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1.
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.  相似文献   

2.
This paper presents the results of polarization observations of asteroid 554 Peraga obtained with the UBVRI polarimeter using the 1.25 m telescope of the Crimean Astrophysical Observatory down to phase angles of 3.1°–16.6° from October to November 2006. The asteroid’s polarization phase curve is shown to have a negative branch with the parameters P min = −1.7% and αmin = 8.4°, which is typical of C-type asteroids. However, these data contradict the results of Zellner and Gradie (1976) obtained in March 1975 that the reflected light from the asteroid’s surface is positively polarized, ≈1% at phase angles of 8°–10°. Since the asteroid’s ecliptic longitudes differ by 160°-145° for the two observation periods, we discuss the possibility that the two sets of observations refer to the asteroid’s two hemispheres with different polarimetric properties.  相似文献   

3.

The results of the first polarimetric measurements of near-Earth asteroid 2014 JO25 and comet 41P/Tuttle-Giacobini-Kresák performed on April 19, 2017, with a CCD sensor at the prime focus (f/3.85) of the 2.6-m Shajn Telescope of the Crimean Astrophysical Observatory in the R filter are reported. The degree of linear polarization of the asteroid is P = 2.69 ± 0.44% at a phase angle of 55.6°, which is typical of an S-type asteroid. Its geometric albedo is ρv ≈ 0.2. A digital filter applied to the direct image of the comet reveals a jet and a tail directed toward the Sun (PA = 45.1°) and away from it (PA = 241.2°), respectively, in the coma. The maximum degree of linear polarization in the near-nucleus region of the comet is 18% at a phase angle of 69.8°. The polarization decreases to 16.2–10.7% in coma regions with a radius of 865–4856 km. Various factors affecting the maximum degree of polarization and the polarization-degree distribution over the coma are discussed.

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4.
Vanscheidt  R.  Bleul  H.  Manthey  E.  Jütte  M.  Pohlen  M.  Schmidtobreick  L.  Altmann  M.  Dieball  A.  Geffert  M.  Sanner  J.  Notni  P.  Schmoll  J. 《Earth, Moon, and Planets》1998,81(3):223-231
Extensive widefield CCD direct imaging of C/1995 O1 (Hale-Bopp) at UBVRI was carried out at Hoher List Observatory with the 1.06 m telescope (field of view 20′ × 20′) and at Potsdam Observatory with the 0.70 m telescope (field of view 8′ × 8′). The corresponding spatial resolution is 850–1000 km pix-1and 525–590 km pix-1, respectively. The data covers 25 nights from February 20 to April 21, 1997. In order to quantify the various features in the apparent inner coma we introduce a new tomographic method that minimizes the morphological bias caused by image processing. The tomographic analysis leads to quantitative maps refering to the position and intensity of the dust ejections for each image frame. Variability and periodicity within the inner coma can be thoroughly deduced due to various sets of consecutive nights in the observation period mentioned above. The results are compared with applications of adaptive Laplace filtering. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

5.
S. Ganesh 《Icarus》2009,201(2):666-673
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.  相似文献   

6.
Jorda  L.  Rembor  K.  Lecacheux  J.  Colom  P.  Colas  F.  Frappa  E.  Lara  L. M. 《Earth, Moon, and Planets》1997,77(3):167-180
We observed comet Hale-Bopp (C/1995 O1) at Pic du Midi Observatory in 1997 from February 2.24 UT to March 31.89 UT with the 1.05-m telescope equipped with a CCD camera and broad- and narrow-band IHW filters. A total of 30000 images were acquired both during night- and day-time. The images were automatically reduced and all the images obtained within 10 min. were co-added to give a set of ∼1000 images used during the analysis. We can identify two jets on the images. The position angle of the brightest jet from February 2.24 UT to March 5.22 UT is measured using an automatic routine which searches for the averaged position angle of the maximum of brightness at a projected distance of 3200–6100 km from the optocenter. A preliminary model of nucleus rotation is used to fit the data and retrieve the rotational parameters of the nucleus. The best fit is found for a source located at a latitude of 64 ± 3°, a sidereal rotation period of 11.35 ± 0.04 h and a right ascension and declination of the North pole of 275 ± 10° and -57 ± 10°. This preliminary analysis shows no evidence for a precession. Grains with velocities of 450–600 m s−1 and radii <;∼ 1 μm dominate the optical scattering cross section in the jets. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

