! Proposal 5845, submission 1 ! PI: David Weintraub ! Received Wed Mar 15 13:45:31 EST 1995 ! From: krs@ls3.jpl.nasa.gov ! Hubble Space Telescope Cycle 5 (1995) Phase II Proposal Template ! $Id: 5845,v 6.1 1995/08/23 19:41:39 pepsa Exp $ ! ! Refer to the HST Phase II Proposal Instructions to fill this out ! ! Anything after a "!" is ignored, and may be deleted ! ! All keywords with multiple entries are comma delimited except the ! Visit_Requirements and Special_Requirements keywords which can be ! delimited with carriage returns or semi-colons, but not commas ! ! For help call your Program Coordinator: Andy Lubenow ! Phone: 410 338-4928 , E-mail: lubenow@stsci.edu ! ! This partially completed template was generated from a Phase I proposal. ! Name of Phase I Proposal: weintraub-575.prop ! Date generated: Fri Dec 16 15:25:06 EST 1994 ! Proposal_Information ! Section 4 Title: A Polarimetric Imaging Study of Reflection Nebulae around T Tauri Stars Proposal_Category: GO Scientific_Category: Interstellar Medium Cycle: 5 Investigators PI_name: David Weintraub PI_Institution: Vanderbilt University CoI_Name: Joel Kastner CoI_Institution: Massachusetts Institute of Technology Contact: ! Y or N (designate at most one contact) CoI_Name: Karl Stapelfeldt CoI_Institution: Jet Propulsion Laboratory Contact: ! Y or N (designate at most one contact) CoI_Name: Chris Burrows CoI_Institution: Space Telescope Science Institute Contact: ! Y or N (designate at most one contact) Abstract: ! Free format text (please update) Disks around pre-main-sequence (PMS) stars are among the most searched for objects in astronomy. Like planets or brown dwarfs around other stars, the potential discovery of such disks carries tremendous significance beyond the traditional boundaries of astronomy. These disks may be the sites of future or active planet formation; therefore, from studies of these disks we will learn about the likelihood of planet formation elsewhere in the galaxy. In turn, from this knowledge, we will learn more about the possibility of life in the universe beyond Earth. We propose to use the polarimetric imaging capabilities of the WFPC2 to obtain 6 AU resolution maps of ``polarization disks'' around six carefully selected T Tauri stars. We propose a unique observing plan in which we will use the planned roll of the telescope to rotate the position angle of the polarizer, thus eliminating many of the systemic errors that might otherwise affect this data set. With this HST data, we will test several models for scattered light from central sources. By doing so, we will confirm or refute a large number of claims that such ``polarization disks'' represent detections of disks of dust grains around PMS objects. These data will lead to improved models of disk formation and evolution and to future searches targeted toward the most promising sources. Questions ! Free format text (please update) Observing_Description: sectionImaging Polarimetry with WFPC2 from HST, using POLQ WFPC2 is capable of carrying out imaging polarimetry using the polarizer quad filter (POLQ). Although the WFPC2 polarizer has not yet been used, the WFPC2 team has plans to carry out a series of polarization observations in Cycle 4 so that this option will be fully calibrated for Cycle 5 observations. We recognize that WFPC2 does have a noticeable instrumental polarization because the telescope beam is fed into WFPC2 by a pickoff mirror at a 45^degrees angle of incidence; however, we should still be capable of obtaining very high precision data for light polarized at 3\ and much of the nebulosity we expect to image will be polarized at levels of 10-70\ Our request totals 18 orbits, corresponding to three orbits per target for six sources. We stress to the TAC that an allocation as small as three orbits (one target) will be of value in assessing the validity of ``polarization disk'' interpretations of ground-based polarization vector maps. Of the sources in our target list, we prioritize them in the following order: 1) HL Tauri, 2) T Tauri, 3) Haro 6- 5B, 4) VW Cha, 5) VV CrA, 6) GG Tauri. sectionAn Innovative Technique To obtain the necessary set of three polarimetric images, we propose to observe in a way that will minimize systemic calibration problems that would result from obtaining images with different cameras having different sensitivities and spatial scales, and different polarizing filters having different throughputs. We propose to utilize the roll of the HST itself to change the effective position angle of the polarizer. We will collect three images at three different roll angles of the spacecraft, providing independent polarization images with effective polarizer position angles of 0^degrees, 120^degrees and 240^degrees. The images will be collected with the source centered in the Planetary Camera (PC1), using the filter