Comparison of X-rays from Comets LINEAR (C/1999 S4) and McNaught-Hartley (C/1999 T1)

The Chandra X-ray Observatory (CXO) observations of Comets McNaught-Hartley (MH) and LINEAR S4 (S4) have been processed in the same way to compare X-rays from those comets. The X-ray isophotes are crescent-like in S4 and more circular in MH because of the different phase angles (98° and 44°, respectively). The peak X-ray brightness is greater in S4 than that in MH by a factor of 1.5 and smaller by a factor of 1.7 after the correction for heliocentric distance. The X-ray luminosities of MH and S4 are equal to 8.6 and 1.4×10¹⁵ erg s⁻¹ inside the apertures of ρ=1.5 and 0.5×10⁴ km, respectively. (Brightness is 20% of the peak value at these ρ.) Efficiencies of X-ray excitation corrected to the solar wind flow are similar and equal to 4.3×10⁻¹⁴ erg AU^3/2 in both comets. This confirms the solar wind excitation of X-rays in comets. Spectra of the comets were extracted with a special care of the background correction and using an energy-dependent spectral resolution code. The MH spectrum consists of ten emissions instead of nine emissions in the previously published spectrum. The new emission at 307 eV fills in a strong minimum in the previous spectrum and removes the major difference between that spectrum and the synthetic spectrum. This emission is assigned to the C⁺⁴ and Mg⁺⁹ lines. The positions of the other emissions and their identification are similar to those in the previous spectrum. The S4 spectrum consists of eight emissions, and four emissions are the same as in MH. The line identification is given. Ion ratios in the solar wind have been extracted from the spectra. O⁺⁸/O⁺⁷ is equal to 0.29±0.04 and 0.14±0.02 in MH and S4, and this difference correlates with the higher solar wind speed in S4. Ne⁺⁹/O⁺⁷ is (15±6)×10⁻³ and (19±7)×10⁻³, and these are the first data on Ne⁺⁹ in the solar wind. C⁺⁶/O⁺⁷ is 0.7±0.2 in both MH and S4. X-ray spectroscopy of comets may be used as a diagnostic tool to study the solar wind composition.     

Orbits of Comets C/1845 L1 (Great June Comet) and C/1846 D1 (de Vico)

Orbits are calculated for Comet C/1845 L1 (the Great June Comet) and C/1846 D1 (de Vico), the former based on 157 observations in right ascension and 152 in declination and the latter on 10 and 9, respectively. Both orbits are hyperbolic and statistically distinguishable from parabolas. Statistical tests indicate that the residuals are random and thus the orbits satisfactory. The Great June Comet is in no way associated with the comet Tycho Brahe observed in 1596 (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Polarimetric Study of Comets C/1995 O1 (Hale–Bopp) and C/2000 Wm1 (Linear)

We made polarimetric observations of comet Hale–Bopp covering awide phase angle range, from 18.8 to 47°. At certain phase angles the heliocentricdistance of the comet was less than 1 AU during its pre and post perihelion passages. Oneof the important findings, based on the data in the visual bands, is the higher polarizationwith stronger wavelength dependence compared to comet Halley, indicating the presenceof much finer grains in comet Hale–Bopp. It may also be noted that comet Hale–Bopphas shown highest degree of polarization known so far for any comet and hence fallsin the class of high polarization comets. Polarimetric observations were made of cometC/2000 WM1 (LINEAR)using narrow band (IHW) filters 4845 Å and 7000 Åand broad bands filters BVR during November 23–26, 2001 when the phase angle rangedfrom 15 to 22°. Some of the results based on these observations are presented anddiscussed.     

New orbits for comets C/1843 J1 (Mauvais) and C/1853 W1 (van Arsdale)

New orbits for comet C/1843 J1 (Mauvais) and comet C/1853 W1 (van Arsdale) are calculated. Both orbits are hyperbolic, with e = 1.001145 and semi‐major axis a = –1412.18 AU for Mauvais and e = 1.000700 and a = –2919.24 AU for van Arsdale. Integrating the orbits backwards indicate that both comets were born in the far Oort cloud. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Nitrogen Sulfide In Comets Hyakutake (C/1996 B2) And Hale–Bopp (C/1995 O1)

The chemistry of both nitrogen and sulfur presents interesting problems in comets.In this paper, we use a model of cometary comae with gas-phase chemical kineticsand gas dynamics to predict molecular abundances in the inner coma region for twoof the brightest comets in the past 20 years, Hyakutake (C/1996 B2) and Hale–Bopp(C/1995 O1). In this progress report we concentrate on the gas-phase chemistry of thenitrogen sulfide (NS) radical at a heliocentric distance of 1 AU to study the abundanceof NS using a detailed photo and chemical reaction network with over 100 species andabout 1000 reactions. The results are compared with recent observations of CometHale–Bopp and reveal that conventional gas-phase reactions schemes do not produceNS in sufficient quantities to explain the observations. We plan to continue therefinement of the model to improve agreement with observational constraints.     

