Fernandez, Y. R. et al Icarus in preparation, 1999.
"Physical Properties of the Nucleus of Comet 2P/Encke"
mid-IR photometry and CCD photometry
Derive a nucleus radius=2.4 +/- 0.3 km using a standard thermal model (which
may or may not be applicable to comets)
Optical linear phase coefficient is 0.06 to 0.07 mag/degree.
Visual albedo 0.049 +/- 0.016.
Determine a rotation period: Best period (assuming double peaked)=15.2+/-0.3 hr
Period is synodic NOT sidereal
Other possible periods: 7.66, 11.46, 22.919, 28.382, 33.652, 38.918 hr.
These are all harmonics and the first two require single peaked light
curve which is inconsistent with light curve resulting from shape
Determine one axial ratio = 2.6 (0.7mag variation) which points to shape
causing lightcurve not albedo
Nucleus precessing quickly with a precession period less than 81 years
(but I found their arguements on this shaky)
Sub-solar temeperature in mid-July 1997 = 365 +/- 14K (around 1au)
Active surface fraction <2% !!
=====
Fink, U. and Hicks, M. D. ApJ 459, 729-743, 1996
"A Survey of 39 Comets Using CCD Spectroscopy"
Based on spectra from 0.55 to 1.0 microns (so O (1D) for H2O).
Observed Encke on 9-11 Oct 1990 with R=0.57 Delta=0.87
Details of fluxes given
Haser model production rates
Q(H2O) = 4.6e28 (at 1au this is Q(H2O)=1.2e28)
Q(C2) = 2.2e26
Q(NH2) = 2.0e25
Q(CN) = 1.15e26
==> Q(H2O)/Q(CN) = 400
=====
A'Hearn. M. F. et al Icarus 118, 223-270, 1995
"The Ensemble Properties of Comets: Results from Narrowband Photometry
of 85 Comets, 1976-1992"
Data for a complete apparition
log Q(CN)/Q(OH) = -2.49
log Q(C2)/Q(OH) = -2.46
log Q(C3)/Q(OH) = -3.35
log Q(NH)/Q(OH) = -2.49
log Q(OH) max = 27.83 at 0.71au ==> log Q(H2O) = 28.6 max at perihelion
based on derived active area
=====
Hughes, D. W. et al, MNRAS 263,247-255 (1993)
"On the variation of cometary coma brightness with comet-Earth distance
(the Delta Effect)"
Important conclusion is that assuming that the cometary brightness
varies as 1/Delta^^2 is correct. Case of Encke used to prove point.
=====
Sanzovo, G. C. et al AJ 106, 1237-1240, 1993
"CS Band Intensity and Column Densities And Production Rates of 15 Comets"
Primarily a discussion of the physical model and the g-factors, this
paper reanalyzes IUE observations from the literature.
For Encke, Observations were obtained in the 1980 and 1984 apparitions.
1980: October and November (R=1.01 and 0.81AU; Delta = 0.29 and 0.31AU).
October: N(CS)=9e10 cm^^{-2}; Q(CS)=3e22 mol/sec.
November: N(CS)~4e11 cm^^{-2}; Q(CS)~2.7e23 mol/sec.
1984: April and May (R=0.75 and 1.06AU; Delta = 0.76 and 0.85AU).
The May observations are an upper limit.
For April, N(CS) ~ 3e10 cm^^{-2}; Q(CS)~1.2e23 mol/sec.
=====
Osip, D. J. et al Icarus 98, 115-124, 1992
"Comets: Groundbased Observations of Spacecraft Mission Candidates"
Photometry of Encke in 1977, 1980, 1984, and 1990 with individual
observations on many dates. Produced Q(OH) and Afrho normalized to 1.5au.
