Physical Sciences and Mathematics Commons^™

Contemporaneous Imaging Comparisons Of The Spotted Giant Σ Geminorum Using Interferometric, Spectroscopic, And Photometric Data, Rachael M. Roettenbacher, John D. Monnier, Heidi Korhonen, Robert O. Harmon, Fabien Baron, Thomas Hackman, Gregory W. Henry, Gail H. Schaefer, Klaus G. Strassmeier, Michael Weber, Theo A. Ten Brummelaar

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Nearby active stars with relatively rapid rotation and large starspot structures offer the opportunity to compare interferometric, spectroscopic, and photometric imaging techniques. In this paper, we image a spotted star with three different methods for the first time. The giant primary star of the RS Canum Venaticorum binary σ Geminorum (σ Gem) was imaged for two epochs of interferometric, high-resolution spectroscopic, and photometric observations. The light curves from the reconstructions show good agreement with the observed light curves, supported by the longitudinally consistent spot features on the different maps. However, there is strong disagreement in the spot latitudes across the …

Detecting The Companions And Ellipsoidal Variations Of Rs Cvn Primaries. Ii. O Draconis, A Candidate For Recent Low-Mass Companion Ingestion, Rachael M. Roettenbacher, John D. Monnier, Francis C. Fekel, Gregory W. Henry, Heidi Korhonen, David W. Latham, Matthew W. Muterspaugh, Michael H. Williamson, Fabien Baron, Theo A. Ten Brummelaar, Xiao Che, Robert O. Harmon, Gail H. Schaefer, Nicholas J. Scott, Judit Sturmann, Laszlo Sturmann, Nils H. Turner

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To measure the stellar and orbital properties of the metal-poor RS CVn binary o Draconis (o Dra), we directly detect the companion using interferometric observations obtained with the Michigan InfraRed Combiner at Georgia State University's Center for High Angular Resolution Astronomy (CHARA) Array. The H-band flux ratio between the primary and secondary stars is the highest confirmed flux ratio (370 ± 40) observed with long-baseline optical interferometry. These detections are combined with radial velocity data of both the primary and secondary stars, including new data obtained with the Tillinghast Reflector Echelle Spectrograph on the Tillinghast Reflector at the Fred Lawrence …

Surprising Variations In The Rotation Of The Chemically Peculiar Stars Cu Virginis And V901 Orionis, Zdeněk Mikulášek, Jiří Krtička, Gregory W. Henry, Jan Janík, Juraj Zverko, Jozef Žižňovský, Miloslav Zejda, Jiri Liška, Pavel Zvěřina, D. O. Kudrjavtsev, Iosif I. Romanyuk, N. A. Sokolov, Theresa Lüftinger, Corrado Trigilio, Coralie Neiner, S. N. De Villiers

Information Systems and Engineering Management Research Publications

Context. The majority of magnetic chemically peculiar (mCP) stars exhibit periodic light, radio, spectroscopic and spectropolarimetric variations that can be adequately explained by the model of a rigidly rotating main-sequence star with persistent surface structures. CU Vir and V901 Ori belong among these few mCP stars whose rotation periods vary on timescales of decades.

Aims. We aim to study the stability of the periods in CU Vir and V901 Ori using all accessible observational data containing phase information.

Methods. We collected all available relevant archived observations supplemented with our new measurements of these stars and analysed the period variations of …

New Precision Orbits Of Bright Double-Lined Spectroscopic Binaries. Vi. Hd 24623 And V923 Scorpii, Francis C. Fekel, Michael H. Williamson, Gregory W. Henry

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Using new radial velocities obtained at KPNO and Fairborn Observatory, we have determined improved spectroscopic orbits for two double-lined F-type binaries, HD 24623 and V923 Sco. The orbital periods are 19.66304 and 34.8386 days, respectively, so it is not surprising that their orbits have relatively high eccentricities of nearly 0.5. The orbital dimensions (a1sin i and a2sin i) and minimum masses (m1sin 3i and m2sin 3i) have accuracies of 0.2% or better. Extensive photometry of HD 24623 with the T4 0.75 m automatic photometric telescope at Fairborn Observatory shows no evidence of eclipses. Instead, a very weak reflection effect is …

