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Full-Text Articles in Astrophysics and Astronomy

Hr 1362: A Test Case For Stellar Dynamo Theories, Klaus G. Strassmeier, Douglas S. Hall, William S. Barksdale, Anthony T. Jusick, Gregory W. Henry Feb 1990

Hr 1362: A Test Case For Stellar Dynamo Theories, Klaus G. Strassmeier, Douglas S. Hall, William S. Barksdale, Anthony T. Jusick, Gregory W. Henry

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An analysis of 11 yr of photometry of HR 1362 = EK Eri has shown a well-established photometric period of 335 days. This confirms an earlier period determination of about 310 days from 3 yr of APT data and is consistent with a new v sin i determination of 2 + or - 2 km/s. Recent Ca II H and K observations show moderately strong H and K emission lines at a flux level of log F prime (K) of about 6.5 ergs sq m/s. If the photometric period is interpreted as the rotation period, this surface flux is more …

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Evolution Of The Starspots In V478 Lyrae From 1980 To 1988, Douglas S. Hall, Gregory W. Henry, James R. Sowell Jan 1990

Evolution Of The Starspots In V478 Lyrae From 1980 To 1988, Douglas S. Hall, Gregory W. Henry, James R. Sowell

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Differential UBV photometry of V478 Lyrae from 1980 to 1988 is given and analyzed as 22 separate light curves, each spanning an average of a dozen rotation cycles. It is shown that spots on V478 Lyr appear to have lifetimes on the order of several months to a year. The amplitude of the light loss produced by a spot can change by a factor of 2 within 20 days. In the only four determinate cases, a spot came into existence at one of the two conjunctions, that is, in the middle of the hemisphere facing (or opposing) the companion star. …

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Chromospheric Ca Ii H And K And H Alpha Emission In Single And Binary Stars Of Spectra Types F6--M2, Klaus G. Strassmeier, Francis C. Fekel, Bernard W. Bopp, Robert C. Dempsey, Gregory W. Henry Jan 1990

Chromospheric Ca Ii H And K And H Alpha Emission In Single And Binary Stars Of Spectra Types F6--M2, Klaus G. Strassmeier, Francis C. Fekel, Bernard W. Bopp, Robert C. Dempsey, Gregory W. Henry

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New observations of the Ca II H and K and H-epsilon region and/or the Balmer H-alpha line are presented for 100 mostly very active stars but also for weak or inactive stars with suspected activity. Correlations between chromospheric activity at Ca II H and K and H-alpha and effective surface temperature and rotation are identified, and several new stars with chromospheric Ca II H and K emission are discovered. No single activity-rotation relation can be derived for all luminosity classes, and there is clear evidence that evolved stars are generally more active than main-sequence stars of the same rotation period. …

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Chromospherically Active Stars. Vii. 39 Ceti=Ay Ceti, Hd185151=V1764 Cygni, And Binary Synchronization, Francis C. Fekel, Joseph J. Eitter Apr 1989

Chromospherically Active Stars. Vii. 39 Ceti=Ay Ceti, Hd185151=V1764 Cygni, And Binary Synchronization, Francis C. Fekel, Joseph J. Eitter

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Improved orbital elements have been determined for 39 Ceti and HD 185151.39 Cet has a circular orbit with an orbital period of 56.82 days, which differs substantially from its rotational period of 75-78 days. An observation of the lithium region of 39 Cet shows that the G5 III component has almost no lithium in its outer atmosphere. HD 185151 has a circular orbit with an orbital period of 40.142 days and has a nearly identical rotational period. The large mass function suggests that the secondary is a late A to mid F type star whose continuum should be visible at …

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The Photometric Variability Of The Chromospherically Active Binary Star Hd 80715, Klaus G. Strassmeier, James T. Hooten, Douglas S. Hall, Francis C. Fekel Jan 1989

The Photometric Variability Of The Chromospherically Active Binary Star Hd 80715, Klaus G. Strassmeier, James T. Hooten, Douglas S. Hall, Francis C. Fekel

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Differential UBVRI photometry of the double-lined BY Dra system HD 80715 (K3 V + K3 V) obtained in December 1987 is presented. The star is found to be a variable with a full amplitude of 0.06 mag in V and a period similar or equal to the orbital period of 3.804 days. The mechanism of the variability is interpreted as rotational modulation due to dark starspots. In an attempt to detect chromospheric activity, high-resolution CCD spectra were obtained at Ca II H and K and at Fe I 6430 A and Ca I 6439 A, the photospheric lines normally used …

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Chromospherically Active Stars. Vi. Hd 136901 = Uv Crb: A Massive Ellipsoidal K Giant Single-Lined Spectroscopic Binary, Francis C. Fekel, J. Davy Kirkpatrick, Xinxing Yang, Klaus G. Strassmeier Jan 1989

Chromospherically Active Stars. Vi. Hd 136901 = Uv Crb: A Massive Ellipsoidal K Giant Single-Lined Spectroscopic Binary, Francis C. Fekel, J. Davy Kirkpatrick, Xinxing Yang, Klaus G. Strassmeier

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The variable star HD 136901 = UV CrB is a chromospherically active K2 III single-lined spectroscopic binary with an orbital period of 18.665 days. It has modest-strength Ca H and K emission and UV features, while H-alpha is a strong absorption feature containing little or no emission. The inclination of the system is 53 + or - 12 deg. The v sin i of the primary is 42 + or - 2 km/s, resulting in a minimum radius of 15.5 + or - 0.8 solar. When compared with the Roche lobe radius, this results in a mass ratio of 2.90 …

