Rotation of the nucleus of comet p/Arend-Rigaux (original) (raw)
Related papers
Rotation of Cometary Nuclei [and Discussion]
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 1984
Asymmetric comas and repetitive appearances of structures in the heads and tails of comets are used to infer nuclei rotation periods. However, periodic behaviour of optically-thick expanding comas or of ion plasma production may contribute spurious results. The spin periods of comets are longer than those of asteroids, ranging generally over 10-100 h and above probable limits for gravitational escape. The periods show a flatter distribution, which may reflect an accretional rather than collisional fragmentation history. Arguments for spin-up with age due to sublimating gases are weak; the converse is possible and spin-down due to preferential escape of particles from equatorial regions appears likely.
Early photometry of comet p/Halley: Development of the Coma
Icarus, 1986
Simple thermal equilibrium sublimation models of a water-ice nucleus are shown to be consistent with weak activity even at R = 5.9 AU, provided the nucleus is dark (Bond albedo A < 0.15) and slowly rotating. The brightness of the comet varies on time scales from hours to days, with a range of nearly 1.0 mag at R = 5.9 AU, reduced to about 0.3 mag at R = 5.1 AU. The decrease in the range of the short-term variations is explained by the increased contribution from the coma to the total brightness of the comet. We find no convincing evidence for a dominant period in the short-term variations.
CCD Photometry of Cometary Nuclei, I: Observations from 1990–1995
Icarus, 2000
CCD photometry of 18 Jupiter family comets, observed at medium and large heliocentric distances, was carried out between April 1990 and July 1995. This is part of a long-term observational program designed to obtain their nuclear magnitudes. The observations were made with the 1.54-m Danish Telescope at ESO La Silla, the 2.5-m Nordic Optical Telescope (NOT) at Observatorio del Roque de los Muchachos (La Palma), the 2.0-m telescope at Pic du Midi, and the 2.15-m telescope at CASLEO, Argentina. Our estimates of the absolute nuclear magnitudes are discussed in comparison with previous determinations. Estimates (sometimes upper limits) for the effective radius (R) of the nuclei are computed considering a typical geometric albedo pv=0.04. The lowest radius found is the one of 37P/Forbes (R=1.0 km) while the largest corresponds to 65P/Gunn (R=11.0 km), but in this case the comet was observed very active.Wherever possible, cometary image profiles are compared with stellar profiles, in order to determine the existence of a faint coma. Seven of the comets were active, six of them at heliocentric distances larger than 4 AU. This unexpected activity is also discussed. We find a strong correlation between activity at large heliocentric distances and recent downward jumps in perihelion distance.
Further Investigation of Changes in Cometary Rotation
The Astronomical Journal, 2018
Samarasinha & Mueller (2013) related changes of cometary rotation to other physical parameters for four Jupiter family comets defining a parameter X, which is approximately constant within a factor of two irrespective of the active fraction of a comet. Two additional comets are added to this sample in this paper and the claim of a nearly constant parameter X for these six comets is confirmed, albeit with a larger scatter. Taking the geometric mean of X for all the comets above excluding 2P/Encke (as X for each comet was determined with respect to that of 2P/Encke), the expected changes in the rotation periods for a sample of 24 periodic comets are derived. We identify comets from this sample that are most likely to show observationally detectable changes in their rotation periods. Using this sample and including the six comets used to determine X, we find a correlation between the parameter ζ (i.e. the total water production per unit surface area per orbit approximated by that inside of 4 au) and the perihelion distance q; specifically we derive ζ ∝ q −0.8 and provide a theoretical basis for this in Appendix A. This relationship between ζ and q enables ready comparisons of activity due to insolation between comets. Additionally, a relationship between the nuclear radius R and the rotation period P is found. Specifically, we find that on average smaller nuclei have smaller rotation periods compared to the rotation periods of larger nuclei. This is consistent with expectations for rotational evolution and spin-up of comet nuclei, providing strong observational evidence for sublimation-driven rotational changes in comets.
