分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We present analysis of the starspot properties and chromospheric activity on HD 134319 using high precision photometry by TESS in sectors 14-16 (T1), 21-23 (T2) and high-resolution spectroscopy by OHP/ELODIE and Keck/HIRES during years 1995-2013. We applied a two-spot model with GLS determined period $P=4.436391\pm0.00137$ day to model chunks sliding over TESS light curve, and measured relative equivalent widths of Ca II H and K, H$\beta$ and H$\alpha$ emissions by subtracting overall spectrum from individual spectrum. It was found that a two-spot configuration, i.e. a primary, slowly evolving and long-lasting spot (P) plus a secondary and rapidly evolving spot (S), was capable of explaining the data, although the actual starspot distribution is unable to derived from collected data. Despite the spot radius-latitude degeneracy revealed in the best-fit solutions, a sudden alternation between P and S radii followed by gradual decrease of S in T1 and the decrease of both P and S from T1 to T2 were significant, corresponding to the evolution of magnetic activity. Besides, S revealed rotation and oscillatory longitude migration synchronized to P in T1, but held much larger migration than P in T2. This might indicate the evolution of internal magnetic configuration. Chromospheric activity indicators were found to tightly correlated with each other and revealed rotational modulation as well as a long-term decrease of emissions, implying the existence and evolution of magnetic acitivity on HD 134319.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We present a Zeeman-Doppler imaging study of two weak-line T Tauri stars TAP 4 and TAP 40, based on the high-resolution spectropolarimetric observations with ESPaDOnS at the Canada-France-Hawaii Telescope in November 2013, in the framework of the MaTYSSE large programme. We apply two Zeeman-Doppler imaging codes to the Stokes I and V profiles to reconstruct their brightness and large-scale magnetic field images. The results given by the two imaging codes are in good agreement with each other. TAP 4 shows a large polar cool spot and several intermediate-latitude warm spots on its surface, whereas TAP 40 exhibits very weak variations in its Stokes I profiles suggesting a mostly unspotted photosphere. We detect Zeeman signatures in the Stokes V profiles of both stars. The reconstructed magnetic maps reveal dominantly toroidal fields, which enclose about 60 per cent of the total magnetic energy for both of TAP 4 and TAP 40. Both stars show prominent circular ring features of the azimuthal magnetic field. We derive a solar-like surface differential rotation on TAP 4 from the tomographic modelling. The brightness image of TAP 4 is used to predict the radial velocity jitters induced by its activity. After filtering out the activity jitter, the RMS of its RVs is reduced from 1.7 km s$^{-1}$ to 0.2 km s$^{-1}$, but we do not detect any periodic signals in the filtered RVs of TAP 4, implying that it is unlikely to host a close-in exoplanet more massive than $\sim$3.5 M$_{\rm Jup}$ at 0.1 au.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Qichun Liu
Jie Lin
Xiaofeng Wang
Shenghong Gu
Jianrong Shi
Liyun Zhang
Gaobo Xi
Jun Mo
Yongzhi Cai
Liyang Chen
Zhihao Chen
Fangzhou Guo
Xiaojun Jiang
Gaici Li
Wenxiong Li
Han Lin
Weili Lin
Jialian Liu
Cheng Miao
Xiaoran Ma
摘要： Tsinghua University-Ma Huateng Telescopes for Survey (TMTS) aims to detect fast-evolving transients in the Universe, which has led to the discovery of thousands of short-period variables and eclipsing binaries since 2020. In this paper, we present the observed properties of 125 flare stars identified by the TMTS within the first two years, with an attempt to constrain their eruption physics. As expected, most of these flares were recorded in late-type red stars with $G_{\rm BP}-G_{\rm RP}$ > 2.0 mag, however, the flares associated with bluer stars tend to be on average more energetic and have broader profiles. The peak flux (F_peak) of the flare is found to depend strongly on the equivalent duration (ED) of the energy release, i.e., $F_{{\rm peak}} \propto {\rm ED}^{0.72\pm0.04}$, which is consistent with results derived from the Kepler and Evryscope samples. This relation is likely related to the magnetic loop emission, while -- for the more popular non-thermal electron heating model -- a specific time evolution may be required