Spectral studies of comet C/2001 Q4 (NEAT)

The paper presents the results of the spectral observations of comet C/2001 Q4 (NEAT) acquired with the Zeiss-600 telescope of the Andrushevka astronomical observatory in May 2004. The spectrum of the comet was obtained in the range of 3600–8200 Å. We identified a number of emission features in the spectrum of comet C/2001 Q4 (NEAT). The emission bands of C₂, C₃, CN, CH, NH₂, H₂O⁺ were detected in the spectrum of the comet, and their intensities were determined. The ratios of gas-production rates Q(C₂)/Q(CN) = 0.23, Q(C₃)/Q(CN) = ?0.79, and Q(NH₂)/Q(CN) = ?0.029 were determined with the Haser model.     

Absolute spectrophotometry of Comet kohoutek 1973f during post-perihelion passage

Absolute spectrophotometry of the coma of Comet Kohoutek 1973f during post-perihelion period has been presented for seven nights in January 1984. Moderately wide range of heliocentric distance (0.436–0.799 AU) covered during observations allowed us to study the flux variation of emission bands with heliocentric distance. The emission features of CN, CH, C₂, C₃, and NaI have been identified in this comet. The abundances of CN and C₂ have been estimated and the production rates of CN, C₂ and C₃ have been derived. Production rates of CN and C₂ seem to vary as r ^–0.33 and r ^–3.50 respectively. The continuum of the comet became more and more redder as the heliocentric distance of the comet increased and phase angle decreased.     

Aperture Polarimetry And Photometry Of Comet Hale-Bopp

We present results of polarimetric and photometric observations of bright comet C/1995 O1 (Hale-Bopp) obtained at the 0.7 m telescope of Kharkov University Observatory from June 18, 1996 to April 24, 1997. The IHW and HB comet filters were used. The C₂ and C₃ production rates for Hale-Bopp are more than one order of magnitude larger and the dust production rates are more than two orders of magnitude larger than the Halley ones at comparable distances. Hence, Hale-Bopp was one of the most dusty comets. The average UC-BC and BC-RC colours of the dust were −0.02 and 0.13 mag, respectively. The polarization of comet Hale-Bopp at small phase angles of 4.8–13.0° was in good agreement with the date for comet P1/Halley at the same phase angles in spite of the fact that the heliocentric distances of comments differed nearly twice. However, at intermediate phase angles of 34–49° the polarization of comet Hale-Bopp was significantly larger than the polarization of the other dusty comets. It is the first case of such a large difference found in the continuum polarization of comets. The wavelength dependence of polarization for Hale-Bopp was steeper than for other dusty comets. The observed degree of polarization for the anti-sunward side of the coma was permanently higher than that for the sunward shell side. The polarization phase dependence of Hale-Bopp is discussed and compared with the polarization curves for other dusty comets. The peculiar polarimetric properties of comet Hale-Bopp are most likely caused by an over-abundance of small or/and absorbing dust particles in the coma. This revised version was published online in July 2006 with corrections to the Cover Date.     

Rapid changes of brightness in P/Halley

Scanner observations of the coma of periodic comet Encke (P/Encke) are presented for four nights in March 1984 during its post-perihelion period. The strong emission features of CN and C₂ molecules have been identified and the abundances of CN and C₂ are estimated. The production rates of these molecules have also been derived from their band luminosities. No trace of sodium emission has been found in this comet.     

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.     

Infrared Spectroscopy of Comet Hale-Bopp

High resolution (λ/δλ ∼ 20,000) spectra of comet C/1995 O1 (Hale-Bopp) in the 2–5 μm region were obtained during UT 2–5 March 1997 using CSHELL at the NASA Infrared Telescope Facility (IRTF) on Mauna Kea. The heliocentric and geocentric distances of the comet were ∼1.1 AU and ∼1.5 AU,respectively. We detected emission lines of the gas-phase molecules H₂O, ₄, C₂H₆, C₂H₂, HCN, and CO and derived absolute production rates and relative abundances for all species. We also used the 2-dimensional nature of the CSHELL data to investigate the spatial distribution of the molecules and find evidence that CO was derived at least partly from an extended source in the coma. This revised version was published online in July 2006 with corrections to the Cover Date.     