POLQ, at approximately 120 day intervals. Each image will be collected on a single orbit. In combination with POLQ, we will use the F555W (WFPC2 V) and F622W filters, both of which operate at wavelengths where POLQ discriminates well between the parallel ( 60\ and perpendicular (<5\ filters will depend on the color of the source. sectionCalibrations In order to do this experiment, the response of PC1 to an unpolarized source must be properly calibrated. The WFPC2 calibration group at STScI is scheduled to obtain the necessary calibration data for the polarizers during Cycle 4. If, however, such data is not obtained prior to and independent from our experiment, we will require additional time for obtaining this important calibration measurement. sectionObserving Strategy Our goal is to image faint nebulosity with high S/N. In some cases, it will be necessary to saturate the star in order to carry out this experiment. We have devised our observing plan assuming that approximately 45 minutes per 97 minute orbit represents usable observing time. Each source requires three orbits for the collection of a complete polarimetric data set. HL Tauri: Almost all of the optical light from HL Tauri is diffuse, surface brightness emission. Stapelfeldt et al. (1994, BAAS abstract 16.06) imaged HL Tauri for 350 s at I band with PC1 and obtained 400 counts as the peak flux. At V band, the star is fainter and the polarizer reduces the throughput by more than 50\ filter (assumed in all calculations below), we estimate we will collect a total of ~5,000 electrons per second or 3*10^6 electrons in 600 s. Because almost all of this is diffuse surface brightness spread over several hundred PC1 pixels, saturation will not occur. For each orbit (a single polarizer position), we propose to take four 600 s exposures to allow post-processing removal of cosmic ray events. These images should yield S/N > 10 for surface brightnesses at least as faint as 25^m. These four 10 minute exposures, plus about three minutes overhead between frames require about 52 minutes. T Tauri: This star has a true stellar core with V = 9.6. we estimate that we will detect ~5*10^5 electrons per second. Stapelfeldt et al. (1994) obtained 14 s images with PC1 at V band in which the star was significantly saturated, affecting approximately 25 pixels by bleeding in each of two columns near the star. The F622W filter has a similar bandwidth as the V filter (F555W). Therefore, images of similar length with F622W but also with the polarizer will be only slightly saturated. For this experiment, we will sacrifice the inner few pixels to saturation in order to obtain longer exposures of the faint surrounding nebulosity while minimizing the overheads per readout. We propose to obtain fourteen (14) exposures each of 20 s. These exposures plus the overheads for readout require about 47 minutes. Haro 6-5B + FS Tau: These two nebulous stars are separated by 17^ and thus will appear in the same PC1 field. The given coordinates are centered between the two targets. At V = 15.7, the brighter source will produce 2000 electrons per second, much of which is diffuse nebulosity. As for HL Tauri, the maximum 600 s exposures will yield the best S/N, utilize the orbit with a minimum of overhead time, and most likely will not saturate anywhere in the image. Our observing strategy will be the same as for HL Tauri. GG Tauri, VW Cha and VV CrA: With V = 12.34, 12.51 and 13.01, these targets will produce 25,000-15,000 electrons per second, assuming these magnitudes represent fluxes from point sources. If half of this flux is diffuse nebulosity, then we can integrate for five seconds without bleeding or saturating the ADC. As we are most interested in the diffuse emission, we propose to integrate for 60 s. We will thereby obtain eleven (11) 60 s exposures for each of these three targets. This strategy requires about 44 minutes per orbit. We note that for the sources which we saturate, the images will have bright diffraction spikes in addition to the saturated pixels. By subtracting a point spread function from the images, we should be able to remove most of the effects of the spikes, although we expect to have some minor residuals left from imperfect cancelling. We do not believe such post- processing residuals will negatively impact our analysis. We also note that by rolling the telescope to get our polarization coverage, we will also roll the diffraction spikes around on the field. Thus for three roll angles, we will have 12 residual spikes present in the final polarization dataset. Although this represents a disadvantage of the telescope rolling option, we believe the advantages of the rolling option more than offset this disadvantage. In addition, we believe nearly all of the diffraction spikes will be removable in processing and thus do not expect