Photometry and polarimetry of comet 46P/Wirtanen in the 2018 apparition

2021 ◽  
Author(s):  
Vera Rosenbush ◽  
Nikolai Kiselev ◽  
Marek Husárik ◽  
Oleksandra Ivanova ◽  
Igor Luk'yanyk ◽  
...  
Keyword(s):  
Rotation Axis ◽  
Digital Processing ◽  
Position Angle ◽  
Active Area ◽  
Degree Of Polarization ◽  
Great Decrease ◽  
Dust Production ◽  
The North ◽  
Spectral Bands ◽  
Phase Angles

Abstract Extensive photometric and polarimetric observations of comet 46P/Wirtanen within the framework of the international 4*P Coma Morphology Campaign were conducted from August 16, 2018 to February 13, 2019 using five telescopes. Digital processing applied to the direct images of the comet revealed the coma and tail, which varied in shape and size. The jet at the position angle 133.5° was found in the images obtained on December 7 and 9, 2018 in the V and R filters. From modelling the formation of the jet, we calculated the coordinates of the north pole of the nucleus rotation axis, α = 220° ± 10°, δ = –20° ± 8°, and the cometocentric latitude of the active area on the nucleus L = 20° ± 6°. The velocity of matter outflow from this active area was estimated to be 0.5 ± 0.05km/ s. The dust production Afρ changed from 12 to 88cm. During our observation period, the coma colour varied from 0.76m to 0.87m and from 0.38m to 0.50m and the reflectivity gradient from 11 to 16.2 per cent per 1000Å and 5.8 to 15.4 per cent per 1000Å for the B–V and V–R spectral bands, respectively. The comparison of the dust production rate of comet 46P/Wirtanen until 2018 and our data for 2018 apparition confirmed its great decrease. The degree of polarization of comet 46P was measured at the phase angles from 27° to 37°. In order to reliably retrieve the polarimetric class of comet 46P, observations at large phase angles are required.

scholarly journals Imaging the disc rim and a moving close-in companion candidate in the pre-transitional disc of V1247 Orionis

2018 ◽  
Vol 621 ◽  
pp. A7 ◽  
Author(s):  
Matthew Willson ◽  
Stefan Kraus ◽  
Jacques Kluska ◽  
John D. Monnier ◽  
Michel Cure ◽  
...  
Keyword(s):  
Dust Emission ◽  
Three Dimensional ◽  
Position Angle ◽  
Asymmetric Structures ◽  
North East ◽  
The North ◽  
Band Emission ◽  
Upper Limits ◽  
Multi Wavelength ◽  
Differential Imaging

Context. V1247 Orionis harbours a pre-transitional disc with a partially cleared gap. Earlier interferometric and polarimetric observations revealed strong asymmetries both in the gap region and in the outer disc. The presence of a companion was inferred to explain these asymmetric structures and the ongoing disc clearing. Aims. Using an extensive set of multi-wavelength and multi-epoch observations we aimed to identify the origin of the previously detected asymmetries. Methods. We have observed V1247 Ori at three epochs spanning ~678 days using sparse aperture masking interferometry with Keck/NIRC2 and VLT/NACO. In addition, we search for signs of accretion through VLT/SPHERE-ZIMPOL spectral differential imaging in Hα and R-band continuum. Our SMA sub-millimetre interferometry in 880 μm continuum and in the CO(3-2) line allows us to constrain the orientation and direction of rotation of the outer disc. Results. We find the L′-band emission to be dominated by static features which trace forward-scattered dust emission from the inner edge of the outer disc located to the north-east. In H- and K-bands, we see evidence for a companion candidate that moved systematically by 45° within the first ~345 days. The separation of the companion candidate is not well constrained, but the observed position angle change is consistent with Keplerian motion of a body located on a 6 au orbit. From the SMA CO moment map, the location of the disc rim, and the detected orbital motion, we deduced the three-dimensional orientation of the disc. We see no indication of accretion in Hα and set upper limits for an accreting companion. Conclusions. The measured contrast of the companion candidate in H and K is consistent with an actively accreting protoplanet. Hence, we identify V1247 Ori as a unique laboratory for studying companion–disc interactions and disc clearing.

