! Proposal 5829, submission 1 ! PI: Paul D. Feldman ! Received Tue Feb 14 17:50:13 EST 1995 ! From: pdf@rowland.pha.jhu.edu ! Hubble Space Telescope Cycle 5 (1995) Phase II Proposal Template ! $Id: 5829,v 13.1 1996/01/25 15:59:47 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: feldman-564.prop ! Date generated: Fri Dec 16 14:42:37 EST 1994 ! Proposal_Information ! Section 4 Title: The Activity of Periodic Comet Schwassmann-Wachmann 1 Proposal_Category: GO Scientific_Category: Solar System Cycle: 5 Investigators PI_name: Paul D. Feldman PI_Institution: The Johns Hopkins University CoI_Name: Michael F. A'Hearn CoI_Institution: University of Maryland Contact: ! Y or N (designate at most one contact) CoI_Name: Gian Paolo Tozzi CoI_Institution: Osservatorio Astrofisico di Arcetri Contact: ! Y or N (designate at most one contact) CoI_Name: Harold A. Weaver CoI_Institution: Space Telescope Science Institute Contact: ! Y or N (designate at most one contact) Abstract: ! Free format text (please update) We propose spectroscopic observations of periodic comet Schwassmann-Wachmann 1 (SW1), a distant comet in a nearly circular orbit at ~6 AU, to observe carbon monoxide fluorescence emission in the CO Fourth Positive Band system. CO was recently successfully detected in SW1 in two independent radio searches at 1.3 mm wavelength. The production rate derived from these observations indicates that the CO ultraviolet emission should be readily detectable with the GHRS. The goal of the investigation is to determine if CO is, in fact, responsible for the activity of this comet, or whether CO2 is the dominant volatile in the nucleus and the observed CO simply a dissociation product of CO2. We will also use the FOS to measure (or set sensitive upper limits on) the coma abundance of OH and CO2+. Questions ! Free format text (please update) Observing_Description: We propose to observe comet SW1 during February 1996 when SW1 will be at opposition and hence at minimum geocentric distance, in order to maximize the flux at Earth. We note that at this time SW1 is approaching aphelion, but this does not seriously degrade the expected signal as the orbit eccentricity of SW1 is only ~4% For this initial program we have decided not to attempt a target-of-opportunity observation at the time of an outburst because of the short duration of the brightening relative to the HST response time. Moreover, our estimates of exposure time given below are based on the abundance of CO derived from the millimeter detection made when the comet was quiescent (Senay and Jewitt 1994). Although the ephemeris for SW1 is well known, we will begin the observation sequence with a PC image using the F702W filter to determine the precise position of the comet's center of brightness, which can then be uplinked to the spacecraft to provide a pointing correction to the ephemeris in the spacecraft memory. The image will also provide quantitative information, at a resolution not possible from the ground, of the distribution of the dust surrounding the nucleus. Two or three exposures, totalling ~1000 seconds, will provide adequate signal-to-noise, based on our recent experience in imaging comet Shoemaker-Levy 9 (1993e), whose visual magnitude was 1-2 magnitudes fainter than SW1, and permit cosmic ray removal. The data of Senay and Jewitt (1994) are used to estimate the expected slit-averaged brightness (in the GHRS Large Science Aperture) of the strongest CO bands in the G140L grating bandpass that we have chosen, 1295 - 1580 Angstrom . They derive a CO production rate for two possible cases, fluorescence and thermal equilibrium of the rotational levels, respectively, of 3.1 * 10^28 and 6.2 * 10^28 molecules/s, the latter assuming a temperature of 80 K. We adopt a rough mean value of 5 * 10^28 molecules s^-1, and assume a radial outflow model with an outflow velocity of 0.2 km/s, again a compromise between the various widths and the blue-shift given by Senay and Jewitt. This model assumes a uniformly vaporizing sphere and is not strictly correct in this case. However, if the observed 0.4 km/s blue-shift is indicative of hemispherical outgassing from the side towards the sun, the CO column density in the LSA will actually be considerably higher than that derived from the model. The fluorescence efficiencies and lifetimes used in the model are appropriate for solar