Page 1 PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID 4305c Report Date: 09-May-96:19:31 Version: ********** Check-in Date: ********** 1.Proposal Title: A CRITICAL EXTENSION OF THE INTERSTELLAR POLARIZATION CURVE: CYCLE3HIGH ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Proposal Type 5. Continuation ID INTERSTELLAR MEDIUM GO Sub Category DUST ------------------------------------------------------------------------------------ 6. Principal Investigator Institution Country Telephone Geoffrey C. Clayton U.COLORADO CASA USA ------------------------------------------------------------------------------------ 7. Abstract WUPPE obtained the first ultraviolet spectropolarimetric observations which provided data on the wavelength dependence of interstellar polarization along 8 lines of sight. The data reveal three distinct UV wavelength dependences: Serkowski, super- Serkowski, and a bump at 2175 A. The behavior of the UV polarization seems to be correlated to Lambda-max. Wolff et al. (1993) use the WUPPE data to re-examine four grain models used to fit the extinction and polarization in the visible and IR. Stringent constraints are placed upon models by the necessity of reproducing both Serkowski and super-Serkowski behavior. In fact, the UV polarimetry allowed Wolff et al. to identify non-physical aspects of several grain models, and to obtain information about grain morphology and environments. However, the observed sample suffers from selection bias. All but one of the objects fall into a narrow band of Lambda-max, critically under sampling the observed range. We propose to add an extreme Lambda-max sightline to the existing sample. This will provide a double impact: 1) verification of the Lambda-max/UV behavior trend and 2) key insight into the physical nature of grains and their environments. HST is uniquely suited to provide these data and Cycle 3 is the last opportunity to do polarimetry with HST. One consequence of the installation of COSTAR will be the permanent loss of HST's polarimetric capabilities. ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ 9. Est obs time (hours) pri: 3.00 par: 0 10. Num targs pri: 1 par: 0 ------------------------------------------------------------------------------------ 11. Instruments requested: FOS ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ Page 2 I. GENERAL FORM Proposal 4305c PI: Geoffrey C. Clayton Proposal Title: A CRITICAL EXTENSION OF THE INTERSTELLAR POLARIZATION CURVE: CYCLE3HIGH ------------------------------------------------------------------------------------ 1. Proposers: Proposers Institution Country ESA ------------------------------------------------------------------------------------ Pi Geoffrey C. Clayton U.COLORADO CASA USA Michael J. Wolff UNIVERSITY OF WISCONSIN USA ------------------------------------------------------------------------------------ 2. Scientific Justification. 2. Scientific Justification ==> Not required for Phase II <== ------------------------------------------------------------------------------------ 3. Description of proposed observations. 3. Short Description of Proposed Observations We plan to use the Faint Object Spectrograph in its polarimetric mode, which will no longer be useful after Cycle 3, to observe HD 204827 which is characterized by an extreme value of lambda-max. Because of the 2175 A Bump and the fact that the deviations from the Serkowski Curve occur primarily below 2500 A, both of which are near the wavelength at which the sensitivities of the two grating systems cross over, it is necessary to make observations with both the G190H and G270H gratings in order fully to cover the ultraviolet polarization curve. Eight waveplate positions will be used. ------------------------------------------------------------------------------------ 4. Justification of need for HST observations. 4. Need for HST The observations obtained by WUPPE clearly demonstrate the complexity of UV polarization. The modeling efforts of Wolff et al. (1993) have clearly delineated the immense potential of these observations to place constraints on the physical characteristics of the interstellar dust grains. Unfortunately, their work was limited by the range of lambda-max values available. It is crucial that the range of lambda-max be properly sampled. The inability of ground-based instrumentation to access UV regime necessitates the use of a space-based facility. Further use of WUPPE is problematic at best and, in any case, will be able to provide only a small number of interstellar objects. The only other spacecraft capable of making these observations in the foreseeable future is the HST. Although a proposal to study interstellar UV polarization has been accepted for Cycle 1 (Somerville et al.), its targets (HD7252, HD 98965, HD161056) have values of lambda-max already sampled by WUPPE (5100, 5900, and 5700 A, respectively). Given the critical nature of extending the UV interstellar polarimetry database and the future loss of FOS's polarimetric capability, Cycle 3 represents the last best opportunity to observe extreme lambda-max objects. Page 3 ------------------------------------------------------------------------------------ 5. Description of special scheduling requirements. 