Author name code: baliunas ADS astronomy entries on 2022-09-14 author:"Baliunas, Sallie" ------------------------------------------------------------------------ Title: Magnetic and Rotational Evolution of ρ CrB from Asteroseismology with TESS Authors: Metcalfe, Travis S.; van Saders, Jennifer L.; Basu, Sarbani; Buzasi, Derek; Drake, Jeremy J.; Egeland, Ricky; Huber, Daniel; Saar, Steven H.; Stassun, Keivan G.; Ball, Warrick H.; Campante, Tiago L.; Finley, Adam J.; Kochukhov, Oleg; Mathur, Savita; Reinhold, Timo; See, Victor; Baliunas, Sallie; Soon, Willie Bibcode: 2021ApJ...921..122M Altcode: 2021arXiv210801088M During the first half of main-sequence lifetimes, the evolution of rotation and magnetic activity in solar-type stars appears to be strongly coupled. Recent observations suggest that rotation rates evolve much more slowly beyond middle age, while stellar activity continues to decline. We aim to characterize this midlife transition by combining archival stellar activity data from the Mount Wilson Observatory with asteroseismology from the Transiting Exoplanet Survey Satellite (TESS). For two stars on opposite sides of the transition (88 Leo and ρ CrB), we independently assess the mean activity levels and rotation periods previously reported in the literature. For the less active star (ρ CrB), we detect solar-like oscillations from TESS photometry, and we obtain precise stellar properties from asteroseismic modeling. We derive updated X-ray luminosities for both stars to estimate their mass-loss rates, and we use previously published constraints on magnetic morphology to model the evolutionary change in magnetic braking torque. We then attempt to match the observations with rotational evolution models, assuming either standard spin-down or weakened magnetic braking. We conclude that the asteroseismic age of ρ CrB is consistent with the expected evolution of its mean activity level and that weakened braking models can more readily explain its relatively fast rotation rate. Future spectropolarimetric observations across a range of spectral types promise to further characterize the shift in magnetic morphology that apparently drives this midlife transition in solar-type stars. Title: How much has the Sun influenced Northern Hemisphere temperature trends? An ongoing debate Authors: Connolly, Ronan; Soon, Willie; Connolly, Michael; Baliunas, Sallie; Berglund, Johan; Butler, C. John; Cionco, Rodolfo Gustavo; Elias, Ana G.; Fedorov, Valery M.; Harde, Hermann; Henry, Gregory W.; Hoyt, Douglas V.; Humlum, Ole; Legates, David R.; Lüning, Sebastian; Scafetta, Nicola; Solheim, Jan-Erik; Szarka, László; van Loon, Harry; Velasco Herrera, Víctor M.; Willson, Richard C.; Yan, Hong; Zhang, Weijia Bibcode: 2021RAA....21..131C Altcode: 2021arXiv210512126C In order to evaluate how much Total Solar Irradiance (TSI) has influenced Northern Hemisphere surface air temperature trends, it is important to have reliable estimates of both quantities. Sixteen different estimates of the changes in TSI since at least the 19th century were compiled from the literature. Half of these estimates are "low variability" and half are "high variability". Meanwhile, five largely-independent methods for estimating Northern Hemisphere temperature trends were evaluated using: 1) only rural weather stations; 2) all available stations whether urban or rural (the standard approach); 3) only sea surface temperatures; 4) tree-ring widths as temperature proxies; 5) glacier length records as temperature proxies. The standard estimates which use urban as well as rural stations were somewhat anomalous as they implied a much greater warming in recent decades than the other estimates, suggesting that urbanization bias might still be a problem in current global temperature datasets - despite the conclusions of some earlier studies. Nonetheless, all five estimates confirm that it is currently warmer than the late 19th century, i.e., there has been some "global warming" since the 19th century. For each of the five estimates of Northern Hemisphere temperatures, the contribution from direct solar forcing for all sixteen estimates of TSI was evaluated using simple linear least-squares fitting. The role of human activity on recent warming was then calculated by fitting the residuals to the UN IPCC's recommended "anthropogenic forcings" time series. For all five Northern Hemisphere temperature series, different TSI estimates suggest everything from no role for the Sun in recent decades (implying that recent global warming is mostly human-caused) to most of the recent global warming being due to changes in solar activity (that is, that recent global warming is mostly natural). It appears that previous studies (including the most recent IPCC reports) which had prematurely concluded the former, had done so because they failed to adequately consider all the relevant estimates of TSI and/or to satisfactorily address the uncertainties still associated with Northern Hemisphere temperature trend estimates. Therefore, several recommendations on how the scientific community can more satisfactorily resolve these issues are provided. Title: The Evolution of Rotation and Magnetic Activity in 94 Aqr Aa from Asteroseismology with TESS Authors: Metcalfe, Travis S.; van Saders, Jennifer L.; Basu, Sarbani; Buzasi, Derek; Chaplin, William J.; Egeland, Ricky; Garcia, Rafael A.; Gaulme, Patrick; Huber, Daniel; Reinhold, Timo; Schunker, Hannah; Stassun, Keivan G.; Appourchaux, Thierry; Ball, Warrick H.; Bedding, Timothy R.; Deheuvels, Sébastien; González-Cuesta, Lucía; Handberg, Rasmus; Jiménez, Antonio; Kjeldsen, Hans; Li, Tanda; Lund, Mikkel N.; Mathur, Savita; Mosser, Benoit; Nielsen, Martin B.; Noll, Anthony; Çelik Orhan, Zeynep; Örtel, Sibel; Santos, Ângela R. G.; Yildiz, Mutlu; Baliunas, Sallie; Soon, Willie Bibcode: 2020ApJ...900..154M Altcode: 2020arXiv200712755M Most previous efforts to calibrate how rotation and magnetic activity depend on stellar age and mass have relied on observations of clusters, where isochrones from stellar evolution models are used to determine the properties of the ensemble. Asteroseismology employs similar models to measure the properties of an individual star by matching its normal modes of oscillation, yielding the stellar age and mass with high precision. We use 27 days of photometry from the Transiting Exoplanet Survey Satellite to characterize solar-like oscillations in the G8 subgiant of the 94 Aqr triple system. The resulting stellar properties, when combined with a reanalysis of 35 yr of activity measurements from the Mount Wilson HK project, allow us to probe the evolution of rotation and magnetic activity in the system. The asteroseismic age of the subgiant agrees with a stellar isochrone fit, but the rotation period is much shorter than expected from standard models of angular momentum evolution. We conclude that weakened magnetic braking may be needed to reproduce the stellar properties, and that evolved subgiants in the hydrogen shell-burning phase can reinvigorate large-scale dynamo action and briefly sustain magnetic activity cycles before ascending the red giant branch. Title: Waldmeier Effect in Stellar Cycles Authors: Garg, Suyog; Karak, Bidya Binay; Egeland, Ricky; Soon, Willie; Baliunas, Sallie Bibcode: 2019ApJ...886..132G Altcode: 2019arXiv190912148G One of the most robust features of the solar magnetic cycle is that the stronger cycles rise faster than the weaker ones. This is popularly known as the Waldmeier Effect, which has been known for more than 100 yr. This fundamental feature of the solar cycle has not only practical implications, e.g., in predicting the solar cycle, but also implications in understanding the solar dynamo. Here we ask whether the Waldmeier Effect exists in other Sun-like stars. To answer this question, we analyze the Ca II H and K S-index from Mount Wilson Observatory for 21 Sun-like G-K stars. We specifically check two aspects of Waldmeier Effect, namely, (1) WE1: the anticorrelation between the rise times and the peaks and (2) WE2: the positive correlation between rise rates and amplitudes. We show that, except for HD 16160, HD 81809, HD 155886, and HD 161239, all stars considered in the analysis show WE2, while WE1 is found to be present only in some of the stars studied. Furthermore, the WE1 correlation is weaker than the WE2. Both WE1 and WE2 exist in the solar S-index as well. Similar to the solar cycles, the magnetic cycles of many stars are asymmetric about their maxima. The existence of the Waldmeier Effect and asymmetric cycles in Sun-like stars suggests that the dynamo mechanism which operates in the Sun is also operating in other stars. Title: Covariations of chromospheric and photometric variability of the young Sun analogue HD 30495: evidence for and interpretation of mid-term periodicities Authors: Soon, W.; Velasco Herrera, V. M.; Cionco, R. G.; Qiu, S.; Baliunas, S.; Egeland, R.; Henry, G. W.; Charvátová, I. Bibcode: 2019MNRAS.483.2748S Altcode: 2018MNRAS.tmp.3133S 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 relation to other observed mid-term periodicities roughly of the same time-scales that had been found recently from not only chromospheric and photospheric activity indices but also from coronal X-ray emissions as observed in a considerably large set of stellar samples including those young Sun analogues from the Kepler satellite project. Thus, there is an apparent universality of such mid-term activity modulation time-scales as this solar-stellar magnetic phenomenon is well observed directly for a host of solar activity related indices covering the photopsheric, chromospheric, coronal, and even the heliospheric (utilizing the measures of incoming galactic cosmic rays as a probe of activity variations) activity records. This is why we made a further attempt to interpret the results in search of a realistic generation mechanism as well as spatio-temporal persistency of the phenomenon under a wide scenario of dynamo simulations. Title: Evolution of Long Term Variability in Solar Analogs Authors: Egeland, Ricky; Soon, Willie; Baliunas, Sallie; Hall, Jeffrey C.; Henry, Gregory W. Bibcode: 2017IAUS..328..329E Altcode: 2017arXiv170402388E Earth is the only planet known to harbor life, therefore we may speculate on how the nature of the Sun-Earth interaction is relevant to life on Earth, and how the behavior of other stars may influence the development of life on their planetary systems. We study the long-term variability of a sample of five solar analog stars using composite chromospheric activity records up to 50 years in length and synoptic visible-band photometry about 20 years long. This sample covers a large range of stellar ages which we use to represent the evolution in activity for solar mass stars. We find that young, fast rotators have an amplitude of variability many times that of the solar cycle, while old, slow rotators have very little variability. We discuss the possible impacts of this variability on young Earth and exoplanet climates. Title: VizieR Online Data Catalog: Calibrated solar S-index time series (Egeland+, 2017) Authors: Egeland, R.; Soon, W.; Baliunas, S.; Hall, J. C.; Pevtsov, A. A.; Bertello, L. Bibcode: 2017yCat..18350025E Altcode: The Mount Wilson HK Program observed the Moon with both the HKP-1 and HKP-2 instruments. After removing 11 obvious outliers, there are 162 HKP-1 observations taken from 1966 September 2 to 1977 June 4 with the Mount Wilson 100 inch reflector, covering the maximum of cycle 20 and the cycle 20-21 minimum. As mentioned in Baliunas+ (1995ApJ...438..269B), observations of the Moon resumed in 1993 with the HKP-2 instrument. After removing 10 obvious outliers, there are 75 HKP-2 observations taken from 1994 March 27 to 2002 November 23 with the Mount Wilson 60 inch reflector, covering the end of cycle 22 and the cycle 23 minimum, extending just past the cycle 23 maximum. The end of observations coincides with the unfortunate termination of the HK Project in 2003.

We seek to extend our time series of solar variability beyond cycle 23 by establishing a proxy to the NSO Sacramento Peak (NSO/SP) observations taken from 1976 to 2016, covering cycles 21 to 24. The spectral intensity scale is set by integrating a 0.53Å band centered at 3934.869Å in the K-line wing and setting it to the fixed value of 0.162.

We extend the S-index record back to cycle 20 using the composite K time series of Bertello+ (2016SoPh..291.2967B). See section 3 for further explanations.

(1 data file). Title: The Mount Wilson Observatory S-index of the Sun Authors: Egeland, Ricky; Soon, Willie; Baliunas, Sallie; Hall, Jeffrey C.; Pevtsov, Alexei A.; Bertello, Luca Bibcode: 2017ApJ...835...25E Altcode: 2016arXiv161104540E The most commonly used index of stellar magnetic activity is the instrumental flux scale of singly ionized calcium H & K line core emission, S, developed by the Mount Wilson Observatory (MWO) HK Project, or the derivative index {R}{HK}\prime . Accurately placing the Sun on the S scale is important for comparing solar activity to that of the Sun-like stars. We present previously unpublished measurements of the reflected sunlight from the Moon using the second-generation MWO HK photometer during solar cycle 23 and determine cycle minimum {S}23,\min =0.1634+/- 0.0008, amplitude {{Δ }}{S}23=0.0143+/- 0.0012, and mean < {S}23> =0.1701+/- 0.0005. By establishing a proxy relationship with the closely related National Solar Observatory Sacramento Peak calcium K emission index, itself well correlated with the Kodaikanal Observatory plage index, we extend the MWO S time series to cover cycles 15-24 and find on average < {S}\min > =0.1621+/- 0.0008, < {{Δ }}{S}{cyc}> =0.0145+/- 0.0012, < {S}{cyc}> =0.1694+/- 0.0005. Our measurements represent an improvement over previous estimates that relied on stellar measurements or solar proxies with non-overlapping time series. We find good agreement from these results with measurements by the Solar-Stellar Spectrograph at Lowell Observatory, an independently calibrated instrument, which gives us additional confidence that we have accurately placed the Sun on the S-index flux scale. Title: Dynamo Sensitivity In Solar Analogs With 50 Years Of Ca II H & K Activity Authors: Egeland, Ricky; Soon, Willie; Baliunas, Sallie; Hall, Jeffrey C.; Pevtsov, Alexei A.; Henry, Gregory W. Bibcode: 2016csss.confE...6E Altcode: 2016csss.confE..73E; 2016arXiv160904756E The Sun has a steady 11-year cycle in magnetic activity most well-known by the rising and falling in the occurrence of dark sunspots on the solar disk in visible bandpasses. The 11-year cycle is also manifest in the variations of emission in the Ca II H & K line cores, due to non-thermal (i.e. magnetic) heating in the lower chromosphere. The large variation in Ca II H & K emission allows for study of the patterns of long-term variability in other stars thanks to synoptic monitoring with the Mount Wilson Observatory HK photometers (1966-2003) and Lowell Observatory Solar-Stellar Spectrograph (1994-present). Overlapping measurements for a set of 27 nearby solar-analog (spectral types G0-G5) stars were used to calibrate the two instruments and construct time series of magnetic activity up to 50 years in length. Precise properties of fundamental importance to the dynamo are available from Hipparcos, the Geneva-Copenhagen Survey, and CHARA interferometry. Using these long time series and measurements of fundamental properties, we do a comparative study of stellar "twins" to explore the sensitivity of the stellar dynamo to small changes to structure, rotation, and composition. We also compare this sample to the Sun and find hints that the regular periodic variability of the solar cycle may be rare among its nearest neighbors in parameter space. Title: The Solar Dynamo Zoo Authors: Egeland, Ricky; Soon, Willie; Baliunas, Sallie; Hall, Jeffrey C.; Pevtsov, Alexei A.; Henry, Gregory W. Bibcode: 2016csss.confE..72E Altcode: We present composite time series of Ca II H & K line core emission indices of up to 50 years in length for a set of 27 solar-analog stars (spectral types G0-G5; within 10% of the solar mass) and the Sun. These unique data are available thanks to the long-term dedicated efforts of the Mount Wilson Observatory HK project, the Lowell Observatory Solar-Stellar Spectrograph, and the National Solar Observatory/Air Force Research Laboratory/Sacramento Peak K-line monitoring program. The Ca II H & K emission originates in the lower chromosphere and is strongly correlated with the presence of magnetic plage regions in the Sun. These synoptic observations allow us to trace the patterns long-term magnetic variability and explore dynamo behavior over a wide range of rotation regimes and stellar evolution timescales.In this poster, the Ca HK observations are expressed using the Mount Wilson S-index. Each time series is accompanied by a Lomb-Scargle periodogram, fundemental stellar parameters derived from the Geneva-Copenhagen Survey, and statistics derived from the time series including the median S-index value and seasonal and long-term amplitudes. Statistically significant periodogram peaks are ranked according to a new cycle quality metric. We find that clear, simple, Sun-like cycles are the minority in this sample. Title: Magnetic cycles at different ages of stars Authors: Oláh, K.; Kővári, Zs.; Petrovay, K.; Soon, W.; Baliunas, S.; Kolláth, Z.; Vida, K. Bibcode: 2016A&A...590A.133O Altcode: 2016arXiv160406701O
Aims: We study the different patterns of interannual magnetic variability in stars on or near the lower main sequence, approximately solar-type (G-K dwarf) stars in time series of 36 yr from the Mount Wilson Observatory Ca II H&K survey. Our main aim is to search for correlations between cycles, activity measures, and ages.
Methods: Time-frequency analysis has been used to discern and reveal patterns and morphology of stellar activity cycles, including multiple and changing cycles, in the datasets. Both the results from short-term Fourier transform and its refinement using the Choi-Williams distribution, with better frequency resolution, are presented in this study. Rotational periods of the stars were derived using multifrequency Fourier analysis.
Results: We found at least one activity cycle on 28 of the 29 stars we studied. Twelve stars, with longer rotational periods (39.7 ± 6.0 days), have simple smooth cycles, and the remaining stars, with much faster rotation (18.1 ± 12.2 days) on average, show complex and sometimes vigorously changing multiple cycles. The cycles are longer and quite uniform in the first group (9.7 ± 1.9 yr), while they are generally shorter and vary more strongly in the second group (7.6 ± 4.9). The clear age division between stars with smooth and complex cycles follows the known separation between the older and younger stars at around 2 to 3 Gyr of age. Title: Dynamo Sensitivity in Solar Analogs with 50 Years of Ca II H & K Activity Authors: Egeland, Ricky; Soon, Willie H.; Baliunas, Sallie L.; Hall, Jeffrey C.; Pevtsov, Alexei A.; Henry, Gregory W. Bibcode: 2016SPD....4720307E Altcode: The Sun has a steady 11-year cycle in magnetic activity most well-known by the rising and falling in the occurrence of dark sunspots on the solar disk in visible bandpasses. The 11-year cycle is also manifest in the variations of emission in the Ca II H & K line cores, due to non-thermal (i.e. magnetic) heating in the lower chromosphere. The large variation in Ca II H & K emission allows for study of the patterns of long-term variability in other stars thanks to synoptic monitoring with the Mount Wilson Observatory HK photometers (1966-2003) and Lowell Observatory Solar-Stellar Spectrograph (1994-present). Overlapping measurements for a set of 27 nearby solar-analog (spectral types G0-G5) stars were used to calibrate the two instruments and construct time series of magnetic activity up to 50 years in length. Precise properties of fundamental importance to the dynamo are available from Hipparcos, the Geneva-Copenhagen Survey, and CHARA interferometry. Using these long time series and measurements of fundamental properties, we do a comparative study of stellar "twins" to explore the sensitivity of the stellar dynamo to small changes to structure, rotation, and composition. We also compare this sample to the Sun and find hints that the regular periodic variability of the solar cycle may be rare among its nearest neighbors in parameter space. Title: The Solar Dynamo Zoo Authors: Egeland, Ricky; Soon, Willie H.; Baliunas, Sallie L.; Hall, Jeffrey C.; Pevtsov, Alexei A.; Henry, Gregory W. Bibcode: 2016SPD....47.1103E Altcode: We present composite time series of Ca II H & K line core emission indices of up to 50 years in length for a set of 27 solar-analog stars (spectral types G0-G5; within ~10% of the solar mass) and the Sun. These unique data are available thanks to the long-term dedicated efforts of the Mount Wilson Observatory HK project, the Lowell Observatory Solar-Stellar Spectrograph, and the National Solar Observatory/Air Force Research Laboratory/Sacremento Peak K-line monitoring program. The Ca II H & K emission originates in the lower chromosphere and is strongly correlated with the presence of magnetic plage regions in the Sun. These synoptic observations allow us to trace the patterns long-term magnetic variability and explore dynamo behavior over a wide range of rotation regimes and stellar evolution timescales. Title: Wilson, Olin Chaddock, Jr. Authors: Baliunas, Sallie Bibcode: 2014bea..book.2351B Altcode: No abstract at ADS Title: Rotation periods of exoplanet host stars Authors: Simpson, E. K.; Baliunas, S. L.; Henry, G. W.; Watson, C. A. Bibcode: 2010MNRAS.408.1666S Altcode: 2010arXiv1006.4121S; 2010MNRAS.tmp.1209S The stellar rotation periods of 10 exoplanet host stars have been determined using newly analysed CaII H&K flux records from the Mount Wilson Observatory and Strömgren b, y photometric measurements from Tennessee State University's automatic photometric telescopes at the Fairborn Observatory. Five of the rotation periods have not previously been reported, with that of HD 130322 very strongly detected at Prot = 26.1 +/- 3.5 d. The rotation periods of five other stars have been updated using new data. We use the rotation periods to derive the line-of-sight inclinations of the stellar rotation axes, which may be used to probe theories of planet formation and evolution when combined with the planetary orbital inclination found from other methods. Finally, we estimate the masses of 14 exoplanets under the assumption that the stellar rotation axis is aligned with the orbital axis. We calculate the mass of HD 92788 b (28 MJ) to be within the low-mass brown dwarf regime and suggest that this object warrants further investigation to confirm its true nature. Title: Differential rotation of some HK-Project stars and the butterfly diagrams Authors: Katsova, M. M.; Livshits, M. A.; Soon, W.; Baliunas, S. L.; Sokoloff, D. D. Bibcode: 2010NewA...15..274K Altcode: We analyze the long-term variability of the chromospheric radiation of 20 stars monitored in the course of the HK-Project at the Mount Wilson Observatory. We apply the modified wavelet algorithm for this set of gapped time series. Besides the mean rotational periods for all these stars, we find reliable changes of the rotational periods from year to year for a few stars. Epochs of slower rotation occur when the activity level of the star is high, and the relationship repeats again during the next maximum of an activity cycle. Such an effect is traced in two stars with activity cycles that are not perfectly regular (but labeled "Good" under the classification in [Baliunas, S.L., Donahue, R.A., Soon, W.H., Horne, J.H., Frazer, J., Woodard-Eklund, L., Bradford, M., Rao, L.M., Wilson, O.C., Zhang, Q. et al., 1995. ApJ 438, 269.]) but the two stars have mean activity levels exceed that of the Sun. The averaged rotational period of HD 115404 is 18.5 days but sometimes the period increases up to 21.5 days. The sign of the differential rotation is the same as the Sun's, and the value ΔΩ / < Ω > = - 0.14. For the star HD 149661, this ratio is -0.074. Characteristic changes of rotational periods occur over around three years when the amplitude of the rotational modulation is large. These changes can be transformed into latitude-time butterfly diagrams with minimal a priori assumptions. We compare these results with those for the Sun as a star and conclude that epochs when surface inhomogeneities rotate slower are synchronous with the reversal of the global magnetic dipole. Title: Multiple and changing cycles of active stars. II. Results Authors: Oláh, K.; Kolláth, Z.; Granzer, T.; Strassmeier, K. G.; Lanza, A. F.; Järvinen, S.; Korhonen, H.; Baliunas, S. L.; Soon, W.; Messina, S.; Cutispoto, G. Bibcode: 2009A&A...501..703O Altcode: 2009arXiv0904.1747O Aims: We study the time variations in the cycles of 20 active stars based on decade-long photometric or spectroscopic observations.
Methods: A method of time-frequency analysis, as discussed in a companion paper, is applied to the data.
Results: Fifteen stars definitely show multiple cycles, but the records of the rest are too short to verify a timescale for a second cycle. The cycles typically show systematic changes. For three stars, we found two cycles in each of them that are not harmonics and vary in parallel, indicating a common physical mechanism arising from a dynamo construct. The positive relation between the rotational and cycle periods is confirmed for the inhomogeneous set of active stars.
Conclusions: Stellar activity cycles are generally multiple and variable. Title: Inter-Division IX-X-XI Working Group Astronomy from The Moon Authors: Baliunas, Sallie L.; Kondo, Yoji; Kaifu, Norio; Engvold, Oddbjørn; Kaifu, Norio; Okuda, Haruyuki; Terzian, Yervant Bibcode: 2009IAUTA..27..356B Altcode: During the period the Working Group had proposed and was granted renewed status by Division XI Space and High-Energy Astrophysics. Additionally the Working Group requested to be extended to Division IX Optical and Infrared Techniques, Division X Radio Astronomy, as well as Division XI. Title: Long-Term Spectroscopic Monitoring of Arcturus Authors: Brown, Kevin I. T.; Gray, David F.; Baliunas, Sallie L. Bibcode: 2008ApJ...679.1531B Altcode: 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 Å to Fe I λ6252.56 Å lines and line bisectors from Fe I λ6252.56 Å 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. Title: Changing stellar activity cycles Authors: Oláh, K.; Strassmeier, K. G.; Granzer, T.; Soon, W.; Baliunas, S. L. Bibcode: 2007AN....328.1072O Altcode: We investigated continuous long-term photometric datasets of thirteen active stars, Ca II variability of one single main-sequence star, and 10.7cm radio data of the Sun, with simple Fourier- and time-frequency analysis. The data reflect the strength of the activity manifested in magnetic spots. All studied stars show multiple (2 to 4) cycles of different lengths. The time-frequency analysis reveals, that in several cases of the sample one or two of the cycles exhibit continuous changes (increase or decrease). For four stars (V711 Tau, IL Hya, HK Lac, HD 100180) and for the Sun we find that the cycle length changes are strong, amounting to 10-50% during the observed time intervals. The cycle lengths are generally longer for stars with longer rotational periods. Title: Division XI / Wg: Astronomy from the Moon Authors: Baliunas, Sallie L.; Kondo, Yoji; Kaifu, Norio; Engvold, Oddbjorn; Kaifu, Norio; Okuda, Haruyuki; Terzian, Yervant; Wamsteker, Willem Bibcode: 2007IAUTB..26..208B Altcode: The Business Meeting opened with a recall of the memory of a member of the Organizing Committee, Willem Wamsteker. N. Kaifu, past president of the Working Group, was thanked for his outstanding service. Title: Patterns of Photometric and Chromospheric Variation among Sun-like Stars: A 20 Year Perspective Authors: Lockwood, G. W.; Skiff, B. A.; Henry, Gregory W.; Henry, Stephen; Radick, R. R.; Baliunas, S. L.; Donahue, R. A.; Soon, W. Bibcode: 2007ApJS..171..260L Altcode: 2007astro.ph..3408L 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 variation has probably now been observed for a majority of the program stars. Twenty-seven stars are deemed variable according to an objective statistical criterion. On a year-to-year timescale, young active stars become fainter when their Ca II emission increases, while older less active stars such as the Sun become brighter when their Ca II emission increases. The Sun's total irradiance variation, scaled to the b and y stellar filter photometry, still appears to be somewhat smaller than stars in our limited sample with similar mean chromospheric activity, but we now regard this discrepancy as probably due mainly to our limited stellar sample. Title: Coronal activity cycles in 61 Cygni Authors: Hempelmann, A.; Robrade, J.; Schmitt, J. H. M. M.; Favata, F.; Baliunas, S. L.; Hall, J. C. Bibcode: 2006A&A...460..261H Altcode: Context: .While the existence of stellar analogues of the 11 years solar activity cycle is proven for dozens of stars from optical observations of chromospheric activity, the observation of clearly cyclical coronal activity is still in its infancy.
Aims: .In this paper, long-term X-ray monitoring of the binary 61 Cygni is used to investigate possible coronal activity cycles in moderately active stars.
Methods: .We are monitoring both stellar components, a K5V (A) and a K7V (B) star, of 61 Cyg with XMM-Newton. The first four years of these observations are combined with ROSAT HRI observations of an earlier monitoring campaign. The X-ray light curves are compared with the long-term monitoring of chromospheric activity, as measured by the Mt.Wilson CaII H+K S-index.
Results: .Besides the observation of variability on short time scales, long-term variations of the X-ray activity are clearly present. For 61 Cyg A we find a coronal cycle which clearly reflects the well-known and distinct chromospheric activity cycle. The changes of coronal properties during the cycle resemble the solar behaviour. The coronal activity of 61 Cyg B also follows the chromospheric variability, although a pronounced sinusoidal chromospheric cycle of large amplitude is not noticeable. This is also reflected in the XMM-Newton observations with a rather complex long-term variability during that time.
Conclusions: .61 Cyg A is the first star where a persistent coronal activity cycle has been observed. Title: Investigating the Rotation Periods of Exoplanet Host Stars Authors: Simpson, Elaine K.; Baliunas, S.; Henry, G. Bibcode: 2006AAS...20915201S Altcode: 2006BAAS...38.1105S Of approximately 200 exoplanet host stars, we investigate a subset of fifty whose fluxes in the Ca II H and K passbands and b and y photometric passbands have been measured and in several cases, accumulated over a period of years or longer.