A Study Of Differential Rotation On Ii Pegasi Via Photometric Starspot Imaging, Rachael M. Roettenbacher, Robert O. Harmon, Nalin Vutisalchavakul, Gregory W. Henry

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We present the results of a study of differential rotation on the K2 IV primary of the RS CVn binary II Pegasi (HD 224085) performed by inverting light curves to produce images of the dark starspots on its surface. The data were obtained in the standard Johnson B and V filter passbands via the Tennessee State University T3 0.4 m Automated Photometric Telescope from JD 2447115.8086–2455222.6238 (1987 November 16–2010 January 26). The observations were subdivided into 79 data sets consisting of pairs of B and V light curves, which were then inverted using a constrained nonlinear inversion algorithm that makes …

Hr 7355 - Another Rapidly Braking He-Strong Cp Star?, Zdeněk Mikulášek, Jiří Krtička, Gregory W. Henry, S. N. De Villiers, Ernst Paunzen, Miloslav Zejda

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Context. Strong meridional mixing induced by rapid rotation is one reason why all hot main-sequence stars are not chemically peculiar. However, the finding that the He-strong CP star HR 7355 is a rapid rotator complicates this concept.
Aims. Our goal is to explain the observed behaviour of HR 7355 based on period analysis of all available photometry.
Methods. Over two years, we acquired 114 new BV observations of HR 7355 at observatories in Arizona, U.S.A and Cape Town, South Africa. We performed period analyses of the new observations along with new analyses of 732 archival measurements from the Hipparcos and …

The Nature Of The Light Variability Of The Silicon Star Hr 7224, Jiří Krtička, Zdeněk Mikulášek, Gregory W. Henry, Juraj Zverko, Jozef Žižňovský, Jan Skalický, Pavel Zvěřina

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Context. Although photometric variations of chemically peculiar (CP) stars are frequently used to determine their rotational periods, the detailed mechanism of their light variability remains poorly understood.
Aims. We simulate the light variability of the star HR 7224 using the observed surface distribution of silicon and iron.
Methods. We used the TLUSTY model atmospheres calculated for the appropriate silicon and iron abundances to obtain the emergent flux and to predict the rotationally modulated light curve of the star. We also obtained additional photometric measurements and employed our own regression procedure to derive a more precise estimate of the light elements. …

Infrared Spectroscopy Of Symbiotic Stars. Vii. Binary Orbit And Long Secondary Period Variability Of Ch Cygni, Kenneth H. Hinkle, Francis C. Fekel, Richard R. Joyce

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High-dispersion spectroscopic observations are used to refine orbital elements for the symbiotic binary CH Cyg. The current radial velocities, added to a previously published 13 year time series of infrared velocities for the M giant in the CH Cyg symbiotic system, more than double the length of the time series to 29 years. The two previously identified velocity periods are confirmed. The long period, revised to 15.6 ± 0.1 yr, is shown to result from a binary orbit with a 0.7 M☉ white dwarf and 2 M☉ M giant. Mass transfer to the white dwarf is responsible for the symbiotic …

The Extremely Rapid Rotational Braking Of The Magnetic Helium-Strong Star Hd 37776, Zdeněk Mikulášek, Jiří Krtička, Gregory W. Henry, Juraj Zverko, Jozef Žižňovský, David A. Bohlender, Iosif I. Romanyuk, Jan Janík, Hrvoje Božić, D. Korčáková, Miloslav Zejda, Ivan Kh. Iliev, Petr Škoda, Miroslav Šlechta, Tomáš Gráf, Martin Netolický, Michal Ceniga

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Context. Light and spectrum variations of the magnetic chemically peculiar (mCP) stars are explained by the oblique rigid rotator model with a rotation period usually assumed to be stable on a long time scale. A few exceptions, such as CU Vir or 56 Ari, have been reported as displaying an increase in their rotation period. A possible increase in the period of light and spectrum variations has also been suggested from observations of the helium-strong mCP star HD 37776 (V901 Ori).

Aims. In this paper we attempt to confirm the possible period change of HD 37776 and discuss a possible …

Patterns Of Photometric And Chromospheric Variation Among Sun-Like Stars: A 20 Year Perspective, G. Wesley Lockwood, Brian A. Skiff, Gregory W. Henry, Stephen M. Henry, Richard R. Radick, Sallie L. Baliunas, Robert A. Donahue, Willie Soon

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We examine patterns of variation of 32 primarily main-sequence Sun-like stars [selected at project onset as stars on or near the main sequence and color index 0.42 ≤ (B - V) ≤ 1.4], extending our previous 7-12 yr time series to 13-20 yr by combining Strömgren b, y photometry from Lowell Observatory with similar data from Fairborn Observatory. Parallel chromospheric Ca II H and K emission data from the Mount Wilson Observatory span the entire interval. The extended data strengthen the relationship between chromospheric and brightness variability at visible wavelengths derived previously. We show that the full range of photometric …

Photometry And Spectroscopy Of 11 Γ Doradus Stars, Gregory W. Henry, Francis C. Fekel, Stephen M. Henry

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We have used precise photometric and high-dispersion spectroscopic observations to study 11 γ Doradus stars, 10 of them newly confirmed. Only five of these 11 γ Doradus stars appear to be single; two are primaries of double-lined spectroscopic binaries, one is the secondary of a double-lined binary, two are primaries of visual binaries and, in the case of the double-lined binary (HD 86371), either or both components could be a pulsating γ Doradus star. We have determined a preliminary orbital period of 5.32 days for the double-lined binary HD 41547. Several of the stars show spectroscopic line-profile and low-amplitude radial …

Spectroscopy And Photometry Of The Double-Lined Binary Hd 149420, Francis C. Fekel, Gregory W. Henry

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We have used new spectroscopic and photometric observations of HD 149420 to obtain an improved orbital element solution and determine some basic properties of the system. This double-lined binary has an orbital period of 3.39430 days, a circular orbit, and a mass ratio of 0.52. The primary is somewhat evolved, with an A9 IV spectral type, while the secondary is estimated to be an F5: dwarf. The secondary may be synchronously rotating, but the primary is rotating substantially slower than its synchronous velocity. Our photometric observations confirm the light variability and period found by Hipparcos. We determine a photometric period …

Chromospherically Active Stars. Xxv. Hd 144110=Ev Draconis, A Double-Lined Dwarf Binary, Francis C. Fekel, Gregory W. Henry, Ceteka Lewis

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New spectroscopic and photometric observations of HD 144110 have been used to obtain an improved orbital element solution and determine some basic properties of the system. This chromospherically active, double-lined spectroscopic binary has an orbital period of 1.6714012 days and a circular orbit. We classify the components as G5 V and K0 V and suggest that they are slightly metal-rich. The photometric observations indicate that the rotation of HD 144110 is synchronous with the orbital period. Despite the short orbital period, no evidence of eclipses is seen in our photometry.

Eleven New Γ Doradus Stars, Gregory W. Henry, Francis C. Fekel, Stephen M. Henry

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We present new high-dispersion spectroscopic and precise photometric observations to identify 11 new γ Doradus variables. Seven of these new γ Doradus stars appear to be single, three are primaries of single-lined binaries, and one has two distant visual companions; none are double-lined or close visual binaries. Several of the stars show spectroscopic line-profile and low-amplitude radial velocity variability indicative of pulsation. All 11 stars are photometrically variable with amplitudes between 8 and 93 mmag in Johnson B and periods between 0.398 and 2.454 days. One star is monoperiodic; the rest have between two and five independent periods. The variability …

Hd 8801: A Unique Single Am Star With Γ Doradus And Δ Scuti Pulsations, Gregory W. Henry, Francis C. Fekel

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We have discovered the first example of a star pulsating intrinsically with both γ Doradus and δ Scuti frequencies. The star, HD 8801, is an Am metallic-line star that appears to be single. Since the vast majority of Am stars are members of binary systems with periods less than 1000 days and also do not pulsate, HD 8801 possesses a very unusual, if not unique, combination of physical properties. Our photometry, acquired with an automatic telescope at Fairborn Observatory, resolves six independent pulsation periods between 0.048 and 0.404 days. The two longest periods lie within the range of γ Dor …

Chromospherically Active Stars. Xxiv. The Giant, Single-Lined Binaries Hd 37824, Hd 181809, And Hd 217188, Francis C. Fekel, Gregory W. Henry

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We have obtained spectroscopy and photometry of three chromospherically active, single-lined spectroscopic binaries, HD 37824 (V1149 Ori), HD 181809 (V4138 Sgr), and HD 217188 (AZ Psc). HD 37824 has a circular orbit with a period of 53.57 days. Its primary is a K0 III star, while the secondary is likely a G or K dwarf. HD 181809 has an orbit with a period of 13.04667 days and a low eccentricity of 0.040. The primary has a spectral type of K0 III-IV, and its secondary is probably an M dwarf. The orbit of HD 217188 has a period of 47.1209 days …

Hd 166181 = V815 Herculis, A Single-Lined Spectroscopic Multiple System, Francis C. Fekel, David J. Barlow, Colin D. Scarfe, Sylvie Jancart, Dimitri Pourbaix

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We have obtained extensive spectroscopic and velocity spectrometer observations of HD 166181, a previously known single-lined spectroscopic binary. Our improved orbit for the G6 V primary has a period of 1.8098343 days and is circular. Although the lines of additional components have not been detected, radial velocity measurements confirm that the system has additional velocity variations with a period of 2092 days, or 5.73 yr. This long-period orbit has an eccentricity of 0.76. An analysis of the Hipparcos observations produces a well-determined astrometric orbit for the long-period system that has an inclination of 78°. Mass estimates of the components in …

Chromospherically Active Stars. Xxii. Hd 18955, A Massive K Dwarf Binary, Francis C. Fekel, Gregory W. Henry, Frank M. Alston

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HD 18955 is a double-lined spectroscopic binary with a period of 43.3214 days and a high eccentricity of 0.761. The spectral types of the components are K0 V and K2-K3 V. The secondary is a typical early K dwarf, although its minimum mass is greater than canonical values. However, this larger mass is consistent with other early K dwarf, spectroscopic binary results. The primary is anomalous, being substantially underluminous for its radius and mass, which are equal to or slightly greater than solar values. A lack of lithium argues that the components are not pre-main-sequence stars. The large minimum masses …

Hd 207651: A Triple System With Δ Scuti And Ellipsoidal Variations But No Γ Doradus Pulsations, Gregory W. Henry, Francis C. Fekel, Stephen M. Henry

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We examine HD 207651 as a possible example of a star exhibiting both γ Doradus and δ Scuti type pulsations. We find photometric periods of 0.06479 and 0.06337 days with peak-to-peak amplitudes in Johnson B of 21 and 13 mmag, respectively, clearly indicating δ Scuti pulsations. Additional light variation with a period of 0.73540 days and an even larger amplitude of 31 mmag is within the range of γ Doradus pulsation periods but results instead from the ellipticity effect. HD 207651 has a composite spectrum with a weak, narrow absorption line superposed near the center of each broad metal line. …

The Orbit And Pulsation Periods Of The Γ Doradus Variable Hr 6844 (V2502 Ophiuchi), Francis C. Fekel, Gregory W. Henry

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We obtained spectroscopic and photometric observations of the γ Doradus variable HR 6844 (=V2502 Ophiuchi). Radial velocities show that this star is a single-lined binary with a period of 4.4852 days. The primary is an F1 V star, while the secondary is likely an M dwarf. Velocity residuals to a circular orbit have a period of 1.3071 days and an amplitude of ∼3 km s-1. Three periods of light variation were detected, 1.30702, 1.4350, and 0.62286 days. The first period is essentially identical to that found in the radial velocities and has the largest amplitude, a peak-to-peak value of 0.067 …

Spectroscopy Of Early F Stars: Γ Doradus Candidates And Possible Metallic Shell Stars, Francis C. Fekel, Phillip B. Warner, Anthony B. Kaye

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We obtained high-resolution spectroscopic observations of 34 γ Doradus candidates. From the red-wavelength spectra, we determined spectral classes, radial velocities, and projected rotational velocities. The spectra of seven late A or early F stars show metallic lines that have composite profiles consisting of a narrow component near the center of a broad line, indicating that they may be shell stars or binaries. Several stars, including HD 152896, HD 173977, HD 175337, and HD 195068/9, show large line profile asymmetries. Two stars, HD 11443 (=α Trianguli) and HD 149420, are ellipsoidal variables and not γ Doradus stars. The percentage of binary …

A Dozen New Γ Doradus Stars, Gregory W. Henry, Francis C. Fekel

Information Systems and Engineering Management Research Publications

We use new high-dispersion spectroscopic and precise photometric observations to identify 12 new γ Doradus stars. Two of the 12 systems are double-lined binaries that show obvious velocity variability. Five other stars have metallic lines with composite profiles characterized by a narrow feature near the center of each broad component. Spectrograms of the Hα line indicate that all five stars are binaries rather than shell stars. The remaining five stars in our sample are probably single. All 12 stars are photometrically variable with amplitudes between 6 and 87 mmag in Johnson B and periods between 0.3 and 1.2 days. Four …

Chromospherically Active Stars. Xxi. The Giant, Single-Lined Binaries Hd 89546 And Hd 113816, Francis C. Fekel, Gregory W. Henry, Joel A. Eaton, Julius Sperauskas, Douglas S. Hall

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We have obtained spectroscopy and photometry of the chromospherically active, single-lined spectroscopic binaries HD 89546 and HD 113816. HD 89546 has a circular orbit with a period of 21.3596 days. Its primary has a spectral type of G9 III and is somewhat metal-poor with [Fe/H]~-0.5. HD 113816 has an orbit with a period of 23.6546 and a low eccentricity of 0.022. Its mass function is extremely small, 0.0007 Msolar, consistent with a very low inclination. The primary is a slightly metal-poor K2 III. A decade or more of photometric monitoring with an automatic telescope demonstrates that both systems display brightness …

Velocity Observations Of Multiple-Mode Asymptotic Giant Branch Variable Stars, Kenneth H. Hinkle, Thomas Lebzelter, Richard R. Joyce, Francis C. Fekel

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Numerous infrared spectroscopic observations were obtained of nine asymptotic giant branch (AGB) field M giants that have multiple periods of light variability. Each star has a short period of several months, which is typical of low amplitude pulsation for stars on the AGB, as well as a long period of 1–3 yr, which is significantly longer than the predicted fundamental-mode pulsations for these stars. The location of these stars in the AGB period-luminosity relation is discussed. For six of the nine giants we found radial-velocity periods that confirm the long-period light variability. Although we considered the possibility that the velocity …

Chromospherically Active Stars. Xx. The Giant Single-Lined Binary Hd 161570, Francis C. Fekel, Gregory W. Henry, Stephen M. Henry

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Spectroscopy of HD 161570 shows it to be a single-lined spectroscopic binary with a period of 45.623 days and a nearly circular orbit. The primary star has spectral type G7 III, and the secondary is most likely a G or K dwarf. A high-resolution spectrum of the 3950 Å region confirms that the primary has Ca II H and K emission lines. The logarithm of the giant's lithium abundance is less than 0.9, indicating that it is not lithium-rich. From photometric observations covering six seasons, we detected periodic short-term light variability with an amplitude ranging from 0.02 to 0.04 mag. …

Chromospherically Active Stars. Xix. A Reexamination Of The Variability Of Hd 10909=Uv Fornacis, Francis C. Fekel, Gregory W. Henry, Keinon Brooks, Douglas S. Hall

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We have obtained new spectroscopy and photometry of the K0 IV, chromospherically active, single-lined spectroscopic binary HD 10909. Those observations show that the previously reported orbital and light variability periods are incorrect. HD 10909 has an orbital period of 30.1067 days and an eccentricity of 0.499. Its rotation period of 64.1 days is more than twice as long as its orbital period. The primary is situated near the base of the first-ascent red giant branch. Thus, its asynchronous rotation is likely the result of its recent evolution through the Hertzsprung gap, combined with its relatively long orbital period and high …

10 New Γ Doradus And Δ Scuti Stars, Gregory W. Henry, Francis C. Fekel, Anthony B. Kaye, Ann Kaul

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We present high-resolution spectroscopy and precision photometry of five new γ Doradus and five new δ Scuti variables. The five new γ Doradus variables substantially increase the number of confirmed stars of this class. All 10 stars fall in the spectral class range F0–F2, but they are cleanly separated into two groups by their luminosity and photometric periods. However, the period gap between the γ Doradus and δ Scuti stars is becoming very narrow since we confirm that HD 155154 is a γ Doradus star with the shortest periods reported to date (the shortest of its four periods is ∼0.312 …

Chromospherically Active Stars. Xviii. Sorting Out The Variability Of Hd 95559 And Gliese 410=Ds Leonis, Francis C. Fekel, Gregory W. Henry

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We have obtained spectroscopy and photometry of HD 95559 and photometry of Gliese 410=DS Leonis. HD 95559 consists of a pair of essentially identical K1 V stars, whose orbital period we refine to 1.52599775+/-0.00000104 days. The system is photometrically variable with a mean period of 1.5264+/-0.0003 days. Despite minimum masses greater than 0.8 Msolar for each component, a search for eclipses proved negative. The lithium abundances of the components of HD 95559 indicate that the system is younger than the Hyades cluster, and its components may even have just arrived on the zero-age main sequence. Gl 410=DS Leo is also …

Time Series Analysis Of V815 Herculis Photometry Between 1984 And 1998, Lauri Jetsu, Thomas Hackman, Douglas S. Hall, Gregory W. Henry, Mariitta Kokko, J. You

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As a case study of the solar-stellar connection, we have analysed a prolonged time series of BV photometry of the chromospherically active binary V815 Her . The surface differential rotation in the rapidly rotating G5{v} primary caused changes of 4.6% in the seasonal photometric rotation periods. This would imply a differential rotation coefficient of k = 0.184, if the rotation of the starspots follows the solar law of differential rotation and the activity is confined within the same latitudinal range as in the Sun, having k = 0.189 and the spectral-type of G2{v}. Our analysis of the primary and secondary …

Photometric Variability In A Sample Of 187 G And K Giants, Gregory W. Henry, Francis C. Fekel, Stephen M. Henry, Douglas S. Hall

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We have used three automatic photoelectric telescopes to obtain photometric observations of 187 G, K, and (a few) M0 field giants. We find low-amplitude photometric variability on timescales of days to weeks on both sides of the coronal dividing line (CDL) in a total of 81 or 43% of the 187 giants. About one-third of the variables have amplitudes greater than 0.01 mag in V. In our sample the percentage of variable giants is a minimum for late-G spectral classes and increases for earlier and later classes; all K5 and M0 giants are variable. We also obtained high-resolution, red wavelength …