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117 results on '"Han, Xianming L."'

1. Radio properties of the OH megamaser galaxy IIZw 096

Author

Wu, Hong, Wu, Zhongzu, Sotnikova, Yu., Chen, Yongjun, Zhang, Bo, Mufakharov, T., Shen, Zhiqiang, Chen, Xi, Mikhailov, A., Mingaliev, M., Han, Xianming L., and Misra, Prabhakar

Subjects
Astrophysics - Astrophysics of Galaxies
Abstract

Based on the two epochs EVN archive data from OH line observations of IIZw 096, we confirm that the high-resolution OH emission in this source mainly comes from two spots (OH1 and OH2) of comp D1 of this merging system. We found no significant variations in the OH line emission. The OH 1665 MHz line emission is detected at about 6 $\sigma$ level in the OH1 region by combining two epoch EVN observations. We found that the comp D1 shows the brightest CO, HCO+ line emission, as well as multi-band radio continuum emission. The environment around D1 shows no clear velocity structure associated with circular motions, making it different from most other OHMs in the literature, which might have been caused by an effect during the merger stage. Meanwhile, we found that the CO emission shows three velocity structures around D1, including the central broad FWHM region, the double peak region where the CO line profile shows two separated peaks, and the region of the high-velocity clouds where the CO line peaks at a high velocity ($\sim$ 11000 \kms). \HI in absorption also show high-velocity clouds around the D1 region, which might be due to inflows caused by the merging of two or more galaxy components. Based on the high-resolution K-band VLA and L-band VLBA observations of the radio continuum emission, we derived the brightness temperature in the range $10^{5}$ K to $10^{6}$ K, which is consistent with other starburst dominant OHM sources in the literature. The multi-band VLA observations show that the radio continuum emission of comp D might also have contributions from free-free emission, besides synchrotron emission. As a concenquence, these results support a starburst origin for the OHMs, without the presence of an AGN., Comment: 11 pages,9 figures, Accepted by A&A

Published
2022
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3. Chromospheric activity on late-type star DM UMa using high-resolution spectroscopic observations

Author

Zhang, LiYun, Pi, QingFeng, Han, Xianming L., Chang, Liang, and Wang, Daimei

Subjects
Astrophysics - Solar and Stellar Astrophysics
Abstract

We present new 14 high-resolution echelle spectra to discuss the level of chromospheric activity of DM UMa in {He I} D3, {Na I} D1, D2, Halpha, and {Ca II} infrared triplet lines (IRT). It is the first time to discover the emissions above the continuum in the {He I} D3 lines on 2015 February 9 and 10. The emission on February 9 is the strongest one ever detected for DM UMa. We analysed these chromospheric active indicators by employing the spectral subtraction technique. The subtracted spectra reveal weak emissions in the {Na I} D1, D2 lines, strong emission in the Halpha line, and clear excess emissions in the {Ca II} IRT lines. Our values for the EW8542/EW8498 ratio are on the low side, in the range of 1.0-1.7. There are also clear phase variations of the level of chromospheric activity in equivalent width (EW) light curves in these chromospheric active lines (especially the Halpha line). These phenomena might be explained by flare events or rotational modulations of the level of chromospheric activity., Comment: 8 pages, 10figures

Published
2016
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14. Properties of PSR J1023+0038 Based on Kepler, TESS, and FAST.

Author

Zhang, Li-yun, Yang, Zilu, Li, Baoda, Su, Tianhao, Misra, Prabhakar, Han, Xianming L., and Long, Liu

Subjects
X-ray binaries, ACCRETION (Astrophysics), MAXIMUM likelihood statistics, LIGHT curves, MAGNETIC reconnection, PULSAR detection, SOLAR flares, DISTRIBUTION (Probability theory)
Abstract

The pulsar system PSR J1023+0038 is a very interesting binary with radio millisecond pulsar and low-mass X-ray binary transitions, which depend on the stellar accretion process. We have used Kepler light curves with 1 minute cadence and TESS light curves with 2 minute cadence to study the flare properties of PSR J1023+0038. We detected 516 flare events in the K2 data and 84 flare events in the TESS survey data. We determined the flare rise and delay times, the flare durations and amplitudes, and flare energies. We obtained a value of the power-law index of 0.359 ± 0.023 between the flare energies and decay times, which is similar to the theoretically predicted value of 1/3. This in turn indicates that PSR J1023+0038 might be exhibiting physical mechanisms described by magnetic reconnection theory. Using the maximum likelihood estimation method, we also calculated the power-law index of the cumulative flare frequency distribution, finding 1.87 ± 0.27 for the Kepler data and 1.74 ± 0.29 for the TESS data. Meanwhile, we reduced six FAST observations of PSR J1023+0038 from 2019–2021 using a standard pulsar search procedure. We report that we detected a prompt signal with a period compatible with that found in previous observations of PSR J1023+0038. However, there are several reasons (statistical, excess DM, pulse shape, etc.) as to why the association is not likely. [ABSTRACT FROM AUTHOR]

