7482( 9) - 12/15/98 08:40 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 7482 Version: 9 Check-in Date: 15-Dec-1998 08:39:48 1.Proposal Title: LONG SLIT OBSERVATIONS OF THE WR CENTRAL STAR OF THE LMC-PN N66 ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 7 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Miriam Pena Instituto de Astronomia CoI: Manuel Peimbert Instituto de Astronomia, Universidad N Nacional Autonoma de Mexico CoI: Silvia Torres-Peimbert Instituto de Astronomia, Universidad N Nacional Autonoma de Mexico CoI: Maria T. Ruiz Depto. de Astronomia, Universidad de Chile N CoI: Wolf-Rainer Hamann Lehrstuhl Astrophysik der Universitat N Potsdam CoI: Roberto H. Mendez Munchen University N ------------------------------------------------------------------------------------ 5. Abstract We propose to follow the remarkable event occurring in the central star of the LMC- PN N66. Before 1987, it showed a weak continuum with a T_eff ~ 120000 K and L_bol ~ 30000 L_sun and in few years its continuum increased by large factors and it developed strong WR features (P-Cygni profiles in NV 1240 A and CIV 1550 A lines, wide He II emission, etc.) resembling a WN4.5. The wind has persisted since 1990, showing some dramatic variations. HST FOS data of this object were obtained in Cycles 5 (prop. 6055) and 6 (prop. 6409) from which we have constructed expanding model atmospheres for the central star; the best-fit for Cycle 6 data are: T_eff ~ 93300 K, L_*=34000 L_sun, R_*=0.71 R_sun, mass loss rate = 10E-5 M_sun/yr, v_infty=2000 km/s. For Cycle 5 data the stellar parameters are the same, but the mass loss rate is slightly larger. The atmosphere is very H deficient (X/Y < 0.1), with N abundance of 0.004 by mass and C and O abundances lower than 0.0002 by mass. This chemical composition is most unusual since all the known PNe with WR nuclei show He- and C-rich winds. Model atmospheres have been calculated for IUE data of 1983 (pre-outburst epoch) and 1995 (maximum stellar brightness) and we found that the stellar luminosity has not changed substantially with time. The atmospheric H- deficiency and the constant L_bol have allowed us to discard the thermal pulse possibility as the triggering mechanism of the outburst. We propose that the star is suffering a violent atmospheric instability which produces large variations of the mass loss rate. The spectrum changes with time scales of months, therefore it is paramount to re-observe the object in Cycles 7 and 8 to follow its evolution, specially at UV wavelengths. HST observations are needed to isolate the stellar emission from the nebular spectrum. We require long-slit STIS observations to cover from 1150 to 11000 Angstrom with a resolution of 1000 to 5000. Thus we can study the star and the nebula separately. Three orbits (CVZ) are requested for each cycle. ------------------------------------------------------------------------------------ 7482( 9) - 12/15/98 08:40 - [ 2] Observations Description ------------------------ For Cycle 7 we plan to use the STIS long slit (52*0.2'') and a combinations of detectors and gratings to cover the 1150 to 11000 Angstrom 30, which includes all the important UV lines: NV 1240 A, CIV 1550 A, HeII 1640 A, and the optical and near-IR nitrogen (NIV 3480 A, NV 4606 A), carbon (CIV 5808 A), HeII and HeI lines. The same wavelength range will allow us to derive accurate physical conditions, kinematics and chemical composition of the nebula. The proposed observations are listed below: 1) Guide star acquisition:....................7 min 2) target acquisition (point source)..........5 min 3) peakup in the 52*0.2 '' slit...............5 min 4) MAMA G140L (1150-1740)....................75 min 5) MAMA G230L (1865-3065)....................48 min 6) CCD G430L (2900-5700; CR -SPLIT=3).........28 min 8) Guide star acquisition:....................7 min 9) target acquisition (point source)..........5 min 10) peakup in the 52*0.2 '' slit...............5 min 11) CCD G430M (4500-4900;CR-SPLIt=1)..........12 min 12) CCD G750L (5240-10200; CR-SPLIT=2)........25 min 13) CCD G750L (6460-11490; CR-SPLIT=2)........25 min------------------------------------------------------ -------- TOTAL EXPOSURE TIME.........................247 min OVERHEADS .................................. 