Q(OH) = 1.0E27
Afrho = 9
Then produced production rate ratios:
Q(OH)/Q(CN) = 510 +/- 150
Q(CN)/Q(C2) = 1.27 +/- 0.3
Q(CN)/Q(C3) = 21.17 +/- 11.0
Q(CN)/Q(NH) = 1.41 +/- 0.40
=====
Kamel L. Icarus 93, 226-245, 1991
"The Evolution of P/Encke's Light Curve: No Secular Fading, a Vanishing
Perihelion Asymmetry"
An evaluation of the historical data on the brightness of Encke.
Points out that the time of peak brightness, relative to perihelion,
has changed from ~19 days preperihelion in the middle of the 19th
century to a few days postperihelion today
When properly account for shift of peak, finds no evidence for a change
in the peak brightness of the comet ==> the comet is not fading
and is not about to die
=====
Sekanina, Z. JRAS Canada 85, 324-376, 1991
"Encke, the Comet"
=====
Luu, J. and Jewitt, D. Icarus 86, 69-81, 1990
"The Nucleus of Comet P/Encke"
CCD observations (photometry and spectra) near aphelion in 1988.
Photometry (Mould R band):
Mean apparent magnitude=19.80 +/- 0.04
Mr(1,1,0) = 14.40 assuming a phase coefficient of 0.04 mag/deg
Delta m = 0.62 +/- 0.04 mag
T = 15.08 |/- 0.08 hr (data compatible with 7.54 +/- 0.04 and 22.62 +/- 0.11)
T = 15.08 produces a phase plot with two minima and maxima per period
derive Bowell and Lumme-type phase coefficient = 0.045 +/- 0.005 mag/deg
lower limit of axis ratio 1.8/1
albedo*cross section = 1.5 +/- 0.1 km^^2
for P=0.04, R=3.5km; for P=0.02, R=4.9km; for P=0.1, R=2.2km
Spectra (4200-6800A):
slightly red
no emissions
=====
Gehrz, R. D. et al Icarus 80, 280-288, 1989
"Infrared Photometry and Spectroscopy of Comet P/Encke 1987"
IR photometry from 2.3 to 18.5 microns during 1974 and 1987 apparitions.
IR spectrum from 3-4 microns in 1987
Detect no superheating of the coma ==> coma has "large" grains
derive grain size of 5-10 microns
Upper limit of radius of 5km
Coma emission dominates nucleus emission near perihelion
grain density in coma has an upper limit of 3e-8 grains cm^{-3}
No feature in the 3-4 micron spectrum so hydrocarbons lacking or underabundant
=====
Newburn, R. L and Spinrad, H. AJ 97, 552-569, 1989
"Spectrophotometry of 25 Comets: Post-Halley Updates for 17 Comets plus
New Observations for Eight Additional Comets"
Reanalysis of earlier paper's data
Observations of Encke 21 Aug - 6 Nov 80 (5 dates)
Derive production rates (also give column densities) using Haser model
Values assume v=1km/sec
Date R Delta Q(O 1D) Q(H2O) O 1D/CN O 1D/C3 O 1D/C2
21 Aug 80 1.89 1.47 1.50e26 2.06e27 99.3 2244 152
7 Sep 80 1.69 1.09 2.33e26 3.15e27 76.6 1879 531
15 Oct 80 1.15 0.37 3.19e26 2.96e27 54.6 1210 48.6
4 Nov 80 0.84 0.31 9.75e26 1.33e28 46.0 956 34.7
=====
Sykes, M. V. ApJ 334, L55-L58, 1988
"IRAS Observations of Extended Zodiacal Structures"
A discussion of IRAS dust trails, including ones attributed to Encke.
The Encke dust trail covers more than 100 degrees of the cometary orbit
including 20 degrees in mean anomaly forward of the comet's orbital
position. The forward portion implies the trail has a component of
particles larger than 1mm.
=====
Sekanina, Z. AJ 96, 1455-1475 1988
"Outgassing Asymmetry of Periodic Comet Encke. II. Apparitions 1868-1918 And A
Study of the Nucleus Evolution"
Continuation of the analysis in paper I (below)
Whenever Encke's perihelion occurs in mid-April, it displays no sunward fan.
