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 …

The Expres Stellar Signals Project Ii. State Of The Field In Disentangling Photospheric Velocities, Lily L. Zhao, Debra A. Fischer, Eric B. Ford, Alex Wise, Michaël Cretignier, Suzanne Aigrain, Oscar Barragan, Megan Bedell, Lars A. Buchhave, João D. Camacho, Heather M. Cegla, Jessi Cisewski-Kehe, Andrew Collier Cameron, Zoe L. De Beurs, Sally Dodson-Robinson, Xavier Dumusque, João P. Faria, Christian Gilbertson, Charlotte Haley, Justin Harrell, David W. Hogg, Parker Holzer, Ancy Anna John, Baptiste Klein, Marina Lafarga, Florian Lienhard, Vinesh Maguire-Rajpaul, Annelies Mortier, Belinda Nicholson, Michael L. Palumbo Iii, Victor Ramirez Delgado, Christopher J. Shallue, Andrew Vanderburg, Pedro T. P. Viana, Jinglin Zhao, Norbert Zicher, Samuel H. C. Cabot, Gregory W. Henry, Rachael M. Roettenbacher, John M. Brewer, Joe Llama, Ryan R. Petersburg, Andrew E. Szymkowiak

Information Systems and Engineering Management Research Publications

Measured spectral shifts due to intrinsic stellar variability (e.g., pulsations, granulation) and activity (e.g., spots, plages) are the largest source of error for extreme-precision radial-velocity (EPRV) exoplanet detection. Several methods are designed to disentangle stellar signals from true center-of-mass shifts due to planets. The Extreme-precision Spectrograph (EXPRES) Stellar Signals Project (ESSP) presents a self-consistent comparison of 22 different methods tested on the same extreme-precision spectroscopic data from EXPRES. Methods derived new activity indicators, constructed models for mapping an indicator to the needed radial-velocity (RV) correction, or separated out shape- and shift-driven RV components. Since no ground truth is known when …

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 …

Tess Hunt For Young And Maturing Exoplanets (Thyme). Iv. Three Small Planets Orbiting A 120 Myr Old Star In The Pisces–Eridanus Stream, E. R. Newton, A. W. Mann, A. L. Kraus, J. H. Livingston, A. Vanderburg, J. L. Curtis, P. C. Thao, K. Hawkins, M. L. Wood, A. C. Rizzuto, A. Soubkiou, B. M. Tofflemire, G. Zhou, I. J. M. Crossfield, L. A. Pearce, K. A. Collins, D. M. Conti, T.-G. Tan, S. Villanueva, A. Spencer, D. Dragomir, S. M. Quinn, Eric L.N. Jensen, K. I. Collins, C. Stockdale, R. Cloutier, C. Hellier, Z. Benkhaldoun, C. Ziegler, C. Briceño, N. Law, B. Benneke, J. L. Christiansen, V. Gorjian, S. R. Kane, L. Kreidberg, F. Y. Morales, M. W. Werner, J. D. Twicken, A. M. Levine, D. R. Ciardi, N. M. Guerrero, K. Hesse, E. V. Quintana, B. Shiao, J. C. Smith, G. Torres, G. R. Ricker, R. Vanderspek, S. Seager, J. N. Winn, J. M. Jenkins, D. W. Latham

Physics & Astronomy Faculty Works

Young exoplanets can offer insight into the evolution of planetary atmospheres, compositions, and architectures. We present the discovery of the young planetary system TOI 451 (TIC 257605131, Gaia DR2 4844691297067063424). TOI 451 is a member of the 120 Myr old Pisces–Eridanus stream (Psc–Eri). We confirm membership in the stream with its kinematics, its lithium abundance, and the rotation and UV excesses of both TOI 451 and its wide-binary companion, TOI 451 B (itself likely an M-dwarf binary). We identified three candidate planets transiting in the Transiting Exoplanet Survey Satellite data and followed up the signals with photometry from Spitzer and …

Nearly 30,000 Late-Type Main-Sequence Stars With Stellar Age From Lamost Dr5, Jiajun Zhang, Terry D. Oswalt, Jingkun Zhao, Xilong Liang, Xianhao Ye, Gang Zhao