Storm surges in the North Sea during the winter 1953-4

1956 ◽  
Vol 235 (1201) ◽  
pp. 260-274 ◽  
Keyword(s):  
Sea Level ◽  
North Sea ◽  
Storm Surges ◽  
Rate Of Change ◽  
The North ◽  
Order Of Magnitude ◽  
The North Sea ◽  
Sea Ports ◽  
Phase Angles

Records of sea level for several North Sea ports for the winter of 1953-4 have been in vestigated. They were split into 14-day intervals, and each 14-day record was Fourieranalyzed to determine if any non-astronomical periods were present. There was evidence of some activity between 40 and 50 h period, and a determination of the phase angles at different ports showed that the activity could be due to a disturbance travelling southwards from the north of the North Sea. The disturbance was partly reflected somewhere near the line from Lowestoft to Flushing, so that one part returned past Flushing and Esbjerg towards Bergen while the other part travelled towards Dover, and there was evidence of its existence on the sea-current records taken near St Margaret's Bay. These results were confirmed by subtracting the predicted astronomical tidal levels from the observed values of sea level and cross-correlating the residuals so obtained for each port with those found at Lowestoft. The residuals at Lowestoft and Aberdeen were compared with the meteorological conditions, and it was found that, although they could be attributed to a large extent to conditions within the North Sea, there was an additional effect due to a travelling surge which was of the same order of magnitude at both Lowestoft and Aberdeen and which was closely related to the rate of change with time of the atmospheric pressure difference between Wick and Bergen.

scholarly journals Brightness and Polarization of the Zodiacal Light: Results of Fixed-Position Observations from Skylab

1980 ◽  
Vol 90 ◽  
pp. 19-22
Author(s):  
J. L. Weinberg ◽  
R. C. Hahn
Keyword(s):  
Asteroid Belt ◽  
Degree Of Polarization ◽  
Zodiacal Light ◽  
Fixed Position ◽  
Vernal Equinox ◽  
The North ◽  
Celestial Pole ◽  
Total Light ◽  
North Galactic ◽  
Pioneer 10

In an earlier paper Sparrow et al. (1976) found the polarized brightness of zodiacal light to have solar color at five sky positions for which there were fixed-position observations from Skylab: north celestial pole, south ecliptic pole, vernal equinox, and two places near the north galactic pole. The brightness and degree of polarization of zodiacal light at these sky positions are derived using Pioneer 10 observations of background starlight from beyond the asteroid belt (Weinberg et al., 1974; Schuerman et al., 1976) and the assumption that the zodiacal light is also solar color in total light.

scholarly journals Symmetric Parsec-Scale Radio Jets in NGC 4261

1998 ◽  
Vol 164 ◽  
pp. 63-64
Author(s):  
Dayton L. Jones ◽  
Ann E. Wehrle
Keyword(s):  
Accretion Disk ◽  
Rotation Axis ◽  
Position Angle ◽  
Narrow Gap ◽  
Apparent Rotation ◽  
Radio Jets

AbstractVLBA observations of NGC 4261 (3C 270) reveal highly symmetric radio structures at both 1.6 and 8.4 GHz. There is little evidence for free-free absorption in the inner few pc, despite the fact that HST imaging shows this galaxy to contain a nearly edge-on disk of gas and dust in its nucleus. However, at our highest resolution we find a narrow gap in emission just east of the radio core which we interpret as evidence for a small (sub-parsec) nearly edge-on accretion disk which is obscuring the base of the counterjet. The position angle of the pc-scale radio axis agrees with the position angle of the VLA-scale jets, which differs from the apparent rotation axis of the nuclear disk seen by HST.

scholarly journals Arctic East Siberia had a lower latitude in the Pleistocene

2007 ◽  
Vol 79 (2) ◽  
pp. 183-193
Author(s):  
Willy Woelfli ◽  
Walter Baltensperger
Keyword(s):  
Solar Radiation ◽  
Rotation Axis ◽  
Equilibrium Shape ◽  
The Arctic ◽  
Lower Latitude ◽  
Particle Collisions ◽  
East Siberia ◽  
The North ◽  
Massive Object ◽  
Arctic Sea

Remains of mammoths in Arctic East Siberia, where there is not sufficient sunlight over the year for the growth of the plants on which these animals feed, indicate that the latitude of this region was lower before the end of the Pleistocene than now. Reconstructing this geographic pole shift, we introduce a massive object, which moved in an extremely eccentric orbit and was hot from tidal work and solar radiation. Evaporation produced a disk-shaped cloud of ions around the Sun. This cloud partially shielded the solar radiation, producing the cold and warm periods characterizing the Pleistocene. The shielding depends on the inclination of Earth's orbit, which has a period of 100. 000 years. The cloud builds up to a point where inelastic particle collisions induce its collapse The resulting near-periodic time dependence resembles that of Dansgaard-Oeschger events. The Pleistocene ended when the massive object had a close encounter with the Earth, which suffered a one per mil extensional deformation. While the deformation relaxed to an equilibrium shape in one to several years, the globe turned relative to the rotation axis: The North Pole moved from Greenland to the Arctic Sea. The massive object split into fragments, which evaporated.

