5890( 6) - 11/27/95 09:43 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 5890 Version: 6 Check-in Date: ********** 1.Proposal Title: Far-UV Extinction for Deeply Embedded Stars in Interstellar Clouds ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle Interstellar Medium GO 5 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Dr. C. Gregory Seab University of New Orleans CoI: Dr. Theodore P. Snow University of Colorado N ------------------------------------------------------------------------------------ 6. Abstract Optical and UV absorption observations of interstellar clouds are inherently limited to studies of only the outer edges of the clouds because of grain extinction. A deeper penetration of the clouds is important to the overall understanding of these objects because the grain properties are expected to change with depth in the clouds by either the coagulation of grains or the accretion of fresh material from the gas phase (ices and/or refractory material). The far-UV grain properties in particular will affect the penetration of UV photons into the cloud cores, with a consequent effect on the cloud chemistry and physical state. In order to elucidate the changes in grain properties and UV fields in dark clouds, an extinction study of targets deep in interstellar clouds is proposed for the FOS instrument of the HST. This instrument can penetrate deeper into the cloud than has been done before. ------------------------------------------------------------------------------------ 5890( 6) - 11/27/95 09:43 - [ 2] Observations Description ------------------------ For this feasiblity study, only one target star will be attempted. In order to measure the complete extinction curves, two gratings are needed. The G160L grating with the Blue camera will cover the wavelength range from 1150 to 2508 Angstrom\ with a dispersion of 6.87 Angstrom- Diode^-1, while the G270H grating with the Red camera will cover from 2222 to 3277 Angstrom\ at the higher resolution of 2.05 Angstrom- Diode^- 1. Exposure time are calculated for various wavelengths for the G160L grating on the BLue side and G270H grating on the Red side by scaling from stars of the appropriate spectral type from the IUE Spectral Atlas (Wu et al. 1991, IUE Newletter No. 43), corrected for the reddening using either the standard curve from Savage and Mathis (1979, ARAA, 17, 73) or the Rho Oph curve (Seab et al. 1981, ApJ, 246, 788). Exposures were calculated for S/N >= 20 where possible. The data will be binned over several pixels to improve the signal. Although the higher dispersion available from unbinned data is preferred in that it allows a clearer detection of the continuum, the binned data should be sufficient to determine the level of the far-UV extinction even in this worst case. Orbit requirements were determined according to the procedures in the Phase I Proposal Instructions manual. Because of the uncertainty in the flux due to the very high and probably anomalous UV extinction, the ACQ/PEAK acquisition method will be needed even though it adds about one extra orbit to the observation schedule. Derivation of the extinction curves will follow the usual pair method of Bless and Savage (1972, ApJ, 171, 293). Since the FOS is limited to stars dimmer than about 9th magnitude, it is not possible to select an adequate grid of unreddened comparison stars for use in this method. We therefore plan to use the standard stars observed with the IUE (e.g., The IUE Spectral Atlas, Wu et al., 1991, IUE Newsletter No. 43) for the purpose. The translation of the IUE data to match the format of the FOS data will need some care; the IUE data will need to be appropriately binned, smoothed, and convolved with the FOS instrument profile so that spurious data processing effects do not corrupt the results. Ideally, one should observe at least one star also seen with the IUE to verify techniques. Since the allotted orbits for this project do not allow for this, we will depend on the archive and calibration data to verify the comparison. Using the IUE archive has the advantage of making available a very large grid of possible comparisons, which will be used to test the effects of spectral typing errors in the target stars, thus giving an indication of the uncertainty level of the results. Real Time Justification ----------------------- No special requirements. Calibration Justification ------------------------- Additional Comments ------------------- The fact that the UV extinction curve is unknown creates an inherent difficulty in estimating exposure times for this type of project. Extensive experience with other instruments such as the IUE shows that a conservative best guess is generally sufficient to get usable data. ------------------------------------------------------------------------------------ 5890( 6) - 11/27/95 09:43 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 5890( 6) - 11/27/95 09:43 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC2024- STAR,B0-B2 V-IV RA = 05H 41M 37.75S +/- 0.01S, J2000 V=12.17 +/- 0.2 054138- DEC = -01D 54' 37.4" +/- 0.2", E(B-V)=1.69 +/- 0.3 015444 PLATE-ID = 06EN TYPE=B0.5V Comments: Rv=4.2, Coordinates updated from GSC Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 1986.132 0.0 0.0 0.0 5890( 6) - 11/27/95 09:43 - [ 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 NGC2024- FOS/BL ACQ/BIN 4.3 MIRROR 1 3S ONBOARD ACQ FOR 2 054138- ARY 015444 Comments: flux levels uncertain because UV extinction curve unknown ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC2024- FOS/BL ACCUM 1.0- G160L STEP- 1 18000S 054138- PAIR-A PATT=SINGLE 015444 ------------------------------------------------------------------------------------------------------------------------------------ 5890( 6) - 11/27/95 09:43 - [ 6] Visit: 02 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 NGC2024- FOS/BL ACQ/BIN 4.3 MIRROR 1 3S ONBOARD ACQ FOR 2 054138- ARY 015444 Comments: flux levels uncertain because UV extinction curve unknown ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC2024- FOS/BL ACQ/PEA 0.25- MIRROR SCAN-STEP- 1 1S ONBOARD ACQ FOR 3 054138- K PAIR-A X=0.11, SCAN- 015444 STEP-Y=0.11, SEARCH-SIZE- X=4, SEARCH- Comments: flux levels uncertain because UV extinction SIZE-Y=4 curve unknown ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC2024- FOS/RD ACCUM 1.0- G270H STEP- 1 4380S 054138- PAIR-A PATT=SINGLE 015444 ------------------------------------------------------------------------------------------------------------------------------------ 5890( 6) - 11/27/95 09:43 - [ 7] Summary Form for Proposal 5890 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations FOS/BL FOS/RD ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ/BINARY ACCUM ACQ/PEAK ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters STEP-PATT=SINGLE SEARCH-SIZE-Y=4 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category Interstellar Medium ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ONBOARD ACQ FOR 2 ONBOARD ACQ FOR 3 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G160L G270H ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC2024-054138-015444 ------------------------------------------------------------------------------------------------------------------------------------