7.
Near-infrared photometric and polarimetric observations of comet Hale-Bopp (1995 O1) using KONIC (Kiso Observatory Near-Infrared Camera) are reported. Observations were carried out on March 18 UT and April 26 UT 1997, when the heliocentric distances of the comet were 0.94 and 1.02 AU, and the phase angles were 48.5 deg and 32.9 deg, respectively. In the J, H, and K′ bands, we obtained linear polarization of the near-nucleus region of 16.4 ± 1.2, 18.8 ± 1.3, and 15.1 ± 0.9 percent on March 18UT and 7.1 ± 1.1, 8.9 ± 1.0, and 6.9 ± 0.6 percent on April 26, respectively. These values were higher than those observed for 1P/Halley. The maximum polarization was found at H band on both dates. Polarization maps showed higher polarization regions toward the anti-solar direction in the J and H bands. No distinct correlation was found between high polarization regions and bright regions. The projected expansion velocity of the arc structure of the dust jet was 375 ± 35.7 m/s on 17–19 March. The periodicity was found to be 11.1 ± 2.8 hours. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

8.
The BL Lac-type object 3C 66A was observed at the Crimean Astrophysical Observatory during the international project OJ-94. Observations were made over 10 nights from February through December 2003 at the Cassegrain focus of the 125-cm AZT-11 telescope with a photopolarimeter capable of simultaneous measurements in the UBVRI bands. In the course of our measurements the brightness of the object increased by more than 1 magnitude in all these bands. Its color indices varied and the degree of polarization decreased from ∼16% in February to ∼3% at the end of our observations. In December 2003 a rapid change in the position angle from 15° to 40° was noticed. The spectral energy distribution Fn is well described by a power law with a spectral index a (Fν ∝ ν −α . The increase in brightness was accompanied by a reduction in the spectral index. The most probable mechanism for the observed changes in the brightness, degree of polarization, and spectral index may be a decrease in the magnetic field strength or a change in its configuration owing to a increase in the chaotic component of the field. __________ Translated from Astrofizika, Vol. 49, No. 1, pp. 41–59 (February 2006).  相似文献   

9.
The Kuiper-Belt Object (29981) 1999 TD10, classified as a Scattered-Disk Object, has been observed at three different phase angles with the ESO 8.2-m VLT and FORS 1 instrument in polarimetric mode in November and December 2003. These observations have been used to compute the Stokes parameter q, which represents the linear polarization degree. We have also used the previously published photometric observations to improve the R-band phase function. The main conclusions are as follows: (i) a negative linear polarization degree decreasing with phase angle α up to, at least, α=3°, (ii) for α=3°, (iii) a possible color effect between the R and V band, the polarization degree being more negative in R. The R-band polarimetric observations can be explained by the coherent-backscattering mechanism and fitted by a two-component Rayleigh-scatterer model for a spherical small body. The rotation period of 15.382±0.001 h published by Mueller et al. (2004, Icarus 171, 506–515) and Choi et al. (2003, Icarus 165, 101–111) is confirmed. The R-band phase curve provides H=8.35±0.02 and G=−0.25±0.022 parameters with the IAU H–G formalism.Based on observations obtained at the Cerro Paranal observatory of the European Southern Observatory (ESO) in Chile.  相似文献   

