arXiv subjects

Yanhui Chen

Publications and source records attributed to Yanhui Chen.

25 records · Page 2Linked to original sources

arXiv2020

Application of a screened Coulomb potential in fitting the DAV star HS 0507+0434B

We use \texttt{WDEC} to evolve grids of DAV star models adopting the element diffusion scheme with pure and screened Coulomb potential effect. The core compositions are thermonuclear burning results which are derived from \texttt{MESA}. \texttt{MESA} yields composition profiles that the version of WDEC used in this work could not accommodate (most notably the presence of helium in the core of the model). According to the theory of rotational splitting, Fu et al. identified 6 triplets for a DAV star HS 0507+0434B based on 206\,h photometric data. The grids of DAV star models are used to fit the 6 reliable $m$ = 0 modes. When adopting the screened Coulomb potential, we obtain a best fitting model of log($M_{\rm He}/M_{\rm *}$) = -3.0, log($M_{\rm H}/M_{\rm *}$) = -6.1, $T_{\rm eff}$ = 11790\,K, $M_{\rm *}$ = 0.625\,$M_{\odot}$, log$g$ = 8.066, and $σ_{RMS}$ = 2.08\,s. Compared with adopting the pure Coulomb potential, the value of $σ_{RMS}$ is improved by 34\%. The study may provide a new method for the research of mode trapping properties.

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arXiv2019

Asteroseismology of the DOV star PG 1159-035

Grids of DOV star models are evolved by \texttt{WDEC} with fixed atmospheric constituent to the spectral values of $X_{C}/X_{He}/X_{O}$ = 50/33/17. The core compositions are from white dwarf models at highest $T_{eff}$ evolved by \texttt{MESA}. The eigenfrequencies are calculated and used to fit the observed modes. Based on 264.1 hours of photometric observations on PG 1159-035, Winget et al. identified 125 individual frequencies. Costa et al. identified 198 pulsation modes for PG 1159-035 according to the WET photometric data from 1983, 1985, 1989, and 2002. Both of them derived frequency splitting values of $δσ_{l=1}$ $\sim$ 4.2\,$μ$Hz and $δσ_{l=2}$ $\sim$ 6.9\,$μ$Hz. According to the values of $δσ_{l=1}$ and $δσ_{l=2}$, 20 triplets and 9 quintuplets are selected and used to constrain the fitting models. Our optimal model has $T_{eff}$ = 129000\,K, $M_{*}$ = 0.63\,$M_{\odot}$, log$g$ = 7.59, log($M_{\rm env}/M_{*}$) = -5.0, and $σ_{RMS}$ = 1.97\,s. The values of $T_{eff}$ and log$g$ are consistent with that values of Córsico et al.. The calculated modes of minimum rate of period change correspond to modes with maximum kinetic energy distributed in the envelope. The observed rates of period change with positive and negative values can also be partially reproduced. In particular, there are negative rates of period change for the calculated modes from our optimal model, which is not found in previous work.

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arXiv2017

Application of screened Coulomb potential in fitting DBV star PG 0112+104

With 78.7 days of observations for PG 0112+104, a pulsating DB star, from Campaign 8 of $Kepler$ 2 mission, Hermes et al. made a detailed mode identification. A reliable mode identification, with 5 $l$ = 1 modes, 3 $l$ = 2 modes, and 3 $l$ = 1 or 2 modes, was identified. Grids of DBV star models are evolved by \texttt{WDEC} with element diffusion effect of pure Coulomb potential and screened Coulomb potential. Fitting the identified modes of PG 0112+104 by the calculated ones, we studied the difference of element diffusion effect between adopting pure Coulomb potential and screened Coulomb potential. Our aim is to reduce the fitting error by studying new input physics. The starting models including their chemical composition profile are from white dwarf models evolved by \texttt{MESA}. They were calculated following the stellar evolution from the main sequence to the start of the white dwarf cooling sequences. The optimal parameters are basically consistent with that of previous spectroscopic and asteroseismological studies. The pure and screened Coulomb potential lead to different composition profiles of the C/O-He interface area. High $k$ modes are very sensitive to the area. However, most of the observed modes for PG 0112+104 are low $k$ modes. The $σ_{RMS}$ taking the screened Coulomb potential is reduced by 4\% compared with taking the pure Coulomb potential when fitting the identified low $k$ modes of PG 0112+104. Fitting the $Kepler$ 2 data with our models improved the $σ_{RMS}$ of the fit by 27\%.

