Polarimetry and Photometry of Comet C/2004 Q2 (Machholz)

We present results of polarimetry and photometry of comet C/2004 Q2 (Machholz) obtained with the 0.7-m telescope of Institute of Astronomy at the Karazin Kharkiv National University on February 3 and 4, and March 4 and 14, 2005. The observations were carried out with a one-channel photoelectric photometer-polarimeter. The IHW continuum UC (λ3650/80 Å), BC (λ4845/65 Å), RC (λ6840/90 Å) and emission filters CN (λ3871/50 Å), C₃ (λ4060/70 Å), and C2 (λ5140/90 Å) were used. Degree of the comet polarization at phase angles ≈ 52° and ≈44° in the red continuum was close to that for so called dusty comets. The comet had a typical spectral gradient of polarization ΔP/Δλ=0.86% per 1000 Å. In the framework of the Haser model we have found the gas production rates Q of the CN, C₃ and C₂ species and the dust production rates Afρ on February 4 and March 14, 2005. The ratio log[Afρ (BC)/Q(CN)] was compared with data for other comets. The normalized spectral gradient of cometary dust S’(BC,RC) was 8.7%/1000 Å for February 4 and 17.0%/1000 Å for March 14. We conclude that comet C/2004 Q2 (Machholz) in many respects is a typical dusty comet.     

Observations of the inner coma of C/1995O1 (Hale-Bopp)—gas and dust production

Hale-Bopp (C/1995 O1) was the most productive recent comet observed in terms of gas and dust output. Since its discovery in 1995 at a distance of 7.14 AU from the Sun, the comet has been well observed, revealing the dynamics of a rare and large comet. Hale-Bopp showed strong emissions of the principle cometary gases CN, C₃, and C₂, as well as an abundance of dust. The production rates of these gases were found to be 1.45×10²⁸, 1.71×10²⁸, and , respectively, with dust production, in terms of Afρ, , as measured in the green continuum (5260 Å). The observations for this paper are presented in two groups spanning 10 days each, one group centered near 32 days prior to and the other 21 days after perihelion. The averages of dust and gas production rates show a slightly higher value for each prior to perihelion than after perihelion, consistent with a possible peak in production a few weeks prior to perihelion passage.     

Narrow-Band Photometry of Comet C/1995 O1 (Hale-Bopp)

Photometric observations of comet C/1995 O1 (Hale-Bopp) carried out at the Stará Lesná Observatory since February to April 1997 are analyzed and discussed. Emission band fluxes and continuum fluxes are presented, from which the total numbers of molecules in the columns of the coma encircled by diaphragms are calculated. The production rates are estimated from the conventional Haser model. We found that the photometric exponent of dust contribution two months prior perihelion was n = 5.2. The photometric exponent n of the cometary magnitude solely to the C₂ emission alone equals 3.3 and that of CN equals 2.5. These values can be explained by a fact that the maximums of production rates of the gases were reached between March 2and 12 and not at the perihelion as it is valid for dust. These results are compared with the values of 1P/Halley (1986 III) under the similar conditions, obtained with the same method and instrument. C/Hale-Bopp exhibited 4.1 times more molecules radiating the CN-emission than 1P/Halley in the same column of the coma. The continuum flux of C/Hale-Bopp was also very strong. The ratios (to 1P/Halley) are 94:1 (Cont. 484.5) and 74:1 (Cont. 365.0). The cometary colour was the same as that of the Sun. This revised version was published online in July 2006 with corrections to the Cover Date.     

Comet C/2010X1 (Elenin). Unrealized expectations

We present the analysis of the photometric and spectroscopic data obtained for comet C/2010 X1 (Elenin) when it was at a distance of 2.92 AU from the Sun. The observations were made at the prime focus of the 6-m BTA telescope with the SCORPIO focal reducer. The magnitude of the comet, measured in the R _c -band with an 9?? aperture radius amounted to 16?8 ± 0?1. The computed dust production rate was estimated to be about 6 kg/s. The cometary coma manifested the emissions in the (0?C0) band of the CN molecule violet system, and a number of emission band heads of the C₃ molecule. The gas production rate of the molecules is determined using the Haser model and amounts to 1.41 × 10²⁴ and 4.20 × 10²³ molecules per second for CN and C₃, respectively. The ratio of gas production rates log[Q(C₃)/Q(CN)] is equal to ?0.85, which is close to the mean value, determined for a significant number of comets. A normalized gradient of the cometary dust reflectivity, calculated for the 4430?C6840 ? spectral range amounts to 14.3 ± 1.2%.     