Optical Spectroscopy of Comet C/2000 WM1 (LINEAR) at the Guillermo Harro Astrophysical Observatory in Mexico

We present a preliminary analysis of medium resolution optical spectra of comet C/2000 WM1 (LINEAR) obtained on 22 November 2001. Theemission lines of the molecules C₂, C₃, CN, NH₂,H₂O⁺ and presumably CO (Asundi and triplet bands) and C₂ ^-were identified in these spectra. By analysing the brightnessdistributions of the C₂, C₃, CN emission lines along theslit of the spectrograph we determined some physical parameters of theseneutrals, such as their lifetimes and expansion velocities inthe coma. The Franck–Condon factors for the CO Asundi bands and C₂ ^- bands were calculated using a Morse potential model.     

Observations of High Resolution Spectra of Comet Hale-Bopp (C/1995 O1) at the SAO of the RAS

We present the results of the preliminary study of the comet Hale-Bopp spectrum obtained April 17, 1997 by K. Churyumov and F. Mussayev with the help of the 1-meter Zeiss reflector and the echelle spectrometer (spectral resolutionλ/Δ λ ≈ 50000), CCD and the long slit, oriented along the radius-vector(“Sun-comet direction”). Energy distributions for three selected regions including the C₃, C₂ (0-0) and CN(Δ ν = 0) molecules emissions of the comet Hale-Bopp spectrum were built. The rotational lines of the CN(Δ ν = 0) band were identified. The nature of the high emission peak near λ 4020 Å in the C₃ band is discussed. The presence of the cometary continuum of the nonsolar origin is assumed.     

The Infrared Spectrum of Comet Hele–Bopp as Seen by the Infrared Space Observatory

Spectra of comet C/1995 O1 (Hale-Bopp) were obtained with the Infrared Space Observatory (ISO) at medium resolution with the grating spectrometer in the photometer (PHT-S) and/or at high resolution with the short wavelength spectrometer (SWS) and long wavelength spectrometer (LWS) in April 1996 (Crovisier et al., 1996), September–October 1996 (Crovisier et al., 1997a, b) and December 1997, at distances from the Sun of 4.6, 2.9 and 3.9 AU, respectively. For the first time, high-resolution spectra of a comet covering the entire 2.4 to 200 μm spectral range were obtained. The vibrational bands of H₂O, CO₂ and CO are detected in emission with PHT-S. Relative production rates of 100:22:70 are derived for H₂O:CO₂:CO at 3 AU pre-perihelion. H₂O is observed at high spectral resolution in the ν₃ group of bands around 2.7 μm and the ν₂ group around 6 μm with SWS, and in several rotational lines in the 100–180 μm region with LWS. The high signal-to-noise ratio of the ν₃ band observed on September–October 1996 allows accurate determinations of the water rotational temperature (28 K) and of its ortho-to-para ratio(2.45 ± 0.10, which significantly differs from the high temperature limit and corresponds to a spin temperature of 25 K). Longward of 6 μm the spectrum is dominated by dust thermal continuum emission, upon which broad emission features are superimposed. The wavelengths of the emission peaks correspond to those of Mg-rich crystalline olivine (forsterite). In the September–October 1996 spectra, emission features at 45 and 65 μm and possible absorption at 2.9–3.2 μm suggest that grains of water ice were present at 3 AU from the Sun. The observations made post-perihelion in late December 1997 led to the detections of H₂O, CO₂ and CO at 3.9 AU from the Sun (Figures 1 and 2). The production rates were ≈3.0 × 10²⁸,3.5 × 10²⁸ and ≈1.5 × 10²⁹ s^-1, respectively. This corresponds to H₂O:CO₂:CO = 100:110:500 and confirms that at such distances from the Sun, cometary activity is dominated by sublimation of CO and CO₂ rather than by H₂O. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

Spectrophotometry of comet West (1975n) after the perihelion passage

In the wavelength range 350 to 650 nm, the flux distribution of comet West (1975n) is presented for various dates following perihelion passage. The variations with heliocentric distance, in the flux of the emission features of the CN band at 388 nm, the C₂ bands at 474 nm, 516 nm and 563 nm and Na at 589 nm, have been discussed. It is concluded that the comet was dust rich.     