The Ca II records from Mount Wilson Observatory's HK Project and highly precise photometric measurements from Tennessee State University's Automated Photoelectric Telescopes at Fairborn Observatory detail variability of surface magnetic features, leading in some cases to a direct measurement of periodicities thought to be associated with rotation.

We discuss findings of rotation in the context of surface magnetic activity, its interannual variability, age and other physical properties of the star. As possible we infer inclination of the stellar rotation axis and its influence on exoplanet detection methods.

This work has been supported by NASA grant JPL-1270064. Title: The Extrasolar Planet ɛ Eridani b Orbit and Mass Authors: Benedict, George F.; McArthur, B. E.; Gatewood, G.; Nelan, E.; Cochran, W.; Hatzes, A.; Endl, M.; Wittenmyer, R.; Baliunas, S.; Walker, G.; Yang, S.; Kurster, M.; Els, S.; Paulson, D. Bibcode: 2006DPS....38.1009B Altcode: 2006BAAS...38.1294B Hubble Space Telescope (HST) Fine Guidance Sensor astrometric observations of the nearby (3.22 pc), K2 V star epsilon Eridani have been combined with ground-based astrometric and radial velocity data to determine the mass of its known companion. We model astrometric and radial velocity measurements simultaneously to obtain the parallax, proper motion, perturbation period, perturbation inclination, and perturbation size. Due to the long period of the companion, epsilon Eridani b, we extend our astrometric coverage to a total of 14.94 years (including the three year span of the HST data) by including lower-precision ground-based astrometry from the Allegheny Multichannel Astrometric Photometer. Radial velocity coverage now spans 1980.8 -2006.3. We obtain a perturbation period, P = 6.85 ± 0.03 yr, semi-major axis α =1.88 ± 0.20 mas, and inclination i = 30.1 ± 3.8°. This inclination is consistent with a previously measured dust disk inclination (Greaves et al. 2005), demonstrating dust disk and exoplanet co-planarity for the first time. Co-planarity is an expected consequence of planet formation theories. Assuming a primary mass M* = 0.83 MΟ, we obtain a companion mass M = 1.55 ± 0.24MJup. Given the relatively young age of epsilon Eridani ( 800 Myr), this accurate exoplanet mass and orbit can usefully inform future direct imaging attempts. We predict the next periastron at 2007.3 with a total separation, ρ = 0.3” at position angle, p.a. = 27°. Orbit orientation and geometry dictate that epsilon Eridani b will appear brightest in reflected light very nearly at periastron. Radial velocities spanning over 25 years indicate an acceleration consistent with a Jupiter-mass object with a period in excess of 50 years, possibly the object responsible for one prominent feature of the dust morphology, the inner cavity. We gratefully acknowledge NASA Grants GO-09167, -09347, -09969, -10610, and 10989. Title: A Survey of Chromospheric Activity in the Solar-Type Stars in the Open Cluster M67 Authors: Giampapa, Mark S.; Hall, Jeffrey C.; Radick, Richard R.; Baliunas, Sallie L. Bibcode: 2006ApJ...651..444G Altcode: 2006astro.ph..7313G We present the results of a spectroscopic survey of the Ca II H and K core strengths in a sample of 60 solar-type stars that are members of the solar-age and solar-metallicity open cluster M67. We adopt the HK index, defined as the summed H+K core strengths in 1 Å bandpasses centered on the H and K lines, respectively, as a measure of the chromospheric activity that is present. We compare the distribution of mean HK index values for the M67 solar-type stars with the variation of this index as measured for the Sun during the contemporary solar cycle. We find that the stellar distribution in our HK index is broader than that for the solar cycle. Approximately 17% of the M67 Sun-like stars exhibit average HK indices that are less than solar minimum. About 7%-12% are characterized by relatively high activity in excess of solar maximum values, while 72%-80% of the solar analogs exhibit Ca II H+K strengths within the range of the modern solar cycle. The ranges given reflect uncertainties in the most representative value of the maximum in the HK index to adopt for the solar cycle variations observed during the period AD 1976-2004. Thus, ~20%-30% of our homogeneous sample of Sun-like stars have mean chromospheric H+K strengths that are outside the range of the contemporary solar cycle. Any cycle-like variability that is present in the M67 solar-type stars appears to be characterized by periods greater than ~6 yr. Finally, we estimate a mean chromospheric age for M67 in the range of 3.8-4.3 Gyr.

The results presented herein are based on data obtained at the WIYN telescope and at the McMath-Pierce Solar Telescope. The WIYN Observatory is a joint facility of the University of Wisconsin-Madison, Indiana University, Yale University, and the National Optical Astronomy Observatory. The McMath-Pierce Solar Telescope Facility is operated by the National Solar Observatory for the National Science Foundation. This paper is WIYN Open Cluster Study XXVIII in the series. Title: The Extrasolar Planet ɛ Eridani b: Orbit and Mass Authors: Benedict, G. Fritz; McArthur, Barbara E.; Gatewood, George; Nelan, Edmund; Cochran, William D.; Hatzes, Artie; Endl, Michael; Wittenmyer, Robert; Baliunas, Sallie L.; Walker, Gordon A. H.; Yang, Stephenson; Kürster, Martin; Els, Sebastian; Paulson, Diane B. Bibcode: 2006AJ....132.2206B Altcode: 2006astro.ph.10247B Hubble Space Telescope (HST) observations of the nearby (3.22 pc) K2 V star ɛ Eridani have been combined with ground-based astrometric and radial velocity data to determine the mass of its known companion. We model the astrometric and radial velocity measurements simultaneously to obtain the parallax, proper motion, perturbation period, perturbation inclination, and perturbation size. Because of the long period of the companion, ɛ Eri b, we extend our astrometric coverage to a total of 14.94 yr (including the 3 yr span of the HST data) by including lower precision ground-based astrometry from the Allegheny Multichannel Astrometric Photometer. Radial velocities now span 1980.8-2006.3. We obtain a perturbation period, P=6.85+/-0.03 yr, semimajor axis α=1.88+/-0.20 mas, and inclination i=30.1d+/-3.8d. This inclination is consistent with a previously measured dust disk inclination, suggesting coplanarity. Assuming a primary mass M*=0.83 Msolar, we obtain a companion mass M=1.55MJ+/-0.24MJ. Given the relatively young age of ɛ Eri (~800 Myr), this accurate exoplanet mass and orbit can usefully inform future direct-imaging attempts. We predict the next periastron at 2007.3 with a total separation ρ=0.3" at position angle P.A.=-27deg. Orbit orientation and geometry dictate that ɛ Eri b will appear brightest in reflected light very nearly at periastron. Radial velocities spanning over 25 yr indicate an acceleration consistent with a Jupiter-mass object with a period in excess of 50 yr, possibly responsible for one feature of the dust morphology, the inner cavity.

Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Title: Decadal and Interdecadal Surface Magnetic Variability of Sunlike and Other Cool Stars Authors: Baliunas, S. L. Bibcode: 2006IAUJD...8E..65B Altcode: Cross sectional and time serial surveys of disk-integrated proxies of surface magnetic features in cool stars - those with non-trivial subsurface convection zones - have yielded information on stellar magnetic variability, which may express in one or more modes. For example, decadal magnetic variability is present on the sun and some lower-main sequence stars. Additionally, evidence for interdecadal magnetic variability, for instance, the solar Maunder Minimum of the 17^th century and first noted in the parameter of Sunspot Number, may also be present. Surface magnetic variability may be viewed as an expression of the action of a dynamo within or just below the convective zone that produces large-scale dynamo waves. Consequences for dynamo models will be discussed, based primarily on results from the near-four-decades-long monitoring program of Ca II H and K emission fluxes of lower main sequence stars at Mount Wilson Observatory, the precision photometry made at Lowell and Fairborn Observatory-Tennessee State University, and solar modulation imprinted in terrestrial ecosystems.. Title: Anharmonic and standing dynamo waves: theory and observation of stellar magnetic activity Authors: Baliunas, S.; Frick, P.; Moss, D.; Popova, E.; Sokoloff, D.; Soon, W. Bibcode: 2006MNRAS.365..181B Altcode: 2005MNRAS.tmp.1044B The familiar decadal cycle of solar activity is one expression of interannual variability of surface magnetism observed in stars on or near the lower main sequence. From studies of time-series of CaII H and K emission fluxes that go back more than 35 yr and have been accumulated for such stars at the Mount Wilson Observatory by the HK Project, we define a quantitative measure, called anharmonicity, of the cyclic component of interannual magnetic variability. Anharmonicity provides a connection between observed variations in magnetic activity and the two-dimensional description of a Parker dynamo model. We explore the parameter space of the Parker dynamo model and find an excellent counterpart in the records of several of the lowest-mass (late K-type to early M-type) active stars in the HK Project sample to the solutions containing highly anharmonic, standing dynamo waves. We interpret anharmonicity apparent in the records as resulting from non-propagating or standing dynamo waves, which operate in a regime that is substantially supercriticial. There, for the majority of a cycle, or pulse of decadal-to-interdecadal variability, the large-scale magnetic fields are generated and maintained by winding of field by differential rotation rather than by the joint action of differential rotation and helical convection. Among the less active stars (the Sun is considered such a star in the HK Project sample) we find a correspondence between anharmonicity and Parker dynamo model solutions that include simple harmonic, migratory and/or intermediate-type dynamo wave patterns over a broad range of dynamo parameters. Title: VizieR Online Data Catalog: Ca II H and K Measurements Made at MWO (Duncan+ 1991) Authors: Duncan, D. K.; Vaughan, A. H.; Wilson, O. C.; Preston, G. W.; Frazer, J.; Lanning, H. H.; Misch, A.; Mueller, J.; Soyumer, D.; Woodard, L.; Baliunas, S. L.; Noyes, R. W.; Hartmann, L. W.; Porter, A.; Zwaan, K.; Middelkoop, F.; Rutter, R.; Mihalas, D. Bibcode: 2005yCat.3159....0D Altcode: Summaries are presented of the photoelectric measurements of stellar CaII H and K line intensity made at Mount Wilson Observatory during the years 1966-1983. These results are derived from 65,263 individual observations of 1296 stars. For each star, for each observing season, the maximum, minimum, mean, and variation of the instrumental H and K index "S" are given, as well as a measurement of the accuracy of observation. A total of 3110 seasonal summaries are reported.

These observations were obtained with two instruments, HKP-1 and HKP-2. The HKP-2 instrument is a four-channel chopping spectrometer which records counts in 1.09{AA} FWHM triangular bandpasses centered in the H and K lines as well as in two 20{AA} reference bandpasses centered on 3901.067 and 4001.067{AA}. The stellar activity is expressed by the index S defined as

S = {alpha} (Nh+Nk)/(Nr+Nv)

where Nh and Nk are the counts (corrected from background) in the H and K lines, Nr and Nv those in the reference continuum bandpasses, and {alpha} is a constant of proportionality used to correct for night-to-night instrumental variations. Higher values of S generally correspond to higher levels of chromospehric activities.

Factors which effect the ability to detect stellar activity variations and accurately measure their amplitudes such as the accuracy of the H and K measurements and scattered light contamination are discussed. Relations are given which facilitate intercomparison of "S" values with residual intensities from ordinary spectrophotometry, and for converting measurements to absolute fluxes.

(1 data file). Title: Anharmonicity of Stellar Cycles: A Wavelet Quantification Authors: Baliunas, S.; Frick, P.; Moss, D.; Popova, E.; Sokoloff, D.; Soon, W. Bibcode: 2004SoPh..224..179B Altcode: 2005SoPh..224..179B Two quantitative measures for the anharmonicity of stellar cycles, as recorded in the Ca II H and K chromospheric activity data as well as in simple dynamo models, are presented and discussed. Title: Time-spectra of chromospheric activity of old solar-type stars: detection of rotational signals from double wavelet analysis Authors: Frick, Peter; Soon, Willie; Popova, Elena; Baliunas, Sallie Bibcode: 2004NewA....9..599F Altcode: We introduce a novel technique, called the double wavelet analysis (DWA), for the determination of stellar rotation periods from time serial data. This first paper aims narrowly at the discussion, introduction and application of the DWA technique to records of surface magnetism in solar-type (relatively old) lower main sequence stars that are obtained by the Mount Wilson Observatory (MWO) HK Project. The technique takes a series of careful steps that seek to optimize wavelet parameters and normalization schemes, ultimately allowing fine-tuned, arguably more accurate, estimates of rotation-modulated signals (with, e.g., periods of days to months) in records that contain longer periodicities such as stellar magnetic activity cycles (with, e.g., period of years). The apparent rotation periods estimated from the DWA technique are generally consistent with results from both ;first-pass; (i.e., ordinary) global wavelet spectrum and earlier classical periodogram analyses. But there are surprises as well. For example, the rotation period of the ancient subdwarf Goombridge 1830 (HD 103095), previously identified as ≈31 days, suggests under the DWA technique a significantly slower period of 60 days. DWA spectra also generally reveal a shift in the cycle period toward high frequencies (hence shorter periods) compared to the first-pass wavelet spectrum. For solar-type stars analyzed here, the character of the DWA spectrum and slope of the first-pass global wavelet spectrum produce a classification scheme that allows a star's record to be placed into one of three categories. Title: A Comparison of Solar Irradiance Variations with those of Similar Stars Authors: Lockwood, G. W.; Radick, R. R.; Henry, G. W.; Baliunas, S. L. Bibcode: 2004AAS...204.0304L Altcode: 2004BAAS...36..671L The photometric variations of Sun-like stars, including one bona fide ``solar twin," HD146233 = 18 Sco, have been observed at Lowell Observatory and Fairborn Observatory in b and y filters of the uvby photometric system over the past 3-18 years. Parallel HK flux measurements were made at the Mount Wilson Observatory. Thirty five stars observed at Lowell and Fairborn for more than a decade combined define a power law relationship of variability as a function of mean chromopsheric activity. On this diagram, the Sun lies 3x lower than stars of similar chromospheric activity. Restricting the sample to stars observed only at Fairborn but for a shorter length of time reduces the discrepancy to less than a factor of two. Nevertheless, the Sun still lies below a fitted power law. We will present an analysis of the various biases possibly present in our data and show some example light curves.

This work was supported by the National Science Foundation, the National Aeronautics and Space Administration, and the Air Force Office of Scientific Research. Title: Stellar magnetic cycles Authors: Baliunas, S. L. Bibcode: 2004AAS...204.3603B Altcode: 2004BAAS...36..707B Is hope for understanding the solar magnetic cycle to be found in stars?

Observations of stars with significant sub-surface convective zones -- masses smaller than about 1.5 solar masses on the lower main sequence and many types of cool, post-main-sequence stars -- indicate the presence of surface and atmospheric inhomogeneities analogous to solar magnetic features, making stellar magnetic activity a cosmically widespread phenomenon. Observations have been made primarily in visible wavelengths, and important information has also been derived from the ultraviolet and x-ray spectrum regions.

Interannual to interdecadal variability of spectrum indicators of stellar magnetic features is common, and in some cases similar in appearance to the 11-year sunspot cycle.

Successful models of the physical processes responsible for stellar magnetic cycles, typically cast as a magnetohydrodynamic dynamo, require advances in understanding not only convection but also the magnetic field's interaction with it. The observed facts that underpin the hope for models will be summarized. Properties of stellar magnetic cycles will be compared and contrasted with those of the sun, including inferences from paleo-environmental reservoirs that contain information on solar century- to millennial-scale magnetic variability.

Partial support of this research came from NASA NAG5-7635, NRC COBASE, CRDF 322, MIT-MSG 5710001241, JPL 1236821, AF 49620-02-1-0194, Richard Lounsberry Foundation, Langley-Abbot, Rollins, Scholarly Studies and James Arthur Funds (Smithsonian Institution) and several generous individuals. Title: Stellar Magnetic Activity, the Earth and Exoplanets: How Future Space Missions Can Contribute to Understanding Solar Activity and Solar-terrestrial Influences Authors: Baliunas, S. L.; Soon, W. W. -H. Bibcode: 2004AAS...204.0809B Altcode: 2004BAAS...36..790B The solar spectral and particle output varies over time scales of minutes to eons; some of those variations are documented or claimed to have influenced the terrestrial environment. The origins of solar variability include the progress of fusion through time and the complex interaction of the interior gas and magnetic fields. The Mount Wilson HK Project has yielded information on stellar magnetic activity on more than 2,000 stars going as far back as 38 years in order to put solar magnetic activity in a physical perspective unavailable from theory and models alone. We discuss how future space missions like Space Interferometry Mission (SIM) and Stellar Imager (SI) would contribute to understanding solar variability that has influenced -- and should continue to influence -- life and the environment on earth.

