Page 1 PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID 4606c Report Date: 09-May-96:19:44 Version: ********** Check-in Date: ********** 1.Proposal Title: SPECTROPOLARIMETRY OF HD197770, A SEARCH FOR A GRAPHITE SIGNATURE IN THE INTERSTELLAR POLARIZATION ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Proposal Type 5. Continuation ID INTERSTELLAR MEDIUM GO 4606 Sub Category DUST ------------------------------------------------------------------------------------ 6. Principal Investigator Institution Country Telephone Dr. Christopher M Anderson UNIVERSITY OF WISCONSIN USA 608-262-0492 PROFESSOR ------------------------------------------------------------------------------------ 7. Abstract The wavelength dependence of the ultraviolet interstellar linear polarization for 8 stars with substantial interstellar extinction was observed by the Wisconsin Ultraviolet Photo Polarimeter Experiment (WUPPE) during the 1990 December Astro-1 mission. One star, HD197770 shows a very distinct polarization feature which coincides with the well known 2175 A extinction bump. Most models of the interstellar grains invoke graphite to explain the extinction bump. Computations by Draine (1988) based on the discrete dipole approximation show that a very good match to the bump can be produced by small (typical size of order 100A) graphite disks (axial ratios of order 1.5). Draine's model also suggests that these grains will produce a feature in the linear polarization like that observed by WUPPE. The birefringence of graphite also introduces circular polarization with a zero crossing at the feature, but its level is too small to be measured in practical exposure times. Thus we propose to utilize the HST FOS to measure linear polarization in the vicinity of 2175 A and thereby confirm the WUPPE result, further substantiate the presence or absence of a small, aligned graphite component of the interstellar medium along this line of sight and test the Draine models. THIS OBSERVATION WILL NOT BE POSSIBLE AFTER HST REFURBISHMENT ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ 9. Est obs time (hours) pri: 1.35 par: 0 10. Num targs pri: 1 par: 0 ------------------------------------------------------------------------------------ 11. Instruments requested: FOS ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ Page 2 I. GENERAL FORM Proposal 4606c PI: Dr. Christopher M Anderson Proposal Title: SPECTROPOLARIMETRY OF HD197770, A SEARCH FOR A GRAPHITE SIGNATURE IN THE INTERSTELLAR POLARIZATION ------------------------------------------------------------------------------------ 1. Proposers: Proposers Institution Country ESA ------------------------------------------------------------------------------------ Pi Christopher M Anderson UNIVERSITY OF WISCONSIN USA ------------------------------------------------------------------------------------ 2. Scientific Justification. See Phase I Submission ------------------------------------------------------------------------------------ 3. Description of proposed observations. We propose to use the Faint Object Spectrograph in its polarimetric mode to observe this one star. Since the 2175 A extinction feature which is the subject of the investigation is near the wavelength at which the sensitivities of the two grating systems cross over, it is necessary to make observations with both gratings in order fully to cover the ultraviolet polarization curve. Since only linear polarization is to be measured, only a 8 filter position polscan is required and superior signal to noise can be achieved in the allotted time. ------------------------------------------------------------------------------------ 4. Justification of need for HST observations. The observations needed to attempt to detect the polarization signature of graphite are in the ultraviolet so that ground-based observations cannot serve this purpose. The Wisconsin Ultraviolet Photo Polarimeter Experiment (WUPPE) which made the observations which motivate this proposal was used only in its linear mode on Astro-1. WUPPE will attempt to observe circular polarization in HD197770 on Astro-2, but the confirmation of the Astro-1 result by a completely different insturment is simply good scientific practice. The HST FOS is the only other existing spacecraft which could make such observations. ------------------------------------------------------------------------------------ 5. Description of special scheduling requirements. No special scheduling requirements apply to this observation, however it should be noted that it this object can be quite close to the continuous viewing zone of the spacecraft. It is thus possible that by proper scheduling a better spacecraft usage efficiency than that predicted by the resource estimator might be achieved. ------------------------------------------------------------------------------------ 6. Description of special calibration exposures. NONE ------------------------------------------------------------------------------------ 7. Data reduction and analysis plans. 