We study the influence of Stark broadening and stratification effects on Si lines in the rapidl... more We study the influence of Stark broadening and stratification effects on Si lines in the rapidly oscillating (roAp) star 10 Aql, where the Si 6142.48 Å and 6155.13 Å lines are asymmetrical and shifted. First we have calculated Stark broadening parameters using the semiclassical perturbation method for three Si lines: 5950.2 Å, 6142.48 Å and 6155.13 Å. We revised the synthetic spectrum calculation code taking into account both Stark width and shift for these lines. From the comparison of our calculations with the observations we found that Stark broadening + the stratification effect can explain asymmetry of the Si 6142.48 Å and 6155.13 Å lines in the atmospere of roAp star 10 Aql.
Using the semiclassical perturbation method, electron-, proton-, and ionized helium-impact line w... more Using the semiclassical perturbation method, electron-, proton-, and ionized helium-impact line widths and shifts
for the nine Cr spectral lines from the 4p 7 P 0 −4d 7 D multiplet were calculated for a perturber density of 10 14 cm −3 and for temperatures T = 2500−50 000 K. The results were used to investigate the influence of Stark broadening effect in the Cr-rich Ap star β CrB atmosphere on line shapes of these lines. It was found that the contribution of proton and He collisions to the line width and shift is significant and comparable, and is sometimes even larger than electron-impact contribution depending of the electron temperature. Moreover, not only the Stark line width, but also the Stark shift may contribute to the blue as well as to the red asymmetry of the same line depending on the electron-, proton-, and He density in stellar atmosphere. The results were used to investigate the influence of Stark broadening effect on Cr line shapes in the atmosphere of the Cr-rich Ap star β CrB.
Isolated cool white dwarf stars more often have strong magnetic fields than young, hotter white d... more Isolated cool white dwarf stars more often have strong magnetic fields than young, hotter white dwarfs, which has been a puzzle because magnetic fields are expected to decay with time but a cool surface suggests that the star is old. In addition, some white dwarfs with strong fields vary in brightness as they rotate, which has been variously attributed to surface brightness inhomogeneities similar to sunspots, chemical inhomogeneities and other magneto-optical effects. Here we describe optical observations of the brightness and magnetic field of the cool white dwarf WD 1953-011 taken over about eight years, and the results of an analysis of its surface temperature and magnetic field distribution. We find that the magnetic field suppresses atmospheric convection, leading to dark spots in the most magnetized areas. We also find that strong fields are sufficient to suppress convection over the entire surface in cool magnetic white dwarfs, which inhibits their cooling evolution relative...
We study the influence of Stark broadening and stratification effects on Si lines in the rapidl... more We study the influence of Stark broadening and stratification effects on Si lines in the rapidly oscillating (roAp) star 10 Aql, where the Si 6142.48 Å and 6155.13 Å lines are asymmetrical and shifted. First we have calculated Stark broadening parameters using the semiclassical perturbation method for three Si lines: 5950.2 Å, 6142.48 Å and 6155.13 Å. We revised the synthetic spectrum calculation code taking into account both Stark width and shift for these lines. From the comparison of our calculations with the observations we found that Stark broadening + the stratification effect can explain asymmetry of the Si 6142.48 Å and 6155.13 Å lines in the atmospere of roAp star 10 Aql.
Using the semiclassical perturbation method, electron-, proton-, and ionized helium-impact line w... more Using the semiclassical perturbation method, electron-, proton-, and ionized helium-impact line widths and shifts
for the nine Cr spectral lines from the 4p 7 P 0 −4d 7 D multiplet were calculated for a perturber density of 10 14 cm −3 and for temperatures T = 2500−50 000 K. The results were used to investigate the influence of Stark broadening effect in the Cr-rich Ap star β CrB atmosphere on line shapes of these lines. It was found that the contribution of proton and He collisions to the line width and shift is significant and comparable, and is sometimes even larger than electron-impact contribution depending of the electron temperature. Moreover, not only the Stark line width, but also the Stark shift may contribute to the blue as well as to the red asymmetry of the same line depending on the electron-, proton-, and He density in stellar atmosphere. The results were used to investigate the influence of Stark broadening effect on Cr line shapes in the atmosphere of the Cr-rich Ap star β CrB.
Isolated cool white dwarf stars more often have strong magnetic fields than young, hotter white d... more Isolated cool white dwarf stars more often have strong magnetic fields than young, hotter white dwarfs, which has been a puzzle because magnetic fields are expected to decay with time but a cool surface suggests that the star is old. In addition, some white dwarfs with strong fields vary in brightness as they rotate, which has been variously attributed to surface brightness inhomogeneities similar to sunspots, chemical inhomogeneities and other magneto-optical effects. Here we describe optical observations of the brightness and magnetic field of the cool white dwarf WD 1953-011 taken over about eight years, and the results of an analysis of its surface temperature and magnetic field distribution. We find that the magnetic field suppresses atmospheric convection, leading to dark spots in the most magnetized areas. We also find that strong fields are sufficient to suppress convection over the entire surface in cool magnetic white dwarfs, which inhibits their cooling evolution relative...
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Papers by D. Shulyak
star 10 Aql, where the Si 6142.48 Å and 6155.13 Å lines are asymmetrical and shifted. First we have calculated Stark broadening parameters using the semiclassical perturbation method for three Si lines: 5950.2 Å, 6142.48 Å and 6155.13 Å. We revised the synthetic spectrum calculation code taking into account both Stark width and shift for these lines. From the comparison of our calculations with the observations we found that Stark broadening + the stratification effect can explain asymmetry of the Si 6142.48 Å and 6155.13 Å lines in the atmospere of roAp star 10 Aql.
for the nine Cr spectral lines from the 4p 7 P 0 −4d 7 D multiplet were calculated for a perturber density of 10 14 cm −3 and for temperatures T = 2500−50 000 K. The results were used to investigate the influence of Stark broadening effect in the Cr-rich Ap star β CrB atmosphere on line shapes of these lines. It was found that the contribution of proton and He collisions to the line width and shift is significant and comparable, and is sometimes even larger than electron-impact contribution depending of the electron temperature. Moreover, not only the Stark line width, but also the Stark shift may contribute to the blue as well as to the red asymmetry of the same line depending on the electron-, proton-, and He density in stellar atmosphere. The results were used to investigate the influence of Stark broadening effect on Cr line shapes in the atmosphere of the Cr-rich Ap star β CrB.
star 10 Aql, where the Si 6142.48 Å and 6155.13 Å lines are asymmetrical and shifted. First we have calculated Stark broadening parameters using the semiclassical perturbation method for three Si lines: 5950.2 Å, 6142.48 Å and 6155.13 Å. We revised the synthetic spectrum calculation code taking into account both Stark width and shift for these lines. From the comparison of our calculations with the observations we found that Stark broadening + the stratification effect can explain asymmetry of the Si 6142.48 Å and 6155.13 Å lines in the atmospere of roAp star 10 Aql.
for the nine Cr spectral lines from the 4p 7 P 0 −4d 7 D multiplet were calculated for a perturber density of 10 14 cm −3 and for temperatures T = 2500−50 000 K. The results were used to investigate the influence of Stark broadening effect in the Cr-rich Ap star β CrB atmosphere on line shapes of these lines. It was found that the contribution of proton and He collisions to the line width and shift is significant and comparable, and is sometimes even larger than electron-impact contribution depending of the electron temperature. Moreover, not only the Stark line width, but also the Stark shift may contribute to the blue as well as to the red asymmetry of the same line depending on the electron-, proton-, and He density in stellar atmosphere. The results were used to investigate the influence of Stark broadening effect on Cr line shapes in the atmosphere of the Cr-rich Ap star β CrB.