to generate this relation. We notice that flares produced by hotter stars have a flatter $F_{{\rm peak}} \propto {\rm ED}$ relation compared to that from cooler stars. This is related to the statistical discrepancy in light-curve shape of flare events with different colors. In spectra from LAMOST, we find that flare stars have apparently stronger H alpha emission than inactive stars, especially at the low temperature end, suggesting that chromospheric activity plays an important role in producing flares. On the other hand, the subclass having frequent flares are found to show H alpha emission of similar strength in their spectra to that recorded with only a single flare but similar effective temperature, implying that the chromospheric activity may not be the only trigger for eruptions.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： High-precision transit observations provide excellent opportunities for characterizing the physical properties of exoplanetary systems. These physical properties supply many pieces of information for unvealing the internal structure, external atmosphere, and dynamical history of the planets. We present revised properties of transiting systems WASP-35 and HAT-P-30/WASP-51 through analyzing newly available TESS photometry and ground-based observations obtained at 1m telescope of Yunnan Observatories as well as from the literature. The improved system parameters are consistent with the previous results. Furthermore, we find that HAT-P-30b/WASP-51b's transits show significant timing variation which cannot be explained by decaying orbit due to tidal dissipation and the R\o mer effect, while both apsidal precession and an additional perturbing body could reproduce this signal through our comprehensive dynamical simulations. Because both of them are valuable targets which are suitable for transmission spectroscopy, we make some predictions for atmospheric properties of WASP-35b and HAT-P-30b/WASP-51b based on newly derived system parameters.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Leilei Sun
Panagiotis Ioannidis
Shenghong Gu
Jürgen H. M. M. Schmitt
Xiaobin Wang
M. B. N. Kouwenhoven
Volker Perdelwitz
Francesco Flammini Dotti
Stefan Czesla
摘要： The discovery of a population of close-orbiting giant planets ($\le$ 1 au) has raised a number of questions about their origins and dynamical histories. These issues have still not yet been fully resolved, despite over 20 years of exoplanet detections and a large number of discovered exoplanets. In particular, it is unclear whether warm Jupiters (WJs) form in situ, or whether they migrate from further outside and are even currently migrating to form hot Jupiters (HJs). Here, we report the possible discovery and characterization of the planets in a highly mutually-inclined ($I_{\rm mut}\simeq 45^\circ$), compact two-planet system (KOI-984), in which the newly discovered warm Jupiter KOI-984$c$ is on a 21.5-day, moderately eccentric ($e\simeq 0.4$) orbit, in addition to a previously known 4.3-day planet candidate KOI-984$b$. Meanwhile, the orbital configuration of a moderately inclined ($I_{\rm mut}\simeq 15^\circ$), low-mass ($m_{c}\simeq 24 M_{\oplus}$;$P_b\simeq 8.6$ days) perturbing planet near 1:2 mean motion resonace with KOI-984$b$ could also well reproduce observed transit timing variations and transit duration variations of KOI-984$b$. Such an eccentric WJ with a close-in sibling would pose a challenge to the proposed formation and migration mechanisms of WJs, if the first scenario is supported with more evidences in near future; this system with several other well-measured inclined WJ systems (e.g., Kepler-419 and Kepler-108) may provide additional clues for the origin and dynamical histories of WJs.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We apply the variational autoencoder (VAE) to the LAMOST-K2 low-resolution spectra to detect the magnetic activity of the stars in the K2 field. After the training on the spectra of the selected inactive stars, the VAE model can efficiently generate the synthetic reference templates needed by the spectral subtraction procedure, without knowing any stellar parameters. Then we detect the peculiar spectral features, such as chromospheric emissions, strong nebular emissions and lithium absorptions, in our sample. We measure the emissions of the chromospheric activity indicators, H$\alpha$ and Ca II infrared triplet (IRT) lines, to quantify