Long-term numerical theories of comet motion

We propose a method of constructing numerical theories of comet motion that cover long time intervals. The method involves the determination of individual values of the constants A ₁, A ₂, and A ₃ (radial, transversal, and normal components of nongravitational acceleration) and photocenter shifts for each appearance with the presence of a sufficient quantity of observations. Moreover, in the case of close planetary approaches, bursts of brightness, or heavy shifts in the cometary gas production maxima against the perihelion when standard models of nongravitational acceleration cannot provide an accurate presentation of the observations, we propose the use of instant velocity measurements. This method was used to construct a unified numerical theory of motion of the Kopff comet in the interval of 1906–2002. The theory encompassed 16 appearances of the comet with the mean error of unit weight σ = 1.40.     

C/1995 O1 (Hale-Bopp): Gas Production Curves And Their Interpretation

The discovery of C/1995 O1 (Hale-Bopp) at 7 AU from the Sun provided the first opportunity to follow the activity of a bright comet over a large range of heliocentric distances r_h. Production rates of a number of parent molecules and daughter species have been monitored both pre- and postperihelion. CO was found to be the major driver of the activity far from the Sun, surpassed by water within 3 AU whose production rate reached 10³¹ s⁻¹ at perihelion. Gas production curves obtained for various species show several behaviours with r_h. Gas production curves contain important information concerning the physical state of cometary ices, the structure of the nucleus and all the processes taking place inside the nucleus leading to outgassing. They are relevant to the study of several other phenomena such as the sublimation from icy grains, dust mantling or seasonal effects. For some species, such as H₂CO or HNC, they permit to constrain their origin in the coma. We discuss models of subsurface gas production in distant comets and predictions of how such a source may vary as the comet moves along its orbit, approaching perihelion and receding again. Features in the observed gas production curves of comet Hale-Bopp are generally interpretable in terms of either subsurface production (typical example: CO at large r_h) or free sublimation (typical example: H₂O). Possible implications for the vertical stratification of the cometary ices are reviewed, and preference is found for a model with crystallization of amorphous ice close to the nuclear surface. This revised version was published online in July 2006 with corrections to the Cover Date.     

Comet C/2002 T7 (LINEAR): Polarimetric and photometric studies

We present the results of polarimetric and photometric observations of dynamically new comet C/2002 T7 (LINEAR) at phase angles from 6° to 26°. During the observations, the comet was at a distance of 2.7–1.3 AU from the Sun and 1.7–2.0 AU from the Earth. The aperture polarimetry was made with the 2.6-m Shain telescope and the 1.25-m AZT-11 telescope of the Crimean Astrophysical Observatory and with the 0.7-m telescope of the Astronomical Institute of the Kharkiv National University during the period from November 21, 2003, to February 21, 2004. The wideband UBVRI and WRC (λ7228/1142 Å) filters and the narrowband GC (λ5260/56 Å) filter were used. The photometric observations of the comet were carried out on February 21, 2004, with narrowband filters isolated the BC (λ4845/65 Å) and RC (λ6840/90 Å) continuum and the C₂ emission (λ5140/90 Å). The phase-angle dependence of linear polarization of the comet has been obtained, and its parameters, such as the minimal polarization P _min = ?1.63%, the phase angle of the minimal polarization α_min = 10.6°, the inversion angle α_inv = 22.7°, and the slope of the phase curve at the inversion angle h = 0.24% per degree, were found. From the photometric observations, the following quantities have been obtained: the column density of molecules C₂ in the line of sight logN (C₂) = ?9.15 mol/cm² and their production rate log Q (C₂) = 27.11 mol/s, the spectral gradient of reflectivity for the dust S′(BC, RC) ≈ 3%/1000 Å, and the dust production parameter Afρ equal to 371 and 273 cm for the blue and red continuum ranges, respectively. According to these results, the physical parameters of comet C/2002 T7 are close to the average characteristics of typical dusty comets.     

