6622( 12) - 10/24/96 09:22 - [ 0] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6622 Version: 12 Check-in Date: 24-Oct-1996 09:20:19 1.Proposal Title: UV Spectroscopy of DR 1, the WO3 Star in IC 1613 and its Surrounding Nebula, S3 ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle HOT STARS GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: ROBIN KINGSBURGH YORK UNIVERSITY CoI: Michael Barlow University College London N CoI: Paul Crowther University College London N CoI: John Hillier University of Pittsburgh N CoI: Peter Storey University College London N ------------------------------------------------------------------------------------ 6. Abstract We propose to obtain UV FOS and GHRS spectra of DR 1, a very luminous WO type Wolf- Rayet star in the metal- poor dwarf irregular galaxy IC 1613. Simultaneously, we will obtain spectra of a portion of S3, its surrounding nebula. The stellar spectra will be analysed using a sophisticated non -LTE radiative transfer code, allowing for spherical extension, stellar winds and non-LTE line blanketing, to determine C/He and O/C abundance ratios which will provide constraints on the He-burning stage of evolution of massive stars. Our quantitative analysis will also yield fundamental physical parameters such as terminal velocity, mass-loss rate and luminosity, thereby allowing tight constraints to be placed on massive star evolutionary theory at very low metallicities. At Z=0.001, IC 1613 is the lowest metallicity region known to house such an evolved massive star. A complementary nebular analysis will yield abundances of N^2+, N^3+, N^4+, C^+, C^2+, C^3+, and O^3+ relative to H^+ (ions which are only observable in the UV), enabling an accurate total abundance analysis in conjunction with existing optical spectra. The UV nebular carbon lines provide the only means of deriving the nebular carbon abundance for this low metallicity region. In addition, a Zanstra and Stoy temperature analysis will be used to constrain the stellar temperature adopted for the non-LTE model, enabling a more accurate overall analysis. HST provides the only means of obtaining UV spectra of DR 1 and S3. ------------------------------------------------------------------------------------ Observations Description ------------------------ We will first acquire DR 1 (V = 20.7) with the FOS via a blind offset from GSC- 19-387, (V=14.2, B-V=0.52, E(B-V)~0) which is ~30 arcseconds from DR 1. We will acquire the star with a 3-stage peak-up sequence (1 orbit) and offset to DR 1. There we will follow with a P3 peak-up of DR 1 (41 minutes). The initial acquisition will take ~ 2 HST orbits. We propose to use the 0.5''-PAIR apertures in order to simultaneously observe DR 1 and S3 with the high resolution FOS gratings, and thus make efficient use of telescope time. Two spectral regions will be observed with the FOS/RD, covering the wavelength range from ~1600-3300A, and provide sufficient overlap with existing 4.2-m WHT optical spectra. The 1100-1900Angstrom region will be observed with the GHRS, as FOS/BL does not have the sensitivity to detect DR 1 in that wavelength range. With FOS/RD, the G190H grating (1590- 2317A) will be used to observe the stellar He~II 1640 and O~VI 2070A features and nebular He~II 1640, N~III 1750, and C~III 1909A features. The G270H grating (2222-3277A) will be used to observe the stellar C~IV 2405, 2530, and OV 2786A features and nebular C~II 2326, Ne~IV 2423 and O~II 2470A features. Following the FOS/RD observations, we will use the GHRS for a 2nd visit (Side 1) to obtain spectra in the far-UV range. We will also acquire DR~1 using a blind offset from GSC-19-387. At V = 14.2, the Side 2 N2 mirror is required to acquire the star, resulting in a 42- minute overhead to switch to Side 1, taking 1 orbit. A FOS/BL-assisted acquisition would also take 1 orbit. SAVE-OFFSET during Visit 1 with FOS/RD is not used, as SAME-ORIENT would be required for Visit 2 with the GHRS, greatly limiting the time window for observation. Therefore, allocating 1 