changed to cycle 21 240844882 ----- Attempting Submission 7 (Fri Sep 05 17:09:59 GMT 2014) ----- SPIRITS--the SPitzer InfraRed Intensive Transients Survey--is an ongoing search for mid-IR (MIR) variables and transients in nearly 200 nearby galaxies, being carried out with the warm Spitzer telescope at 3.6 and 4.5 microns. It is the first large-scale search for luminous MIR transients in the local universe. Among the many variables that SPIRITS has discovered is a puzzling new class of luminous MIR transients which lack conspicuous optical, or in most cases even near-IR, counterparts in our deepest ground-based followup images. We suggest the name SMIRTs for these objects--Spitzer Mid-IR Transients. The luminosities of SMIRTs exceed those of classical novae, but they are not as bright as any known classes of supernovae. Lying in spiral arms, they appear to be associated with young populations. The properties of SMIRTs are somewhat similar to the recently discovered, but still mysterious, class of intermediate-luminosity red transients, as well as LBVs and "supernova impostors." However, these known types of objects all have bright optical counterparts. We propose a small program of HST imaging, using the WFC3 IR channel at J and H, and the WFC3 UVIS channel at I, to explore the nature of SMIRTs. We have selected 2 representatives, all in outburst at the time of writing, with a range of eruption timescales. Both have archival pre-explosion HST optical imaging, and one also has archival WFC3/IR. Our aims are: search for faint optical and NIR counterparts while they are still in eruption; extend the SEDs to shorter wavelengths to refine dust temperatures and search for faint photospheres/outflows; and attempt to identify progenitor stars in the archival HST images. For both of the two targets, we will devote one HST orbit each to imaging with the WFC3 UVIS and IR channels. We will use 3-point dither patterns and the UVIS F814W filter and the IR F110W and F160W filters. COOL STARS Default false false false false false SUPPORTED EXT-STAR CIRCUMSTELLAR MATTER EJECTA IRREGULAR VARIABLE NOVA-LIKE SUPERNOVA J2000 J2000 EXT-STAR CIRCUMSTELLAR MATTER EJECTA IRREGULAR VARIABLE NOVA-LIKE SUPERNOVA J2000 J2000 WFC3/UVIS Imaging No No F814W WFC3/IR Imaging No No F110W WFC3/IR Imaging No No F160W WFC3/UVIS Imaging No No F814W WFC3/IR Imaging No No F110W WFC3/IR Imaging No No F160W POS-TARG DITHER 0.135 LINE false true 3 46.84 WFC3-UVIS-DITHER-LINE-3PT 1 false POS-TARG DITHER 0.605 LINE false false 3 41.788 WFC3-IR-DITHER-LINE-3PT 2 false 1409856375480 The scheduling data was generated by CASM 22.2. CASM was run in Phase II mode. 54.1 (Tic-Visit :proposal-id 13935 :visit-id "01" :proposal-version -1 :trans-version "20140605" :date "04-Sep-2014 14:46:12.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 96544 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 13935 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 13935 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2908 :al-overhead-at-end 0 :internal-dur-at-end 187 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3246.0 :pcs-gap 0 ) false 1 0 1409859018840 The scheduling data was generated by CASM 22.2. CASM was run in Phase II mode. 54 (Tic-Visit :proposal-id 13935 :visit-id "02" :proposal-version -1 :trans-version "20140605" :date "04-Sep-2014 15:30:13.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 89344 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 13935 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 13935 :visit-id "02" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2905 :al-overhead-at-end 0 :internal-dur-at-end 179 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3240.0 :pcs-gap 0 ) false 1 0