The Open University ’ s repository of research publications and other research outputs Dust properties in the Galactic bulge

Context. It has been suggested that the ratio of total-to-selective extinction R V in dust in the interstellar medium differs in the Galactic bulge from its value in the local neighborhood. Aims. We attempt to test this suggestion. Methods. The mid-infrared hydrogen lines in 16 Galactic bulge PNe measured by the Spitzer Space Telescope are used to determine the extinction corrected Hβ flux. This is compared to the observed Hβ flux to obtain the total extinction at Hβ. The selective extinction is obtained from the observed Balmer decrement in these nebulae. The value of R V can then be found. Results. The ratio of total-to-selective extinction in the Galactic bulge is consistent with the value R V = 3.1, which is the same as has been found in the local neighborhood. Conclusions. The suggestion that R V is different in the Galactic bulge is incorrect. The reasons for this are discussed.