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Chromospherically Active Stars. V. Hd 91816=Lr Hya: A Double-Lined By Draconis Type Binary, Francis C. Fekel, Kim Gillies, John L. Africano, Robert Quigley Oct 1988

Chromospherically Active Stars. V. Hd 91816=Lr Hya: A Double-Lined By Draconis Type Binary, Francis C. Fekel, Kim Gillies, John L. Africano, Robert Quigley

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Observations of HD 91816=LR Hya obtained between 1982 and 1988 show it to consist of two nearly identical K0 dwarfs and to have an orbital period of 6.866 days and an orbital eccentricity of 0.014 + or - 0.003. The results suggest that the system has an age equal to or greater than that of the Hyades cluster. A spectroscopic parallax of 0.027 is obtained, and individual minimum masses of 0.55 solar masses each are found, implying an inclination of 61 + or - 3 deg.

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Chromospherically Active Stars. Iv. Hd 178450=V478 Lyr: An Early-Type By Draconis Type Binary, Francis C. Fekel Jan 1988

Chromospherically Active Stars. Iv. Hd 178450=V478 Lyr: An Early-Type By Draconis Type Binary, Francis C. Fekel

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The variable star HD 178450 = V478 Lyr is a chromospherically active G8 V single-lined spectroscopic binary with a period of 2.130514 days. This star has strong ultraviolet emission features and a filled-in Hα absorption line which is variable in strength. It is classified as an early-type BY Draconis system and is similar in many respects to the BY Dra star HD 175742 = V775 Her. The unseen secondary of HD 178450 has a mass of about 0.3 M_sun; and is probably an M2-M3 dwarf. The inclination of the system is 67°±12°. The lithium abundance of the G8 dwarf results …

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Chromospherically Active Stars. Iii. Hd 26337 = Ei Eri: An Rs Cvn Candidate For The Doppler-Imaging Technique, Francis C. Fekel, Robert Quigley, Kim Gillies, John L. Africano Sep 1987

Chromospherically Active Stars. Iii. Hd 26337 = Ei Eri: An Rs Cvn Candidate For The Doppler-Imaging Technique, Francis C. Fekel, Robert Quigley, Kim Gillies, John L. Africano

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The variable star HD 26337 = EI Eri is a chromospherically active G5 IV single-lined spectroscopic binary with a period of 1.94722 days. It has moderate strength Ca II H and K emission and strong ultraviolet emission features, while Hα is a weak absorption feature that is variable in strength. The inclination of the system is 46°±12°, and the unseen secondary is most likely a late K or early M dwarf. The v sin i of the primary is 50±3 km s-1, resulting in a minimum radius of 1.9±0.1 R_sun;. A mass ratio of M1/M2 ≥ 2.6 and a mass …

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Chromospherically Active Stars. Ii. Hd 82558, A Young Single By Draconis Variable., Francis C. Fekel, Bernard W. Bopp, John L. Africano, Bret D. Goodrich, Leigh Hunter Palmer, Robert Quingley, Theodore Simon Nov 1986

Chromospherically Active Stars. Ii. Hd 82558, A Young Single By Draconis Variable., Francis C. Fekel, Bernard W. Bopp, John L. Africano, Bret D. Goodrich, Leigh Hunter Palmer, Robert Quingley, Theodore Simon

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It is presently noted that the HD 82558 chromospherically active star is a young and rapidly rotating K2 V single BY Draconis variable with very strong far-UV emission features and an H-alpha line filled to the continuum level by emission. HD 82558 has constant velocity and is not a member of the Hyades Supercluster. Its light curve behavior, which appears to have been stable for several hundred rotation cycles, is reminiscent of that of the young, rapidly rotating, single K V variable H II 1883 in the Pleiades; this stability may be characteristic of young, single, chromospherically active stars.

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Chromospherically Active Stars. I. Hd 136905., Francis C. Fekel, Douglas S. Hall, John L. Africano, Kim Gillies, Robert Quigley, Robert E. Fried Dec 1985

Chromospherically Active Stars. I. Hd 136905., Francis C. Fekel, Douglas S. Hall, John L. Africano, Kim Gillies, Robert Quigley, Robert E. Fried

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The variable star HD 136905, recently designated GX Librae, is a chromospherically active K1 III single-lined spectroscopic binary with a period of 11.1345 days. It has moderate strength Ca II H and K and ultraviolet emission features, while Hα is strongly in absorption. The inclination of the systems is 58°±17° and the unseen secondary is most likely a G or K dwarf. The v sin i of the primary, 32±2 km s-1, results in a minimum radius of 7.0±0.4 R_sun;. Since the star fills a substantial fraction of its Roche lobe, the double-peaked light curve seen by photometric observers is …

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Mm Herculis: An Eclipsing Binary Of The Rs Cvn Type, James R. Sowell, Douglas S. Hall, Gregory W. Henry, Edward W. Burke Jr., Eugene F. Milone Jan 1983

Mm Herculis: An Eclipsing Binary Of The Rs Cvn Type, James R. Sowell, Douglas S. Hall, Gregory W. Henry, Edward W. Burke Jr., Eugene F. Milone

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Differential photoelectric photometry in V, B, and U has been obtained for the eclipsing binary MM Her, a member of the RS Canum Venaticorum class. The light outside eclipse was Fourier-analyzed to study the wave. The migration and amplitude of the wave and the mean light level of the system now have been monitored from 1976 through 1980. The phase of wave minimum has decreased from 0P.80 to 0P.25, the wave amplitude has varied between 0m.06 and 0m.12, and the mean light level has fluctuated between 0.94 and 0.99. Observations …

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