Publications

We construct a sample of nearly 30,000 main-sequence stars with 4500K < Teff < 5000K and stellar ages estimated by the chromospheric activity−age relation. This sample is used to determine the age distribution in the R − Z plane of the Galaxy, where R is the projected Galactocentric distance in the disk midplane and Z is the height above the disk midplane. As |Z| increases, the percentage of old stars becomes larger. It is known that scale-height of Galactic disk increases as R increases, which is called flare. A mild flare from R ∼ 8.0 to 9.0 kpc in stellar age distribution is found. We also find that the velocity dispersion increases with age as confirmed by previous studies. Finally we present spiral-shaped structures in Z − υZ phase space in three stellar age bins. The spiral is clearly seen in the age bin of [0, 1] Gyr, which suggests that a vertical perturbation to the disk probably took place within the last ∼ 1.0 Gyr.

Access: Confirmation Of No Potassium In The Atmosphere Of Wasp-31b, Chima D. Mcgruder, Mercedes López-Morales, Néstor Espinoza, Benjamin V. Rackham, Dániel Apai, Andrés Jordán, David J. Osip, Munazza K. Alam, Alex Bixel, Jonathan J. Fortney, Gregory W. Henry, James Kirk, Nikole K. Lewis, Florian Rodler, Ian C. Weaver

Information Systems and Engineering Management Research Publications

We present a new optical (400–950 nm) transmission spectrum of the hot Jupiter WASP-31b (M = 0.48 MJ; R = 1.54 RJ; P = 3.41 days), obtained by combining four transit observations. These transits were observed with IMACS on the Magellan Baade Telescope at Las Campanas Observatory as part of the ACCESS project. We investigate the presence of clouds/hazes in the upper atmosphere of this planet, as well as the contribution of stellar activity on the observed features. In addition, we search for absorption features of the alkali elements Na i and K i, with particular focus on K i, …

Detection Of Na, K, And H2o In The Hazy Atmosphere Of Wasp-6b, Aarynn L. Carter, Nikolay Nikolov, David K. Sing, Munazza K. Alam, Jayesh M. Goyal, Thomas Mikal-Evans, Hannah R. Wakeford, Gregory W. Henry, Sam Morrell, Mercedes López-Morales, Barry Smalley, Panayotis Lavvas, Joanna K. Barstow, Antonio García Muñoz, Neale P. Gibson, Paul A. Wilson

Information Systems and Engineering Management Research Publications

We present new observations of the transmission spectrum of the hot Jupiter WASP-6b both from the ground with the Very Large Telescope FOcal Reducer and Spectrograph (FORS2) from 0.45 to 0.83 μm, and space with the Transiting Exoplanet Survey Satellite from 0.6 to 1.0 μm and the Hubble Space Telescope (HST) Wide Field Camera 3 from 1.12 to 1.65 μm. Archival data from the HST Space Telescope Imaging Spectrograph (STIS) and Spitzer are also re-analysed on a common Gaussian process framework, of which the STIS data show a good overall agreement with the overlapping FORS2 data. We also explore the …

The Hubble Pancet Program: An Extensive Search For Metallic Ions In The Exosphere Of Gj 436 B, Leonardo A. Dos Santos, David Ehrenreich, Vincent Bourrier, Alain Lecavelier Des Etangs, Mercedes López-Morales, David K. Sing, Gilda E. Ballester, Lofti Ben-Jaffel, Lars A. Buchhave, Antonio García Muñoz, Gregory W. Henry, Tiffany Kataria, Baptiste Lavie, Panayotis Lavvas, Nikole K. Lewis, Thomas Mikal-Evans, Jorge Sanz-Forcada, Hannah R. Wakeford

Information Systems and Engineering Management Research Publications

Context. The quiet M2.5 star GJ 436 hosts a warm Neptune that displays an extended atmosphere that dwarfs its own host star. Predictions of atmospheric escape in such planets state that H atoms escape from the upper atmosphere in a collisional regime and that the flow can drag heavier atoms to the upper atmosphere. It is unclear, however, what astrophysical mechanisms drive the process.

