* Astronomy

Blobrana · L

RE: Comet C/2004 Q2 (Machholz)

Blobrana · L

Title: Comet Machholz (C/2004 Q2): morphological structures in the inner coma and rotation parameters
Authors: Federico Manzini, Raoul Behrend, Lorenzo Comolli, Virginio Oldani, Cristiano B. Cosmovici, Roberto Crippa, Cesare Guaita, Gottfried Schwarz, Josep Coloma

Extensive observations of comet C/2004 Q2 (Machholz) were carried out between August 2004 and May 2005. The images obtained were used to investigate the comet's inner coma features at resolutions between 350 and 1500 km/pixel. A photometric analysis of the dust outflowing from the comet's nucleus and the study of the motion of the morphological structures in the inner coma indicated that the rotation period of the nucleus was most likely around 0.74 days. A thorough investigation of the inner coma morphology allowed us to observe two main active sources on the comet's nucleus, at a latitude of +85° ±5° and +45° ±5°, respectively. Further sources have been observed, but their activity ran out quite rapidly over time; the most relevant was at latcom. = 25° ±5°. Graphic simulations of the geometrical conditions of observation of the inner coma were compared with the images and used to determine a pole orientation at RA=95° ±5°, Dec=+35° ±5°. The comet's spin axis was lying nearly on the plane of the sky during the first decade of December 2004.

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Blobrana · L

Title: Comet C/2004 Q2 (MACHHOLZ): Parent Volatiles, a Search for Deuterated Methane, and Constraint on the CH4 Spin Temperature
Authors: Boncho P. Bonev, Michael J. Mumma, Erika L. Gibb, Michael A. Disanti, Geronimo L. Villanueva, Karen Magee-Sauer, Richard S. Ellis

High-dispersion (l/dl ~ 25,000) infrared spectra of Comet C/2004 Q2 (Machholz) were acquired on Nov. 28-29, 2004, and Jan. 19, 2005 (UT dates) with NIRSPEC at the Keck-2 telescope on Mauna Kea. We detected H2O, CH4, C2H2, C2H6, CO, H2CO, CH3OH, HCN, and NH3 and we conducted a sensitive search for CH3D. We report rotational temperatures, production rates, and mixing ratios (with respect to H2O) at heliocentric distances of 1.49 AU (Nov. 2004) and 1.21 AU (Jan. 2005). We highlight three principal results: (1) The mixing ratios of parent volatiles measured at 1.49 AU and 1.21 AU agree within confidence limits, consistent with homogeneous composition in the mean volatile release from the nucleus of C/2004 Q2. Notably, the relative abundance of C2H6/C2H2 is substantially higher than those measured in other comets, while the mixing ratios C2H6/H2O, CH3OH/H2O, and HCN/H2O are similar to those observed in comets, referred to as "organics-normal". (2) The spin temperature of CH4 is > 35-38 K, an estimate consistent with the more robust spin temperature found for H2O. (3) We obtained a 3s upper limit of CH3D/CH4 < 0.020 (D/H < 0.005). This limit suggests that methane released from the nucleus of C/2004 Q2 is not dominated by a component formed in extremely cold (near 10 K) environments. Formation pathways of both interstellar and nebular origin consistent with the measured D/H in methane are discussed. Evaluating the relative contributions of these pathways requires further modelling of chemistry including both gas-phase and gas-grain processes in the natal interstellar cloud and in the protoplanetary disk.

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Blobrana · L

Orbital elements:
    C/2004 Q2 (Machholz)
T 2005 Jan. 27.370 TT                                   MPC
q   1.28614              (2000.0)            P               Q
                   Peri.   14.807       -0.299154       -0.728033
                   Node    95.921       +0.800265       -0.543493
e   1.0            Incl.   38.326       +0.519694       +0.417832
From 25 observations 2004 Aug. 27-28.

MPEC 2004 -Q58

Blobrana · L

Title: The rotation and coma profiles of comet C/2004 Q2 (Machholz)
Authors: Maarten Reyniers, Pieter Degroote, Dennis Bodewits, Jan Cuypers, Christoffel Waelkens

Aims. Rotation periods of cometary nuclei are scarce, though important when studying the nature and origin of these objects. Our aim is to derive a rotation period for the nucleus of comet C/2004 Q2 (Machholz). Methods. C/2004 Q2 (Machholz) was monitored using the Merope CCD camera on the Mercator telescope at La Palma, Spain, in January 2005, during its closest approach to Earth, implying a high spatial resolution (50km per pixel). One hundred seventy images were recorded in three different photometric broadband filters, two blue ones (Geneva U and B) and one red (Cousins I). Magnitudes for the comet's optocentre were derived with very small apertures to isolate the contribution of the nucleus to the bright coma, including correction for the seeing. Our CCD photometry also permitted us to study the coma profile of the inner coma in the different bands.
Results. A rotation period for the nucleus of P = 9.1 ± 0.2 h was derived. The period is on the short side compared to published periods of other comets, but still shorter periods are known. Nevertheless, comparing our results with images obtained in the narrowband CN filter, the possibility that our method sampled P/2 instead of P cannot be excluded. Coma profiles are also presented, and a terminal ejection velocity of the grains v_gr = 1609 ± 48 m/s is found from the continuum profile in the I band.

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