the stellar magnetic activity. The excess emissions of H$\alpha$ and Ca II IRT lines of the active stars are correlated well to the rotational periods and the amplitudes of light curves derived from the K2 photometry. We degrade the LAMOST spectra to simulate the slitless spectra of the China Space Station Telescope (CSST) and apply the VAE to the simulated data. For cool active stars, we reveal a good agreement between the equivalent widths (EWs) of H$\alpha$ line derived from the spectra with two resolutions. The result indicates the ability of identifying the magnetically active stars in the future CSST survey, which will deliver an unprecedented large database of low-resolution spectra as well as simultaneous multi-band photometry of stars.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Qichun Liu
Jie Lin
Xiaofeng Wang
Shenghong Gu
Jianrong Shi
Liyun Zhang
Gaobo Xi
Jun Mo
Yongzhi Cai
Liyang Chen
Zhihao Chen
Fangzhou Guo
Xiaojun Jiang
Gaici Li
Wenxiong Li
Han Lin
Weili Lin
Jialian Liu
Cheng Miao
Xiaoran Ma
摘要： Tsinghua University-Ma Huateng Telescopes for Survey (TMTS) aims to detect fast-evolving transients in the Universe, which has led to the discovery of thousands of short-period variables and eclipsing binaries since 2020. In this paper, we present the observed properties of 125 flare stars identified by the TMTS within the first two years, with an attempt to constrain their eruption physics. As expected, most of these flares were recorded in late-type red stars with $G_{\rm BP}-G_{\rm RP}$ > 2.0 mag, however, the flares associated with bluer stars tend to be on average more energetic and have broader profiles. The peak flux (F_peak) of the flare is found to depend strongly on the equivalent duration (ED) of the energy release, i.e., $F_{{\rm peak}} \propto {\rm ED}^{0.72\pm0.04}$, which is consistent with results derived from the Kepler and Evryscope samples. This relation is likely related to the magnetic loop emission, while -- for the more popular non-thermal electron heating model -- a specific time evolution may be required to generate this relation. We notice that flares produced by hotter stars have a flatter $F_{{\rm peak}} \propto {\rm ED}$ relation compared to that from cooler stars. This is related to the statistical discrepancy in light-curve shape of flare events with different colors. In spectra from LAMOST, we find that flare stars have apparently stronger H alpha emission than inactive stars, especially at the low temperature end, suggesting that chromospheric activity plays an important role in producing flares. On the other hand, the subclass having frequent flares are found to show H alpha emission of similar strength in their spectra to that recorded with only a single flare but similar effective temperature, implying that the chromospheric activity may not be the only trigger for eruptions.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We present a Zeeman-Doppler imaging study of two weak-line T Tauri stars TAP 4 and TAP 40, based on the high-resolution spectropolarimetric observations with ESPaDOnS at the Canada-France-Hawaii Telescope in November 2013, in the framework of the MaTYSSE large programme. We apply two Zeeman-Doppler imaging codes to the Stokes I and V profiles to reconstruct their brightness and large-scale magnetic field images. The results given by the two imaging codes are in good agreement with each other. TAP 4 shows a large polar cool spot and several intermediate-latitude warm spots on its surface, whereas TAP 40 exhibits very weak variations in its Stokes I profiles suggesting a mostly unspotted photosphere. We detect Zeeman signatures in the Stokes V profiles of both stars. The reconstructed magnetic maps reveal dominantly toroidal fields, which enclose about 60 per cent of the total magnetic energy for both of TAP 4 and TAP 40. Both stars show prominent circular ring features of the azimuthal magnetic field. We derive a solar-like surface differential rotation on TAP 4 from the tomographic modelling. The brightness image of TAP 4 is used to predict the radial velocity jitters induced by its activity. After filtering out the activity jitter, the RMS of its RVs is reduced from 1.7 km s$^{-1}$ to 0.2 km s$^{-1}$, but we do not detect any periodic signals in the filtered RVs of TAP 4, implying that it is unlikely to host a close-in exoplanet more massive than $\sim$3.5 M$_{\rm Jup}$ at 0.1 au.
点击量
待评议
点击量
下载量
评论
