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1.
The coma morphology and short-term evolution was investigated of three non-periodic comets in retrograde orbits, C/2001 Q4 (NEAT), C/2002 T7 (LINEAR), and C/2003 K4 (LINEAR). All three comets display distinct coma features, which were very different from one comet to the next and remained rather constant in shape during the observational period. A single, broad feature perpendicular to the sun-tail direction dominated the coma of C/2003 K4 in all used filters (B,V,R,I), whereas the coma of Comet C/2002 T7 exhibited different features in blue and red filters. C/2001 Q4 showed rather complex coma morphology with clear short-term variability in coma brightness. Therefore, these non-periodic comets neither show a featureless coma nor any similarities of the features detected. The overall distribution of coma material was investigated from the shape of radial coma profiles averaged around the comet nucleus. For C/2001 Q4 and C/2002 T7, the slopes fitted to the linear part of these profiles are flatter in the blue than in the red, which can be explained by the presence of coma gas. For C/2003 K4 no such difference is indicated in the May observations (r = 2.3 AU), while in July (r = 1.7 AU) the profiles in the B-filter are flatter than in V, R, and I, hence gas contamination was relevant at least in the B filter. The R and I filter images were used to determine approximate Afρ values of each comet as a function of time.  相似文献   

2.
We present preliminary results of observations of the spectrum of comet C/2001 A2(LINEAR) obtained with the Multipupil Fiber Spectrograph, installed in the PrimeFocus of the 6-m Telescope of the SAO of the RAS (Northern Caucasus, NizhnyArkhyz), on August 11/12, 12/13 and 14/15, 2001. High resolution spectra of thecomet were obtained in the range from 3800–5200 AA. The emission lines in the spectrum of comet C/2001 A2 (LINEAR) on Aug. 12, 2001 were identified. Thefluorescent continuum in the spectrum of comet C/2001 A2 (LINEAR) on Aug. 12,2001 is detected.  相似文献   

3.
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.  相似文献   

4.
The evolution of the morphology of C/1999 S4 (LINEAR) is examined from aseries of images taken from shortly before the disruption of the nucleus until10 days afterwards. This is combined with light curve data to provide a uniquedocumentation of the early evolution of the disruption event. Neither imagesfrom the 1-m Jacobus Kapteyn Telescope nor the 2.5-m Isaac Newton Telescopeat the Roque de los Muchachos Observatory (La Palma, Canary Islands, Spain)show no evidence of bright sub-nuclei, although the presence of a well-definedstable lance-point structure in the head of the comet indicates that a dust and gasproducing source remained active in this region. The centre of brightness of thecoma moved in the anti-solar direction at a few tens of metres per second afterdisruption indicating that it was a mainly dust structure. The contrast in thefragmentation history of comets such as C/1999 S4, C/2001 A2 and 141P/Machholz2 suggests that there is a wide variation in nucleus properties from highly unstableand loosely bound rubble piles to relatively consolidated conglomerates.  相似文献   

5.
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).  相似文献   

6.
The majority of new ground-based discoveries of comets comes from large surveys devoted, predominantly, to Near Earth Asteroids. The first step in distinguishing these newly discovered members of the population of cometary bodies consists inconfirmatory astrometric observations along with detection of their cometaryfeatures. Although both amateur and professional stations take part in suchconfirmatory observations, only some of them do a preliminary analysis of thecometary activity of a particular newly discovered body. A timely recognitionof cometary features of a particular body having an unusual orbit can help inplanning further observing campaigns.A main goals of the Klet Observatory NEO astrometric follow-upprogramme consists of an analysis of possible cometary activity of newlydiscovered unusual bodies. Here, we describe several examples (comets C/1999 S4 (LINEAR) and so on). We also mention an extension of our programme to fainterobjects after the completion ofa new 1-m telescope at the Klet Observatory.  相似文献   