scholarly journals Spectropolarimetry and modeling of WR156

2014 ◽  
Vol 9 (S307) ◽  
pp. 387-388
Author(s):  
Olga Maryeva
Keyword(s):  
Numerical Modeling ◽  
Position Angle ◽  
Degree Of Polarization ◽  
Special Astrophysical Observatory ◽  
Medium Resolution ◽  
The Galaxy ◽  
First Time ◽  
Rayet Star

AbstractFor the first time spectropolarimetric observations of Wolf-Rayet star WR156 (WN8h) were conducted. Medium resolution spectropolarimetric data in the range of 3500-7200 ÅÅ were obtained at Russian 6-m telescope of Special Astrophysical Observatory (SAO RAS). These data show that the light from the star is significantly polarized, with the degree of polarization P=1.38±0.06%, and the position angle Θ=77.4°±1.2°. This polarization, most probably, has an interstellar origin, as its magnitude and orientation are similar to the ones of field stars. Also, we present results of numerical modeling of WR156 atmosphere performed using cmfgen code. According to it, WR156 is the richest hydrogen Wolf-Rayet star of WN8 type in the Galaxy.

A new look at Belgian aeromagnetic and gravity data through image-based display and integrated modelling techniques

1993 ◽  
Vol 130 (5) ◽  
pp. 583-591 ◽  
Author(s):  
B. C. Chacksfield ◽  
W. De Vos ◽  
L. D'Hooge ◽  
M. Dusar ◽  
M. K. Lee ◽  
...  
Keyword(s):  
Large Scale ◽  
Gravity Data ◽  
Bouguer Anomaly ◽  
Digital Processing ◽  
Integrated Modelling ◽  
Magnetic Data ◽  
Gravity Gradient ◽  
The North ◽  
Anomaly Map ◽  
Shaded Relief

AbstractDigital processing and image-based display techniques have been used to generate contour and shaded-relief maps of Belgian aeromagnetic data at a scale of 1:300000 for the whole of Belgium. These highlight the important anomalies and structural trends, particularly over the Brabant Massif. North and vertically illuminated shaded-relief plots, enhanced structural belts trending west–east to northwest–southeast in the Brabant Massif and west–east to southwest–northeast in the core of the Ardennes. The principal magnetic lineaments have been identified from the shaded-relief plots and tentatively correlated to basement structures. Most short lineaments are correlated with individual folds while the more extensive lineaments are correlated with large scale fault structures. Magnetic highs within the Brabant Massif are attributed to folded sediments of the Tubize Group. The magnetic basement in the east of Belgium is sinistrally displaced to the north by an inferred deep NNW–SSE crustal fracture. The Bouguer anomaly map of Belgium identifies the Ardennes as a negative area, and the Brabant Massif as a positive area, with the exception of a WNW–trending gravity low in its western part. The southern margin of the Brabant Massif is defined by a steep gravity gradient coincident with the Faille Bordiere (Border Fault). Trial modelling of the gravity and magnetic data, carried out along profiles across the Brabant and Stavelot massifs, has identified probable acid igneous intrusions in the western part of the Brabant Massif, and a deep magnetic lower density body underlying the whole Ardennes region, which is thought to be a distinctive Precambrian crustal block.

scholarly journals Tracking error analysis of primary mirror in Linear Fresnel heat collecting field

2021 ◽  
Vol 256 ◽  
pp. 01046
Author(s):  
Zhang ZhiYong ◽  
Kong LingGang ◽  
Fan DuoJin ◽  
Yao XiaoMing
Keyword(s):  
Rotation Axis ◽  
Structural Characteristics ◽  
Tracking Error ◽  
Shape Error ◽  
Tracking Accuracy ◽  
Temperature Drift ◽  
Angle Sensor ◽  
Primary Mirror ◽  
The North ◽  
Collecting System

Aiming at the tracking error of the primary mirror in the Linear Fresnel concentrated light and heat field, according to the structural characteristics of the Linear Fresnel concentrating and heat collecting system, the analysis model of the system concentrating error is established. By analyzing the mirror shape error of the Linear Fresnel system, the installation error of the secondary mirror (CPC), the errors of the north-south layout of the mirror field, the deviation of the primary mirror rotation axis and the deviation of the temperature drift of the angle sensor, and the factors were calculated by MATLAB simulation. The concentrating error factors affecting the Linear Fresnel concentrating and heat collecting system are analyzed quantitatively. From the simulation results: during the whole day, the influence of the north-south layout deviation of the mirror field and the deviation of the primary mirror rotation axis on the tracking accuracy is time-varying, and the influence is greater in the midday period. During the whole year, the influence factors of the north-south deviation of the mirror field and the temperature drift of the angle sensor on the tracking accuracy are incident, and the influence is greater in winter and less in summer. The installation error of CPC has a constant influence on the tracking accuracy.

