An HR diagram annotated to show several ranges of photometerically determined periods has been co... more An HR diagram annotated to show several ranges of photometerically determined periods has been constructed for the magnetic CP stars whose periods have been determined by the author and his collaborators. The distribution of periods reflects both the initial conditions as well as the subsequent stellar histories. Since the stellar magnetic field does not penetrate the convective core, eventually a shear zone near the core-radiative envelope boundary may develop which produces turbulence and modifies the field. Many, but not all, of the most rapidly rotating mCP stars are close to the ZAMS and some of the least rapidly rotating mCP stars are the furthest from the ZAMS.
Publications of the Astronomical Society of the Pacific, 2005
Differential Strömgren uvby observations obtained with the Four College Automated Photoelectric T... more Differential Strömgren uvby observations obtained with the Four College Automated Photoelectric Telescope (FCAPT) are presented for the magnetic chemically peculiar (mCP) stars 36 Aur, HR 2722, 13 And, and HD 220147. The new data help to better define the light curves. The period for 36 Aur was found to be 14.368 days, close to that for the previous study with FCAPT data. The period for HR 2722 is unchanged, at 2.31523 days. Comparisons between Hipparcos and FCAPT photometry were used to refine the periods individually derived by each source to 1.47931 days for 13 And and to 10.983 days for HD 220147.
Publications of the Astronomical Society of the Pacific, 2008
I obtained additional differential Strömgren uvby observations of four magnetic CP stars HR 1297,... more I obtained additional differential Strömgren uvby observations of four magnetic CP stars HR 1297, 25 Sex, BX Boo, and 49 Her with the Four College Automated Photoelectric Telescope (FCAPT). The seasonal light curves of 25 Sex do not show definite differences. The period of Manfroid & Renson of 4.37900 days is confirmed. The other three stars usually have light curves in phase or nearly so, but there are differences between observing seasons. As the local properties of the photosphere change very slowly with time for these stars that have radiative atmospheres and strong magnetic fields, we are viewing slightly different hemispheres at the same phase. To produce this result, their rotational axes precess about their magnetic axes. For HR 1297, which has moderate amplitudes of variation, the period of Adelman is refined to 15.7505 days. The additional observations of BX Boo do not change the best estimate of its period, 2.88756 days. Although its amplitudes of variation are less than those of HR 1297, there are similar differences between observing seasons. For 49 Her the period of 0.93663 days of Adelman et al. is verified. There are probably small season-to-season light curve differences. Of the mCP stars for which I have FCAPT Strömgren observations, at least 13% exhibit variability among their light curves for different years.
Publications of the Astronomical Society of the Pacific, 2006
The Four College Automated Photoelectric Telescope obtained differential Strömgren uvby observati... more The Four College Automated Photoelectric Telescope obtained differential Strömgren uvby observations of the magnetic chemically peculiar (mCP) stars HD 20629, HR 3724, 45 Leo, and HD 192678. HD 20629, a moderately large amplitude variable, has a period of 2.9934 days. Analyses of this new photometry with published uvby values show that HR 3724 and 45 Leo had periods of 33.984 and 1.44404 days, respectively, for at least 30 yr. New observations of HD 192678 refine the period of this small-amplitude variable to 6.4193 days.
Publications of the Astronomical Society of the Pacific, 1968
... and Seyfert 1959) in conjunction with the distance modulus of 8Φ9 ( Crawford 1961 ) gives the... more ... and Seyfert 1959) in conjunction with the distance modulus of 8Φ9 ( Crawford 1961 ) gives the absolute magnitude Mv = -0φ8. This value is very close to - 0^43 found by Hyland (1967) for λ 4200-Si stars in three southern galactic clusters and - 0φ5 by Sargent and Eggen (1965 ...
Publications of the Astronomical Society of the Pacific, 1985
Color temperatures have been estimated by comparing ultraviolet observations of HgMn and magnetic... more Color temperatures have been estimated by comparing ultraviolet observations of HgMn and magnetic Ap stars with those of normal stars. Ultraviolet data from the OAO-2, ANS, TD-1, and IUE satellites generally give similar results. The values for the normal stars were derived from comparison of fluxes predicted by solar-composition fully line-blanketed model atmospheres with optical region spectrophotometry. The ultraviolet temperatures of the HgMn stars cover a narrower temperature range than do their optical region values. Magnetic Ap stars with similar optical region temperatures can show substantial differences in their ultraviolet color temperatures. This may result from magnetic field configuration and abundance differences.
Publications of the Astronomical Society of the Pacific, 1993
Lines belonging to the companion of the primary star of HR 104 have been found on high-dispersion... more Lines belonging to the companion of the primary star of HR 104 have been found on high-dispersion spectrograms. Both components are extremely sharp lined. By combining data from two quite different observing programs a new orbit has been determined.