This research funded in part by MIT-MSG 5710001241, JPL 1236821, AF 49620-02-1-0194, a grant from NASA HQ and GSFC to SAO for the SI Vision Mission Study, NASA NAG5-7635, NRC COBASE, CRDF 322, Richard Lounsberry Foundation, Langley-Abbot, Rollins, Scholarly Studies and James Arthur Funds (Smithsonian Institution) and several generous individuals. Title: High-amplitude, long-term X-ray variability in the solar-type star HD 81809: The beginning of an X-ray activity cycle? Authors: Favata, F.; Micela, G.; Baliunas, S. L.; Schmitt, J. H. M. M.; Güdel, M.; Harnden, F. R., Jr.; Sciortino, S.; Stern, R. A. Bibcode: 2004A&A...418L..13F Altcode: 2004astro.ph..3142F We present the initial results from our XMM-Newton program aimed at searching for X-ray activity cycles in solar-type stars. HD 81809 is a G2-type star (somewhat more evolved than the Sun, and with a less massive companion) with a pronounced 8.2 yr chromospheric cycle, as evident from from the Mt. Wilson program data. We present here the results from the initial 2.5 years of XMM-Newton observations, showing that large amplitude (a factor of ≃10) modulation is present in the X-ray luminosity, with a clearly defined maximum in mid 2002 and a steady decrease since then. The maximum of the chromospheric cycle took place in 2001; if the observed X-ray variability is the initial part of an X-ray cycle, this could imply a phase shift between chromospheric and coronal activity, although the current descent into chromospheric cycle minimum is well reflected into the star's X-ray luminosity. The observations presented here provide clear evidence for the presence of large amplitude X-ray variability coherent with the activity cycle in the chromosphere in a star other than the Sun. Title: Estimation and representation of long-term (>40 year) trends of Northern-Hemisphere-gridded surface temperature: A note of caution Authors: Soon, Willie W. -H.; Legates, David R.; Baliunas, Sallie L. Bibcode: 2004GeoRL..31.3209S Altcode: 2004GeoRL..3103209S Several quantitative estimates of surface instrumental temperature trends in the late 20th century are compared by using published results and our independent analyses. These estimates highlight a significant sensitivity to the method of analysis, the treatment of data, and the choice of data presentation (i.e., size of the smoothing filter window). Providing an accurate description of both quantitative uncertainties and sensitivity to the treatment of data is recommended as well as avoiding subjective data-padding procedures. Title: Variability in a Large Sample of Sun-Like Stars Authors: Fekel, F. C.; Henry, G. W.; Baliunas, S. L.; Donahue, R. A. Bibcode: 2004IAUS..219..269F Altcode: 2003IAUS..219E.168F At Fairborn Observatory we have observed a sample of about 350 nearby late-F to early-K dwarfs and subgiants of various ages. In particular over half of the sample are G0--G5 dwarfs. For up to a decade photometric obervations have been obtained with a nightly precision of 0.001 mag and 0.0001 mag for yearly means. Complimentary high-dispersion spectra obtained at Kitt Peak National Observatory have been used to determine spectral types radial velocities projected rotational velocities and estimate metallicities for the stars in the sample. The photometric results will be examined in the context of contemporaneous Mt. Wilson Observatory measurements of chromospheric emission a proxy for magnetic activity. Preliminary results on short-term and long-term light variability will be discussed. The Sun's position in this stellar sample will be examined. Title: The Variability of Sunlike Stars on Decadal Timescales Authors: Radick, R. R.; Lockwood, G. W.; Henry, G. W.; Baliunas, S. L. Bibcode: 2004IAUS..219..264R Altcode: 2003IAUS..219E.214R Thirty-four stars similar to the Sun have been monitored in chromospheric Ca II HK emission since 1966 from Mount Wilson Observatory and in Strömgren b and y photometry between 1984-2000 from Lowell Observatory and since 1993 from Fairborn Observatory. We have just completed an updated analysis of these time series in which we have successfully merged the Lowell and Fairborn data. We find that the precision per observation of these two photometric datasets is almost identical although the Fairborn observations are considerably more plentiful. Overall our results confirm what we published previously (Radick et al. 1998 ApJ Suppl 118 239): the Sun's variability pattern is not uncommon among sunlike stars. The Sun's current behavior however may be unusually regular - many of the stars in our sample vary more erratically than the Sun. We also encounter stars whose chromospheric and photometric ouputs appear to be uncoupled - one varying but not the other. Finally we continue to find examples of stars with time-averaged chromospheric emission levels comparable to that of the present-day Sun but photometric amplitudes several times larger. Such ""ill-behaved"" stars may be telling us about activity patterns that deviate from the ""standard"" solar model. Title: View from the mountaintop Authors: Baliunas, Sallie Bibcode: 2003Ast....31i..60B Altcode: Mount Wilson Observatory offers astronomers some of the best seeing anywhere. Title: Evidence for coronal activity cycles on 61 Cygni A and B Authors: Hempelmann, A.; Schmitt, J. H. M. M.; Baliunas, S. L.; Donahue, R. A. Bibcode: 2003A&A...406L..39H Altcode: 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. Title: Chromospheric Activity in Solar-Type Stars Authors: Giampapa, M. S.; Hall, J. C.; Radick, R. R.; Baliunas, S. L. Bibcode: 2003SPD....34.0710G Altcode: 2003BAAS...35..821G We present an update on the results of a survey of chromospheric activity in the solar-age and solar-metallicity open cluster, M67. The objective of the survey is to gain insight on the potential range of amplitudes of the solar cycle through observations of solar analogs that are presumably at random phases in their cycles of magnetic activity. We find that there is a significant overlap of the levels of Ca II H and K emission in the sun-like stars in M67 with the range of activity seen in the contemporary solar cycle. However, there are also stars that exhibit levels of activity outside of this range, including stars that are "super-solar" in their Ca II H and K emission. The implications of these results will be discussed.

The data presented in this investigation were obtained with the WIYN 3.5-m telescope on Kitt Peak. The WIYN Observatory is a joint facility of the University of Wisconsin-Madison, Indiana University, Yale University, and the NOAO. The NSO and the NOAO are operated by AURA for the National Science Foundation. Title: Multispectral analysis of asteroid 3 Juno taken with the 100-inch telescope at Mount Wilson Observatory Authors: Baliunas, Sallie; Donahue, Robert; Rampino, Michael R.; Gaffey, Michael J.; Shelton, J. Christopher; Mohanty, Subhanjoy Bibcode: 2003Icar..163..135B Altcode: High-resolution multispectral images of main-belt asteroid 3 Juno were taken at visible and near-IR wavelengths with the 100-inch telescope at Mount Wilson Observatory equipped with an adaptive optics system. The images show spectral features that may represent a large relatively recent impact that deeply excavated the coarse-grained olivine-pyroxene-rich crust of the asteroid. Title: Photometric and Chromospheric Variability of Sun-Like Stars Authors: Lockwood, G. W.; Radick, R. R.; Henry, G. W.; Baliunas, S. L. Bibcode: 2003AAS...202.3213L Altcode: 2003BAAS...35..745L By merging Stromgren b and y photometry of a sample of 34 Sun-like stars measured at the Lowell Observatory and Fairborn Observatory we can now compare 18 years of photometric data with parallel measurements of chromospheric activity from the Mount Wilson HK program. Nearly doubling the length of the 7-11 year time series discussed previously (Radick et al. 1998, ApJS 118, 239; Lockwood et al. 1992 Nature 360, 653) firms up the statistical significance of previously noted patterns of variation. The full range of variability has probably now been observed for most stars in our sample.

Stellar brightness and chromospheric variations follow fairly tight power law relations with respect to mean chromospheric activity. Both diminish with decreasing mean chromospheric activity (or increasing stellar age). The Sun's chromospheric variability lies slightly above the mean stellar power law, but its brightness variations (less than 0.1% over the 11-year solar cycle) appear somewhat low compared with stars of similar activity levels.

Stellar brightness variations are negatively or positively correlated with chromospheric variations depending on mean chromospheric activity, The Sun lies close to the dividing line. A few stars appear to violate the general pattern. Title: Theories of solar eruptions: a review Authors: Lin, J.; Soon, W.; Baliunas, S. L. Bibcode: 2003NewAR..47...53L Altcode: This review highlights current theoretical research on eruptive phenomena in the solar atmosphere. We start by looking back upon the early theories and their development. Any theory and model of solar eruptions must explain two key aspects of eruption physics. The first aspect concerns the original cause of the eruption and the second pertains to the nature of the morphological features that form during its evolution. Those features include rapid ejection of large-scale magnetic flux and plasma into interplanetary space, and the separating of ribbons of H α emission on the solar disk joined by a rising arcade of soft X-ray and H α loops, with hard X-ray emission at their summits and feet. We intercompare relevant theories and models by discussing their advantages as well as by pointing out important aspects that need improvement. Title: Proxy climatic and environmental changes of the past 1000 years Authors: Soon, W.; Baliunas, S. L. Bibcode: 2003ClRe...23...89S Altcode: No abstract at ADS Title: Reconstructing climatic and environmental changes of the past 1000 years: A reappraisal Authors: Soon, W.; Baliunas, S. L.; Idso, C.; Idso, S.; Legates, D. Bibcode: 2003En&En..14..233S Altcode: No abstract at ADS Title: Global warming Authors: Soon, W.; Baliunas, S. L. Bibcode: 2003PrPhG..27..448S Altcode: No abstract at ADS Title: A False Planet around HD 192263 Authors: Henry, Gregory W.; Donahue, Robert A.; Baliunas, Sallie L. Bibcode: 2002ApJ...577L.111H Altcode: We present new high-precision Strömgren photometry and Ca II H and K spectrophotometry of HD 192263. Based on radial velocity variations detected previously by two groups, this K2 V star was thought to host a 0.75 MJup (minimum mass) planetary companion in a 24 day orbit. Our photometric observations reveal periodic variations that match the purported planetary orbital period, while the Ca II H and K emission fluxes are modulated on half the planetary period. This suggests that rotational modulation of the visibility of stellar surface activity is the source of the observed radial velocity variations. Therefore, HD 192263 should be removed from lists of stars with well-established planetary companions unless further observations and analysis can support the existence of the planet in spite of the star's intrinsic variations. Title: Gauging the Sun: Comparative photometric and magnetic activity measurements of sunlike stars, 1984-2001 Authors: Lockwood, G. W.; Hall, J. C.; Skiff, B. A.; Henry, G. W.; Radick, R. R.; Baliunas, S. L.; Soon, W.; Donahue, R. A. Bibcode: 2002AAS...200.0709L Altcode: 2002BAAS...34..651L Visible light photometric observations of a small sample of sunlike stars with mean chromospheric activity levels similar to or slightly lower than the Sun's suggest that total solar irradiance variations on activity cycle timescales may be comparatively small (Lockwood et al. 1992, Nature 360, 653; Radick et al. 1998, ApJS 118, 239). The Sun's irradiance variation over the past two cycles is 0.04% rms compared with 0.1% rms for the stellar sample measured at Lowell from 1984 to 1995. This assertion can now be tested using new photometric measurements from Fairborn Observatory automated telescopes (1993-2001) that extend the duration of stellar observations to 17 years. Chromospheric activity measurements for these stars come from the Mount Wilson HK program (1966-2001) and the Lowell Observatory Solar Stellar Spectrograph program (1993-2001). In this presentation we will describe efforts to merge the overlapping Lowell and Fairborn photometry and the Mt. Wilson and Lowell HK measurements with the goal of reducing the uncertainties in previous efforts to characterize stellar photometric variations near the limit of detection. Title: Sources of solar variability responsibile for global warming of the upper ocean on decadal period scales Authors: White, W.; Dettinger, M.; Soon, W.; Baliunas, S. Bibcode: 2002cosp...34E1318W Altcode: 2002cosp.meetE1318W Global-average warming and cooling of upper ocean temperature on decadal period scales of ~0.1 K are aligned with decadal changes in the SunSs irradiance of ~0.5 W m-2 throughout the 20th Century at lags ranging from 0 to 18 months. This apparent upper ocean temperature response to solar forcing is ~3 times that expected from the Stefan-Boltzmann radiation balance for the EarthSs surface. Yet, this global-average temperature change is a small residual in the spatial integration of relatively large temperature changes of O(1.0 K) associated with a global pattern of variability that is similar to that of the El Nino-Southern Oscillation (Tourre et al., 2001). Since the latter exhibits global-average warming and cooling of 0.2 K in the absence of solar forcing (White et al., 2001), the SunSs decadal signal needs simply to excite this particular decadal mode in the EarthSs ocean-atmosphere-terrestrial system in order to produce the observed global-average temperature change. The question is, by what mechanism does it do this? Here we examine the global-average diabatic heat storage budget for the upper ocean on decadal period scales using the NCEP/NCAR atmospheric reanalysis and the SIO oceanic reanalysis. First, we find the global-average variability dominated by the tropical global-average. Second, we find the peak tropical warm phase associated with higher troposphere moisture content and cloud fraction, driven by an increase in outgoing sensible-plus-latent heat flux and outgoing longwave-minusshortwave radiative heat flux of comparable magnitudes. The sources of the anomalous warming tendency during the onset phase is the reduction in the net poleward Ekman heat flux out of the tropics and the reduction in outgoing sensible-plus-latent heat flux of similar magnitude, both in response to reduced trade wind intensity. Thus, the increase in cloud fraction during the peak tropical warm phase does not heat the underlying ocean, as assumed by Marsh and Svensmark (2000). Rather, the reduction in trade wind intensity during the onset phase is consistent with that simulated by Haigh (1996) in response to heating of the lower stratosphere by the UV portion of the total solar irradiance spectrum. Here we find a slow downward propagation of zonal wind anomalies from the lower stratosphere to the lower troposphere contributing to this reduction in trade wind intensity. Title: Global warming Authors: Baliunas, S. Bibcode: 2002WTGSB..41....4B Altcode: No abstract at ADS Title: Extrasolar Planet Inferometric Survey (EPIcS) Authors: Shao, Michael; Baliunas, Sallie; Boden, Andrew; Kulkarni, Shrinivas; Lin, Douglas N. C.; Loredo, Tom; Queloz, Didier; Shaklan, Stuart; Tremaine, Scott; Wolszczan, Alexander Bibcode: 2002swsi.conf....7S Altcode: No abstract at ADS Title: Reply to Comments on "Modeling climatic effects of anthropogenic CO2 emissions: Unknowns and uncertainties Authors: Risbey, James; Soon, W.; Baliunas, S.; Idso, S. B.; Kondratyev, K. Ya.; Posmentier, E. S. Bibcode: 2002ClRe...22..187R Altcode: No abstract at ADS Title: The scientific case against catastrophic global warming and the Kyoto Protocol Authors: Baliunas, S.; Macrae, A.; Patterson, T. Bibcode: 2002PPEGG..30...20B Altcode: No abstract at ADS Title: No planet for HD 166435 Authors: Queloz, D.; Henry, G. W.; Sivan, J. P.; Baliunas, S. L.; Beuzit, J. L.; Donahue, R. A.; Mayor, M.; Naef, D.; Perrier, C.; Udry, S. Bibcode: 2001A&A...379..279Q Altcode: 2001astro.ph..9491Q The G0 V star HD 166435 has been observed by the fiber-fed spectrograph ELODIE as one of the targets in the large extra-solar planet survey that we are conducting at the Observatory of Haute-Provence. We detected coherent, low-amplitude, radial-velocity variations with a period of 3.7987 days, suggesting a possible close-in planetary companion. Subsequently, we initiated a series of high-precision photometric observations to search for possible planetary transits and an additional series of Ca II H and K observations to measure the level of surface magnetic activity and to look for possible rotational modulation. Surprisingly, we found the star to be photometrically variable and magnetically active. A detailed study of the phase stability of the radial-velocity signal revealed that the radial-velocity variability remains coherent only for durations of about 30 days. Analysis of the time variation of the spectroscopic line profiles using line bisectors revealed a correlation between radial velocity and line-bisector orientation. All of these observations, along with a one-quarter cycle phase shift between the photometric and the radial-velocity variations, are well explained by the presence of dark photospheric spots on HD 166435. We conclude that the radial-velocity variations are not due to gravitational interaction with an orbiting planet but, instead, originate from line-profile changes stemming from star spots on the surface of the star. The quasi-coherence of the radial-velocity signal over more than two years, which allowed a fair fit with a binary model, makes the stability of this star unusual among other active stars. It suggests a stable magnetic field orientation where spots are always generated at about the same location on the surface of the star. Title: Modeling climatic effects of anthropogenic CO2 emissions: Unknows and uncerta inties Authors: Soon, W.; Baliunas, S.; Demirchan, K. S.; Idso, S. B.; Kondratyev, K. Ya.; Posmentier, E. S. Bibcode: 2001ClRe...18..259S Altcode: No abstract at ADS Title: Global Climate Change: Conceptual Aspects, 2001 Authors: Kondratyev, K. Ya.; Adamenko, V. N.; Demirchian, K. S.; Baliunas, S.; Boehmer-Christiansen, S.; Idso, S. B.; Kukla, G.; Posmentier, E. S.; Soon, W. Bibcode: 2001rass.rept.....K Altcode: No abstract at ADS Title: The impact of anthropogenic CO2 emissions: Unknows and uncertainties Authors: Soon, W.; Baliunas, S.; Demirchan, K. S.; Idso, S. B.; Kondratyev, K. Ya.; Posmentier, E. S. Bibcode: 2001PRGS..133....1S Altcode: No abstract at ADS Title: Evidence for a Long-Period Planet Orbiting ɛ Eridani Authors: Hatzes, Artie P.; Cochran, William D.; McArthur, Barbara; Baliunas, Sallie L.; Walker, Gordon A. H.; Campbell, Bruce; Irwin, Alan W.; Yang, Stephenson; Kürster, Martin; Endl, Michael; Els, Sebastian; Butler, R. Paul; Marcy, Geoffrey W. Bibcode: 2000ApJ...544L.145H Altcode: 2000astro.ph..9423H High-precision radial velocity (RV) measurements spanning the years 1980.8-2000.0 are presented for the nearby (3.22 pc) K2 V star ɛ Eri. These data, which represent a combination of six independent data sets taken with four different telescopes, show convincing variations with a period of ~7 yr. A least-squares orbital solution using robust estimation yields orbital parameters of period P=6.9 yr, velocity amplitude K=19 m s-1, eccentricity e=0.6, projected companion mass Msini=0.86 MJupiter, and semimajor axis a2=3.4 AU. Ca II H and K S-index measurements spanning the same time interval show significant variations with periods of 3 and 20 yr yet none at the RV period. If magnetic activity were responsible for the RV variations, then it produces a significantly different period than is seen in the Ca II data. Given the lack of Ca II variation with the same period as that found in the RV measurements, the long-lived and coherent nature of these variations, and the high eccentricity of the implied orbit, Keplerian motion due to a planetary companion seems to be the most likely explanation for the observed RV variations. The wide angular separation of the planet from the star (approximately 1") and the long orbital period make this planet a prime candidate for both direct imaging and space-based astrometric measurements. Based on observations collected at McDonald Observatory, Lick Observatory, European Southern Observatory at La Silla, and the Canada-France-Hawaii Telescope. Title: The Curious case of the carbon forest source Authors: Baliunas, S.; Soon, W. Bibcode: 2000WCRp....6f...3B Altcode: No abstract at ADS Title: Searching for Global oscillations of Jupiter Authors: Murphy, N.; Smith, E. J.; Rogers, W.; Gillam, S.; Rosner, R.; Baliunas, S. Bibcode: 2000DPS....32.6516M Altcode: 2000BAAS...32.1642M The detection of global oscillations of Jupiter would lead to significant advances in our understanding of giant planet internal structure, analogous to the enormous increase in knowledge of the sun's interior facilitated by helioseismology. In particular, the frequencies of p-mode oscillations will be strongly affected by the presence of density discontinuities and the planet's core size and structure. While it is clear from previous observations that such oscillations probably only exist with very small amplitudes, current instrumentation may still be able to detect them. We will describe a proposed experiment to detect (or place a firm upper amplitude limit on) global p-mode oscillations of Jupiter, using a magneto-optical filter on the Mt Wilson 100" telescope. We will describe the operation of the instrument, present preliminary data and describe models of instrument response which show that with 7 nights of data we can expect to detect signals with amplitudes less than 20 cm/s. Title: Solar-Stellar Connection: Activity and Brightness Changes of Solar-Type Stars Authors: Baliunas, S. Bibcode: 2000eaa..bookE2237B Altcode: The surface and outer atmosphere of the Sun are dominated by the presence of localized magnetic fields. They influence the structure of and energy transport through the solar atmosphere and wind, outward to the distance of the heliopause (see SOLAR WIND: MAGNETIC FIELD). In addition, the occurrence of the magnetic features varies on characteristic time scales. Chief among them is the roughly 11 y... Title: Millennial climate Authors: Baliunas, S.; Soon, W. Bibcode: 2000WCRp....6b...3B Altcode: No abstract at ADS Title: 100000110011 (Computer Year 2099) Authors: Baliunas, S.; Soon, W. Bibcode: 2000WCRp....5v...3B Altcode: No abstract at ADS Title: Man vs. Milky Way revisited Authors: Baliunas, S.; Soon, W. Bibcode: 2000WCRp....5s...3B Altcode: No abstract at ADS Title: A Survey of Activity in the Solar-Type Stars in M67 Authors: Giampapa, M. S.; Radick, R. R.; Hall, J. C.; Baliunas, S. L. Bibcode: 2000SPD....3102120G Altcode: 2000BAAS...32..832G We present an update on a long-term study of the solar-type stars in the solar-age and solar-metallicity open cluster, M67. The primary objective of this program is to gain insight on the possible range of solar chromospheric activity and the associated, potential long-term variability of the Sun through the observation of stellar analogs of the Sun. Spectra in the Ca II H & K line region of over 100 stars in M67, including 76 `solar-type' stars (with unreddened colors in the range +0.60 <= B-V <= +0.76) and 21 `solar-twins' (+0.63 <= B-V <= +0.67), were obtained with the 3.5-m WIYN telescope on Kitt Peak in conjunction with the Hydra multi-fiber positioner to perform multi-object spectroscopy over a 1 degree field. We find that the distribution of chromospheric H&K line strengths in the solar-type stars is broader than the distribution of H&K line emission recorded in modern observations of the Sun, suggesting that the potential excursion in the amplitude of the solar cycle is greater than what we have seen so far in the contemporary record. Approximately 30% of the solar-type stars in M67 exhibit levels of activity that are outside the present envelope of solar activity. We interpret this to mean that the Sun can be in a state of magnetic activity---either exceptional quiescence similar to the Maunder-minimum episode or enhanced activity---about 30% of the time. The authors gratefully acknowledge both the NOAO Telescope Allocation Committee and the WIYN Queue Program for their support of this investigation. The WIYN Observatory is a joint facility of the University of Wisconsin-Madison, Indiana University, Yale University, and the NOAO. The NSO and NOAO are operated by AURA, Inc., under cooperative agreement with the National Science Foundation. Title: Climate hypersensitivity to solar forcing? Authors: Soon, W.; Posmentier, E.; Baliunas, S. Bibcode: 2000AnGeo..18..583S Altcode: We compare the equilibrium climate responses of a quasi-dynamical energy balance model to radiative forcing by equivalent changes in CO2, solar total irradiance (Stot) and solar UV (SUV). The response is largest in the SUV case, in which the imposed UV radiative forcing is preferentially absorbed in the layer above 250 mb, in contrast to the weak response from global-columnar radiative loading by increases in CO2 or Stot. The hypersensitive response of the climate system to solar UV forcing is caused by strongly coupled feedback involving vertical static stability, tropical thick cirrus ice clouds and stratospheric ozone. This mechanism offers a plausible explanation of the apparent hypersensitivity of climate to solar forcing, as suggested by analyses of recent climatic records. The model hypersensitivity strongly depends on climate parameters, especially cloud radiative properties, but is effective for arguably realistic values of these parameters. The proposed solar forcing mechanism should be further confirmed using other models (e.g., general circulation models) that may better capture radiative and dynamical couplings of the troposphere and stratosphere. Title: The Trouble with Ozone Authors: Baliunas, S.; Soon, W. Bibcode: 2000WCRp....5o...3B Altcode: No abstract at ADS Title: Photometric and Ca II H and K Spectroscopic Variations in Nearby Sun-like Stars with Planets. III. Authors: Henry, Gregory W.; Baliunas, Sallie L.; Donahue, Robert A.; Fekel, Francis C.; Soon, Willie Bibcode: 2000ApJ...531..415H Altcode: We present the results of an analysis of time-series photometry, Ca II H and K spectrophotometry, and high-dispersion visible spectra of nine nearby Sun-like stars recently identified as having planets. For the six stars whose presumed planets have orbital periods of less than 4 months (τ Boo, 51 Peg, υ And, ρ1 Cnc, ρ CrB, and 70 Vir), sine-curve fits to the photometric data show no variations with semiamplitude greater than 1 or 2 parts in 104. Photometric variations in 47 UMa are similarly small, although our photometric data of this star are slightly affected by variability of the comparison star. Nonvariability at this level of precision is sufficient to rule out surface magnetic activity as the cause of the observed radial-velocity variations in these seven stars and makes nonradial pulsations unlikely as well. Thus, our photometry provides indirect but strong support for true reflex motions-planets-in these seven stars, but cannot yet so support the planetary hypothesis for the two additional stars, 16 Cyg B and Gl 411. Continued photometric monitoring of the short-period systems may soon result in the direct detection of these planets in reflected light. We have used our photometric fluxes to search for possible transits of the extrasolar planets. Transits definitely do not occur in τ Boo, 51 Peg, υ And, and ρ1 Cnc, and probably do not occur in ρ CrB and 70 Vir. Our transit-search results are inconclusive for 47 UMa, and we cannot address the issue for 16 Cyg B and Gl 411. The precision of our photometry is sufficient to detect transits of planets even if they are not gas giants, as currently assumed, but much smaller objects with rocky compositions. The chance of finding at least one transit in the six stars is ~40%. We find significant year-to-year photometric variability only in τ Boo, which is not only the youngest star in the sample but also the star with the shallowest convective zone. The interseasonal range in its yearly mean photometric flux is ~0.002 mag, roughly twice the 0.0008 mag decadal variation in the Sun's total irradiance. Monitoring of the relative Ca II H and K fluxes began between 1966 and 1968 for 51 Peg, τ Boo, ρ CrB, and Gl 411, between 1990 and 1993 for 47 UMa, 70 Vir, 16 Cyg B, and ρ1 Cnc, and in 1996 for υ And. The data have been newly recalibrated for improved long-term instrumental stability, resulting in better precision of the Ca II records. Five of the nine stars in this study have little or no detectable year-to-year variation in Ca II flux. The remaining four show moderate or pronounced variability: τ Boo, whose radial-velocity and photometric variations have comparatively high amplitudes; Gl 411, whose planetary companion was inferred astrometrically, not spectroscopically; ρ1 Cnc, which may undergo decadal cyclic activity; and υ And, which shows moderate year-to-year variability. Except for 47 UMa, intraseasonal variability consistent with rotation was detected in the Ca II records of all stars. However, the rotation periods determined for υ And, 70 Vir, and 16 Cyg B are of low confidence. An examination of the recalibrated Ca II records for 51 Peg finds a rotation period of 22 days, in contrast to our previous result of 37 days. Ages have been estimated from the mean Ca II flux and, where possible, the rotation period. We find general consistency with the ages determined by others comparing properties determined from high-resolution spectroscopy to evolutionary models, although the uncertainties are, in general, large. Based on observations made at Mount Wilson Observatory, operated by the Mount Wilson Institute, under an agreement with the Carnegie Institution of Washington and the automatic photoelectric telescope at Fairborn Observatory in the Patagonia Mountains of southern Arizona. Title: Calculating the Climatic Impacts of Increased CO2: the Issue of Model Validation Authors: Soon, W.; Baliunas, S.; Idso, S. B.; Kondratyev, K. Ya.; Posmentier, E. S. Bibcode: 2000ESASP.463..243S Altcode: 2000sctc.proc..243S No abstract at ADS Title: Commission 12: Solar Radiation and Structure (Radiation et Structure Solaires) Authors: Foukal, Peter; Solanki, Sami; Mariska, J.; Baliunas, S.; Dravins, D.; Duvall, T.; Fang, C.; Gaizauskas, V.; Heinzel, P.; Kononovich, E.; Koutchmy, S.; Melrose, D.; Stix, M.; Suematsu, Y.; Deubner, F. Bibcode: 2000IAUTA..24...73F Altcode: No abstract at ADS Title: The rains of Ranchipur Authors: Baliunas, S.; Soon, W. Bibcode: 2000WCRp....5j...3B Altcode: No abstract at ADS Title: Division XI: Space and High Energy Astrophysics(Astrophysique Spatiale et Des Hautes Energies) Authors: Wamsteker, Willem; Baliunas, S.; Brosch, N.; Cesarsky, C.; Courvoisier, Th. -J. L.; da Costa, J. M.; Domingo, V.; Fransson, C.; Fabian, A.; Fazio, G.; Hasinger, G.; Inoe, H.; Li, Zhongyuan; O'Brien, P.; Oertel, G.; Okuda, H.; Quintana, H.; Rangarajan, T. N.; Schilizzi, R.; Shustov, B.; Thronson, H.; Vilhu, O.; Wang, Zhenru Bibcode: 2000IAUTA..24..357W Altcode: No abstract at ADS Title: The sun also warms Authors: Baliunas, S.; Soon, W. Bibcode: 2000stcl.rept...21B Altcode: No abstract at ADS Title: Variations of solar coronal hole area and terrestrial lower tropospheric air temperature from 1979 to mid-1998: astronomical forcings of change in earth's climate? Authors: Soon, W.; Baliunas, S.; Posmentier, E. S.; Okeke, P. Bibcode: 2000NewA....4..563S Altcode: The temperature anomaly of the terrestrial lower troposphere, inferred from the Microwave Sounding Unit (MSU) radiometers, is found to be inversely correlated with the area of the Sun covered by coronal holes. The correlation between the monthly time series of global tropospheric temperature anomaly and total coronal hole area from January 1979 to April 1998 has a Pearson coefficient of -0.46, which is different from zero at a 95% confidence level. Physical reasonings for the explained and unexplained parts of the correlation are discussed. The coronal hole area is a physical proxy for both the global-scale, 22-yr geometrical and shorter-term, dynamical components of the cosmic ray modulation, as well as the corpuscular emission of the Sun. Other solar parameters that may indicate a solar radiative effect on climate are also evaluated. It is concluded that variable fluxes either of solar charged particles or cosmic rays modulated by the solar wind, or both, may influence the terrestrial tropospheric temperature on timescale of months to years. Title: Generations of Hurricanes Authors: Baliunas, S.; Soon, W. Bibcode: 1999WCRp....5f...3B Altcode: No abstract at ADS Title: Almighty Chance and the Dance of El Nino Authors: Baliunas, S.; Soon, W. Bibcode: 1999WCRp....5d...3B Altcode: No abstract at ADS Title: Large asymmetrical temperature trends at Mount Wilson, California Authors: Balling, Robert C., Jr.; Periconi, Darlene A.; Cerveny, Randall S.; Baliunas, Sallie L. Bibcode: 1999GeoRL..26.2753B Altcode: We compiled and analyzed a daily time series of temperatures and precipitation totals from Mount Wilson, California from 1918 to 1998. Our results show a large decline in maximum temperature, no change or an upward trend in minimum temperature, and a substantial decline in the diurnal temperature range (DTR). The interannual variations in monthly maximum temperature and DTR are significantly correlated with monthly precipitation levels, sea-surface temperatures (SSTs) off the coast of Southern California, and the Southern Oscillation Index (SOI). El Niño periods and/or months with high SST anomalies tend to be wet with lower maximum temperatures and DTR while La Niña periods and/or months of lower SSTs are hotter and drier with higher DTR values. It is noteworthy that the SOI and SSTs have significant trends toward more El Niño-like conditions with higher SSTs off Southern California. Title: Pioneers in the Greenhouse Effect Authors: Baliunas, S.; Soon, W. Bibcode: 1999WCRp....4s....B Altcode: No abstract at ADS Title: Pioneers in the Greenhouse Effect Authors: Baliunas, S.; Soon, W. Bibcode: 1999WCRp....4S...6B Altcode: No abstract at ADS Title: The Suns of M67 Authors: Giampapa, M. S.; Radick, R. R.; Baliunas, S. L. Bibcode: 1999AAS...194.9212G Altcode: 1999BAAS...31..988G The results of our program to survey the level of chromospheric Ca II H&K emission in ~ 100 solar analogs in the galactic cluster M67 are discussed. This cluster is an appropriate target of observation for the study of solar-type stars since it is approximately the same age and has the same chemical composition as the Sun. The key objective of our program is to investigate the nature of solar variability. In particular, we interpret the range of Ca II H&K emission observed in the sun-like stars in M67 as indicative of the possible amplitudes of cycle-related variability that can occur in the Sun itself. In this way, we can efficiently gain insights on the potential long-term variability of the Sun that would not otherwise be possible with the modern solar Ca II synoptic database of just a few decades. This is especially important given that the amplitude of long-term solar (and stellar) variations in brightness are correlated with cycle variations in chromospheric emission. In view of the fact that the Sun is the engine that drives climate on the Earth, any variation in the solar ``constant" must be taken into account in the study of the long-term behavior of the global climate. The NOAO is operated by the Association of Universities for Research in Astronomy, Inc., under cooperative agreement with the National Science Foundation. Title: The Mysteries of Carbon Dioxide Authors: Baliunas, S.; Soon, W. Bibcode: 1999WCRp....4R...6B Altcode: No abstract at ADS Title: Aerosols are Cool Authors: Baliunas, S.; Soon, W. Bibcode: 1999WCRp....4k...6B Altcode: No abstract at ADS Title: Aerosols are Cool Authors: Baliunas, S.; Soon, W. Bibcode: 1999WCRp....4Q...6B Altcode: No abstract at ADS Title: Cycles and Long-Term Variability in Solar-Type Stars Authors: Giampapa, Mark S.; Radick, Richard R.; Hall, Jeffrey C.; Baliunas, Sallie L. Bibcode: 1999noao.prop..226G Altcode: We propose a long-term extension of our current WIYN/Hydra program to study chromospheric activity cycles in the `Suns of M67.' Our results thus far have revealed that the distribution of activity among the solar- type stars in M67 is broader than what would be expected from a comparison with the solar cycle. The next step is to determine whether our results arise from the cyclic modulation of activity alone or if the relative amplitudes of cycles in solar-type stars and the Sun are actually similar and the spread in M67 is due to differences in the mean level of activity. Only a long-term monitoring program of regular observations can address these questions. The results of this program are expected to reveal all the potential modes and amplitudes of magnetic cycles in sun-like stars and, by inference, in the Sun itself, with important implications for dynamo models and models of global climate change. Title: Extremes of Ecofeminism Authors: Baliunas, S. Bibcode: 1999frfo.rept.....B Altcode: No abstract at ADS Title: Natural variability in an-ocean-atmosphere climate model Authors: Posmentier, E. S.; Soon, W. H.; Baliunas, S. L. Bibcode: 1999JFMal..19..157P Altcode: No abstract at ADS Title: Extreme Ecomfeminism: The view from Science Authors: Baliunas, S. Bibcode: 1999exfe.rept....7B Altcode: No abstract at ADS Title: Silvery-blue Cloudlets of the Night Authors: Baliunas, S.; Soon, W. Bibcode: 1999WCRp....4....5B Altcode: No abstract at ADS Title: Environmental effects of increased atmospheric carbon dioxide Authors: Soon, W.; Baliunas, S.; Robinson, A.; Robinson, Z. W. Bibcode: 1999ClRe...13..149S Altcode: No abstract at ADS Title: Lifetime of Surface Features and Stellar Rotation: A Wavelet Time-Frequency Approach Authors: Soon, Willie; Frick, Peter; Baliunas, Sallie Bibcode: 1999ApJ...510L.135S Altcode: 1998astro.ph.11114S We explore subtle variations in disk-integrated measurements spanning <~18 yr of stellar surface magnetism by using a newly developed time-frequency gapped wavelet algorithm. We present results based on analysis of the Mount Wilson Ca II H and K emission fluxes in four, magnetically active stars (HD 1835 [G2 V], HD 82885 [G8 IV-V], HD 149661 [K0 V], and HD 190007 [K4 V]) and sensitivity tests using artificial data. When the wavelet basis is appropriately modified (i.e., when the time-frequency resolution is optimized), the results are consistent with the existence of spatially localized and long-lived Ca II features (assumed here as activity regions that tend to recur in narrowly confined latitude bands), especially in HD 1835 and HD 82885. This interpretation is based on the observed persistence of relatively localized Ca II wavelet power at a narrow range of rotational timescales, enduring as long as >~10 yr. Title: Cold World: Model Analysis shows icy trend Authors: Baliunas, S.; Soon, W. Bibcode: 1998WCRp....4g...6B Altcode: No abstract at ADS Title: Activity in Old Dwarf and Subgiant Stars Authors: Slesnick, C. L.; Donahue, R. A.; Baliunas, S. L. Bibcode: 1998AAS...193.9903S Altcode: 1998BAAS...30R1395S Chromospheric Ca \sc ii H and K fluxes of ~ 150 F and G stars on or near the main sequence were analyzed to determine whether previously established relationships between stellar magnetic activity and rotation (age) hold for those stars that have begun to evolve off the Main Sequence. Each star's time series (up to 33 years) was analyzed year by year to detect variability which could be attributed to rotation. In several cases, more than one locus of periods was measured for a star. These periods were compared to the estimated rotation periods from a relationship derived by Noyes et al. (1984) using a star's B-V color and the mean emission flux level of the chromospheric Ca \sc ii H and K lines. In general, the periods observed correspond to the predicted rotation period. Those which did not were analyzed in further detail in order to posit a cause for their values. Rotational velocities inferred from the observed periods and the calculated radius of each star were compared to v sin i values collected from the Stellar Rotational Velocity Catalog (Bernacca & Perinotto 1970, 1971, 1973). In several cases the observed periods are inconsistent with rotation; however, a few stars which have begun to evolve off the Main Sequence may show characteristically longer periods than expected, suggesting that they have either begun to lose angular momentum or are conserving it by slowing their velocity as they expand. Title: The Miner's Canary is Still Singing Authors: Baliunas, S.; Soon, W. Bibcode: 1998WCRp....4c...6B Altcode: No abstract at ADS Title: Patterns of Variation among Sun-like Stars Authors: Radick, Richard R.; Lockwood, G. W.; Skiff, B. A.; Baliunas, S. L. Bibcode: 1998ApJS..118..239R Altcode: We examine the patterns of variation among a sample of 35 stars that includes the Sun, particularly on the timescale of the 11 yr solar activity cycle. Our investigation uses contemporaneous photometric and chromospheric HK emission time series measurements from the Lowell and Mount Wilson Observatories, and comparable solar data. We find that the photometric and HK variability of the stars in our sample can be related to their average level of chromospheric activity by power laws. The photometric variability of the Sun may be somewhat subdued for its average activity level. We find that the younger, more active stars in our sample tend to become fainter as their HK emission increases, whereas the older, less active stars tend to become brighter as their HK emission increases, as the Sun does during its activity cycle. Title: The summer of our discontent Authors: Baliunas, S.; Soon, W. Bibcode: 1998WCRp....3c..10B Altcode: No abstract at ADS Title: The life and times of Alfonso Nino and family Authors: Baliunas, S.; Soon, W. Bibcode: 1998WCRp....3s..10B Altcode: No abstract at ADS Title: The Milky Way and the clouds of Earth Authors: Baliunas, S.; Soon, W. Bibcode: 1998WCRp....3o..10B Altcode: No abstract at ADS Title: The Sun as a Star, by Roger J. Tayler Authors: Baliunas, Sallie Bibcode: 1998PhT....51d..63B Altcode: No abstract at ADS Title: Nature speaks of many things, Of missing flux and butterfly wings Authors: Baliunas, S.; Soon, W. Bibcode: 1998WCRp....3k...6B Altcode: No abstract at ADS Title: Differential Rotation and Meridional Flow for Fast-rotating Solar-Type Stars Authors: Rüdiger, Günther; von Rekowski, Brigitta; Donahue, Robert A.; Baliunas, Sallie L. Bibcode: 1998ApJ...494..691R Altcode: Observations indicate that normalized surface differential rotation decreases for fast-rotating stars, that is, | ΔΩ |/Ω ~ Ω-0.3. An increase of | ΔΩ |/Ω is provided, however, by the current Reynolds stress theory of differential rotation in stellar convection zones, without the inclusion of meridional flow. We compute both the pole-equator difference of the surface angular velocity and the meridional drift for various Taylor numbers to demonstrate that the inclusion of meridional flow in the computations for fast rotation yields a systematic reduction of the resulting differential rotation. Our model's adiabatic and density-stratified convection zone, with stress-free surfaces and a thickness of 0.3 stellar radii, yields the relation | ΔΩ |/Ω ~ Ω-(0.15 ... 0.30) for stars with faster rotation than the Sun, in agreement with previous observations. If the Coriolis number rather than the Taylor number is varied, we find a maximum differential rotation of 20%. For stars with fast rotation, exponents of up to n' ~= 0.4 are found. All rotation laws exhibit superrotating equators. Title: An Assessment of the Sun-Climate Relation on Time Scales of Decades to Centuries: The Possibility of Total Irradiance Variations Authors: Baliunas, S. L.; Soon, W. H. Bibcode: 1998sers.conf..401B Altcode: No abstract at ADS Title: Environmental effects of increased atmospheric carbon dioxide Authors: Robinson, A.; Baliunas, S. L.; Soon, W.; Robinson, Z. W. Bibcode: 1998MeSen...3..171R Altcode: No abstract at ADS Title: Activity Cycles in Lower Main Sequence and POST Main Sequence Stars: The HK Project Authors: Baliunas, Sallie L.; Donahue, Robert A.; Soon, Willie; Henry, Gregory W. Bibcode: 1998ASPC..154..153B Altcode: 1998csss...10..153B In 1966, Olin Wilson began making monthly measurements at Mount Wilson Observatory of the relative fluxes in the Ca II H (396.8 nm) and K (393.3 nm) emission cores of approximately 100 stars on or near the lower main sequence. In the late 1970's the Ca II fluxes of nearly 1,000 lower main-sequence stars were sampled, and by 1980 the program had expanded to include near-nightly observations of the stars in Wilson's sample. In 1984 the project was again extended to include the measurement of post-main sequence stars. Today, the project monitors the Ca II fluxes of 400 dwarf and giant stars, with great emphasis on stars close in mass and age to the Sun. The relative Ca II fluxes are thought to closely correspond to the strength and coverage of surface magnetism on such stars. Three general classes of long-term variations of surface magnetism have been seen in lower main sequence and post main sequence stars: 1. substantial fluctuations on time scales of a few years, with little observed repitition of periodicity; 2. nearly-periodic variations with time scales of a decade or more, with some variability in the amplitude, length and shape of each successive cycle; 3. either low-amplitude modulation on time scales of several decades or more, or essentially no long-term variability. In the lower main-sequence stars both the class of long-term variability and the time-averaged level of Ca II fluxes are influenced primarily by a star's angular momentum. In a related matter, most of the detected extra-solar planets (with orbital periods ranging from 3 to 1200 days) orbit sun-like stars with long-term Ca II flux records that are virtually flat (Class 3, above). The lack of variability is an observational bias that enhances detection of extra-solar planets orbiting sun-like stars. Title: Activity in old dwarf and subgiant stars Authors: Slesnick, C.; Baliunas, S. L.; Donahue, R. A.; Soon, W. H. Bibcode: 1998reu..rept.....S Altcode: No abstract at ADS Title: Solar activity and temperature data: A wavelet analysis Authors: Zakharov, V.; Baliunas, S.; Frick, P.; Soon, Wa; Sokoloff, D. Bibcode: 1998geoc.conf.....Z Altcode: No abstract at ADS Title: Science with the ADOPT system on Mt. Wilson [3126-80] Authors: Shelton, J. C.; Schneider, T.; Baliunas, S. L. Bibcode: 1997SPIE.3126..321S Altcode: No abstract at ADS Title: Coronal and chromospheric emission from cool stars in near-simultaneous ROSAT all-sky survey and Mount Wilson data. Authors: Piters, A. J. M.; Schrijver, C. J.; Schmitt, J. H. M. M.; Rosso, C.; Baliunas, S. L.; van Paradijs, J.; Zwaan, C. Bibcode: 1997A&A...325.1115P Altcode: Mt. Wilson Ca II H&K line-core emission fluxes for 215 F-, G- and K-type stars were obtained within at most a few days of the corresponding ROSAT All-Sky Survey observations. These stars cover wide ranges of stellar activity, spectral type and luminosity class. In this paper we study the well-known relationship between the Ca II H&K line-core emission in excess of the minimum emission and the soft X-ray emission. We find that flux densities normalised with the bolometric flux densities are the best quantity in which to express activity when comparing radiative emission in different temperature regimes. We find a power-law relationship, in which the X-ray normalised emission varies approximately quadratically with the normalised excess Ca II H&K line-core emission. This relationship does not depend on luminosity class at least up to luminosity class III, and it does not depend on effective temperature. The scatter around this relationship is consistent with the measurement errors. The X-ray spectral hardness ratios of main-sequence stars increase with the X-ray flux densities; a similar trend, but with substantially larger scatter, is also present for evolved stars. A comparison between values from different passbands of the Mt. Wilson HK spectrophotometer shows that relatively hot stars ((B-V)<=0.50) appear to have a Ca II line core emission peak about a factor 2 to 3 wider than cooler stars. Title: Wavelet Analysis of Stellar Chromospheric Activity Variations Authors: Frick, P.; Baliunas, S. L.; Galyagin, D.; Sokoloff, D.; Soon, W. Bibcode: 1997ApJ...483..426F Altcode: Observations of chromospheric activity variations for some lower main-sequence stars from the Mount Wilson Observatory's HK project reveal a cyclic behavior comparable to the sunspot cycle. Even in the relatively short interval that they have been observed, those stars show stellar cycles and other features, like grand minima. The quasi-periodic nature of such variations is not completely compatible with the standard Fourier analysis, so we applied a wavelet analysis to study the nature of regularities in the data. We computed wavelet transforms and energy spectra for the 25 yr records of surface magnetic activity in four stars: HD 3651, HD 10700, HD 10476, and HD 201091. We present a modified wavelet technique that is suitable for analysis of data with gaps and find that the common aliasing problems due to the finite length of the observations and irregularly spaced gaps between data can be reduced on both large and small scales by applying this algorithm. Title: Time scales and trends in the central England temperature data (1659-1990): A wavelet analysis Authors: Baliunas, Sallie; Frick, Peter; Sokoloff, Dmitry; Soon, Willie Bibcode: 1997GeoRL..24.1351B Altcode: We have applied the standard wavelet and the adaptive wavelet transform algorithms to the record of the Central England Temperature (CET) from 1659-1990. Peaks in the CET spectra include 7.5±1.0 yr, 14.4±1.0 yr, 23.5±2.0 yr, as well as a previously unreported variation at 102±15 yr. Our wavelet analysis of CET agrees with previous results from Singular Spectrum Analysis (SSA) by Plaut et al. [1995] and gives additional results of variability on longer timescales. The interdecadal and century-scale variability in CET is strongly dependent on the interval of analysis. Estimates of a data trend are also shown to be sensitive to the cutoff timescale of the filter. A cooling of ≈ 0.3°C during 1659-1720 is found relative to the temperatures during the 1800s. The complex time dependence of the actual data cautions against using model-derived representations of natural variability on such long timescales. Title: VizieR Online Data Catalog: Near-simultaneous ROSAT and Mt Wilson data (Piters+ 1997) Authors: Piters, A. J. M.; Schrijver, C. J.; Schmitt, J. H. M. M.; Rosso, C.; Baliunas, S. L.; van Paradijs, J.; Zwaan, C. Bibcode: 1997yCat..33251115P Altcode: Table 1 lists near-simultaneous X-ray data and Ca II H&K line-core emission data from the ROSAT All-Sky Survey and from the Mt. Wilson H&K spectrometer, respectively. The stars in this sample are 215 bright F-, G-, and K-type stars. Table 2 lists the derived excess Ca II H&K line-core and the X-ray flux densities for the same stars. (2 data files). Title: Persistent Sub-Yearly Chromospheric Variations in Lower Main-Sequence Stars: Tau Booe and alpha COM Authors: Maulik, Davesh; Donahue, Robert A.; Baliunas, Sallie L. Bibcode: 1997sao..rept.....M Altcode: The recent discoveries of extrasolar planetary systems around lower main-sequence stars such as tau Booe (HD 120136) has prompted further investigation into their stellar activity. A cursory analysis of tau Booe for cyclic chromospheric activity, based on its 30-yr record of Ca 2 H and K fluxes obtained as part of the HK Project from Mount Wilson Observatory, finds an intermediate, sub-yearly period (approximately 117 d) in chromospheric activity in addition to, and separate from, both its rotation (3.3 d) and long-term variability. As a persistent sub-yearly period in surface magnetic activity is unprecedented, we investigate this apparent anomaly further by examining chromospheric activity levels of other stars with similar mass, searching for variability in chromospheric activity with periods of less than one year, but longer than measured or predicted rotation. An examination of the time series of 40 mid-to-late F dwarfs yielded one other star for further analysis: alpha Com (HD 114378, P approximately 132 d). The variations for these two stars were checked for persistence and coherence. Based on these determinations, we eliminate the possibilities of rotation, long-term activity cycle, and the evolution of active regions as the cause of this variation in both stars. In particular, for tau Booe we infer that the phenomenon may be chromospheric in origin; however, beyond this, it is difficult to identify anything further regarding the cause of the activity variations, or even whether the observed modulation in the two stars have the same origin. Title: A Combined MG II/CA II Survey of Stellar Magnetic Activity in the Solar Neighborhood Authors: Wicklund, B. M.; Donahue, R. A.; Dobson, A. K.; Baliunas, Sallie L. Bibcode: 1997sao..rept.....W Altcode: We use nearly contemporaneus low-resolution IUE observations of Mg II h + k emission and Mount Wilson Observatory Ca II H + K S indices for 33 pairs of observations of lower main sequence stars to formulate a relationship that will permit accurate predictions of S values as a function of (B - V) color and Mg II h + k flux. The resulting relationship is useful because it will extend the set of solar neighborhood stars for which a uniform estimate of chromospheric activity is available to include stars that are not observable from Mount Wilson as well as providing additional estimates of activity levels for stars that are on the Mount Wilson HK Project observing list. Title: Stellar Active Region Evolution - I. Estimated Lifetimes of Chromospheric Active Regions and Active Region Complexes Authors: Donahue, R. A.; Dobson, A. K.; Baliunas, S. L. Bibcode: 1997SoPh..171..191D Altcode: The lifetimes of chromospheric active regions and active region complexes ('active longitudes') for 35 lower-Main-Sequence stars observed at Mount Wilson Observatory are estimated from the relative distribution of pooled variance at different time scales. The time scale of active region evolution (i.e., the lifetime of large active regions) is approximately 50 days, while the lifetime of active region complexes is on the order of 1 year. These estimates can be used to clarify the contribution of active regions to variance in short-term (i.e., <1 yr) time series data. Previously unpublished mean rotation periods are documented for several stars. Title: Stellar Active Region Evolution - II. Identification and Evolution of Variance Morphologies in CA II H+K Time Series Authors: Donahue, R. A.; Dobson, A. K.; Baliunas, S. L. Bibcode: 1997SoPh..171..211D Altcode: 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. Title: Properties of Sun-like Stars with Planets: 51 Pegasi, 47 Ursae Majoris, 70 Virginis, and HD 114762 Authors: Henry, Gregory W.; Baliunas, Sallie L.; Donahue, Robert A.; Soon, Willie H.; Saar, Steven H. Bibcode: 1997ApJ...474..503H Altcode: Radial velocity variations have revealed planets orbiting 51 Peg, 47 UMa, and 70 Vir, and a low-mass companion orbiting HD 114762. We analyze parallel records of photometric measurements in Strömgren b and y and Johnson V, R, and I passbands and Ca II H and K fluxes in those stars. In the case of 51 Peg, the high precision of the differential photometric measurements made by the 0.75 m Automatic Photoelectric Telescope and the nonvariability of the star would allow the detection of a transit of a planet as small as Earth (corresponding to an amplitude of 0.0001 mag) if its orbit were nearly coplanar with our line of sight. No transits were observed.

For 51 Peg and 70 Vir, the upper limit of nondetection of photometric variability at their companion's orbital periods is Δ(b + y)/2 < 0.0002 +/- 0.0002 mag. For HD 114762, it is ΔV < 0.0007 +/- 0.0004 mag. Such small amplitudes of photometric variability seem to eliminate periodic velocity variations expected from p-mode oscillations.

All four stars are magnetically quiet; that is, they lack the typical Ca II and photometric variability due to rotation and activity cycles expected from surface magnetic activity in solar-type stars. Such quiescence produces an interesting observational bias that favors the detection of planets from low-amplitude radial velocity or photometric variations by minimizing the contribution from intrinsic stellar variability. We discuss the circumstances for which the probability of planet detections is improved by the reduced level of variability from surface magnetic activity in G and K stars. Stars with low variability in surface activity should be the best candidates for planet searches using radial velocity and photometric techniques. Searches for planets around younger, more active stars will be impeded by variations in velocity or brightness caused by time-varying surface features.

The Ca II H and K fluxes indicate that all four stars are older than 5 Gyr. Ages were estimated from the average levels of Ca II H and K fluxes and an existing relationship of the decrease of Ca II fluxes with age on the lower main sequence and were drawn from previous results based on theoretical isochrone fitting. Values of the projected rotational velocity, v sin i, are determined for 70 Vir and 47 UMa from high-resolution spectra.

Based on observations made at Mount Wilson Observatory, operated by the Mount Wilson Institute under an agreement with the Carnegie Institution of Washington, and at the National Solar Observatory, administered by AURA, Inc. for the NSF. Title: Properties of Sun-like Stars with Planets: ρ1 Cancri, τ Bootis, and υ Andromedae Authors: Baliunas, Sallie L.; Henry, Gregory W.; Donahue, Robert A.; Fekel, Francis C.; Soon, Willie H. Bibcode: 1997ApJ...474L.119B Altcode: Planets have been reported orbiting the Sun-like stars ρ1 Cnc, τ Boo, and υ And based on low-amplitude radial velocity variations. We have derived information on the first two stars from analysis of spectra, as well as parallel records of high-precision Strömgren b and y photometry and Ca II H + K fluxes. In the case of ρ1 Cnc, the upper limit (peak to peak) of nondetection of photometric variability at the orbital period is Δy ~ 0.0004 mag. The possibility of a planetary transit cannot be ruled out completely from the photometric data. Variations of the Ca II fluxes suggest a rotational period of ~42 days, in agreement with the inferred v sin i ~ 2 km s-1. The age of ρ1 Cnc is ~5 Gyr, based on its average Ca II flux and a relation between Ca II flux and age.

The star τ Boo, unlike the other reported solar-type stars with planets, is relatively young (~2 Gyr). Despite its young age, it is photometrically nonvariable at the orbital period with an amplitude of Δ(b + y)/2 ~ 0.0004 mag (peak to peak); however, small-amplitude interseasonal variability is seen. No planetary transits were found in the photometry, which limits the inclination of the planet's orbital plane to Earth's line of sight to less than 83° (where 90° is coplanar). The Ca II record shows a weakly significant rotational period near 3.3 days, coincident with the orbital period of the companion. The Ca II record also shows a period of 116 days that has persisted for 30 years and is not seen in the photometric record. The persistence and timescale of this Ca II variation mean that it has no counterpart in Sun-like magnetic activity. The amplitude of the reflex velocity of the parent star (~450 m s-1) is much larger than the radial velocity perturbations expected from the presence of either surface inhomogeneities or line-bisector variations. Thus the anticipated perturbations from those stellar effects do not refute the inference of reflex velocities.

We have few Ca II flux measurements for υ And. Its age and rotational period are estimated to be ~5 Gyr and 12 days, respectively. Our results for ρ1 Cnc and τ Boo are consistent with the explanation of planets as the cause of the velocity variations.

Based on observations made at Mount Wilson Observatory, operated by the Mount Wilson Institute under an agreement with the Carnegie Institution of Washington. Title: Mount Wilson Reborn: A New ERA Dawns for 'America's Observatory'. Authors: Jastrow, R.; Baliunas, S. L. Bibcode: 1997ASSL..210...10J Altcode: 1997ilsn.proc...10J No abstract at ADS Title: The Rotation of the G0 Dwarf β Comae Authors: Gray, David F.; Baliunas, Sallie L. Bibcode: 1997ApJ...475..303G Altcode: The rotation of β Comae (HR 4983, HD 114710, G0 V) is studied using the available information from spectral line broadening and from rotational modulation. The line broadening yields v sin i = 4.10 +/- 0.06 km s-1, which agrees with previous values. Rotational modulation was looked for but not seen in the photospheric parameters of temperature and granulation, although this might be a result of data sampling not being well suited for modulation studies. Rotational modulation is seen in the S index of the Ca II chromospheric emission. Two period sequences characterize β Comae between 1981 and 1994. The periods decline monotonically with time, paralleling the decline in magnetic activity as indicated by the average strength of the Ca II emission. We interpret the decrease in period as differential rotation coupled with systematic migration in latitude of the active regions. It is not possible to separate the differential rotation profile of β Comae from its rate and sense of latitude migration. We compare the changes of β Comae with the Sun's and point out similarities and differences. Title: Inference of Solar Irradiance Variability from Terrestrial Temperature Changes, 1880--1993: an Astrophysical Application of the Sun-Climate Connection Authors: Soon, W. H.; Posmentier, E. S.; Baliunas, S. L. Bibcode: 1996ApJ...472..891S Altcode: Information can be inferred on the timing and amplitude of solar total irradiance changes over t880- t993 by simulating the global terrestrial surface temperature changes produced by these irradiance changes and comparing them with observed temperatures. The profiles of solar irradiance variations used in the climate simulations are adopted from several different proxies: (t) the length of the sunspot cycle, (2) the mean sunspot number, and (3) a composite proxy that includes the two previous indicators plus the equatorial solar rotation rate, the fraction of penumbral spot coverage, and the rate of decay of the sunspot cycle. We use a seasonal energy-conservation climate/upwelling-diffusion ocean model, forced by the assumed profiles of solar total irradiance variations, combined with variations in anthropogenic greenhouse gases. Optimized cases imply total irradiance changes during t880-t993 in the range 0.18%-0.77%.

If the solar irradiance profiles found from the climate simulations are required to be consistent with recent satellite observations, then the composite solar profile reconstructed by Hoyt & Schatten, combined with the anthropogenic greenhouse forcing, explains the highest fraction of the variance of observed global mean temperatures. In this case, the solar and greenhouse combination accounts for 92% of the observed long-term temperature variance during t880-t993. The simulation implies that the solar part of the forcing alone would account for 7t% of the global mean temperature variance, compared to 5t% for the greenhouse gases' part alone. It also suggests a solar total irradiance variation of 0.5% during the interval t880-t993. Such an amplitude of solar total irradiance change is consistent with astrophysical limits of brightness changes on timescales of decades to centuries independently derived from observations of solar-type stars (including the Sun). Title: Multiwavelength Activity Profiles of Cool Stars Authors: Hall, J. C.; Baliunas, S. L. Bibcode: 1996AAS...189.8108H Altcode: 1996BAAS...28.1383H We have constructed detailed observing histories of a large number of cool stars by combining measurements of magnetic-activity-sensitive lines in ground-based data and space archival data into what we term multiwavelength activity profiles (MAPs) of these stars. To construct a MAP, we first combine the Mt. Wilson Observatory HK project data and the Lowell Observatory Solar-Stellar Spectrograph (SSS) near-UV to near-IR data for a given target into absolute-flux-calibrated records of the star's chromospheric variability. We then add IUE NEWSIPS-processed spectra and available EUV and X-ray data to produce the final MAP, which provides a comprehensive picture of the long-term variability in the target stars from their low chromospheres to their coronae. In this poster we present representative MAPs for nine stars with large space-based data sets (HDs 20630, 22049, 35296, 39587, 61421, 72905, 115383, 131156A, and 201091). We first describe how we combine the various data into a uniformly calibrated MAP, and then examine the response of different regions of the stellar atmospheres to cyclic, rotational, and short-term variability. Title: Possible Detection of a Residual Non-Cyclic Distributed Dynamo in ``Maunder Minimum'' Stars Authors: Saar, S. H.; Deluca, E. E.; Baliunas, S. L.; Donahue, R. A. Bibcode: 1996AAS...189.8104S Altcode: 1996BAAS...28.1382S We have analyzed HST and IUE ultraviolet spectra of five dwarfs which have extremely low, non-variable levels of Ca II HK emission. These stars appear to be in the stellar analog of the solar ``Maunder minimum'' - a period when the normal cyclic magnetic dynamo went into temporary quiescence. The stars all have very low levels of chromospheric and transition region (TR) emission. The ratio of TR (Si IV and C IV) to chromospheric emission (C II) is smaller than expected from published estimates of the ``basal'' emission, and increases with decreasing T_eff. This is in contrast to the lack of such a trend in dwarfs with variable Ca II HK (``normal'' operating magnetic dynamos) and the reverse of the trend expected if the emission was acoustic in origin. The existence of significant TR emission in ``Maunder minimum'' stars suggests that they are still generating magnetic flux, but it is apparently in some form which enhances chromospheric emission relative to the TR. A possible explanation for the observations is that a residual ``Maunder minimum'' magnetic flux is a generated by a non-cyclic distributed-type dynamo (a less efficient mechanism which operates throughout the convective zone, and thus grows with increased convective zone depth). If this scenario is correct, our data are the first observational evidence of such a dynamo operating in a star which is not fully convective. Title: M.I.T. Space Grant Program Photoelectric Observations of Variable Stars for High School Students Authors: Baliunas, Sallie Bibcode: 1996sao..reptR....B Altcode: This progress report covers work by three undergraduate and two advanced high school students on intensive astrophysical research. Subject areas included: chromospheric activity in evolved stars, ages of sunlike stars from IUE satellite observations, Sunlike stars with planets, adaptive optics - surface features of Vesta, and rotation of lower main sequence stars. Title: The Stellar Dynamo Authors: Nesme-Ribes, Elizabeth; Baliunas, Sallie L.; Sokoloff, Dmitry Bibcode: 1996SciAm.275b..46N Altcode: No abstract at ADS Title: A Relationship between Mean Rotation Period in Lower Main-Sequence Stars and Its Observed Range Authors: Donahue, Robert A.; Saar, Steven H.; Baliunas, Sallie L. Bibcode: 1996ApJ...466..384D Altcode: Chromospheric Ca II H and K fluxes have been measured in a sample of ~100 stars on or near the main sequence at Mount Wilson Observatory. Observations were made several times a week and span more than ten years. Within an observing season, many stars show periodic variations due to rotation. Thirty-six of the stars have highly-significant periods in at least five seasons. We compute the range in the observed period, Delta P, and suggest that it is a measure of, and a lower limit to, the surface differential rotation (SDR). Several physical and selection effects can affect the measured Delta P value. An analysis of the cumulative variance distribution at various time scales, however, demonstrates that Ca II variations due to active region growth and decay are of longer period and smaller amplitude than those due to rotation. We argue that other effects (e.g., multiple active regions, latitude bands) are either small, or primarily act to reduce the measured Delta P relative to its true value. Including results for the Sun, we find that Delta P depends on the mean seasonal rotation period

, such that Delta P is proportional to

to the power of 1.3 +/- 0.1, independent of mass. We briefly discuss this in the context of dynamo models, and other observations of surface differential rotation and active region structure. Title: Magnetic, Photometric, Temperature, and Granulation Variations of XI Bootis A 1984--1993 Authors: Gray, David F.; Baliunas, Sallie L.; Lockwood, G. W.; Skiff, Brian A. Bibcode: 1996ApJ...465..945G Altcode: The magnetically active G8 dwarf star, ξ Boo A = HR 5544 = HD 13 1156 is studied for magnetic- cycle type variations over the 1984-1993 interval. We present measurements of Ca II H and K emission as an indirect indicator of magnetic activity, blue and visual magnitudes as an indication of the power output and temperature, line-depth ratios of V I λ6251.83 to Fe I λ6252.57 as a measure of temperature, and line bisectors as a measure of the star's granulation. The season means of all these parameters show the same pattern of variation with several irregular rises and falls, rather different from the relatively smooth variations seen for the Sun. As found for several other stars in previous studies, the magnetic signal leads the others in time. Time lags relative to the H and K index variation are 1.4±0.4 yr for the photometric brightness, 1.5±0.5 yr for the b -y color index, 1.8±0.3 yr for the line-depth ratio, and 2.1±0.4 yr for the line bisectors. The ≍1.7 year temperature lag for ξ Boo A is close to the linear relation between lag and effective temperature found for the other stars that have been measured. Title: A Dynamo Interpretation of Stellar Activity Cycles Authors: Baliunas, S. L.; Nesme-Ribes, E.; Sokoloff, D.; Soon, W. H. Bibcode: 1996ApJ...460..848B Altcode: Twenty-five-year records of Ca II H and K chromospheric emission fluxes measured in single lower main-sequence stars at Mount Wilson Observatory reveal surface magnetic activity cycles in one-third of the sample of roughly 100 stars. For those stars with cycles, we compare the ratio of the observed periods of the cycle of magnetic activity and axial rotation, Pcyc/Prot, to predictions available from stellar dynamo theory. Theoretical considerations suggest that the ratio is the observational equivalent of the stellar dynamo number, D.

