分类： 天文学 >> 天体物理学 提交时间： 2023-07-23
摘要： The distance $D$ to an exoplanet system with imaging and spectral measurement can be obtained by using the orbit as a ruler. The measurement of the Distance to a typical exoplanet system with imaging and spectral measurement can be accurate to $\delta D/D\sim 0.2$, if the orbital velocity of the planet can be accurate to $\sim 3 {\ \rm km/s}$.
分类： 天文学 >> 天文学 提交时间： 2023-07-15
摘要： In observational astronomy, we essentially measure the location, flux density (at certain frequency and certain time), distance and angular size of the sources. A parameter space of observational astronomy can be constructed with the parameters such as the sample size of sources, frequency (bandwidth and frequency resolution), time (observing length and time resolution), sensitivity, and angular resolution of the telescope. Based on the previous experience, we would always obtain new knowledge of the universe with instruments that fill in the blanks in the parameter space, e.g. telescopes used for better surveys (which enlarge the sample sizes of sources), telescopes with higher sensitivity, angular resolution, frequency resolution or time resolution.
分类： 天文学 >> 天体物理学 提交时间： 2023-07-11
摘要： We propose to use the rotation period to constrain the average density of an object with gravitationally confined surface. The average density is inverse proportional to the square of the rotation period, while independent of the size of the object. The lower limit of the average density can be written as $\rho_0=10.9 {\ \rm g\ cm^{-3}}\left(\frac{{\ \rm hours}}{P}\right)^2$. An asteroid with rotating period shorter than 0.7 h should consist of some unknown matter, or it is a whole rock or a bulk of ice with no rubble piles on the surface.
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