6772( 5) - 03/21/97 10:58 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6772 Version: 5 Check-in Date: 21-Mar-1997 10:42:15 1.Proposal Title: Dust properties in the Beta Pictoris ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle INTERSTELLAR MEDIUM GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: MARK CLAMPIN SPACE TELESCOPE SCIENCE INSTITUTE CoI: Pawel Artymowicz University of Stockholm N CoI: Francesco Paresce European Southern Observatory N CoI: Sebastiano Ligori University of Turin N ------------------------------------------------------------------------------------ 6. Abstract Multicolor imaging polarimetry is an excellent diagnostic of dust grain properties and scattering geometries. We propose to obtain U, B and V band imaging polarimetry of the Beta Pictoris disk to probe the dust grain distribution and composition over the region of the disk extending 4"--15" (65 AU--245 AU) from the central star. This region has been chosen so we can study the transition at 100 AU, reported from coronographic observations, which cannot be explained by current disk models. We plan to use the polarization data to compare grain size distribution and composition in the inner (65 AU--100 AU) and outer (>100 AU) regions of the disk. In addition, we will confirm the polarization asymmetries possibly measured at distances >165 AU, by previous ground- based polarization observations. We will use Mie-theory dust grain modelling to investigate the variations in grain size distribution and composition responsible for these asymmetries. The angular resolution of HST is essential to this program, as polarimetric observations cannot be made this close to the star from the ground. Circumstellar disks around main-sequence stars are generally interpreted as evidence of planetary-system formation: the characterization of their properties is a step towards an understanding of the formation and evolution of planetary systems. ------------------------------------------------------------------------------------ 6772( 5) - 03/21/97 10:58 - [ 2] Observations Description ------------------------ Polarimetric observations with WFPC2 require careful design in order to avoid constraints imposed by the design of the quadrant polarizer filter. In order to achieve our stated science goals, we have adopted an observing strategy recommended by STScI (Biretta and Sparks, WFPC2 ISR 95-01). Observations of the target are made at relative polarization angles of 0^o, 60^o and 120^o using a combination of partial filter rotations and telescope roll angles. The proposed strategy offers several advantages: beginitemize em The required roll angles are small and minimize scheduling constraints by allowing all three sets of observations ( 0^o, 60^o and 120^o) to be made during consecutive orbits. em In each case the target is placed on WF2, so the same flat field is applied to all three polarimetric observations. The main element which dominates precision of polarimetric measurements with WFPC2 is the calibration of the flat field which is currently uncertain to ~2-3% over the field of view of each CCD. We have chosen to conduct all of our observations on WF2 to avoid the further complication of calibrating CCD-to-CCD flat field and zero point effects which would compound the overall uncertainty of our polarimetric calibration. By adopting this strategy we aim to keep the absolute uncertainty of our measurements to the same order of magnitude as the flat field error, i.e., ~2- 3%, although the relative accuracy should be higher. em The partial filter rotations required permit a maximum field of view of 30", which is adequate to observe the Beta Pictoris disk out to ~15" (245 AU). em It has also been shown (WFPC2 Handbook 1995) that bright objects should be observed in the wide field cameras, as the PC suffers from an elevated level of scattered light. em We have employed the same strategy in our cycle 4 HST program, imaging polarimetry of another bright object, the Eta Carinae homunucleus. enditemize To study the polarization of the Beta Pictoris disk, at distances of 4 "-15" from the star, we will make the following set of observations, which require a total of 3 orbits. , 6pt begintabularllll Filter & Integration time & Relative Polarization angle , F300W+POLQ & 2x550 secs & 0^o, 60^o , 120^o , F450W+POLQ & 2x200 secs & 0^o, 60^o, 120^o , F555W+POLQ & 2x200 secs & 0^o, 60^o, 120^o , endtabular 6pt Our choice of filters is designed to produce observations with bandpasses located close to the U, B, and V bands. WFPC2 has a U band filter, F336W, but it has a large redleak, so we have chosen F300W which has been used in other WFPC2 GO polarimetry programs. While desirable an I band observations is not feasible with the WFPC2 polarizer. The exposure times are designed to yield a minimum S/N of at least 40 pixel^-1 for a surface brightness of 16 mag/arcsec^2, which corresponds to a distance of 100 AU from Beta Pictoris. Beta Pictoris is a bright object (V=3.8) and so the feasibility of the proposed observations must be addressed. Since it has now been observed in two different WFPC2 imaging programs, it is clear that Beta Pictoris can be observed by WFPC2. In addition, we are avoiding the technically challenging region very close to the star within 40 AU, where uncertainties in the HST PSF wings dominate the observational errors, even with HST. The observations we have proposed are not feasible without HST. Ground-based imaging polarimetry of the Beta Pictoris disk is not possible in the 4-10" region of the disk (see Wolstencroft 1995), which is crucial to our scientific goals. Equally important, we require excellent spatial sampling across the width of the disk, which is only just resolved from the ground, in order to map the polarization vectors as a function of distance from the midplane. In summary, we require a total of 3 orbits on Beta Pictoris to obtain sufficient observations for our theoretical analysis. Real Time Justification ----------------------- See above. This program will have to be carried out at two pre-selected telescope rolls, which can be scheduled sequentially. None. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 6772( 5) - 03/21/97 10:58 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: STSCI Ship Via: Email: clampin@stsci.edu ------------------------------------------------------------------------------------ 6772( 5) - 03/21/97 10:58 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 HD39060 ISM,PROTOPLANETARY DISK RA=05H 46M 5.935S +/- 0.1S,DEC=- B1950 V = 3.9 51D 5' 1.75" +/- 0.1" Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) B1950 0.0005 0.087 0.0 6772( 5) - 03/21/97 10:58 - [ 5] Visit: 01 Visit Requirements: ORIENTation 88D to 92D 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 ------------------------------------------------------------------------------------------------------------------------------------ 10 HD39060 WFPC2 IMAGE WF3 POLQ, CR-SPLIT=NO,CLOCKS=YES, 1 260 S POS TARG -33,0 F555W ATD-GAIN=15,READ=3 ------------------------------------------------------------------------------------------------------------------------------------ 20 HD39060 WFPC2 IMAGE WF3 POLQ, ATD-GAIN=15,CLOCKS=YES, 1 600 S SAME POS AS 10 F336W CR-SPLIT=NO,READ=3 ------------------------------------------------------------------------------------------------------------------------------------ 30 HD39060 WFPC2 IMAGE WF3 POLQ, CR-SPLIT=NO,CLOCKS=YES, 1 260 S POS TARG 33,0 F555W ATD-GAIN=15,READ=3 ------------------------------------------------------------------------------------------------------------------------------------ 40 HD39060 WFPC2 IMAGE WF3 POLQ, ATD-GAIN=15,CLOCKS=YES, 1 600 S SAME POS AS 30 F336W CR-SPLIT=NO,READ=3 ------------------------------------------------------------------------------------------------------------------------------------ 6772( 5) - 03/21/97 10:58 - [ 6] Visit: 02 Visit Requirements: ORIENTation 58D TO 62D FROM 1 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 ------------------------------------------------------------------------------------------------------------------------------------ 10 HD39060 WFPC2 IMAGE WF3 POLQ, CR-SPLIT=NO,CLOCKS=YES, 1 260 S POS TARG -33,0 F555W ATD-GAIN=15,READ=3 ------------------------------------------------------------------------------------------------------------------------------------ 20 HD39060 WFPC2 IMAGE WF3 POLQ, ATD-GAIN=15,CLOCKS=YES, 1 600 S SAME POS AS 10 F336W CR-SPLIT=NO,READ=3 ------------------------------------------------------------------------------------------------------------------------------------ 30 HD39060 WFPC2 IMAGE WF3 POLQ, CR-SPLIT=NO,CLOCKS=YES, 1 260 S POS TARG 33,0 F555W ATD-GAIN=15,READ=3 ------------------------------------------------------------------------------------------------------------------------------------ 40 HD39060 WFPC2 IMAGE WF3 POLQ, ATD-GAIN=15,CLOCKS=YES, 1 600 S SAME POS AS 30 F336W CR-SPLIT=NO,READ=3 ------------------------------------------------------------------------------------------------------------------------------------ 6772( 5) - 03/21/97 10:58 - [ 7] Visit: 03 Visit Requirements: ORIENTation 118D TO 122D FROM 1 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 ------------------------------------------------------------------------------------------------------------------------------------ 10 HD39060 WFPC2 IMAGE WF3 POLQ, CR-SPLIT=NO,CLOCKS=YES, 1 260 S POS TARG -33,0 F555W ATD-GAIN=15,READ=3 ------------------------------------------------------------------------------------------------------------------------------------ 20 HD39060 WFPC2 IMAGE WF3 POLQ, ATD-GAIN=15,CLOCKS=YES, 1 600 S SAME POS AS 10 F336W CR-SPLIT=NO,READ=3 ------------------------------------------------------------------------------------------------------------------------------------ 30 HD39060 WFPC2 IMAGE WF3 POLQ, CR-SPLIT=NO,CLOCKS=YES, 1 260 S POS TARG 33,0 F555W ATD-GAIN=15,READ=3 ------------------------------------------------------------------------------------------------------------------------------------ 40 HD39060 WFPC2 IMAGE WF3 POLQ, ATD-GAIN=15,CLOCKS=YES, 1 600 S SAME POS AS 30 F336W CR-SPLIT=NO,READ=3 ------------------------------------------------------------------------------------------------------------------------------------ 6772( 5) - 03/21/97 10:58 - [ 8] Summary Form for Proposal 6772 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO CLOCKS=YES ATD-GAIN=15 READ=3 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category INTERSTELLAR MEDIUM ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENTation 88D to 92D POS TARG -33,0 SAME POS AS 10 POS TARG 33,0 SAME POS AS 30 ORIENTation 58D TO 62D FROM 1 ORIENTation 118D TO 122D FROM 1 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements POLQ,F555W POLQ,F336W ------------------------------------------------------------------------------------------------------------------------------------ Target Names HD39060 ------------------------------------------------------------------------------------------------------------------------------------