Abstract
Vega, the second brightest star in the northern hemisphere, serves as a primary spectral type standard1. Although its spectrum is dominated by broad hydrogen lines, the narrower lines of the heavy elements suggested slow to moderate rotation, giving confidence that the ground-based calibration of its visible spectrum could be safely extrapolated into the ultraviolet and near-infrared (through atmosphere models2), where it also serves as the primary photometric calibrator. But there have been problems: the star is too bright compared to its peers3 and it has unusually shaped absorption line profiles, leading some4,5 to suggest that it is a distorted, rapidly rotating star seen pole-on. Here we report optical interferometric observations that show that Vega has the asymmetric brightness distribution of the bright, slightly offset polar axis of a star rotating at 93 per cent of its breakup speed. In addition to explaining the unusual brightness and line shape peculiarities, this result leads to the prediction of an excess of near-infrared emission compared to the visible, in agreement with observations6,7. The large temperature differences predicted across its surface call into question composition determinations, adding uncertainty to Vega's age and opening the possibility that its debris disk8 could be substantially older than previously thought9,10.
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Interferometric observations of rapidly rotating stars
The Astronomy and Astrophysics Review Open Access 14 March 2012
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References
Morgan, W. W. & Keenan, P. C. Spectral classification. Annu. Rev. Astron. Astrophys. 11, 29–50 (1973)
Bohlin, R. C. & Gilliland, R. L. Hubble Space Telescope absolute spectrophotometry of Vega from the far-ultraviolet to the infrared. Astron. J. 127, 3508–3515 (2004)
Petrie, R. M. Spectroscopic absolute magnitudes of early-type stars from hydrogen absorption—a revision. Publ. Dominion Astrophys. Obs. 12, 317–338 (1964)
Gray, R. O. The spectroscopic and photometric effects of rotation in the A-type stars. J. R. Astron. Soc. Can. 82, 336–348 (1988)
Gulliver, A. F., Hill, G. & Adelman, S. J. Vega: A rapidly rotating pole-on star. Astrophys. J. 429, L81–L84 (1994)
Blackwell, D. E., Leggett, S. K., Petford, A. D., Mountain, C. M. & Selby, M. J. Absolute calibration of the infrared flux from Vega at 1.24, 2.20, 3.76 and 4.6 microns by comparison with a standard furnace. Mon. Not. R. Astron. Soc. 205, 897–905 (1983)
Leggett, S. K., Bartholomew, M., Mountain, C. M. & Selby, M. J. Narrow-band 1- to 5-µm photometry of A-type stars. Mon. Not. R. Astron. Soc. 223, 443–447 (1986)
Aumann, H. H. et al. Discovery of a shell around Alpha Lyrae. Astrophys J. 278, L23–L27 (1984)
Habing, H. J. et al. Disappearance of stellar debris disks around main-sequence stars after 400 million years. Nature 401, 456–458 (1999)
Song, I., Caillault, J.-P., y Navascués, D. B. & Stauffer, J. R. Ages of A-type Vega-like stars from uvbyβ photometry. Astrophys. J. 546, 352–357 (2001)
Thompson, R. A., Moran, J. & Swenson, G. Jr Interferometry and Synthesis in Radio Astronomy (Wiley-VCH, Weinhein, 2004)
Armstrong, J. T. et al. The Navy Prototype Optical Interferometer. Astrophys. J. 496, 550–571 (1998)
Jennison, R. C. A phase sensitive interferometer technique for the measurement of the Fourier transforms of spatial brightness distributions of small angular extent. Mon. Not. R. Astron. Soc. 118, 276–284 (1958)
Baldwin, J. E. et al. The first images from an optical aperture synthesis array: mapping of Capella with COAST at two epochs. Astron. Astrophys. 306, L13–L16 (1996)
von Zeipel, H. The radiative equilibrium of a slightly oblate rotating star. Mon. Not. R. Astron. Soc. 84, 684–701 (1924)
Hardorp, J. & Strittmatter, P. A. The effect of rotation on radiation from stars I. Properties of the continuum. Astrophys. J. 151, 1057–1073 (1968)
Peterson, D. M. et al. Resolving the effects of rotation in Altair with long-baseline interferometry. Astrophys. J. 636, 1087–1097 (2006)
Domiciano de Souza, A. et al. Gravitational-darkening of Altair from interferometry. Astron. Astrophys. 442, 567–578 (2005)
Ohishi, N., Nordgren, T. E. & Hutter, D. J. Asymmetric surface brightness distribution of Altair observed with the Navy Prototype Optical Interferometer. Astrophys. J. 612, 463–471 (2004)
Press, W. H., Flannery, B. P., Teukolsky, S. A. & Vetterling, W. T. Numerical Recipes in C 2nd edn (Cambridge Univ. Press, Cambridge, 1992)
Hill, G., Gulliver, A. F. & Adelman, S. J. in The A-Star Puzzle (eds Zverko, J., Ziznovsky, J., Adelman, S. J. & Weiss, W. W.) 35–42 (IAU Symp. 224, Cambridge Univ. Press, Cambridge, 2004)
Leggett, S. K. The flux distribution of Vega for the wavelength region from 10 to 100 microns, and the calibration of IRAS at 12 microns and 25 microns. Astron. Astrophys. 153, 273–277 (1985)
Bessel, M. S., Castelli, F. & Plez, B. Model atmospheres broad-band colors, bolometric corrections and temperature calibrations for O - M stars. Astron. Astrophys. 333, 231–250 (1998)
Su, K. Y. L. et al. The Vega debris disk: A surprise from Spitzer. Astrophys. J. 628, 487–500 (2005)
Collins, G. W. II Continuum emission from a rapidly rotating stellar atmosphere. Astrophys. J. 138, 1134–1146 (1963)
Girardi, L., Bressan, A., Bertelli, G. & Chiosi, C. Evolutionary tracks and isochrones for low- and intermediate-mass stars: From 0.15 to 7 M⊙, and from z = 0.0004 to 0.03. Astron. Astrophys. Suppl. 141, 371–383 (2000)
Castelli, F. & Kurucz, R. L. Model atmospheres for Vega. Astron. Astrophys. 281, 817–832 (1994)
Kurucz, R. L. ATLAS9 Stellar Atmospheres and 2 km/s Grid (CD-ROM No. 13, Smithsonian Astrophysical Observatory, Cambridge, MA, 1993); 〈http://kurucz.harvard.edu/cdroms.html〉
Van Hamme, W. New limb-darkening coefficients for modeling binary light curves. Astron. J. 106, 2096–2117 (1993)
Acknowledgements
We thank R. Kurucz for advice on calculating broadband fluxes using model atmospheres. The NPOI facility is a collaboration between the Naval Research Laboratory and the US Naval Observatory in association with Lowell Observatory, and is funded by the Office of Naval Research and the Oceanographer of the Navy. This research has made use of the SIMBAD literature database, operated at CDS, Strasbourg, France, and of NASA's Astrophysics Data System.
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Supplementary information
Supplementary Discussion
Contains Supplementary Information; Supplementary Figure S1; Supplementary Tables 1 and 2. (PDF 151 kb)
Supplementary Data
The full, calibrated closure phase data set for May 25, 2001 for Vega. Except for the first few lines, which give the format, this is machine readable. (TXT 14 kb)
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Peterson, D., Hummel, C., Pauls, T. et al. Vega is a rapidly rotating star. Nature 440, 896–899 (2006). https://doi.org/10.1038/nature04661
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DOI: https://doi.org/10.1038/nature04661
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