Physical Sciences and Mathematics Commons^™

Topological Changes In The Magnetic Field Of Lq Hya During An Activity Minimum, Jyri J. Lehtinen, Maarit J. Käpylä, Thomas Hackman, Oleg Kochukhov, Teemu Willamo, Stephen C. Marsden, Sandra V. Jeffers, Gregory W. Henry, Lauri Jetsu

Information Systems and Engineering Management Research Publications

Aims. Previous studies have related surface temperature maps, obtained with the Doppler imaging (DI) technique, of LQ Hya with long-term photometry. Here, we compare surface magnetic field maps, obtained with the Zeeman Doppler imaging (ZDI) technique, with contemporaneous photometry, with the aim of quantifying the star’s magnetic cycle characteristics.

Methods. We inverted Stokes IV spectropolarimetry, obtained with the HARPSpol and ESPaDOnS instruments, into magnetic field and surface brightness maps using a tomographic inversion code that models high signal-to-noise ratio mean line profiles produced by the least squares deconvolution (LSD) technique. The maps were compared against long-term ground-based photometry acquired with …

Interferometric Imaging Of Λ Andromedae: Evidence Of Starspots And Rotation, J. Robert Parks, Russel J. White, Frédérique Baron, John D. Monnier, Brian Kloppenborg, Gregory W. Henry, Gail Schaefer, Xiao Che, Ettore Pedretti, Nathalie Thureau, Ming Zhao, Theo Ten Brummelaar, Harold Mcalister, Stephen T. Ridgway, Nils Turner, Judit Sturmann, Laszlo Sturmann

Information Systems and Engineering Management Research Publications

Presented are the first interferometric images of cool starspots on the chromospherically active giant λ Andromedae. Using the Michigan Infra-Red Combiner coupled to the Center for High Angular Resolution Astronomy Array, 26 interferometric observations were made between 2008 August 17 and 2011 September 24. The photometric time series acquired at Fairborn Observatory spanning 2008 September 20 to 2011 January 20 is also presented. The angular diameter and power-law limb-darkening coefficient of this star are 2.759 ± 0.050 mas and 0.229 ± 0.111, respectively. Starspot properties are obtained from both modeled and SQUEEZE reconstructed images. The images from 2010 through 2011 …

Observing The Changing Surface Structures Of The Active K Giant Σ Geminorum With Song★, Heidi Korhonen, Rachael M. Roettenbacher, Shenghong Gu, Frank Grundahl, Mads Fredslund Andersen, Gregory W. Henry, Jens Jessen-Hansen, Victoria L. Antoci, P. L. Pallé

Information Systems and Engineering Management Research Publications

Aims. We aim to study the spot evolution and differential rotation in the magnetically active cool K-type giant star σ Gem from broadband photometry and continuous spectroscopic observations that span 150 nights.

Methods. We use high-resolution, high signal-to-noise ratio spectra obtained with the Hertzsprung SONG telescope to reconstruct surface (photospheric) temperature maps with Doppler imaging techniques. The 303 observations span 150 nights and allow for a detailed analysis of the spot evolution and surface differential rotation. The Doppler imaging results are compared to simultaneous broadband photometry from the Tennessee State University T3 0.4 m Automated Photometric Telescope. The activity from …

Wasp-52b. The Effect Of Star-Spot Correction On Atmospheric Retrievals, Giovanni Bruno, Nikole K. Lewis, Munazza K. Alam, Mercedes López-Morales, Joanna K. Barstow, Hannah R. Wakeford, David K. Sing, Gregory W. Henry, Gilda E. Ballester, Vincent Bourrier, Lars A. Buchhave, Ofer Cohen, Thomas Mikal-Evans, Antonio García Muñoz, Panayotis Lavvas, Jorge Sanz-Forcada

Information Systems and Engineering Management Research Publications

We perform atmospheric retrievals on the full optical to infrared (0.3−5μm⁠) transmission spectrum of the inflated hot Jupiter WASP-52b by combining HST/STIS, WFC3 IR, and Spitzer/IRAC observations. As WASP-52 is an active star that shows both out-of-transit photometric variability and star-spot crossings during transits, we account for the contribution of non-occulted active regions in the retrieval. We recover a 0.1–10× solar atmospheric composition, in agreement with core accretion predictions for giant planets, and no significant contribution of aerosols. We also obtain a star-spots, a measure which is likely affected by the models used to fit instrumental effects in …

Long-Term Spot Monitoring Of The Young Solar Analogue V889 Herculis, Teemu Willamo, Thomas Hackman, Jyri J. Lehtinen, Maarit J. Käpylä, Ilya Ilyin, Gregory W. Henry, Lauri Jetsu, Oleg Kochukhov, Nikolai Piskunov

Information Systems and Engineering Management Research Publications

Context. Starspots are important manifestations of stellar magnetic activity. By studying their behaviour in young solar analogues, we can unravel the properties of their magnetic cycles. This gives crucial information of the underlying dynamo process. Comparisons with the solar cycle enable us to infer knowledge about how the solar dynamo has evolved during the Sun’s lifetime.