Aims. Our objective is to leverage the extensive coverage of observations of the far-ultraviolet (FUV) spectrum of GJ 436 obtained with the Cosmic Origins Spectrograph (COS) to search for signals of metallic ions in the upper …

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 …

Covariations Of Chromospheric And Photometric Variability Of The Young Sun Analogue Hd 30495: Evidence For And Interpretation Of Mid-Term Periodicities, Willie Soon, Victor M. Velasco Herrera, Rodolfo G. Cionco, S. Qiu, Sallie Baliunas, Ricky Egeland, Gregory W. Henry, Ivanka Charvátová

Information Systems and Engineering Management Research Publications

This study reports the synchronization between the chromospheric and photometric variability at time-scale of about 1.6–1.8 yr as observed for the young, rapidly rotating solar analogue HD 30495. In addition, HD 30495 may be presenting evidence of surface differential rotation at time-scales of about 11 d and 21 d, as well as the sunspot-like decadal cycles at 11–12 yr or so. We apply a new gapped wavelet method of time–frequency analysis for studying the variability in a new composite of the chromospheric S-index (1967–2018) and the longest photometric Δ(b + y)/2 index (1993–2018). We discuss and interpret our results in …

The 55 Cancri System Reassessed, Vincent Bourrier, Xavier Dumusque, Caroline Dorn, Gregory W. Henry, Nicola Astudillo-Defru, Javiera Rey, Björn Benneke, Guillaume Hébrard, Christophe Lovis, Brice-Olivier Demory, C. Moutou, David Ehrenreich

Information Systems and Engineering Management Research Publications

Orbiting a bright, nearby star the 55 Cnc system offers a rare opportunity to study a multiplanet system that has a wide range of planetary masses and orbital distances. Using two decades of photometry and spectroscopy data, we have measured the rotation of the host star and its solar-like magnetic cycle. Accounting for this cycle in our velocimetric analysis of the system allows us to revise the properties of the outermost giant planet and its four planetary companions. The innermost planet 55 Cnc e is an unusually close-in super-Earth, whose transits have allowed for detailed follow-up studies. Recent observations favor …

Patterns Of Variation For The Sun And Sun-Like Stars, Richard R. Radick, G. Wesley Lockwood, Gregory W. Henry, Jeffrey C. Hall, Alexei A. Pevtsov

Information Systems and Engineering Management Research Publications

We compare patterns of variation for the Sun and 72 Sun-like stars by combining total and spectral solar irradiance measurements between 2003 and 2017 from the SORCE satellite, Strömgren b, y stellar photometry between 1993 and 2017 from Fairborn Observatory, and solar and stellar chromospheric Ca ii H+K emission observations between 1992 and 2016 from Lowell Observatory. The new data and their analysis strengthen the relationships found previously between chromospheric and brightness variability on the decadal timescale of the solar activity cycle. Both chromospheric H+K and photometric b, y variability among Sun-like stars are related to average chromospheric activity by …

The First Post-Kepler Brightness Dips Of Kic 8462852, Tabetha S. Boyajian, Roi Alonso, Alex Ammerman, David Armstrong, Andrés Asensio Ramos, K. Barkaoui, Thomas G. Beatty, Zouhair Benkhaldoun, Paul Benni, Rory O. Bentley, Andrei Berdyugin, Svetlana Berdyugina, Serge Bergeron, Allyson Bieryla, Michaela G. Blain, Alicia Capetillo Blanco, Eva H. L. Bodman, Anne Boucher, Mark Bradley, Stephen M. Brincat, Thomas G. Brink, John Briol, David J. A. Brown, Jan Budaj, Artem Burdanov, Bryson Cale, Miguel Aznar Carbo, R. Castillo García, Wendy J. Clark, Geoffrey C. Clayton, James L. Clem, Phillip H. Coker, Evan M. Cook, Chris M. Copperwheat, Jason L. Curtis, Roc M. Cutri, Borbála Cseh, C. H. Cynamon, Alex J. Daniels, James R. A. Davenport, Hans J. Deeg, Roberto De Lorenzo, Thomas De Jaeger, Jean-Bruno Desrosiers, John Dolan, D. J. Dowhos, Franky Dubois, Russell Durkee, Shawn Dvorak, Lynn Easley, Nick Edwards, Tyler G. Ellis, Emery Erdelyi, Steve Ertel, Rafael G. Farfán, Jay Farihi, Alexei V. Filippenko, Emma Foxell, Davide Gandolfi, Faustino Garcia, Frank Giddens, Michaël Gillon, Juan-Luis González-Carballo, Carlos González-Fernández, Jonay I. González Hernández, Keith A. Graham, Kenton A. Greene, Joao Gregorio, Na'ama Hallakoun, Ottó Hanyecz, Gerry R. Harp, Gregory W. Henry, E. Herrero, Caleb F. Hildbold, D. Hinzel, Gonzalo Holgado, Bernadett Ignácz, Ilya Ilyin, Valentin D. Ivanov, ‪Emmanuel Jehin, Helen E. Jermak, Steve Johnston, Stella Kafka, Csilla Kalup, Emmanuel Kardasis, Shai Kaspi, Grant M. Kennedy, F. Kiefer, Collin L. Kielty, Dennis Kessler, Harri Kiiskinen, Thomas L. Killestein, Ronald A. King, Vladimír Kollar, Heidi Korhonen, C. Kotnik, Réka Könyves-Tóth, Levente Kriskovics, Nathan Krumm, Vadim Krushinsky, E. Kundra, Francois-Rene Lachapelle, Daryll Lacourse, P. Lake, Kristine Lam, Gavin P. Lamb, Dave Lane, Marie Wingyee Lau, Pablo Lewin, Chris Lintott, Carey Lisse, Ludwig Logie, Nicolas Longeard, M. Lopez Villanueva, E. Whit Ludington, Amy Mainzer, Lison Malo, Chris Maloney, Andrew Mann, A. Mantero, Massimo Marengo, Jon Marchant, María Jesús Martínez González, Joseph R. Masiero, Jon C. Mauerhan, James Mccormac, Aaron Mcneely, Huan Y. A. Meng, Mike Miller, Lawrence A. Molnar, Juan Carlos Morales, Brett M. Morris, Matthew W. Muterspaugh, David Nespra, Carrie R. Nugent, Katherine M. Nugent, A. Odasso, Derek O'Keeffe, Arto Oksanen, John M. O'Meara, András Ordasi, Hugh Osborn, John J. Ott, J. R. Parks, Diego Rodriguez Perez, Vance Petriew, Roger Pickard, András Pál, Peter Plavchan, Don Pollacco, Francisco Pozo-Nuñez, Francisco J. Pozuelos, Steve Rau, Seth Redfield, Howard Relles, Ignasi Ribas, Jon Richards, Joonas L. O. Saario, Emily J. Safron, J. Martin Sallai, Krisztián Sárneczky, Bradley E. Schaefer, Clea F. Schumer, Madison Schwartzendruber, Michael H. Siegel, Andrew P. V. Siemion, Brooke D. Simmons, Joshua D. Simon, Sergio Simón-Díaz, Michael L. Sitko, Hector Socas-Navarro, Ádám Sódor, Donn Starkey, Iain A. Steele, Geoff Stone, Klaus G. Strassmeier, Rachel A. Street, Tricia Sullivan, Jari Suomela, Jon J. Swift, Gyula M. Szabó, Róbert Szabó, Róbert Szakáts, Tamás Szalai, Angelle M. Tanner, Borja Toledo-Padrón, Tamás Tordai, Amaury H. M. J. Triaud, Jake D. Turner, Joseph H. Ulowetz, Marian Urbanik, Siegfried Vanaverbeke, Andrew Vanderburg, Krisztián Vida, Brad P. Vietje, József Vinkó, Kaspar Von Braun, Elizabeth O. Waagen, Dan Walsh, Christopher A. Watson, R. C. Weir, Klaus Wenzel, Carlos Westendorp, Michael W. Williamson, Jason T. Wright, Mark C. Wyatt, Weikang Zheng, Gabriella Zsidi

