opened a new window in fundamental astrophysics. The empirical zero-point constants of the bolometric corrections, 𝐶2 (𝜉), and the absolute/apparent magnitudes, 𝐶𝜉 /𝑐 𝜉 , for the Gaia passbands were obtained from 88 Gaia XP spectra, and absolute bolometric/filtered magnitudes. The individual zero-pointconstants ⟨𝐶2⟩ of the bolometric corrections (𝐵𝐶𝜉 ) for each star revealed weighted averages of ⟨𝐶2 (𝐺)⟩ = 0.8677 ± 0.0109 mag, ⟨𝐶2 (𝐺BP)⟩ = 1.0449 ± 0.0116 mag, and ⟨𝐶2 (𝐺RP)⟩ = 2.0510 ± 0.0087 mag. Furthermore, 𝐶Bol = 71.197425... mag and 𝑐Bol = −18.997351...mag announced by IAU2015GARB2, and using the definition of 𝐶2 = 𝐶Bol − 𝐶𝜉 = 𝑐Bol − 𝑐 𝜉 ,where the subscript 2 indicate the wavelength ranges of two in which one is for bolometric and the other for one of the three filters, the zero-point constants of magnitudes for Gaia filters as 𝐶G = 70.1525 ± 0.0109 mag and 𝑐G = −19.8651 ± 0.0105 mag, 𝐶GBP = 70.1525±0.0116 mag and 𝑐GBP = −20.0423±0.0116 mag, and𝐶GRP = 69.1464±0.0087 mag and 𝑐GRP = −21.0484±0.0087 mag, if 𝐿𝜉 and 𝑓𝜉 are in SI units, assuming no extinction. Lastly, spectroscopic 𝐵𝐶s for Gaia magnitudes of 88 stars and the spectroscopic 𝐵𝐶 − 𝑇eff relation for each Gaia filter are presented.