Riess, Adam G.Filippenko, Alexei V.Liu, Michael C.Challis, PeterClocchiatti, AlejandroDiercks, AlanGarnavich, Peter M.Hogan, Craig J.Jha, SaurabhKirshner, Robert P.Leibundgut, B.Phillips, M. M.Reiss, DavidSchmidt, Brian P.Schommer, Robert A.Smith, R. ChrisSpyromilio, J.Stubbs, ChristopherSuntzeff, Nicholas B.Tonry, JohnWoudt, PatrickBrunner, Robert J.Dey, ArjunGal, RoyGraham, JamesLarkin, JamesOdewahn, Steve C.Oppenheimer, Ben2019-09-252000Riess, Adam G., Alexei V. Filippenko, Michael C. Liu, Peter Challis, Alejandro Clocchiatti, Alan Diercks, Peter M. Garnavich, et al. 2000. “Tests of the Accelerating Universe with Near‐Infrared Observations of a High‐Redshift Type Ia Supernova.” The Astrophysical Journal 536 (1): 62–67. https://doi.org/10.1086/308939.0004-637X1538-4357http://nrs.harvard.edu/urn-3:HUL.InstRepos:41399860We have measured the rest-frame B-, V-, and I-band light curves of a high-redshift type Ia supernova (SN 1a), SN 1999Q (z = 0.46), using the Hubble Space Telescope (HST) and ground-based near-infrared detectors. A goal of this study is the measurement of the color excess, E(B-I), a sensitive indicator of interstellar or intergalactic dust, which could affect recent cosmological measurements from high-redshift SNe Ia. Our observations disfavor a 30% opacity of SN Ia visual light by dust as an alternative to an accelerating universe. This statement applies to both Galactic-type dust (rejected at the 3.4 sigma confidence level) and grayer dust (grain size > 0.1 mu m, rejected at the 2.3-2.6 sigma confidence level) as proposed by Aguirre. The rest-frame I-band light curve shows the secondary maximum 1 month after the B maximum typical of nearby SNe fa of normal luminosity, providing no indication of evolution as a function of redshift out to z approximate to 0.5. An expanded set of similar observations could improve the constraints on any contribution of extragalactic dust to the dimming of high-redshift SNe Ia.en-USJournal Article2019-09-2510.1086/308939