arXiv subjects

Dong-Yang Gao

Publications and source records attributed to Dong-Yang Gao.

14 recordsLinked to original sources

arXiv2026

Flare-driven habitability: Expanding life's potential around low-mass stars

The traditional definition of the circumstellar habitable zone (HZ) focuses on liquid water, but neglects the crucial role of ultraviolet (UV) radiation in prebiotic chemistry. Low-mass stars typically emit insufficient UV radiation for photochemistry throughout the liquid water HZs during quiescent states. However, frequent flares can provide substantial UV fluxes, potentially fostering habitable conditions. We refine the concept of a UV habitable zone (UV-HZ) by incorporating a temperature-dependent model for RNA precursor synthesis. Furthermore, we explore a parameterized spectral energy distribution model and adopt an empirical flare frequency distribution for flares on different stars to quantify their UV contribution. Applying this framework to different flaring stars, we find the UV-HZ around low-mass stars can extend to inner regions, and overlap with the traditional HZ in wide ranges. Apply the analysis to 9 planets around Kepler flaring stars, three planets are located within both the refined UV-HZ and liquid water habitable zone (LW-HZ) without causing ozone depletion. Our findings highlight the significant role of flares in expanding the potential for life around low-mass stars, offering a revised perspective on exoplanet habitability criteria.

astro-ph.EP↗

arXiv2025

Spectroscopic and Decade-long Photometric Observations of the Contact Binary V2790 Ori: Evidence for a Brown Dwarf Companion and a Solar-like Magnetic Activity Cycle

We present 22 sets of light curves and one radial velocity curve for the W UMa-type total eclipse contact binary system V2790 Ori, derived by combining all available public photometric data, the photometric data in previous studies, and our own spectroscopic and decade-long photometric observations. Our simultaneous analysis of the light curves and radial velocity curve shows that V2790 Ori is a W-subtype contact binary with a mass ratio of $q = 0.322(\pm0.001)$ and a shallow contact degree of $14.8(\pm0.6)\%$. The orbital period analysis based on 445 eclipsing minima reveals a secular decrease at a rate of $\dot P = -3.18 (\pm 0.75) \times 10^{-8}\mathrm{d~yr^{-1}}$, superimposed with a cyclic variation with an amplitude of $A = 8.98 (\pm 2.19) \times 10^{-4}~\mathrm{d}$ and a period of $ P_3 = 7.44 (\pm 0.52)~\mathrm{yr}$. The secular decrease is caused by AML via magnetic braking, while the cyclic period variation is explained by the light-travel time effect due to a third body, which is likely to be a brown dwarf. Furthermore, our analysis indicates a mass transfer from the more massive component to the less massive one at a rate of $1.22(\pm0.29) \times 10^{-8}~\mathrm{M_{\odot}~yr^{-1}}$. A model with a cool spot on each component was adopted to fit the O'Connell effect observed in the light curves. Since the O'Connell effect varies over time, we identified a solar-like magnetic activity cycle with a period of approximately 5.4 yr by analyzing the magnitude difference ($Δm$) at the two light maxima and the O'Connell effect ratio. In addition, evolutionary analysis suggests that V2790 Ori is a newly formed contact binary that evolved from a detached phase into the present contact configuration.

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arXiv2025

Optical Flares Detected on a Contact Binary: The First Photometric and Spectroscopic Analysis of a Long-period Low Mass Ratio Contact Binary HAT 307-0007476

This paper presents the photometric and spectroscopic analysis of a long-period totally eclipsing contact binary (HAT 307-0007476) for the first time. This system is a low mass ratio ($q\sim0.114$) and medium contact binary ($f\sim37.1\%$). Two flare events were detected in multiple bands observations in December 2022. The interval between the two flare events is 4 days. The average duration of these two flares is about 2289s. Both the two flares achieve the energy levels of superflares. The excess emission of the H$_α$ line in the LAMOST spectra of this object was analyzed, indicating its chromospheric activity. The $O-C$ diagram showed a long-term orbital period increase, which is due to the mass transfer between the two component stars. We conclude that HAT 307-0007476 is currently in a stable region based on both $J_{spin}/J_{orb}$ and the comparison between the instability parameters and its current values.

astro-ph.SR↗

arXiv2024

Search for and analysis of eclipsing binaries in the LAMOST Medium-Resolution Survey field. I. RA: $\textbf{23}^h$$\textbf{01}^m$$\textbf{51}^s$, Dec: +34$^\circ$36$^\prime$45$^{\prime \prime}$

