Physical Sciences and Mathematics Commons^™

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 …

Acurate Low-Mass Stellar Models Of Koi-126, Gregory A. Feiden, Brian Chaboyer, Aaron Dotter

Dartmouth Scholarship

The recent discovery of an eclipsing hierarchical triple system with two low-mass stars in a close orbit (KOI-126) by Carter et al. (2011) appeared to reinforce the evidence that theoretical stellar evolution models are not able to reproduce the observational mass-radius relation for low-mass stars. We present a set of stellar models for the three stars in the KOI-126 system that show excellent agreement with the observed radii. This agreement appears to be due to the equation of state implemented by our code. A significant dispersion in the observed mass-radius relation for fully convective stars is demonstrated; indicative of the …

A Spitzer Transmission Spectrum For The Exoplanet Gj 436b, Evidence For Stellar Variability, And Constraints On Dayside Flux Variations, Heather Knutson, Nikku Madhusudhan, Nicolas B. Cowan, Jessie L. Christiansen, Eric Agol, Drake Deming, Jean-Michel Désert, David Charbonneau, Gregory W. Henry, Derek Homeier, Jonathan Langton, Gregory Laughlin, Sara Seager

Information Systems and Engineering Management Research Publications

In this paper, we describe a uniform analysis of eight transits and eleven secondary eclipses of the extrasolar planet GJ 436b obtained in the 3.6, 4.5, and 8.0 μm bands using the IRAC instrument on the Spitzer Space Telescope between UT 2007 June 29 and UT 2009 February 4. We find that the best-fit transit depths for visits in the same bandpass can vary by as much as 8% of the total (4.7σ significance) from one epoch to the next. Although we cannot entirely rule out residual detector effects or a time-varying, high-altitude cloud layer in the planet's atmosphere as …

Polarization Of The Charge-Exchange X-Rays Induced In The Heliosphere, M. Gacesa, H.-R. Müller, R. Côté, V. Kharchenko

Dartmouth Scholarship

We report results of a theoretical investigation of polarization of the X-ray emissions induced in charge-exchange collisions of fully stripped solar wind ions C6+and O8+ with the heliospheric hydrogen atoms. The polarization of X-ray emissions has been computed for line-of-sight observations within the ecliptic plane as a function of solar wind ion velocities, including a range of velocities corresponding to the slow and fast solar wind, and Coronal Mass Ejections. To determine the variability of polarization of heliospheric X-ray emissions, the polarization has been computed for solar minimum conditions with self-consistent parameters of the solar wind plasma and heliospheric gas …

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 …