Title: The Interstellar Extinction Law & Dust Model in the Mid-Infrared 

　Speaker: Biwei Jiang (Beijing Normal University) 

　Time: Wednesday, 3:00pm, October 28th 

　Location: Lecture Hall, 3rd floor 

  Abstract: 

The mid-infrared (MIR) extinction law has already been widely studied. The MIR extinction law is found to be much flatter than the classical dust model derived from the UV/optical extinction curve. On the other hand, some studies claim that the MIR extinction law varies with sight-lines, e.g. with spiral arms or the Galactic longitude or environment. As previous studies are mostly based on stellar photometry, the uncertainty is induced when assuming a constant intrinsic colour for the selected extinction-tracer sample stars and brings about the uncertainty in the results. With the availability of stellar parameters (mainly Teff, log g and Z) from the APOGEE spectroscopic survey, the stellar intrinsic colours can be calculated with significantly higher accuracy than from photometry only. Based on this spectroscopically derived intrinsic colours, the MIR extinction law is revisited. The extinctions relative to the KS band are derived in the 2-24μm range, covering the photometric bands involved in the WISE, Spitzer/IRAC, Spitzer/MIPS and AKARI surveys. The derived extinction law agrees well with the WD01 dust model given RV=5.5. Furthermore, a dust model is constructed to explain the observed flat extinction curve in the mid-infrared while consistent with the UV/optical extinction curve. We found that the extinction from the UV to the mid-IR could be closely reproduced by a mixture of submicrometer-sized amorphous silicate dust, submicrometer-sized graphitic dust, and an addition of micrometer-sized dust.