Evidence for a rapid decrease in Pluto's atmospheric pressure revealed by a stellar occultation in 2019

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.Comment: 7 pages, 3 figures, accepted for publication in Astronomy and Astrophysic

Auroral O+ 732/733 nm emission and its relation to ion upflow

Observations of auroral oxygen ion emission at 732/733 nm were made at the Aurora station in Longyearbyen (78.2.N, 16.3.E; lm=74.9.) using an all-sky spectrograph (ASG) during the winter season of 2000/2001. A statistical analysis showed that the highest occurrence of oxygen ion auroras at Longyearbyen was seen in the dayside of the 09-12MLT region; the intensities of these auroras were also larger than those on the night side. To study the mechanism of ion up゜ow in the polar ionosphere, ASG data obtained on December 7, 2000, was analyzed together with simultaneous ionospheric data obtained by EISCAT Svalbard radar (ESR). Enhancements of electron temperature and ion upward velocity were associated with an increase in the auroral OII intensity at the magnetic zenith. This result suggests that an ambipolar electric field associated with electron temperature enhancement caused by soft electron precipitation may be involved in the mechanisms that drive ionospheric ions upward

A new meridian imaging spectrogarph for the auroral spectroscopy

Spectroscopic and monochromatic imaging observations of emissions in the upper atmosphere are mutually complementary. A meridian imaging auroral spectrograph (ASG) that can measure a spectrum in the visible region along a meridian has been developed for research on the auroral physics and the polar upper-atmosphere dynamics. Combination of a fast optical system inherited from a monochromatic all-sky imager, a grism as a dispersive element, and a cooled CCD camera has enabled a wide field-of-view of 180° along a meridian, spectral coverage of 420-730 nm, spectral resolution of 1.5-2.0 nm, and high sensitivity to be obtained. The absolute sensitivity over a full-image field was calibrated using a National Institute of Standards and Technology (NIST) traceable integrating sphere and determined to be 0.06 cts/s/R at a wavelength of 560 nm at the zenith. The ASG was installed at Longyearbyen in March 2000, and routine operation was started in the 2000/2001 winter season. An example of an auroral spectral image is presented in this report to demonstrate the performance of the ASG

3-years Occurrence Variability of Concentric Gravity Waves in the Mesopause Observed by IMAP/VISI

第6回極域科学シンポジウム分野横断型セッション：[IM] 横断　中層大気・熱圏11月17日（火）　統計数理研究所 セミナー室2（D304

Southward propagating auroral structure in meso-micro scale obtained from ground-based multiple observations at Poker Flat Research Range

第3回極域科学シンポジウム/第36回極域宙空圏シンポジウム 11月26日（月）、27日（火） 国立極地研究所 2階ラウン

High-precision broadband linear polarimetry of early-type binaries IV. Binary system of DH Cephei in the open cluster of NGC 7380

DH~Cephei is a well known massive O+O-type binary system on the northern sky, residing in the young open cluster NGC~7380. Our high-precision multi-band polarimetry has clearly revealed that variations of linear polarizations in this system are synchronous with the phase of the orbital period. We have used the observed variations of Stokes parameters $q$ and $u$ to derive the orbital inclination $i$, orientation $\Omega$, and the direction of rotation. In order to determine the contribution from interstellar polarization, we have carried out new observations of polarization of field stars with precisely measured parallaxes. The variations of Stokes parameters in all three $B$, $V$, and $R$ passbands clearly exhibit an unambiguous periodic signal at 1.055 d with the amplitude of variations $\sim$$0.2\%$ which corresponds to half of known orbital period of 2.11 d. This type of polarization variability is expected for a binary system with light scattering material distributed symmetrically with respect to the orbital plane. Even though most of the observed polarization ($\sim$2$\%$) is of interstellar origin, about one third of it is due to the intrinsic component. In addition to the regular polarization variability, there is a non-periodic component, strongest in the $B$ passband. We obtained in the $V$ passband our most reliable values for the orbital inclination $i = 46^{\circ}+11^{\circ}/-46^{\circ}$ and the orientation of the orbit on the sky $\Omega = 105^{\circ} \pm 55^{\circ}$, with 1$\sigma$ confidence intervals. The direction of the binary system rotation on the plane of the sky is clockwise

Temporal and spatial variations of pulsating auroras in fine-scale obtained from ground-based observations

第2回極域科学シンポジウム/第35回極域宙空圏シンポジウム 11月16日（水） 統計数理研究所 3階リフレッシュフロ