Quasar absorption lines (QALs), created by the light of celestial objects billions of light-years away, can be used to trace gas components from distant galaxies and thus are crucial to the study of galaxy evolution. Ca II QALs, in particular, are important for studying both star formation and recent galaxies because they are one of the dustiest QALs and are located at lower redshifts. However, Ca II QALs are quite difficult to detect, so the number of known Ca II QALs is extremely low, leaving many important models and theories unconfirmed. In this work, we developed an accurate and efficient approach to search for Ca II QALs using deep learning. We created large amount of simulation data for our training set, while we used an existing Ca II QAL catalog for our test set. We also designed a novel preprocessing method aimed at discovering weak Ca II absorption lines. Our solution achieved an accuracy of 96% on the test dataset and runs thousands of times faster than traditional methods. Our trained neural network model was applied to quasar spectra from the Sloan Digital Sky Survey’s Data Releases 7, 12, and 14, and discovered 542 brand-new Ca II QALs and. This is currently the largest catalog of Ca II QALs ever discovered, which will play a significant role in creating new theories and confirming existing theories. Furthermore, our approach can be applied to the search of virtually any other type of QAL, opening up opportunities for ground-breaking research about galaxy evolution.
An innovative Chinese space mission, the Earth 2.0 (ET) mission, is being developed to combine the transit and microlensing method together to search for Earth-sized exoplanets in the Galaxy, including the most precious ones—Earth 2.0s, i.e., habitable Earth-sized (0.8-1.25 Earth radii) planets orbiting solar type stars, cold and free-floating low-mass planets. ET’s 6 transit telescopes will monitor a FoV of 500 square degrees (covering the Kepler field) continuously for at least four years and generate a huge database containing high-cadence and ultra-high photometry precision light curves of 1.2 million FGKM dwarfs. With such a high value database in hand, many unsolved issues in the exoplanet field and even stellar sciences will be well addressed. Besides looking for Earth 2.0s and constraining its occurrence rate, ET will be dedicated to map a much wider radius-period diagram of terrestrial-like exoplanets than ever and reveal how it depends on the stellar properties and environments. With the 4-yr legacy data of Kepler, ET will observe some planet systems for up to 8 years and catch additional components in a multi-planet system, e.g. cold Giant, cold sub-Earths, exomoons, exorings and even exocomets. Are exomoons and exocomets common in a planet system? What’s the favorite number of planets in a multi-planet system? What’s the most common orbital configuration of planet systems? With these new data, ET will deepen our understandings on how unique our Solar system is and how do multi-planet systems evolve. In addition to exoplanet sciences, ET’s time series data will also benefit the studies in asteroseismology, archeology in the Galaxy, time-domain astrophysics and black hole science.
A space mission called “Earth 2.0 (ET)” is being developed in China to address a few of fundamental questions in the exoplanet field: How frequently habitable Earth-like planets orbit solar type stars (Earth 2.0s)? How do terrestrial planets form and evolve? Where did floating planets come from? ET consists of six 30 cm diameter transit telescope systems with each field of view of 500 square degrees and one 35 cm diameter microlensing telescope with a field of view of 4 square degrees. The ET transit mode will monitor ~1.2M FGKM dwarfs in the original Kepler field and its neighboring fields continuously for four years while the microlensing mode monitors over 30M I< 20.6 stars in the Galactic bulge direction. ET will merge its photometry data with that from Kepler to increase the time baseline to 8 years. This enhances the transit signal-to-noise ratio, reduce false positives, and greatly increases the chance to discover Earth 2.0s. Simulations show that ET transit telescopes will be able to identify ~17 Earth 2.0s, about 4,900 Earth-sized terrestrial planets and about 29,000 new planets. In addition, ET will detect about 2,000 transit-timingvariation (TTV) planets and 700 of them will have mass and eccentricity measurements. The ET microlensing telescope will be able to identify over 1,000 microlensing planets. With simultaneous observations with the ground-based KMTNet telescopes, ET will be able to measure masses of over 300 microlensing planets and determine the mass distribution functions of free-floating planets and cold planets. ET will be operated at the Earth-Sun L2 orbit with a designed lifetime longer than 4 years.
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