Photometric studies of comet C/2009 P1 (Garradd) before the perihelion

The results of the photometric observations of comet C/2009 P1 (Garradd) performed at the 60-cm Zeiss-600 telescope of the Terskol observatory have been analyzed. During the observations, the comet was at the heliocentric and geocentric distances of 1.7 and 2.0 AU, respectively. The CCD images of the comet were obtained in the standard narrowband interference filters suggested by the International research program for comet Hale-Bopp and correspondingly designated the “Hale-Bopp (HB) set.” These filters were designed to isolate the BC (λ4450/67 Å), GC (λ5260/56 Å) and RC (λ7128/58 Å) continua and the emission bands of C₂ (λ5141/118 Å), CN (λ3870/62 Å), and C₃ (λ4062/62 Å). From the photometric data, the dust production rate of the comet and its color index and color excess were determined. The concentration of C₂, CN, and C₃ molecules and their production rates along the line of sight were estimated. The obtained results show that the physical parameters of the comet are close to the mean characteristics typical of the dynamically new comets.     

Spectrophotometric observations of Comet Austin (1982g)

Spectrophotometric observations of Comet Austin (1982g) in the bands of CN, C₂, and C₃ are presented, and fit to a Haser model for the cometary brightness distribution. The lifetimes of the parent and daughter molecules, as well as the velocity of the molecules leaving the cometary surface are determined from the model fit. The absolute production rate of molecules is also determined.     

Radio Line Observations Of Molecular And Isotopic Species In Comet C/1995 O1 (Hale-Bopp)

We present here a review of the radio observations of the remarkable comet Hale-Bopp C/1995 O1 in which most major radio astronomical facilities have been involved. These observations started in August 1995, soon after the discovery of the comet (it was then at ∼7 AU from the sun), and well before its perihelion on April 1st, 1997; they are still going on, hopefully up to end of 1998. Extended cartographies have been obtained using multibeam receivers and on-the-fly techniques. High spatial resolution (a few ″) has been achieved with interferometers. Submillimetric observations are playing an increasing role, and high resolution (R ∼ 10⁶−10⁷) spectroscopy of cometary lines is now performed from decimetric to submillimetric wavelengths. The number of species observed at radio wavelengths now reaches ∼28,when it was ∼14 for comet C/1996 B2 Hyakutake. Most of these species are parent molecules. However, ions have been observed for the first time at radio wavelengths, and their velocities measured. Several isotopic species (involving D,¹³C,³⁴S,¹⁵N) have been sought, allowing isotopic enrichment determinations. The abundances of cometary molecules present many similarities and some differences with the abundances of interstellar molecules in regions where grain mantles are believed to be evaporated to the gas phase (hot cores, bipolar flows). They will be discussed for their implications on the origin of cometary ices and of comets themselves. This revised version was published online in July 2006 with corrections to the Cover Date.     

A comparison of modeled and observed intensity profiles for C2, CN, and the blue continuum for Comet Bradfield (1987s)

Intensity profiles were obtained for the C₂ and CN emission and blue continuum of Comet Bradfield (1987s), from observations obtained over a 10 week period starting shortly before perihelion. Model intensity profiles were produced and then fitted to the observed profiles, and used to put constraints on some of the dust and gas parameters. Most of these parameters, including the gas and dust outflow speeds from the cometary nucleus and the molecular lifetimes, were consistent with expected values. The best fitting models incorporate significant dust particle fragmentation and extended emission of CN from dust, both occurring in the inner coma. In addition, although there may have been enhancement of gas and dust emission on the sunward side of the cometary nucleus, it appears that the tailward side maintained a significant level of activity.     

Placing the Deep Impact Mission into context: Two decades of observations of 9P/Tempel 1 from McDonald Observatory

We report on low-spectral resolution observations of Comet 9P/Tempel 1 from 1983, 1989, 1994 and 2005 using the 2.7 m Harlan J. Smith telescope of McDonald Observatory. This comet was the target of NASA's Deep Impact mission and our observations allowed us to characterize the comet prior to the impact. We found that the comet showed a decrease in gas production from 1983 to 2005, with the decrease being different factors for different species. OH decreased by a factor 2.7, NH by 1.7, CN by 1.6, C₃ by 1.8, CH by 1.4 and C₂ by 1.3. Despite the decrease in overall gas production and these slightly different decrease factors, we find that the gas production rates of OH, NH, C₃, CH and C₂ ratioed to that of CN were constant over all of the apparitions. We saw no change in the production rate ratios after the impact. We found that the peak gas production occurred about two months prior to perihelion. Comet Tempel 1 is a “normal” comet.     

