! +====================+ ! | PED OUTPUT PRODUCT | ! +====================+ ! ! /spectre/data1/aroman/proposals/6562.prop ! Generated by PREPROCESSOR, version 6.3a ! Date: Tue Jun 4 15:14:56 EDT 1996 Proposal_Information Title: Shock Waves and Momentum Transfer in the Young Stellar Outflow Cepheus A Proposal_Category: GO Scientific_Category: INTERSTELLAR MEDIUM Cycle: 6 Investigators PI_Name: Patrick Hartigan PI_Institution: Rice University CoI_Name: Jon Morse CoI_Institution: University of Colorado Contact: Y CoI_Name: John Bally CoI_Institution: University of Colorado Contact: N Abstract: We propose to obtain new WFPC2 images of the shocked optical emission lines in the outflow from the region of massive star formation Cepheus A. The proposed O III, HAlpha and S II images of Cep A will define the location of the bow shocks, Mach disks, and cooling regions of the J-shocks in the flow, and by comparing the spatial positions of the optical lines with ground-based H_2 images we will be able to distinguish between J-shock, C-shock, magnetic precursor, reformation, and fluorescence models for the molecular emission. Together, the radio, infrared, and optical emission line images of Cepheus A enable us to observe how winds from massive stars create bubbles in the ISM, and the new observations will clarify how shock waves in these highly supersonic flows transfer momentum and energy to their environments. Questions Observing_Description: We can use our Cycle 4 WFPC2 observations of the stellar jet HH 47 (GO-5504) as a guide in estimating exposure times in Cepheus A. The brightest HAlpha emission-line object in Cepheus A is knot `S', with a total HAlpha flux of roughly 6* 10^-14 ergs,cm^-2s^-1, or about half the HAlpha flux present in the bright bow shock HH 47A. Our Cycle 4 WFPC2 HAlpha and S II images of HH 47 were 11,900s per filter, just deep enough to reveal the detail necessary to identify the location of J-shocks and cooling zones in the flow. Hence, we are requesting images of Cepheus A with comparable exposure times to discern similar detail. We can quantify our estimate of the exposure times by calculating the S/N ratios we will obtain given the observed S II surface brightness in the bow shocks along the northern edge of the H_2 emission in Figure 2, where it is most important to compare the proposed HST images with the H_2 data. Our WFPC2 observations of HH 47 achieved a S/N per WFC pixel of ~ 40 in 11,900s for the bright HH 47A bow shock, which has an average surface brightness of 9 * 10^-15 ergs,cm^-2s^-1arcsec^-2. The observed S II surface brightness of the fainter bow shocks we wish to study in Cep A is ~\\\\\\\\ 3* 10^-16 erg,cm^-2s^-1arcsec^- 2, which implies a S/N of ~ 7 per WFC pixel for an exposure time of 12,000s. O III emission in HH objects is often faint or nonexistent, but the shock velocities in Cep A are high enough that the O III/HBeta ratio is ~ 1 in several objects^14. Fortunately, Cep A lies in the middle of the CVZ zone, so it is possible to complete this project within a single visit ( i.e. <= 9 orbits). The WFPC2 field of view covers the entire region of bright optical emission associated with the H_2 shells in Cep A. The desired exposure time can be reached in 2 CVZ orbits for S II, and 3 orbits for HAlpha. A total of 3 orbits will show where the brightest O III is located with respect to the HAlpha and S II, which will provide important diagnostic information in the fastest shocks. Reflection nebulae surround the HH objects, so we will need continuum observations at `V' to subtract this component from the O III image, and at `R' to subtract from the HAlpha and S II images. The filters we propose to use for these continuum images (F547M and F791W) avoid the brightest emission lines present in HH objects. Owing to the wider bandpasses of these filters, a single CVZ orbit should suffice for the continuum images. We request a total of 9 CVZ orbits. Real_Time_Justification: CVZ. Cepheus A is in the middle of the northern CVZ. We can obtain longer integrations while reducing the total number of orbits needed for this project by observing throughout the ~ 96 minute orbit of HST. Excellent imagery of Cep A can be obtained within one 9 orbit visit, which will meet our scientific goals. Our H_2 image taken with the CFHT (Figure 2) will need to be redone to eliminate positional offsets