A practical step-by-step guide to wavelet analysis is given, with examples taken from time series of the El Nino–Southern Oscillation (ENSO). The guide includes a comparison to the windowed Fourier transform, the choice of an appropriate wavelet basis function, edge effects due to finite-length time series, and the relationship between wavelet scale and Fourier frequency. New statistical significance tests for wavelet power spectra are developed by deriving theoretical wavelet spectra for white and red noise processes and using these to establish significance levels and confidence intervals. It is shown that smoothing in time or scale can be used to increase the confidence of the wavelet spectrum. Empirical formulas are given for the effect of smoothing on significance levels and confidence intervals. Extensions to wavelet analysis such as filtering, the power Hovmoller, cross-wavelet spectra, and coherence are described. The statistical significance tests are used to give a quantitative measure of change...

https://atoc.colorado.edu/research/wavelets/bams_79_01_0061.pdf

A Practical Guide to Wavelet Analysis.

Changes in Atmospheric Constituents and in Radiative Forcing

The presence of a Jupiter-mass companion to the star 51 Pegasi is inferred from observations of periodic variations in the star's radial velocity. The companion lies only about eight million kilometres from the star, which would be well inside the orbit of Mercury in our Solar System. This object might be a gas-giant planet that has migrated to this location through orbital evolution, or from the radiative stripping of a brown dwarf.

A Jupiter-Mass Companion to a Solar-Type Star

This chapter should be cited as: Myhre, G., D. Shindell, F.-M. Bréon, W. Collins, J. Fuglestvedt, J. Huang, D. Koch, J.-F. Lamarque, D. Lee, B. Mendoza, T. Nakajima, A. Robock, G. Stephens, T. Takemura and H. Zhang, 2013: Anthropogenic and Natural Radiative Forcing. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA. Coordinating Lead Authors: Gunnar Myhre (Norway), Drew Shindell (USA)

Anthropogenic and Natural Radiative Forcing

We substantially update the capabilities of the open source software package Modules for Experiments in Stellar Astrophysics (MESA), and its one-dimensional stellar evolution module, MESA star. Improvements in MESA star's ability to model the evolution of giant planets now extends its applicability down to masses as low as one-tenth that of Jupiter. The dramatic improvement in asteroseismology enabled by the space-based Kepler and CoRoT missions motivates our full coupling of the ADIPLS adiabatic pulsation code with MESA star. This also motivates a numerical recasting of the Ledoux criterion that is more easily implemented when many nuclei are present at non-negligible abundances. This impacts the way in which MESA star calculates semi-convective and thermohaline mixing. We exhibit the evolution of 3-8 M ? stars through the end of core He burning, the onset of He thermal pulses, and arrival on the white dwarf cooling sequence. We implement diffusion of angular momentum and chemical abundances that enable calculations of rotating-star models, which we compare thoroughly with earlier work. We introduce a new treatment of radiation-dominated envelopes that allows the uninterrupted evolution of massive stars to core collapse. This enables the generation of new sets of supernovae, long gamma-ray burst, and pair-instability progenitor models. We substantially modify the way in which MESA star solves the fully coupled stellar structure and composition equations, and we show how this has improved the scaling of MESA's calculational speed on multi-core processors. Updates to the modules for equation of state, opacity, nuclear reaction rates, and atmospheric boundary conditions are also provided. We describe the MESA Software Development Kit that packages all the required components needed to form a unified, maintained, and well-validated build environment for MESA. We also highlight a few tools developed by the community for rapid visualization of MESA star results.

/pdf/modules-for-experiments-in-stellar-astrophysics-mesa-planets-29j324a9bq.pdf

Modules for Experiments in Stellar Astrophysics (MESA): Planets, Oscillations, Rotation, and Massive Stars

A review of the research literature concerning the environmental consequences of increased levels of atmos- pheric carbon dioxide leads to the conclusion that increases dur- ing the 20th Century have produced no deleterious effects upon global weather, climate, or temperature. Increased carbon diox- ide has, however, markedly increased plant growth rates. Pre- dictions of harmful climatic effects due to future increases in minor greenhouse gases like CO2 are in error and do not con- form to current experimental knowledge. SUMMARY World leaders gathered in Kyoto, Japan, in December 1997 to consider a world treaty restricting emissions of ''greenhouse gases,'' chiefly carbon dioxide (CO2), that are thought to cause ''global warming'' - severe increases in Earth's atmospheric and surface temperatures, with disastrous environmental consequences. Predictions of global warming are based on computer climate modeling, a branch of science still in its infancy. The empirical evi- dence - actual measurements of Earth's temperature - shows no man-made warming trend. Indeed, over the past two decades, when CO2 levels have been at their highest, global average temperatures have actually cooled slightly. To be sure, CO2 levels have increased substantially since the In- dustrial Revolution, and are expected to continue doing so. It is rea- sonable to believe that humans have been responsible for much of this increase. But the effect on the environment is likely to be benign. Greenhouse gases cause plant life, and the animal life that depends upon it, to thrive. What mankind is doing is liberating carbon from beneath the Earth's surface and putting it into the atmosphere, where it is available for conversion into living organisms.

