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Curlometer and gradient techniques: past and future applications
Escoubet, C. P.; Dunlop, M. W.; Shen, C. +5 more
We review the range of applications and use of multi spacecraft techniques, applicable to close formation arrays of spacecraft, focusing on spatial gradient based methods, and the curlometer in particular. The curlometer was originally applied to Cluster multi-spacecraft magnetic field data, but later was updated for different environments and mea…
Semi-supervised spectral classification of DESI white dwarfs by dimensionality reduction
Bonsor, Amy; Manser, Christopher J.; Rogers, Laura K. +1 more
As a new generation of large-sky spectroscopic surveys comes online, the enormous data volume poses unprecedented challenges in classifying spectra. Modern unsupervised techniques have the power to group spectra based on their dominant features, circumventing the complete reliance on training data suffered by supervised methods. We outline the use…
The ap Prediction Tool Implemented by the A.Ne.Mo.S./NKUA Group
Mavromichalaki, Helen; Livada, Maria; Stassinakis, Argyris +4 more
A novel tool utilizing machine learning techniques was designed to forecast ap index values for the next three consecutive days (24 values). The tool employs time series data from the 3 h ap index of solar cycles 23 and 24 to train the Long Short-Term Memory (LSTM) model, predicting ap index values for the next 72 h at three-hour intervals. During…
Calcium Bright Knots and the Formation of Chromospheric Anemone Jets on the Sun
Shibata, Kazunari; Singh, Kunwar Alkendra Pratap; Nishida, Keisuke
Space-based observations show that the solar atmosphere from the solar chromosphere to the solar corona is filled with small-scale jets and is linked with small-scale explosions. These jets may be produced by mechanisms similar to those of large-scale flares and such jets may be related to the heating of the corona and chromosphere as well as the …
The HST Large Programme on ω Centauri: VII. The white dwarf cooling sequence
Salaris, M.; Apai, D.; Anderson, J. +9 more
We present a study of the white dwarf (WD) cooling sequence (CS) in the globular cluster (GC) Omega Centauri (or NGC 5139; hereafter, ω Cen), the primary goal of a dedicated Hubble Space Telescope (HST) programme. We find that the peak at the termination of the WD CS is located at mF606W = 30.1 ± 0.2 (equivalent to V ∼ 31). The brighter…
Evidence of the γ-ray counterpart of nova FM Cir from Fermi-LAT
Takata, J.; Wang, H. H.; Lin, L. C. -C. +2 more
We report the results of an analysis of X-ray and γ-ray data from the nova FM Cir taken by Swift and Fermi-LAT. The γ-ray emission from FM Cir can be identified with a significance level of ~3σ within ~40 d after the nova eruption (2018 January 19) when we bin the light curve per day. The significance can exceed the 4σ confidence level if we accum…
Physical Parameters and Magnetic Activity of M-type Stars Based on the LAMOST DR9, SDSS, and TESS Surveys
Han, Xianming L.; Misra, Prabhakar; Zhang, Li-yun +3 more
We analyze a catalog comprising 781,232 spectra from 641,095 M dwarf stars from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) low-resolution spectroscopic data release 9. Based on the equivalent width of the Hα line, we ascertain the activity properties of the stars, identifying a total of 107,134 active stars, with 31,175…
Geomagnetic Pulsations in the 1-4 mHz Frequency Range (Pc5/Pi3) in the Magnetotail. Internal and Extramagnetospheric Sources
Yagova, N. V.; Evsina, N. S.
Spectral and spatial parameters of nonstorm Pc5/Pi3 geomagnetic pulsations in the geomagnetic tail are studied based on magnetic measurements on Cluster satellites under different conditions in the interplanetary medium. Both the average values of the magnetic field components in front of the bow shock and fluctuations in the pulsations' frequency…
Possible anticorrelations between pulsation amplitudes and the disc growth of Be stars in giant-outbursting Be X-ray binaries
Soria, Roberto; Ricker, George R.; Vanderspek, Roland +15 more
The mechanism of X-ray outbursts in Be X-ray binaries remains a mystery, and understanding their circumstellar discs is crucial for a solution of the mass-transfer problem. In particular, it is important to identify the Be star activities (e.g. pulsations) that cause mass ejection and, hence, disc formation. Therefore, we investigated the relation…
Distinguishing exoplanet companions from field stars in direct imaging using Gaia astrometry
Bailer-Jones, Coryn A. L.; Samland, Matthias; Herz, Philipp
Direct imaging searches for exoplanets around stars detect many spurious candidates that are in fact background field stars. To help distinguish these from genuine companions, multi-epoch astrometry can be used to identify a common proper motion with the host star. Although this is frequently done, many approaches lack an appropriate model for the…