Abstract

The angular size of a star is a critical factor in determining its basic properties1. Direct measurement of stellar angular diameters is difficult: at interstellar distances stars are generally too small to resolve by any individual imaging telescope. This fundamental limitation can be overcome by studying the diffraction pattern in the shadow cast when an asteroid occults a star2, but only when the photometric uncertainty is smaller than the noise added by atmospheric scintillation3. Atmospheric Cherenkov telescopes used for particle astrophysics observations have not generally been exploited for optical astronomy due to the modest optical quality of the mirror surface. However, their large mirror area makes them well suited for such high-time-resolution precision photometry measurements4. Here we report two occultations of stars observed by the Very Energetic Radiation Imaging Telescope Array System (VERITAS)5 Cherenkov telescopes with millisecond sampling, from which we are able to provide a direct measurement of the occulted stars’ angular diameter at the ≤0.1 mas scale. This is a resolution never achieved before with optical measurements and represents an order of magnitude improvement over the equivalent lunar occultation method6. We compare the resulting stellar radius with empirically derived estimates from temperature and brightness measurements, confirming the latter can be biased for stars with ambiguous stellar classifications.

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Data availability

The datasets generated and/or analysed in this study are available from the corresponding authors on request.

Code availability

The computer code used to analyse the data in this study is available from the corresponding authors on request.

Additional information

Journal peer review information: Nature Astronomy thanks Gerard van Belle, Andrea Richichi and Ellyn Baines for their contribution to the peer review of this work.

Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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Acknowledgements

This research is supported by grants from the US Department of Energy Office of Science, the US National Science Foundation and the Smithsonian Institution, by NSERC in Canada, and by the Young Investigators Program of the Helmholtz Association. We acknowledge the excellent work of the technical support staff at the Fred Lawrence Whipple Observatory and at the collaborating institutions in the construction and operation of the instrument. This work has made use of data and updates by S. Preston from http://www.asteroidoccultation.com; data from the JPL Small-Body Database browser at http://ssd.jpl.nasa.gov; data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortium); and the SIMBAD database, operated at CDS, Strasbourg, France. The authors acknowledge discussions with S. Cikota and J. Cortina.

Author information

Author notes

    • D. Nieto

    Present address: Facultad de Ciencias Físicas and IPARCOS, Universidad Complutense de Madrid, Madrid, Spain

    • C. Rulten

    Present address: Department of Physics, University of Durham, Durham, UK

Affiliations

  1. Center for Astrophysics | Harvard & Smithsonian, Fred Lawrence Whipple Observatory, Amado, AZ, USA

    • W. Benbow
    • , M. K. Daniel
    • , G. Hughes
    •  & E. Roache
  2. Department of Physics and Astronomy, University of California, Los Angeles, CA, USA

    • R. Bird
    •  & R. A. Ong
  3. Department of Astronomy / Department of Physics, Columbia University, New York, NY, USA

    • A. Brill
    • , Q. Feng
    • , J. P. Halpern
    • , T. B. Humensky
    • , D. Nieto
    •  & A. Petrashyk
  4. Institute of Physics and Astronomy, University of Potsdam, Potsdam-Golm, Germany

    • R. Brose
    • , M. Pohl
    • , I. Sushch
    •  & A. Wilhelm
  5. DESY, Zeuthen, Germany

    • R. Brose
    • , C. Giuri
    • , O. Gueta
    • , T. Hassan
    • , N. Kelley-Hoskins
    • , M. Krause
    • , G. Maier
    • , M. Nievas-Rosillo
    • , M. Pohl
    • , E. Pueschel
    • , I. Sadeh
    •  & A. Wilhelm
  6. Department of Physics and Astronomy, Iowa State University, Ames, IA, USA

    • A. J. Chromey
    •  & R. M. Wells
  7. Department of Physics and Astronomy, Purdue University, West Lafayette, IN, USA

    • J. P. Finley
    •  & G. H. Sembroski
  8. School of Physics and Astronomy, University of Minnesota, Minneapolis, MN, USA

    • L. Fortson
    • , C. Rulten
    •  & K. Shahinyan
  9. Department of Physics, California State University, East Bay, Hayward, CA, USA

    • A. Furniss
  10. School of Physics, National University of Ireland Galway, Galway, Ireland

    • G. H. Gillanders
    • , A. M. Joyce
    • , M. J. Lang
    •  & P. Moriarty
  11. Physics Department, McGill University, Montreal, Quebec, Canada

    • D. Hanna
    • , T. T. Y. Lin
    • , S. O’Brien
    •  & K. Ragan
  12. Department of Physics and Astronomy and the Bartol Research Institute, University of Delaware, Newark, DE, USA

    • J. Holder
    • , G. T. Richards
    •  & T. J. Williamson
  13. Department of Physics and Astronomy, University of Iowa, Iowa City, IA, USA

    • P. Kaaret
    •  & P. Wilcox
  14. Department of Physics and Astronomy, University of Utah, Salt Lake City, UT, USA

    • P. Kar
    • , D. Kieda
    •  & N. Matthews
  15. Department of Physics and Astronomy, DePauw University, Greencastle, IN, USA

    • M. Kertzman
  16. Department of Physics and Astronomy, Barnard College, Columbia University, New York, NY, USA

    • R. Mukherjee
  17. School of Physics, University College Dublin, Dublin, Ireland

    • S. O’Brien
    •  & J. Quinn
  18. WIPAC and Department of Physics, University of Wisconsin-Madison, Madison, WI, USA

    • N. Park
  19. Department of Physical Sciences, Cork Institute of Technology, Cork, Ireland

    • P. T. Reynolds
  20. Department of Physics and Astronomy, University of Alabama, Tuscaloosa, AL, USA

    • M. Santander
  21. Enrico Fermi Institute, University of Chicago, Chicago, IL, USA

    • S. P. Wakely
  22. Santa Cruz Institute for Particle Physics and Department of Physics, University of California, Santa Cruz, CA, USA

    • D. A. Williams

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Contributions

All authors contributed equally to the operation of the VERITAS telescopes. M.K.D. conceived the enhanced current monitor system used in these observations; T.H. proposed the occultation observations; A.M.J., D.A.W., T.J.W., J.Q. and A.B. took the observations; M.K.D., T.H. and N.M. reduced and analysed the data; M.K.D. and T.H. wrote the main paper and Methods.

Competing interests

The authors declare no competing interests.

Corresponding authors

Correspondence to M. K. Daniel or T. Hassan.

About this article

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DOI

https://doi.org/10.1038/s41550-019-0741-z