6073( 8) - 07/05/96 10:14 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6073 Version: 8 Check-in Date: 05-Jul-1996 10:11:27 1.Proposal Title: The Chemical Composition of the Magellanic Bridge ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle Hot Stars GO 5 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Philip Dufton THE QUEEN'S UNIVERSITY OF BELFAST CoI: Rolf-Peter Kudritzki Universitaets-Sternwarte Muenchen N CoI: Danny Lennon Universitaets-Sternwarte Muenchen N CoI: Francis Keenan Queen's University of Belfast N CoI: Nigel Hambly Queen's University of Belfast N CoI: Robert Rolleston Armagh Observatory N ------------------------------------------------------------------------------------ 6. Abstract Early-type stars are excellent probes of the current chemical composition of our own and external galaxies. Main sequence stars are particularly useful as the physics of their atmospheres are well understood, while their surfaces should be unaffected by the products of interior nuclear reactions. We have used such targets to map the chemical composition of our galaxy and to provide accurate abundances for the SMC and LMC. Our attempts to determine the chemical composition of the Magellanic Bridge have been less successful despite generous allocations of 4m telescope time. This has been principally because of the absence of optical metal absorption lines due to the large metal depletion of the Bridge material and for some elements (e.g. iron) the intrinsic weakness of their optical spectra. Here we propose ultra-violet observations of a B0V Bridge star, DI 1388, which should provide reliable abundances of both the lighter (e.g. carbon and nitrogen) and heavier metals (e.g. silicon and iron). The HST observations will be supplemented by our existing (and possible additional) AAT high resolution echelle spectra. Non-LTE model atmosphere analyses of the optical hydrogen and hydrogen lines will be used to estimate atmospheric parameters, which will then form the basis for non-LTE analyses of the ultra-violet spectra. Using differential methods, abundances accurate to 0.1-0.2 dex should be achievable, which will constrain the origin and evolutionary history of this material. ------------------------------------------------------------------------------------ 6073( 8) - 07/05/96 10:14 - [ 2] Observations Description ------------------------ We will observe DI 1388 using the GHRS and two gratings, viz. beginenumerate em the low resolution grating G140L (resolution ~ 150kms) in two spectral ranges 1200- 1486Angstrom and 1500-1786Angstrom. These regions contain the resonance lines of N, v 1240Angstrom, C, ii 1335Angstrom, Si, iv 1400Angstrom, C, iv 1540Angstrom and N, iv 1740Angstrom, together with other important features such as the Si, iii triplet multiplet at 1294-1305Angstrom (all wavelengths approximate). em the moderate resolution grating G200M (resolution ~ 14kms) in the spectral region 1890- 1930Angstrom. This region contains the strong Fe III multiplet that we have previously used to estimate iron abundances from IUE spectra of B-type stars (see section 2). endenumerate All these feature should be observable even if the metal depletion in the Bridge material is substantially greater than in the SMC. Our optical spectra indicated that DI 1388 has a moderate rotational velocity (approximately 180kms), which should well match the proposed spectral resolution of the G140L grating. For the higher resolution spectra we will bin together four pixels to improve our single-to-noise ratio without significantly compromising our spectral resolution. Count rates and exposure times have been estimated from a Kurucz low metallicity model atmosphere with the appropriate effective temperature and gravity and assuming an E(B-V) of 0.^m05. Our low resolution IUE observations of the cooler Magellanic Bridge supergiant, DI 1194, implies that reddening in this region is very small and hence our count rates and signal-to-noise ratios may be slightly conservative. In the first orbit, we will undertake both the low resolution observations with exposure times of around 10 and 40 minutes per spectral region resulting in a signal- to-noise ratio of ~50 at 1500Angstrom. In the second orbit, the observations of the iron lines will be made and after binning a signal-to-noise ratio of at least 30 per resolution element should be obtained in approximately 50 minutes. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 6073( 8) - 07/05/96 10:14 - [ 3] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 STAR-025713- STAR,B0-B2 V-IV RA=2H 57M 11.94S +/- 0.1S, DEC=- 2000 V=150 V = 14.39 725256 72D 52' 54.6" +/- 1", PLATE- TYPE=B0V ID=00RE B-V = -0.26 E(B-V) = 0.05 F(1350)=2.32e-13 F(1670)=1.53e-13 F(1910)=1.14e-13 Comments: Fluxes from ATLAS model Teff=32000 logg=4.0 and SMC extinction 6073( 8) - 07/05/96 10:14 - [ 4] Visit: 01 Visit Requirements: PCS MODE F 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 STAR-025713 HRS ACQ 2.0 MIRROR-N2 BRIGHT=RETURN 1 9 S ONBOARD ACQ FOR 2-4 -725256 Comments: STEP-TIME=1S ------------------------------------------------------------------------------------------------------------------------------------ 2 STAR-025713 HRS ACCUM 2.0 G200M 1910 FP-SPLIT=STD 1 1414.4 -725256 ------------------------------------------------------------------------------------------------------------------------------------ 3 STAR-025713 HRS ACCUM 2.0 G140L 1343 FP-SPLIT=STD 1 761.6 S -725256 ------------------------------------------------------------------------------------------------------------------------------------ 4 STAR-025713 HRS ACCUM 2.0 G140L 1643 FP-SPLIT=STD 1 1849.6 -725256 ------------------------------------------------------------------------------------------------------------------------------------ 6073( 8) - 07/05/96 10:14 - [ 5] Summary Form for Proposal 6073 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations HRS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BRIGHT=RETURN FP-SPLIT=STD ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category Hot Stars ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PCS MODE F ONBOARD ACQ FOR 2-4 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR-N2 G200M G140L ------------------------------------------------------------------------------------------------------------------------------------ Target Names STAR-025713-725256 ------------------------------------------------------------------------------------------------------------------------------------