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. For analysis purposes a wide variety of interstellar dust modeling programs are available at the PI's institution and will be used. In particular should the signature be found, a diverse population of discrete dipole approximation computations will be done and mixed to explore the fitting parameters of the signature. ------------------------------------------------------------------------------------ 8. Additional comments or special requests. NONE ------------------------------------------------------------------------------------ 9. Description of previous HST work. NONE Page 3 ------------------------------------------------------------------------------------ 10. Resources to be supplied by investigator's institution(s). The University of Wisconsin will provide the computer facilities of the Midwestern Astronomical Data Reduction and Analysis Facility (MADRAF) for the analyis work on this project. ------------------------------------------------------------------------------------ 11. Address Information Name: CHRISTOPHER M ANDERSON Category: PI Institution: UNIVERSITY OF WISCONSIN Address: DEPARTMENT OF ASTRONOMY 475 NORTH CHARTER STREET City: MADISON State: WI Zip Code: 53706 Country: USA Telephone: 608-262-0492 Telex (or e-mail): 265452 UOFSISC MDS ------------------------------------------------------------------------------------ TARGET LIST a) Fixed Targets ID = 4606c [ 4] ------------------------------------------------------------------------------------------------------------------------------------ 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 HD197770 A,111, RA = 20H 41M 57.95S +/- 1950 1 V=6.32+/-0.02, TYPE=B2III, 0.02S, DEC = +56D 55' 58.2" +/- 0.2", ------------------------------------------------------------------------------------------------------------------------------------ EXPOSURE LOGSHEET ID = 4606c [ 5] ------------------------------------------------------------------------------------------------------------------------------------ 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 ------------------------------------------------------------------------------------------------------------------------------------ 0.1 HD197770 FOS/BL ACQ/ 4.3 G190H SEARCH-SIZE-X=1 1 1S 1 1 CYCLE 3 / 0.1-2 PEAK SEARCH-SIZE-Y=3 ONBOARD ACQ FOR SCAN-STEP-Y=1.4 0.2 ------------------------------------------------------------------------------------------------------------------------------------ 0.2 HD197770 FOS/BL ACQ/ 1.0 G190H SEARCH-SIZE-X=6 1 1S 1 1 ONBOARD ACQ FOR 1- PEAK SEARCH-SIZE-Y=2 2 SCAN-STEP-Y=0.7 SCAN-STEP-X=0.7 ------------------------------------------------------------------------------------------------------------------------------------ 1 HD197770 FOS/BL ACCUM 1.0 G190H, 1954 POLSCAN=8B 1 2299.0S 1000 1 1 POL0-B ------------------------------------------------------------------------------------------------------------------------------------ 2 HD197770 FOS/BL ACCUM 1.0 G270H, 2820 POLSCAN=8B 1 1294.0S 1000 1 1 POL0-B ------------------------------------------------------------------------------------------------------------------------------------ Summary Form for Proposal 4606c [ 6] Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations FOS/BL ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ/PEAK ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters SEARCH-SIZE-X=1 SEARCH-SIZE-Y=3 SCAN-STEP-Y=1.4 SEARCH-SIZE-X=6 SEARCH-SIZE-Y=2 SCAN-STEP-Y=0.7 SCAN-STEP-X=0.7 POLSCAN=8B ------------------------------------------------------------------------------------------------------------------------------------ Proposal for GO ------------------------------------------------------------------------------------------------------------------------------------ S/C Hours 1.35 ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category INTERSTELLAR MEDIUM ------------------------------------------------------------------------------------------------------------------------------------ Scientific Sub-category DUST ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements CYCLE 3 / 0.1-2; ONBOARD ACQ FOR 0.2; ONBOARD ACQ FOR 1-2; ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G190H G190H,POL0-B G270H,POL0-B ------------------------------------------------------------------------------------------------------------------------------------ Target Names HD197770 ------------------------------------------------------------------------------------------------------------------------------------