A new approach to distant solar system object detection in large survey data sets

Context. The recently postulated existence of a giant ninth planet in our solar system has sparked search efforts for distant solar system objects (SSOs) both via new observations and archival data analysis. Due to the likely faintness of the object in the optical and infrared regime, it has so far eluded detection. Aims. We set out to re-analyze data acquired by the Wide-Field Infrared Survey Explorer (WISE), an all-sky survey well suited for the detection of SSOs. Methods. We present a new approach to SSO detection via parallactic fitting. Using the heliocentric distance as a fit parameter, our code transforms groups of three or more single-observation point sources to heliocentric coordinates under the assumption that all data stem from an object. The fact that the orbit of a distant SSO is approximately linear in heliocentric coordinates over long time-scales can be utilized to produce candidates, which can then be confirmed with follow-up observations. Results. We demonstrate the feasibility of the approach by a posteriori detecting the outer SSO Makemake within WISE data. An all-sky search for Planet Nine yielded no detection. Conclusions. While the postulated Planet Nine eluded detection by our algorithm, we tentatively predict that this new approach to moving-object analysis will enable the discovery of new distant SSOs that cannot be discovered by other algorithms. Especially in cases of sparse data observed over long time spans, our approach is unique and robust due to the use of only one fit parameter.

A Statistical Study on Force-Freeness of Solar Magnetic Fields in the Photosphere

It is an indisputable fact that solar magnetic fields are force-free in the corona, where force-free fields mean that current and magnetic fields are parallel and there is no Lorentz force in the fields. While the force-free extent of photospheric magnetic fields remains open, in this paper, we give its statistical results. Vector magnetograms (namely, Bx, By, and Bz in heliocentric coordinates) employed are observed by the Solar Magnetic Field Telescope at Huairou Solar Observing Station. We study and calibrate 925 magnetograms calibrated by two sets of calibration coefficients, which indicate the relation between magnetic fields and the strength of the Stokes spectrum and can be calculated either theoretically or empirically. The statistical results show that the majority of active region magnetic fields are not consistent with the force-free model.

Solar Oscillations Instrument at an Infrared Wavelength of 1.6 μm at Yunnan Observatory

A photometric solar seismograph, as part of an international network, was installed at Yunnan Observatory, the Chinese Academy of Sciences, and put into operation in the spring of 1991. This instrument is used to detect solar oscillations by measuring the continuum radiation intensity on the solar disk with a spatial resolution of 50 arcsec, in heliocentric coordinates, for research on p-modes and g-modes when l < 50, where l is the angular degree of the eigenfunction. The solar oscillations can be observed simultaneously at two wavelengths of the detector with a sensitivity of 10 of the average intensity. This paper reports on the optical system of the instrument. Also introduced in this paper is the compensation system for the noise signals produced by the changes in the transparency of the Earth's atmosphere. This is based on solar photometry at wavelengths of 0.55 mm and 1.6 mm.