The stellar sample is comprised of two groups separated by their mean level of activity, <R'HK>, and rotation, Prot: one group has high levels of average activity and fast rotation, while the other group has relatively low levels of activity and slower rotation. Both groups also occupy different regions on the diagram of X-ray flux versus stellar dynamo number. For the older group of stars (ages &#8819 2 Gyr) which includes the current Sun, we find a statistically significant inverse relation between the intensity of the cycle, C = ΔRHK/<R'HK>, and the stellar dynamo number, empirically determined to be D ∼ (Pcyc/Prot)1.35+0.65-0.35. Title: The writing on the wall. Authors: Baliunas, S. L. Bibcode: 1996Mercu..25a..18B Altcode: Scientists has two choices: continue to fight for money in the current system of federal research funding, with diminishing returns, or push for alternatives. One alternative, in keeping with the spirit of the age, is to create incentives for private support of research. Title: Magnetic Field and Rotation in Lower Main-Sequence Stars: an Empirical Time-dependent Magnetic Bode's Relation? Authors: Baliunas, Sallie; Sokoloff, Dmitry; Soon, Willie Bibcode: 1996ApJ...457L..99B Altcode: We find a significant correlation between the magnetic and rotational moments for a sample of 112 lower main-sequence stars. The rotational moment is calculated from measurements of the rotation period in most of the stars (not from the projected rotational velocity inferred from Doppler broadening). The magnetic moment is computed from a database of homogeneous measurements of the mean level of Ca II H and K emission fluxes sampled for most of the stars over an interval of 25 yr. The slope connecting the logarithm of the magnetic moment and the logarithm of the rotational moment is about +0.5--0.6, with a Pearson correlation coefficient of about +0.9. The scatter of points from the mean relation has a component that is natural and caused by decade-long surface variability. Title: Physical Properties of the Contact Binaries of the Old Open Cluster NGC 188 Authors: Bradstreet, D. H.; Baliunas, S. L.; Guinan, E. F. Bibcode: 1996ASPC...90..135B Altcode: 1996oedb.conf..135B No abstract at ADS Title: A Survey of Ca II H and K Chromospheric Emission in Southern Solar-Type Stars Authors: Henry, Todd J.; Soderblom, David R.; Donahue, Robert A.; Baliunas, Sallie L. Bibcode: 1996AJ....111..439H Altcode: More than 800 southern stars within 50 pc have been observed for chromospheric emission in the cores of the Ca II H and K lines. Most of the sample targets were chosen to be G dwarfs on the basis of colors and spectral types. The bimodal distribution in stellar activity first noted in a sample of northern stars by Vaughan and Preston in 1980 is confirmed, and the percentage of active stars, about 30%, is remarkably consistent between the northern and southern surveys. This is especially compelling given that we have used an entirely different instrumental setup and stellar sample than used in the previous study. Comparisons to the Sun, a relatively inactive star, show that most nearby solar-type stars have a similar activity level, and presumably a similar age. We identify two additional subsamples of stars -- a very active group, and a very inactive group. The very active group may be made up of young stars near the Sun, accounting for only a few percent of the sample, and appears to be less than ~0.1 Gyr old. Included in this high-activity tail of the distribution, however, is a subset of very close binaries of the RS CVn or W UMa types. The remaining members of this population may be undetected close binaries or very young single stars. The very inactive group of stars, contributting ~5%--10% to the total sample, may be those caught in a Maunder Minimum type phase. If the observations of the survey stars are considered to be a sequence of snapshots of the Sun during its life, we might expect that the Sun will spend about 10% of the remainder of its main sequence life in a Maunder Minimum phase. Title: The Sun-Climate Connection Authors: Baliunas, Sallie; Soon, Willie Bibcode: 1996S&T....92...38B Altcode: No abstract at ADS Title: Interpretation of stellar Ca II activity cycles. Authors: Baliunas, S. L.; Nesme-Ribes, E.; Sokoloff, D.; Soon, W. Bibcode: 1996sube.conf...57B Altcode: Twenty-five year records of Ca II H and K chromospheric emission fluxes measured in lower main-sequence stars reveal surface magnetic activity cycles which are comparable to that of the Sun's. The observed variations can be interpreted in terms of stellar dynamo theory. The authors find the ratio of the period of stellar cycle to the period of stellar axial rotation, Pcyc/Prot, to be representative of a stellar dynamo number, D. Title: Variations of beta Comae through a Magnetic Minimum Authors: Gray, David F.; Baliunas, Sallie L.; Lockwood, G. W.; Skiff, Brian A. Bibcode: 1996ApJ...456..365G Altcode: The dwarf star β Com = HR 4983 = HD 114710 (GO V, B-V = 0.57) is close to the Sun in the H-R diagram, being only ≍260 K hotter. We present measurements done over several years of (1) the line depth ratios of V I λ6251.83 to Fe I λ6252.57 to establish the temperature, (2) the line bisectors as a measure of the star's granulation, (3) Ca II H and K emission as an indirect indicator of magnetic activity, and (4) the blue and visual magnitudes as an indication of the power output. All these parameters show a similar variation consisting of a broad minimum extending over approximately 5 years, but the minima do not occur at the same epoch. The magnetic signature leads the others in time. Time lags relative to the magnetic variation are 0.9±0.3 yr for the photometric data, 2.9±0.3 yr for the temperature, and 2.9±0.5 yr for the granulation. A 1% variation in radius during the 5 yr interval is indicated. Title: The chromospheric activity of the many "suns" in M67. Authors: Giampapa, M. S.; Baliunas, S. L.; Radick, R. R. Bibcode: 1996BAAS...28.1197G Altcode: No abstract at ADS Title: The stellar dynamo. Authors: Nesme-Ribes, E.; Baliunas, S. L.; Sokoloff, D. Bibcode: 1996SciAm.275b..30N Altcode: No abstract at ADS Title: Low-Resolution IUE Observations of Chromospheric MG II H and K Emissions Authors: Wicklund, B. M.; Donahue, B.; Baliunas, S. Bibcode: 1995AAS...18710301W Altcode: 1995BAAS...27Q1430W Low-resolution IUE observations of the 280 nm Mg II h and k lines of 67 G--K type stars are used to formulate a relationship between Mg II and Ca II chromospheric emission. The resulting relationship can be used to convert Mg II flux measurements to Ca II flux measurements. This expands the database currently being compiled by the HK Project at Mount Wilson Observatory by providing measurements of chromospheric activity for stars not observable from Mount Wilson. This data will be of use to projects currently using Ca II H and K fluxed from the HK Project. Title: Are Variations in the Length of the Activity Cycle Related to Changes in Brightness in Solar-Type Stars? Authors: Baliunas, Sallie; Soon, Willie Bibcode: 1995ApJ...450..896B Altcode: We compare the average level of chromospheric activity and cycle length for solar-type stars as determined from 25 yr records of Ca II fluxes and from the sunspot record from 1750 to 1990. Both sets of data show an inverse relation between the cycle length and average activity level, with only a minor difference in the slopes. In turn, the amplitude of Ca II variability is positively correlated with the photometric brightness change during an activity cycle. The relationship between those observables provides a physical basis for the close correlation between the length of the sunspot cycle and mean terrestrial temperature over the last few centuries as shown by Friis-Christensen & Lassen.

Solar brightness variations over the last several centuries can be estimated from this relationship by including stars with low Ca II fluxes which, we assume, are in states resembling the phase of solar activity known as the Maunder minimum (circa 1645-1715). Although the value of the slope connecting the mean level of Ca II activity and the cycle length is sensitive to the statistical treatment of the data, a lower limit to the slope can be determined reliably. This lower limit yields an increase of 0.4% of solar brightness from the solar Maunder minimum to the cyclic phase of sunspot activity which immediately followed the Maunder minimum. Title: First tests of the Cassegrain adaptive optics system of the Mount Wilson 100-in telescope Authors: Shelton, J. Christopher; Schneider, T.; McKenna, Daniel; Baliunas, Sallie L. Bibcode: 1995SPIE.2534...72S Altcode: In January 1994, we began construction of a modern adaptive optics system for the newly refurbished 100-inch telescope. The design philosophy of the adaptive optics system is to achieve a working system in the visible in a short time at relatively low cost. This means wavefront sensing with natural guide stars and implementation at the bent Cassegrain focus of the telescope. The system has an integrated wavefront sensor and finder camera, and is automated for one-person operation. It uses off-the-shelf components where possible. The deformable mirror, which has 241 actuators, is on loan from the U.S. Air Force. The use of an existing mirror imposes constraints that have driven some of the design considerations. The system is operating at the telescope, with early results described below. Title: A Study of Variability in a Sample of G and K Giants Authors: Choi, Hyung-Jin; Soon, Willie; Donahue, Robert A.; Baliunas, Sallie L.; Henry, Gregory W. Bibcode: 1995PASP..107..744C Altcode: Eight years of Ca II surface activity records from Mount Wilson Observatory measured for 12 bright G-K III stars have been analyzed in order to detect periodic variations attributable to rotation. We also present photometric V-band data for these stars from the Fairborn 0.25m Automatic Photometric Telescope (APT) that yielded a photometric period in one case and rms deviations from apparently constant brightness levels for the remaining 11 stars. The Ca II data yielded rotation periods for 10 out of 12 giant stars. We demonstrate that the photometric variability and non-variability of these stars can be predicted from their Rossby numbers calculated from our observed rotation periods and convective turnover times scaled up from the main sequence. (SECTION: Stars) Title: Estimated Lifetimes of Chromospheric Active Regions and Active Region Complexes Authors: Dobson, A. K.; Donahue, R. A.; Baliunas, S. L. Bibcode: 1995AAS...186.2111D Altcode: 1995BAAS...27..839D The relative distribution of pooled variance at different time scales for some 40 lower main sequence stars observed at Mt Wilson Observatory are used to derive estimates for the lifetimes of chromospheric active regions and active region complexes. For the sample stars, the time scale of AR evolution is approximately 50 days, while the lifetime of AR complexes is on the order of 1 year. These estimates can be used to clarify the contribution of active regions to short-term (i.e., less than 1 y) time series data. Title: Pulsation Timescales and Amplitudes in a Sample of Bright Semi-Regular Variable Stars Authors: Cristian, V. -Cristina; Donahue, Robert A.; Soon, Willie H.; Baliunas, Sallie L.; Henry, Gregory W. Bibcode: 1995PASP..107..411C Altcode: We have analyzed the differential V-band photometric variations of records up to 8 years long in ten M III semi-regular (SR) variable stars. Periodograms constructed from each star's entire record and seasoned intervals were used to find repetitive occurrences of pulsation periods in the range of 10 to 250 days. For every star at least one locus of periods was observed, with many stars showing two distinct distributions of pulsation timescales. The observed pulsation periods and differential V-magnitude semi-amplitudes appear to be correlated such that longer periods correspond to larger semi-amplitudes. (SECTION: Stars) Title: Identification and Evolution of Variance Morphologies in CA II H+K Time Series Authors: Donahue, Robert A.; Dobson, Andrea K.; Baliunas, Sallie L. Bibcode: 1995AAS...186.2213D Altcode: 1995BAAS...27Q.843D The relative distribution of pooled variance at different time scales for the chromospheric activity of approximately 100 stars observed at Mount Wilson Observatory may be divided into three basic morphological types which depend to a large extent on their mean activity level (i.e., age) and color (i.e., mass). Analysis of the pooled variance plots possibly provide a technique for determining the lifetimes of stellar active regions and their influence on chromospheric time series used for determining rotation and activity cycle periods. Title: Identification and evolution of variance morphoplogies in Ca II H+K time series. Authors: Donahue, R. A.; Dobson, A. K.; Baliunas, S. L. Bibcode: 1995BAAS...27R.843D Altcode: No abstract at ADS Title: Chromospheric Activity and Age of Solar-Type Stars Authors: Baliunas, S. L.; Donahue, R. A.; Soon, W.; Gilliland, R.; Soderblom, D. R. Bibcode: 1995AAS...186.2109B Altcode: 1995BAAS...27..839B Main-sequence stars near one solar mass show an average level of Ca II H and K emission and rotation that decrease with age. Although the mechanism governing surface magnetism and rotation is not theoretically well-understood, the measurement of rotation or average activity level can yield an estimate of the age of a solar-mass star. Several empirically-determined functions of the decay of rotation and activity have been developed over the last several decades, but more have concentrated on stars much younger than the Sun, whose Ca II activity and rotation have been relatively easy to measure. Observations of the Ca II H and K emission were obtained of solar-mass stars in the old open clusters NGC 752 and M 67 with the KPNO 4-m telescope and HYDRA spectrograph. Those spectra yield a large (>50) smaple of stars close to one solar mass and close to the age of the Sun. Those spectra have been calibrated to the system of measurement of Ca II H and K emission fluxes of nearly 1000 lower main sequence stars obtained at Mount Wilson Observatory. The combined sample of Ca II fluxes yield: (1) a refined calibration of age as a function of activity, using rotation as an indicator of age; (2) the range of Ca II activity at a given age, caused by variations of surface magnetic activity over time scales of decades to centuries; and (3) an estimate of the uncertainty of age inferred from a measurement of the instantaneous activity level. Title: Magnetic Activity Variations of epsilon Eridani Authors: Gray, David F.; Baliunas, Sallie L. Bibcode: 1995ApJ...441..436G Altcode: The variations in magnetic activity, temperature and granulation of epsilon Eri (HR 1084, HD 22049, K2 V, B-V = 0.88) in the interval from 1986 to 1992 are discussed in this paper. We monitored the magnetic activity with the Ca II H and K-line emission, the temperature with the ratio of depths of two spectral lines, and the granulation with spectral-line asymmetries. Rotational modulation is seen only in the H and K emission, and it shows a period of 11.10 +/- 0.03 days, in agreement with earlier published values. The star has one dominant activity longitude. The magnetic activity of epsilon Eri is strong and shows irregular excursions that may be superposed on a cyclic variation having a period approximately equal to 5 yr. During the 1986-1992 interval the magnetic activity went through a broad relative minimum. Temperature and granulation changes mimic the variation in H and K emission, with excursions approximately equal to 15 K and approximately equal to 35 m/s, repectively. No long-term photometric observations are available for epsilon Eri, but we calculate a 1.2% variation in luminosity and 0.014 mag in V to have occurred, assuming the radius of the star is constant. Title: Is HD 3651 entering a "Maunder minimum" phase? Authors: Donahue, R. A.; Baliunas, S. L.; Soon, W. H.; McMillan, F. M. Bibcode: 1995IAUS..176P..72D Altcode: No abstract at ADS Title: Chromospheric Variations in Main-Sequence Stars. II. Authors: Baliunas, S. L.; Donahue, R. A.; Soon, W. H.; Horne, J. H.; Frazer, J.; Woodard-Eklund, L.; Bradford, M.; Rao, L. M.; Wilson, O. C.; Zhang, Q.; Bennett, W.; Briggs, J.; Carroll, S. M.; Duncan, D. K.; Figueroa, D.; Lanning, H. H.; Misch, T.; Mueller, J.; Noyes, R. W.; Poppe, D.; Porter, A. C.; Robinson, C. R.; Russell, J.; Shelton, J. C.; Soyumer, T.; Vaughan, A. H.; Whitney, J. H. Bibcode: 1995ApJ...438..269B Altcode: The fluxes in passbands 0.1 nm wide and centered on the Ca II H and K emission cores have been monitored in 111 stars of spectral type F2-M2 on or near the main sequence in a continuation of an observing program started by O. C. Wilson. Most of the measurements began in 1966, with observations scheduled monthly until 1980, when observations were scheduled sevral times per week. The records, with a long-term precision of about 1.5%, display fluctuations that can be identified with variations on timescales similar to the 11 yr cycle of solar activity as well as axial rotation, and the growth and decay of emitting regions. We present the records of chromospheric emission and general conclusions about variations in surface magnetic activity on timescales greater than 1 yr but less than a few decades. The results for stars of spectral type G0-K5 V indicate a pattern of change in rotation and chromospheric activity on an evolutionary timescale, in which (1) young stars exhibit high average levels of activity, rapid rotation rates, no Maunder minimum phase and rarely display a smooth, cyclic variation; (2) stars of intermediate age (approximately 1-2 Gyr for 1 solar mass) have moderate levels of activity and rotation rates, and occasional smooth cycles; and (3) stars as old as the Sun and older have slower rotation rates, lower activity levels and smooth cycles with occasional Maunder minimum-phases. Title: Pulsation and Long-Periods in Three Nearby M Supergiants Authors: Smith, M. A.; Teays, T. J.; Taylor, L. L.; Wasatonic, R.; Guinan, E. F.; Baliunas, S. Bibcode: 1995ASPC...83..403S Altcode: 1995IAUCo.155..403S; 1995aasp.conf..403S No abstract at ADS Title: The Current State of Target Selection for NASA's High Resolution Microwave Survey Authors: Henry, T.; Soderblom, D.; Baliunas, S.; Davis, R.; Donahue, R.; Latham, D.; Stefanik, R.; Torres, G.; Duquennoy, A.; Mayor, M.; Andersen, J.; Nordstrom, B.; Olsen, E. Bibcode: 1995ASPC...74..207H Altcode: 1995psel.conf..207H No abstract at ADS Title: Variations in Surface Activity of the Sun and Solar Type Stars Authors: Soon, W. H.; Baliunas, S. L.; Zhang, Q. Bibcode: 1994SoPh..154..385S Altcode: Twenty-five-year records of relative CaII H and K emission fluxes of lower Main-Sequence stars have been measured at Mount Wilson Observatory and reveal surface activity in most of the older G- and K-type dwarf stars that is similar to the aperiodical activity cycle of the contemporary Sun (i.e., the cyclic and the occasional episode of reduced activity in the past few centuries). We find an inverse relationship between the amplitude of the activity cycle and the length of the cycle for the ensemble of those solar-type stars. We also find a similar relationship using the 250-year sunspot record (Cycles 1 to 21). The similarity between the two inverse relationships for the solar-type stars observed for 25 years and the Sun for a longer interval of time may suggest one common underlying physical mechanism that is responsible for the variations in surface activity ranging from decades to centuries. Title: The Activity Cycle of tau Ceti Authors: Gray, David F.; Baliunas, Sallie L. Bibcode: 1994ApJ...427.1042G Altcode: The temperature, granulation, and chromospehric emission of tau Ceti (HR 509, HD 10700, G8 V, B-V = 0.72) in the 1984-1992 interval are studied for magnetic-cycle type variations. Yearly-mean temperature measurements are determined to +/- 3-4 K using ratios of spectral line depths, and show no systematic variations over the 9 yr interval. Granulation is monitored using the asymmetries of spectral lines. There is some indication of systematic variation in velocity span, but this variation is not well established. The Ca II H and K line emission, although weak by stellar standards, may show two cycles of variability in the 1970-1992 time span with a period of approximately = 11 yr. No rotation modulation is seen in any of the parameters, but the very narrow spectral lines of tau Cet points to a nearly pole-on orientation so that none would be expected. Title: A Method of Determining Possible Brightness Variations of the Sun in Past Centuries from Observations of Solar-Type Stars Authors: Zhang, Q.; Soon, W. H.; Baliunas, S. L.; Lockwood, G. W.; Skiff, B. A.; Radick, R. R. Bibcode: 1994ApJ...427L.111Z Altcode: Observations of the Sun and a number of stars with mass and age close to the Sun show that changes in magnetic activity and brightness are directly correlated over an activity cycle. The ratio of the two correlated changes shows considerable scatter. If we assume that the scatter represents variability of the one solar-type star at different epochs, the aggregate data may represent the range of variation of the Sun over centuries. We illustrate a technique of inferring possible brightness variations of the Sun from a sample of solar-type stars. The observed scatter of the ratio of all 10 solar-type stars in our sample (stars with (B-V) greater than or approximately equal to 0.55 and less than or approximately equal to 1.2 and mean level of chromospheric activity R primeHK less than or approximately equal to -4.75 in the Lockwood et al. 1992 sample) plus the Sun yields a possible increase of 0.2% - 0.6% in solar brightness as magnetic activity has increased from the Maunder Minimum (ca. A.D. 1660-1710) to the decade of the 1980s. The limited sample of solar-type stars will need to be extended in order to improve the range of the estimate provided. Title: Adaptive Optics at Mount Wilson Observatory Authors: Shelton, J. C.; Baliunas, S. L.; Russell, J.; Donahue, R. A. Bibcode: 1994ESOC...48...53S Altcode: 1994aao..conf...53S No abstract at ADS Title: Adaptive Optics at Mount Wilson Observatory: Results from the 60-inch Telescope. Authors: Baliunas, S. L.; Shelton, J. C.; Russell, J.; Donahue, R. A. Bibcode: 1994ASPC...55...56B Altcode: 1994oaem.conf...56B No abstract at ADS Title: Evidence of Surface Differential Rotation (SDR) in Lower Main-Sequence Stars. Authors: Donahue, R. A.; Baliunas, S. L. Bibcode: 1994ASPC...64..396D Altcode: 1994csss....8..396D No abstract at ADS Title: The Evolution of Stellar Dynamo Variations. Authors: Saar, S. H.; Brandenburg, A.; Donahue, R. A.; Baliunas, S. L. Bibcode: 1994ASPC...64..468S Altcode: 1994csss....8..468S No abstract at ADS Title: A technique for estimating long-term variations of solar total irradiance : Preliminary estimates based on observations of the Sun and solar-type stars Authors: Soon, W. H.; Baliunas, S. L.; Zhang, Q. Bibcode: 1994seit.conf..133S Altcode: No abstract at ADS Title: Second Generation Adaptive Optics: Plans for the Mount Wilson 100-Inch Telescope. Authors: Shelton, J. C.; Baliunas, S. Bibcode: 1994ASPC...55...68S Altcode: 1994oaem.conf...68S No abstract at ADS Title: The Mount Wilson Story Authors: Bester, M.; Baliunas, S.; Shelton, C.; Webster, L. Bibcode: 1994vuae.conf..105B Altcode: No abstract at ADS Title: The Mount Wilson Observatory Metallicity Index, C RV: Comparison with Other Photometric Systems Authors: Soon, W. H.; Zhang, Q.; Baliunas, S. L.; Kurucz, R. L. Bibcode: 1993ApJ...416..787S Altcode: A new spectrophotometric index, CRV, is assessed as a metallicity indicator for late-type stars. The index is the ratio of the measured photospheric fluxes in 20 Å wide passbands centered at 400t and 3901 Å. CRV correlates directly with the metallicity index, m1, of the Strömgren uvby system and with the metallicity index hk, of Anthony-Twarog et al. (1991).

Using observations of 236 dwarfs and 140 giants combined with stellar atmosphere models (Kurucz 1991), we compared the sensitivity of the CRV, m1, and hk indices to metal abundance. We also studied the sensitivity of the CRV, C1, and hk indices to surface gravity. The effect of interstellar extinction on all the indices was also studied from published mean extinction laws.

