The kinematics of about 2000 classical Cepheids of the Milky Way with data from Gaia EDR3 catalog has been studied.For some of these stars,there are line-of-sight velocities.On the basis of the nonlinear rotation mode...The kinematics of about 2000 classical Cepheids of the Milky Way with data from Gaia EDR3 catalog has been studied.For some of these stars,there are line-of-sight velocities.On the basis of the nonlinear rotation model,the parameters of the rotation curve of the Galaxy were determined.The circular linear rotation velocity of the near-solar neighborhood around the Galaxy center was V0=236±3 km s^(−1) for the assumed Sun's galactocentric distance R0=8.1±0.1 kpc.Analysis of residual velocities of Cepheids based on the linear Ogorodnikov–Milne model showed the presence of the following significantly different from zero gradients:∂U/∂x,∂U/∂z,∂V/∂x,∂V/∂z and∂W/∂x,which behave differently depending on the selection radius.The most interesting is the gradient∂W/∂x∼−0.5±0.1 km s^(−1) kpc^(−1)(positive rotation of this star system around the Galactic axis y,Ωy)since the velocities W are free of Galactic rotation.Here we have an indirect influence of various effects leading to a perturbation of the vertical velocities of the Galactic disk stars.Based on a simpler model,a more accurate estimate of this rotation is obtained,Ωy=0.51±0.07 km s^(−1) kpc^(−1).展开更多
In this paper, we study the age and spatial distributions of Cepheids in the Small Magellanic Cloud （SMC） as a function of their ages using data from the OGLE III photometric catalogue. A period - age relation deriv...In this paper, we study the age and spatial distributions of Cepheids in the Small Magellanic Cloud （SMC） as a function of their ages using data from the OGLE III photometric catalogue. A period - age relation derived for Classical Cepheids in the Large Magellanic Cloud （LMC） has been used to find the ages of Cepheids. The age distribution of the SMC Classical Cepheids is found to have a peak at log（Age） ： 8.40 ± 0.10 which suggests that a major star formation event might have occurred in the SMC about 250 4- 50 Myr ago. It is believed that this star forming burst had been triggered by close interactions of the SMC with the LMC and/or the Milky Way. A comparison of the observed spatial distributions of the Cepheids and open star clusters has also been carried out to study the star formation scenario in the SMC.展开更多
A recently found double-mode Cepheid with the shortest known period in our Galaxy and abnormal period ratio, V371 Per, is investigated by linear nonadiabatic pulsation models. V371 Per is likely to be crossing the ins...A recently found double-mode Cepheid with the shortest known period in our Galaxy and abnormal period ratio, V371 Per, is investigated by linear nonadiabatic pulsation models. V371 Per is likely to be crossing the instability strip for the first time, because the mass derived from pulsation models is larger than the evolution mass for the second or higher crossing objects. This result seems to support the conclusion obtained from spectroscopic observation. We also found that models with observed period and period ratio of V371 Per need to have mass and Teff in a narrow range which shifts as heavy element abundance Z changes. We have checked the agreement between Teffranges estimated observationally and derived from pulsation models using observational Z. We found that those ranges overlap marginally. We need more spectroscopic estimations of Teff and [Fe/H], and more photometric monitoring to estimate the evolutional period change for confirmation of our result.展开更多
The theoretical frame developed by A. S. Eddington is used in this paper in order to study the problem of internal structure and stars stability. A new hypothesis is developed that consists of assuming that at early s...The theoretical frame developed by A. S. Eddington is used in this paper in order to study the problem of internal structure and stars stability. A new hypothesis is developed that consists of assuming that at early stage of their evolution, all gaseous stars generate an intense magnetic field whose mission is to contribute to their stability. A simple methodology is shown to calculate the magnitude of the self-generated magnetic field at any point of the star, and diagrams are built for two specific cases, where the way in which this field varies from the center to the surface can be seen. Finally, the problem of the Cepheid type variables is studied obtaining an expression for the oscillation period carried out from the differential equation of the simple harmonic movement in terms of the appropriate parameters of the star.展开更多
Background:Respiratory viruses,such as influenza A and B and respiratory syncytial virus(RSV),pose a severe threat to public health.The precise identification and distinction of these viruses are crucial in clinical l...Background:Respiratory viruses,such as influenza A and B and respiratory syncytial virus(RSV),pose a severe threat to public health.The precise identification and distinction of these viruses are crucial in clinical laboratories.Here,we comparatively evaluated the performance of the Accunome DXcellence assay and the Cepheid GeneXpert assay in the detection of influenza A and B and RSV in nasopharyngeal swab specimens.Methods:Four hundred archived nasopharyngeal swab specimens collected for routine clinical analysis were tested in parallel with the Accunome DXcellence assay and Cepheid GeneXpert assay.RNA standards were serially diluted and tested with the Accunome DXcellence assay to calculate the limit of detection(LOD).Results:The positive and negative percentage agreement between the Accunome DXcellence assay and the Cepheid GeneXpert assay was as follows:94.9%(74/78)and 100%(321/321),respectively,for influenza A;98.1%(104/106)and 100%(293/293),respectively,for influenza B;and 100%(22/22)and 100%(377/377),respectively,for RSV.The LODs of the Accunome DXcellence assay for influenza A and B and RSV were 100,87.5,and 62.5 copies/mL,respectively.Conclusions:The performance of the Accunome DXcellence assay was similar to that of the Cepheid GeneXpert assay in the detection of influenza A,B,and RSV in nasopharyngeal swab specimens,indicating that the Accunome DXcellence assay is a useful diagnostic tool when these viruses are cocirculating.展开更多
文摘The kinematics of about 2000 classical Cepheids of the Milky Way with data from Gaia EDR3 catalog has been studied.For some of these stars,there are line-of-sight velocities.On the basis of the nonlinear rotation model,the parameters of the rotation curve of the Galaxy were determined.The circular linear rotation velocity of the near-solar neighborhood around the Galaxy center was V0=236±3 km s^(−1) for the assumed Sun's galactocentric distance R0=8.1±0.1 kpc.Analysis of residual velocities of Cepheids based on the linear Ogorodnikov–Milne model showed the presence of the following significantly different from zero gradients:∂U/∂x,∂U/∂z,∂V/∂x,∂V/∂z and∂W/∂x,which behave differently depending on the selection radius.The most interesting is the gradient∂W/∂x∼−0.5±0.1 km s^(−1) kpc^(−1)(positive rotation of this star system around the Galactic axis y,Ωy)since the velocities W are free of Galactic rotation.Here we have an indirect influence of various effects leading to a perturbation of the vertical velocities of the Galactic disk stars.Based on a simpler model,a more accurate estimate of this rotation is obtained,Ωy=0.51±0.07 km s^(−1) kpc^(−1).
基金Indian Academy of Sciences(IASc),Bangalore for the financial assistance provided through the IAS-SRFP 2014the grant received under the Indo-Russian project INT/RUS/RFBR/P-219 funded by Department of Science and Technology,New Delhi
文摘In this paper, we study the age and spatial distributions of Cepheids in the Small Magellanic Cloud （SMC） as a function of their ages using data from the OGLE III photometric catalogue. A period - age relation derived for Classical Cepheids in the Large Magellanic Cloud （LMC） has been used to find the ages of Cepheids. The age distribution of the SMC Classical Cepheids is found to have a peak at log（Age） ： 8.40 ± 0.10 which suggests that a major star formation event might have occurred in the SMC about 250 4- 50 Myr ago. It is believed that this star forming burst had been triggered by close interactions of the SMC with the LMC and/or the Milky Way. A comparison of the observed spatial distributions of the Cepheids and open star clusters has also been carried out to study the star formation scenario in the SMC.
文摘A recently found double-mode Cepheid with the shortest known period in our Galaxy and abnormal period ratio, V371 Per, is investigated by linear nonadiabatic pulsation models. V371 Per is likely to be crossing the instability strip for the first time, because the mass derived from pulsation models is larger than the evolution mass for the second or higher crossing objects. This result seems to support the conclusion obtained from spectroscopic observation. We also found that models with observed period and period ratio of V371 Per need to have mass and Teff in a narrow range which shifts as heavy element abundance Z changes. We have checked the agreement between Teffranges estimated observationally and derived from pulsation models using observational Z. We found that those ranges overlap marginally. We need more spectroscopic estimations of Teff and [Fe/H], and more photometric monitoring to estimate the evolutional period change for confirmation of our result.
文摘The theoretical frame developed by A. S. Eddington is used in this paper in order to study the problem of internal structure and stars stability. A new hypothesis is developed that consists of assuming that at early stage of their evolution, all gaseous stars generate an intense magnetic field whose mission is to contribute to their stability. A simple methodology is shown to calculate the magnitude of the self-generated magnetic field at any point of the star, and diagrams are built for two specific cases, where the way in which this field varies from the center to the surface can be seen. Finally, the problem of the Cepheid type variables is studied obtaining an expression for the oscillation period carried out from the differential equation of the simple harmonic movement in terms of the appropriate parameters of the star.
文摘Background:Respiratory viruses,such as influenza A and B and respiratory syncytial virus(RSV),pose a severe threat to public health.The precise identification and distinction of these viruses are crucial in clinical laboratories.Here,we comparatively evaluated the performance of the Accunome DXcellence assay and the Cepheid GeneXpert assay in the detection of influenza A and B and RSV in nasopharyngeal swab specimens.Methods:Four hundred archived nasopharyngeal swab specimens collected for routine clinical analysis were tested in parallel with the Accunome DXcellence assay and Cepheid GeneXpert assay.RNA standards were serially diluted and tested with the Accunome DXcellence assay to calculate the limit of detection(LOD).Results:The positive and negative percentage agreement between the Accunome DXcellence assay and the Cepheid GeneXpert assay was as follows:94.9%(74/78)and 100%(321/321),respectively,for influenza A;98.1%(104/106)and 100%(293/293),respectively,for influenza B;and 100%(22/22)and 100%(377/377),respectively,for RSV.The LODs of the Accunome DXcellence assay for influenza A and B and RSV were 100,87.5,and 62.5 copies/mL,respectively.Conclusions:The performance of the Accunome DXcellence assay was similar to that of the Cepheid GeneXpert assay in the detection of influenza A,B,and RSV in nasopharyngeal swab specimens,indicating that the Accunome DXcellence assay is a useful diagnostic tool when these viruses are cocirculating.