Physical Properties of the Nucleus of Comet 2P/Encke
Icarus, 2000
We report a new study of the nucleus of Comet 2P/Encke, which the CONTOUR spacecraft is scheduled to encounter in November 2003. During the comet's close approach to Earth in July 1997, we measured the mid-infrared thermal and optical scattered continua with data from the TIMMI instrument (imaging) at the ESO 3.6-m telescope (wavelength λ from 8 to 12 µm), the ISOPHOT instrument (photometry) aboard ISO (3.6 µm ≤ λ ≤ 100 µm), and the STIS instrument (imaging) aboard HST (5500Å ≤ λ ≤ 11000Å ). The optical images show the nucleus with very little coma contamination, and the ISO photometry allowed us to separate the comatic and nuclear contributions to the ESO images. We used the Standard Thermal Model for slow rotators to calculate an effective nuclear radius of 2.4 km ± 0.3 km. The comet's mid-IR light curve implies a nuclear rotation period of 15.2 h ± 0.3 h, although some subharmonics of this also satisfy the data. If we assume that the nucleus is a triaxial ellipsoid in principal short axis rotation with the axis direction in 1985 as derived by Sekanina (1988, Astron. J. 95, 911), then by combining our data with light curves from the 1980s we find that the nucleus' angular momentum vector migrates, making a would-be circle in less than 81 years, and that one axial ratio is at least 2.6. The nucleus' optical linear phase coefficient is 0.06 mag/degree, making it one of the most phasedarkened objects known. The surface is also rougher than that of 146 FERNÁNDEZ ET AL. most asteroids. The visual geometric albedo is 0.05 ± 0.02, within the range found for other cometary nuclei. c 2000 Academic Press Key Words: comets; infrared observations. 12 µm. The images have 64 2 pixels and cover (21.8 ) 2 . Each pixel width covered 65 to 87 km at the comet during the observing run. The plate scale was measured using the known relative positions of α Cen A and B . The pointspread function's (PSF) full width at half-maximum (FWHM) varied from 0.7 to 1.0 arcsec. Chopping of the secondary mirror northward and nodding of the telescope westward, with typical throws of 30 arcsec, were employed. An array flat field was created by measuring the relative photometry of a bright star at 23 different locations on the array and then interpolating a surface with a minimum of curvature. We observed the comet at three wavelengths, but only at λ = 10.7 µm was the comet bright enough to let us build a well-sampled time series of data. Absolute flux calibration was done using α Cen A, whose 10.7-µm magnitude is −1.56 ± 0.05, interpolating from photometric data given by . The magnitude scale zero point is 35.7 Jy. Color corrections were done and were at most
Earth, Moon, and Planets, 2009
We present preliminary results of the narrow-band CN observations of comet 8P/Tuttle from early January 2008, realized as part of a project consisting of nearsimultaneous spectroscopic monitoring of HCN at millimeter-wavelengths and optical imaging of the coma. The mean-image subtraction method revealed low-contrast CN envelopes. Using the image cross-correlation technique we measured the projected velocity of these shells. For the sunward part we found it to be equal to 0.96 ± 0.03 km s -1 on January 4 and 1.10 ± 0.01 km s -1 on January 9, whereas the anti-sunward part reached 0.73 ± 0.05 and 0.80 ± 0.02 km s -1 , respectively. The periodicity of gas emission was investigated using a repeatability of the shells, their kinematics, and an aperture photometry of the near nucleus region. We found a period of 5.70 ± 0.07 h (along with multiples), consistent with previous findings by other authors. A toy Monte Carlo model was implemented to reproduce the time-series of the CN images. We show that emission of HCN into a relatively wide cone by a single active region on a rotating nucleus is the most probable scenario.