5. Justification of Exposure Times The fact that the super-Serkowski behavior is most obvious below 2500 A necessitates the use of both the G190H and G270H gratings. In order to be able to unambiguously characterize the UV polarimetry behavior, we required that the deviation be at least 3 sigma in a 100 A bin around 1900 A and 2400 A (using about 3 A per diode which accounts for the loss of resolution due to the aberration). An example calculation for HD204827 (Pmax=5.6%, lambda-max=4600 A) is included below to demonstrate the feasibility of this project. The second column gives the counts per diode taking all correction factors into consideration. The 3rd and 4th columns indicate the 1 sigma polarimetric error, for a 100 A and a 200 A bin centered around the given wavelength. The right-hand column gives the extrapolation of the Serkowski relationship into the UV. The "deviation" indicated is the difference in the Serkowski extrapolation and the amount of polarization expected if HD204827 has a super-Serkowski behavior similar to that of HD25443. l (A) cts/diode 100 A bin 200 A bin Serkowski P(%) 1700 3800 0.23 0.16 2.60 1900 2800 0.27 0.19 3.06 ("deviation" is 1.1%) 2100 1100 0.42 0.30 3.48 2300 1600 0.35 - - 3.86 2500 23000 0.16 -- 4.20 ("deviation" is 0.8%) ------------------------------------------------------------------------------------ 6. Description of special calibration exposures. 6. a. Justification of special scheduling requests ==> none <== 6. b. Special calibration requirements ==> none <== ------------------------------------------------------------------------------------ 7. Data reduction and analysis plans. 7. Data Reduction and Analysis It is expected that the standard data reduction routines of the Institute will suffice for the data reduction. We include funds for a one week visit to the Institute for this purpose. Data analysis will initially be an extension of the grain modeling approach and methods employed by Wolff et al. (1993). This will entail the use of several grain morphologies and computational techniques. Analytical formulae are available for both the homogeneous and the concentric (core-mantle) infinite cylinders as well as homogeneous spheroids. These shapes have been successful in reproducing the general shape of the interstellar polarization curve. However, actual dust grains are likely to have irregular shapes for which exact analytical solutions do not exit. Thus, we will also utilize the Discrete-Dipole Approximation (DDA) which represents a grain as a collection of spherical dipoles. The utility of this method has been significantly advanced in the past three years through major improvements in theory, application of efficient numerical algorithms, and faster computers. As recent advances in the study of dust have provided motivation for the existence of composite grains, our analysis work will consider several grain possibilities. Unfortunately, no exact methods exist for the theoretical determination of bulk optical constants for a mixture of materials. Effective medium theory, with neglects the subparticle interactions, may be used to approximate such constants. In addition, we will again utilize the DDA which dispenses with the previous approximation. ------------------------------------------------------------------------------------ 8. Additional comments or special requests. 8. Special Comments ==> none <== ------------------------------------------------------------------------------------ 9. Description of previous HST work. 9. Previous HST observing Time ==> none <== Page 4 ------------------------------------------------------------------------------------ 10. Resources to be supplied by investigator's institution(s). 10. Resources to be Supplied by Institution(s) The Pine Bluff Observatory (University of Wisconsin) will provide (near-) simultaneous spectropolarimetry for the target as well as variability studies in order to maximize the utility of the FOS observations. Computer facilities at the CASA and at the Midwestern Astronomical Data Reduction and Analysis Facility (MADRAF) will be available for the analysis work on this project. CASA provides six months of support for G. Clayton. ------------------------------------------------------------------------------------ 11. Address Information Name: GEOFFREY C. CLAYTON Category: PI Institution: U.Colorado CASA Address: CAMPUS BOX 389 City: BOULDER State: CO Zip Code: 80309 Country: USA Telephone: 303-492-4057 Telex (or e-mail): ------------------------------------------------------------------------------------ TARGET LIST a) Fixed Targets ID = 4305c [ 5] ------------------------------------------------------------------------------------------------------------------------------------ 