7.
I. Toth  C.M. Lisse 《Icarus》2006,181(1):162-177
Here we estimate the regions of stability, fragmentation, and destruction for cometary bodies versus rotational breakup in the radius-rotational period plane. By testing different plausible physical models of the cometary nucleus equation of state, we show that the plane is divided into 3 segments: the allowed, damaged, and forbidden regions. We then compare the location of well-observed comets with respect to the separation lines. The range of constituent material parameters from the literature for cometary nuclei are used to show that all the observed comets lie in the allowed region, except for Comet C/1995 O1 (Hale-Bopp), which resides in the damaged region (where the body is fractured and only held together gravitationally). We speculate that the extremely high activity demonstrated by Comet Hale-Bopp during the 1997 apparition may have been due to its highly fractured state. Comet Hyakutake, observed to emit fragments at perigee in 1996, may be near the boundary of the damaged region. Comet C/1999 S4 (LINEAR) was solidly in the rotationally allowed region, making its disintegration in July 2000 due to centrifugal forces unlikely. In contrast to the comets, the centaurs do not cluster in the allowed region, with the majority falling instead into the rotationally damaged and forbidden regions. The centaurs are only stable against breakup assuming much stronger solid water ice properties, strongly suggesting that on the whole, these bodies have different bulk physical properties than cometary nuclei.  相似文献   

8.
Our polarimetric database contains six comets, C/1975 V1 (West), 16P/Brooks 2,C/1988 A1 (Liller), D/1996 Q1 (Tabur), C/1999 S4 (LINEAR), and C/2001 A2(LINEAR), which can be related to the group of split comets. Comets West, S4(LINEAR) and A2 (LINEAR) were observed during splitting. We compare thepolarimetric measurements of the dust particles in these comets, sometimes togetherwith available photometric and colorimetric data, with those in normal comets. Weconclude that there is no significant evidence for differences of polarization betweentidally split comets (e.g., Brooks 2), dissipating comets (e.g., Tabur), non-tidally splitcomets (e.g., West) and normal comets. The total disintegration of Comet S4 (LINEAR), however, did produce significant changes in the observed properties of dust.  相似文献   

9.
We report on the preliminary analysis of the high-resolution spectrum of CometC/2000 WM1 (LINEAR), obtained on Dec. 1, 2001 with the Fiber fed ExtendedRange Optical Spectrograph (FEROS) installed on the 1.52-m telescope of ESO(Chile). Many emission lines of the molecules C2, C3, CN, CH, CH+,NH2, CO, CO+, H2O+ and, presumably, C2 - were identifiedin the spectral range 400–900 nm. Also, near-infrared photometry was performed on Dec. 2 and 3, with the infraredcamera (CamIV) attached to the 0.60-m Boller and Chivens telescope of the Picodos Dias Observatory (LNA/MCT), Brazil. We report the preliminary and comparativeanalysis of the I-J and J-H color indices.  相似文献   

10.
Micha? Drahus  Wac?aw Waniak 《Icarus》2006,185(2):544-557
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.  相似文献   

11.
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.  相似文献   

12.
The ortho-to-para ratio (OPR) of a cometary molecule is one of primordial character in comets. The OPR which is characterized by a spin temperature, is thought to reflect the formation conditions of the molecule. In this paper we show the high-dispersion spectrum of cometary NH2 in Comet C/2001 A2 (LINEAR), from which the OPR of NH2 is determined based on the fluorescence excitation model. Since the NH2 is a photodissociation product of cometary ammonia, we applied the permutation group theory to the whole reaction system (i.e. the photodissociation reaction of ammonia to NH2 and H) in order to derive the OPR of ammonia from that of NH2. The derived OPR of ammonia is 1.12 ± 0.03 in Comet C/2001 A2 (LINEAR). This value corresponds to a spin temperature of 30+3 -2 K. If this reflects the temperature where the comet formed in the protosolar nebula, our result indicates that thiscomet was formed in the region of the giant planets between Jupiter and Neptune.  相似文献   