this to negatively impact our program. This is will not be an issue at all in the data sets for HL Tauri and Haro 6-5B and the diffraction spikes will likely be minor effects for most of the other target sources. Only for T Tauri does this represent a significant issue; however, the importance of this source in studies of PMS stars is such that we believe the observations in this observing mode are worthwhile. Real_Time_Justification: The innovative aspect of our observing program requires utilizing the planned roll of the HST spacecraft to change the effective position angle of the polarizing filter. Observations of each target will require a total of three orbits, one for each of the three necessary polarizer position angles (0^degrees, 120^degrees and 240^degrees). The respective orbits will be about 120 days apart. We have confirmed that this program is technically possible based on the spacecraft orientations over a period of several months. The exact spacing of the orbits will be determined by scheduling and roll requirements of HST. We would prefer that the three orbits for a single target provide position angle spacings of as close as possible to 120^degrees and 240^degrees from the original orbit; however, an HST schedule that yields position angles that are off by a few degrees will not seriously damage our program. This should provide sufficient planning flexibility to permit our observations to be scheduled. There are no special dark-time, CVZ or TOO observations required for this program. No supporting/coordinated observations involved in this program. Calibration_Justification: Additional_Comments: Fixed_Targets ! Section 5.1 Target_Number: 1 Target_Name: HL-TAU Alternate_Names: HBC 47 Description: STAR, T TAURI STAR Position: RA= 4H 28M 44.4S +/- 0.100S, DEC= 18D 7' 36.0" +/- 0.10" Equinox: B1950.00 RV_or_Z: RA_PM: ! Units are seconds of time per year Dec_PM: ! Units are seconds of arc per year Epoch: Annual_Parallax: Flux: V= 14.5 B-V = 1.37 ! Include at least V and B-V Comments: ! This is a template for a single visit containing a single exposure ! Repeat exposure and visit blocks as needed Visits Visit_Number: 01 Visit_Requirements: Orient 85d to 85d On_Hold_Comments: Visit_Comments: Exposure_Number: 11 Target_Name: HL-TAU Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F555W,POLQ Optional_Parameters: ATD-GAIN=15, CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 700S Special_Requirements: pos targ 8.0, 8.0 Comments: Exposure_Number: 12 Target_Name: HL-TAU Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F555W,POLQ Optional_Parameters: ATD-GAIN=15, CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 700S Special_Requirements: same pos as 11 Comments: Exposure_Number: 13 Target_Name: HL-TAU Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F555W,POLQ Optional_Parameters: ATD-GAIN=15, CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 700S Special_Requirements: same pos as 11 Comments: Visit_Number: 02 Visit_Requirements: ORIENT 320d to 330d On_Hold_Comments: Visit_Comments: REQUIRES OPPOSITION CAMPAIGN IF SADE RESTRICTIONS ARE STILL IN PLACE Exposure_Number: 21 Target_Name: HL-TAU Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F555W,POLQ Optional_Parameters: ATD-GAIN=15, CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 700S Special_Requirements: pos targ 8.0, 8.0 Comments: Exposure_Number: 22 Target_Name: HL-TAU Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F555W,POLQ Optional_Parameters: ATD-GAIN=15, CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 700S Special_Requirements: same pos as 21 Comments: Exposure_Number: 23 Target_Name: HL-TAU Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F555W,POLQ Optional_Parameters: ATD-GAIN=15, CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 700S Special_Requirements: same pos as 21 Comments: Visit_Number: 03 Visit_Requirements: ORIENT 20d to 30d On_Hold_Comments: Visit_Comments: REQUIRES OPPOSITION CAMPAIGN IF SADE RESTRICTIONS ARE STILL IN PLACE Exposure_Number: 31 Target_Name: HL-TAU Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F555W,POLQ Optional_Parameters: ATD-GAIN=15, CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 700S Special_Requirements: pos targ 8.0, 8.0 Comments: Exposure_Number: 32 Target_Name: HL-TAU Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F555W,POLQ Optional_Parameters: ATD-GAIN=15, CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 700S Special_Requirements: same pos as 31 Comments: Exposure_Number: 33 Target_Name: HL-TAU Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F555W,POLQ Optional_Parameters: ATD-GAIN=15, CR-SPLIT=NO Number_of_Iterations: 1 Time_Per_Exposure: 700S Special_Requirements: same pos as 31 Comments: Data_Distribution Medium: 8MM Blocking_Factor: 10 Ship_To: PI_Address Ship_Via: UPS Recipient_Email: