We present chromospheric activity index SHK measurements for 119 995 F, G and K stars with high signal-to-noise ratio（S/N 〉 80） spectra, extracted from LAMOST DR1 in SDSS g band. The index δS for each of these sta...We present chromospheric activity index SHK measurements for 119 995 F, G and K stars with high signal-to-noise ratio（S/N 〉 80） spectra, extracted from LAMOST DR1 in SDSS g band. The index δS for each of these stars is calculated by the difference between its SHK value and the baseline determined from very inactive stars. The effect of metallicity on measurement of δS varies with stellar Teff. No evident Vaughan-Preston gap appears in our sample. The relation between δS and vertical distance from the Galactic plane is determined for stars with Teff 〈 5500 K. Stars with higher δS tend to be closer to the Galactic plane. Two open clusters in the DR1 sample, M45 and M67, exhibit the expected general trend that δS decays with age.For stars with Teff 〉 5500 K, similar δS levels appear in both young and old cluster stars, which supports Pace＇s suggestion that caution should be exercised when deriving the age of a single star by using its chromospheric activity. Finally, we investigate the relation between δS and the kinematics of our sample.展开更多
We carried out time-series photometric observations in the Re-band of the young, poorly studied open cluster ASCC 5 during November and December, 2012, to search for magnetically active stars, and discovered four ecli...We carried out time-series photometric observations in the Re-band of the young, poorly studied open cluster ASCC 5 during November and December, 2012, to search for magnetically active stars, and discovered four eclipsing binary stars in this field. In order to characterize these four newly discovered binaries, we derived their orbital periods by their times of light minimum, estimated their effective tem- peratures based on their （J - H） colors and analyzed their light curves using the Wilson-Devinney light curve modeling technique. Our analyses reveal that all of them are contact binaries with short orbital periods of less than 0.5 d, with spectral types from late-F to mid-K. Among them, one is a typical A subtype contact binary with a mass ratio around 0.5 and a period of 0.44 d, and one is an H subtype contact binary with a high mass ratio around 0.9 and a short period of about 0.27 d. The other two systems show low amplitudes of light variation （Ant 〈0.11m）; their actual photomet- ric mass ratios could not be determined by the light curve modelings, probably due to their attributes of being partially eclipsing stars. A preliminary analysis for these two systems indicates that both of them are likely to be W subtype contact binaries with low orbital inclinations. In addition, both of these two low amplitude variables show asymmetric distorted light curves （e.g., O＇Connell effect of ARc --~0.02m） during the observing runs, suggesting the presence of starspots on these two systems. More inter- estingly, the one showing a large case of the O＇Connell effect presented a remarkable variation in the shape of the light curve on a time scale of one day, indicating that this star is in a very active state. Therefore, these two stars need spectroscopic observations to precisely determine their parameters, as well as further photometric observations to understand the properties of their magnetic activity, e.g., the evolution of starspots.展开更多
We present a CCD photometry study of a newly discovered active eclipsing binary in the field of open cluster NGC 1348 based on the first time-series photometric observation. From the minimum times, we determined an or...We present a CCD photometry study of a newly discovered active eclipsing binary in the field of open cluster NGC 1348 based on the first time-series photometric observation. From the minimum times, we determined an orbital period of P = 0.691363 d. Among our datasets, the BV（.RI）c light curves obtained in November 2008 were analyzed using the Wilson-Devinney light curve modeling tech- nique. Because of the uncertainty of the membership of this binary in open cluster NGC 1348, we have analyzed the photometric data in two cases with different primary effective temperatures： Case A （T1 = 7750K） and Case B （T1 = 5250K）. Our anal- yses reveal that, for Case A, it is a deep （f 〉 70%）, very low mass ratio （q - 0.096） binary system, indicating that it is now in the late evolution stage of a contact binary; while for Case B, it is a red system with extraordinarily long orbital period with respect to the period-color relation for normal contact binaries, which suggests that this binary has evolved off the main sequence. The well known O＇Connell effect （e.g., AB 0.03 mag） was found in the dataset obtained in November 2008, which could be due to the existence of starspots on the components, therefore the corresponding spot properties （for Case A： hot spot; for Case B： dark spot） were determined using the Wilson-Devinney code. With the purpose of analyzing the dark spot activity for Case B, we compared the light curves derived in different observing runs, and found that a slight change appeared from November to December, 2008, which indicates the evolution of spot activity on at least one component over a time scale of about one month.展开更多
The simultaneous photometric and spectroscopic observations of the spotted G dwarf AP149 in the young open cluster α Persei are analyzed here. We reconstruct the observed light curves with a two-starspot model by mea...The simultaneous photometric and spectroscopic observations of the spotted G dwarf AP149 in the young open cluster α Persei are analyzed here. We reconstruct the observed light curves with a two-starspot model by means of a light curve modeling technique, and find that the active regions shift oppositely along longitude on a time scale of one day. Combining with the observational data obtained by other groups, we discuss the evolution of spotted regions in the photosphere, and find that its starspots evolve not only on a short time scale but also on a long time scale. The pure chromospheric emissions for Ca IIHK and Hβ lines are derived by using the spectral subtraction technique. The variation of Ca IIHK lines＇ excess emission is spatially correlated to the starspot regions. There is no clear rotational modulation for the Hβ line＇s excess emission, probably due to the contamination of prominence emission.展开更多
基金supported by the National Key Basic Research Program of China (973 program, 2014CB845701 and 2014CB845703)the National Natural Science Foundation of China (Grant Nos. U1431106, 11390371, 11233004, 11222326, 11150110135 and 11103034)Support from the US National Science Foundation (AST-1358787) to Embry-Riddle Aeronautical University
文摘We present chromospheric activity index SHK measurements for 119 995 F, G and K stars with high signal-to-noise ratio（S/N 〉 80） spectra, extracted from LAMOST DR1 in SDSS g band. The index δS for each of these stars is calculated by the difference between its SHK value and the baseline determined from very inactive stars. The effect of metallicity on measurement of δS varies with stellar Teff. No evident Vaughan-Preston gap appears in our sample. The relation between δS and vertical distance from the Galactic plane is determined for stars with Teff 〈 5500 K. Stars with higher δS tend to be closer to the Galactic plane. Two open clusters in the DR1 sample, M45 and M67, exhibit the expected general trend that δS decays with age.For stars with Teff 〉 5500 K, similar δS levels appear in both young and old cluster stars, which supports Pace＇s suggestion that caution should be exercised when deriving the age of a single star by using its chromospheric activity. Finally, we investigate the relation between δS and the kinematics of our sample.
基金supported by the National Natural Science Foundation of China (Grants Nos. 10373023 10773027 and 11263001)
文摘We carried out time-series photometric observations in the Re-band of the young, poorly studied open cluster ASCC 5 during November and December, 2012, to search for magnetically active stars, and discovered four eclipsing binary stars in this field. In order to characterize these four newly discovered binaries, we derived their orbital periods by their times of light minimum, estimated their effective tem- peratures based on their （J - H） colors and analyzed their light curves using the Wilson-Devinney light curve modeling technique. Our analyses reveal that all of them are contact binaries with short orbital periods of less than 0.5 d, with spectral types from late-F to mid-K. Among them, one is a typical A subtype contact binary with a mass ratio around 0.5 and a period of 0.44 d, and one is an H subtype contact binary with a high mass ratio around 0.9 and a short period of about 0.27 d. The other two systems show low amplitudes of light variation （Ant 〈0.11m）; their actual photomet- ric mass ratios could not be determined by the light curve modelings, probably due to their attributes of being partially eclipsing stars. A preliminary analysis for these two systems indicates that both of them are likely to be W subtype contact binaries with low orbital inclinations. In addition, both of these two low amplitude variables show asymmetric distorted light curves （e.g., O＇Connell effect of ARc --~0.02m） during the observing runs, suggesting the presence of starspots on these two systems. More inter- estingly, the one showing a large case of the O＇Connell effect presented a remarkable variation in the shape of the light curve on a time scale of one day, indicating that this star is in a very active state. Therefore, these two stars need spectroscopic observations to precisely determine their parameters, as well as further photometric observations to understand the properties of their magnetic activity, e.g., the evolution of starspots.
基金supported by the National Natural Science Foundation of China(Grant Nos. 10373023 and 10773027)grants from the Sik Sik Yuen of Hong Kong,China
文摘We present a CCD photometry study of a newly discovered active eclipsing binary in the field of open cluster NGC 1348 based on the first time-series photometric observation. From the minimum times, we determined an orbital period of P = 0.691363 d. Among our datasets, the BV（.RI）c light curves obtained in November 2008 were analyzed using the Wilson-Devinney light curve modeling tech- nique. Because of the uncertainty of the membership of this binary in open cluster NGC 1348, we have analyzed the photometric data in two cases with different primary effective temperatures： Case A （T1 = 7750K） and Case B （T1 = 5250K）. Our anal- yses reveal that, for Case A, it is a deep （f 〉 70%）, very low mass ratio （q - 0.096） binary system, indicating that it is now in the late evolution stage of a contact binary; while for Case B, it is a red system with extraordinarily long orbital period with respect to the period-color relation for normal contact binaries, which suggests that this binary has evolved off the main sequence. The well known O＇Connell effect （e.g., AB 0.03 mag） was found in the dataset obtained in November 2008, which could be due to the existence of starspots on the components, therefore the corresponding spot properties （for Case A： hot spot; for Case B： dark spot） were determined using the Wilson-Devinney code. With the purpose of analyzing the dark spot activity for Case B, we compared the light curves derived in different observing runs, and found that a slight change appeared from November to December, 2008, which indicates the evolution of spot activity on at least one component over a time scale of about one month.
基金supported by the National Natural Science Foundation of China(Grant Nos.10373023 and 10773027)a grant from the Sik Sik Yuen of Hong Kong,China
文摘The simultaneous photometric and spectroscopic observations of the spotted G dwarf AP149 in the young open cluster α Persei are analyzed here. We reconstruct the observed light curves with a two-starspot model by means of a light curve modeling technique, and find that the active regions shift oppositely along longitude on a time scale of one day. Combining with the observational data obtained by other groups, we discuss the evolution of spotted regions in the photosphere, and find that its starspots evolve not only on a short time scale but also on a long time scale. The pure chromospheric emissions for Ca IIHK and Hβ lines are derived by using the spectral subtraction technique. The variation of Ca IIHK lines＇ excess emission is spatially correlated to the starspot regions. There is no clear rotational modulation for the Hβ line＇s excess emission, probably due to the contamination of prominence emission.