Eclipsing binaries (EBs) play an important astrophysical role in studying stellar properties and evolution. By analyzing photometric data in the LAMOST Medium-Resolution Survey field, RA: $23^h$$01^m$$51.00^s$, Dec: +34$^\circ$36$^\prime$45$^{\prime \prime}$, 48 EBs are detected and 2 are newly discovered. This specific field has been observed 52 times by the LAMOST Medium-Resolution Survey DR 9, which facilitates a comprehensive analysis of the EBs. For EBs with LAMOST medium-resolution spectra, radial velocity curves were obtained, and their precise orbital parameters were determined by simultaneously analyzing photometric light curves and radial velocity curves. For the other EBs with only photometric light curves, we used the q-search or the temperature ratio method to determine their initial mass ratios and then determined the orbital parameters. It is found that 15 EBs belong to detached systems, 1 to semi-detached systems, and 32 to contact systems. Based on the O-C analysis for 26 EBs with sufficient eclipsing times, we found a long-term decrease in the orbital period of 11 EBs and a continuous increase of 5 EBs, which are due to the material transfer between the two components. The O-C curve of 1 EB shows a distinct periodic variation, which is caused by the light travel time effect, and the third body is likely to be a black hole. By applying the spectral subtraction method to 13 EBs with LAMOST medium-resolution spectra, 10 systems exhibit distinct H$α$ emission lines, in which 1 system exhibits double-peaked lines near phases 0.25 and 0.75, implying strong chromospheric activity. In the mass-luminosities and mass-radius distributions, most of the more massive components are less evolved than the less massive ones.

astro-ph.SR↗

arXiv2024

Detection of the lowest mass ratio contact binary in the universe: TYC 3801-1529-1

This paper presents the first analysis of the contact binary TYC 3801-1529-1. We observed four sets of multiple bands complete light curves and one set of radial velocity curve of the primary component. Based on a simultaneous investigation of our observed and TESS light curves and the radial velocity curve, we found that TYC 3801-1529-1 is an extremely low-mass-ratio, medium contact binary with $q=0.0356$, with the contribution of the third light at a level of about 10\%. Its mass ratio is lower than V1187 Her, making TYC 3801-1529-1 the lowest mass-ratio contact binary ever found in the universe. The light curves observed in 2022 are asymmetric, which is aptly explained by a hot spot on the primary component. A 16-year eclipse timings analysis indicates a secular increase orbital period with a rate of dp/dt$=7.96(\pm0.35)\times10^{-7}$ d yr$^{-1}$. We studied the stability of this target and identified that not only the value of $J_{spin}/J_{orb}$, but also the mass ratio surpass the unstable boundary. Hence, TYC 3801-1529-1 presents a challenge to theoretical research and ought to be considered a progenitor of a contact binary merger.

astro-ph.SR↗

arXiv2023

Correcting Stellar Flare Frequency Distributions Detected by TESS and Kepler

The habitability of planets is closely connected with the stellar activity, mainly the frequency of flares and the distribution of flare energy. Kepler and TESS find many flaring stars are detected via precise time-domain photometric data, and the frequency and energy distribution of stellar flares on different types of stars are studied statistically. However, the completeness and observational bias of detected flare events from different missions (e.g. Kepler and TESS) vary a lot. We use a unified data processing and detection method for flares events based on the light curve from Kepler and TESS. Then we perform injection and recovery tests in the original light curve of each star for each flare event to correct the completeness and energy of flares. Three samples of flaring stars are selected from Kepler and TESS, with rotating periods from 1 to $\sim$ 5 days. Adopting a hot-blackbody assumption, our results show that the cumulative flare frequency distributions (FFDs) of the same stars in Kepler and TESS bands tend to be consistent after correction, revealing a more natural flaring frequency and energy distribution. Our results also extend the low-energy limit in cumulative FFD fitting to $10^{31.5-33}$ erg on different types of stars. For solar-type stars, the average power-law index of cumulative FFD ($α_{\rm cum}$) is $-0.84$, which indicates that low-energy flares contribute less to the total flare energy. With a piecewise correlation between $α_{\rm cum}$ and $T_{\rm eff}$, $α_{\rm cum}$ first rises with $T_{\rm eff}$ from M2 to K1 stars, then slightly decreases for stars hotter than K1.

astro-ph.SR↗

arXiv2022

The First Photometric and Orbital Period Investigation of an Extremely Low Mass Ratio Contact Binary with a Sudden Period Change, TYC 4002-2628-1

Photometric observations for the totally eclipsing binary system TYC 4002-2628-1, were obtained between November 2020 and November 2021. To determine the stellar atmospheric parameters, a spectral image was taken with the 2.16 m telescope at National Astronomical Observatory of China (NAOC). TYC 4002-2628-1 is a low-amplitude (about 0.15 mag for $V$ band), short-period (0.3670495 d), contact eclipsing binary with a total secondary eclipse. Intrinsic light curve variations and the reversal of the O'Connell effect are detected in the light curves, which may be due to spot activity. Based on the photometric solutions derived from the multi-band time series light curves, TYC 4002-2628-1 is an extremely low mass ratio contact binary with a mass ratio of $q\sim$ 0.0482 and a fill-out factor of $f\sim5\%$. By analyzing the $O-C$ variations, we find that its orbital period remains unchanged when BJD < 2458321 . Then the orbital period changed suddenly around BJD 2458743 and has an increasing rate of $dP/dt=1.62\times{10^{-5}}day\cdot yr^{-1}=140$ $second\cdot century^{-1}$ . If confirmed, TYC 4002-2628-1 would be the contact binary with the highest orbital period increasing rate so far. By investigating the ratio of orbital angular momentum to the spin angular momentum ( $J_{orb}$/$J_{spin}$ $<3$) , the instability mass ratio ($q_{inst}/q=1.84$) and the instability separation ($A_{inst}/A=1.35$), TYC 4002-2628-1 can be regarded as a merger candidate.

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arXiv2021

Two contact binaries with mass ratios close to the minimum mass ratio

The cut-off mass ratio is under debate for contact binaries. In this paper, we present the investigation of two contact binaries with mass ratios close to the low mass ratio limit. It is found that the mass ratios of VSX J082700.8+462850 (hereafter J082700) and 1SWASP J132829.37+555246.1 (hereafter J132829) are both less than 0.1 ($q\sim0.055$ for J082700, and $q\sim0.089$ for J132829). J082700 is a shallow contact binary with a contact degree of $\sim$19%, and J132829 is a deep contact system with a fillout factor of $\sim$70%. The $O-C$ diagram analysis indicated that both the two systems manifest long-term period decrease. In addition, J082700 exhibits a cyclic modulation which is more likely resulted from Applegate mechanism. In order to explore the properties of extremely low mass ratio contact binaries (ELMRCBs), we carried out a statistical analysis on contact binaries with mass ratios of $q\lesssim0.1$ and discovered that the values of $J_{spin}/J_{orb}$ of three systems are greater than 1/3. Two possible explanations can interpret this phenomenon. One is that some physical processes, unknown to date, are not considered when Hut presented the dynamically instability criterion. The other is that the dimensionless gyration radius ($k$) should be smaller than the value we used ($k^2=0.06$). We also found that the formation of ELMRCBs possibly has two channels. The study of evolutionary states of ELMRCBs reveals that their evolutionary states are similar with those of normal W UMa contact binaries.

astro-ph.SR↗

arXiv2021

Spectroscopic evidence for a large spot on the dimming Betelgeuse

During October 2019 and March 2020, the luminous red supergiant Betelgeuse demonstrated an unusually deep minimum of its brightness. It became fainter by more than one magnitude and this is the most significant dimming observed in the recent decades. While the reason for the dimming is debated, pre-phase of supernova explosion, obscuring dust, or changes in the photosphere of the star were suggested scenarios. Here, we present spectroscopic studies of Betelgeuse using high-resolution and high signal-to- noise ratio near-infrared spectra obtained at Weihai Observatory on four epochs in 2020 covering the phases of during and after dimming. We show that the dimming episode is caused by the dropping of its effective temperature by at least 170 K on 2020 January 31, that can be attributed to the emergence of a large dark spot on the surface of the star.

astro-ph.SR↗

arXiv2021

Photometric study and absolute parameters estimation of six totally eclipsing contact binaries

High precision CCD observations of six totally eclipsing contact binaries were presented and analyzed. It is found that only one target is an A-type contact binary (V429 Cam), while the others are W-type contact ones. By analyzing the times of light minima, we discovered that two of them exhibit secular period increase while three manifest long-term period decrease. For V1033 Her, a cyclic variation superimposed on the long-term increase was discovered. By comparing the Gaia distances with those calculated by the absolute parameters of 173 contact binaries, we found that Gaia distance can be applied to estimate absolute parameters for most contact binaries. The absolute parameters of our six targets were estimated by using their Gaia distances. The evolutionary status of contact binaries was studied, we found that the A- and W- subtype contact binaries may have different formation channels. The relationship between the spectroscopic and photometric mass ratios for 101 contact binaries was presented. It is discovered that the photometric mass ratios are in good agreement with the spectroscopic ones for almost all the totally eclipsing systems, which is corresponding to the results derived by Pribulla et al. and Terrell & Wilson.

