Ground-based optical observations of
D
1
and
D
2
line emissions from Jupiter’s sodium nebula, which extend over several hundreds of jovian radii, were carried out at Mt. Haleakala, Maui, Hawaii using ...a wide field filter imager from May 19 to June 21, 2007. During this observation, the east–west asymmetry of the nebula with respect to the Io’s orbital motion was clearly identified. Particularly, the
D
1
+
D
2
brightness on the western side of Jupiter is strongly controlled by the Io phase angle. The following scenario was developed to explain this phenomenon as follows: First, more ionospheric ions like
NaX
+
, which are thought to produce fast neutral sodium atoms due to a dissociative recombination process, are expected to exist in Io’s dayside hemisphere rather than in the nightside one. Second, it is expected that more
NaX
+
ionospheric ions are picked up by the jovian co-rotating magnetic field when Io’s leading hemisphere is illuminated by the Sun. Third, the sodium atom ejection rate varies with respect to Io’s orbital position as a result of the first two points. Model simulations were performed using this scenario. The model results were consistent with the observation results, suggesting that Io’s ionosphere is expected to be controlled by solar radiation just like Earth.
We resolved the vertical emissivity profiles of H sub(3) super(+) overtone, H sub(3) super(+) hot overtone, and H sub(2) emission lines of the Jovian northern auroras in K band obtained in December ...2011 observed by the IR Camera and Spectrograph of the Subaru 8.2m telescope with the adaptive optics system (AO188). The spatial resolution achieved was ~0.2arcsec, corresponding to ~600km at Jupiter. We derived the vertical emissivity profiles at three polar regions close to the Jovian limb. The H sub(3) super(+) overtone and H sub(3) super(+) hot overtone lines had similar peak altitudes of 700-900km and 680-950km above the 1bar level, which were 100-300km and 150-420km lower, respectively, than the model values. On the contrary, the H sub(2) peak emission altitude was high, 590-720km above the 1bar level. It was consistent with the value expected for precipitation of ~1keV electron, which favors a higher-altitude emissivity profile. We concluded that the lower peak altitudes of H sub(3) super(+) overtone and hot overtone lines were caused by the nonlocal thermodynamic equilibrium effect stronger than the model assumption. We could reproduce the observational emissivity profiles from the model by including this effect. It has been proposed that neutral H sub(2) and ionized H sub(3) super(+) emissions can have different source altitudes because of their different morphologies and velocities; however, our observed results with a general circulation model show that the peak emission altitudes of H sub(3) super(+) and H sub(2) can be similar even with different velocities. Key Points * Vertical emissivity profiles of Jovian IR aurora were resolved in K band * H sub(3) super(+) overtone and hot overtone lines had lower peak altitudes than the model * This lower peak was caused by the non-LTE effect stronger than the model
We analyse the light curve in the R band of the blazar OJ287, gathered during the 2015/2016 observing season. We did a search for quasi-periodic oscillations (QPOs) using several methods over a wide ...range of timescales. No statistically significant periods were found in the high-frequency domain both in the ground-based data and in Kepler observations. In the longer-period domain, the Lomb-Scargle periodogram revealed several peaks above the 99% significance level. The longest one-about 95 days-corresponds to the innermost stable circular orbit (ISCO) period of the more massive black hole. The 43-day period could be an alias, or it can be attributed to accretion in the form of a two-armed spiral wave.
Aims. We aim to investigate how polarimetric observations can improve our understanding of the nature and diversity of M/X-type asteroids. Methods. Polarimetric observations of the selected M/X-type ...asteroids were carried out at the Tohoku 0.6-m telescope at Haleakala Observatory, Hawaii (simultaneously in BVR filters), the 2-m telescope of the Bulgarian National Astronomical Observatory in Rozhen (in R filter), and the 2.15-m telescope of the Complejo Astronómico El Leoncito (CASLEO), Argentina (in V filter). We analysed the polarimetric characteristics of M/X-type asteroids along with the available data obtained by other techniques. Results. New polarimetric observations of 22 M/X-type asteroids combined with published observations provide a data set of 41 asteroids for which the depth of a negative polarisation branch and/or inversion angle were determined. We found that the depth of the negative polarisation branch tends to increase with decreasing steepness of the near-infrared spectra. Asteroids with a deeper negative polarisation branch tend to have a higher radar circular polarisation ratio. We show that, based on the relationship of the depth of the negative polarisation branch and inversion angle, two main sub-types can be distinguished among M-type asteroids. We suggest that these groups may be related to different surface compositions similar to (1) irons and stony-irons and (2) enstatite and iron-rich carbonaceous chondrites.