The nucleus precesses with a rate averaging 1 degree/revolution
Sense of the rotation is prograde, with obliquity ranging from 69 to 76 degrees
between 1868 and 1984
Individual vents much evolve appreciably over peiods of time as short as 100 yr.
A vent's floow should recede at a rate of ~10m per revolution relative to
the ambient regolith. As the vent deepens, the jet becomes more collimated.
=====
Sekanina, Z. AJ 95, 911-924, 1988
"Outgassing Asymmetry of Periodic Comet Encke. I. Apparitions 1924-1984"
Examines reports of orientation of the fan in the coma, including
the image of Djorgovski and Spinrad, to determine the pole orientation.
Rotation pole area is an irregular pentagon some 8 degrees across, with
RA between 200 and 208 degrees and with dec between 0 and +7 degrees
(equinox 1950)
Rotation pole (in rounded off eulerian units) argument Phi = 230, obliquity
i=70
Two sources of activity:
Source 1, active on inbound leg until 12 and 6 days preperihelion and
again three months after perihelion
latitude +55 degrees
Source 2, active between 6 days preperihelion and 46 days post-perihelion
latitude -75 degrees
Dismisses rotation period of Jewitt and Meech as not being possible
with the solution here and asserts it is activity
=====
Ferrin, I. and Gil, C. A&A 194, 288-296, 1988
"The Aging of Comets Halley and Encke"
Using historical visual estimates of the cometary magnitude, derives
lifetime and size of the comet.
extinction date = 2060 +/- 15 AD
absolute magnitude = 14.9 +/- 0.3
diameter = 6.2 +/- 2.5 km
active surface fraction = 0.2%
=====
Campins, H. Icarus 73, 508-515, 1988
"The Anomalous Dust Production in Periodic Comet Encke"
Report thermal infrared (10.6 microns) observations of Encke in 1980 and 1984.
Encke does not behave like other comets at this wavelength and
does not behave like a bare nucleus.
Derive an UPPER LIMIT for the size of the nucleus of 2.2km. Allowing
for CCD lightcurve variations of Jewitt and Meech, radius would be
2.9km - 4.4km with albedo > 4%.
There is an asymmetry of the thermal IR emission around perihelion similar
to the lightcurve, CN and C2 values.
=====
A'Hearn, M. F. and Schleicher, D. G. ApJ 331, L47-L51, 1988
"Comet P/Encke's Nongravitational Force"
IUE high resolution observations from 1980 and 1987 both pre- and
post-perihelion were compared with models of the OH fluorescence. A
marked Greenstein effect is seen in the pre-perihelion data (but post-perihelion
is inconclusive). From this, the non-gravitational forces are
determined and a crude mass estimate made:
m = 7e15 g
Q(OH) = 1.02e28 3 Nov 1980 R=0.838 pre-perihelion
Q(OH) = 1.30e28 15 Aug 1987 R=0.776 post-perihelion
=====
Jewitt, D. and Meech, K. AJ 93, 1542-1548, 1987
"CCD Photometry of Comet P/Encke"
Observations obtained with a CCD and a Mould R filter on two runs a year
apart. R=3-4AU. No coma apparent.
1985 amplitude >0.8mag
1986 amplitude ~0.4mag
Derive a photometric period of 22.43 +/- 0.08 hr (with other possible
periods at 2/3, 1/2 and 1/3 of this (2min/2max).
All four periods show up in both data sets.
Persistence of periodicity --> rotation of a nucleus, not albedo
equatorial axis ratio ~2/1
phase coefficient of ~4 to 5 mag per 100 degrees of phase.
Adopting an albedo of 0.04, they derive a radius of 4.5 km.
[ 2.8 < R < 6.4 km for albedos from 0.1 to 0.02]
Only 1% of the surface active
Their observations are inconsistent with the Whipple and Sekanina precession
model
=====
Goraya, P. S. et al Earth, Moon and Planets 37, 53-58, 1987
"Study of periodic comet Encke during its apparition in 1984"
=====
A'Hearn, M. F. et al Icarus 64, 1-10, 1985
"Comet Encke: Gas Production and Lightcurve"
Ground-based and IUE observations of Encke during the 1984 apparition.
