Optical polarimetry of Comet NEAT C/2001 Q4

Comet NEAT C/2001 Q4 was observed for linear polarization using the optical polarimeter mounted at the 1.2 m telescope at Mt. Abu Observatory, during the months of May and June 2004. Observations were conducted through the International Halley Watch narrow band (continuum) and BVR broad band filters. During the observing run the phase angle ranged from 85.6° in May to 55° in June. As expected, polarization increases with wavelength in this phase angle range. Polarization colour in the narrow bands changes at different epochs, perhaps related to cometary activity or molecular emission contamination. The polarization was also measured in the cometary coma at different locations along a line, in the direction of the tail. As expected, we notice minor decrease in the polarization as photocenter (nucleus) is traversed while brightness decreases sharply away from it. Based on these polarization observations we infer that the Comet NEAT C/2001 Q4 has high polarization and a typical grain composition—mixture of silicates and organics.     

哈雷彗星的彗发光谱

用云南天文台一米望远镜卡焦摄谱仪(f=175mm相机),在哈雷彗星的日心距分别为1.11AU和0.83AU时,作了两次彗发光谱观测,得到了典型的彗发光谱。本文绘出了各带系清晰的分子发射光谱图及认证结果。此外,本文还给出了彗发CN的(0—1)带(λ4216)和C_3的蓝紫发射(λ4052)及C_2的(2—0)带(λ4365)的强度比CN/C_3和CN/C_2,其值分别为CN/C_3=1.03,CN/C_2=1.00。最后,我们还将结果与其他作者在这次回归中所得到的结果进行了比较。     

Absolute spectrophotometry of Comet Kohoutek 1973f: I. Column densities of cyanogen

Absolute spectrophotometry of the coma of Comet Kohoutek 1973f is discussed for the nights of January 24 and 26, 1974. Specific intensities are measured for spectral features and a continuum band in the wavelength region λλ3460–6062Å. The (0, 0) band of the Δν = 0 sequence of the violet system of the cyanogen molecule is analyzed and column densities of 1.7 × 10¹⁵m^?2 and 3.4 × 10¹⁴m^?2 are found for January 24 and 26, 1974, respectively. The analysis of the bands of C₂ will be reported in a second paper of this series.     

The rotational structure of the B-X system of sulfur dimers in the spectra of Comet Hyakutake (C/1996 B2)

We have constructed line-by-line fluorescence models for the ro-vibrational bands of the B-X system of sulfur dimers (S₂). For the first time the detailed rotational lines of the bands are clearly resolved in the high-resolution echelle spectra of Comet Hyakutake (C/1996 B2), which were obtained at the Kitt Peak 4-m telescope on 26.4 March 1996 (UT). In order to construct satisfactory band models of the B-X system, we first compared the models to laboratory spectra available in literature, and then compared the models including Swings effects to the high-resolution spectra of Hyakutake. From the model fits, we derived a rotational temperature of 70±10 K, which should represent a temperature of a coma region close to the nucleus, where most of the S₂ emissions originate. We present previously proposed scenarios for the origin of S₂ in cometary comae, and compare them with our spectral analysis.     

A deep radio survey in the ISO-ELAIS fields: optical identification with the APM catalogue/atl>

The optical identification programme is presented for a complete sample of 867 radio sources that were observed with the Very Large Array (VLA) within 4.22 deg² to S _{1.4 GHz} ≥ 0.135 mJy (5 σ). The area covered by the VLA survey is part of the regions of the sky that have been surveyed in the mid and far Infrared over the wavelength range 6.7–175 μmwith ISO as part of the European Large Area ISO Survey (ELAIS). Optical identifications are made using the Automatic Plate-measuring Machine (APM) optical catalogue in E (∼ R) and O (∼ B) bands with approximate limiting magnitudes of ∼ 20.0 and 21.5 mag, respectively. For 220 out of the 867 radio sources, likely identifications are proposed with an a posteriori identification percentage of 25%. The sample of identification has a reliability of 96% and a completeness of 80%. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

Rydberg Matter as the dust atmosphere in comets: Spectroscopic and polarization signatures

