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How Do Spitzer IRAC Fluxes Compare to HST CALSPEC?

Bohlin, Ralph C. and Krick, Jessica E. and Gordon, Karl D. and Hubeny, Ivan (2022) How Do Spitzer IRAC Fluxes Compare to HST CALSPEC? Astronomical Journal, 164 (1). Art. No. 10. ISSN 0004-6256. doi:10.3847/1538-3881/ac6fe1.

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An accurate tabulation of stellar brightness in physical units is essential for a multitude of scientific endeavors. The HST/CALSPEC database of flux standards contains many stars with spectral coverage in the 0.115–1 μm range, with some extensions to longer wavelengths of 1.7 or 2.5 μm. Modeled flux distributions to 32 μm for calibration of JWST complement the shorter-wavelength HST measurements. Understanding the differences between IRAC observations and CALSPEC models is important for science that uses IR fluxes from multiple instruments, including JWST. The absolute flux of Spitzer IRAC photometry at 3.6–8 μm agrees with CALSPEC synthetic photometry to 1% for the three prime HST standards: G191B2B, GD153, and GD71. For a set of 17–22 A-star standards, the average IRAC difference rises from agreement at 3.6 μm to 3.4% ± 0.1% brighter than CALSPEC at 8 μm. For a smaller set of G-type stars, the average of the IRAC photometry falls below CALSPEC by as much as 3.7% ± 0.3% for IRAC1, while one G-type star, P330E, is consistent with the A-star ensemble of IRAC/CALSPEC ratios.

Item Type:Article
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URLURL TypeDescription Paper
Bohlin, Ralph C.0000-0001-9806-0551
Krick, Jessica E.0000-0002-2413-5976
Gordon, Karl D.0000-0001-5340-6774
Hubeny, Ivan0000-0001-8816-236X
Additional Information:© 2022. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Received 2022 February 18; revised 2022 May 11; accepted 2022 May 13; published 2022 June 15. Support for this work was provided by NASA through the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS5-26555. This work is based on observations made with the Spitzer Space Telescope, which was operated by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Subject Keywords:Flux calibration; Spectrophotometric standards; Infrared photometry
Issue or Number:1
Classification Code:Unified Astronomy Thesaurus concepts: Flux calibration (544); Spectrophotometric standards (1555); Infrared photometry (792)
Record Number:CaltechAUTHORS:20220722-769540000
Persistent URL:
Official Citation:Ralph C. Bohlin et al 2022 AJ 164 10
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:115798
Deposited By: George Porter
Deposited On:22 Jul 2022 21:13
Last Modified:02 Aug 2022 16:32

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