C2 and CN follow the behavior of the visual lightcurve but OH does not
"The observations show, however, that the production of trace species becomes
high relative to OH inside 0.75 AU preperihelion but then is very low relative
to OH postperihelion."
Table IV - production of gas (note uses V=1km/sec) from Haser model
R logQ(CS) logQ(OH) logQ(CN) logQ(C3) logQ(C2)
1.162 -- <27.8 <23.9 -- <22.6
0.902 -- 27.49 25.31 23.90 25.13
0.726 -- 27.75 25.72 -- 25.56
0.634 -- 27.60 25.72 -- 25.50
0.537 -- -- (25.73) -- (23.37)
0.554 -- -- 25.86 23.61 25.50
0.625 -- 28.04 25.50 -- 25.28
0.698 -- 27.98 25.22 -- 25.13
0.718 -- 27.95 25.26 23.63 25.06
0.753 24.72 27.94 -- -- --
0.765 24.59 27.92 -- -- --
0.770 -- 27.79 25.00 -- --
0.791 -- -- 25.10 23.45 24.93
0.808 -- -- 25.05 23.44 24.86
0.876 -- 27.62 24.87 -- 24.84
0.893 -- 27.76 24.85 -- 24.83
0.913 -- -- 24.85 23.51 24.73
0.927 -- 27.74 -- -- --
1.054 -- 27.39 -- -- --
1.056 <23.7 27.55 -- -- --
=====
Djorgovski, S. and Spinrad, H. AJ 90, 869-876, 1985
"Surface Photometry of Comet P/Encke"
Digitized J and F plates obtained during the 1980 apparition.
R=1.24AU; Delta=0.47AU
Asymetrical image, brighter on sunward side. Asymmetry decreases
with increasing distance from nucleus.
Strong color gradient with outer coma ver blue.
Front fan reddest
Fan lag angle is about 23 degrees from solar.
Flow seems collimated.
=====
Newburn, R. L. and Spinrad, H. AJ 90, 2591-2608, 1985
"Spectrophotometry of Seventeen Comets. II. The Continuum"
Continuum measurements and models of area-geometric albedo products and
mass loading.
Observations of Encke 21 Aug - 6 Nov 1980 (8 dates and various positions)
Data too complex to include here
Encke mass production 1.13 -- 4.64 Kg/sec
Mass loading for Encke more than an order of magnitude lower than for the
lowest found for other comets.
Dust production roughly constant with heliocentric distance.
=====
Newburn, R. L. and Spinrad, H. AJ 89, 289 - 309, 1984
"Spectrophotometry of 17 Comets. I. The Emission Features"
Production rates from Haser models
Values are Q/v
R Q(CN) Q(C3) Q(C2) CN/O
1.89 1.35e24 5.95e22 1.29e24 9.6e-3
1.70 2.58e24 1.25e23 3.12e24
1.69 2.83e24 1.50e23 4.65e24 1.3e-2
1.15 6.02e24 2.90e23 1.22e25 3.2e-2
0.85 -- -- 3.70e25
0.84 1.53e25 8.96e23 7.56e25 2.0e-2
0.82 1.72e25 9.44e23 8.59e25
0.78 1.21e25 7.09e23 5.40e25
=====
Feldman, P. D. et al Icarus 60, 455-463, 1984
"The Ultraviolet Spectrum of Periodic Comet Encke (1980 XI)"
IUE observations on 24 Oct and 3 to 5 Nov 1980. R between 1.014 and 0.81 AU;
delta ~0.3au.
OH(0,0) 11.6 kR; values given for H, O, C, S, CS, CO2+ and other OH bands
derive Q(H2O) (0.83au) = 1.8e28 and varies as R^{-3.3}.
