Day 722

Thursday.

1408.2825
Progress with the Prime Focus Spectrograph for the Subaru telescope: a massively multiplexed optical and near-infrared fiber spectrograph
Sugai, et al

The PSF is an optical/NIR multi-fiber spectrograph with 2394 science fibers, which are distributed in 1.3 degree diameter FoV at the Subaru 8.2m telescope.  The simultaneous wide wavelength coverage from 0.38 um to 1.26 um, with the resolving power of 3000, strengthens its ability to target 3 main survey programs: cosmology, galactic archaeology, and galaxy/AGN evolution.  A medium resolution mode with resolving power of 5000 for 0.71um to 0.89 um also will be available by simply exchanging dispersers.  PFS takes the role for the spectroscopic part of the Subaru Measurement of Images and Redshifts project, while Hyper Suprime-Cam works on the imaging part.  To transform the telescope plus WFC focal ratio, a 3-mm thick broad-band coated glass-molded micro lens is glued to each fiber tip.  A higher transmission fiber is selected for the longest part of the cable system, while one with a better FRD performance is selected for the fiber-positioned and fiber-slit components, given the more frequent fiber movements and tightly curved structure.  Each Fiber positioned consists of two stages of piezo-electric rotary motors.  Its engineering model has been produced and tested.  Fiber positioning will be performed iteratively by taking an image of artificially back-illuminated fibers with the Metrology camera located in the Cassegrain container.  The camera is carefully designed so that fiber position measurements are unaffected by small amounts of high spatial-frequency inaccuracies in WFC lens surface shapes.  Target light carried through the fiber system reaches one of four identical fast-Schmidt spectrograph modules, each with three arms.  Prototype VPH gratings have been optically tested.  CCD production is complete, with standard fully-depleted CCDs for red arms and more-challenging thinner fully-depleted CCDs with blue-optimized coating for blue arms.

1408.2832
Finding rocky asteroids around white dwarfs by their periodic thermal emission
Lin, Leob

Since old WDs are exceptionally dim, the contrast between the thermal emission of an orbiting object and a WD is dramatically enhanced compared to a MS host.  Furthermore, rocky object much smaller than the moon have no atmospheres and are tidally locked to the WD if they orbit near the Roche zone.  Show that this leads to temperature contrasts between the is day and night side of order unity that should lead to temporal variations in IR flux over an orbital period of 0.2 to 2 days.  Ground based telescopes could detect objects with a mass as small as 1% of the lunar mass M_L around Sirius B with a few hours of exposure.  JWST may be able to detect objects as small as 1e-3 M_L around most nearby WDs.  The tightest constraints will typically be placed on 12k K WDs, whose Roche zone coincides with the dust sublimation zone.  Constraining the abundance of minor planets around WDs as a function of their surface temperatures (and therefore age) provides a novel probe for the physics of planetary formation.