Coma morphology and constraints on the rotation of Comet HaleBopp (C/1995 O1)
Earth, Moon, and Planets, 1997
We present constraints on the spin state of comet Hale-Bopp based on coma morphology. Three cases of rotational states are compatible with near perihelion observations: (1) principal-axis rotation, (2) complex rotational state with a small precessional angle, or (3) complex rotational state with a large ratio between the component periods. For principal axis rotators, images from 1996 (pre-perihelion) are consistent with a rotational angular momentum vector, M, directed at ecliptic longitude and latitude (250 • , −5 • ) while images from late 1997 (post-perihelion) indicate (310 • , −40 • ). This may suggest a change in M. A complex rotational state with small precessional angle requires only a small or no change in M over the active orbital arc. In this case, M is directed near ecliptic longitude and latitude (270 • , −20 • ). A rotationally excited nucleus with a large ratio between component periods requires the nucleus to be nearly spherical. The transformation of dust coma morphology from near-radial jets to bright arcs and then again to near-radial jets is interpreted as a heliocentric and geocentric distance dependent evolutionary sequence. The spiral structures seen in CN filters near perihelion (in contrast to sunward side arcs seen in continuum) can be explained if the precursor of CN molecules (likely sub-micron grains) are emitted from the nucleus at low levels (≈ 10% of the peak daytime emission) during the nighttime. This may be indicative of a nucleus with a CO-rich active area(s).
The Astronomical Journal, 2000
Time series CCD photometry of the inner coma of active comets has been used over the last twenty years to determine the rotation period of their nucleus. Usually, the photometry is performed by using very small apertures with the aim of isolating as much as possible the brightness contribution of the nucleus with respect to the brightness of the coma or of measuring short-term gas/dust production rate diurnal variations. The e †ect of seeing variations in the brightness proÐle of the comet and their consequences on the measured magnitude in such small apertures has never been studied before. The aim of this paper is to study this "" seeing e †ect.ÏÏ A series of simulated images of two comets is generated by using di †erent seeing values. The brightness of the simulated comets is measured by using very small apertures ranging from 2 to 16 pixels. A strong correlation between the measured magnitudes and the seeing is found. This systematic e †ect can produce false variations of several tenths of magnitudes in the light curve in nights with variable seeing conditions. A new method to correct this seeing e †ect on real observations is proposed and applied to CCD observations of comets 29P/Schwassmann-Wachmann 1 and 21P/Giacobini-Zinner, carried out with the 82 cm IAC-80 Telescope at Teide Observatory (Canary Islands, Spain). The seeing e †ect is clearly present in the observations, and the method is shown to be very efficient in correcting it.
The Increasing Rotation Period of Comet 10P/Tempel 2
2010
We imaged comet 10P/Tempel 2 on 32 nights from 1999 April through 2000 March. R-band lightcurves were obtained on 11 of these nights from 1999 April through 1999 June, prior to both the onset of significant coma activity and perihelion. Phasing of the data yields a double-peaked lightcurve and indicates a nucleus rotational period of 8.941 +/- 0.002 hr with a peak-to-peak amplitude of ~0.75 mag. Our data are sufficient to rule out all other possible double-peaked solutions as well as the single- and triple- peaked solutions. This rotation period agrees with one of five possible solutions found in post-perihelion data from 1994 by Mueller and Ferrin (1996, Icarus, 123, 463-477), and unambiguously eliminates their remaining four solutions. We applied our same techniques to published lightcurves from 1988 which were obtained at an equivalent orbital position and viewing geometry as in 1999. We found a rotation period of 8.932 +/- 0.001 hr in 1988, consistent with the findings of previous authors and incompatible with our 1999 solution. This reveals that Tempel 2 spun-down by ~32 s between 1988 and 1999 (two intervening perihelion passages). If the spin-down is due to a systematic torque, then the rotation period prior to perihelion during the 2010 apparition is expected to be an additional 32 s longer than in 1999.
2000
The current understanding of cometary rotation is reviewed from both theoretical and ob- servational perspectives. Rigid-body dynamics for principal axis and non-principal-axis rota- tors are described in terms of an observer's point of view. Mechanisms for spin-state changes, corresponding timescales, and spin evolution due to outgassing torques are discussed. Differ- ent observational techniques and their pros and cons are presented