Spitzer mid-ir spectra of dust debris around a and late b type stars: Asteroid belt analogs and power-law dust distributions

Farisa Y. Morales, M. W. Werner, G. Bryden, P. Plavchan, K. R. Stapelfeldt, G. H. Rieke, K. Y.L. Su, C. A. Beichman, C. H. Chen, K. Grogan, S. J. Kenyon, A. Moro-Martin, S. Wolf

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56 Scopus citations

Abstract

Using the Spitzer/Infrared Spectrograph (IRS) low-resolution modules covering wavelengths from 5 to 35 μm, we observed 52 main-sequence A and late B type stars previously seen using Spitzer/Multiband Imaging Photometer (MIPS) to have excess infrared emission at 24 μm above that expected from the stellar photosphere. The mid-IR excess is confirmed in all cases but two. While prominent spectral features are not evident in any of the spectra, we observed a striking diversity in the overall shape of the spectral energy distributions. Most of the IRS excess spectra are consistent with single-temperature blackbody emission, suggestive of dust located at a single orbital radius - a narrow ring. Assuming the excess emission originates from a population of large blackbody grains, dust temperatures range from 70 to 324 K, with a median of 190 K corresponding to a distance of 10 AU. Thirteen stars however, have dust emission that follows a power-law distribution, F ν = F 0λα, with exponent α ranging from 1.0 to 2.9. The warm dust in these systems must span a greater range of orbital locations - an extended disk. All of the stars have also been observed with Spitzer/MIPS at 70 μm, with 27 of the 50 excess sources detected (signal-to-noise ratio > 3). Most 70 μm fluxes are suggestive of a cooler, Kuiper Belt-like component that may be completely independent of the asteroid belt-like warm emission detected at the IRS wavelengths. Fourteen of 37 sources with blackbody-like fits are detected at 70 μm. The 13 objects with IRS excess emission fit by a power-law disk model, however, are all detected at 70 μm (four above, three on, and six below the extrapolated power law), suggesting that the mid-IR IRS emission and far-IR 70 μm emission may be related for these sources. Overall, the observed blackbody and power-law thermal profiles reveal debris distributed in a wide variety of radial structures that do not appear to be correlated with spectral type or stellar age. An additional 43 fainter A and late B type stars without 70 μm photometry were also observed with Spitzer/IRS; results are summarized in Appendix B.

Original languageEnglish (US)
Pages (from-to)1067-1086
Number of pages20
JournalAstrophysical Journal
Volume699
Issue number2
DOIs
StatePublished - Jan 1 2009

Keywords

  • Circumstellar matter
  • Infrared: stars
  • Planetary systems: formation

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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    Morales, F. Y., Werner, M. W., Bryden, G., Plavchan, P., Stapelfeldt, K. R., Rieke, G. H., Su, K. Y. L., Beichman, C. A., Chen, C. H., Grogan, K., Kenyon, S. J., Moro-Martin, A., & Wolf, S. (2009). Spitzer mid-ir spectra of dust debris around a and late b type stars: Asteroid belt analogs and power-law dust distributions. Astrophysical Journal, 699(2), 1067-1086. https://doi.org/10.1088/0004-637X/699/2/1067