We find that the CRV index is sensitive to the variation of metal abundance, [M], over the range examined (-5.0 ≲ [M] ≲ 0.5). CRV is also more sensitive than the m1 index at metal-poor conditions ([M] ≲ -2.0). The CRV index has the following advantages: (1) the passbands of CRV are dominated by Fe lines, which reduce the uncertainty that may be introduced by the presence of lines of α-process elements with enhanced abundances at metal-poor conditions; (2) the effect of interstellar reddening is limited because the two passbands are separated in wavelength by only 100 Å. We also find that the atmospheric models produce results that agree qualitatively with the trends of observed indices on stellar parameters such as effective temperature, metallicity, and surface gravity. Title: An Interpretation of Cycle Periods of Stellar Chromospheric Activity Authors: Soon, W. H.; Baliunas, S. L.; Zhang, Q. Bibcode: 1993ApJ...414L..33S Altcode: We propose (P(cyc)/P(rot))-squared, the square of the ratio of the characteristic oscillatory timescales of stellar chromospheric activity to the rotation period, as a useful parameterization of the stellar activity cycle and as the observational equivalent of the theoretical dynamo number, N(D). (P(cyc)/P(rot))-squared can be obtained observationally from 25-yr activity records of stellar Ca II H and K chromospheric emission fluxes of the Mount Wilson Observatory HK Project. Using that parameterization, we study the relationships between the period of the activity cycle and mass or age (estimated from the average level of chromospheric emission and its calibration with age). The quantity (P(cyc)/P(rot))-squared increases as B-V decreases, in qualitative agreement with the expectation that as the fractional depth of convective zone decreases (i.e., toward higher mass stars), N(D) increases (i.e., the variability of stellar activity tends to be more irregular). (P(cyc)/P(rot))-squared seems independent on age for young stars but has a well-defined dependence on age for the older stars. The difference in the behavior of (P(cyc)/P(rot))-squared with age is another aspect of chromospheric activity that changes as a star ages; the time of the transition depends on mass but occurs roughly near stellar age of about 1-3 billion yr. Title: Results of adaptive optics at Mt. Wilson Obseratory Authors: Shelton, J. Christopher; Baliunas, Sallie L. Bibcode: 1993SPIE.1920..371S Altcode: We have mounted an early adaptive optics system, the Atmospheric Compensation Experiment (ACE), on the 60-inch telescope at Mount Wilson Observatory in California in a program designed to investigate the performance of ACE at an astronomical site and to evaluate the usefulness of adaptive optics for astronomy. Despite its development as a non-astronomical instrument, ACE has produced positive results, including the obtaining of images of single and double stars with a resolution (full-width half-maximum) of 117 milliarcseconds at 700 nm. Improvement of image quality is obtained for guide objects with a B magnitude brighter than 5.9. To deepen this limiting magnitude, we have embarked on a low-noise high-speed CCD fabrication project jointly with JPL. First devices have been fabricated. We have applied post- processing techniques borrowed from speckle methodology to the adaptive optics images, and find that the pre- and post-processing techniques complement each other powerfully. We conclude that an adaptive optics system designed specifically for visible-wavelength astronomy would be a low-order system with good site thermal control, combined with post-processing. Such a system could be effective, robust and relatively low cost. Title: Correlated Optical/UV Variations of α Her and α Sco Authors: Taylor, L. L.; Smith, M. A.; Teays, T. J.; Guinan, E. F.; Baliunas, S. L. Bibcode: 1993AAS...182.4624T Altcode: 1993BAAS...25Q1242T No abstract at ADS Title: Correlated optical/UV variations of alpha HER and alpha Sco. Authors: Taylor, L. L.; Smith, M. A.; Teays, T. J.; Guinan, E. F.; Baliunas, S. L. Bibcode: 1993BAAS...25.1242T Altcode: No abstract at ADS Title: Mount Wilson: America's Observatory Authors: Jastrow, Robert; Baliunas, Sallie Bibcode: 1993S&T....85...18J Altcode: New developments at the Mount Wilson Observatory are reviewed. The renovation of the 100-inch Hooker reflector is described, and projects involving interferometry and adaptive optics are examined. Major new programs in support of science education and amateur astronomy are discussed. Title: CAII H and K Variations of a Sample of Hybrid Stars - do Hybrids Pulsate Authors: Rao, L. M.; Baliunas, S. L.; Robinson, C. R.; Frazer, J.; Woodard, L.; Donahue, R. A. Bibcode: 1993ASPC...45..300R Altcode: 1993lhls.work..300R No abstract at ADS Title: Longterm Photometric Monitoring of the Yellow Supergiant 89-HERCULIS Authors: Donahue, R. A.; Rao, L. M.; Baliunas, S. L.; Dupree, A. K. Bibcode: 1993ASPC...45..285D Altcode: 1993lhls.work..285D No abstract at ADS Title: X-ray/Optical Survey of Late-Type Stars Authors: Piters, A. J. M.; Schmitt, J. H. M. M.; Schrijver, C. J.; Baliunas, S.; Zwaan, C.; van Paradijs, J. Bibcode: 1993ASSL..183..377P Altcode: 1993pssc.symp..377P No abstract at ADS Title: The Activity Cycle of sigma Draconis Authors: Gray, David F.; Baliunas, Sallie L.; Lockwood, G. W.; Skiff, Brian A. Bibcode: 1992ApJ...400..681G Altcode: Investigations of the temperature and granulation of Sigma Draconis (HR 7462, HD 185144, K0 V) are discussed. Temperature is monitored using a line-depth ratio, and temperature variations of about 5 K are seen. Intermediate-band photometry and Ca II H and K-line emission mimic the temperature changes: a monotonic decline from the 1984 season, a smooth minimum around 1988, followed by a rise back to the 1984 values at the current time. The temperature variations are physically compatible with the photometric ones, implying a constant radius over the activity cycle. Granulation is invariant during this portion of the activity cycle, at least to the level of about +/- 3 m/s, or about +/- 5 percent. The temperature variations by themselves can also be interpreted as rotational modulation with a 20.3-d period, but no evidence of this period is seen in the photometry, the H and K emission, or the line asymmetries, and it is argued to be a chance occurrence. Title: Activity cycles in dwarfs: σ Draconis. Authors: Gray, D. F.; Baliunas, S. L.; Lockwood, G. W.; Skiff, B. A. Bibcode: 1992JRASC..86..277G Altcode: No abstract at ADS Title: Long-term solar brightness changes estimated from a survey of Sun-like stars Authors: Lockwood, G. W.; Skiff, Brian A.; Baliunas, Sallie L.; Radick, Richard R. Bibcode: 1992Natur.360..653L Altcode: THE brightness of the Sun varies during the 11-year solar cycle, typically by less than 0.1% (refs 1, 2), and a larger brightness variation is thought to have occurred during the Maunder minimum, from AD 1645 to 1715 (refs 3-5). But because individual solar cycles are different in form, amplitude and length, and because accurate solar data have been available only for the most recent two or three cycles, there is no direct way of understanding long-term solar variability. Here we present a compilation of eight years of observations of 33 Sun-like stars and report year-to-year brightness changes that substantially exceed the analogous solar fluctuations. We have also measured chromospheric magnetic activity in these stars and find that it correlates with the brightness variations. During 1980-88, solar chromospheric variability was comparable to that observed in the stellar survey, but solar brightness variations were only one-quarter as large. This suggests that the Sun is in an unusually steady phase compared to similar stars, which means that reconstructing the past historical brightness record, for example from sunspot records, may be more risky than has been generally thought. Title: Periodogram Analysis of 240 Years of Sunspot Records Authors: Donahue, Robert A.; Baliunas, Sallie L. Bibcode: 1992SoPh..141..181D Altcode: We have analyzed the direct records of sunspot number between 1749 and 1990 with the same technique currently used in the study of stellar activity cycles observed with Mount Wilson Observatory's 60-inch telescope. In order to mimic the stellar time series, which span only two decades, we analyzed twenty- and fifty-year intervals of the sunspot data in comparison to the entire record. We also examined the reliability of the oldest (pre-1850) sunspot records. The mean solar cycle period determined from the entire record (1749-1990) is 11.04 yr with a computed precision of ± 0.01 yr, but an overall accuracy of only ±1.1 yr. The large uncertainty is caused by variation of the cycle period with time and not observational uncertainty. Title: Evidence of Differential Surface Rotation in the Solar-Type Star HD 114710 Authors: Donahue, Robert A.; Baliunas, Sallie L. Bibcode: 1992ApJ...393L..63D Altcode: Observations of the chromospheric Ca II H and K emission variability of the intermediate-age solar-type star HD 114710 obtained at Mount Wilson Observatory over the past 10 years reveal a secular change in the seasonal rotation period that can be interpreted as surface differential rotation. The dependence of rotation period on chromospheric flux (i.e., activity-cycle phase) suggests that the star may have two latitudinal zones of activity: one in which changes in rotation period appear to follow the starspot activity cycle, and another confined to a narrow range of periods that does not. The pattern of rotation that depends on stellar cycle phase is opposite that of the sun: the rotation period increased as activity declined during the last activity cycle. Active region growth and decay is ruled out as the explanation for the systematic change of the seasonal rotation periods. Title: The Magnetic Cycle of Kappa Ceti Authors: Saar, S. H.; Baliunas, S. L. Bibcode: 1992ASPC...27..197S Altcode: 1992socy.work..197S Observations of chromospheric Mg II and Ca II fluxes and photospheric magnetic flux (spanning 10, 22, and 6 years, respectively) of the active G5 dwarf, Kappa Ceti, show long-term variations analogous to the solar cycle. Ca II emission varies with a period of P_cyc = 5.6 yr, and we detect a decrease in magnetic flux (~ fB) during the declining phase of a recent cycle (1984-1988) of the form: Delta F_HK ~ (fB)^{0.4 +/- 0.2}. This is the first direct evidence for a magnetic cycle on a star other than the Sun. Title: The Maunder-Minimum Phase of Old K-Dwarf Stars in the Ultraviolet Authors: Baliunas, Sallie L. Bibcode: 1992iue..prop.4208B Altcode: We propose observations and analysis of chromospheric and transition-region fluxes of C II, C IV, Mg II and Ca II of a small sample of old, K-dwarf stars, According to 25 years of Ca II H and K magnetic activity records from Mount Wilson Observatory, three of the five target stars currently show periodic magnetic activity on timescales of a decade, similar to the sun's 11-year cycle. Another star has been in a Maunder-minimum state (e.g., low and flat magnetic activity) since roughly 1981; the remaining star had been in the minimum state since at least 1966, but in 1989, the star began a slow increase in activity. The ultraviolet spectra of the K-dwarf stars will be compared to similar IUE observations of solar-type stars made in 1991. We intend to model and compare the cyclic and Maunder-minimum states of magnetic activity of the sun, solar-type stars and the old, K-dwaxf stars. Title: Recent Advances in Stellar Cycle Research Authors: Saar, S. H.; Baliunas, S. L. Bibcode: 1992ASPC...27..150S Altcode: 1992socy.work..150S We review recent work on stellar cycles, focusing on a preliminary analysis of the first 25 years of data from the Mount Wilson Ca II program. Cyclic variations are generally solar-like (rapid increase, slow decline), but some stars show multiple cycle periods. About 10-15% of the stars may be in the stellar equivalent of "Maunder minima": epochs when cycles, but not all magnetic activity, temporarily cease. Well-determined cycle periods show no clear dependence on single stellar parameters, but do show correlations with more complex formulations (e.g., alpha-Omega dynamo number) when normalized to the magnetic diffusion timescale. The relation between this normalized cycle frequency (Omega*_cyc) and dynamo number appears to change with activity or age. Cycle amplitudes also correlate with Omega*_cyc, and tend to increase with convection zone depth and P_rot. Giants in young clusters also exhibit many of these phenomena, suggesting similar, dynamo-related origins. Stellar differential rotation can differ markedly from the Sun in both amplitude and form. Photometric variability increases rapidly with increasing Ca II emission, first reversing, and eventually eliminating the correlation between brightness and activity. Dynamos of active stars thus appear to produce a larger spot-to-plage ratio than inactive stars; more high-latitude spots are also seen. Surface convective properties may also change during the cycle. Title: Unfolding Mysteries of Stellar Cycles Authors: Baliunas, S.; Saar, S. Bibcode: 1992Ast....20...42B Altcode: No abstract at ADS Title: Vulcan's Sun Authors: Baliunas, S.; Donahue, R.; Nassiopoulos, G.; Roddenberry, G. Bibcode: 1991S&T....82R...5B Altcode: No abstract at ADS Title: CA II H and K Measurements Made at Mount Wilson Observatory, 1966--1983 Authors: Duncan, Douglas K.; Vaughan, Arthur H.; Wilson, Olin C.; Preston, George W.; Frazer, James; Lanning, Howard; Misch, Anthony; Mueller, Jean; Soyumer, David; Woodard, L.; Baliunas, Sallie L.; Noyes, Robert W.; Hartmann, Lee W.; Porter, Alain; Zwaan, Cornelis; Middelkoop, Frans; Rutten, Rene G. M.; Mihalas, Dimitri Bibcode: 1991ApJS...76..383D Altcode: Summaries are presented of the photoelectric measurements of stellar Ca II H and K line intensity made at Mount Wilson Observatory during the years 1966-1983. These results are derived from 65,263 individual observations of 1296 stars. For each star, for each observing season, the maximum, minimum, mean, and variation of the instrumental H and K index 'S' are given, as well as a measurement of the accuracy of observation. A total of 3110 seasonal summaries are reported. Factors which affect the ability to detect stellar activity variations and accurately measure their amplitudes, such as the accuracy of the H and K measurements and scattered light contamination, are discussed. Relations are given which facilitate intercomparison of 'S' values with residual intensities derived from ordinary spectrophotometry, and for converting measurements to absolute fluxes. Title: A Comparision of the Photometric and Chromospheric Variability of 33 Lower Main-Sequence Stars During the Years 1984-1989 Authors: Radick, R. R.; Lockwood, G. W.; Baliunas, S. L. Bibcode: 1991BAAS...23..876R Altcode: No abstract at ADS Title: The Maunder-Minimum Phase of Solar-Type Stars in the Ultraviolet Authors: Baliunas, Sallie L. Bibcode: 1991iue..prop.3938B Altcode: We propose observations and analysis of Mg II h and k line profiles and fluxes as well as the chromospheric and transition-region fluxes of C II and C IV in a small sample of solar-type stars. The surface magnetic activity (Ca II H and K relative fluxes) of the selected solar-type stars has been monitored for over two decades at Mount Wilson Observatory. Analysis of the Ca II magnetic activity records suggests that solar-type stars spend most of their time in a cyclic state, with periodicities roughly on the order of a decade. However, solar-type stars apparently spend some time in a prolonged lull in magnetic activity, denoted by low and nearly constant values of magnetic activity and assumed to be similar to the Sun's Maunder Minimum. We intend to compare the ultraviolet chromospheric and transition-region properties of the cyclic magnetic state to the Maunderminimum state of the solar-type stars, and compare them both to the known range of the Sun's variability. From the ultraviolet data we will construct model atmospheres and chromospheres of the solar-type stars and compare them to models of the Sun. Title: What can other stars tell us about the Sun? Authors: Noyes, Robert W.; Baliunas, S. L.; Guinan, E. F. Bibcode: 1991sia..book.1161N Altcode: The authors focus on those aspects of the solar-stellar connection where observations of other stars give information about the Sun which could not be obtained from study of the Sun alone. Solar-like phenomena on other stars with a range of values for key parameters (e.g., rotation) yield the dependence on those parameters and hence better physical insight into the governing mechanisms. A key presumption is that the Sun is a normal star, so that the same mechanisms govern its behavior. Also if the Sun is normal, then study of stars with similar masses but different ages gives information on the evolution of solar properties, such as structure, internal dynamics, activity, etc. First, the authors discuss stellar observations which yield information on the internal structure of solar-like stars, including central density, and helium abundance. Such results support the standard value for the solar helium abundance, as well as standard stellar structure theory. The authors note how stellar seismology can, in principle, determine the stellar radius, as well as the degree of mixing in stellar cores, as a function of age. Next, the authors discuss information on the internal dynamics of the Sun, and its evolution, as inferred from the study of the time history of surface rotation in solar-type stars. They use the rotation-activity-age connection to infer how the Sun's rotation and activity level has changed with age. The authors discuss what the dependence of activity on mass and rotation can tell us about the nature and location of the solar dynamo. Finally, they discuss the solar activity cycle and its likely change over the lifetime of the Sun, inferred from observation of other stars. Title: The Past, Present and Future History of Solar Magnetism: Stellar Magnetic Activity Authors: Baliunas, Sallie Bibcode: 1991suti.conf..809B Altcode: Many stars show magnetic activity, and of those that do, the majority appear to show variability that is cyclic, on time scales ranging roughly from as short as 2 yr to as long as several tens of yr. Studies of magnetic activity of other stars may yield understanding of the complex physics underlying solar magnetism. In this regard, two broad classes of observations of magnetic activity are useful: (1) studies of the dependence of the mean level of magnetic activity on stellar properties such as mass, age and rotation; and (2) studies of the variability with time of magnetic activity of individual stars. Results from the first class of studies are briefly described as the underpinning for discussion of the time variability of stellar magnetism. Solar-type stars display activity in one of two states: approximately two-thirds of the solar-type stars show magnetic variability that is cyclic, analogous to the 11-yr sunspot cycle. About one-third of the solar-type stars have lower mean levels of magnetic activity and little or no variability. Such prolonged states of low and constant magnetic activity may be similar to the sun during the Maunder minimum. These tentative results suggest that solar-type stars undergo significant changes in magnetic activity on time scales of centuries. If correlated with magnetic variations, accompanying brightness changes for solar-type stars could be larger during entry to and exit from the Maunder minimum state than irradiance changes observed for the sun during the 11-yr cycle. Title: Evidence for long-term brightness changes of solar-type stars Authors: Baliunas, Sallie; Jastrow, Robert Bibcode: 1990Natur.348..520B Altcode: CHANGES in the brightness of the Sun may introduce further uncertainties into forecasts of global warming by the greenhouse effect. The Sun is known to vary in brightness, on a timescale of years, by 0.1% in phase with changes in magnetic activity during the solar cycle1-3, and variations of up to 0.4%, also correlated with surface magnetic activity, have been found in stars similar to the Sun4. To delimit the magnitude of solar luminosity variations on a timescale of centuries, we have looked at the magnetic behaviour of a number of solar-type stars over several years. Observed in random phases of their long-term variability, they give a sample of the behaviour of a solar-type star over a long period of time. We find indirect evidence that these stars undergo brightness changes of more than the 0.1% observed during the last solar cycle, a result that calls into question the assumption of a constant Sun in calculations using general circulation models for climate forecasting. Title: A Period Analysis of the Semi-Regular Variable SW Vir Authors: Armour, J. E.; Henry, G. W.; Baliunas, S. L. Bibcode: 1990IBVS.3521....1A Altcode: No abstract at ADS Title: 89 Her: The Atmosphere of a Strange Yellow Supergiant Authors: Dupree, A. K.; Baliunas, S. L.; Zucker, D.; Bond, H. E.; Meakes, M. Bibcode: 1990BAAS...22.1200D Altcode: No abstract at ADS Title: Long-Term Variation of Magnetic and Chromospheric Flux on κ Ceti Authors: Saar, S. H.; Baliunas, S. L. Bibcode: 1990BAAS...22.1200S Altcode: No abstract at ADS Title: Magnetic Activity Cycles of the Hyades and Praesepe Giant Stars Authors: Baliunas, S. L.; Rao, L.; Frazer, J.; Robinson, C.; Woodard, L. Bibcode: 1990BAAS...22.1199B Altcode: No abstract at ADS Title: Studies of solar type stars. Authors: Baliunas, Sallie; Jastrow, Robert Bibcode: 1990NASCP3086....7B Altcode: 1990cisv.nasa....7B Satellite observations show a change of 0.1 percent in solar irradiance over the past decade. The question arises as to whether larger changes in irradiance may occur over century time scales. Researchers approached this question by looking at changes in surface magnetism, since the satellite observations also show that irradiance and surface magnetism are correlated. To obtain information on possible variations in surface magnetism over century-long intervals, researchers looked at records of surface magnetism spanning up to 20 years for a sample of 74 stars of solar type, i.e., of similar age and mass to the sun. The histories of these stars, observed in random phases of their long-term variability, give a snapshot at any one time of the behavior of a solar-type star over long periods of time. Evidence on Maunder Minimum phases and levels of magnetic activity in these solar-type stars are compared with information on solar magnetism. Implications for solar irradiance changes are discussed. Title: Trends in solar variability. Authors: Jastrow, Robert; Baliunas, Sallie Bibcode: 1990NASCP3086..115J Altcode: 1990cisv.nasa..115J Radiocarbon (delta C-14) records suggest a 200-year periodicity in solar activity in the last millennium. Researchers examined the Carbon-14 record going back 8 millennia for this and other periodicities. The computation differs from that in most previous work in its use of techniques developed for unevenly spaced sampling without rebinning the data to equally spaced intervals. A variation with a 200-year period is a strong feature of the Carbon-14 record going back several millennia. Periodicities that appear to be significant are listed and their physical interpretation discussed. Title: Automated Precision Differential Photometry Authors: Young, A. T.; Boyd, L. J.; Genet, R. M.; Epand, D. H.; Lockwood, G. W.; Baliunas, S. L.; Pyper Smith, D.; Donahue, R. Bibcode: 1990IAPPP..39....5Y Altcode: No abstract at ADS Title: Stellar Activity and Brightness Variations: A Glimpse at the Sun's History Authors: Radick, Richard R.; Lockwood, G. W.; Baliunas, Sallie L. Bibcode: 1990Sci...247...39R Altcode: Radiometric measurements during the past decade from the Solar Maximum Mission and Nimbus 7 satellites have shown that the total solar irradiance varies in step with the sun's 11-year magnetic activity cycle. Stellar observations from the Lowell and Mount Wilson observatories now confirm and elaborate this discovery. These measurements show that older stars similar to the sun tend to become brighter as their magnetic activity level increases, just as the sun does during its 11-year activity cycle. Younger stars, however, tend to become fainter as their magnetic activity level increases. This contrasting behavior suggests that the balance between the competing phenomena that influence solar brightness variability has shifted during the sun's lifetime. Title: Alpha Ori: evidence for pulsation. Authors: Dupree, A. K.; Baliunas, S. L.; Guinan, E. F.; Hartmann, L.; Sonneborn, G. Bibcode: 1990ASPC...11..468D Altcode: 1990cbsp.proc..468D The bright cool supergiant α Ori (Betelgeuse, M2 Iab) shows a periodic modulation of the ultraviolet continuum and Mg II emission line fluxes of about 420 days that has lasted over 6.5 years of observation: 1984.0-1990.5. This modulation is identified with pulsation in the supergiant's atmosphere. The authors' monitoring program has also demonstrated that the longer 5.8 year period of variability identified in the 1930's has disappeared. A longer variation of ≡11 years is evident, and noted here for the first time. Its origin is obscure. Title: Global Warming Report Authors: Lindzen, Richard S.; Nierenberg, William A.; Jastrow, Robert; Baliunas, Sallie; Stuiver, Minze; Roberts, Leslie Bibcode: 1990Sci...247...14L Altcode: No abstract at ADS Title: 1889 - the Beginnings of Astronomy at Mount-Wilson