The long-lived excited state of matter called Rydberg Matter (RM) may explain several spectroscopic features in space, like the diffuse interstellar bands (DIBs) and the unidentified infrared bands (UIR, UIB). RM is here used to interpret some previously unexplained or inconsistent features in comets: (1) line absorption in the emission from the nucleus, (2) IR band emission from the coma, (3) selective and variable molecular line emission from the coma, (4) extended sources of molecules in the coma, (5) degree of linear polarization of light scattered from the coma. (1) The unexplained IR absorptions observed in the flyby of the nucleus of the Comet Borrelly agree well with RM emission bands observed by stimulated emission in the laboratory. It is proposed that RM is the so-called ultrared matter or at least formed from it. (2) The IR bands previously attributed to silicate particles are shown to be better described by RM theory. Transitions in atoms in RM are shown to dominate. (3) The inverted RM medium will optically amplify light from molecular transitions in the comet comae, in agreement with observations that many of the molecular IR emission lines lie within the emission bands from RM, or much too close to Rydberg transitions to be accidental. (4) The unexplained extended sources observed, e.g., for CO are proposed to be due to release of molecules previously incorporated in the RM clusters at low temperature. Such clusters may be the very small particles observed by space probes. (5) Finally, the largely unexplained measurements of the degree of linear polarization of scattered sunlight from comets are explained as due to scattering by the planar RM clusters. Quantitative agreement is demonstrated.     

The ultraviolet absorption band at 2175 Å: Correlations with other interstellar features

The hump in the ultraviolet part of the interstellar extinction curve is interpreted as a broad diffuse absorption band. Its equivalent width is estimated for 36 stars by means of OAO-2 data. The equivalent widths are correlated with the following parameters: colour excessE(B-V), colour excessE(B – V), depth of the band m _max, equivalent widths of the diffuse bands at 5780 and 6284 Å, and the column density of neutral hydrogenN _HI. The physical parameters half-width and oscillator strength of the band at 2175 Å are estimated.     

The cyanogen bands of Comet Bennett 1970 II

The CN band spectrum of Comet Bennett 1970 II was photographed on April 14, 1970. In addition to the (0,0) band, some other faint lines were observed, which arise either from the (1,1) band of the normal isotopic species or from the (0,0) band of ¹³CN. The Swings effect was investigated theoretically and found to give good agreement with observation. An estimate is made of the pure rotational transition rate in the ground state of CN.Absolute intensities of the CN lines were found by comparison with the lunar spectrum. From these measurements the distribution, density and total mass of cyanogen in the gaseous coma of the comet are estimated.     

Negative ions in the Enceladus plume

During Cassini’s Enceladus encounter on 12th March 2008, the Cassini Electron Spectrometer, part of the CAPS instrument, detected fluxes of negative ions in the plumes from Enceladus. It is thought that these ions include negatively charged water group cluster ions associated with the plume and forming part of the ‘plume ionosphere’. In this paper we present our observations, argue that these are negative ions, and present preliminary mass identifications. We also suggest mechanisms for production and loss of the ions as constrained by the observations. Due to their short lifetime, we suggest that the ions are produced in or near the water vapour plume, or from the extended source of ice grains in the plume. We suggest that Enceladus now joins the Earth, Comet Halley and Titan as locations in the Solar System where negative ions have been directly observed although the ions observed in each case have distinctly different characteristics.     

Global properties of star formation in spiral galaxies

Samples of spiral galaxies from two catalogues of 21 cm line observations and a catalogue of near-infrared observations of nearby galaxies have been used in conjunction with Infrared Astronomical Satellite data to study correlations involving M_G, the dynamic mass of the galaxies, the luminosities in theH band (1.6Μm), the blue band and the far infrared bands and the mass of atomic hydrogen, it is found that both the blue and the far-IR luminosities which are indicators of star formation averaged over ∼3 × l0⁹ and ∼10⁷ years respectively, have a linear dependence onM _G On the other hand, theH luminosity which is a measure of star formation averaged over the lifetime of galaxies, has a steeper power law dependence onM _G. The correlations observed do not have significant dependence on the morophological type of the galaxies There is a poor correlation between the far-infrared luminosity and the mass of atomic hydrogen. The mass of atomic hydrogen has a dependence of the formM _G. Because of the decrease in the mean mass for later morphological types and due to differences in power law dependences of luminosities in different bands onM _G, the mean value of luminosity-to-mass ratio is a constant for blue and far-IR bands, decreases for theH band and the gas-to-mass ratio increases as morphological type increases.     

