分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The nearby bright M-dwarf star L~98-59 has three terrestrial-sized planets. One challenge remaining in characterizing atmospheres around such planets is that it is not known a priori whether they possess any atmospheres. Here we report the study of the atmospheres of L~98-59~c and L~98-59~d using the near-infrared spectral data from the G141 grism of HST/WFC3. We can reject the hypothesis of a clear atmosphere dominated by hydrogen and helium at a confidence level of $\sim$ 3~sigma for both planets. Thus they may have a primary hydrogen-dominated atmosphere with an opaque cloud layer, or have lost their primary hydrogen-dominated atmosphere and re-established a secondary thin atmosphere, or have no atmosphere at all. We cannot distinguish between these scenarios for the two planets using the current HST data. Future observations with JWST would be capable of confirming the existence of atmospheres around L~98-59~c and d and determining their compositions.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： It is common to assume that all narrow absorption lines (NALs) at extreme high-velocity shifts form in cosmologically intervening gas or galaxies unrelated to quasars. However, previous detailed studies of individual quasars have shown that some NALs at these large velocity shifts do form in high-speed quasar ejecta. We search for extreme high-velocity NAL outflows (with speeds $\sim$0.1-0.2c) based on relationships with associated absorption lines (AALs) and broad absorption-line (BAL) outflows. We find that high-velocity NALs are strongly correlated with AALs, BALs, and radio loudness, indicating that a significant fraction of high-velocity systems are either ejected from the quasars or form in material swept up by the radio jets (and are not unrelated intervening gas). We also consider line-locked C IV doublets as another indicator of high-velocity NALs formed in outflows. The fact that line-locked NALs are highly ionized and correlated with BAL outflows and radio-loud quasars implies that physical line locking due to radiative forces is both common and real, which provides indirect evidence that a significant fraction of high-velocity NALs are intrinsic to quasars.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Xian-Yu Wang
Yong-Hao Wang
Songhu Wang
Zhen-Yu Wu
Malena Rice
Xu Zhou
Tobias C. Hinse
Hui-Gen Liu
Bo Ma
Xiyan Peng
Hui Zhang
Cong Yu
Ji-Lin Zhou
Gregory Laughlin
摘要： We present 127 new transit light curves for 39 hot Jupiter systems, obtained over the span of five years by two ground-based telescopes. A homogeneous analysis of these newly collected light curves together with archived spectroscopic, photometric, and Doppler velocimetric data using EXOFASTv2 leads to a significant improvement in the physical and orbital parameters of each system. All of our stellar radii are constrained to accuracies of better than 3\%. The planetary radii for 37 of our 39 targets are determined to accuracies of better than $5\%$. Compared to our results, the literature eccentricities are preferentially overestimated due to the Lucy-Sweeney bias. Our new photometric observations therefore allow for significant improvement in the orbital ephemerides of each system. Our correction of the future transit window amounts to a change exceeding $10\,{\rm min}$ for ten targets at the time of JWST's launch, including a $72\,{\rm min}$ change for WASP-56. The measured transit mid-times for both literature light curves and our new photometry show no significant deviations from the updated linear ephemerides, ruling out in each system the presence of companion planets with masses greater than $0.39 - 5.0\, rm M_{\oplus}$, $1.23 - 14.36\, \rm M_{\oplus}$, $1.65 - 21.18\, \rm M_{\oplus}$, and $0.69 - 6.75\, \rm M_{\oplus}$ near the 1:2, 2:3, 3:2, and 2:1 resonances with the hot Jupiters , respectively, at a confidence level of $\pm 1\,\sigma$. The absence of resonant companion planets in the hot Jupiter systems is inconsistent with the conventional expectation from disk migration.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Galactic short-period close white dwarf binaries (CWDBs) are important objects for space-borne gravitational-wave (GW) detectors in the millihertz frequency bands. Due to the intrinsically low luminosity, only about 25 identified CWDBs are detectable by the Laser Interferometer Space Antenna (LISA), which are also known as verification binaries (VBs). The Gaia Early Data Release 3 (EDR3) provids a catalog containing a large number of CWDB candidates, which also includes parallax and photometry measurements. We crossmatch the Gaia EDR3 and Zwicky Transient Facility public data release 8, and apply period-finding algorithms to obtain a sample of periodic variables. The phase-folded light curves are inspected, and finally we obtain a binary sample containing 429 CWDB candidates. We further classify the samples into eclipsing binaries (including 58 HW Vir-type binaries, 65 EA-type binaries, 56 EB-type binaries, and 41 EW-type binaries) and ellipsoidal variations (209 ELL-type binaries). We discovered four ultrashort period binary candidates with unique light-curve shapes. We estimate the GW amplitude of all of our binary candidates, and calculate the corresponding signal-to-noise ratio (S/N) for TianQin and LISA. We find two (six) potential GW candidates with S/Ns greater than 5 in the nominal mission time of TianQin (LISA), which increases the total number of candidate VBs for TianQin (LISA) to 18 (31).