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arXiv2016

Exploring the helium core of the delta Scuti star CoRoT 102749568 with asteroseismology

Based on regularities in rotational splittings, we seek possible multiplets for the observed frequencies of CoRoT 102749568. Twenty-one sets of multiplets are identified, including four sets of multiplets with $l=1$, nine sets of multiplets with $l=2$, and eight sets of multiplets with $l=3$. In particular, there are three complete triplets ($f_{10}$, $f_{12}$, $f_{14}$), ($f_{31}$, $f_{34}$, $f_{35}$), and ($f_{41}$, $f_{43}$, $f_{44}$). The rotational period of CoRoT 102749568 is estimated to be $1.34^{+0.04}_{-0.05}$ days. When doing model fittings, three $l=1$ modes ($f_{12}$, $f_{34}$, and $f_{43}$) and the radial first overtone $f_{13}$ are used. Our results shows that the three nonradial modes ($f_{12}$, $f_{34}$, and $f_{43}$) are mixed modes, which mainly provide constraints on the helium core. The radial first overtone $f_{13}$ mainly provides constraint on the stellar envelope. Hence the size of the helium core of CoRoT 102749568 is determined to be $M_{\rm He}$ = 0.148 $\pm$ 0.003 $M_{\odot}$ and $R_{\rm He}$ = 0.0581 $\pm$ 0.0007 $R_{\odot}$. The fundamental parameters of CoRoT 102749568 are determined to be $M$ = 1.54 $\pm$ 0.03 $M_{\odot}$, $Z=$ 0.006, $f_{\rm ov}$ = 0.004 $\pm$ 0.002, $\log g$ = 3.696 $\pm$ 0.003, $T_{\rm eff}$ = 6886 $\pm$ 70 K, $R$ = 2.916 $\pm$ 0.039 $R_{\odot}$, and $L$ = 17.12 $\pm$ 1.13 $L_{\odot}$.

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arXiv2016

Asteroseismology of the DBV star CBS 114

Asteroseismology is an unique and powerful tool to detect the internal structure of stars. CBS 114 is the sixth known pulsating DBV star. It was observed by Handler, Metcalfe, \& Wood at South African Astronomical Observatory over 3 weeks in 2001. Then, it was observed by Metcalfe et al. at Bohyunsan Optical Astronomy Observatory and McDonald Observatory respectively for 7 nights in 2004. Totally 2 triplets, 4 doublets, and 5 singlets were identified. The frequency splitting values are very different, from 5.2 $μ$Hz to 11.9 $μ$Hz, which may reflect differential rotations. We evolve grids of white dwarf models by \texttt{MESA}. Cores, added with He/C envelopes, of those white dwarf models are inserted into \texttt{WDEC} to evolve grids of DBV star models. With those DBV star models, we calculate eigenperiods. Those calculated periods are used to fit observed periods. A best-fitting model is selected. The parameters are $T_{eff}$ = 25000 K, $M_{*}$ = 0.740 $M_{\odot}$, and log($M_{He}/M_{*}$) = -4.5. With the massive stellar mass, the effective temperature is close to previous spectroscopic result. In addition, kinetic energy distributions are calculated for the best-fitting model. We find that the observed modes with large frequency splitting values are fitted by the calculated modes with much kinetic energy distributed in C/O core. After preliminary analysis, we suggest that the C/O core may rotate at least 2 times faster than the helium layer for CBS 114.

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arXiv2016

The dispersion of period spacing for DAV stars

Three groups of DAV star models are evolved with time-dependent element diffusion by \texttt{WDEC}. The core compositions of these models are directly from white dwarf models evolved by \texttt{MESA}, which are results of thermonuclear burning. Based on these DAV star models, we try to study the dispersion of period spacing. The thickness of hydrogen atmosphere can seriously affect the deviation degree of minimal period spacings. The minimal period spacings dominate the dispersion of period spacing. The thinner the hydrogen atmosphere, basically, the more dispersive the period spacing. Standard deviations are used to analyze the dispersion of period spacing. Studying the dispersion of period spacing on a DAV star KUV03442+0719 preliminarily, we suggest that log($M_{\rm H}/M_{*}$) is from -8.5 to -5.5. In addition, modes partly trapped in C/O core are found based on those DAV star models. The identified modes and average period spacings indicate that KUV03442+0719 may be the first star to 'observe' modes partly trapped in C/O core.

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arXiv2014

Asteroseismology of DAV star EC14012-1446, mode identification and model fittings

EC14012-1446 was observed by Handler et al. in April 2004, June 2004, May 2005, and April 2007, and by Provencal et al. in 2008. We review the observations together and obtain 34 independent frequencies. According to the frequency splitting and the asymptotic period spacing law, we identify 6 $l$=1 modes, 4 $l$=2 modes, 5 $l$=3 modes, 10 $l$=1 or 2 modes. Grids of white dwarf models are generated by WDEC with H, He, C, O diffusion in a four-parameter space. The core compositions are directly from white dwarf models generated by MESA. The best-fitting model has $M_{*}$=0.710\,$M_{\odot}$, $T_{\rm eff}$=12200\,K, log($M_{\rm He}/M_{*}$)=-2.5, log($M_{\rm H}/M_{*}$)=-7.0, log\,$g$=8.261, and $ϕ$=3.185\,s. There are 4, 2, and 1 modes identified as trapped in H envelope for observed $l$=1, 2, and 3 modes, respectively. Trapped modes jump the queue of uniform period spacing.

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