Fast Variations of Spectra of Comet Halley

Results of the analysis of the Comet Halley spectrophotometry,which has been carried out by H.K. Nazarchuk in 1985 with the TVscanner of the 6-meter telescope (SAO, Russia) are presented. Timevariations in the intensities of the CN, CH, C₂ and NH₂bands were investigated using the series of spectra obtained inthe spectral region λλ=410÷ 510 nm. Theauto-correlation functions for all the bands, thecross-correlation functions for C₂ lines and their Fouriertransformations are calculated to determine the frequencies andperiods of the variations. A possibility is considered thathigh-amplitude fast variations of spectral lines in Comet Halleyare caused by solar flares. The daily numbers of solar spots andproton fluxes with energies of more then 1 MeV are compared withthe spectral variations of these lines. It is shown that in theobservation periods the comet was projected onto an active regionof the Sun, but, among all the kinds of solar activity, mainlythe solar proton flux with energies less than 4 MeV coincides intime with fast intensity variations in the spectral lines. Analgorithm of cross-correlation analysis of discrete samplingseries with gaps is built, and average cross-correlation coefficientsare calculated.     

Calibrating models of ultralow‐mass stars

Evolutionary and atmospheric models have become available for young ultralow‐mass objects. These models are being used to determine fundamental parameters from observational properties. TiO bands are used to determine effective temperatures in ultralow‐mass objects, and together with Na‐ and K‐lines to derive gravities at the substellar boundary. Unfortunately, model calibrations in (young) ultralow‐mass objects are rare. As a first step towards a calibration of synthetic spectral features, I show molecular bands of TiO, which is a main opacity source in late M‐dwarfs. The TiO ε ‐band at 8450 Å is systematically too weak. This implies that temperatures determined from that band are underestimated, and I discuss implications for determining fundamental parameters from high resolution spectra. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Emissions from the head of Comet Bradfield (1978c)

The flux distribution in the head of Comet Bradfield (1978c) during the pre-perihelion period has been obtained in the wavelength range 400–640 nm. The emission fluxes at 474 nm, 516 nm, 564 nm and 589 nm are reported. By use of the observed monochromatic brightness of the Swan band sequences, the number of C₂ molecules in the head of the comet are estimated.     

The organic composition of C/2001 A2 (LINEAR): II. Search for heterogeneity within a comet nucleus

The nucleus of Comet C/2001 A2 (LINEAR) split several times during its recent apparition, presenting an unusual opportunity to search for chemical differences in freshly exposed material. We conducted this search using NIRSPEC at the W.M. Keck Observatory on four dates in 2001: 9.5 and 10.5 July and 4.4 and 10.5 August. We detected the R0 and R1 lines of the ν₃ vibrational band of CH₄ near 3.3 μm on all dates. The R2 line was detected on 4.4 and 10.5 August. When we compare production rates of CH₄ to H₂O, we find evidence of a significant enhancement in August relative to that found in July. H₂CO was securely detected via its ν₁ and ν₅ bands on 9.5 July. On 10.5 July, H₂CO emission was much weaker, and its mixing ratio had dropped by a factor of about four. The mixing ratios for other detected volatile species did not change significantly over the course of the observations. We discuss the implications of this evidence for chemical heterogeneity in the nucleus of Comet C/2001 A2.     

Spectrophotometry of Comet Bradfield (1980t) during post-perihelion period

Spectrum scans of the head of Comet Bradfield (1980t) covering the wavelength range 365–640 nm were made on two nights when the heliocentric distance of the comet varied from 0.55 to 0.58 AU. The emission features of the CN band at 388 nm and Swan band sequence of C₂ at 474 nm, 516 nm, and 563 nm are identified and absolute fluxes in these bands as well as in the continuum are derived. The continuum energy distribution curves of the comet have been compared with those of the Sun and the star Crv (G5 III). An estimate of the number of C₂ and CN molecules in the head of the comet has been made through the measured intensities of their respective bands lying in this region.     

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.     

Emission band ratios in Comet Kohoutek (1973f)

Preliminary results of a spectrum scanner study of Comet Kohoutek (1973f) are reported. Ratios of band sequence fluxes and their variations with solar distance have been determined for three sequences of C₂, and two sequences of CN from observations obtained on eleven dates. The λ4050 feature of C₃ was visible on two dates, and CH (λ4300) detectable once.     

A Model of The 2–4 μm Spectrum of Comet Halley

Recent observations of Halley's Comet show a broad absorption band centred at 3.4 μm and which can be explained on the basis of a bacterial grain model. This revised version was published online in July 2006 with corrections to the Cover Date.