6082( 6) - 09/28/95 13:07 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6082 Version: 6 Check-in Date: ********** 1.Proposal Title: GHRS Spatially Resolved Spectra of Nova Cygni 1992 ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle Interstellar Medium GO 5 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Steven Shore Indiana University South Bend CoI: Thomas Ake Computer Sciences Corp./GSFC N CoI: Robert Gehrz University of Minnesota N CoI: Rosario Gonzalez-Riestra European Space Agency/Vilspa N CoI: Peter Hauschildt Arizona State University N CoI: Joachim Krautter Landessternwarte-Heidelberg N CoI: George Sonneborn NASA Goddard Space Flight Center N CoI: Sumner Starrfield Arizona State University N ------------------------------------------------------------------------------------ 6. Abstract We willobtain spatially resolved low resolution, 120 km s^-1 GHRS small science aperture spectra of a UV emitting knot in the ejecta of the bright Galactic OMgNe nova Cygni 1992. With the good spectral resolution, FUV sensitivity, and photon counting capabilities of the GHRS and the SSA, we will study the structure and dynamics of the nova Cyg 1992 ejecta at an intermediate stage of its expansion, very soon after the turnoff of the central nuclear source. We will determine abundances for key species in the ejecta, especially neon. These observations will provide a detailed picture of physical conditions and abundances of the ejecta that has never before been available from UV spectra, including those taken before the COSTAR installation. The knots are likely the result of a Rayleigh- Taylor instability during the explosion, and the differential mixing that may have accompanied it can be studied using the knot spectra. We will also obtain an LSA G160M medium resolution (R=15000) spectrum of the spatially integrated He II 1640 line profile. Finally, we will also obtain moderate S/N LSA G140L low resolution observations of the UV continuum of the hot central star and high S/N spatially integrated line profile data for the nebula in order to study the physical conditions in the post- thermonuclear runaway envelope. ------------------------------------------------------------------------------------ 6082( 6) - 09/28/95 13:07 - [ 2] Observations Description ------------------------ begincenter Proposed Observations endcenter Low resolution G140L spectra (resolution 120 - 200 km s^-1) will be obtained for two settings, covering the region from 1200 - 1760 Angstrom, with a resolution of R=1500, for the central star with the LSA (which will include the nebula). One spectrum, centered at 1622 Angstrom, will be obtained for the brightest knot with the G140L and the SSA with the full resolution of 2500. In addition, we will obtain an LSA G160M spectrum at the central star with nebula at He II 1640,. The exposure times (15 min per G140L spectrum) provide S/N=20-40 at the peak of the emission lines and S/N=5-10 per resolution element in the stellar continuum. We will obtain spectra for the UV-brightest knot in the FOC images and a set of spectra pointing at the central star. We also propose to use the G140L grating to obtain two high S/N low resolution observations of the entire short wavelength spectrum in order to determine the flux distribution of the remnant's photosphere. We will require 65 minutes to obtain spectra with sufficient S/N to study the central star with settings at 1340Angstrom\ and 1518Angstrom\ to cover the continuum, especially the LyAlpha profile. Predicted exposures are based on our most recent IUE observation obtained on 1994 Nov. 22. The overall decrease in emission line intensity and decreased ionization fraction (based on the N III/N IV/N V strengths followed since the beginning of the optically thin stage in 1992 June) was used to predict the spectrum for a generic observation in 1995 Aug. We have used the observed power law decline, roughly t^-3, and the COSTAR SSA throughput to predict the count rates. The observations will use FP- SPLIT=2 and quarter-stepping to obtain the highest spectral resolution and highest S/N ratio. Astrometry will be obtained for the brightest knots from the pre- and post- COSTAR FOC images. Our preliminary assessment is based on ERO observations taken post-COSTAR and also on the published information about the 31 May 1993 UV image obtained with the FOC. Thus, we will not require a separate pre-acquisition images, substantially reducing the time required for these observations. All acquisitions will be on Side 2 (N2) with LSA peakup and then SAMs to the astrometrically identified knot. begincenter Method of Analysis endcenter We will obtain the density, pressure, and neon abundance for the knot and forthe integrated spectrum of the nebula (taken to matchbthe conditions of the earlier, pr-COSTAR, observations). The G140L knot spectrum will be centered on the [Ne V] and [Ne IV] lines near 1600 Angstrom to determine the neon abundance, a critical number for studying the explosion. The density at the end of 1994 was still above the critical density for the key nebular transitions. It is likely that this situation will remain true for the filaments for quite some time. Given this uncertainty, we must perform a complete photoionization analysis (CLOUDY supplemented by line profile modeling) in order to be certain of the accuracy of the derived physical conditions for the knots. We have developed a new procedure for determining the physical parameters for the knots using CLOUDY coupled with a global Metropolis Monte Carlo algorithm (Austin et al. 1994, BAAS) and will use this to determine the parameters for the individual knots. We will continue IUE observations of Nova Cyg 1992 