Monitor the bias in the 1x1, 1x2, 2x1, and 2x2 bin settings at gain=1, and 1x1 at gain = 4, to build up high-S/N superbiases and track the evolution of hot columns.
STIS Cycle 17 MAMA Dark Monitor
This proposal monitors the behavior of the dark current in each of the MAMA detectors.
The basic monitor takes two 1380s ACCUM darks each week with each detector. However, starting Oct 5, pairs are only included for weeks that the LRP has external MAMA observations planned. The weekly pairs of exposures for each detector are linked so that they are taken at opposite ends of the same SAA free interval. This pairing of exposures will make it easier to separate long and short term temporal variability from temperature dependent changes.
For both detectors, additional blocks of exposures are taken once every six months. These are groups of five 1314s FUV-MAMA Time-Tag darks or five 3x315s NUV ACCUM darks distributed over a single SAA-free interval. This will give more information on the brightness of the FUV MAMA dark current as a function of the amount of time that the HV has been on, and for the NUV MAMA will give a better measure of the short term temperature dependence.
Massive Star CSI: Has The Progenitor of SN2008S Vanished?
SN2008S in NGC6946 is the prototype of a new class of optical transients. Its luminosity was low for a Type II supernova, and the progenitor star was identified as a completely dust obscured log (L/Lsun)=4.5, T=440K massive star (~10 Msun) in archival Spitzer data. It is uncertain whether this is a new class of low-luminosity supernova (e.g. an electron capture supernova) or a new class of massive star outburst. The transient has now faded to the point where the source is again invisible in the optical. Near-IR detections are consistent with a somewhat hotter source, T~1200K, somewhat brighter than the progenitor and still fading at ~3 mag/year. Using two epochs of IRAC observations to constrain the mid-IR emission, and two epochs of HST H-band/J-band observations to constrain emission from cool stars, we will solve this mystery by either identifying and characterizing the surviving progenitor or ruling out its survival.
Illuminating the HI Structure of a Proto-cluster Region at z=2.84
We propose very deep intermediate-band Lyman alpha imaging in the field of a newly-discovered proto-cluster region surrounding the extremely luminous QSO HS1549+19 at z=2.844. The large structure, initially discovered in a spectroscopic survey of galaxies in fields surrounding the brightest QSOs at z=2.5-2.8, represents an ideal laboratory for studying the response of the intergalactic medium to a source of ionizing photons that exceeds the UV background by factors >1000. Within a single pointing of WFC3-UVIS there are already more
than 45 known Lyman alpha emitters, most of which are already spectroscopically confirmed, and at least 3 of which are giant ``Lyman alpha blobs''. Many of the objects have properties similar to those expected from the process of fluorescence, in which Lyman alpha emission is induced by the UV radiation field of the QSO in any HI gas that dense enough to remain partially self-shielded. Fortuitously, the F467M filter (Stromgren "b") in WFC3-UVIS is a perfect match to Lyman alpha at z=2.844. In combination with an equally deep broad-band continuum image, the observations will allow the construction of a Lyman alpha map tracing dense gas throughout the inner parts of a proto-cluster region at sub-kpc resolution. The ability to measure the spatial sub-structure and surface brightness distribution of Lya emission, relative to known protocluster galaxies and AGN, will illuminate the ?cosmic web'' in a dense region caught in a violent stage of formation.
WFC3 UVIS CCD Daily Monitor
The behavior of the WFC3 UVIS CCD will be monitored daily with a set of full-frame, four-amp bias and dark frames. A smaller set of 2Kx4K subarray biases are acquired at less frequent intervals throughout the cycle to support subarray science observations. The internals from this proposal, along with those from the anneal procedure (Proposal 11909), will be used to generate the necessary superbias and superdark reference files for the calibration pipeline (CDBS).