Abstract
We present photometric detections of dust emission at 850 and 450 � m around the pre-main-sequence M1 dwarf TWA 7 using the SCUBA camera on the James Clerk Maxwell Telescope. These data confirm the presence of a cold dustdiskaroundTWA7,amemberoftheTWHydraeAssociation(TWA).Basedonthe850 � mflux,weestimatethe massof thedisktobe18Mlunar (0.2M� )assumingamassopacityof1.7cm 2 g � 1 withatemperatureof 45K.Thismakes the TWA 7 disk (d ¼ 55 pc) an order of magnitude more massive than the disk reported around AU Microscopii (GL 803),theclosest (9.9pc) debrisdiskdetectedaroundanM dwarf.ThisisconsistentwithTWA 7beingslightlyyounger than AU Mic. We find that the mid-IR and submillimeter data require the disk to be comprised of dust at a range of temperatures. A model in which the dust is at a single radius from the star, with a range of temperatures according to grain size, isas effective atfittingthe emissionspectrumas a model in whichthe dust isofuniform size, but has a range of temperatures according to distance. We discuss this disk in the context of known disks in the TWA and around lowmass stars; a comparison of masses of disks in the TWA reveals no trend in mass or evolutionary state (gas-rich vs. debris) as a function of spectral type. Subject headingg circumstellar matter — stars: individual (TWA 7) — stars: pre‐main-sequence — submillimeter
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