minimum values of the solar ultraviolet flux. The results are given in Table 1. For the C I multiplet we used the vectorial model of Festou (1981), but here the parameters are more uncertain than for the CO. In general, in cometary spectra the C I emissions are much stronger than the CO bands (see Fig. reffig1), but this is not the case at ~6 AU where the photodestruction rate of CO is considerably smaller than its value at 1 AU. Table 1: GHRS Side 1 Observations _____________________________________________________________________ Feature Wavelength (A) Brightness in LSA S/N for (Rayleighs) 120 minutes _____________________________________________________________________ CO (1,0) 1509 14 5.0 CO (2,0) 1478 16 6.7 CO (3,0) 1447 9 4.5 C I 1561 10 2.5 _____________________________________________________________________ The signal-to-noise ratio for the GHRS observation (also given in Table 1) was estimated using the equation for Case 2 in section 3.4.5.1 of the GHRS Handbook 5.0. Our experience with two recent programs that utilized the GHRS Side 1 with G140L to observe Jupiter and Europa (Program IDs 5373 and 5376) shows that the S/N actually obtained on these extended sources is very closely given by this equation, and so we are confident that CO can be detected in the ultraviolet from comet SW1 with the proposed two-hour integrations. Since dark time is required for the GHRS observations, and 24 minutes of dark time is available per orbit, this will require 5 orbits. It also appears that the S/N can be further enhanced using the new option FLYLIM described in section 8.6.3 of the Handbook, but we have not pursued this possibility at the present time. For the FOS observations of OH to determine the water production rate, we have demonstrated that we can reach a 3-sigma limit of 2 * 10^27 molecules/s with a 60-minute integration for a comet at a heliocentric distance of 5.45 AU (Weaver et al. 1994b). This was based on an outflow velocity of 0.4 km/s adopted for analysis of our July 1993 observations of comet Shoemaker- Levy 9 (1993e), and so represents a fairly conservative upper limit that is a factor of 25 below the mean CO production rate given by Senay and Jewitt. Real_Time_Justification: Dark time is required for the GHRS observations because our spectral range includes the terrestrial airglow emission of O I lambda1304, which is also one of the cometary emissions that we wish to observe. We also require that the observation be made when comet SW1 is close to opposition in order to maximize the ultraviolet flux from the comet. This occurs in Cycle 5 during February 1996. Note that the two requirements are, in fact, the same since dark time is optimized when the comet is at opposition. Ground-based monitoring of the activity of comet SW1 will be provided by co-I A'Hearn and his collaborators at Lowell Observatory and at Perth, Australia. We intend to seek coordinated CO millimeter observations as well. Calibration_Justification: ! Move appropriate text from Real_Time_Justification Additional_Comments: Solar_System_Targets ! Section 5.2 ! Target_Number: 1 ! Target_Name: SW1 ! Description: COMET SCHWASSMANN-WACHMANN-1 ! Level_1: STD = SCHWASSMANN-WACHMANN-1 ! Satellite of Sun ! Level_2: ! Satellite of Level_1 ! Level_3: ! Satellite of Level_2 ! Window: RANGE SW1 EARTH LT 5.5 ! Flux: R = 18.0 +/- 0.5 ! Include at least V and B-V ! B-V = 0.65 ! V-R = 0.5 ! Comments: May be in outburst. Minimum range is 5.3 AU (opposition). ! Requires ephemeris correction. R magnitude given is for ! 0.7 arc-second radius aperture. Target_Number: 1 Target_Name: SW1 Description: COMET SCHWASSMANN-WACHMANN-1 Level_1: TYPE = COMET, ! Satellite of Sun Q = 5.7484583, E = 0.0440579, I = 9.38499, O = 312.82689, W = 46.24130, T = 09-SEP-89:15:15:27.9 EQUINOX = J2000, EPOCH = 27-APR-96 Window: RANGE SW1 EARTH LT 5.5 Flux: R = 18.0 +/- 0.5 ! Include at least V and B-V B-V = 0.65 V-R = 0.5 Comments: May be in outburst. Minimum range is 5.3 AU (opposition). Requires ephemeris correction. R magnitude given is for 0.7 arc-second radius aperture. ! This is a template for a single visit containing a single exposure ! Repeat exposure and visit blocks as needed Visits ! Section 6 Visit_Number: 1 Visit_Requirements: BETWEEN 23-JAN-96 AND 05-APR-96 SEQ 1-3 WITHIN 24H GUID TOL 0.2" On_Hold_Comments: Visit_Comments: Visit should be completed in one