caused by proper motions^18 between 1993 and 1996. This observation can be done with one or two nights on a 4-m telescope with good seeing. We also plan to observe the region with a Fabry- Perot spectrometer to better define the velocities in the cooling regions behind the J-shocks in this object. Our experience with other objects has been that we must analyze images of jets and outflows together with radial velocities and line ratios in order to put together coherent models of these objects. JM is an expert in the acquisition and reduction of FP data and will lead these observations. JB will be in charge of supplying and interpreting the radio observations, PH and JB will be responsible for obtaining additional IR images, and PH will coordinate the effort and run any shock models necessary for the interpretation. Calibration_Justification: Additional_Comments: Fixed_Targets Target_Number: 1 Target_Name: CEPHEUS-A Alternate_Names: Description: ISM,HII Region,Reflection Nebula,Molecular Cloud,Bipolar Outflow,Herbig-Haro Object Position: RA=22H 54M 9.95S +/- 0.01S,DEC=61D 46' 15.1" +/- 0.1" Equinox: B1950 RV_or_Z: RA_PM: 0.0 Dec_PM: 0.0 Epoch: Annual_Parallax: 0.0 Flux: SURF-LINE(6724)=3+/-1e-16 SURF(R) = 22+/-1 Comments: A MIXTURE OF REFLECTION AND INTRINSIC EMISSION AT THE EDGE OF A DARK CLOUD EXPOSURE TIMES LIMITED BY 15 MAG STARS IN FOV Solar_System_Targets Generic_Targets Scan_Data Visits Visit_Number: 01 Visit_Requirements: ORIENT 44.0D TO 47.0D CVZ On_Hold_Comments: Visit_Comments: Exposure_Number: 100 Target_Name: CEPHEUS-A Config: WFPC2 Opmode: IMAGE Aperture: WFALL-FIX Sp_Element: F673N Wavelength: Optional_Parameters: DITHER-TYPE=LINE,CLOCKS=YES Number_of_Iterations: 3 Time_Per_Exposure: 800 S Special_Requirements: Comments: Exposure_Number: 105 Target_Name: CEPHEUS-A Config: WFPC2 Opmode: IMAGE Aperture: WFALL-FIX Sp_Element: F673N Wavelength: Optional_Parameters: DITHER-TYPE=LINE,CLOCKS=YES Number_of_Iterations: 2 Time_Per_Exposure: 800 S Special_Requirements: Comments: Exposure_Number: 107 Target_Name: CEPHEUS-A Config: WFPC2 Opmode: IMAGE Aperture: WFALL-FIX Sp_Element: F673N Wavelength: Optional_Parameters: DITHER-TYPE=LINE,CLOCKS=YES Number_of_Iterations: 2 Time_Per_Exposure: 800 S Special_Requirements: Comments: Exposure_Number: 110 Target_Name: CEPHEUS-A Config: WFPC2 Opmode: IMAGE Aperture: WFALL-FIX Sp_Element: F673N Wavelength: Optional_Parameters: CLOCKS=YES Number_of_Iterations: 1 Time_Per_Exposure: 300 S Special_Requirements: Comments: Exposure_Number: 120 Target_Name: CEPHEUS-A Config: WFPC2 Opmode: IMAGE Aperture: WFALL-FIX Sp_Element: F656N Wavelength: Optional_Parameters: DITHER-TYPE=LINE,CLOCKS=YES Number_of_Iterations: 3 Time_Per_Exposure: 2000 S Special_Requirements: Comments: Exposure_Number: 130 Target_Name: CEPHEUS-A Config: WFPC2 Opmode: IMAGE Aperture: WFALL-FIX Sp_Element: F502N Wavelength: Optional_Parameters: DITHER-TYPE=LINE,CLOCKS=YES Number_of_Iterations: 2 Time_Per_Exposure: 2555 S Special_Requirements: Comments: Visit_Number: 02 Visit_Requirements: SAME ORIENT AS 01 CVZ On_Hold_Comments: Visit_Comments: Exposure_Number: 200 Target_Name: CEPHEUS-A Config: WFPC2 Opmode: IMAGE Aperture: WFALL-FIX Sp_Element: F656N Wavelength: Optional_Parameters: CLOCKS=YES Number_of_Iterations: 2 Time_Per_Exposure: 2000 S Special_Requirements: Comments: Exposure_Number: 202 Target_Name: CEPHEUS-A Config: WFPC2 Opmode: IMAGE Aperture: WFALL-FIX Sp_Element: F814W Wavelength: Optional_Parameters: CLOCKS=YES Number_of_Iterations: 6 Time_Per_Exposure: 8 S Special_Requirements: Comments: Exposure_Number: 205 Target_Name: CEPHEUS-A Config: WFPC2 Opmode: IMAGE Aperture: WFALL-FIX Sp_Element: F814W Wavelength: Optional_Parameters: DITHER-TYPE=LINE,CLOCKS=YES Number_of_Iterations: 4 Time_Per_Exposure: 160 S Special_Requirements: Comments: Exposure_Number: 210 Target_Name: CEPHEUS-A Config: WFPC2 Opmode: IMAGE Aperture: WFALL-FIX Sp_Element: F547M Wavelength: Optional_Parameters: CLOCKS=YES Number_of_Iterations: 3 Time_Per_Exposure: 60 S Special_Requirements: Comments: Exposure_Number: 215 Target_Name: CEPHEUS-A Config: WFPC2 Opmode: IMAGE Aperture: WFALL-FIX Sp_Element: F547M Wavelength: Optional_Parameters: DITHER-TYPE=LINE,CLOCKS=YES Number_of_Iterations: 3 Time_Per_Exposure: 300 S Special_Requirements: Comments: Data_Distribution ! 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