Aims. Here we study the correlation between photometric brightness variations, spottedness, and mean temperature in V889 Her, a young solar analogue. Our data covers 18 years of spectroscopic and 25 years of photometric observations.

Methods. We use Doppler imaging to derive …

Orbital Elements And Stellar Parameters Of The Active Binary Ux Arietis, Christian A. Hummel, John D. Monnier, Rachael M. Roettenbacher, Guillermo Torres, Gregory W. Henry, Heidi Korhonen, Anthony Beasley, Gail H. Schaefer, Nils H. Turner, Theo A. Ten Brummelaar, Chris D. Farrington, Judit Sturmann, Laszlo Sturmann, Frédérique Baron, Stefan Kraus

Information Systems and Engineering Management Research Publications

Stellar activity observed as large surface spots, radio flares, or emission lines is often found in binary systems. UX Arietis exhibits these signs of activity, originating on the K0 subgiant primary component. Our aim is to resolve the binary, measure the orbital motion, and provide accurate stellar parameters such as masses and luminosities to aid in the interpretation of the observed phenomena. Using the CHARA six-telescope optical long-baseline array on Mount Wilson, California, we obtained amplitudes and phases of the interferometric visibility on baselines up to 330 m in length, resolving the two components of the binary. We reanalyzed archival …

Activity Trends In Young Solar-Type Stars, Jyri J. Lehtinen, Lauri Jetsu, Thomas Hackman, Perttu Kajatkari, Gregory W. Henry

Information Systems and Engineering Management Research Publications

Aims. We study a sample of 21 young and active solar-type stars with spectral types ranging from late F to mid K and characterize the behaviour of their activity.

Methods. We apply the continuous period search (CPS) time series analysis method on Johnson B- and V-band photometry of the sample stars, collected over a period of 16 to 27 years. Using the CPS method, we estimate the surface differential rotation and determine the existence and behaviour of active longitudes and activity cycles on the stars. We supplement the time series results by calculating new log R'_HK = …

Detecting Differential Rotation And Starspot Evolution On The M Dwarf Gj 1243 With Kepler, James R. A. Davenport, Leslie Hebb, Suzanne L. Hawley

Physics & Astronomy

We present an analysis of the starspots on the active M4 dwarf GJ 1243, using 4 years of time series photometry from Kepler. A rapid P = 0.592596 ± 0.00021 days rotation period is measured due to the ~2.2% starspot-induced flux modulations in the light curve. We first use a light curve modeling approach, using a Monte Carlo Markov Chain sampler to solve for the longitudes and radii of the two spots within 5 day windows of data. Within each window of time the starspots are assumed to be unchanging. Only a weak constraint on the starspot latitudes can …

Multiperiodicity, Modulations, And Flip-Flops In Variable Star Light Curves. Iii. Carrier Fit Analysis Of Lq Hydrae Photometry For 1982–2014, Nigul Olspert, Maarit J. Käpylä, Jaan Pelt, Elizabeth M. Cole, Thomas Hackman, Jyri J. Lehtinen, Gregory W. Henry

Information Systems and Engineering Management Research Publications

Aims. We study LQ Hya photometry for 1982–2014 with the carrier fit (CF) method and compare our results to earlier photometric analysis and recent Doppler imaging maps.

Methods. As the rotation period of the object is not known a priori, we utilize different types of statistical methods first (least-squares fit of harmonics, phase dispersion statistics) to estimate various candidates for the carrier period for the CF method. Secondly, a global fit to the whole data set and local fits to shorter segments are computed with the period that is found to be optimal.

Results. The harmonic least-squares analysis of all …

Periodicity In Some Light Curves Of The Solar Analogue V352 Canis Majoris, Perttu Kajatkari, Lauri Jetsu, Elizabeth M. Cole, Thomas Hackman, Gregory W. Henry, Sirkka-Liisa Joutsiniemi, Jyri J. Lehtinen, V. Mäkelä, Sebastian Porceddu, Kyösti Ryynänen, V. Solea

Information Systems and Engineering Management Research Publications

Aims. We applied the Continuous Period Search (CPS) method to 14 yr of V-band photometry of the active G6.5 solar analog V352 CMa. Our aim was to show that CPS can successfully model the presence or absence of periodicity in low-amplitude light curves.

Methods. CPS computes values for the mean brightness, photometric period, amplitude and minimum of selected datasets. We also applied the Power Spectrum Method (PSM) to these datasets and compared the performance of this frequently applied method to that of CPS.

Results. We found an apparent 11.7 ± 0.5 yr cycle in the mean brightness. The mean of …

Spot Activity Of The Rs Canum Venaticorum Star Σ Geminorum, Perttu Kajatkari, Thomas Hackman, Lauri Jetsu, Jyri J. Lehtinen, Gregory W. Henry

Information Systems and Engineering Management Research Publications

Aims. We model the photometry of RS CVn star σ Geminorum to obtain new information on the changes of the surface starspot distribution, that is, activity cycles, differential rotation, and active longitudes.

Methods. We used the previously published continuous period search (CPS) method to analyse V-band differential photometry obtained between the years 1987 and 2010 with the T3 0.4 m Automated Telescope at the Fairborn Observatory. The CPS method divides data into short subsets and then models the light-curves with Fourier-models of variable orders and provides estimates of the mean magnitude, amplitude, period, and light-curve minima. These light-curve parameters …

Multiperiodicity, Modulations And Flip-Flops In Variable Star Light Curves Ii. Analysis Of Ii Pegasus Photometry During 1979–2010, Marjaana Lindborg, Maarit J. Mantere, Nigul Olspert, Jaan Pelt, Thomas Hackman, Gregory W. Henry, Lauri Jetsu, Klaus G. Strassmeier

Information Systems and Engineering Management Research Publications

Aims. According to previously published Doppler images of the magnetically active primary giant component of the RS CVn binary II Peg, the surface of the star was dominated by one single active longitude that was clearly drifting in the rotational frame of the binary system during 1994-2002; later imaging for 2004–2010, however, showed decreased and chaotic spot activity, with no signs of the drift pattern. Here we set out to investigate from a more extensive photometric dataset whether this drift is a persistent phenomenon, in which case it could be caused either by an azimuthal dynamo wave or be an …

Spot Activity Of Lq Hydra From Photometry Between 1988 And 2011, Jyri J. Lehtinen, Lauri Jetsu, Thomas Hackman, Perttu Kajatkari, Gregory W. Henry

Information Systems and Engineering Management Research Publications

Aims. We investigate the spot activity of the young magnetically active main sequence star LQ Hya. Our aims are to identify possible active longitudes, estimate the differential rotation, and study long and short term changes in the activity.

Methods. Our analysis is based on 24 years of Johnson V-band photometry of LQ Hya obtained with the T3 0.4 m Automated Telescope at the Fairborn Observatory. We use the previously published continuous period search (CPS) method to model the evolution of the light curve of LQ Hya. The CPS fits a Fourier series model to short overlapping subsets …

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

Information Systems and Engineering Management Research Publications

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 …

The Continuous Period Search Method And Its Application To The Young Solar Analogue Hd 116956, Jyri J. Lehtinen, Lauri Jetsu, Thomas Hackman, Perttu Kajatkari, Gregory W. Henry

Information Systems and Engineering Management Research Publications

Aims. We formulate an improved time series analysis method for the analysis of photometry of active stars. This new continuous period search (CPS) method is applied to 12 years of V band photometry of the young solar analogue HD 116956 (NQ UMa).

Methods. The new method is developed from the previous three stage period analysis (TSPA) method. Our improvements are the use of a sliding window in choosing the modelled datasets, a criterion applied to select the best model for each dataset and the computation of the time scale of change of the light curve. We test the …

Discovery Of Cyclic Spot Activity On The G8 Giant Hd 208472, Orkun Özdarcan, Serdar Evren, Klaus G. Strassmeier, Thomas Granzer, Gregory W. Henry

Information Systems and Engineering Management Research Publications

We present and analyze 17 consecutive years of UBVRI time-series photometry of the spotted giant component of the RS CVn binary HD 208472. Our aim is to determine the morphology and the evolution of its starspots by using periodsearch techniques and two-spot light-curve modelling. Spots on HD208472 always occur on hemispheres facing the observer during orbital quadrature and flip their location to the opposite hemisphere every approximately six years. The times when the spots change their preferential hemisphere correspond to times when the light curve amplitudes are the smallest and when abrupt changes of the photometric periods are observed. During …

The Chromospherically Active, Triple, Ellipsoidal, And Eclipsing Binary Hd 6286 = Be Piscium: A Laboratory For Binary Evolution, Klaus G. Strassmeier, János Bartus, Francis C. Fekel, Gregory W. Henry

Information Systems and Engineering Management Research Publications

Aims. We present a detailed analysis of the star HD 6286 = BE Psc from 16 years of spectroscopic observations and 18 seasons of photometric ones. The star is an evolved, chromospherically active, eclipsing binary, consisting of a K1 giant plus an F6 dwarf/subgiant in a circular orbit with a period of 35.671 days. A faint, close visual companion of spectral type ≈G0 makes the system triple. The orbital inclination of the eclipsing pair is 818.