同位素丰度比^12C／^13C与恒星演化及其核过程

近２０年中在银河系及河外星系中同位素丰度比＾１２Ｃ／＾１３Ｃ的毫米波及光学观测取得了一些结果,同位素丰度比＾１２Ｃ／＾１３Ｃ在研究恒星演化及其核过程方面具有重要意义,银河系中的＾１２Ｃ／＾１３Ｃ随银心距ＤＧＣ呈梯度分布,附近河外星系中明显较高的＾１２Ｃ／＾１３Ｃ表明银河系中心处于一个较为宁静的物理相,恒星中不同的＾１２Ｃ／＾１３Ｃ值则反映了各自不同的演化阶段,进一步高精度,大样本的观测将有助于人们     

Orbit of Comet C/1857 D1 (d'Arrest)

Comet C/ 1857 D1 (d'Arrest) is one of a large number of comets with parabolic orbits. Given that there are sufficient observations of the comet, 299 in right ascension and 279 in declination, it proves possible to calculate a better orbit. The calculations are based on a 12th order predictor‐corrector method. The comet's orbit is highly elliptical, e = 0.99982 and, from calculated mean errors, statistically different from a parabola. The comet will not return for at least 44000 years and thus represents no immediate NEO threat (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

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).     

Split Comet C/2001 A2 (LINEAR)

Comet C/2001 A2 experienced several splitting events duringits 2001 perihelion passage. The first break-upevent was observed in March 2001 (IAUC 7616).In this paper we report the first results of ourextensive imaging and spectroscopic monitoring campaignwith ESO telescopes over several weeks before andafter the perihelion passage on May 25 2001.     

Spectroscopic Monitoring of Comet C/1995 O1 (Hale-Bopp)

Earth, Moon, and Planets -     

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.     

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.     

Near-infrared observations of Comet C/2004 Q2 (Machholz)

Our observations of Comet C/2004 Q2 (Machholz) in the range from 1.2 to 4.8 µm indicate that the material outflowed from the cometary surface in the form of fragments that separated into gas and dust under sublimation on time scales of the order of days. The albedo of these fragments in the range under study was wavelength independent, while the dust was heated by the Sun to an equilibrium temperature at a cross section Qλ inversely proportional to the wavelength.     

Evolution of C/2006 M4 (SWAN) comet tails

We studied variations in the structure of plasma and dust tails of the C/2006 M4 (SWAN) comet during a long observation period (September–December 2006). We found sizes of grains ejected by the comet from the synchronic-syndynamic analysis of comet images. We calculated solar wind speed for high heliographic latitudes from calculations of the aberration angle of the comet plasma tail. Rapid changes in the calculated values of the solar wind speed are caused by its variable transversal component.     

Very Small Dust Particles (VSDP's) in Comet C/1996 B2 (Hyakutake)

X-ray fluxes observed from comet C/1996 B2 (Hyakutake) are readily explained in terms of scattering by carbonaceous particles with radii of several tens of Angstroms. A few tenths of a megatonne of such particles appear to have been present in the cometary coma on March 26–28, 1996. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

Spectra Of Split Comet C/1999 S4 (Linear)

We obtained spectra of comet C/1999 S4 (LINEAR) with the UAGS spectrograph(long slit and CCD) installed on the 1-m Zeiss reflector of the SAO of the RAS(Northern Caucuses, Nizhny Arkhyz) on July 23/24, 26/27 and 27/28, 2000. OnJuly 22/23, before the splitting of the cometary nucleus, several emission lines,such as C₂, C₃, CN, NH, CH, NH₂, CO⁺, H₂O⁺ wereclearly identified in the spectra. The inspections of the CCD spectra obtainedon July 27/28, 2000 reveals only very weak emission lines superimposed on thesolar reflection spectrum. From analyzing the surface brightness profile of C₂ along the slit the velocity of separation of two secondary fragments (V = 10 km/h) and the energy of the fragment separation (E = 8.7 × 10¹⁵ erg) were estimated. A luminescence cometary continuum of 26% of the total continuum level is detected in the spectra of the comet at 5000 Å. Possible mechanisms of nucleus splitting are discussed.     

Very small dust particles (VSDP's) in comet C/1996 B2 (Hyakutake)

X-ray fluxes observed from comet C/1996 B2 (Hyakutake) are readily explained in terms of scattering by carbonaceous particles with radii of several tens of Angstroms. A few tenths of a megatonne of such particles appear to have been present in the cometary coma on March 26–28 1996.     

Non-constant rotation period of Comet C/2001 K5 (LINEAR)

The article presents results of CCD photometry in R-band of a dynamically new Comet C/2001 K5 (LINEAR), obtained at a heliocentric distance of about 5.6 AU, after the perihelion passage. Being so distant from the Sun, this comet was extremely active (Afρ close to 2000 cm), exhibiting quite well developed dust coma and tail. During the observations, general photometric behavior of the comet with heliocentric distance r was well described by the 2.5nlog(r) function with coefficient n=5. The radial profiles of the coma were found to be undulated, with mean slope of the dependence between cometary magnitude and 2.5log of aperture radius (at comet distance) equal to . The light curve of Comet LINEAR exhibited short-term variability which we attributed to cyclic changes of dust emission, induced by nucleus rotation. Model computations by some authors have revealed that active comets can change their spin status quite substantially even during a single orbital revolution. Thus, attempting to search for a rotation frequency, we have modified the classical PDM approach by including the spin acceleration term. Such DynamicalPDM (DPDM) method revealed the most reliable solution for the frequency f₀=0.019048±0.000013 h⁻¹ and its first time-derivative (index “zero” denotes reference to the mid time of the whole observing run), indicating a rapid spin-down of the nucleus. These parameters are equivalent to the rotation period of 52.499±0.036 h and its relative increment of 0.02729±0.00013. We present the most probable evolution of the rotation frequency of Comet LINEAR, based on the results of periodicity analysis and a simple, almost parameter independent, dynamical model of nucleus rotation. It is also shown that the DPDM may be an effective tool for determination of a nucleus radius, which provided us with the value of 1.53±0.25 km for Comet LINEAR.