Since the Voyager mission flybys in 1979, we have known the moon Io to be extremely volcanically active as well as to be the main source of plasma in the vast magnetosphere of Jupiter. Material lost ...from Io forms neutral clouds, the Io plasma torus and ultimately the extended plasma sheet. This material is supplied from the upper atmosphere and atmospheric loss is likely driven by plasma-interaction effects with possible contributions from thermal escape and photochemistry-driven escape. Direct volcanic escape is negligible. The supply of material to maintain the plasma torus was estimated from various methods at roughly one ton per second. Most of the time the magnetospheric plasma environment of Io is stable on timescales from days to months. Similarly, Io's atmosphere was found to have a stable average density on the dayside, although it exhibits lateral, diurnal and seasonal variations. There is a potential positive feedback in the Io torus supply: collisions of torus plasma with atmospheric neutrals likely are a significant loss process, which increases with torus density. The stability of the torus environment might be maintained by limiting mechanisms of either torus supply from Io or the loss from the torus by centrifugal interchange in the middle magnetosphere. Various observations suggest that occasionally the plasma torus undergoes major transient changes over a period of several weeks, apparently overcoming possible stabilizing mechanisms. Such events (and more frequent minor changes) are commonly explained by some kind of change in volcanic activity that triggers a chain of reactions which modify the plasma torus state via a net increase in supply of new mass. However, it remains unknown what kind of volcanic event can trigger torus events, whether Io's atmosphere undergoes a change before or during such magnetospheric events, and what processes could enable such a change.
We report observations of a stellar occultation by Pluto on 2019 July 17. A single-chord high-speed (time resolution \(= 2\,\)s) photometry dataset was obtained with a CMOS camera mounted on the ...Tohoku University 60 cm telescope (Haleakala, Hawaii). The occultation light curve is satisfactorily fitted to an existing Pluto's atmospheric model. We find the lowest pressure value at a reference radius of \(r = 1215~{\rm km}\) among those reported after 2012, indicating a possible rapid (approximately \(21^{+4}_{-5} \%\) of the previous value) pressure drop between 2016 (the latest reported estimate) and 2019. However, this drop is detected at a \(2.4\sigma\) level only and still requires confirmation from future observations. If real, this trend is opposite to the monotonic increase of Pluto's atmospheric pressure reported by previous studies. The observed decrease trend is possibly caused by ongoing \({\rm N_2}\) condensation processes in the Sputnik Planitia glacier associated with an orbitally driven decline of solar insolation, as predicted by previous theoretical models. However, the observed amplitude of the pressure decrease is larger than the model predictions.
The two rings of (50000) Quaoar Pereira, C L; Sicardy, B; Morgado, B E ...
arXiv (Cornell University),
04/2023
Paper, Journal Article
Odprti dostop
Quaoar is a classical Trans-Neptunian Object (TNO) with an area equivalent diameter of 1,100 km and an orbital semi-major axis of 43.3 astronomical units. Based on stellar occultations observed ...between 2018 and 2021, an inhomogeneous ring (Q1R, Quaoar's first ring) was detected around this body. Aims. A new stellar occultation by Quaoar was observed on August 9th, 2022 aiming to improve Quaoar's shape models and the physical parameters of Q1R while searching for additional material around the body. Methods. The occultation provided nine effective chords across Quaoar, pinning down its size, shape, and astrometric position. Large facilities, such as Gemini North and the Canada-France-Hawaii Telescope (CFHT), were used to obtain high acquisition rates and signal-to-noise ratios. The light curves were also used to characterize the Q1R ring (radial profiles and orbital elements). Results. Quaoar's elliptical fit to the occultation chords yields the limb with an apparent semi-major axis of \(579.5\pm4.0\) km, apparent oblateness of \(0.12\pm0.01\), and area-equivalent radius of \(543\pm2\) km. Quaoar's limb orientation is consistent with Q1R and Weywot orbiting in Quaoar's equatorial plane. The orbital radius of Q1R is refined to a value of \(4,057\pm6\) km. The radial opacity profile of the more opaque ring profile follows a Lorentzian shape that extends over 60 km, with a full width at half maximum (FWHM) of \(\sim5\) km and a peak normal optical depth of 0.4. Besides the secondary events related to the already reported rings, new secondary events detected during the August 2022 occultation in three different data sets are consistent with another ring around Quaoar with a radius of \(2,520\pm20\) km, assuming the ring is circular and co-planar with Q1R. This new ring has a typical width of 10 km and a normal optical depth of \(\sim\)0.004. Like Q1R, it also lies outside Quaoar's classical Roche limit.
We investigate the linear polarization produced by interstellar dust aligned by the magnetic field in the solar neighborhood (d< 50 pc). We also look for intrinsic effects from circumstellar ...processes, specifically in terms of polarization variability and wavelength dependence. We aim to detect and map dust clouds which give rise to statistically significant amounts of polarization of the starlight passing through the cloud, and to determine the interstellar magnetic field direction from the position angle of the observed polarization. High-precision broad-band (BVR) polarization observations are made of 361 stars in spectral classes F to G, in the magnitude range 4-9, with detection sensitivity at the level of or better than 10E-5 (0.001 %). Statistically significant (>3 sigma) polarization is found in 115 stars, and > 2 sigma detection in 178 stars, out of the total sample of 361 stars. Polarization maps based on these data show filament-like patterns of polarization position angles which are related to both the heliosphere geometry, the kinematics of nearby clouds, and the Interstellar Boundary EXplorer (IBEX) ribbon magnetic field. From long-term multiple observations, a number (18) of stars show evidence of intrinsic variability at the 10E-5 level. This can be attributed to circumstellar effects (e.g., debris disks and chromospheric activity). The star HD 101805 shows a peculiar wavelength dependence, indicating size distribution of scattering particles different from that of a typical interstellar medium.
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