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

2025年5月22日Scientific Exploration of the Lunar Frontier Workshop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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2025-02-27
[天文所公告] 114學年度天文研究所碩士班考試入學口試公告

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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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圖: 小行星各家族 (Hungaria, Flora, Baptistina, Phocaea, Massalia, Vesta, Nysa-Polana, Maria, Adeona, Eunomia, Juno, Agnoa, Eos, Koronis, Hygiea, Themis, Euphrosyne, and Hilda families)的相位曲線在HG1G2模型中的分佈情形

小行星的分類與大小不再局限於多色測光與光譜觀測
小行星是圍繞太陽運動的岩石或者金屬天體，它們是太陽系形成早期未能發生吸積的殘留物質，因此仍然保存著太陽系原始星雲的信息。 S型和C型是最常見的小行星類型，分別代表了小行星兩種不同的光譜特徵，與它們的物質成分相關。1984年Tholen使用色測光數據將小行星進一步分類，隨後可見光與紅外波段的光譜將小行的分類更加細分，然而小行星光譜觀測與大樣本多色測光數據耗費大量觀測資源，因此尋找替代小行星光譜的分類方法便成為科學家近年來的主要目標。近年來各研究機構陸續使用大型望遠鏡展開巡天計畫，這些巡天計畫往往為了巡天效率多使用單一濾鏡或者少數濾鏡來節省巡天時間，這縮短的時間對瞬變天體很有時效性，但對區分小行星類型是無助益的，因為無法使用多色測光數據得到小行星的色指數，進一步對多個色指數開展主成分分析!
林忠義博士利用Zwicky Transient Facility（ZTF）(位於加利福尼亞州帕洛馬山的施密特望遠鏡擁有觀測視野達到47平方度)巡天資料將小行星進行光譜分類，論文研究方法為使用單一顏色濾鏡(雖然ZTF有三種濾鏡，但仍以r’觀測資料為最多)求得小行星光度隨相位角之間的關係，也稱之為小行星的相位函數，並將其分類。最後是用分類結果將小行星大小算出，隨後比較各小行星家族的大小分佈函數(size distribution)，了解各家族形成的時間與關聯性。這些研究成果已於今(2025)年6月20日發表於國際期刊《皇家天文學會月報》(Monthly Notices of the Royal Astronomical Society)。

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圖: SLT三色合成影像SN 2024ggi與其宿主星系NGC 3621。

由陳婷琬教授主持的Kinder計畫，透過鹿林天文台40公分SLT望遠鏡，在SN 2024ggi爆炸後僅14小時即成功取得其極早期的光度與溫度演化資料。SN 2024ggi 位於星系 NGC 3621，由大稀奇天體實驗室參與的ATLAS 計畫所發現，是近十年來距離地球最近的核心塌縮超新星之一（約 6.6 Mpc）。本研究特別結合了來自臺灣與香港的公民天文學家之力量，透過他們提供的光度觀測與鹿林SLT的早期觀測相互補強，提高時間解析度，使研究團隊得以重建SN 2024ggi爆炸初期的完整光變曲線。另外，這也是鹿林天文台首次實現「超新星夢幻連動觀測」：LOT負責光譜，SLT觀測光度！觀測顯示該超新星在早期階段光度迅速上升、顏色轉藍，並伴隨窄發射譜線，顯示其爆炸受到周圍環星物質的顯著影響。研究團隊推測，其前身星為紅超巨星，在爆炸前每年流失約10⁻³個太陽質量，並被約0.4個太陽質量的環星物質所包圍。本成果已發表於《The Astrophysical Journal》（Chen et al. 2025, ApJ, 983, 86）。

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圖：AT 2024gsa的LOT發現影像（左上），以及後續由Pan-STARRS1（右上）與Gemini望遠鏡（左下）取得的追蹤觀測影像。同時右下角顯示的是來自DECam的歷史影像。

由陳婷琬助理教授主持的Kinder計畫，使用鹿林天文台一米望遠鏡（LOT）偵測到天關衛星EP240414a事件的光學對應體 AT 2024gsa，並且通報給天文社群。這是天關衛星所發現的第二個具光學對應體的快速X射線瞬變源。該源位於其可能宿主星系（紅移 z ≈ 0.4）外圍，投影距離約27千秒差距。AT 2024gsa 的可見光光變曲線顯示出三個明顯的演化階段。第一階段為自初次觀測起的快速光度衰減，鹿林的早期觀測成功捕捉到這段變化，其光度演化與伽瑪射線暴（Gamma-Ray Bursts）餘輝模型相符。第二階段則是一次再增亮事件，約在兩日（已校正紅移後的時間）內急遽增亮至絕對星等Mr ≈ −21。儘管其明亮亮度與衰減速率類似於高亮度快速藍色光學瞬變（Fast Blue Optical Transients），但AT 2024gsa的色溫卻顯著偏紅，且其峰值亮度與熱輻射模型不符，暗示其並非高亮度快速藍色光學瞬變。第三階段則在快速X射線瞬變源事件發生後約16天達到另一個光度高峰，絕對星等Mi ≈ -19，可能與一顆逐漸顯現的超新星有關。

綜合EP240414a與歷來所有具有紅移資訊的快速X射線瞬變源事件，我們提出：天關衛星所發現的這類快速X射線瞬變源很可能主要來自高紅移的伽瑪射線暴，與早期所知的低紅移、低光度快速X射線瞬變源族群在起源與性質上有明顯差異。本成果已發表於《The Astrophysical Journal Letters》（Srivastav, Chen, Gillanders三位共同第一作者, 2025, ApJL, 978, L21）。

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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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