orbit for acquisition for Visit 2 is preferred. The GHRS LSA will be used for the observations. The GHRS spectra will be binned to FOS resolution. The G140L grating (1100-1900A) will be used to observe the stellar OIV 1341, OV 1370 and C~IV 1550A features and nebular N~IV 1486 and C~IV 1550A features. The region from 1150-1600A is also very important as it contains emission lines due to Fe~V and Fe~VI, ions which cannot be observed elsewhere. Fe~V and Fe~VI lines play a crucial role in driving the wind, and their strong blocking shortward of 900A can significantly modify the resulting ionization and spectral appearance. It is imperative that we have diagnostics of Fe~V and Fe~VI line formation. The overlapping observations of the He~II 1640A feature with GHRS G140L and FOS/RD G190 will allow us to match the spectral regions. The exposure times and projected S/N are given in Table 1 below, and have been estimated as follows: V = 20.7 was derived by KB95. The stellar continuum flux was predicted adopting F_Lambda vs. Lambda power law of --3, as seen in other WR stars (Morris et al., 1993, ApJ, 412, 324) and predicted by our preliminary models. Estimates for E(B --V) for DR 1 range from 0.03 (Garnett et al., 1991, ApJ, 373, 458) to 0.06 (Kingsburgh and Barlow, 1995, A\\&A, 295, 171 gives), so predicted observed fluxes take these two values into account, and are given in Table 1 below (ergs cm^-2 s^-1 AA^- 1). Note that they are continuum fluxes, and the emission line strengths will be several times the height of the continuum. Also note that with our selected aperture, the nebular continuum in the UV will be ~1000X weaker than the stellar continuum. The exposure times and S/N per diode were calculated incorporating the background count rates of 0.01 and 0.008 counts s^ -1 diode^-1 for the FOS/RD and GHRS Side 1 respectively. The exposure time for peak up on DR~1 was estimated using table 2-4 in the FOS handbook, interpolating for a power law of alpha =-1, appropriate for WR stars. We require observations of a flux standard, in addition to the standard flat field and wavelength calibrations. Any residual shift in wavelength will be easily compensated for using the nebular lines. ============================================================ Table 1: Exposure Time Estimations ------------------------------------------------------------ grating wave rng Lam F_Lam(1) F_Lam(2) exp S/N S/N # (A) (A) (min) (1) (2) orbits ------------------------------------------------------------ FOS/RD G190H 1590-2317 1850 3.85(-16) 3.10(-16) 119 10.7 9.4 3 G270H 2222-3277 2800 1.20(-16) 1.01(-16) 82 15.3 13.8 2 GHRS Side1 G140L 1100-1900 1300 1.17(-15) 8.79(-16) 111 9.7 8.1 3 ------------------------------------------------------- ----- Notes to Table 1: (1) if E(B--V)=0.03; (2) if E(B--V)=0.06 ============================================================ Real Time Justification ----------------------- None None Calibration Justification ------------------------- Additional Comments ------------------- 0.5-pair aperture used to observe simultaneously WR star and portion of surrounding nebular ------------------------------------------------------------------------------------ Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 6622( 12) - 10/24/96 09:22 - [ 1] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 IC1613- STAR RA=01H 05M 03.0S +/- 0.05S, J2000 V = 14.2 OFFSET DEC=02D 04' 53.3" +/- 0.7", B-V = 0.52+/-0.05 PLATE-ID=04YD E(B-V) = 0.02+/-0.02 Comments: b-y=0.354 2 IC1613- EXT-STAR, EXT-MEDIUM, RA-OFF=-01.40S+/-0.033S, DEC- J2000 V = 20.7 010502+02042 HII REGION OFF=-32.6"+/-0.5", FROM 1 PLATE- E(B-V) = 0.04+/-0.02 1 ID=04YD F-CONT(1300)=1.0+/-0.2e-15 F-CONT(1850)=3.5+/-0.4e-16 F-CONT(2800)=1.1+/-0.1e-16 Comments: Note: stellar line fluxes will be several times the height of the continuum 6622( 12) - 10/24/96 09:22 - [ 2] 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 IC1613-OFFS FOS/RD ACQ/BIN 4.3 MIRROR BRIGHT=58900 1 2.17 S ONBOARD ACQ FOR 2 ET ARY Comments: STAGE 1 (Z) OF 3-STAGE PEAK UP