Page 1 PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID 5361 Report Date: 18-Jul-95:17:14 Version: ********** Check-in Date: ********** 1.Proposal Title: THE NUCLEUS OF COMET P/BORELLY AND ITS DUST AND GAS EMISSIONS CYCLE4MEDIUM ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Proposal Type 5. Continuation ID SOLAR SYSTEM GO Sub Category COMETS ------------------------------------------------------------------------------------ 6. Principal Investigator Institution Country Telephone Philippe L Lamy 5446 FRANCE 33 91055932 ------------------------------------------------------------------------------------ 7. Abstract We propose to observe with the planetary camera (PC) of HST the short- period comet P/Borrelly during the month following its perihelion passage (1 November 1994) and ending with its closest approach to Earth at 0.62 AU (4 december 1994). The spatial resolution (2 pixels) will range from 48 to 41 km allowing to discriminate the nucleus against the coma, to image the possible dust and gas structures in the coma "down to the nucleus" and to follow their temporal evolution. It will be possible to obtain the magnitude of the nucleus and derive its projected cross- section as a function of time (assuming a constant albedo). Combined with ground-based observations and a model of the dust-gas expansion, it will also be possible to map the sources of dust and gas on the nucleus and constrain its rotational properties. HST will extend the present insight we have of a few comets (P/Halley, Levy, P/Faye ...) to another comet, an important step in the current exploration and understanding of primitive bodies in the solar system. Altered 10/3/94 to observe in one group, around closest approach, and to change the F702W to F675W and ATD-GAIN from 15 to 7 (ADS). ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ 9. Est obs time (hours) pri: 0.78 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 5361 PI: Philippe L Lamy Proposal Title: THE NUCLEUS OF COMET P/BORELLY AND ITS DUST AND GAS EMISSIONS CYCLE4MEDIUM ------------------------------------------------------------------------------------ 1. Proposers: Proposers Institution Country ESA ------------------------------------------------------------------------------------ Philippe L Lamy 5446 FRANCE X Eberhard Grun 5544 GERMANY X Uwe Keller 5540 GERMANY X Zdenek Sekanina 2370 USA Imre Toth 5720 HUNGARY Richard West 5520 GERMANY X ------------------------------------------------------------------------------------ 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 < 0.7 AU) for resolution, having an elongation larger than 50 degrees and apparent motion less than 0.21 arc sec per sec to satisfy HST conditions. An oustanding opportunity exists in the cycle 4 of HST, comet P/Borrelly 1987 XXXIII. During a period of about one month following its perihelion passage on 1 November 1994 (q = 1.365 AU), it will remain within 0.7 AU of the Earth reaching closest approach on 4 December (Delta = 0.618 AU). The elongation will vary from 106 to 122 deg. The observational program consists in imaging the coma with the PC and two filters - F702 W for the dust (this broad spectral region ensures a high signal for the continuum with only slight contamination by gas emissions) - F390 N for CN. The dust observations will be repeated 5 times (5 visits) while the CN observations will only be performed during 3 of the 5 visits. The 5 visits will be scheduled to cover a broad range of possible rotational periods of the nucleus and to monitor temporal variations of the coma. Past experience with comet P/Faye has shown the difficulty to select specific time intervals due ot the operational constraints of the HST. We shall closely work with the operators at ST ScI to optimize the time intervals of the observations. ------------------------------------------------------------------------------------ 4. Justification of need for HST observations. HST high spatial resolution makes it possible to directly detect the cometary nucleus and to resolve structures in its immediate proximity. Therefore confusion is minimal and structures may be directly traced back to the nucleus. Minimum sky background improves detectability of low- contrast features. Its low level and stability considerably improves the signal-to-noise ratio in the outer parts of the coma. As discussed in section 2, ground-based observations of cometary nuclei have been limited to a few cases where they are presumably dormant (Jewitt, in "Comets in the post-Halley era", p. 19, 1991). Near nucleus studies using both photographic and CCD techniques are more extended. However, due to limited resolution and other problems discussed in section 2, the results are not always firmly conclusive. The two kind of observations are sometime consistent (P/Temple 2) and sometime inconsistent (P/Encke). The best results obtained so far were the high resolution images of the nucleus and the inner most coma of P/Halley with the GIOTTO and VEGA space probes. ------------------------------------------------------------------------------------ 5. Description of special scheduling requirements. The observations are time critical since they must be performed during a period of approximately one month extending roughly from 4 November 1994 (a few days after perihelion passage) to 4 December 1994 (closest approach to Earth). The precise timing of the 5 visits will be optimized with operators at ST ScI to satisfy the HST scheduling constraints (see section 3a). Page 3 ------------------------------------------------------------------------------------ 6. Description of special calibration exposures. None ------------------------------------------------------------------------------------ 8. Additional comments or special requests. Early observations of the selected comet will be performed for astrometric positions in order to refine the ephemeris.High-resolution, ground-based images will later 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. The HST program P2231 entitled "Heterogeneity of dust and gas emissions on a cometary nucleus" carried out during cycle 1 pursued the same scientific objectives as the present proposal. The above program consisted in 7 visits to comet P/Faye while it was within 0.6 AU of the Earth, the spatial resolution (2 pixels) being 40 km. Each visit has provided two identical, well-exposed images in the continuum (F702W). C2 was not detected due to its very low abundance. The influence of