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2022

Prof. Chow-Choong Ngeow: Using ZTF data, we derived the contact binaries period-luminosity relations in the gr-band for the first time. These contact binaries were located in the globular clusters (black filled circles), showing a remarkable good agreement with the contact binaries located in the Solar neighborhood (purple crosses, after transformed the BV-band to gr-band) in the period-luminosity relation. This work is published in Ngeow et al 2021, AJ, 162, 63

DOI: 10.3847/1538-3881/ab930b

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Prof. Yen-Chen Pan: Ejecta velocity of SNe Ia is one powerful tool to differentiate between progenitor scenarios and explosion mechanisms. In this paper we investigate the relation between ejecta velocity (using photospheric Si II 6355 line) and host-galaxy properties with ∼280 SNe Ia. We find a significant trend that SNe Ia with faster ejecta velocities tend to explode in massive environments, whereas their slower counterparts can be found in both lower-mass and massive environments. We suggest this relation is likely caused by at least two populations of SNe Ia. We conclude metallicity is likely the dominant factor in forming high-velocity SNe Ia. This also implies their potential evolution with redshift and impact on the precision of SN Ia cosmology. This result has been published in Pan (2020), ApJL, 897, L5.

DOI: 10.3847/2041-8213/ab8e47

Young Supernova Experiment, YSE, presents panchromatic observations of supernova SN 2020tlf at ~130 days from mass-loss episodes to the explosion, which involved Prof. Yen-Chen Pan at the graduate institute of astronomy in NCU. This project was led by Ph.D. student Wynn Jacobson-Galán at UC Berkeley to detect a supernova explosion in 2022, by using the Pan-STARRS telescope. SN 2020tlf is far from earth about one hundred million light-years. YSE detected “flash” spectroscopy about one days before its explosion, which is the first time revealed the light curve fluctuated before the explosion of a supernova. Astronomers considered it was due to the mass-loss episodes. So, the tiny changes can only be detected by a sensitive telescope. This may be the reason why it has never been revealed before. This observation can also help us understand the dying process of the massive star. Observations of SN 2020tlf were also obtained with the 1 m Lulin telescope located at Lulin Observatory, which contributed to BVgr bands before the explosion. Lulin observatory played a key role with its excellent location. It can contribute to those events in the future. This important result has been also reported by CNN. This result is published in Jacobson-Galán et al. 2022, ApJ, 924, 15 (Including Prof. Yen-Chen Pan).

DOI: 10.3847/1538-4357/ac3f3a

[Image caption] The left and right images are GIT and LOT images that captured the JWST, marked with the green and red circles, respectively. The yellow circles are a reference star to compare the relative locations of JWST on these images.
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The next generation space telescope, the James Webb Space Telescope (JWST), was successfully launched on Christmas Day of 2021. After nearly a month of journey, JWST finally reached its destination – the second Lagrange point L2. This location is about 1.5 million km away from the Earth, therefore using two distant telescopes on Earth it is possible to measure the parallax of JWST. On 08 February 2022, both the Lulin One-meter Telescope (LOT) and the 0.7m GROWTH India Telescope (GIT) imaged the sky where the JWST was expected to be located. Based on the relative locations of JWST on both images taken with LOT and GIT, we measured the parallax of JWST and hence derived its distance to be 1.54 million km. We thank the observing staff at Lulin Observatory for the assistance in carrying out the observations.