WITH POINTING ACCURACY OF 0.04 ------------------------------------------------------------------------------------------------------------------------------------ 2 IC1613-OFFS FOS/RD ACQ/PEA 0.25-PA G570H SCAN-STEP-Y=0.17,SCAN-STEP-X=0.17 1 1.0 S ONBOARD ACQ FOR 3 ET K IR ,SEARCH-SIZE-Y=5,SEARCH-SIZE-X=5 Comments: STAGE 2 (P1) OF 3 STAGE PEAK UP WITH POINTING ACCURACY OF 0.04; G570H GRATING USED FOR ACQUISITION ONLY ------------------------------------------------------------------------------------------------------------------------------------ 3 IC1613-OFFS FOS/RD ACQ/PEA 0.25-PA G570H SCAN-STEP-Y=0.07,SCAN-STEP-X=0.07 1 1.0 S ONBOARD ACQ FOR 4 ET K IR-A ,SEARCH-SIZE-Y=4,SEARCH-SIZE-X=4 Comments: STAGE 3 (MODIFIED P3) OF 3 STAGE PEAK UP WITH POINTING ACCURACY OF 0.04 ------------------------------------------------------------------------------------------------------------------------------------ 4 IC1613-0105 FOS/RD ACQ/PEA 0.25-PA G650L 4580-48 SCAN-STEP-Y=0.07,SCAN-STEP-X=0.07 1 55 S ONBOARD ACQ FOR 5-6 02+020421 K IR-A 00 ,SEARCH-SIZE-Y=5,SEARCH-SIZE-X=5 Comments: REPEAT OF STAGE 3 PEAK UP ON TARGET. WAVELENGTH RANGE RESTRICTED TO +/- 100 A OF 4686 STELLAR FEATURE ------------------------------------------------------------------------------------------------------------------------------------ 5 IC1613-0105 FOS/RD ACCUM 0.5-PAI G190H STEP-PATT=OBJ-OBJ 1 118 M 02+020421 R-A ------------------------------------------------------------------------------------------------------------------------------------ 6 IC1613-0105 FOS/RD ACCUM 0.5-PAI G270H STEP-PATT=OBJ-OBJ 1 75 M 02+020421 R-A ------------------------------------------------------------------------------------------------------------------------------------ 6622( 12) - 10/24/96 09:22 - [ 3] Visit: 02 Visit Requirements: On Hold Comments: Additional Comments: standard wavelength and flux calibrations are suitable for this programme Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 IC1613-OFFS HRS ACQ 2.0 MIRROR-N2 BRIGHT=RETURN,SEARCH-SIZE=3, 1 36 S ONBOARD ACQ FOR 2-4 ET LOCATE=YES Comments: STEP-TIME = 4, side 2 assisted acquisition ------------------------------------------------------------------------------------------------------------------------------------ 2 IC1613-0105 HRS ACCUM 2.0 G140L 1459 COMB=FOUR,STEP-PATT=DEF, 7 544.0 S 02+020421 DOPPLER=DEF,STEP-TIME=0.2, CENSOR=YES ------------------------------------------------------------------------------------------------------------------------------------ 3 IC1613-0105 HRS ACCUM 2.0 G140L 1459 COMB=FOUR,STEP-PATT=DEF, 7 544.0 S 02+020421 DOPPLER=DEF,STEP-TIME=0.2, CENSOR=YES ------------------------------------------------------------------------------------------------------------------------------------ 4 IC1613-0105 HRS ACCUM 2.0 G140L 1459 COMB=FOUR,STEP-PATT=DEF, 1 54.4 S 02+020421 DOPPLER=DEF,STEP-TIME=0.2, CENSOR=YES ------------------------------------------------------------------------------------------------------------------------------------ 6622( 12) - 10/24/96 09:22 - [ 4] Summary Form for Proposal 6622 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations FOS/RD HRS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ/BINARY ACQ/PEAK ACCUM ACQ ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BRIGHT=58900 SEARCH-SIZE-X=5 SEARCH-SIZE-X=4 SEARCH-SIZE-Y=5 STEP-PATT=OBJ-OBJ LOCATE=YES CENSOR=YES STEP-TIME=0.2 DOPPLER=DEF ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category HOT STARS ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ONBOARD ACQ FOR 2 ONBOARD ACQ FOR 3 ONBOARD ACQ FOR 4 ONBOARD ACQ FOR 5-6 ONBOARD ACQ FOR 2-4 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G570H G650L G190H G270H MIRROR-N2 G140L ------------------------------------------------------------------------------------------------------------------------------------ Target Names IC1613-OFFSET IC1613-010502+020421 ------------------------------------------------------------------------------------------------------------------------------------