Publications of the Astronomical Society of the Pacific, 1994
We extend fine analyses of the B and A stars, gamma Geminorum, 7 Sextantis, HR 4817, and HR 5780 ... more We extend fine analyses of the B and A stars, gamma Geminorum, 7 Sextantis, HR 4817, and HR 5780 using additional spectroscopic data from the Kitt Peak National Observatory (KPNO) coude feed telescope with a TI CCD, camera 5, and grating A, and ATLAS9 model atmospheres. In addition we study HD 60825, which had colors similar to the FHB A
An HR diagram annotated to show several ranges of photometerically determined periods has been co... more An HR diagram annotated to show several ranges of photometerically determined periods has been constructed for the magnetic CP stars whose periods have been determined by the author and his collaborators. The distribution of periods reflects both the initial conditions as well as the subsequent stellar histories. Since the stellar magnetic field does not penetrate the convective core, eventually a shear zone near the core-radiative envelope boundary may develop which produces turbulence and modifies the field. Many, but not all, of the most rapidly rotating mCP stars are close to the ZAMS and some of the least rapidly rotating mCP stars are the furthest from the ZAMS.
Publications of the Astronomical Society of the Pacific, 2005
Differential Strömgren uvby observations obtained with the Four College Automated Photoelectric T... more Differential Strömgren uvby observations obtained with the Four College Automated Photoelectric Telescope (FCAPT) are presented for the magnetic chemically peculiar (mCP) stars 36 Aur, HR 2722, 13 And, and HD 220147. The new data help to better define the light curves. The period for 36 Aur was found to be 14.368 days, close to that for the previous study with FCAPT data. The period for HR 2722 is unchanged, at 2.31523 days. Comparisons between Hipparcos and FCAPT photometry were used to refine the periods individually derived by each source to 1.47931 days for 13 And and to 10.983 days for HD 220147.
Publications of the Astronomical Society of the Pacific, 2008
I obtained additional differential Strömgren uvby observations of four magnetic CP stars HR 1297,... more I obtained additional differential Strömgren uvby observations of four magnetic CP stars HR 1297, 25 Sex, BX Boo, and 49 Her with the Four College Automated Photoelectric Telescope (FCAPT). The seasonal light curves of 25 Sex do not show definite differences. The period of Manfroid & Renson of 4.37900 days is confirmed. The other three stars usually have light curves in phase or nearly so, but there are differences between observing seasons. As the local properties of the photosphere change very slowly with time for these stars that have radiative atmospheres and strong magnetic fields, we are viewing slightly different hemispheres at the same phase. To produce this result, their rotational axes precess about their magnetic axes. For HR 1297, which has moderate amplitudes of variation, the period of Adelman is refined to 15.7505 days. The additional observations of BX Boo do not change the best estimate of its period, 2.88756 days. Although its amplitudes of variation are less than those of HR 1297, there are similar differences between observing seasons. For 49 Her the period of 0.93663 days of Adelman et al. is verified. There are probably small season-to-season light curve differences. Of the mCP stars for which I have FCAPT Strömgren observations, at least 13% exhibit variability among their light curves for different years.
Publications of the Astronomical Society of the Pacific, 2006
The Four College Automated Photoelectric Telescope obtained differential Strömgren uvby observati... more The Four College Automated Photoelectric Telescope obtained differential Strömgren uvby observations of the magnetic chemically peculiar (mCP) stars HD 20629, HR 3724, 45 Leo, and HD 192678. HD 20629, a moderately large amplitude variable, has a period of 2.9934 days. Analyses of this new photometry with published uvby values show that HR 3724 and 45 Leo had periods of 33.984 and 1.44404 days, respectively, for at least 30 yr. New observations of HD 192678 refine the period of this small-amplitude variable to 6.4193 days.
Publications of the Astronomical Society of the Pacific, 1968
... and Seyfert 1959) in conjunction with the distance modulus of 8Φ9 ( Crawford 1961 ) gives the... more ... and Seyfert 1959) in conjunction with the distance modulus of 8Φ9 ( Crawford 1961 ) gives the absolute magnitude Mv = -0φ8. This value is very close to - 0^43 found by Hyland (1967) for λ 4200-Si stars in three southern galactic clusters and - 0φ5 by Sargent and Eggen (1965 ...
Publications of the Astronomical Society of the Pacific, 1985
Color temperatures have been estimated by comparing ultraviolet observations of HgMn and magnetic... more Color temperatures have been estimated by comparing ultraviolet observations of HgMn and magnetic Ap stars with those of normal stars. Ultraviolet data from the OAO-2, ANS, TD-1, and IUE satellites generally give similar results. The values for the normal stars were derived from comparison of fluxes predicted by solar-composition fully line-blanketed model atmospheres with optical region spectrophotometry. The ultraviolet temperatures of the HgMn stars cover a narrower temperature range than do their optical region values. Magnetic Ap stars with similar optical region temperatures can show substantial differences in their ultraviolet color temperatures. This may result from magnetic field configuration and abundance differences.
Publications of the Astronomical Society of the Pacific, 1993
Lines belonging to the companion of the primary star of HR 104 have been found on high-dispersion... more Lines belonging to the companion of the primary star of HR 104 have been found on high-dispersion spectrograms. Both components are extremely sharp lined. By combining data from two quite different observing programs a new orbit has been determined.
Publications of the Astronomical Society of the Pacific, 1994
We extend fine analyses of the B and A stars, gamma Geminorum, 7 Sextantis, HR 4817, and HR 5780 ... more We extend fine analyses of the B and A stars, gamma Geminorum, 7 Sextantis, HR 4817, and HR 5780 using additional spectroscopic data from the Kitt Peak National Observatory (KPNO) coude feed telescope with a TI CCD, camera 5, and grating A, and ATLAS9 model atmospheres. In addition we study HD 60825, which had colors similar to the FHB A
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