=====
A'Hearn, M. F. et al Icarus 55, 250-258, 1983
"The Disappearance of OH from Comet P/Encke"
Combines data from many studies and technigues and from several apparitions
to try to compare gas with the visual lightcurve.
Lightcurve summary: There is a brightness excess of 2-3 mag in the period 3 to
4 weeks prior to perihelion
Paper includes uniformly reduced production rates.
OH: from 0.79 < R < 1.23 AU, OH production varies as R^{-3.8 +/- 0.2}
Sharp drop in OH seen at 0.75 AU
The observed production of OH drops sharply when the cometocentric latitude
of the sub-solar point decreases to approx. 30 degrees.
OH production follows the visual lightcurve
C2 and CN: do not show the sharp decrease exhibited by OH at R=0.75AU
Does follow the lightcurve
production rate ratios: H2O/C2/CN/C3 are 100/0.43/0.21/0.01 (normal)
=====
Kamoun, P. G. et al Science 216, 293-295, 1982
"Comet Encke: Radar Detection of Nucleus"
Radar observations of Encke obtained 2-8 November 1980. Comet was detected.
Central peak of echo is offset by 7.5Hz from predicted position but could
be errors in prediction as well as real
Derive radar cross-section of 1.1 +/- 0.7 km^2
Using various model parameters, derive a radius of
R = 1.5 +2.3/-1.0 km
Dependent on model parameters chosen. Assumes pole of Whipple and Sekanina
1979 which Sekanina (1988 above) show to be wrong. Assumes their
rotation period of 6 hrs 20 min +/- 40 minutes which Jewitt and Meech
and Fernandez et al show to be wrong
Other model parameters will yield R from 0.3 to 4.5 km
=====
Weaver, H. A. et al Icarus 47, 449-463, 1981
"IUE Observations of Faint Comets"
Observations of Encke yielded:
Date R delta B(OH) Q(H2O)
(AU) (AU) (kR) (mol/sec)
5 Nov 1980 0.81 0.32 12 2.0e28
24 Oct 1980 1.01 0.29 2.7 0.96e28
(slit 10X15 arcsec)
NOTE: my running of the vectorial model for the 24 Oct brightness yields
Q(H2O)=2.1e27
=====
Barker, E. S. et al in "Modern Observational Techniques for Comets" JPL
Publication 81-68, ed. Brandt, J. C., Greenberg, J. M., Donn, B. and
Rahe, J. 1981 pp. 150--155
"Observations of Faint Comets at McDonald Observatory: 1978-1980"
Observations with a Digital Area Photometer of Encke near aphelion in 1979.
An outburst of 1.1 magnitudes was detected. Encke was bluer in outburst
than out of outburst and the amplitude was 0.07 mag and random.
However, no significant coma was detected during the outburst (but a coma
of 8000km could be hidden in the seeing disk).
Uncalibrated spectra near 1au are also shown. Normal emissions were detected.
=====
A'Hearn, M. F. et al AJ 84, 570-579, 1979
"Gas and Dust in Some Recent Periodic Comets"
(perihelion 17 Aug 1977)
Date R delta log Q(CN) log Q(C2) diaphram (arcsec)
24 Jul 77 0.850 1.617 25.26 -- 58
7 Sep 77 0.632 1.223 25.39 25.79 155
9 Sep 77 0.669 1.226 25.23 25.59 155
11 Sep 77 0.705 1.223 25.25 25.55 155
=====
Newburn, R. L. and Johnson, T. V. Icarus 35, 360-368, 1978
"Postperihelion Interference Filter Photometry of the 'Annual' Comet P/Encke"
Photometric observations on 14 June 1974 with delta=0.363 AU and R=1.07 AU.
Errors could be as large as up to 50% of the quoted values
Use a Haser model to derive:
Q(CN) = 4.1e23
Q(C3) = 5.3e23
Q(C2) = 4.3e24
Did not detect continuum so derive an upper limit of the solids production
of 4700 g/sec
=====