Photometric calibration of the Unistellar telescopes to the Johnson-Cousins System

Our purpose is to provide photometric data and tools to compute magnitudes from images obtained by Unistellar telescopes and enhance their usefulness to the broader astronomical community. To do so, we provide relationships transforming Unistellar complementary metal oxide semiconductor sensor Bayer filter bands (blue Be, green Ge, and red Re) to the Johnson-Cousins photometric system. To enable this calibration, stars with known spectra were observed with Unistellar telescopes by citizen scientists in the Unistellar Network. We obtained the zero-point magnitudes of the telescopes for each band by combining those spectra with the telescope sensor responses. Using the observations of 794 stars with known Johnson-Cousins magnitudes, we established the relations to transform the Unistellar magnitudes. The zero-point magnitudes and their associated errors for the three bands were derived. Polynomial expressions for the relation between the Unistellar colour Be−Re and the Johnson-Cousins magnitudes were obtained for stars with Unistellar colour −0.15<Be−Re<0.5. The uncertainties on these transformations increase linearly with the Re magnitude. These relations were applied to the observation of a type II supernova and an exoplanet transit, with the supernova example showing consistency with other published magnitudes but also demonstrating that narrow-line emission or absorption can bias the transformed magnitudes. Other limitations of the transformations were also identified, largely stemming from significant infrared contributions to all color channels and variability between individual telescope sensors. Nevertheless, the values and color relationships provided here can be used by professional and citizen astronomers alike to compute observed magnitudes and provide measurements in a standard system. This enhances the Unistellar Network’s ability to contribute accurate photometry to the astronomical community that can be easily and faithfully combined with measurements from other instruments.

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Publication Details

Journal
Journal of Astronomical Telescopes Instruments and Systems
Published
2025-04-29
DOI
https://doi.org/10.1117/1.jatis.11.2.028002
Primary Topic
Astronomy and Astrophysical Research
Type
article
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0.00

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article

Photometric calibration of the Unistellar telescopes to the Johnson-Cousins System

Tateki Goto, Daniel Potts, Chelsey Logan, John K. Bradley et al.
Journal of Astronomical Telescopes Instruments and Systems
Astronomy and Astrophysical Research
article

Photometric calibration of the Unistellar telescopes to the Johnson-Cousins System

Tateki Goto, Daniel Potts, Chelsey Logan, John K. Bradley, Georges Simard, Koichi Yamaguchi, Mario Billiani, E. Bonilla, M. Smallen, Haroon Ahmed Khan, Jennifer L. W. Siders, G. De Tommaso, S. G. Roux, Jean-Marie Laugier, George Dvorsky, Michael Mitchell, Bruce Parker, Bob Eramia, Kendra Sibbernsen, M.J.D. Rushton, Fadi Saibi, Michaël Gagnon, Ryuichi Kukita, Benjamin Mirwald, James Keen, Petri Kuossari, Bryan Tobias, Ruyi Xu, Thomas M. Esposito, Stefan Will, Eric Miny, Daniel O’Conner Peluso, T. Mueller, Bruno Guillet, Amaury Perrocheau, Scott Kardel, Olivier Clerget, Guillaume Blaclard, Margaret A. Loose, Matthieu Lauvernier, Patrick Huth, J. Theurer, Wai-Chun Yue, J. S. Perko, Christopher C. M. Kyba, David Koster, Martin Davy, J.W. Archer, Josh Chubb, Michael Sibbernsen, Ian Transom, John W. Pickering, Aad Verveen, Raymund John Ang, Darren A. Rivett, Michael Howard Meylan, F Gagnon, W. Golisch, Alain Lambert, Michael Primm, Masao Shimizu, Franck Marchis, Neil Yoblonsky, Ariel Graykowski, Ron Janetzke, Petri Tikkanen, Justus Randolph, Matthew Ryno, Barbara Wiart, Dana Adhis, Fabrice Mortecrette, Gerrit Dreise, Jiří Dvořáček, Kevin Borrot, Kevin Heider, Liouba Leroux, Roberto Poggiali, Sophie Saibi, Yvan Arnaud, Steven Adkinson, Keiichi Fukui, Frédéric Simard, Enner Chung, Dave Gary, Stephen Lawrence, Byungki Kim, Susan A. Lancelle, Robert Foster, Karen Fischer, Stéphan Latour, R. M. Blake, Markus Lorber, Michael Cunningham, E. Heinrich, Takaya Okada, Nicolas Delaunoy, Wataru Ono, Sebastian Knöfel, Arnoud Buurman, Van Ruckman, William Langvad, Baptiste Montoya, Yohann Lorand, Bryce Fifield, David Havell, David Swalander, Evante Garza-Licudine, Fabien Richardot, Isabelle Brocard, Ivan Venzor, Jericho Kuehl, Joseph Kornowski, Larissa Swalander, Laurent Millart, Alain Cagna, Lydia Tamez, Maik Schmalstich, Noémie Kuchler-Mayor, Andrew Wendelborn, Paul Heafner, Phil Yehle
article en

Abstract

Our purpose is to provide photometric data and tools to compute magnitudes from images obtained by Unistellar telescopes and enhance their usefulness to the broader astronomical community. To do so, we provide relationships transforming Unistellar complementary metal oxide semiconductor sensor Bayer filter bands (blue Be, green Ge, and red Re) to the Johnson-Cousins photometric system. To enable this calibration, stars with known spectra were observed with Unistellar telescopes by citizen scientists in the Unistellar Network. We obtained the zero-point magnitudes of the telescopes for each band by combining those spectra with the telescope sensor responses. Using the observations of 794 stars with known Johnson-Cousins magnitudes, we established the relations to transform the Unistellar magnitudes. The zero-point magnitudes and their associated errors for the three bands were derived. Polynomial expressions for the relation between the Unistellar colour Be−Re and the Johnson-Cousins magnitudes were obtained for stars with Unistellar colour −0.15<Be−Re<0.5. The uncertainties on these transformations increase linearly with the Re magnitude. These relations were applied to the observation of a type II supernova and an exoplanet transit, with the supernova example showing consistency with other published magnitudes but also demonstrating that narrow-line emission or absorption can bias the transformed magnitudes. Other limitations of the transformations were also identified, largely stemming from significant infrared contributions to all color channels and variability between individual telescope sensors. Nevertheless, the values and color relationships provided here can be used by professional and citizen astronomers alike to compute observed magnitudes and provide measurements in a standard system. This enhances the Unistellar Network’s ability to contribute accurate photometry to the astronomical community that can be easily and faithfully combined with measurements from other instruments.

Journal of Astronomical Telescopes Instruments and SystemsVol. 11(02)
Délégation Provence et Corse (FR), Search for Extraterrestrial Intelligence (US)
National Aeronautics and Space Administration, Gordon and Betty Moore Foundation, Nuclear Safety and Security Commission, Secretário de Ciência, Tecnologia e Ensino Superior, Governo do Estado de Parana
Affordable and clean energy
Openalex Percentile: Top 91%
Astronomy and Astrophysical Research
DOIOpen Access PDFOpenAlex
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