10.
On March 31 and April 1, 1997, simultaneous photometry and polarimetry of comet Hale-Bopp's dust was conducted with the two-channel focal reducer of the Max-Planck-Institute for Aeronomy attached to the 2 m telescope of Pik Terskol Observatory (Northern Caucasus). Interference filters at642 nm and 443 nm selected red and blue narrow-band continuum windows. The observations have been averaged over the one hour of timethe comet could be observed. The polarization maps cover an area of about1 arcmin2 around the nucleus. The values of polarization degree measured close to the nucleus agree very well with observations obtained with aperture polarimetry. They are lower than in the surrounding coma by about 1%. In our field of view the polarization increases along the sun-comet line from the solar to the antisolar side by about 3%. The dust shells are visible in the polarization images. The polarization in the shells is higher by 1 to 2%and this increase is higher in the red than in the blue range. Therefore the ratio of red to blue polarization (≈ 1.2) increases in the shells by ≈ 0.03. In principle, the polarization excess in the shells, the ratio of red/blue polarization and the higher integrated polarization as compared to other comets can be explained by an excess of particles of radius of about 0.1 μm. Such particles, however, are subject to strong radiation pressure and will be pushed back into the tail before they reach the observed location of the shells. Real Rayleigh particles cannot explain the observed increase in the ratio of red/blue polarization. One therefore cannot exclude the possibility that the excess polarization in the shells is caused by fluffy aggregates via effects which are presently not well understood. The colour map shows features not well related to intensity and polarization, perhaps another dust shell of a different particle size. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

11.
We propose a modification of the method of polarimetric measurements of the twilight sky, traditionally performed in a zenith direction, to study physical properties of the stratospheric aerosol (at altitudes higher than 30 km). The measurements carried out in zenith directions as a rule limit phase angles by values of 80–100°. We suggest setting up the declination of the telescope equal to the declination of the sun and measuring the polarization degree of the twilight sky at different values of the right ascension. It will allow us not only to enhance the range of the phase angles but also to plan observations in a way to obtain data on the phase dependence of the polarization degree of the light scattered by atmospheric layers at different altitudes.  相似文献   

12.
During the recent apparition of comet Hale—Bopp (1995 O1) near infrared photometric observations were carried out in the J, H, K filter bands and also in the 3.0—3.4 μm region at the 1.2 m telescope at Gurushikkar, India. The effective temperature of the comet was substantially higher than the equilibrium blackbody temperature. A mean superheat value of 1.83 was derived in the post-perihelion phase which implies that a large fraction of the grain population are made up of small and hot grains with radii <0.5 μm. High albedo values of ∼0.4 were also derived in the scattering angle range 135° to 160° which could explain the unusual brightness of comet Hale—Bopp. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

13.
We have observed the coma of Comet 9P/Tempel 1, the target of the Deep Impact mission, by the polarization imaging technique, before and after the impact event (−32, −7, +43 and +65 h). Our observations were conducted in the red wavelength domain from Haute-Provence Observatory (France), with the 80-cm telescope. The overall polarization of 9P/Tempel 1, as obtained near 41° phase angle, is monitored and compared to data from other (active and less active) comets studied by the same technique. The linear polarization of the dust ejected by the impact is compared to previous observations of dust present in jets, ejected during outbursts or released when comets happen to split. At phase angles of about 41°, the difference in polarization between the comets with a low maximum in polarization and the comets with a high maximum in polarization is about 1%; it may thus be difficult to conclude about the classification. Nevertheless, the overall polarization after the impact rapidly reached a value corresponding to the high polarization class of comets, and later progressively decreased to its initial value. The polarization was measured to be slightly lower (about 1%) before the impact than after it in a 26,000-km aperture. The plume formed from dust ejected by the impact was still present 65 h after it. The variations of the intensity and the polarization in the coma provide some clues to variations of the physical properties of the particles; comparison with other techniques corroborates the presence of large particles and of submicron-sized grains in aggregates.  相似文献   

14.
A new millimeter-wave facility is in operation at the Bordeaux Observatory for spectroscopic observations of interstellar and stratospheric molecules. A cooled receiver has been installed on a 2·5m radio telescope. The overall system temperature is in the range 400 to 600 K (single side band) in the operating frequency range 75 to 115 GHz. The relatively broad beam of the telescope (∼ 5 arcmin) combined with a sensitive receiver will permit studies of extended molecular cloud complexes.  相似文献   

15.
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 αmin = 10.6°, the inversion angle αinv = 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.  相似文献   

16.
The next list of spectral data on blue stellar objects (BSOs) is presented. 58 FBS objects in a zone with a central declination δ = + 35° were observed with the 2.6-m telescope at the Byurakan Observatory during 1990–1991. In addition, 3 objects were observed (3 CCD spectra were obtained) with the BAO 2.6-m and OHP 1.93-m telescopes in 1997–2000 using modern instrumentation. 9 white dwarfs, 47 hot subdwarfs, and 2 HBB stars have been discovered. Spectra of the 10 most interesting objects are given. __________ Translated from Astrofizika, Vol. 51, No. 2, pp. 277–283 (May 2008).  相似文献   