orbit. Uplink offset correction to comet ephemeris before Visit 2. RANGE and BETWEEN requirements define same window. Exposure_Number: 11 ! Section 6.5 Target_Name: SW1 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F702W Wavelength: Optional_Parameters: CR-SPLIT = NO Number_of_Iterations: 1 Time_Per_Exposure: 120S Special_Requirements: SAVE OFFSET SW1 ! Section 7.2 Comments: Determines ephemeris correction for visits 2-3. Exposure_Number: 12 ! Section 6.5 Target_Name: SW1 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F702W Wavelength: Optional_Parameters: CR-SPLIT = NO Number_of_Iterations: 1 Time_Per_Exposure: 480S Special_Requirements: min dur 480s ! Section 7.2 Exposure_Number: 13 ! Section 6.5 Target_Name: SW1 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F702W Wavelength: Optional_Parameters: cr-split=0.5, cr-tolerance=0 Number_of_Iterations: 1 Time_Per_Exposure: 1200S Special_Requirements: ! Section 7.2 Visits ! Section 6 Visit_Number: 2 Visit_Requirements: BETWEEN 23-JAN-96 AND 05-APR-96 GUID TOL 0.2" On_Hold_Comments: Visit_Comments: Uplink required for ephemeris offset after visit 1. Use "remember offset" for all exposures this visit. Exposure_Number: 21 ! Section 6.5 Target_Name: SW1 Config: FOS/RD Opmode: ACQ Aperture: 4.3 Sp_Element: MIRROR Wavelength: Optional_Parameters: Number_of_Iterations: 1 Time_Per_Exposure: 480S Special_Requirements: USE OFFSET SW1 Comments: Exposure_Number: 22 ! Section 6.5 Target_Name: SW1 Config: FOS/RD Opmode: ACCUM Aperture: 4.3 Sp_Element: G270H Wavelength: Optional_Parameters: Number_of_Iterations: 1 Time_Per_Exposure: 24M Special_Requirements: USE OFFSET SW1 EXPAND no split end orbit ! Section 7.2 Comments: Exposure_Number: 23 ! Section 6.5 Target_Name: SW1 Config: FOS/RD Opmode: ACCUM Aperture: 4.3 Sp_Element: G270H Wavelength: Optional_Parameters: Number_of_Iterations: 1 Time_Per_Exposure: 15M Special_Requirements: USE OFFSET SW1 EXPAND no split ! Section 7.2 Comments: Exposure_Number: 24 ! Section 6.5 Target_Name: SW1 Config: FOS/RD Opmode: ACCUM Aperture: 4.3 Sp_Element: G270H Wavelength: Optional_Parameters: Number_of_Iterations: 1 Time_Per_Exposure: 15M Special_Requirements: USE OFFSET SW1 EXPAND no split end orbit ! Section 7.2 Comments: Visits ! Section 6 Visit_Number: 3 Visit_Requirements: GUID TOL 0.2" On_Hold_Comments: Visit_Comments: Use "remember offset" from visit 1 Exposure_Number: 31 ! Section 6.5 Target_Name: SW1 Config: HRS Opmode: ACCUM Aperture: 2.0 Sp_Element: G140L Wavelength: 1295-1575 Optional_Parameters: fp-split=std Number_of_Iterations: 2 Time_Per_Exposure: 14.5M Special_Requirements: USE OFFSET SW1 Exposure_Number: 33 ! Section 6.5 Target_Name: SW1 Config: HRS Opmode: ACCUM Aperture: 2.0 Sp_Element: G140L Wavelength: 1295-1575 Optional_Parameters: fp-split=std Number_of_Iterations: 6 Time_Per_Exposure: 15M Special_Requirements: USE OFFSET SW1 Comments: Should take 3 orbits. Visits ! Section 6 Visit_Number: 4 Visit_Requirements: after 1 by 12h to 24h GUID TOL 0.2" On_Hold_Comments: Visit_Comments: Visit should be completed in one orbit. Exposure_Number: 41 ! Section 6.5 Target_Name: SW1 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F702W Wavelength: Optional_Parameters: CR-SPLIT = NO Number_of_Iterations: 1 Time_Per_Exposure: 120S Special_Requirements: ! Section 7.2 Comments: Exposure_Number: 42 ! Section 6.5 Target_Name: SW1 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F702W Wavelength: Optional_Parameters: CR-SPLIT = NO Number_of_Iterations: 1 Time_Per_Exposure: 480S Special_Requirements: ! Section 7.2 Exposure_Number: 43 ! Section 6.5 Target_Name: SW1 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F702W Wavelength: Optional_Parameters: cr-split=0.5 cr-tolerance=0.0 Number_of_Iterations: 1 Time_Per_Exposure: 1200S Special_Requirements: ! Section 7.2 Data_Distribution ! Defaults indicated; change if desired Medium: 8MM ! 8MM or 6250BPI or 1600BPI Blocking_Factor: 10 ! 10 or 1 ! Only astronomers with very old 9- ! track tape drives should consider ! a blocking factor of 1 Ship_To: PI_Address ! STSCI or PI_Address or ! PI Address from Phase I is: ! ! Department of Physics and Astro ! nomy , Baltimore, MD 21218 ! ! Ship_Via: UPS ! UPS (2-day) or OVERNIGHT ! Overnight shipping done at PI expense Recipient_Email: ! Needed if Ship_To: is not PI_Address ! ! 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