during the entire period leading up to and including the proposed GHRS observations. We will compare these new spectra with the ones we have from 1992 and 1993. Since we have excellent velocity resolution in the earlier data, although not the spatial resolution, we will be able to identify the knots in the integrated ejecta profiles and study their development. We knew that the knots were there by comparing the 1993 April. GHRS observations with those taken in 1992 September. The filamentary emission component decreased less rapidly than the wings of the profiles on all of the emission lines. The diffuse high velocity matter was clearly distinguished from the slower moving interior knots. The contrast growth in the profiles in the second spectrum was due to a decrease in the emission measure of high velocity gas that was masking the inner, slower moving shell. We have already crudely modeled this aspect of the outburst (Shore et al. 1993) (see Starrfield and Shore (1994) for a comparison of Ne IV 1602 at the two phases). The data will be obtained, extracted, and reduced by Shore, Ake, and Starrfield. Shore and Ake are members of the GHRS Science Team and are thoroughly familiar with the instrument and the data reduction. Shore, Sonneborn, Starrfield, and Gonzalez- Riestra will be observing with IUE. Shore, Starrfield, Hauschildt, and Austin have experience modeling the emission spectrum of novae and are also involved with hydrodynamic models of the ejecta evolution. Hauschildt, Starrfield, and Shore performed the atmosphere analysis of the white dwarf atmosphere. The HST data will be reduced using the GHRS Science Team software and many special purpose routines, written by our group, for the analysis of nova spectra. Optical observations will be processed at GSFC and ASU. Additional analysis will be performed at IUSB, especially the merger of the UV and groundbased data. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- The LSA G160M observation makes use the the available time following target acquisition with side 2. The N2 mirror is required for adequate S/N; there is enough time remaining (RPS2 processing) to allow for a medium resolution He II 1640 observation for comparison with 1992 and 1993 spectra at the central star. Side switch will be performed during occultation. The knot spectrum should be taken contemporaneously with the central star on a single visit. We will continue monitoring the integrated 1200 - 2000Angstrom\ flux of Cyg 1992 with IUE through the period of these observations. Groundbased spectra will be obtained from the MMT to support the observations by Starrfield and his students. The spectra should be obtained as soon as possible after the start of Cycle 5 in order to insure that the knots are brighter than .8e-15 erg/s/cm^2/A. IUE will not be available after 31 Sept. 1995, so the observations should be scheduled as closely as possible to that time. ------------------------------------------------------------------------------------ 6082( 6) - 09/28/95 13:07 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: Steve Shore*c/o Tom Ake*Code 681/CSC*Goddard Space Flight Center*Greenbelt, MD 20771 Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 6082( 6) - 09/28/95 13:07 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NOVA-CYG- STAR, CLASSICAL NOVA, RA=20H 29M 07.0S +/- 0.05S, 1950.0 F-LINE(1602)=1.0E-14 1992-CENTRAL PLANETARY NEBULA DEC=52D 27' 44" +/- 0.05" -STAR CENTRAL STAR Comments: FLUX BASED ON IUE SPECTRA NOV 1994 2 NOVA-CYG- STAR, CLASSICAL NOVA, RA-OFF = -0.0093S +/- 0.0001S, 1950.0 F-LINE(1602)=1.0E-14 1992-KNOT-2 KNOT, EJECTA DEC-OFF = -0.280" +/- 0.01", FROM 1 Comments: FLUX BASED ON IUE SPECTRA NOV 1994 6082( 6) - 09/28/95 13:07 - [ 5] Visit: 01 Visit Requirements: BEFORE 30-SEP-1995 On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NOVA-CYG- HRS ACQ 2.0 MIRROR-N2 1 36S ONBOARD ACQ FOR 2-5; NO SPLIT 1992- CENTRAL- Comments: STEP-TIME=4S TO YIELD 500 COUNTS ------------------------------------------------------------------------------------------------------------------------------------ 2 NOVA-CYG- HRS ACCUM 2.0 G160M 1640 FP-SPLIT=TWO 4 326.4S 1992- CENTRAL- ------------------------------------------------------------------------------------------------------------------------------------ 3 NOVA-CYG- HRS ACCUM 2.0 G140L 1340 FP-SPLIT=TWO 12 326.4S 1992- CENTRAL- ------------------------------------------------------------------------------------------------------------------------------------ 4 NOVA-CYG- HRS ACCUM 2.0 G140L 1618 FP-SPLIT=TWO 12 326.4S 1992- CENTRAL- ------------------------------------------------------------------------------------------------------------------------------------ 5 NOVA-CYG- HRS ACCUM 0.25 G140L 1618 FP-SPLIT=TWO 27 326.4S 1992-KNOT-2 ------------------------------------------------------------------------------------------------------------------------------------ 6082( 6) - 09/28/95 13:07 - [ 6] Summary Form for Proposal 6082 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations HRS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters FP-SPLIT=TWO ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category Interstellar Medium ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BEFORE 30-SEP-1995 ONBOARD ACQ FOR 2-5; NO SPLIT ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR-N2 G160M G140L ------------------------------------------------------------------------------------------------------------------------------------ Target Names NOVA-CYG-1992-CENTRAL-STAR NOVA-CYG-1992-KNOT-2 ------------------------------------------------------------------------------------------------------------------------------------