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial |Acqui|FLX| Flux data No | Name | Description | Position |Eqnx | Vel. |Prblm|REF| | | | | | | | | ------------------------------------------------------------------------------------------------------------------------------------ 1 HD204827 A,110 RA=322.24040D +/- 0.3", 2000 1 V=7.95 +/- 0.01, TYPE=B0V GSC03977- DEC=58.74001D +/-0.3", 2 B-V=0.80 +/- 0.01 00961 PLATE-ID=00C6 3 E(B-V)=1.10 +/- 0.05 4 F-CONT(3200)=12 +/- 1E-13 5 F-CONT(2400)=2 +/- 0.1E-13 6 F-CONT(2000)=1 +/- 0.1E-13 7 F-CONT(1600)=1 +/- 0.1E-13 ------------------------------------------------------------------------------------------------------------------------------------ EXPOSURE LOGSHEET ID = 4305c [ 6] ------------------------------------------------------------------------------------------------------------------------------------ 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |10 | 11 | 12 |13 |14| 15 ------------------------------------------------------------------------------------------------------------------------------------ Line | Seq | Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | S/N |Flx|Pr| Special Number | Name | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| |Rel. Time|Ref| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 HD204827 FOS/BL ACQ/ 4.3 G190H 1900 1 0.7S 70 1 1 ONBOARD ACQ FOR 2 PEAK SPATIAL SCAN CYCLE 3/1-4 SEQ 1-4 NO GAP Comments: PEAKUP ACQUISITION FOR BRIGHT STAR. ------------------------------------------------------------------------------------------------------------------------------------ 2 HD204827 FOS/BL ACQ/ 1.0 G190H 1900 1 1S 70 1 1 ONBOARD ACQ FOR 3- PEAK 4 SPATIAL SCAN Comments: PEAKUP IN 1 ARCSEC APERTURE. ------------------------------------------------------------------------------------------------------------------------------------ 3 HD204827 FOS/BL ACCUM 4.3 G190H 1900 POLSCAN=4B 1 2182.5S 77 6 1 4365S ------------------------------------------------------------------------------------------------------------------------------------ 3.1 HD204827 FOS/BL ACCUM 4.3 G190H 1900 POLSCAN=4B 1 2182.5S 77 6 1 4365S ------------------------------------------------------------------------------------------------------------------------------------ 4 HD204827 FOS/BL ACCUM 4.3 G270H 2700 POLSCAN=8B 1 500S 130 4 1 500S ------------------------------------------------------------------------------------------------------------------------------------ Scan Paramters Form Proposal ID: 4305c [ 7] ------------------------------------------------------------------------------------------------------------------------------------ Data ID: 1 Exposure Logsheet lines: 1 FGS Scan: N DWELL Dwell Only: dwell points/line: 3 Seconds per dwell: 1.00 Scan width (arc-secs): 0.0000 Scan length (arc-secs): 2.8000 Angle between sides (degrees) 90.00 Number of lines: 1 Scan rate (arc-sec/sec): 0.0000 PA of first scan line (degrees) 0.000 Scan frame (CEL or S/C): S/C Length Offset (arc-sec): 1.4000 Width Offset (arc-sec): 0.0 ------------------------------------------------------------------------------------------------------------------------------------ Data ID: 2 Exposure Logsheet lines: 2 FGS Scan: N DWELL Dwell Only: dwell points/line: 6 Seconds per dwell: 1.00 Scan width (arc-secs): 0.7000 Scan length (arc-secs): 3.5000 Angle between sides (degrees) 90.00 Number of lines: 2 Scan rate (arc-sec/sec): 0.0000 PA of first scan line (degrees) 90.000 Scan frame (CEL or S/C): S/C Length Offset (arc-sec): 1.7500 Width Offset (arc-sec): 0.3500 ------------------------------------------------------------------------------------------------------------------------------------ Summary Form for Proposal 4305c [ 8] Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations FOS/BL ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ/PEAK ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters POLSCAN=4B POLSCAN=8B ------------------------------------------------------------------------------------------------------------------------------------ Proposal for GO ------------------------------------------------------------------------------------------------------------------------------------ S/C Hours 3.00 ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category INTERSTELLAR MEDIUM ------------------------------------------------------------------------------------------------------------------------------------ Scientific Sub-category DUST ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ONBOARD ACQ FOR 2; SPATIAL SCAN; CYCLE 3/1-4; SEQ 1-4 NO GAP ONBOARD ACQ FOR 3-4; SPATIAL SCAN ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G190H G270H ------------------------------------------------------------------------------------------------------------------------------------ Target Names HD204827 GSC03977-00961 ------------------------------------------------------------------------------------------------------------------------------------