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The nearby bright M-dwarf star L~98-59 has three terrestrial-sized planets. One challenge remaining in characterizing atmospheres around such planets is that it is not known a priori whether they possess any atmospheres. Here we report the study of the atmospheres of L~98-59~c and L~98-59~d using the near-infrared spectral data from the G141 grism of HST/WFC3. We can reject the hypothesis of a clear atmosphere dominated by hydrogen and helium at a confidence level of $\sim$ 3~sigma for both planets. Thus they may have a primary hydrogen-dominated atmosphere with an opaque cloud layer, or have lost their primary hydrogen-dominated atmosphere and re-established a secondary thin atmosphere, or have no atmosphere at all. We cannot distinguish between these scenarios for the two planets using the current HST data. Future observations with JWST would be capable of confirming the existence of atmospheres around L~98-59~c and d and determining their compositions.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Galactic short-period close white dwarf binaries (CWDBs) are important objects for space-borne gravitational-wave (GW) detectors in the millihertz frequency bands. Due to the intrinsically low luminosity, only about 25 identified CWDBs are detectable by the Laser Interferometer Space Antenna (LISA), which are also known as verification binaries (VBs). The Gaia Early Data Release 3 (EDR3) provids a catalog containing a large number of CWDB candidates, which also includes parallax and photometry measurements. We crossmatch the Gaia EDR3 and Zwicky Transient Facility public data release 8, and apply period-finding algorithms to obtain a sample of periodic variables. The phase-folded light curves are inspected, and finally we obtain a binary sample containing 429 CWDB candidates. We further classify the samples into eclipsing binaries (including 58 HW Vir-type binaries, 65 EA-type binaries, 56 EB-type binaries, and 41 EW-type binaries) and ellipsoidal variations (209 ELL-type binaries). We discovered four ultrashort period binary candidates with unique light-curve shapes. We estimate the GW amplitude of all of our binary candidates, and calculate the corresponding signal-to-noise ratio (S/N) for TianQin and LISA. We find two (six) potential GW candidates with S/Ns greater than 5 in the nominal mission time of TianQin (LISA), which increases the total number of candidate VBs for TianQin (LISA) to 18 (31).