Spectrophotometric study of comet Austin (1989 C1)

Spectrophotometric observations of the head of comet Austin (1989 C1) during five nights in May 1990 are presented. Emission bands due to CN, C₂ and C₃ molecules have been identified. An estimate of their column densities and production rates have been made.     

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%.     

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.     

Spectrophotometric study of P/Halley during post perihelion passage

Spectrophotometric observations of P/Halley are presented for four nights in the optical region (3200–7000 ) during post-perihelion period. Emission features due to CN, CH, C₃ and C₂ molecules are identified and the total apparent fluxes in each emission band are measured. It is found that the comet display large variations in the emission bands as well as continuum.     

Narrow band filter photometry of Comet Kohoutek

Narrow band photoelectric measurements of CN(3870), CO⁺(4250), C₂(4700), and C₂(5120) were made on twelve nights in December and January of comet Kohoutek. CN and C₂ appear to be stronger after perihelion, and CO⁺ showed a strong post perihelion increase coincident with the first appearance of a strong gas tail and then decreased to a fairly constant level.     

Spectroscopy of comet P/Schaumasse

Column density profiles for CN, C₃, C₂ and NH have been determined from a long-slit CCD spectrum of periodic comet P/Schaumasse (1992x). Comparisons of these profiles with Haser models indicate that the ratios of the CN, C₃ and C₂ production rates are typical for a short-period comet. Although the scale lengths for NH and its parent species are uncertain, the results indicate that the production rate for NH is much greater than for either C₂ or CN.     

Spectrophotometry of P/Halley (1982i)

Spectral scans of the head of periodic Comet Halley (1982i) have been presented in the optical region (3200–7000 Å) for six nights. Emission features due to NH, CN, CH, C₃, C₂ and NH₂ molecules have been identified. It is found that the comet exhibits night-to-night variation of emission bands. The abundances and production rates of CN and C₂ species have been derived.     

Surface Photometry of Comet Hale-Bopp Carbon Images

A very long series of photographic observations of the comet Hale-Bopp has been made during January–April 1997 at the double astrograph (400/2000) of the Main Astronomical Observatory (Kyiv, Ukraine). Some of the cometary photos were obtained with two wide-band filter combinations. One of these combinations isolates C₂ emission, another — the nearby dust continuum. The images were digitized by means of AMDPH-XY machine and then calibrated following the standard procedure. After subtraction of the dust continuum the distribution of surface brightness in the C₂ emission coma of comet Hale-Bopp was studied. We found an asymmetric brightness distribution both pre- and post-perihelion. On 21.77 April 1997 a secondary brightness peak is found at the distance of 1.03 × 10⁵ km from the nucleus. It is possible that this peak is related to the extended source of the C₂ molecules. This revised version was published online in July 2006 with corrections to the Cover Date.     

A Molecular Survey of Comet C/1995 O1 (Hale-Bopp) at the IRAM Telescopes

Spectroscopic observations of comet Hale-Boppwere undertaken near perihelion at millimetre wavelengths with the Institut de Radioastronomie Millimétrique (IRAM) telescopes at Plateau de Bure (France)and Pico Veleta (Spain). They resulted in the first detections of HCOOH,SO₂, NH₂CHO and HCOOCH₃ in a comet. HDO was detected through its3₁₂–2₂₁ line at 225.897 GHz,complementing the observation of the 1₀₁–0₀₀ line at 464.925 GHz at the James Clerk Maxwell Telescope (Meier et al., 1998,Science 279, 842).Several unidentified lines are present in the spectra. Observations of HC₃N, HNCO, OCS, SO, CN, CO₊, HCO₊, in addition to more ‘classical’species CO, HCN, HNC, CH₃CN, CH₃OH, H₂CO, CS and H₂S (Biveret al., this issue) permit us to make out an extensive inventory of the composition of the coma of comet Hale-Bopp at its perihelion. It presents strong analogies with gas-phase abundances measured in interstellar hot cores and bipolar flows, which are believed to reflect the composition of interstellar grains. This revised version was published online in July 2006 with corrections to the Cover Date.