/pdf/environmental-effects-of-increased-atmospheric-carbon-1gwe3ongei.pdf

Environmental Effects of Increased Atmospheric Carbon Dioxide

The visible Ca II K and International Ultraviolet Explorer spectra from the four K0 III stars (theta-1, gamma, delta, and epsilon Tau) in the Hyades, along with a field giant of similar spectral type, beta Gem, have been measured. Among the Hyades giants, the range of the high-temperature emissions can be a factor of 6 or more for C IV and an order of magnitude in the X-ray luminosity measured by Stern et al. (1981). For these presumably coeval cluster giants with similar macroscopic parameters, such as age, mass, effective temperature, gravity, and projected rotational velocity, the observed range in chromospheric and coronal emissions is not easily explained by the dominant factors thought to control these emissions in cool stars. It is possible that the emissions are time variable, on a time scale longer than six months. This would be the first evidence that giants undergo magnetic activity cycles similar to those of dwarf stars.

Chromospheric and coronal emissions from the giants in the Hyades

The relative distribution of pooled variance computed at various time scales for records of chromospheric activity has been calculated for approximately 100 stars observed at Mount Wilson Observatory. As shown in Paper I, analysis of the pooled variance provides a technique for estimating the lifetimes of stellar active regions and their influence on chromospheric time series used for determining rotation and activity cycle periods. Pooled variance diagrams may be divided into three morphological types which depend to a large extent on a star's mean level of chromospheric activity (i.e., age) and B-V color (i.e., mass), and possibly depend on star's evolutionary state.

Stellar Active Region Evolution - II. Identification and Evolution of Variance Morphologies in CA II H+K Time Series

We evaluate observed spectroscopic activity of Arcturus (HR 5340, K2 III) from 1984 to 2007 using high-resolution spectroscopy and Ca II H+K emission. Line-depth ratios of the V I λ6251.83 A to Fe I λ6252.56 A lines and line bisectors from Fe I λ6252.56 A are used to evaluate spectroscopic activity. Chromospheric emission within H+K lines is used as a magnetic activity indicator. We observe a significant portion of what appears to be a magnetic cycle with a period of ≥14 yr. Line-depth ratios show comparable variation, but with a time lag of -->2.0 ± 0.5 yr with respect to H+K variations. This time lag is qualitatively similar to previous observations of G and K dwarfs. No corresponding variation is observed in line bisectors. H+K and line bisectors also show variability within seasons. A Fourier analysis reveals periods of 253 and 207 days during the 1984-1989 H+K seasons. Line bisectors show excess power over the range of 115-200 days from 1992 to 2007. We attribute this intraseason variability to inferred magnetic activity along active longitudes. The range of periods observed in H+K and line bisectors (115-253 days) may result from migration of active regions within longitude bands, implying differential rotation. We compare these observations with the Sun and other solar-type stars. A 1/f noise component to the Fourier spectrum of the line bisector variations is also observed.

http://iopscience.iop.org/article/10.1086/587783/pdf

Long-Term Spectroscopic Monitoring of Arcturus

We investigate a four-and-one-half year time-series of ROSAT HRI pointed observations of 61 Cyg A and B and compare the X-ray light curves with the chromospheric Ca HK variability. The ROSAT sampling rate was two pointings per year and typical errors lie in the range of 5–10%. The chromospheric cycles are well-known for both stars from the Mt. Wilson Ca HK survey. Although the time basis of our ROSAT observations is shorter than the 7-and 12-year cycles of components A and B, respectively, we find the long-term trend of coronal activity in close correlation with the chromospheric activity during the observation period, between 1993 and 1998. The chromospheric activity increased through maximum activity down to a minimum for component A, and from maximum to minimum activity for component B. The same behaviour is observed for the X-ray light curves but with much higher amplitudes by factors 2.5–3. The remaining scatter observed around low-order regression curves of coronal activity is small. We conclude that both stars do show coronal cycles and that coronal cycles are the dominant source of variability for 61 Cygni.

/pdf/evidence-for-coronal-activity-cycles-on-61-cygni-a-and-b-awdtirsv3d.pdf

Sallie L. Baliunas

Papers

Environmental Effects of Increased Atmospheric Carbon Dioxide

Chromospheric and coronal emissions from the giants in the Hyades

Stellar Active Region Evolution - II. Identification and Evolution of Variance Morphologies in CA II H+K Time Series

Long-Term Spectroscopic Monitoring of Arcturus

Evidence for coronal activity cycles on 61 Cygni A and B