! Hubble Space Telescope Cycle 5 (1995) Phase II Proposal ! $Id: 6039 ! Proposal_Information ! Section 4 Title: The Young, Rapidly-Evolving Planetary Nebula He 3-1357 Proposal_Category: GO Scientific_Category: Interstellar Medium Cycle: 5 Investigators PI_name: Matthew Bobrowsky PI_Institution: CTA INCORPORATED CoI_Name: M. Parthasarathy CoI_Institution: Indian Institute of Astrophysics Contact: ! Y or N (designate at most one contact) CoI_Name: Kailash Sahu CoI_Institution: European Southern Observatory Contact: ! Y or N (designate at most one contact) CoI_Name: Pedro Garcia-Lario CoI_Institution: ESA IUE Observatory Contact: ! Y or N (designate at most one contact) Abstract: ! Free format text (please update) He 3-1357 has apparently become a planetary nebula only within the last 40 years. IUE and ground-based observations have revealed that its spectrum changes noticeably over just a few years, showing stellar evolution ``caught in the act''. HST images resolved it for the first time (in Cycle 2) and we are now in a position to study both its spectral and morphological evolution. It is of crucial importance to determine whether the unique spectral changes observed in He 3-1357 are related to a sporadic episode of mass loss enhancement, or whether they constitute the evidence for continuous temporal evolution through the H-R diagram. We propose a combination of imaging and spectral observations, not only to derive the physical conditions and chemical abundances in the nebula, but also to investigate the stellar wind (which is known to be changing in time as well) and understand the characteristics of the central star. The extremely compact nature of He 3-1357 makes necessary the use of the high-resolution capabilities of HST to determine how the chemical abundances vary throughout the nebula. These results will be important not only for understanding this rapidly-changing object, but also for understanding the formation process of planetary nebulae in general and for testing the models trying to explain the early evolution of planetary nebulae. Questions ! Free format text (please update) Observing_Description: We propose to obtain FOS spectra and WFPC2 narrowband images of He 3-1357 in order to understand the rapid changes in this object which have been detected. The planetary camera images will enable us to detect morphological changes, as well as identifying the spatial extent of various ions. Line fluxes from He 3-1357 (Parthasarathy et al. 1993) were used to determine exposure times for PC images with narrow-band filters --- F588N, F631N, F487N, F502N, F656N, F658N, and F673N. As an example, filter F588N has a system throughput of 13%. The flux from He 3-1357 at 5877 Angstrom is 1.74 * 10^-12 erg cm^-2 s^-1 and, at this wavelength, the number of quanta per unit of energy is 2.95 * 10^11 photons erg^-1. The effective telescope collecting area is 3.9 * 10^4 cm^2. Multiplying all of these together and then dividing by the number of pixels (10^3) over which the target will be spread, yields 2.6 counts s^-1 pixel^-1. At this count rate, a S/N of 50 can be achieved in 16 min., i.e., in less than one orbit even with overhead and data readout. Images using all relevant WFPC2 filters can be acquired in five orbits. The FOS spectra, taken through the 0.3" aperture, cover important lines in the visible and UV. They will provide line intensities from which we will calculate abundances and the physical conditions in three different parts of the nebula indicated in Figure 1. With grating G130H, we will derive the temperature of the central star and study the stellar wind features of CIV 1550 Angstrom and SiIV 1400 Angstrom. The wavelength region covered by G190H will allow us to study the CIII 1909 Angstrom and He II 1640 Angstrom lines, as well as contributing to the flux distribution used to derive the central star temperature. Exposure times for FOS spectra were calculated using (a corrected version of) the first formula in Table 1.2.1 in the FOS handbook. As a sample