Information Systems and Engineering Management Research Publications

We present a photometric detection of the first brightness dips of the unique variable star KIC 8462852 since the end of the Kepler space mission in 2013 May. Our regular photometric surveillance started in 2015 October, and a sequence of dipping began in 2017 May continuing on through the end of 2017, when the star was no longer visible from Earth. We distinguish four main 1%–2.5% dips, named "Elsie," "Celeste," "Skara Brae," and "Angkor," which persist on timescales from several days to weeks. Our main results so far are as follows: (i) there are no apparent changes of the stellar …

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

Information Systems and Engineering Management Research Publications

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 …

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 …

General Model For Light Curves Of Chromospherically Active Binary Stars, Lauri Jetsu, Gregory W. Henry, Jyri J. Lehtinen

Information Systems and Engineering Management Research Publications

The starspots on the surface of many chromospherically active binary stars concentrate on long-lived active longitudes separated by 180°. Shifts in activity between these two longitudes, the "flip-flop" events, have been observed in single stars like FK Comae and binary stars like σ Geminorum. Recently, interferometry has revealed that ellipticity may at least partly explain the flip-flop events in σ Geminorum. This idea was supported by the double-peaked shape of the long-term mean light curve of this star. Here we show that the long-term mean light curves of 14 chromospherically active binaries follow a general model that explains the connection …

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 = …

Sun-Like Magnetic Cycles In The Rapidly Rotating Young Solar Analog Hd 30495, Ricky Egeland, Travis S. Metcalfe, Jeffrey C. Hall, Gregory W. Henry

Information Systems and Engineering Management Research Publications

A growing body of evidence suggests that multiple dynamo mechanisms can drive magnetic variability on different timescales, not only in the Sun but also in other stars. Many solar activity proxies exhibit a quasi-biennial (∼2 year) variation, which is superimposed upon the dominant 11 year cycle. A well-characterized stellar sample suggests at least two different relationships between rotation period and cycle period, with some stars exhibiting long and short cycles simultaneously. Within this sample, the solar cycle periods are typical of a more rapidly rotating star, implying that the Sun might be in a transitional state or that it has …

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

Information Systems and Engineering Management Research Publications

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 …

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 …

Stellar Activity And Its Implications For Exoplanet Detection On Gj 176, Paul Robertson, Michael Endl, Gregory W. Henry, William D. Cochran, Phillip J. Macqueen, Michael H. Williamson

Information Systems and Engineering Management Research Publications

We present an in-depth analysis of stellar activity and its effects on radial velocity (RV) for the M2 dwarf GJ 176 based on spectra taken over 10 yr from the High Resolution Spectrograph on the Hobby–Eberly Telescope. These data are supplemented with spectra from previous observations with the HIRES and HARPS spectrographs, and V- and R-band photometry taken over six years at the Dyer and Fairborn observatories. Previous studies of GJ 176 revealed a super-Earth exoplanet in an 8.8-day orbit. However, the velocities of this star are also known to be contaminated by activity, particularly at the 39-day stellar rotation …

Hst Hot-Jupiter Transmission Spectral Survey: Haze In The Atmosphere Of Wasp-6b, Nikolay Nikolov, David K. Sing, Adam S. Burrows, Jonathan J. Fortney, Gregory W. Henry, Frederic Pont, Gilda E. Ballester, Suzanne Aigrain, Paul A. Wilson, Catherine M. Huitson, Neale P. Gibson, Jean-Michel Désert, Alain Lecavelier Des Etangs, Adam P. Showman, Alfred Vidal-Madjar, Hannah R. Wakeford, Kevin J. Zahnle

Information Systems and Engineering Management Research Publications

We report Hubble Space Telescope optical to near-infrared transmission spectroscopy of the hot-Jupiter WASP-6b, measured with the Space Telescope Imaging Spectrograph and Spitzer's InfraRed Array Camera. The resulting spectrum covers the range 0.29–4.5 μm. We find evidence for modest stellar activity of WASP-6 and take it into account in the transmission spectrum. The overall main characteristic of the spectrum is an increasing radius as a function of decreasing wavelength corresponding to a change of Δ (Rp / R*) = 0.0071 from 0.33 to 4.5 μm. The spectrum suggests an effective extinction cross-section with a power law of index consistent with …