13.
We are conducting a ground-based observational study of distant cometary nuclei with the aim of increasing the current database of physical parameters of individual objects, and to estimate the overall distributions of size, rotation period, axial ratio, and color indices. Additionally, we are obtaining CCD spectroscopy and photometry of established and potential targets of current and future spacecraft missions. The results presented here are derived from CCD imaging obtained using the 2.3-m Bok telescope of Steward Observatory (Arizona), obtained in May 2001, and the 5-m Hale telescope at Palomar Observatory (California), obtained in May 2000 and March 2001. Comets observed include 4P/Faye, 6P/d'Arrest, 22P/Kopff, 36P/Whipple, 50P/Arend, 78P/Gehrels 2, 92P/Sanguin, 107P/Wilson-Harrington, and 128P/Shoemaker-Holt 1-A. Of the nine comets observed, only Comets 4P/Faye and 50P/Arend displayed visible coma activity. We have performed either single R filter or multi-filter (BVRI) measurements on these comets, from which we obtain radius and broadband color estimates as well as Afρ values for the active comets. For selected objects we have performed time-series R filter imaging from which we have derived the rotation period and lower limits on the nuclear axial ratio and density. The radius results obtained are included in the cometary nucleus size distribution estimate by Weissman and Lowry (2003).  相似文献   

14.
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.  相似文献   

15.
The Canada-France-Hawaii Telescope Legacy Survey, specifically the Very Wide segment of data, is used to search for possible main-belt comets. In the first data set, 952 separate objects with asteroidal orbits within the main-belt are examined using a three-level technique. First, the full-width-half-maximum of each object is compared to stars of similar magnitude, to look for evidence of a coma. Second, the brightness profiles of each object are compared with three stars of the same magnitude, which are nearby on the image to ensure any extended profile is not due to imaging variations. Finally, the star profiles are subtracted from the asteroid profile and the residuals are compared with the background using an unpaired T-test. No objects in this survey show evidence of cometary activity. The second survey includes 11438 objects in the main-belt, which are examined visually. One object, an unknown comet, is found to show cometary activity. Its motion is consistent with being a main-belt asteroid, but the observed arc is too short for a definitive orbit calculation. No other body in this survey shows evidence of cometary activity. Upper limits of the number of weakly and strongly active main-belt comets are derived to be 630±77 and 87±28, respectively. These limits are consistent with those expected from asteroid collisions. In addition, data extracted from the Canada-France-Hawaii Telescope image archive of main-belt Comet 176P/LINEAR is presented.  相似文献   

16.
We present the results of the blazar 3C 345 monitoring in Johnson‐Cousins BVRI bands for the period 1996–2006. We have collected 29 V and 43 R data points for this period; the BI light curves contain a few measurements only. The accuracy of our photometry is not better than 0.03 mag in the VR bands. The total amplitude of the variability obtained from our data is 2.06 mag in the V and 2.25 mag in the R band. 3C 345 showed periods of flaring activity during 1998/99 and 2001: a maximum of the blazar brightness was detected in 2001 February – 15.345 mag in the V and 14.944 mag in the R band. We confirm that during brighter stages 3C 345 becomes redder; for higher fluxes the colour index seems to be less dependent on the magnitude. The intra‐night monitoring of 3C 345 in three consecutive nights in 2001 August revealed no significant intra‐night variability; 3C 345 did not show evident flux changes over timescales of weeks around the period of the intra‐night monitoring. This result supports the existing facts that intra‐night variability is correlated with rapid flux changes rather than with specific flux levels. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

17.
Splitting events affect cometary nuclei to a different level of severity ranging from complete disruption of the nucleus (e.g., C/1999 S4 LINEAR) to separation of major fragments (e.g., 73P/Schwassmann-Wachmann 3) and spill-offs of smaller boulders (e.g., C/2001 A2 LINEAR).Fragmentation of comets produces secondary products over a wide range of sizes (from cometesimals to sub-micron dust). It is detectable through the presence of fragments (with own comae and tails) in the coma of the parent nucleus, through outbursts in its activity and through arc-lets (“coma wings”)associated with fragments. The secondaries have different life times and show different non-gravitational forces. Nucleus splitting is also considered to generate whole families of comets (Kreutz group) or — if gravitational bound — multiple nuclei (e.g., C/1995 O1 Hale-Bopp). It may explain the striae phenomena seen in dust tails of bright comets (C/1995 O1 Hale-Bopp) and the detection of chains of impact craters onother bodies in the solar system. As process of significant mass loss it is relevant for the scenario of nucleus extinction, at the same time it also plays a role for the number statistics of existing (observable) comets and for the size distribution of comet nuclei. Various model scenarios for nucleus splitting are proposed: tidal disruption, rotational splitting, break-up due to internal gas pressure, fragmentation due to collision with other bodies. Only in one case, Comet D/1993 F1Shoemaker-Levy 9, the physical process of fragmentation could be undoubtedly identified. In any case, comet splitting provides important insights inthe internal structure, surface layering and chemistry of comet nuclei.  相似文献   