exposure time calculation for a spectrum, consider the observation of one point in the equatorial ring of gas (Fig. 1) using grating G400H. The 0.3" aperture looks at ~3\ from the nebula, which works out to be 1.5 * 10^-15 erg cm^-2 s^- 1 ang^-1. With grating G400H, the dispersion is 3 Angstrom diode^-1, the system efficiency is 0.04, and the throughput is 0.8. This results in a count rate of 1.64 counts diode^- 1. In this case, S/N=50 will be achieved in 26 min, i.e., less than one orbit, even with instrumental overhead and a target acquisition. The time needed for all FOS spectra is 10 orbits. Adding on the five WPFC2 orbits yields a total spacecraft time of 15 orbits. Real_Time_Justification: No Special Requirements We plan to continue to monitor He 3-1357 using ground-based telescopes and IUE. Observations of He 3-1357 will be carried out at several epochs with IUE (next foreseen observations in September 1994 and April 1995). This observing time has recently been approved by the IUE Allocation Commitee. We also applied for observing time at La Silla but haven't yet heard the outcome. The observation of He 3-1357 is part of a wide program of observation of post- AGB stars and young PNe showing spectral changes. Calibration_Justification: ! Move appropriate text from Real_Time_Justification Additional_Comments: Fixed_Targets ! Section 5.1 Target_Number:1 Target_Name:HE3-1357-OFFSET Alternate_Names:CPD-59D6926,IRAS17119-5926 Description:ISM,PLANETARY NEBULA,BIPOLAR OUTFLOW Position:RA=17H 16M 21.104S +/- 0.01S, DEC=-59D 29' 21.30" +/- 0.1", PLATE-ID=02F7 ! Most common specification format is ! RA=0H 0M 0.00S +/- 0S, ! DEC=0D 0' 0.0" +/- 0", ! PLATE-ID=0000 Equinox:J2000 RV_or_Z: RA_PM: ! Units are seconds of time per year Dec_PM: ! Units are seconds of arc per year Epoch: Annual_Parallax: Flux:V=10.95 +/- 0.2, B-V=-0.04 +/- 0.02 Comments: Target_Number:2 Target_Name:HE3-1357-RING Alternate_Names: Description:ISM,PLANETARY NEBULA Position:RA=17H 16M 21.054S +/- 0.01S, DEC=-59D 29' 21.01" +/- 0.1", PLATE-ID=02F7 Equinox:J2000 RV_or_Z: RA_PM: ! Units are seconds of time per year Dec_PM: ! Units are seconds of arc per year Epoch: Annual_Parallax: Flux:SURF(V)=12.1 +/- 1.0 Comments: Target_Number:3 Target_Name:HE3-1357-SHELL Alternate_Names: Description:ISM,PLANETARY NEBULA Position:RA=17H 16M 21.056S +/- 0.01S, DEC=-59D 29' 20.24" +/- 0.1", PLATE-ID=02F7 Equinox:J2000 RV_or_Z: RA_PM: ! Units are seconds of time per year Dec_PM: ! Units are seconds of arc per year Epoch: Annual_Parallax: Flux:SURF(V)=12.4 +/- 1.0 Comments: Target_Number:4 Target_Name:REV-HE3-1357-OFFSET Alternate_Names:CPD-59D6926,IRAS17119-5926 Description:ISM,PLANETARY NEBULA,BIPOLAR OUTFLOW Position:RA=17H 16M 20.9324S +/- 0.01S, DEC=-59D 29' 23.408" +/- 0.1", PLATE-ID=02F7 ! Most common specification format is ! RA=0H 0M 0.00S +/- 0S, ! DEC=0D 0' 0.0" +/- 0", ! PLATE-ID=0000 Equinox:J2000 RV_or_Z: RA_PM: ! Units are seconds of time per year Dec_PM: ! Units are seconds of arc per year Epoch: Annual_Parallax: Flux:V=10.95 +/- 0.2, B-V=-0.04 +/- 0.02 Comments: Target_Number:5 Target_Name:REV-HE3-1357-RING Alternate_Names: Description:ISM,PLANETARY NEBULA Position:RA=17H 16M 20.8899S +/- 0.01S, DEC=-59D 29' 23.041" +/- 0.1", PLATE-ID=02F7 Equinox:J2000 RV_or_Z: RA_PM: ! Units are seconds of time per year Dec_PM: ! Units are seconds of arc per year Epoch: Annual_Parallax: Flux:SURF(V)=12.1 +/- 1.0 Comments: Target_Number:6 Target_Name:REV-HE3-1357-SHELL Alternate_Names: Description:ISM,PLANETARY NEBULA Position:RA=17H 16M 20.8583S +/- 0.01S, DEC=-59D 29' 22.427" +/- 0.1", PLATE-ID=02F7 Equinox:J2000 RV_or_Z: RA_PM: ! Units are seconds of time per year Dec_PM: ! Units are seconds of arc per year Epoch: Annual_Parallax: Flux:SURF(V)=12.4 +/- 1.0 Comments: ! 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 | Gyro] ! GUIDing TOLerance ! ORIENTation TO ! ORIENTation TO FROM ! ORIENTation TO FROM NOMINAL ! SAME ORIENTation AS ! CVZ ! PARallel ! AFTER [BY [TO ]] ! AFTER ! BEFORE ! BETWEEN AND ! GROUP WITHIN