41 min CVZ Orbits........................................3 Real Time Justification ----------------------- We are requesting CVZ because is the most efficient way to observe the proposed target. Besides the exposure with STIS/MAMA FUV (G140L) requires 75 min to achieve an appropriate S/N, so ``long duration" orbits are necessary for this observation. In this way, the target acquisition and the scientific observations will be accomplished in only 3 orbits with visibility of 96 min each. In the non- CVZ mode, the total number of orbits required would be 5. The target is being observed in the optical each 4 or 5 months from different observatories (CTIO, ESO) to closely follow its evolution and probably changes. Calibration Justification ------------------------- no special requirements Additional Comments ------------------- ------------------------------------------------------------------------------------ Data Distribution Paper Products: Media: ELECTRONIC Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 7482( 9) - 12/15/98 08:40 - [ 3] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 LMC-N66-CS EXT-STAR, PLANETARY RA=05H 36M 20.8S +/- 0.2S, DEC=- J2000 V = 17.5+/-0.2 NEBULA CENTRAL STAR 67D 18' 08" +/-0.5", PLATE- B-V = -0.2 ID=06B0 E(B-V) = 0.1+/-0.05 TYPE=WN-EARLY F-CONT(1300)=10+/-3e-15 F-CONT(4000)=1.0+/-0.3e-15 F-LINE(1640)=7.+/-0.3e-13 F-LINE(4686)=1.+/-0.3e-13 7482( 9) - 12/15/98 08:40 - [ 4] Visit: 01 Visit Priority: Visit Requirements: CVZ On Hold Comments: Additional Comments: WE REQUEST TO SCHEDULE THIS OBSERVATION IN THE FIRST OPPORTUNITY, WHICH IS OCTUBER 97 DUE TO THE LARGE VARIABILITY OF THE TARGET Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 11 LMC-N66-CS STIS/C ACQ F28X50L MIRROR ACQTYPE=POINT 1 5.0 S ONBOARD ACQ FOR 12-14 CD P ------------------------------------------------------------------------------------------------------------------------------------ 12 LMC-N66-CS STIS/F ACCUM 52X0.2 G140L 1425 1 75 M UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 13 LMC-N66-CS STIS/N ACCUM 52X0.2 G230L 2376 1 48 M UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 14 LMC-N66-CS STIS/C ACCUM 52X0.2 G430L 4300 CR-SPLIT=3 1 28 M CD ------------------------------------------------------------------------------------------------------------------------------------ 7482( 9) - 12/15/98 08:40 - [ 5] Visit: 02 Visit Priority: Visit Requirements: CVZ GROUP 1, 2 WITHIN 30D On Hold Comments: Additional Comments: WE REQUEST TO SCHEDULE THIS OBSERVATION IN THE FIRST OPPORTUNITY, WHICH IS OCTUBER 97 DUE TO THE LARGE VARIABILITY OF THE TARGET Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 21 LMC-N66-CS STIS/C ACQ F28X50L MIRROR ACQTYPE=POINT 1 5.0 S ONBOARD ACQ FOR 22-24 CD P ------------------------------------------------------------------------------------------------------------------------------------ 22 LMC-N66-CS STIS/C ACCUM 52X0.2 G430M 4706 CR-SPLIT=2 1 22 M CD ------------------------------------------------------------------------------------------------------------------------------------ 23 LMC-N66-CS STIS/C ACCUM 52X0.2 G750L 7751 CR-SPLIT=2 1 38 M CD ------------------------------------------------------------------------------------------------------------------------------------ 24 CCDFLAT STIS/C ACCUM 52X0.2 G750L 7751 2 DEF CD ------------------------------------------------------------------------------------------------------------------------------------ 7482( 9) - 12/15/98 08:40 - [ 6] Summary Form for Proposal 7482 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures F28X50LP 52X0.2 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD STIS/FUV-MAMA STIS/NUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ACQTYPE=POINT CR-SPLIT=3 CR-SPLIT=2 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements CVZ ONBOARD ACQ FOR 12-14 CVZ GROUP 1, 2 WITHIN 30D ONBOARD ACQ FOR 22-24 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G140L G230L G430L G430M G750L ------------------------------------------------------------------------------------------------------------------------------------ Target Names LMC-N66-CS CCDFLAT ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 1425 2376 4300 4706 7751 ------------------------------------------------------------------------------------------------------------------------------------