Mechanistic studies on the decomposition of carbon suboxide in a cometary ice analog

A cometary ice analog sample consisting primarily of carbon suboxide ice (C₃O₂) was produced from the irradiation of its precursor, carbon monoxide. This carbon suboxide sample was subjected to irradiation with energetic electrons at 10 K to simulate the interaction of carbon suboxide-rich cometary analog ices with ionizing radiation. The destruction of carbon suboxide as well as the production of the primary degradation products, dicarbon monoxide (C₂O), and carbon monoxide (CO), were monitored quantitatively by infrared spectroscopy in situ; the gas phase was simultaneously sampled via quadrupole mass spectrometry. A kinetic model was produced to help explain the decomposition kinetics of carbon suboxide in cometary ices and to infer the underlying reaction mechanisms.     

Infrared measurements of the chemical composition of C/2006 P1 McNaught

C/2006 P1 McNaught is a dynamically new comet from the Oort cloud that passed very close to the Sun, driving overall volatile production rates up to about 10³¹ molecules s⁻¹. Post-perihelion observations were obtained in a target-of-opportunity campaign using the CSHELL instrument at the NASA Infrared Telescope Facility atop Mauna Kea, Hawaii, on UT 2007 January 27 and 28. Eight parent volatiles (H₂O, CH₄, C₂H₂, C₂H₆, HCN, CO, NH₃, H₂CO) and two daughter fragments (OH and NH₂) were detected, enabling the determination of a rotational temperature and production rate for H₂O on UT January 27 and absolute and relative production rates for all the detected parent species on UT January 28. The chemical composition measured in the coma suggests that this close perihelion passage stripped off processed outer surface layers, likely exposing relatively fresh primordial material during these observations. The post-perihelion abundances we measure for CO and CH₄ (relative to H₂O) are slightly depleted while C₂H₂, NH₂ and possibly NH₃ are enhanced when compared to the overall comet population. Measured abundances for other detected molecular species were within the range typically observed in comets.     

Cyanide Chemistry in Comet Hale-Bopp (C/1995 O1)

Observations of comet Hale-Bopp (C/1995 O1) have been carried out near perihelion (1997 March) at millimeter wavelengths using the NRAO 12 m telescope. The J=1-->0, 2-->1, and 3-->2 lines of HCN at 88, 177, and 265 GHz were measured in the comet as well as the J=3-->2 lines of H13CN, HC15N, and HNC. The N=2-->1 transition of CN near 226 GHz was also detected, and an upper limit was obtained for the J=2-->1 line of HCNH+. From the measurements, column densities and production rates have been estimated. A column density ratio of [HCN]/[HNC] = 7+/-1 was observed near perihelion, while it was found that [HCN]/[HCNH+] greater, similar 1. The production rates at perihelion for HCN and CN were estimated to be Q(HCN) approximately 1x1028 s-1 and Q(CN) approximately 2.6x1027 s-1, respectively, resulting in a ratio of [HCN]/[CN] approximately 3. Consequently, HCN is sufficiently abundant to be the parent molecule of CN in Hale-Bopp, and HCNH+ could be a source of HNC. Finally, carbon and nitrogen isotope ratios of 12C/13C = 109+/-22 and 14N/15N = 330+/-98 were obtained from HCN measurements, in agreement with previous values obtained from J=4-->3 data. Such ratios suggest that comet Hale-Bopp formed coevally with the solar system.     

CCD Observations of Comet Hale-Bopp at Shajn Telescope I. Coude spectra

Spectroscopic observations of Comet Hale-Bopp were made at the 2.6 m Shajn Telescope of the Crimean Astrophysical Observatory. Some spectra were obtained with high spectral resolution, FWHM = 0.18–0.4Å, in the coude focus on February 22 and 26, 1997. The observations were made in selected spectral windows (4805–4872 Å,6528–6595 Å, 7186–7253 Å, 8276–8408 Å).The spectrograph slit was centered on the nucleus and had dimensions of 25.2 × 0.6 arcsec² on the plane of the sky. The continuum spatial profiles were extremely asymmetrical toward the Sun. However, the continuum-subtracted spatial profiles of the molecular emissions were symmetrical relative to the nucleus, except for C₂. The shape of the spatial profiles of the C₂ emissions is similar to that one of continuum but is more flattened. So, there are evidences that dust can be an additional source of the C₂ radicals in the cometary coma. The main aim of our research was identification of the cometary emissions. Using recent laboratory spectroscopic data we identified newlines of C₂ associated with the transitions from high rotational levels in the 4805–4872 Å spectral region. We detected cometary H_α emission as well. Emissions of NH₂, H₂O⁺,and C₂ (Phillips system) were found in the red spectral windows. Some emission features are still unassigned.     