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 …

The Stellar Activity-Rotation Relationship, Nick J. Wright, Jeremy J. Drake, Eric E. Mamajek, Gregory W. Henry

Information Systems and Engineering Management Research Publications

Using a new catalog of 824 solar and late-type stars with measured X-ray luminosities and rotation periods we have studied the relationship between rotation and stellar activity that is believed to be a probe of the underlying stellar dynamo. Using an unbiased subset of the sample we calculate the power law slope of the unsaturated regime of the activity-rotation relationship as LX/Lbol α Roβ, where β = –2.70 ± 0.13. Notably this is inconsistent with the canonical β = –2 slope to a confidence of 5σ are argues for an interface-type dynamo. Super-saturation is observed for the fastest rotators in …

The Hd 192263 System: Planetary Orbital Period And Stellar Variability Disentangled, Diana Dragomir, Stephen R. Kane, Gregory W. Henry, David R. Ciardi, Debra A. Fischer, Andrew W. Howard, Eric L. N. Jensen, Gregory Laughlin, Suvrath Mahadevan, Jaymie M. Matthews, Genady Pilyavsky, Kaspar Von Braun, Sharon X. Wang, Jason T. Wright

Information Systems and Engineering Management Research Publications

As part of the Transit Ephemeris Refinement and Monitoring Survey, we present new radial velocities and photometry of the HD 192263 system. Our analysis of the already available Keck-HIRES and CORALIE radial velocity measurements together with the five new Keck measurements we report in this paper results in improved orbital parameters for the system. We derive constraints on the size and phase location of the transit window for HD 192263b, a Jupiter-mass planet with a period of 24.3587 ± 0.0022 days. We use 10 years of Automated Photoelectric Telescope photometry to analyze the stellar variability and search for planetary transits. …

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 …

The Relationship Between Γ Cassiopeiae’S X-Ray Emission And Its Circumstellar Environment, Myron A. Smith, Raimundo Lopes De Oliveira, Christian Motch, Gregory W. Henry, Noel D. Richardson, Karen S. Bjorkman, Philippe Stee, Denis Mourard, John D. Monnier, Xiao Che, R. Bücke, E. Pollmann, Douglas R. Gies, Gail Schaefer, Theo A. Ten Brummelaar, Harold Mcalister, Nils H. Turner, Judit Sturmann, Laszlo Sturmann, Stephen T. Ridgway

Information Systems and Engineering Management Research Publications

γ Cas is the prototypical classical Be star and is recently best known for its variable hard X-ray emission. To elucidate the reasons for this emission, we mounted a multiwavelength campaign in 2010 centered around four XMM-Newton observations. The observational techniques included long baseline optical interferometry (LBOI) from two instruments at CHARA, photometry carried out by an automated photometric telescope and Hα observations. Because γ Cas is also known to be in a binary, we measured radial velocities from the Hα line and redetermined its period as 203.55 ± 0.20 days and its eccentricity as near zero. The LBOI observations …

The Stellar-Activity–Rotation Relationship And The Evolution Of Stellar Dynamos, Nicholas J. Wright, Jeremy J. Drake, Eric E. Mamajek, Gregory W. Henry

Information Systems and Engineering Management Research Publications

We present a sample of 824 solar and late-type stars with X-ray luminosities and rotation periods. This is used to study the relationship between rotation and stellar activity and derive a new estimate of the convective turnover time. From an unbiased subset of this sample the power-law slope of the unsaturated regime, LX/Lbol∝Roβ, is fit as β = −2.70 ± 0.13. This is inconsistent with the canonical β = −2 slope to a confidence of 5σ, and argues for an additional term in the dynamo number equation. From a simple scaling analysis this implies ΔΩ/Ω∝Ω0.7, i.e., the differential rotation of …