8462( 5) - 06/21/99 08:42 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 8462 Version: 5 Check-in Date: 21-Jun-1999 08:41:52 1.Proposal Title: LONG SLIT OBSERVATIONS OF THE WR CENTRAL STAR OF THE LMC-PN N66-CYCLE 8 CONTINUATION ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 8 ------------------------------------------------------------------------------------ 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 are following 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 lines, 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 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 the pre-outburst epoch and for 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 with large variations of the mass loss rate. Long-slit STIS observations, covering the spectral range 1100-7000A were performed in January 99 (Cycle 7). These data are being analized. Preliminar results show that since 1997 the star has been slowly fading. The stellar spectrum still shows WR features at NV 1240, CIV 1550, all the UV and visible HeII lines, and others, but much fainter than before showing that the stellar wind is diminishing. The `false photosphere' generated by the optically thick wind receds, while the surface temperature increases. To re-observe the object in Cycle 8 is paramount to follow its evolution, specially at UV. HST observations are needed to isolate the stellar emission from the nebular spectrum. Thus we can study the star and the nebula separately. Three CVZ orbits have been granted for Cycle 8. WE REQUEST THAT MAMA VISIT AND CCD VISIT ARE PROGRAMMED AS CLOSE AS POSSIBLE Qu estions ------------------------------------------------------------------------------------ 8462( 5) - 06/21/99 08:42 - [ 2] Observations Description ------------------------ none given Real Time Justification ----------------------- none Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ Data Distribution Paper Products: Media: ELECTRONIC Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 8462( 5) - 06/21/99 08:42 - [ 3] TARGET LIST 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 = 17.9+/-0.3 NEBULA CENTRAL STAR 67D 18' 8" +/- 0.5", PLATE- B-V = -0.2 ID=06B0 E(B-V) = 0.1+/-0.05 TYPE=WN-EARLY F-CONT(1300)=6+/-3e-15 F-CONT(4000)=4.8+/-0.3e-16 F-LINE(1640)=2.+/-0.3e-13 F-LINE(4686)=3.4+/-0.3e-14 8462( 5) - 06/21/99 08:42 - [ 4] Visit: 01 Visit Priority: Visit Requirements: GROUP 1-2 WITHIN 7D CVZ On Hold Comments: Additional Comments: VARIABLE TARGET: WE REQUEST THIS VISIT AS NEAR AS POSSIBLE TO VISIT 2 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 12-13 CD P Comments: : ------------------------------------------------------------------------------------------------------------------------------------ 12 LMC-N66-CS STIS/F ACCUM 52X0.2 G140L 1425 1 100 M UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 13 LMC-N66-CS STIS/N ACCUM 52X0.2 G230L 2376 1 61 M UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 8462( 5) - 06/21/99 08:42 - [ 5] Visit: 02 Visit Priority: Visit Requirements: CVZ On Hold Comments: Additional Comments: VARIABLE TARGET: WE REQUEST THIS VISIT AS NEAR AS POSSIBLE TO VISIT 1 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 22-23 CD P ------------------------------------------------------------------------------------------------------------------------------------ 22 LMC-N66-CS STIS/C ACCUM 52X0.2 G430L 4300 CR-SPLIT=3 1 34 M CD ------------------------------------------------------------------------------------------------------------------------------------ 23 LMC-N66-CS STIS/C ACCUM 52X0.2 G430M 4961 CR-SPLIT=3 1 35 M CD ------------------------------------------------------------------------------------------------------------------------------------ 8462( 5) - 06/21/99 08:42 - [ 6] Summary Form for Proposal 8462 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 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements GROUP 1-2 WITHIN 7D CVZ ONBOARD ACQ FOR 12-13 CVZ ONBOARD ACQ FOR 22-23 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G140L G230L G430L G430M ------------------------------------------------------------------------------------------------------------------------------------ Target Names LMC-N66-CS ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 1425 2376 4300 4961 ------------------------------------------------------------------------------------------------------------------------------------