scholarly journals Blue, white, and red ocean planets

2019 ◽  
Vol 626 ◽  
pp. A129 ◽  
Author(s):  
V. J. H. Trees ◽  
D. M. Stam
Keyword(s):  
Phase Angle ◽  
Surface Albedo ◽  
Color Change ◽  
Water Flux ◽  
Angular Distance ◽  
Total Flux ◽  
Degree Of Polarization ◽  
Reflected Light ◽  
Phase Functions ◽  
Phase Angles

Context. An exoplanet’s habitability will depend strongly on the presence of liquid water. Flux and/or polarization measurements of starlight that is reflected by exoplanets could help to identify exo-oceans. Aims. We investigate which broadband spectral features in flux and polarization phase functions of reflected starlight uniquely identify exo-oceans. Methods. With an adding-doubling algorithm, we computed total fluxes F and polarized fluxes Q of starlight that is reflected by cloud-free and (partly) cloudy exoplanets, for wavelengths from 350 to 865 nm. The ocean surface has waves composed of Fresnel reflecting wave facets and whitecaps, and scattering within the water body is included. Results. Total flux F, polarized flux Q, and degree of polarization P of ocean planets change color from blue, through white, to red at phase angles α ranging from ~134° to ~108° for F, and from ~123° to ~157° for Q, with cloud coverage fraction fc increasing from 0.0 (cloud-free) to 1.0 (completely cloudy) for F, and to 0.98 for Q. The color change in P only occurs for fc ranging from 0.03 to 0.98, with the color crossing angle α ranging from ~88° to ~161°. The total flux F of a cloudy, zero surface albedo planet can also change color, and for fc = 0.0, an ocean planet’s F will not change color for surface pressures ps ≿ 8 bars. Polarized flux Q of a zero surface albedo planet does not change color for any fc. Conclusions. The color change of P of starlight reflected by an exoplanet, from blue, through white, to red with increasing α above 88°, appears to identify a (partly) cloudy exo-ocean. The color change of polarized flux Q with increasing α above 123° appears to uniquely identify an exo-ocean, independent of surface pressure or cloud fraction. At the color changing phase angle, the angular distance between a star and its planet is much larger than at the phase angle where the glint appears in reflected light. The color change in polarization thus offers better prospects for detecting an exo-ocean.

scholarly journals NaCo polarimetric observations of Sz 91 transitional disc: a remarkable case of dust filtering

2019 ◽  
Vol 492 (2) ◽  
pp. 1531-1542 ◽  
Author(s):  
Karina Maucó ◽  
Johan Olofsson ◽  
Hector Canovas ◽  
Matthias R Schreiber ◽  
Valentin Christiaens ◽  
...  
Keyword(s):  
Polarized Light ◽  
Position Angle ◽  
Radiative Transfer Model ◽  
Transfer Model ◽  
Remarkable Case ◽  
The North ◽  
Near Ir ◽  
Hot Start ◽  
Low Mass ◽  
Rule Out

ABSTRACT We present polarized light observations of the transitional disc around Sz 91 acquired with VLT/NaCo at H (1.7μm) and Ks (2.2μm) bands. We resolve the disc and detect polarized emission up to ∼0.5 arcsec (∼80 au) along with a central cavity at both bands. We computed a radiative transfer model that accounts for the main characteristics of the polarized observations. We found that the emission is best explained by small, porous grains distributed in a disc with a ∼45 au cavity. Previous ALMA observations have revealed a large sub-mm cavity (∼83 au) and extended gas emission from the innermost (<16 au) regions up to almost 400 au from the star. Dynamical clearing by multiple low-mass planets arises as the most probable mechanism for the origin of Sz 91’s peculiar structure. Using new L′-band ADI observations, we can rule out companions more massive than Mp ≥ 8 MJup beyond 45 au assuming hot-start models. The disc is clearly asymmetric in polarized light along the minor axis, with the north side brighter than the south side. Differences in position angle between the disc observed at sub-mm wavelengths with ALMA and our NaCo observations were found. This suggests that the disc around Sz 91 could be highly structured. Higher signal-to-noise near-IR and sub-mm observations are needed to confirm the existence of such structures and to improve the current understanding of the origin of transitional discs.

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