polarimetric and photometric observations of split comet C/2001 A2 (LINEAR)

We present the results of polarimetric and photometricobservations of split Comet C/2001 A2 (LINEAR), which wereobtained at the 70-cm telescope of the Astronomical Observatoryof Kharkiv National University between 30 June and 31 July 2001.The brightest fragment of the comet, nucleus B, was observed.Eight narrowband cometary filters in the continuum and in emissionbands and a wideband red filter have been used. The comet wasobserved through apertures of 88, 33, and 19 arcsec. Polarizationphase curves were obtained for the continuum and for the firsttime, for NH₂(0, 7, 0) emission. The degree of polarization ofthe light scattered by the dust decreases with the increase ofaperture size. An important temporal variation of the polarizationwith a rotation of the polarization plane was observed at twophase angles (26.5° and 36.2°). Molecular column densities and production rates of CN, C₂,C₃, and NH₂ species are calculated in the framework of theHaser model. A comparative analysis of the temporal variations ofthe visual magnitudes, gas and dust production rates, dust colorand polarization are presented.     

Vaporization of comet nuclei: Light curves and life times

We have examined the effects of vaporization from the nucleus of a comet and show that a latitude dependence of vaporization can, in some cases, explain asymmetries in cometary light curves. We also find that a non-uniform distribution of solar radiation over a comet can considerably shorten the vaporization lifetime compared to the results normally obtained by assuming that the nuclear surface is isothermal.Independent of any latitude effects, comets with CO₂-dominated nuclei and with perihelion distances less than 0.5 AU have vaporization lifetimes less than or comparable to their dynamical ejection times. This may explain the observed deficit of comets with small perihelion distances. Similarly comets with CO₂-dominated nuclei and perihelia near Jupiter's orbit have vaporization lifetimes that are shorter than the time for capture into short-period orbits. We suggest, therefore, that at least some new comets are composed in large part of CO₂, while only H₂O-dominated comets, with lower vaporization rates, can survive to be captured into short-period orbits.     

Monte Carlo modeling of neutral gas and dust in the coma of Comet 1P/Halley

The neutral gas environment of a comet is largely influenced by dissociation of parent molecules created at the surface of the comet and collisions of all the involved species. We compare the results from a kinetic model of the neutral cometary environment with measurements from the Neutral Mass Spectrometer and the Dust Impact Detection System onboard the Giotto spacecraft taken during the fly-by at Comet 1P/Halley in 1986. We also show that our model is in good agreement with contemporaneous measurements obtained by the International Ultraviolet Explorer, sounding rocket experiments, and various ground based observations.The model solves the Boltzmann equation with a Direct Simulation Monte Carlo technique (Tenishev, V., Combi, M., Davidsson, B. [2008]. Astrophys. J. 685, 659-677) by tracking trajectories of gas molecules and dust grains under the influence of the comet’s weak gravity field with momentum exchange among particles modeled in a probabilistic manner. The cometary nucleus is considered to be the source of dust and the parent species (in our model: H₂O, CO, H₂CO, CO₂, CH₃OH, C₂H₆, C₂H₄, C₂H₂, HCN, NH₃, and CH₄) in the coma. Subsequently our model also tracks the corresponding dissociation products (H, H₂, O, OH, C, CH, CH₂, CH₃, N, NH, NH₂, C₂, C₂H, C₂H₅, CN, and HCO) from the comet’s surface all the way out to 10⁶ km.As a result we are able to further constrain cometary the gas production rates of CO (13%), CO₂ (2.5%), and H₂CO (1.5%) relative to water without invoking unknown extended sources.     

Light curves and photometric parameters of the comets C/1999 S4 (LINEAR), C/2001 Q4 (NEAT), C/2002 T7 (LINEAR), C/2002 V1 (NEAT), C2004 Q2 (Machholz), and 153P/2002 C1 (Ikeya-Zhang)

Light curves of six comets, C/1999 S4 (LINEAR), C/2001 Q4 (NEAT), C/2002 T7 (LINEAR), C/2002 V1 (NEAT), C/2004 Q2 (Machholz), and 153P/2002 C1 (Ikeya-Zhang), were built and investigated. The photometric parameters H ₀, H ₁₀, and n were calculated for these comets, and they were found to change both before and after perihelion. The shift of light curve peak with respect to perihelion passage moment was determined for each comet. Our white-light curves are compared to the results of polarimetric and electrophotometric observations of the comets C/2002 T7 (LINEAR) and C/2004 Q2 (Machholz).