astro-ph.SR↗

arXiv2019

Contact binaries at the short period cut-off I. statistics and the first photometric investigations of ten totally eclipsing systems

The period distribution of contact binaries exhibits a very sharp short period cut-off at 0.22 days. In order to provide valuable information on this short period limit, we observed ten totally eclipsing contact binaries with orbital periods near this cut-off. By detailed analysis using W-D code, we determined that two of these systems are A-subtype contact binaries while the others are W-subtype contact binaries and all the targets show shallow contact configurations. Half of the targets exhibit stellar spot activity and four of them have third light. A statistical work on well studied USPCBs was carried out, and physical parameters of fifty-five USPCBs were obtained. Some common properties for these systems were derived. Due to the study of the period-color diagram of USPCBs, we found that the period-color relation of USPCBs is different from other W UMa type contact binaries and USPCBs are metal poor old stars. In addition, the evolutionary states of these systems were discussed by constructing the color-density diagram. We derived that the evolutionary states of the two components of USPCBs show identical characteristics of other contact binaries despite slower evolutionary status caused by smaller mass. We suggested that both the fully convective limit claimed by Rucinski (1992) and the AML theory recommended by Stepien (2006) can produce the short period cut-off and a tertiary companion is very important during the formation of the short period contact binaries by removing angular momentum from the host eclipsing pairs under certain circumstances.

astro-ph.SR↗

arXiv2016

WES - Weihai Echelle Spectrograph

The Weihai Echelle Spectrograph (WES) is the first fiber-fed echelle spectrograph for astronomical observation in China. It is primarily used for chemical abundance and asteroseismology studies of nearby bright stars, as well as radial velocity detections for exoplanets. The optical design of WES is based on the widely demonstrated and well-established white-pupil concept. We describe the WES in detail and present some examples of its performance. A single exposure echelle image covers the spectral region 371-1,100 nm in 107 spectral orders over the rectangular CCD. The spectral resolution $R=λ/Δλ$ changes from 40,600 to 57,000 through adjusting the entrance slit width from full to 2.2 pixels sampling at the fiber-exit. The limiting magnitude scales to $V=8$ with a signal-to-noise ratio (SNR) of more than 100 in $V$ for an hour exposure, at the spectral resolution R$\approx$40,000 in the median seeing of 1.7$^{\prime\prime}$ at Weihai Observatory (WHO) for the 1-meter telescope. The radial velocity (RV) measurement accuracy of WES is estimated to be $<$10 m/s in 10 months (302 days) and better than 15 m/s in 4.4 years (1,617 days) in the recent data processing.

astro-ph.IM↗

arXiv2016

The Night Sky Spectrum of Xinglong Observatory: Changes from 2004 to 2015

We present spectroscopic measurements on the night sky of Xinglong Observatory for a period of 12 years from 2004 to 2015. The spectra were obtained on moonless clear nights using the OMR spectrograph mounted on a 2.16-m reflector with a wavelength coverage of 4000-7000A. The night sky spectrum shows the presence of emission lines from Hg I and Na I due to local artificial sources, along with the atmospheric emission lines, i.e., O I and OH molecules, indicating the existence of light pollution. We have monitored the night sky brightness during the whole night and found some decrement in the sky brightness with time, but the change is not significant. Also, we monitored the light pollution level in different azimuthal directions and found that the influence of light pollution from the direction of Beijing is stronger compared with that from the direction of Tangshan and other areas. An analysis of night sky spectra for the entire data set suggested that the zenith sky brightness of Xinglong Observatory has brightened by about 0.5 mag arcsec -2 in the V and B bands from 2004 to 2015. We recommend consecutive spectroscopic measurements of the night sky brightness at Xinglong Observatory in the future, not only for monitoring but also for scientific reference.

astro-ph.IM↗

arXiv2014

Sky Brightness at Weihai Observatory of Shandong University

In this paper, a total of about 28000 images in $V$ and $R$ band obtained on 161 nights using the one-meter optical telescope at Weihai Observatory (WHO) of Shandong University since 2008 to 2012 have been processed to measure the sky brightness. It provides us with an unprecedented database, which can be used to study the variation of the sky brightness with the sky position, the moonlight contribution, and the twilight sky brightness. The darkest sky brightness is about 19.0 and 18.6 $mag$ $arcsec^{-2}$ in $V$ and $R$ band, respectively. An obvious darkening trend is found at the first half of the night at WHO, and the variation rate is much larger in summer than that in other seasons. The sky brightness variation depends more on the azimuth than on the altitude of the telescope pointing for WHO. Our results indicate that the sky brightness at WHO is seriously influenced by the urban light.

astro-ph.IM↗