Page 1 PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID 23 Report Date: 18-Jul-95:16:13 Version: ********** Check-in Date: ********** 1.Proposal Title: HETEROGENEITY OF DUST AND GAS EMISSIONS ON A COMETARY NUCLEUS ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Proposal Type 5. Continuation ID SOLAR SYSTEM GO Sub Category COMET ------------------------------------------------------------------------------------ 6. Principal Investigator Institution Country Telephone Dr. Joe Astronomer STSCI USA (301) 338-4700 ------------------------------------------------------------------------------------ 7. Abstract We propose to observe with the planetary camera (PC) of HST the short-period comet P/Faye at its closest approach to the Earth (0.6 AU). The high spatial resolution (40 km) over a large field will allow to image the dust and gas jets "down to the nucleus" and to follow their temporal evolution over a period of approximately 10 days. Combined with ground-based observations as a model of the dust/gas expansion, it will be possible to map the discrete sources of emission on the nucleus and study its rotational properties. HST will extend the present insight we have of comet Halley to another comet, an important step in the current exploration and understanding of primitive bodies in the solar system. ------------------------------------------------------------------------------------ 8. Scientific Key Words: COMET ------------------------------------------------------------------------------------ 9. Est obs time (hours) pri: 0.45 par: 0 10. Num targs pri: 1 par: 0 ------------------------------------------------------------------------------------ 11. Instruments requested: WF/PC ------------------------------------------------------------------------------------ 12. Special sched req: Time Critical obs. ------------------------------------------------------------------------------------ Page 2 I. GENERAL FORM Proposal 23 PI: Dr. Joe Astronomer Proposal Title: HETEROGENEITY OF DUST AND GAS EMISSIONS ON A COMETARY NUCLEUS ------------------------------------------------------------------------------------ 1. Proposers: Proposers Institution Country ESA ------------------------------------------------------------------------------------ Dr. Joe Astronomer SPACE TELESCOPE SCIENCE USA INSTITUTE Dr. Joseph Uppercase SPACE TELESCOPE SCIENCE USA INSTITUTE ------------------------------------------------------------------------------------ 3. Description of proposed observations. Observation of a short-period comet of more than one apparition (to limit acquisition problems) coming sufficiently close to the Sun (q<1.6 AU) for activity and to the Earth (delta<0.6 AU) for resolution, having an elongation larger than 50 deg and apparent motion less than 0.21 arcsec per sec to satisfy HST conditions. An excellent opportunity exists in the proposed HST period: comet P/Faye 1984XI. The observational program consists in imaging the coma with PC and two filters: -F702W for the dust (this broad spectral region ensures a high signal for the continuum with only slight contamination by gas -F517N for C2. The PC/F702W observations are repeated 7 times at selected time intervals (96, 48, 24, 12, 6, 3 hours) to cover a broad range of possible rotational period of the nucleus. The PC/F517N observation is performed only one time, just following the seventh PC/F702W observation. ------------------------------------------------------------------------------------ 4. Justification of need for HST observations. HST high spatial resolution (40 km for comet P/Faye with PC) makes it possible to resolve jets in the immediate vicinity of the nucleus where rotational and radiation pressure effects are negligible. Therefore, confusion of jets is minimal and individual jets can be traced back to the nucleus. No restriction on observing time (due to elevation of target above local horizon and weather conditions) allow us to optimize the observation sequence for best sampling strategy. Finally, minimun sky back- ground (only zodiacal light and star background) improves detectability of low contrast features. Low level and time stability of background improve signal-to-noise ratio in the outer part of the coma considerably. Near nucleus studies of comets have been performed by ground- based observations using both photographic and CCD techniques. However, due to limited resolution and other problems, the results are not always firmly conclusive (c.f. Sekanina Z. and Larson S.M., 1986, Astron. J. 92, 462 and Nature 321, 357; Sekanina Z., 1987, Nature 325, 326).Even space probe observations which are not limited by resolution (Keller H.U. and Thomas N., 1988, Nature 333, 146) in conjunction with ground-based observations did not provide a unique solution due to insufficient observational coverage. Page 3 ------------------------------------------------------------------------------------ 5. Description of special scheduling requirements. One comet will be observed 7 times at specified time intervals with PC. The exposure time for the dust coma is calculated from a light curve based on total visual estimates by several observers after correcting for instrumental effects and normalizing at 1 AU. The observations during the last two apparitions (1976/77 and 1984) provide a very smooth flat curve. Then the total magnitude is predicted for the oct/nov 1991 period. A 1/r radial variation of the coma brightness is assumed and converted to absolute unit to match the predicted magnitude. A check is made with a calibrated image of the coma of P/Halley obtained with GIOTTO/HMC at a resolution similar to HST, adopting a realistic scaling of the dust production rate. Typical exposure times are 55s for F702W and 1400s for F517N (we consider that the brightness in the inner coma is still due mostly to the dust, C2 adding up further out). The brightness of the nucleus is based on Roemer et al.'s observations from the 1961 and 1969 apparitions after proper corrections. The derived absolute magnitude