Methods. We have obtained simultaneous solutions with our extensive set of radial velocities and light curves that include the star spot variability of …

Starspots And Relativity: Applied Doppler Imaging For The Gravity Probe B Mission, Stephen C. Marsden, Svetlana V. Berdyugina, Jean-Francois Donati, Joel A. Eaton, Michael H. Williamson

Information Systems and Engineering Management Research Publications

We present Doppler images and surface differential rotation measurements for the primary of the RS CVn binary IM Pegasi, the guide star for the Gravity Probe B experiment. The data used is a subset of that taken during optical support of the mission and was obtained almost nightly over a near three year period from the Automatic Spectroscopic Telescope operated by Tennessee State University. Using the technique of least-squares deconvolution to increase the signal-to-noise ratio of the data, we have reconstructed 31 maximum entropy Doppler images of the star. The images show that the spot features are relatively stable for …

Butterfly Diagram And Activity Cycles In Hr 1099, Svetlana Berdyugina, Gregory W. Henry

Information Systems and Engineering Management Research Publications

We analyze photometric data of the active RS CVn-type star HR 1099 for the years 1975-2006 with an inversion technique and reveal the nature of two activity cycles of 15-16 yr and 5.3 ± 0.1 yr duration. The 16 yr cycle is related to variations of the total spot area and is coupled with the differential rotation, while the 5.3 yr cycle is caused by the symmetric redistribution of the spotted area between the opposite stellar hemispheres (flip-flop cycle). We recover long-lived active regions comprising two active longitudes that migrate in the orbital reference frame with a variable rate because …

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

Information Systems and Engineering Management Research Publications

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.

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

Information Systems and Engineering Management Research Publications

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 …

Photospheric Temperature Measurements In Young Main Sequence Stars, Katia Biazzo, Antonio Frasca, Gregory W. Henry, S. Catalano, Ettore Marilli

Information Systems and Engineering Management Research Publications

As part of our program to study stellar photospheric and chromospheric activity, we have examined several young solar type stars with activity levels intermediate between the Sun and the very active RS CVn binaries. We have analysed contemporaneous spectroscopic data obtained at Catania Observatory (Serra La Nave station, Mt. Etna) and photometric data acquired in the Stromgren bands with an automatic photometric telescope (APT) at Fairborn Observatory (Arizona, USA). Surface inhomogeneities have been detected from the rotational modulation of stellar brightness as well as from the modulation of several photospheric line-depth ratios (LDRs). The presence of chromospheric plage-like regions has …

Why Do Some Spotted Stars Become Bluer As They Become Fainter?, Vidar Aarum-Ulvås, Gregory W. Henry

Information Systems and Engineering Management Research Publications

Chromospherically active, spotted stars generally become redder as well as fainter when large starspots rotate into view on the stellar disc. However, the RS CVn system UX Ari (a triple-lined system), becomes bluer as it gets fainter. One possible explanation is that hot, bright facular regions accompany the cool, dark photospheric spots of the active component. The bluer flux of the hotter, inactive component does not appear to be sufficient to explain the observed behaviour. We have begun a search for additional chromospherically active stars with a similar relation between colour and brightness, to investigate whether these relations can be …

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

Information Systems and Engineering Management Research Publications

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 …

Bv Photometry Of Ux Ari In The Period 1987–2002, Vidar Aarum Ulvås, Gregory W. Henry

Information Systems and Engineering Management Research Publications

We present 14.3 years of previously unpublished photometric observations of UX Ari. The observations were obtained between 1987.9 and 2002.2 using the T3 0.4-metre Automatic Photoelectric Telescope at Fairborn Observatory and consist of 1228 B band and 1213 V band measurements. The comparison star was 62 Ari. We have analyzed the new data together with previously published photometric observations. The V magnitude shows variations with dominant periods of about 12 and 25 years, where the longest period seems to correspond to an activity cycle. The previously reported anticorrelation between the colour and V magnitude variations is confirmed.

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

Information Systems and Engineering Management Research Publications

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 …

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

Information Systems and Engineering Management Research Publications

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

Information Systems and Engineering Management Research Publications

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 …

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

Information Systems and Engineering Management Research Publications

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 …

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

Information Systems and Engineering Management Research Publications

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 …