17.
From the ground-based colorimetry performed for two surface regions of the near side of the Moon, images of the phase ratio of the color index C(600 nm/470 nm) have been built for the phase angles between 2° and 95°. It has been found that for phase angles smaller than α ∼ 40°–50°, the color index of the highlands grows with the phase quicker than that of the mare regions. For larger phase angles, α > 50°, a reverse situation is observed. The laboratory data on the spectrophotometry of the lunar samples confirm the peculiarities found in the phase dependence of color. The influence of multiple scattering on the phase dependence of the color of the mare and highland regions of the Moon are discussed.  相似文献   

18.
We report the results of position, photometric, and polarimetric observations of two near-Earth asteroids made with the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences. 1.2-hour measurements of the photometric variations of the asteroid 2009 DL46 made onMarch 8, 2016 (approximately 20m at a distance of about 0.23 AU from the Earth) showed a 0.m2-amplitude flash with a duration of about 20 minutes. During this time the polarization degree increased from the average level of 2–3% to 14%. The angle of the polarization plane and the phase angle were equal to 113° ± 1° and 43°, respectively. Our result indicates that the surface of the rotating asteroid (the rotation period of about 2.5 hours) must be non-uniformly rough. Observations of another asteroid—1994 UG—whose brightness was of about 17m and which was located at a geocentric distance of 0.077 AU, were carried out during the night of March 6/7, 2016 in two modes: photometric and spectropolarimetric. According to the results of photometric observations in Johnson’s B-, V-, and R-band filters, over one hour the brightness of the asteroid remained unchanged within the measurement errors (about 0.m02). Spectropolarimetric observations in the 420–800 nm wavelength interval showed the polarization degree to decrease from 8% in the blue part of the spectrum to 2% in the red part with the phase angle equal to 44?, which is typical for S-type near-Earth asteroids.  相似文献   

19.
We present an analysis of the results of photometric investigations of two distant comets, C/2002 VQ94 (LINEAR) and 29P/Schwassmann-Wachmann-1, obtained with the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences. The comets under study demonstrate sufficient activity out of the zone of water ice sublimation (at heliocentric distances longer than 5 AU). In the spectra of the investigated comets, we found the CO+ and N2+ emission. The presence of this emission may say that the comets were formed in the outer parts of the Solar System, in a protoplanetary cloud at a temperature ≤25 K. We found that the photometric maximum of the ionosphere (in the CO+ filter) of the comet C/2002 VQ94 (LINEAR) is shifted relative to the photometric center of the dust coma by 1.4″ (7.44 × 103 km) in the direction deflected by 63° from the direction to the Sun. Using special filters to process the images, we picked out active structures (jets) in the dust coma of the 29P/Schwassmann-Wachmann-1 comet.  相似文献   

20.
Photopolarimetric observations of comet Austin with the IAU/IHW filter system were obtained on the 2.34 m Vainu Bappu Telescope (VBT) of the Indian Institute of Astrophysics, at Kavalur, India, during pre-perihelion phase on February 20,1990 and on the 1.2 m telescope of the Physical Research Laboratory at Gurusikhar, Mount Abu during postperihelion phase on May 2 and 4, 1990. The comet appeared bluer than a solar analog during post-perihelion phase on May 2 and 4. The percent polarization shows a sharp increase towards the red on May 2 and 4. The dominant sizes of the dust particles appear to lie in a narrow range of 0.1 to 0.5 Μm. Regarding the molecular band emission, CN and C2 bands are quite strong; C3 emission was also found to be strong though the observations on May 2 and 4 show significant variation as compared to C2 emission. Molecular band polarization for CN, C3, C2 and H2 O+ have been calculated. It has been found that emission polarization in CN, C2 and C3 is between 1–7% (phase angle between 107.4–109 degrees). For CN and C2 the polarization values are close to the theoretically predicted values, but for C3 the polarization value falls much below the theoretically predicted value. A similar result was found for comet Halley.  相似文献   

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