of 14.4 at zero phase angle implies a nucleus diameter of 8.6 km assuming a geometric albedo of 0.04. The nucleus is therefore a bright object for PC: the typical exposure time for F702W is 20s. In order to prevent signal chain saturation, the exposure times must be limited to 26s for F702W and 350s for F517N and repeated as necessary. The final strategy for the exposure times takes this into account as well as the possibility of a brighter or fainter object during the 1991 apparition. ------------------------------------------------------------------------------------ 6. Description of special calibration exposures. The observations are time critical from two aspects: they should take place during a period of about 15 days when the comet is closest to the Earth (maximum resolution); they should be sequenced to properly sample a wide range of possible rotational periods (time intervals are 96, 48, 24, 12, 6 and 3 hours). ------------------------------------------------------------------------------------ 7. Data reduction and analysis plans. The plans for data reduction and analysis include the steps: 1)apply standard HST calibrations to generate corrected images in absolute units of brightness 2)check history of HST guiding of the comet 3)perform image processing enhancement to reveal the jets 4)study the temporal evolution of the jets and compare with ground-based images and a model of dust/gas expansion from the nucleus; compare the origin of dust and gas jets 5)map the active zones on the nucleus and study the rotational period and the orientation of the spin axis vector; failure to find a "simple" rotational solution would probably indicate a complex motion (e.g., rotation and precession). ------------------------------------------------------------------------------------ 8. Additional comments or special requests. Early observations of comet P/Faye in 1990 and 1991 will be performed for astrometric positions. An updated ephemeris (or orbital elements) based on these observations will be sent to ST-SCI at least 2 months before the HST observations. This will give an accuracy of 1 to 3 arcsec appropriate for blind pointing. High-resolution ground-based images of the comet will be obtained over a period overlapping the HST observations in order to complement them and put them in a broader interval of cometary activity. ------------------------------------------------------------------------------------ 9. Description of previous HST work. A description of any previous HST data goes here. ------------------------------------------------------------------------------------ 10. Resources to be supplied by investigator's institution(s). All participating investigators have extensive in-house image and data analysis capabilities. ------------------------------------------------------------------------------------ 11. Address Information Page 4 Name: JOE ASTRONOMER Category: PI Institution: STSCI Address: 3700 SAN MARTIN DRIVE City: BALTIMORE State: MD Zip Code: 21218 Country: USA Telephone: (301) 338-4700 Telex (or e-mail): ------------------------------------------------------------------------------------ TARGET LIST b)Solar System Targets ID = 23 [ 5] ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 1 | TARGET NAME: COMET1 ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: COMET FAYE 1984XI ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | TYPE = COMET, Q = 1.5933855, | E = 0.5781845, I = 9.09095, | O = 198.88006, W = 203.95376, | T = 16-NOV-1991:04:38:54, | EQUINOX = B1950, | EPOCH = 31-OCT-1991, | A1 = 0.45E-8, A2 = -0.49E-10, A3 = 0.0, | ACQ = 3.0 | | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | WND1 = 26-OCT-1991 TO 10-NOV-1991 | ------------------------------------------------------------------------------------------------------------------------------------ REF | DATA | COMMENTS | | 1 |V = 14.5 +/- 0.3 | FLUXVAL_1 IS THE PREDICTED VISUAL 2 |V = 9.2 +/- 0.5 | MAGNITUDE OF THE COMET NUCLEUS, 3 |SIZE = 60 | FLUXVAL_2 IS THE PREDICTED TOTAL | | MAGNITUDE OF THE EXTENDED COMA IN A | | CIRCULAR APERTURE OF 60" DIAM DURING | | THE SPECIFIED WINDOW. A RADIAL | | BRIGHTNESS VARIATION 1/R IS ASSUMED | | IN THE COMA. | ------------------------------------------------------------------------------------------------------------------------------------ EXPOSURE LOGSHEET ID = 23 [ 6] ------------------------------------------------------------------------------------------------------------------------------------ 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 ------------------------------------------------------------------------------------------------------------------------------------ 1 COMET1 WFPC2 IMAGE WFALL F555W 1 26S 10 1 1 PERIOD 3D +/- 1D 4S ZERO-PHASE 23-JUN- 1994 PHASE 0.3 +/- 0.1 CYCLE 3 Comments: test of phase ------------------------------------------------------------------------------------------------------------------------------------ Summary Form for Proposal 23 [ 7] Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ------------------------------------------------------------------------------------------------------------------------------------ Proposal for GO ------------------------------------------------------------------------------------------------------------------------------------ S/C Hours 0.45 ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category SOLAR SYSTEM ------------------------------------------------------------------------------------------------------------------------------------ Scientific Sub-category COMET ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PERIOD 3D +/- 1D; ZERO-PHASE 23-JUN-1994; PHASE 0.3 +/- 0.1; CYCLE 3; ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F555W ------------------------------------------------------------------------------------------------------------------------------------ Target Names COMET1 ------------------------------------------------------------------------------------------------------------------------------------