6724( 5) - 02/08/96 13:56 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6724 Version: 5 Check-in Date: 08-Feb-1996 13:52:35 1.Proposal Title: The P Cygni Nebula ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle HOT STARS GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Richard White Space Telescope Science Institute CoI: Chris Skinner Space Telescope Science Institute N CoI: Bob Becker University of California, Davis N ------------------------------------------------------------------------------------ 6. Abstract P Cygni is the closest and best known example of a Luminous Blue Variable. LBVs are believed to be very massive stars in the late stages of their evolution. Typically they exhibit heavy mass loss via stellar winds which are slower than typical OB stars', large optical nebulae which are frequently bipolar, and unpredictable luminosity variations including occasional explosive outbursts. P Cyg displays all of these characteristics, but its optical nebula has only very recently been discovered owing to its low surface brightness. We have made a detailed study of P Cyg at radio wavelengths, discovering that it can vary dramatically on a very short timescale, and that it has a large nebula morphologically almost identical the optical nebula. Using ground-based instrumentation it has not been possible to ascertain whether the P Cyg nebula comprises a set of inhomogeneous, concentric rings (corresponding to discrete outbursts), or a continuous distribution of blobs or filaments. We propose to use HST to obtain images in the NII Lambda6548, SII Lambda6731, and HAlpha lines with WFPC2. These images will be used to determine the morphology and to measure the N/S abundance ratio, which theory predicts should increase as the star evolves. The FOC will also be used to obtain high spatial resolution images in the HBeta line and nearby continuum. Further images obtained on a timescale of about 5 years will allow a direct measurement of the angular expansion of the nebula, and hence the distance and luminosity of P Cyg. ------------------------------------------------------------------------------------ 6724( 5) - 02/08/96 13:56 - [ 2] Observations Description ------------------------ Through narrowband filters using WFPC2 we will require 3 integration times to adequately expose the whole nebula from the bright core (for which a 2 sec image should provide a little over half full well in the HAlpha and NII lines) to the 1.5 arcmin arcs. In the NII line, the nebula has a surface brightness of about 5times10^-16erg/cm^2/s/arcsec^2 at a radius of about 11arcsec, rising to almost 10^5 times this at the position of the star. Thus at 11 arcsec, the edge of the inner nebula, we should accumulate roughly 0.2 electrons per second, and estimate that a total integration time of 2500 seconds should provide sufficient S/N, so that we would make exposures of 2, 100 and 2500 seconds in the NII and HAlpha filters. >From the images of Barlow et al. (1994) we are able to estimate that the outer arcs are about a factor five fainter than the outer edge of the inner nebula in NII. The SII line is about a factor 8 fainter than the NII line throughout the inner nebula. We therefore require total exposure times of about 2, 200 and 5000 seconds in this line. Finally, because of the extreme brightness of P Cyg, there will be a large halo of scattered light generated in the WFPC2. Additionally, some of the starlight is scattered in the stellar wind by electrons (e.g. Taylor et al. 1991), so that the halo for P Cyg should be somewhat brighter than for a typical star of the same magnitude. In order to approximately remove this from our images (which are all at similar wavelengths), we propose to take 2, 100 and 1000 second exposures in the F631N (OI) filter, in which there is not expected to be significant line emission from the nebula. The star will be placed on the PC, a few arcseconds from the inner corner of the L-shaped WFC, so that most artifacts due to the bright star (which will grossly saturate at the longer exposure times), will be confined to the PC within a few arcsec of the star. Because the nebula is so large, a fraction of it will be lost because of the small size of the PC; however, this will only represent a small fraction of the total area, and will not be a significant loss. Two exposures will be needed with the FOC, each of 2500 seconds (roughly 1 orbit). In the first, the F486N, F195W and F8ND filters will be combined, resulting in a peak count rate of about 0.5 count/sec, and comprising a mixture of continuum and HBeta line emission. Good S/N should be obtained as far as about 3 arcsec from the star, filling in the region we cannot observe from the ground, and which will be most compromised by the undersampling of WFPC2. Once again, it will be necessary to obtain an image in continuum light to remove the electron scattered halo, and for this we propose a similar exposure through the F430W, F550W and F4ND filters, which admit a continuum region free of strong emission lines and should yield a peak count rate of about 0.5 count/sec again. (We do not wish to use the occulting fingers to reduce the stellar flux partly because this would be dangerous, since a positioning error could then damage the FOC, and partly because this would occult a region very close to the star in which we are interested.) Real Time Justification ----------------------- For FOC observations we will require the CHECK-FILTER=YES option for acquiring the target. We have already obtained the deepest radio images of P Cyg, including MERLIN images with similar spatial resolution to the FOC, and ground- based optical coronagraph images of the nebula (which have been used to calculate required exposure times for this proposal). Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 6724( 5) - 02/08/96 13:56 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: STSCI Ship Via: Email: skinner@stsci.edu , ------------------------------------------------------------------------------------ 6724( 5) - 02/08/96 13:56 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 P-CYGNI STAR,B0-B2 III- RA=20H 17M 47.198S +/- J2000.0 V = 4.9+/-0.2 I,IRREGULAR 0.2",DEC=38D 01' 58.23" +/- 0.2" VARIABLE,ETA CARINAE STAR,EMISSION LINE Comments: Coordinates are from Hipparcos INCA Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) J2000.0 -0.0007 -0.014 0.0 6724( 5) - 02/08/96 13:56 - [ 5] Visit: 01 Visit Requirements: 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 P-CYGNI FOC/96 IMAGE 512X512 F4ND,F550 CHECK- 1 2300S M,F140M,F FILTER=YES 480LP ------------------------------------------------------------------------------------------------------------------------------------ 2 P-CYGNI FOC/96 IMAGE 512X512 F486N,F12 CHECK- 1 2400S 0M,F2ND FILTER=YES ------------------------------------------------------------------------------------------------------------------------------------ 4 P-CYGNI WFPC2 IMAGE PC1 F631N 1 1S POS TARG -17.6,-17.8 ------------------------------------------------------------------------------------------------------------------------------------ 5 P-CYGNI WFPC2 IMAGE PC1 F631N 1 120S SAME POS AS 4 ------------------------------------------------------------------------------------------------------------------------------------ 6 P-CYGNI WFPC2 IMAGE PC1 F658N 1 120S SAME POS AS 4 ------------------------------------------------------------------------------------------------------------------------------------ 7 P-CYGNI WFPC2 IMAGE PC1 F656N 1 100S SAME POS AS 4 ------------------------------------------------------------------------------------------------------------------------------------ 8 P-CYGNI WFPC2 IMAGE PC1 F673N 1 200S SAME POS AS 4 ------------------------------------------------------------------------------------------------------------------------------------ 9 P-CYGNI WFPC2 IMAGE PC1 F631N CR-SPLIT=0.5 1 1100S SAME POS AS 4 ------------------------------------------------------------------------------------------------------------------------------------ 10 P-CYGNI WFPC2 IMAGE PC1 F658N CR-SPLIT=0.5 1 2500S SAME POS AS 4 ------------------------------------------------------------------------------------------------------------------------------------ 11 P-CYGNI WFPC2 IMAGE PC1 F656N CR-SPLIT=0.5 1 2500S SAME POS AS 4 ------------------------------------------------------------------------------------------------------------------------------------ 12 P-CYGNI WFPC2 IMAGE PC1 F658N 1 1S SAME POS AS 4 ------------------------------------------------------------------------------------------------------------------------------------ 13 P-CYGNI WFPC2 IMAGE PC1 F656N 1 1S SAME POS AS 4 ------------------------------------------------------------------------------------------------------------------------------------ 14 P-CYGNI WFPC2 IMAGE PC1 F673N 1 1S SAME POS AS 4 ------------------------------------------------------------------------------------------------------------------------------------ 15 P-CYGNI WFPC2 IMAGE PC1 F673N CR-SPLIT=0.5 1 2000S SAME POS AS 4 ------------------------------------------------------------------------------------------------------------------------------------ 16 P-CYGNI WFPC2 IMAGE PC1 F673N CR-SPLIT=0.5 1 2520S SAME POS AS 4 ------------------------------------------------------------------------------------------------------------------------------------ 6724( 5) - 02/08/96 13:56 - [ 6] Summary Form for Proposal 6724 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations FOC/96 WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CHECK-FILTER=YES CR-SPLIT=0.5 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category HOT STARS ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements POS TARG -17.6,-17.8 SAME POS AS 4 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F4ND,F550M,F140M,F480LP F486N,F120M,F2ND F631N F658N F656N F673N ------------------------------------------------------------------------------------------------------------------------------------ Target Names P-CYGNI ------------------------------------------------------------------------------------------------------------------------------------