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We are using archived data from HST of transiting exoplanet L~98-59~b to place constraints on its potentially hot atmosphere. We analyze the data from five transit visits and extract the final combined transmission spectrum using Iraclis. Then we use the inverse atmospheric retrieval code TauREx to analyze the combined transmission spectrum. There is a weak absorption feature near 1.40~$\mu m$ and 1.55~$\mu m$ in the transmission spectrum, which can be modeled by a cloudy atmosphere with abundant HCN. However, the unrealistically high abundance of HCN derived cannot be explained by any equilibrium chemical model with reasonable assumptions. Thus, the likeliest scenario is that L~98-59~b has a flat, featureless transmission spectrum in the WFC3/G141 bandpass due to a thin atmosphere with high mean molecular weight, an atmosphere with an opaque aerosol layer, or no atmosphere, and it is very unlikely for L~98-59~b to have a clear hydrogen-dominated primary atmosphere. Due to the narrow wavelength coverage and low spectral resolution of HST/WFC3 G141 grism observation, we cannot tell these different scenarios apart. Our simulation shows future higher precision measurements over wider wavelengths from the James Webb Space Telescope (JWST) can be used to better characterize the planetary atmosphere of L~98-59~b.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We are using archived data from HST of transiting exoplanet L~98-59~b to place constraints on its potentially hot atmosphere. We analyze the data from five transit visits and extract the final combined transmission spectrum using Iraclis. Then we use the inverse atmospheric retrieval code TauREx to analyze the combined transmission spectrum. There is a weak absorption feature near 1.40~$\mu m$ and 1.55~$\mu m$ in the transmission spectrum, which can be modeled by a cloudy atmosphere with abundant HCN. However, the unrealistically high abundance of HCN derived cannot be explained by any equilibrium chemical model with reasonable assumptions. Thus, the likeliest scenario is that L~98-59~b has a flat, featureless transmission spectrum in the WFC3/G141 bandpass due to a thin atmosphere with high mean molecular weight, an atmosphere with an opaque aerosol layer, or no atmosphere, and it is very unlikely for L~98-59~b to have a clear hydrogen-dominated primary atmosphere. Due to the narrow wavelength coverage and low spectral resolution of HST/WFC3 G141 grism observation, we cannot tell these different scenarios apart. Our simulation shows future higher precision measurements over wider wavelengths from the James Webb Space Telescope (JWST) can be used to better characterize the planetary atmosphere of L~98-59~b.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Apsidal motion is a gradual shift in the position of periastron. The impact of dynamic tides on apsidal motion has long been debated, because the contribution could not be quantified due to the lack of high quality observations. KIC 4544587 with tidally excited oscillations has been observed by \textit{Kepler} high-precision photometric data based on long time baseline and short-cadence schema. In this paper, we compute the rate of apsidal motion that arises from the dynamic tides as $19.05\pm 1.70$ mrad yr$^{-1}$ via tracking the orbital phase shifts of tidally excited oscillations. We also calculate the procession rate of the orbit due to the Newtonian and general relativistic contribution as $21.49 \pm 2.8$ and $2.4 \pm 0.06$ mrad yr$^{-1}$, respectively. The sum of these three factors is in excellent agreement with the total observational rate of apsidal motion $42.97 \pm 0.18$ mrad yr$^{-1}$ measured by eclipse timing variations. The tidal effect accounts for about 44\% of the overall observed apsidal motion and is comparable to that of the Newtonian term. Dynamic tides have a significant contribution to the apsidal motion. The analysis method mentioned in this paper presents an alternative approach to measuring the contribution of the dynamic tides quantitatively.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Jian Ge
Hui Zhang
Weicheng Zang
Hongping Deng
Shude Mao
Ji-Wei Xie
Hui-Gen Liu
Ji-Lin Zhou
Kevin Willis
Chelsea Huang
Steve B. Howell
Fabo Feng
Jiapeng Zhu
Xinyu Yao
Beibei Liu
Masataka Aizawa
Wei Zhu
Ya-Ping Li
Bo Ma
Quanzhi Ye
摘要： We propose to develop a wide-field and ultra-high-precision photometric survey mission, temporarily named "Earth 2.0 (ET)". This mission is designed to measure, for the first time, the occurrence rate and the orbital distributions of Earth-sized planets. ET consists of seven 30cm telescopes, to be launched to the Earth-Sun's L2 point. Six of these are transit telescopes with a field of view of 500 square degrees. Staring in the direction that encompasses the original Kepler field for four continuous years, this monitoring will return tens of thousands of transiting planets, including the elusive Earth twins orbiting solar-type stars. The seventh telescope is a 30cm microlensing telescope that will monitor an area of 4 square degrees toward the galactic bulge. This, combined with simultaneous ground-based KMTNet observations, will measure masses for hundreds of long-period and free-floating planets. Together, the transit and the microlensing telescopes will revolutionize our understandings of terrestrial planets across a large swath of orbital distances and free space. In addition, the survey data will also facilitate studies in the fields of asteroseismology, Galactic archeology, time-domain sciences, and black holes in binaries.
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