Variations of the interstellar extinction law within the nearest kiloparsec |
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| Authors: | G A Gontcharov |
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| Institution: | 1.Pulkovo Astronomical Observatory,Russian Academy of Sciences,St. Petersburg,Russia |
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| Abstract: | Multicolor photometry from the Tycho-2 and 2MASS catalogues for 11 990 OB and 30 671 K-type red giant branch stars is used
to detect systematic large-scale variations of the interstellar extinction law within the nearest kiloparsec. The characteristic
of the extinction law, the total-to-selective extinction ratio Rv, which also characterizes the size and other properties of interstellar dust grains, has been calculated for various regions
of space by the extinction law extrapolation method. The results for the two classes of stars agree: the standard deviation
of the “red giants minus OB” Rv differences within 500 pc of the Sun is 0.2. The detected Rv variations between 2.2 and 4.4 not only manifest themselves in individual clouds but also span the entire space near the
Sun, following Galactic structures. In the Local Bubble within about 100 pc of the Sun, Rv has a minimum. In the inner part of the Gould Belt and at high Galactic latitudes, at a distance of about 150 pc from the
Sun, Rv reaches a maximum and then decreases to its minimum in the outer part of the Belt and other directions at a distance of
about 500 pc from the Sun, returning to its mean values far from the Sun. The detected maximum of Rv at high Galactic latitudes is important when allowance is made for the interstellar extinction toward extragalactic objects.
In addition, a monotonic increase in Rv by 0.3 per kpc toward the Galactic center has been found near the Galactic equator. It is consistent with the result obtained
by Zasowski et al. (2009) for much of the Galaxy. Ignoring the Rv variations and traditionally using a single value for the entire space must lead to systematic errors in the calculated
distances reaching 10%. |
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