the spherical aberrations has been more severe than anticipated as the wings of the PSF of the bright nucleus amount to roughly 10 % of the coma creating artificial structures at a level higher than possible real coma structures. All images have been presently restored using the Richardson-Lucy technique. The nucleus has a R magnitude varying between 16.5 and 17.0, fainter than the prediction. Assuming a constant albedo of 0.04, a standard phase law and projected circular cross-sections, its radius varies between 0.9 and 1.2 km suggesting a rather spherical body. The inner coma (within 500 km) is asymmetric suggesting a broad fan which is neither oriented in the solar or the anti-solar directions. The outer coma, on a scale of several thousands km presents also an asymmetry along direction different from that of the inner coma. A preliminary comparison with a standard model of steady-state coma expansion including the effect of radiation pressure does not appear compatible with the observed isophotes. ------------------------------------------------------------------------------------ 10. Resources to be supplied by investigator's institution(s). All participating laboratories have extensive in-house image processing and data analysis capabilities. The european members have further access to the ST-ECF at ESO (FRG) Models of cometary comae have been developped and are available at JPL, MPIAe, MPIK. Specific research grants will be sought to support the HST activities of the team. ------------------------------------------------------------------------------------ 11. Address Information Name: PHILIPPE L LAMY Category: PI Institution: 5446 Address: BP 8 City: MARSEILLE State: Zip Code: 13376 Country: FRANCE Telephone: 33 91055932 Telex (or e-mail): (SPAN) LASM0A::LAMY ------------------------------------------------------------------------------------ Name: Category: CON Institution: Address: City: State: Zip Code: Country: Telephone: Telex (or e-mail): ------------------------------------------------------------------------------------ TARGET LIST b)Solar System Targets ID = 5361 [ 4] ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 1 | TARGET NAME: COMET-BORRELLY-1987XXXIII ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: COMET BORRELLY 1987XXXIII ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | TYPE = COMET, Q = 1.3651154, | E = 0.6228036, I = 30.26946, | O = 74.73634, W = 353.34589, | T = 01-NOV-1994:11:48:51, | EQUINOX = B1950, | EPOCH = 15-OCT-1994, | A1 = 0.20E-8, A2 = -3.98E-10, A3 = 0.0, | ACQ = 2.0 | | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | WND1 = 05-NOV-1994 TO 05-DEC-1994 | ------------------------------------------------------------------------------------------------------------------------------------ REF | DATA | COMMENTS | | 1 |V = 16.4 +/- 0.3 | FLUXVAL_1 IS THE PREDICTED VISUAL 2 |V = 7.5 +/- 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 = 5361 [ 5] ------------------------------------------------------------------------------------------------------------------------------------ 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 DEFINE COMET- WFPC2 IMAGE PC1-FIX F675W CR-SPLIT=0.25 2 40S 80 1 1 GUID TOL 0.2" / 1- DUST BORRELLY- CLOCKS=YES 40S 2 9 1987XXXIII ATD-GAIN=7 3 Comments: S_TO_N CALCULATED IN ONE PIXEL AT A DISTANCE OF 1000 KM FROM NUCLEUS ------------------------------------------------------------------------------------------------------------------------------------ 2 DEFINE COMET- WFPC2 IMAGE PC1-FIX F675W CR-SPLIT=0.25 2 40S 80 1 1 DUSTGAS BORRELLY- CLOCKS=YES 40S 2 1987XXXIII ATD-GAIN=7 3 Comments: S_TO_N CALCULATED IN ONE PIXEL AT A DISTANCE OF 1000 KM FROM NUCLEUS ------------------------------------------------------------------------------------------------------------------------------------ 3 DEFINE COMET- WFPC2 IMAGE PC1-FIX F390N CR-SPLIT=NO 2 400S 2.7 1 1 SEQ 2-3 NO GAP DUSTGAS BORRELLY- CLOCKS=YES 400S 2 1987XXXIII ATD-GAIN=7 3 Comments: S_TO_N CALCULATED IN ONE PIXEL AT A DISTANCE OF 1000 KM FROM NUCLEUS ------------------------------------------------------------------------------------------------------------------------------------ 4 USE CYCLE 4 DUSTGAS AT 01-DEC-1994 +/- 3D ------------------------------------------------------------------------------------------------------------------------------------ 5 USE CYCLE 4 DUSTGAS AFTER 4 BY 192M +/ - 20M ------------------------------------------------------------------------------------------------------------------------------------ 6 USE CYCLE 4 DUST AFTER 4 BY 384M +/ - 20M ------------------------------------------------------------------------------------------------------------------------------------ 7 USE CYCLE 4 DUST AFTER 6 BY 96M +/- 10M ------------------------------------------------------------------------------------------------------------------------------------ 8 USE CYCLE 4 DUSTGAS AFTER 7 BY 96M +/- 10M ------------------------------------------------------------------------------------------------------------------------------------ 9 USE CYCLE 4 DUST AFTER 8 BY 96M +/- 10M ------------------------------------------------------------------------------------------------------------------------------------ Summary Form for Proposal 5361 [ 6] Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT CLOCKS ATD-GAIN ------------------------------------------------------------------------------------------------------------------------------------ Proposal for GO ------------------------------------------------------------------------------------------------------------------------------------ S/C Hours 0.78 ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category SOLAR SYSTEM ------------------------------------------------------------------------------------------------------------------------------------ Scientific Sub-category COMETS ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements GUID TOL 0.2" / 1-9 SEQ 2-3 NO GAP CYCLE 4; AT 01-DEC-1994 +/- 3D AFTER 4 BY 192M +/- 20M AFTER 4 BY 384M +/- 20M AFTER 6 BY 96M +/- 10M AFTER 7 BY 96M +/- 10M AFTER 8 BY 96M +/- 10M ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F675W F390N ------------------------------------------------------------------------------------------------------------------------------------ Target Names COMET-BORRELLY-1987XXXIII ------------------------------------------------------------------------------------------------------------------------------------