Published
2024
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29. Radio properties of the OH megamaser galaxy IIZw 096

Author

Wu, Hong, primary, Wu, Zhongzu, additional, Sotnikova, Yu., additional, Chen, Yongjun, additional, Zhang, Bo, additional, Mufakharov, T., additional, Shen, Zhiqiang, additional, Chen, Xi, additional, Mikhailov, A., additional, Mingaliev, M., additional, Han, Xianming L., additional, and Misra, Prabhakar, additional

Published
2022
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43. Magnetic activity based on LAMOST medium-resolution spectra and the Kepler survey.

Author

Zhang, Li-yun, Long, Liu, Shi, Jianrong, Lu, Hong-peng, Gao, Qi, Han, Xianming L, Wang, Haifeng, Prabhakar, Misra, and Collaboration, LAMOST MRS

Subjects
COOL stars (Astronomy), ROSSBY number, STELLAR chromospheres, STELLAR activity, STELLAR mass, STELLAR rotation
Abstract

Stellar magnetic activity is an interesting phenomenon in late-type stars. We use the medium-resolution spectroscopic observations of 406 069 late-type stars from LAMOST to explore their properties. We perform a statistical analysis on the magnetic activity of the stars and their associated physical parameters. Our samples are cross-matched with other data bases (LAMOST DR5, VSX, and SDSS DR12) to obtain additional observational properties. The equivalent widths (EWs) of Hα lines, an indicator of chromospheric activity, are calculated. According to the EWs of the Hα line, we detect 8816 spectra with apparent Hα emission for a total of 2115 stars among the 2 108 565 spectra analysed. Furthermore, 1521 of these stars show variability in their Hα lines. In addition, we detect 2132 flare events associated with 41 542 stars from the catalogue by cross-matching our LAMOST medium-resolution samples and the Kepler and K2 data bases. We also confirm a weak relationship of the flare amplitude with increasing Rossby number. There is a clear decease in the strength of chromospheric activity (L Hα/ L bol) with increasing rotation period. Moreover, the ratio of the flare energy and stellar luminosity is found to decrease with the stellar mass. [ABSTRACT FROM AUTHOR]

Published
2020
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44. Spectroscopic and photometric studies of four W UMa-type eclipsing binaries – II.

Author

Zhang, Liyun, Zhu, ZhongZhong, Yue, Qiang, Terheide, Rachel, Han, Xianming L, Long, Liu, Lu, Hongpeng, Pi, Qingfeng, and Jiang, Linyiang

Subjects
LIGHT curves, CURVE fitting, MOLECULAR spectra, ECLIPSING binaries
Abstract

We performed photometric and spectroscopic studies on four W Ursae Majoris eclipsing binaries (V384 Ser, AQ Psc, V480 Gem and 2MASS J07095549+3643564). The binaries were observed from 2015 to 2018. The orbital period of V384 Ser showed an interesting cyclic variation overlaying a decreasing period, which may be caused by the light-time effect (LITE) of approximately 2.84 ± 0.01 yr or the magnetic activity cycle of 2.83 ± 0.01 yr. For AQ Psc, we found cyclic variations in its period caused by the LITE either as a result of a tertiary companion or because of a magnetic activity cycle. We derived the cycle of the tertiary component of AQ Psc as 23.87 (±0.14) yr or a magnetic cycle of 44.08 (±1.15) yr. We revised the linear ephemeris of eclipsing binaries V480 Gem and 2MASS J07095549+3643564. We also determined their orbital parameters and star-spot parameters by fitting the light curves. In addition, we found weak excess emissions in the LAMOST spectra of V384 Ser, AQ Psc, V480 Gem and 2MASS J07095549+3643564 in the Hα line, which indicates weak chromospheric activities. [ABSTRACT FROM AUTHOR]

Published
2020
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