Proposal_Information ! Section 4 Title: High-resolution imagery of the next bright Galactic nova Proposal_Category: GO Scientific_Category: INTERSTELLAR MEDIUM Cycle: 6 Investigators PI_name: Michael Shara PI_Institution: Space Telescope Science Institute CoI_Name: Mario Livio CoI_Institution: Space Telescope Science Institute Contact: ! Y or N (designate at most one contact) CoI_Name: Dina Prialnik CoI_Institution: Tel-Aviv University Contact: ! Y or N (designate at most one contact) CoI_Name: Robert Williams CoI_Institution: Space Telescope Science Institute Contact: ! Y or N (designate at most one contact) CoI_Name: David Zurek CoI_Institution: Space Telescope Science Institute Contact: ! Y or N (designate at most one contact) Abstract: ! Free format text (please update) The recurrent nova T Pyxidis is one of only ~20 novae with known shells, and the only recurrent nova with clearly resolved circumstellar matter. A unique and once-only opportunity will exist during T Pyxidis' next eruption (now overdue) to determine: 1) The uniformity and isotropy of material (both dust and different chemical elements) ejected in previous eruptions, and 2) The smallest structures formed in nova eruptions. We propose to use WFPC2 to image T Pyx after it erupts to search for fluorescence and reflection light echoes from, and small-scale structure in, the nova circumstellar gas and dust ejecta. Only two novae are presently known to have a highly structured shell that can be defined as ``very'' clumpy. These novae are GK Per (known from the ground) and T Pyx (HST cycle 4 WFPC2 images). It's unclear if this structure is common to all nova shells or, if it is, how the structure is created. Though T Pyx is ``overdue'' it may take several years before it goes off again. We therefore propose to use the TOO time, if allocated, to follow the eruption of the next bright Galactic nova with WFPC2 (if T Pyx does not erupt) to determine how quickly the ejecta of a nova becomes clumpy. Questions ! Free format text (please update) Observing_Description: Should T Pyx erupt during cycle 6, we request that (as soon as possible) we image for 3 orbits in the narrowband filters of Hydrogen, Nitrogen, Oxygen and Helium as well as blue and red broadband filters. We then request that T Pyx be reobserved for 3 orbits one week later, 3 weeks later, 7 weeks later, 16 weeks later, 24 weeks later and then every six months for the next 2 years. If a bright Galactic nova erupts (and T Pyx has not yet erupted) then we request that this nova be acquired ~2 to 3 weeks after maximum and be imaged for 3 orbits with the same filters as T Pyx. We then request that the nova be reimaged about once every 3 to 4 months to monitor the ejecta development. Real_Time_Justification: T Pyx is overdue to erupt. Should T Pyx erupt in cycle 6 we request that HST begin observations as soon as possible (ie. ~4 days). A bright Galactic nova (m_max <~ 7) occurs every few years and thus it is quite likely that such an event will occur during cycle 6. We request that once a bright Galactic nova has erupted that HST observations begin within two weeks of maximum light. none Calibration_Justification: ! Move appropriate text from Real_Time_Justification Additional_Comments: Generic_Targets ! Section 5.3 Target_Number: 1 Target_Name: Nova-1996 Description: STAR,Classical Nova Criteria: A bright nova reaching about 7th magnitude Flux: V = 7.0 +/- 0.5, B-V = 0.0 +/- 0.5 Comments: The next bright nova will be choosen to observe the evolution of the shell. ! This is a template for a single visit containing a single exposure ! Repeat exposure and visit blocks as needed Visits ! Section 6 Visit_Number: 1 Visit_Requirements: ! Section 7.1 ! Uncomment or copy visit level special requirements needed ! Most of these requirements (including ORIENT) will limit scheduling PCS MODE Fine ! GUIDing TOLerance ! DROP TO GYRO IF NECESSARY [NO REACQuisition] ! ORIENTation TO ! ORIENTation TO FROM ! ORIENTation TO FROM NOMINAL ! SAME ORIENTation AS ! CVZ ! PARallel ! SCHEDulability ! AFTER [BY [TO ]] ! AFTER ! BEFORE ! BETWEEN AND ! GROUP WITHIN