# # Program information file # PROGRAM_ID 2023B074 PROGRAM_TITLE Optical-Infrared Spectroscopic Extinction Curves in the Diffuse Interstellar Medium PROGRAM_INV1 Kenji Emerson PROGRAM_INV2 Adwin Boogert PROGRAM_INV3 PROGRAM_INV4 PROGRAM_INV5 PROGRAM_SCICAT galactic/interstellar medium PROGRAM_ABSTRACT_BEG Interstellar extinction curves are a prime diagnostic of the properties of dust grains in the interstellar medium [ISM]. They reflect the grain size and composition distributions and are thus a tool to measure grain growth and destruction. The growth of grains from the diffuse to dense medium and protoplanetary disks is a key topic in astronomy. Also, extinction curves are needed to correct for foreground extinction in many areas of astronomy. Extinction curves are usually measured using broad-band photometry of OB stars. The lack of resolving power limits the accuracy of the photospheric continuum and line absorption correction. The few studies that measure extinction curves spectroscopically focus on subsets of the optical-infrared wavelength range. We propose to fill this gap by observing spectroscopic extinction curves across the full optical and infrared [0.4-4 micron]. We will implement stricter target selection criteria than before. We also propose to extend the sample to later spectral types, enabling the tracing of a wider range of ISM environments. We propose to use IRTF/SpeX SXD and LXD_short to obtain the infrared spectra [0.7-4.0 micron] of reddened stars [E[B-V]=0.08-1.46; A[V]=0.25-4.5 mag]. This will be complemented by a UH88/SNIFS proposal for the optical [0.4-1.0 micron] spectra. To correct for the intrinsic stellar spectra, we also propose to observe stars of similar spectral types at low extinction. We will compare our extinction curves of the diffuse ISM to models from the literature to link the observed variations to grain size distribution variations, and thus grain growth and destruction scenarios. In future work we will propose to extend this to dense cloud and shocked sightlines, tracing the paths of grain growth and destruction. PROGRAM_ABSTRACT_END