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Articles 271 - 287 of 287

Full-Text Articles in Astrophysics and Astronomy

Line Profile Asymmetries In Chromospherically Active Stars, Robert C. Dempsey, Bernard W. Bopp, Klaus G. Strassmeier, Arno F. Granados, Gregory W. Henry, Douglas S. Hall Jun 1992

Line Profile Asymmetries In Chromospherically Active Stars, Robert C. Dempsey, Bernard W. Bopp, Klaus G. Strassmeier, Arno F. Granados, Gregory W. Henry, Douglas S. Hall

Information Systems and Engineering Management Research Publications

A powerful, new probe of chromospheric activity, cross-correlation, has been developed and applied to a variety of stars. In this particular application, an entire CCD spectrum of an active star is correlated with the spectrum of a narrow-line, inactive star of similar spectral type and luminosity class. Using a number of strong lines in this manner enables the detection of absorption profile asymmetries at moderate resolution (lambda/Delta lambda about 40,000) and S/N 150:1. This technique has been applied to 14 systems mostly RS CVn's, with 10 not greater than nu sin i not greater than 50 km/s and P not …

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Speckle And Spectroscopic Orbits Of The Early A-Type Triple System In Virginis, William I. Hartkopf, Harold A. Mcalister, Xinxing Yang, Francis C. Fekel Jun 1992

Speckle And Spectroscopic Orbits Of The Early A-Type Triple System In Virginis, William I. Hartkopf, Harold A. Mcalister, Xinxing Yang, Francis C. Fekel

Information Systems and Engineering Management Research Publications

Eta Virginis is a bright (V = 3.89) triple system of composite spectral type A2 IV that has been observed for over a dozen years with both spectroscopy and speckle interferometry. Analysis of the speckle observations results in a long period of 13.1 yr. This period is also detected in residuals from the spectroscopic observations of the 71.7919 day short-period orbit. Elements of the long-period orbit were determined separately using the observations of both techniques. The more accurate elements from the speckle solution have been assumed in a simultaneous spectroscopic determination of the short- and long-period orbital elements. The magnitude …

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Hr 266=Ads 784: An Early Type Spectroscopic, Speckle Astrometric Multiple System, Warren A. Cole, Francis C. Fekel, William I. Hartkopf, Harold A. Mcalister, Jocelyn Tomkin Apr 1992

Hr 266=Ads 784: An Early Type Spectroscopic, Speckle Astrometric Multiple System, Warren A. Cole, Francis C. Fekel, William I. Hartkopf, Harold A. Mcalister, Jocelyn Tomkin

Information Systems and Engineering Management Research Publications

The detection and nature of a 'speckle astrometric' system are reported with attention given to alternative interpretations of the system components. The HR 226 = ADS 784 system is described as a short-period binary (with a period of 4.241148 +/- 0.000008 d) orbiting an unseen companion (with a period of 1769 +/- 10 d), and the triple's visual orbit is 83.10 +/- 0.20 yr. The elements of the various orbits taken from spectroscopic data are employed to develop the model scenarios. The masses and spectral types of the components are developed and used to calculate the inclinations of the short-, …

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Chromospherically Active Stars. Ix. Hd 33798 = V390 Aurigae: A Lithium-Rich Rapidly Rotating Single Giant., Francis C. Fekel, Laurence A. Marschall Oct 1991

Chromospherically Active Stars. Ix. Hd 33798 = V390 Aurigae: A Lithium-Rich Rapidly Rotating Single Giant., Francis C. Fekel, Laurence A. Marschall

Information Systems and Engineering Management Research Publications

Results are presented of spectroscopic observations of HD 33798 obtained to determine if this star is a short-period binary and to examine its evolutionary status. Analysis of 40 radial velocities indicates no periodic velocity variations, suggesting that the star is single, so its rapid rotation is highly unusual. This rotation is inconsistent with the rotational brake hypothesis advanced by Gray (1989). It is proposed that HD 33798 is in a post-main-sequence phase of evolution. Its space motion is similar to FK Com, suggesting that it is a coalesced binary in the process of spinning down. Scenarios are presented to explain …

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The Extraordinary 1989 December 14/15 Optical Flare Events On V711 Tauri, Gregory W. Henry, Douglas S. Hall May 1991

The Extraordinary 1989 December 14/15 Optical Flare Events On V711 Tauri, Gregory W. Henry, Douglas S. Hall

Information Systems and Engineering Management Research Publications

Photometry in B and V taken with the Vanderbilt Tennessee State 16 inch (41 cm) robotic telescope confirms the intense broad-band optical continuum flare activity reported by Chinese observers on the active chromosphere binary V711 Tau on December 14/15, 1989. Twelve hours after the flare reported from China, there occurred a separate and more intense flare with B and V amplitudes of 0.69 and 0.42 mag, respectively. These amplitudes correspond to peak flare luminosities of approximately 2 x 10 to the 33rd ergs/s in B and 1 x 10 to the 33rd ergs/s in V. The observed color of its …

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Chromospherically Active Stars. Viii. Hd 155683 = V972 Herculis: Observational Constraints On Evolutionary Theory, Francis C. Fekel Apr 1991

Chromospherically Active Stars. Viii. Hd 155683 = V972 Herculis: Observational Constraints On Evolutionary Theory, Francis C. Fekel

Information Systems and Engineering Management Research Publications

V792 Her is an eclipsing RS CVn binary with an orbital period of 27.54 days whose components have spectral types of K0 III and F2 IV. New spectroscopic observations combined with existing photometry have resulted in masses of 1.47 + or - 0.003 solar mass and 1.41 + or - 0.003 solar mass for the K giant and F star, respectively. Additional fundamental parameters are derived. Standard evolutionary models were specifically computed by VandenBerg (1990) for the two stars. The best fit occurs if the components are somewhat metal poor with Fe/H/ = - 0.46. Ages of about 2.3 x …

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The Luminosities Of Bright H N Regions In Ngc 628 And Its O Star Formation Rate, Ted Von Hippel, Greg Bothun Aug 1990

The Luminosities Of Bright H N Regions In Ngc 628 And Its O Star Formation Rate, Ted Von Hippel, Greg Bothun

Publications

Using narrow band CCD imaging we have identified 183 bright H n regions in the Sc galaxy NGC 628. These H n regions have luminosities which indicate that they are powered by young star clusters which contain ^ 100 ionizing stars. We attempt to reproduce the H ii region LF with and without models including stellar evolution. We find stellar evolution an important parameter in understanding the H n region LF and find that it allows star-forming galaxies to be more robust to star bursting episodes. Ranking the H n regions by luminosity and assuming that luminosity evolution is due …

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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

Information Systems and Engineering Management Research Publications

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

Information Systems and Engineering Management Research Publications

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

Information Systems and Engineering Management Research Publications

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

Information Systems and Engineering Management Research Publications

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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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

Information Systems and Engineering Management Research Publications

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

Information Systems and Engineering Management Research Publications

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

Information Systems and Engineering Management Research Publications

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

Information Systems and Engineering Management Research Publications

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

Information Systems and Engineering Management Research Publications

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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Physical Conditions In The Accretion Disk Of V603 Aquilae, Gary J. Ferland, D. L. Lambert, M. L. Mccall, G. A. Shields, M. Slovak Sep 1982

Physical Conditions In The Accretion Disk Of V603 Aquilae, Gary J. Ferland, D. L. Lambert, M. L. Mccall, G. A. Shields, M. Slovak

Physics and Astronomy Faculty Publications

Ultraviolet and optical spectra of the old nova V603 Aql are discussed. The UV-optical continuum is dominated by emission from the accretion disk. Emission lines from ions of H, He, C, N, and 0 are identified. These lines are probably formed in a circumstellar shell with radius comparable to the binary separation, density ~1010 cm-3, and a roughly solar chemical composition. This corona is probably heated by radiation emitted by the underlying accretion disk. Photoionization calculations of the structure and emission-line spectrum of the corona are presented, and the effects of this gas on the X-ray continuum …

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