18.
Though optimized to discover and track fast moving Near-Earth Objects (NEOs), the Near-Earth Asteroid Tracking (NEAT) survey dataset can be mined to obtain information on the comet population observed serendipitously during the asteroid survey. We have completed analysis of over 400 CCD images of comets obtained during the autonomous operations of two 1.2-m telescopes: the first on the summit of Haleakala on the Hawaiian island of Maui and the second on Palomar Mountain in southern California. Photometric calibrations of each frame were derived using background catalog stars and the near-nucleus comet photometry measured. We measured dust production and normalized magnitudes for the coma and nucleus in order to explore cometary activity and comet size-frequency distributions. Our data over an approximately two-year time frame (2001 August-2003 February) include 52 comets: 12 periodic, 19 numbered, and 21 non-periodic, obtained over a wide range of viewing geometries and helio/geocentric distances. Nuclear magnitudes were estimated for a subset of comets observed. We found that for low-activity comets (Afρ<100 cm) our model gave reasonable estimates for nuclear size and magnitude. The slope of the cumulative luminosity function of our sample of low-activity comets was 0.33 ± 0.04, consistent with the slope we measured for the Jupiter-family cometary nuclei collected by Fernández et al. [Fernández, J.A., Tancredi, G., Rickman, H., Licandro, J., 1999. Astron. Astrophys. 392, 327-340] of 0.38 ± 0.02. Our slopes of the cumulative size distribution α=1.50±0.08 agree well with the slopes measured by Whitman et al. [Whitman, K., Morbidelli, A., Jedicke, R., 2006. Icarus 183, 101-114], Meech et al. [Meech, K.J., Hainaut, O.R., Marsden, B.G., 2004. Icarus 170, 463-491], Lowry et al. [Lowry, S.C., Fitzsimmons, A., Collander-Brown, S., 2003. Astron. Astrophys. 397, 329-343], and Weissman and Lowry [Weissman, P.R., Lowry, S.C., 2003. Lunar Planet. Sci. 34. Abstract 34].  相似文献   

19.
We have launched the Cometary Archives for Amateur Astronomers, CARA, aiming at coordinated collection of homogeneous, long-time based, continuous data set of bright comet observations. The project is based on a collaboration between professional and amateur astronomers. The archived quantity is a set of the photometric Afρ, measured in I, R or red continuum 647/10 nm filters. To derive coma profiles, Afρ is measured in at least different radii selected from a set of 50,000, 25,000, 12,500, 6,000 and 3,000 km. The data are free to download for registered users, special requests are available upon personal contact. We also provide aspecific code with a tutorial for the aperture photrometry of comets. The purpose of this paper is to introduce the observing methods, tools, software supports and web resources of project CARA.  相似文献   

20.
In the Kepler/K2 data analysis performed to date, aperture photometry has generally been used, but this method has not given any reasonable results when examining nearby sources due to the insufficient number of pixels on Kepler's CCD camera. The point-spread function (PSF) technique prepared by Libralato et al. (2016a), which presents promising results in undersampled pixels even in crowded star groups, was used in this study. Open cluster stars M 35 and NGC 2158 in the K2 Campaign 0 were selected as the target field. By applying the PSF method to the high angular resolution input catalogue prepared using the Asiago Schmidt telescope, M 35 and NGC 2158 provided the opportunity to examine the light curves of faint stars (Kp > 15.5) in crowded regions and gave better results compared to aperture photometry. In this study, I detrended ~50 000 raw light curves from systematic effects and spacecraft motion effects. I ultimately found two candidate host stars that could have possible planetary transits.  相似文献   

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