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

Speaker: Biwei Jiang (BNU)

Time & place: Wednesday, 3:00pm, Oct. 28th, 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. 

Biog: Biwei obtained her undergraduate education at Beijing Normal University before moving to Beijing Astronomical Observatory (now NAOC) for her Masters degree. She went to Japan to complete her PhD, working on SiO maser observations of evolved stars at the Nobeyama Radio Observatory (National Astronomical Observatory of Japan). In 1997 Biwei returned to Beijing, first at NAOC and then, in 2002, to take up a professorship at Beijing Normal University. Her research interests span a wide range of topics from variable stars and Galactic structure, to dust and interstellar extinction.