NCU Institute of Astronomy

Asia-Pacific Astronomy Sideways Workshop合照

中央大學台達電子文教基金會年輕天文學者講座Dr. Thiem Hoang演講合照

中大及其他天文台

鹿林天文台空拍

鹿林天文台一米望遠鏡

一米望遠鏡控制室

鹿林天文台一米望遠鏡

中大天文台(科一館)

兩米望遠鏡

GROWTH

Credit: LSST

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Caption: Evolution of 4U 1820-30 superorbital phases from 1987 to 2023. The dotted, solid and dashed lines represent the best fits for linear, glitch and quadratic models, respectively. The shaded area indicates the low power state between MJD 50,773 and 52,627, and the vertical dash-dot line represents the period glitch time MJD 52,380±4145, evaluated by the glitch model, with the horizontal error bar indicating the 1σ uncertainty of the glitch time.

Master student Jun-Lei Wu and Prof. Yi Chou studied the superorbital modulation of low mass X-ray binary 4U 1820-30.It was long believed by the astronomers that the superorbital modulation of the low-mass X-ray binary 4U 1820-30, with a period of 171 days, was a resonance effect induced by a third star orbiting the binary system—an explanation known as the triple model. The stability of this superorbital period predicted by this model is crucial for verifying this hypothesis. A research team led by Prof. Yi Chou analyzed X-ray light curves collected by six monitoring and scanning telescopes over a span of 36 years. They discovered that the superorbital period had significantly changed from 171 days to 167 days during this time. Further phase analysis revealed that this change either occurred abruptly between early 2001 and mid-2003 or evolved gradually with a period derivative of Ṗ=(-4.20±0.72)x10^-4 day/day. Their findings indicate that the superorbital period of 4U 1820-30 is not as stable as predicted by the triple model, strongly challenging this hypothesis. Instead, they propose an irradiation-induced mass transfer instability scenario to explain the observed superorbital modulation. The research paper has been published in the Astrophysical Journal ( Yi Chou et al. 2025 ApJ 981 43 ). Its preprint, posted on arXiv in September 2024, was reported on the renowned public outreach website Phys.org under the title "Study Inspects Unusual Behavior of an X-ray Binary" .

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The team led by Prof. Pan investigated the relation between SN Ia ejecta velocity and their host-galaxy environment, and found that there could exist a relationship between the two parameters. This study focused on the local environmental properties of SNe Ia and revealed possible trend that high-velocity SNe Ia tend to be associated with old stellar populations, while normal-velocity SNe Ia can be found in both old and young stellar populations. This result implies that the normal SNe Ia are likely produced by more than one channel, challenging the previous consensus that they are associated with a single and uniform population. This work has been published in Lin & Pan et al., 2024, MNRAS, 531, 1988

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Virgo III is a newly discovered ultra-faint dwarf (UFD) galaxy. We used the Lulin One-meter Telescope (LOT) to search for RR Lyrae associated with this UFD.With deep exposures of LOT that can reach to r~23 mag, we discovered three RR Lyrae, labeled as V1, V2, and V3 in this deep LOT images. Using the discovered RR Lyrae, we measured a distance of 154 kpc to Virgo III.

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An international team led by Prof. Pan studied the data obtained from Pan-STARRS1 Medium Deep Survey (PS1-MDS) and found the type Ia supernovae (SNe Ia) could evolve with time. As one of the most mature cosmological probes, SNe Ia have homogeneous properties, and they were expected to be consistent and similar during the evolution of our Universe. However, this work suggests that SNe Ia are likely to have at least two different populations, as separated by their ejecta velocities. The fractions between different populations tend to evolve with time. This result could impact the precision of SNe Ia in probing the cosmic expansion and dark energy. This work has been published in Pan et al., 2024, MNRAS, 532, 1887 .

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