Authors: Woodard, L. A.; Baliunas, S. L. Bibcode: 1989PASP..101..889W Altcode: No abstract at ADS Title: Ca II H and K Flux Monitoring in Cool Stars: Rotation and Activity Cycles Authors: Robinson, C. R.; Baliunas, S. L.; Bennett, W.; Briggs, J.; Frazer, J.; Noyes, R. W.; Shelton, C.; Woodard, L.; Vaughan, A. H.; Wilson, O. C. Bibcode: 1989BAAS...21.1115R Altcode: No abstract at ADS Title: Long-term Changes in Surface Activity of Solar-Type Stars Authors: Baliunas, S.; Jastrow, R. Bibcode: 1989BAAS...21R1115B Altcode: No abstract at ADS Title: Call for Participation in A Global Network of Automatic Telescopes Authors: Baliunas, S. L. Bibcode: 1989IAPPP..35...12B Altcode: No abstract at ADS Title: Automatic Photoelectric Telescope Service: Third Annual Summer Workshop Authors: Baliunas, S. L.; Pyper Smith, D.; Genet, R. M. Bibcode: 1988IAPPP..34...37B Altcode: No abstract at ADS Title: Methods of period analysis in the study of variable stars with applications to AF Cygni. Authors: Robinson, C. R.; Baliunas, S. L.; Mattei, J. A. Bibcode: 1988JAVSO..17Q.147R Altcode: No abstract at ADS Title: Long-Term Variations in the Light Curve of Beta Lyrae Authors: Guinan, E. F.; McCook, G. P.; Bergin, E. A.; Robinson, C. R.; Baliunas, S. L.; Theokas, A. C. Bibcode: 1988BAAS...20..954G Altcode: No abstract at ADS Title: Starspots Cycles and Paleoclimatology Authors: Baliunas, S. L. Bibcode: 1988BAAS...20.1030B Altcode: No abstract at ADS Title: The Mount Wilson Observatory HK Project: The Continuing Analysis of Rotation and Stellar Magnetic Cycles Authors: Baliunas, S. L.; Bennett, W.; Briggs, J.; Frazer, J.; Noyes, R. W.; Robinson, C. R.; Shelton, C.; Woodard, L.; Vaughan, A. H.; Wilson, O. C. Bibcode: 1988BAAS...20Q.994B Altcode: No abstract at ADS Title: On the Relation Between Stellar Luminosity Variations and Chromospheric Activity Authors: Radick, R. R.; Lockwood, G. W.; Skiff, B. A.; Baliunas, S. L. Bibcode: 1988BAAS...20..995R Altcode: No abstract at ADS Title: An Analysis of Photometric and Spectroscopic Observations of the Enigmatic Eclipsing Binary Beta Lyrae Authors: Robinson, C. R.; Baliunas, S. L.; Bopp, B. W.; Dempsey, R. C. Bibcode: 1988BAAS...20..954R Altcode: No abstract at ADS Title: Periodic modulation of the atmosphere of alpha Orionis. Authors: Dupree, A. K.; Baliunas, S. L.; Guinan, E. F.; Hartmann, L.; Nassiopoulos, G. E.; Sonneborn, G. Bibcode: 1988ESASP.281a.365D Altcode: 1988IUE88...1..365D; 1988uvai....1..365D Alpha Orionis (Betelgeuse; M2 Iab) was monitored with IUE since 1984. Discovery of a 420-day periodic modulation of the flux in the optical and ultraviolet continua, and in the Mg II h and k line emission cores suggests that periodic photospheric pulsations were present from 1984 to 1986. This behavior continues through 1987. However, the general flux level of the ultraviolet continuum and the Mg II lines is decreasing, and the amplitude of the variation may be reduced. These decreases may be the emerging signature of an additional longer period. The density sensitive C II diagnostic, 2325.4/2328.1, indicates the chromospheric densities range between log Ne (cm-3) = 8.7 and 9.5, but periodicities are not evident. Title: Photometric Variations of Bright Stars Observed with the SAO 0.25m APT Authors: Robinson, C. R.; Baliunas, S. L.; Boyd, L.; Genet, R.; Donahue, R. A. Bibcode: 1988BAAS...20..675R Altcode: No abstract at ADS Title: Stellar Activity Cycles and Rotation in Cool Stars Observed from Mt. Wilson Observatory Authors: Baliunas, S. L.; Briggs, J.; Frazer, J.; Noyes, R. W.; Robinson, C. R.; Carroll, S.; Donahue, R. A.; Shelton, C.; Woodard, L.; Vaughan, A. H.; Wilson, O. C. Bibcode: 1988BAAS...20Q.697B Altcode: 1988BAAS...20Z.697B No abstract at ADS Title: APT Monitoring of Luminous Cool Stars Authors: Dupree, A. K.; Baliunas, S. L.; Robinson, C. R. Donahue, R. A. Bibcode: 1988BAAS...20..674D Altcode: No abstract at ADS Title: Activity Cycles in Cool Dwarfs Authors: Baliunas, Sallie L. Bibcode: 1988iue..prop.3059B Altcode: Our project encompasses both archival and new IUE measurements. Approximately 100 cool dwarf stars have been monitored at Mt. Wilson over the past 20 years for long-term chromospheric Ca II variations. Many of these stars also have archival IUE Mg II observations spanning the last decade, which we will use to study long-term variations ("starspot activity cycles" akin to the 11-year sunspot cycle). We plan to augment the archival Mg II spectra with new data of several stars at critical phases of their long-term chromospheric activity curves. We wish to investigate activity cycle variations in chromospheric radiative losses (using Mg II and Ca II), magnetic flux (from high-resolution optical spectra) and spot coverage (from broadband photometry). Our goal is to study the magnetic dynamodriven cycles as a function of stellar parameters (e.g., mass and age). The activity cycles are welldefined by the Mt. Wilson Ca II fluxes; we propose to examine the behavior of the Mg II fluxes, at extrema in the activity curves in order to extract the chromospheric radiative losses, which are better identified at Mg II compared to Ca II due to the smaller photospheric contribution. In addition, some of the selected stars have a history of magnetic-field strength and distribution measurements, as well as photometric ("starspots") coverage. Title: Luminosity and Magnetic Activity Variations on Cool Stars Authors: Baliunas, S. Bibcode: 1988srov.proc..230B Altcode: No abstract at ADS Title: Ff Agr Authors: Baliunas, Sallie L. Bibcode: 1988iue..prop.3060B Altcode: Our long-term investigations of FF Aqr, an eclipsing binary system with G8 III and subdwarf component stars reveals that the chromospheric activity in FF Aqr is intense and extreme, primarily because the G8 III star rotates synchronously with its 9-day orbital period. Using the hot subdwarf star as a probe of the atmospheric structure of the G8 III star, we have found that the ultraviolet lineforming region of the G8 III star extends at least 1.5 stellar radii above its photosphere. We plan to diagnose the extended atmosphere with a high-resolution Mg II profile. We propose to investigate the masses and absolute dimensions of the system and its components with radial velocities derived from ultraviolet and visible spectra and thereby study the evolutionary status of this unusual system. In addition, ground-based spectroscopic and photometric observations of FF Aqr will be carried out at Oak Ridge and Villanova observatories. Title: Long-Term Variations of Stellar Magnetic Activity in Lower Main Sequence Stars Authors: Baliunas, Sallie L. Bibcode: 1988ASIC..241..319B Altcode: 1988felm.conf..319B No abstract at ADS Title: Shock Heating in V CVN Authors: Baliunas, Sallie L. Bibcode: 1988iue..prop.3062B Altcode: We propose to investigate non-radiative heating presumably caused by relatively slow-moving shock waves through the atmosphere of the bright, pulsating, semi-regular variable V CVn (M4-M6IIIe). Previous visible-light investigations show a persistent 192-day pulsation with a range in V-light of 7^m.0-9^m.5. A second, weaker pulsation often appears with a period between 170-190 days. H-alpha emission accompanies both pulsations but is strongest (3x nearby continuum) for the primary pulsation. The photospheric velocity amplitude is rather modest (4-5 km s^-1) for such bright H-alpha emission. Shock models appropriate for red, low gravity stars predict significant nonradiative losses in ultraviolet lines, for example, Mg II (2800) and Si II (1820). While Mira variables are known to show strong Mg II emission, we would like to test the shock models by obtaining the ultraviolet emissions from the less luminous semi-regular variable V CVn. Title: The Sun among the stars: what stars indicate about solar variability. Authors: Soderblom, D. R.; Baliunas, S. L. Bibcode: 1988ssgv.conf...25S Altcode: The authors briefly review the kinds of solar-like phenomena seen on other solar-type stars, including chromospheric and coronal activity, spots, and magnetic fields. The stages of evolution of a one solar mass star are described, particularly with respect to the levels of magnetic activity that characterize those phases. Finally, the authors examine evidence for long-term varability in solar-like stars. Title: The Automatic Photoelectric Telescope service. Authors: Genet, R. M.; Boyd, L. J.; Kissell, K. E.; Crawford, D. L.; Hall, D. S.; Hayes, D. S.; Baliunas, S. L. Bibcode: 1987PASP...99..660G Altcode: Automatic observatories have the potential of gathering sizable amounts of high-quality astronomical data at low cost. The Automatic Photoelectric Telescope Service (APT Service) has realized this potential and is routinely making photometric observations of a large number of variable stars. However, without observers to provide on-site monitoring, it was necessary to incorporate special quality checks into the operation of the APT Service at its multiple automatic telescope installation on Mount Hopkins. Title: Periodic Photospheric and Chromospheric Modulation in Alpha Orionis (Betelgeuse) Authors: Dupree, A. K.; Baliunas, S. L.; Guinan, E. F.; Hartmann, L.; Nassiopoulos, G. E.; Sonneborn, G. Bibcode: 1987ApJ...317L..85D Altcode: The bright cool supergiant Alpha Orionis has been monitored spectroscopically and photometrically over the past three years (1984-1986) in the optical and the ultraviolet wavelength regions. A 420-day periodic modulation of the flux is observed in the optical and ultaviolet continua, and in the Mg II line emission cores. Periodic photospheric pulsations are the most likely explanation of these observations. This identification is based on the large amplitude of the variation, the correlation of the continuum and chromospheric fluxes, and the length of the observed period. Pulsation may heat and extend the atmosphere of Alpha Ori and initiate the mass flow from the star. Title: Photometric light curves for seven rapidly-rotating K dwarfs in the Pleiades and alpha Persei clusters. Authors: Stauffer, John R.; Schild, Rudolph A.; Baliunas, Sallie L.; Africano, John L. Bibcode: 1987PASP...99..471S Altcode: Light curves and period estimates were obtained for several Pleiades and Alpha Persei cluster K dwarfs which were identified as rapid rotators in earlier spectroscopic studies. A few of the stars have previously-published light curves, making it possible to study the long-term variability of the light-curve shapes. The general cause of the photometric variability observed for these stars is an asymmetric distribution of photospheric inhomogeneities (starspots). The presence of these inhomogeneities combined with the rotation of the star lead to the light curves observed. The photometric periods derived are thus identified with the rotation period of the star, making it possible to estimate equatorial rotational velocities for these K dwarfs. These data are of particular importance because the clusters are sufficiently young that stars of this mass should have just arrived on the main sequence. These data could be used to estimate the temperatures and sizes of the spot groups necessary to produce the observed light curves for these stars. Title: The Automatic Photoelectric Telescope Service - An Update Authors: Kissell, K. E.; Genet, R. M.; Boyd, L. J.; Baliunas, S. L.; Hall, D. S. Bibcode: 1987BAAS...19..747K Altcode: No abstract at ADS Title: Objective Characterization of Stellar Activity Cycles. I. Methods and Solar Cycle Analyses Authors: Gilliland, Ronald L.; Baliunas, Sallie L. Bibcode: 1987ApJ...314..766G Altcode: A large set of high-quality chromospheric activity index data of sufficient temporal extent to allow quantitative characterization of stellar cycles now exists thanks to the work, begun two decades ago, by Olin Wilson. In this paper the authors discuss the methods which can be used in analyzing the 18 yr records of Ca II H and K index data. It is shown that derivation of accurate periods and characterization of cycle morphology (ratio of rise to decay time) is possible, but that the background noise, especially the growth and decay of activity, is an important and troublesome factor to consider. Title: Stellar Activity and the Rotation of Hyades Stars Authors: Radick, Richard R.; Baliunas, Sallie L. Bibcode: 1987LNP...291..217R Altcode: 1987csss....5..217R; 1987LNP87.291..217R No abstract at ADS Title: Automatic Photometric Monitoring of Cool Stars Authors: Genet, Russell M.; Boyd, Louis J.; Hayes, Donald S.; Baliunas, Sallie L.; Crawford, David L.; Hall, Douglas S.; Genet, David R. Bibcode: 1987LNP...291..473G Altcode: 1987csss....5..473G No abstract at ADS Title: Cool star automated photometry. Authors: Genet, R. M.; Boyd, L. J.; Baliunas, S. L.; Hall, D. S. Bibcode: 1987PASP...99R1147G Altcode: No abstract at ADS Title: Broadband photometry of bright stars: the first year of APTS at the F. L. Whipple Observatory. Authors: Baliunas, S. L.; Donahue, R. A.; Loeser, J. G.; Guinan, E. F.; Genet, R. M.; Boyd, L. J. Bibcode: 1987ngst.symp...97B Altcode: The authors present time series of broadband V, R, and I photometry. Time serial measurements of photometric variations of bright stars contain insight into the physical processes of stellar pulsation, winds, and mass loss in stars of a wide range of spectral type across the H-R diagram. Additionally, photometric variations in cool stars have signaled the presence of large starspots. Title: Automated K-line photometry of active chromosphere stars. Authors: Baliunas, S. L.; Boyd, L. J.; Genet, R. M.; Hayes, D. S. Bibcode: 1987ngst.symp...65B Altcode: The relative chromospheric emission strength in weak-emission-line solar-type stars is detectable with a 0.75-meter telescope and the K-line filter photometer described in the paper. Integration times for stars as faint as apparent magnitude V = 5.0 are short enough for about 80 stars to be observed per night. Title: Combined ultraviolet studies of astronomical sources Authors: Baliunas, S. L.; Dupree, A. K.; Elvis, M.; Huchra, J. P.; Kenyon, S.; Raymond, J. C. Bibcode: 1986sao..rept.....B Altcode: Topics addressed include: Cygnus Loop; P Cygni profiles in dwarf novae; YY Gem; nova shells; HZ Herculis; activity cycles in cluster giants; Alpha Ori; metal deficient giant stars; ultraviolet spectra of symbiotic stars detected by the Very Large Array; time variability in symbiotic stars; blue galaxies; and quasistellar objects with X-ray spectra. Title: Ultraviolet and Visible Observations of the Atmospheric Structure of the Active G8III Component of FF Aquarii Authors: Loeser, J. G.; Baliunas, S. L.; Raymond, J. C.; Guinan, E. F.; Dorren, J. D. Bibcode: 1986BAAS...18..983L Altcode: No abstract at ADS Title: Period Analysis of Sunspot Data Authors: Donahue, R. A.; Baliunas, S. L. Bibcode: 1986BAAS...18..981D Altcode: No abstract at ADS Title: Flares and active sectors on YY Geminorum. Authors: Baliunas, S. L.; Raymond, J. C.; Loeser, J. G. Bibcode: 1986ESASP.263..181B Altcode: 1986niia.conf..181B; 1986NIA86......181B With IUE ultraviolet and Hβ emission spectra obtained during one week, the authors have mapped the atmospheric activity on the component stars of YY Gem (dM1e+dM1e, P = 19h.5) as a function of orbital and rotational phases. They have observed several flares in Hβ on both component stars, as well as two flare-like brightenings in the ultraviolet. The behavior of the line ratios of the C II, C IV, and He II features is similar to that of solar surges during the ultraviolet brightenings. The spatial extent of the ultraviolet phenomena is likely small. In the ultraviolet and visible, certain phases or areas of the stars are apparently more active than others. Title: Evidence of large-scale structures in the atmosphere of the active K-dwarf component of V471 Tauri. Authors: Guinan, E. F.; Wacker, S. W.; Baliunas, S. L.; Loesser, J. G.; Raymond, J. C. Bibcode: 1986ESASP.263..197G Altcode: 1986NIA86......197G; 1986niia.conf..197G The authors have analyzed contemporaneous IUE ultraviolet spectra and visible photoelectric data of the eclipsing binary V471 Tauri (K2 V+DA) between 1979 and 1985. The combined data detail the three-dimensional structure of atmospheric loops and their associated starspots on the K dwarf. The distribution of starspot regions on the surface of the K star has been inferred from the visible photometry. When spots are located near the limb of the K dwarf prior to and shortly after the total eclipse of the white dwarf, absorption lines such as C II, C III, C IV, and Si IV appear superimposed on the continuum of the white dwarf. These absorption lines are likely caused by "cool coronal loops" overlying the spots in the atmosphere of the K dwarf. Occasionally, the loops can extend nearly one stellar radius above the surface of the K2 V star. Title: Longterm Spectroscopic Monitoring of Alpha-Orionis Authors: Sonneborn, G.; Baliunas, S. L.; Dupree, A. K.; Guinan, E. F.; Hartmann, L. Bibcode: 1986ESASP.263..221S Altcode: 1986niia.conf..221S; 1986NIA86......221S Ultraviolet spectroscopy and optical photometry of Alpha Orionis (M2 Iab) have been obtained at approximately two-week intervals from January 1984 through April 1986. The ultraviolet (2950 Å - 3050 Å) and optical continua are found to vary in phase with each other. The Mg II h and k total emission flux is similarly modulated, but lags the optical light curve by about 0.25 years. However, the h and k line fluxes vary by different amounts and in a manner which suggests a periodicity of about one year. These and other spectral variations may be causally linked to atmospheric disturbances, possibly related to a close stellar companion. Title: Short-Term Periodic Variability in Alpha Orionis Authors: Dupree, A. K.; Baliunas, S. L.; Guinan, E. F.; Hartmann, L.; Sonneborn, G. S. Bibcode: 1986BAAS...18..982D Altcode: No abstract at ADS Title: Rotation and Long-term Activity in Evolved Stars Authors: Baliunas, S. L.; Donahue, R. A.; Noyes, R. W.; Duncan, D. K.; Frazer, J.; Misch, A.; Mueller, J.; Woodard, L.; Vaughan, A. H. Bibcode: 1986BAAS...18Q.983B Altcode: No abstract at ADS Title: The surface and atmospheric structure of the active G8III star FF Aquarii. Authors: Baliunas, S. L.; Loesser, J. G.; Raymond, J. C.; Guinan, E. F.; Dorren, J. D. Bibcode: 1986ESASP.263..185B Altcode: 1986niia.conf..185B; 1986NIA86......185B IUE ultraviolet investigations of the eclipsing binary FF Aquarii (G8 III+sdOB, P = 9d.2) reveal intense and extreme chromospheric activity in the cool star. The giant star's ultraviolet spectrum can be observed during total eclipse of the subdwarf. IUE spectra obtained during ingress and egress of the total eclipse show that some absorption lines in the subdwarf spectrum, for example, C II and C IV are doubled in strength relative to quadrature. This excess absorption is likely caused by a geometrically extended atmosphere of the G8 III star and the enhancements are present at least to 1.5 stellar radii above the surface of the G8 III star. Since the enhancements have persisted for three years, they cannot be transient phenomena. Title: A Prescription for Period Analysis of Unevenly Sampled Time Series Authors: Horne, J. H.; Baliunas, S. L. Bibcode: 1986ApJ...302..757H Altcode: A technique is presented for detecting the presence and significance of a period in unequally sampled time series data. The calculation of the modified periodogram for unevenly sampled data is reviewed. The proper definition of the variance that is used to normalize the power of the modified periodogram is clarified. It is proven that the probability that a peak in the periodogram is noise or signal can be easily assessed by the method given here only when the total variance of the data is used to normalize the periodogram power. The crucial choice of independent frequencies in calculating both the periodogram and the false alarm probability from unevenly sampled data is discussed. An empirical formula for estimating the number of independent frequencies is derived. In addition, the formula for the uncertainty of a frequency identified in the periodogram is reviewed. A method for detecting the presence of an alias frequency caused by the interaction of the window and signal is prescribed. With some examples of periodic signals, the minimum number of points required to measure reliably a signal are shown. The signal-to-noise ratio and the number of points required to extract signals when one or two periodicities are present in the time series are investigated. Title: The Beginnings of the Automatic Photoelectric Telescope Service Authors: Boyd, Louis J.; Genet, Russell M.; Baliunas, Sallie L. Bibcode: 1986IAPPP..25...15B Altcode: No abstract at ADS Title: Recent Spectroscopic Observations of Alpha Orionis Authors: Dupree, A. K.; Baliunas, S. -L.; Guinan, E. F.; Hartmann, L.; Sonneborn, G. S. Bibcode: 1986LNP...254..411D Altcode: 1986csss....4..411D No abstract at ADS Title: Light, Velocity, and H-α Variations in the Pulsating Red Giant V CVn Authors: Loeser, J. G.; Baliunas, S. L.; Guinann, E. F.; Mattei, J. A.; Wackern, S. Bibcode: 1986LNP...254..460L Altcode: 1986csss....4..460L No abstract at ADS Title: A Flare Event on the Quiet dM Star HD 95735 Authors: Donahue, R. A.; Baliunas, S. L.; Frazer, J.; French, H.; Lanning, H. Bibcode: 1986LNP...254..281D Altcode: 1986csss....4..281D No abstract at ADS Title: The Beginnings of the Automatic Photoelectric Telescope Service Authors: Boyd, Louis J.; Genet, Russell M.; Baliunas, Sallie L. Bibcode: 1986apt..conf...15B Altcode: No abstract at ADS Title: Stellar activity cycles Authors: Baliunas, Sallie L. Bibcode: 1986LNP...254....1B Altcode: No abstract at ADS Title: Stellar activity cycles in lower main sequence stars. Authors: Baliunas, S. L. Bibcode: 1986AdSpR...6h.231B Altcode: 1986AdSpR...6R.231B No abstract at ADS Title: Two-Dimensional Mapping of the Activity in FF Aquari Authors: Baliunas, Sallie Bibcode: 1986iue..prop.2412B Altcode: Our long-term investigations of FF Aqr, an eclipsing binary system with G8 III and subdwarf component stars reveals that the chromospheric activity in FF Aqr is intense and extreme, primarily because the G8 III star rotates synchronously with its 9-day orbital period. Using the hot subdwarf star as a probe of the atmospheric structure of the G8 III star, we have found that the ultraviolet line-forming region of the GS III star extends at least 1.5 stellar radii above its photosphere. We propose to time the disappearance of the G8 III star's influence on the subdwarf spectrum and thereby measure the geometric extent of the ultraviolet structure through the G8 III star's atmosphere. We plan to diagnose the physical structure of the extended atmosphere with line strengths and ratios. Finally, we plan to investigate the nature of the H-alpha emission enhancement as a function of orbital phase. The subdwarf apparently causes H-alpha emission to reach maximum strength near secondary eclipse, probably by the irradiation of the facing hemisphere of the cool star by the hotter component. In addition, ground-based spectroscopic and photometric observations of FF Aqr will be carried out at Oak Ridge and Villanova observatories. Title: Stellar Activity Cycles Authors: Baliunas, S. L. Bibcode: 1986LNP...254....3B Altcode: 1986csss....4....3B No abstract at ADS Title: Automatic Photoelectric Telescope III The Mount Hopkins Site Authors: Baliunas, S. L.; Boyd, L. J.; Genet, R. M.; Hall, D. S.; Criswell, S. Bibcode: 1985IAPPP..22...47B Altcode: No abstract at ADS Title: Design of a Dedicated 1-Meter System for Automatic Ca II K-Line Photometry of Evolved Stars Authors: Baliunas, S. L.; Boyd, L. J.; Genet, R. M.; Guinan, E. F. Bibcode: 1985IAPPP..22...32B Altcode: No abstract at ADS Title: Book-Review - Activity in Red Dwarf Stars Authors: Baliunas, S. L. Bibcode: 1985JRASC..79..327B Altcode: 1985JRASC..79..320B No abstract at ADS Title: Post-Main Sequence Evolution of Rotation and Chromospheric Activity Authors: Baliunas, S. L.; Donahue, R. L.; Horne, J. H.; Duncan, D. K.; Frazer, J.; Lanning, H.; Misch, A.; Mueller, J.; Vaughan, A. H.; Woodward, L. Bibcode: 1985BAAS...17Q.877B Altcode: 1985BAAS...17..877B No abstract at ADS Title: Book-Review - Cool Stars Stellar Systems and the Sun Authors: Baliunas, S. L.; Hartmann, L. Bibcode: 1985S&T....70Q.231B Altcode: No abstract at ADS Title: Combined ultraviolet studies of astronomical source Authors: Dupree, A. K.; Baliunas, S. L.; Blair, W. P.; Hartmann, L. W.; Huchra, J. P.; Raymond, J. C.; Smith, G. H.; Soderblom, D. R. Bibcode: 1985sao..reptR....D Altcode: As part of its Ultraviolet Studies of Astronomical Sources the Smithsonian Astrophysical Observatory for the period 1 Feb. 1985 to 31 July 1985 observed the following: the Cygnus Loop; oxygen-rich supernova remnants in 1E0102-72; the Large Magellanic Cloud supernova remnants; P Cygni profiles in dwarf novae; soft X-ray photoionization of interstellar gas; spectral variations in AM Her stars; the mass of Feige 24; atmospheric inhomogeneities in Lambda Andromedae and FF Aquarii; photometric and spectroscopic observation of Capella; Alpha Orionis; metal deficient giant stars; M 67 giants; high-velocity winds from giant stars; accretion disk parameters in cataclysmic variables; chromospheric emission of late-type dwarfs in visual binaries; chromospheres and transient regions of stars in the Ursa Major group; and low-metallicity blue galaxies. Title: Time-series measurements of chromospheric CA II H and K emission in cool stars and the search for differential rotation. Authors: Baliunas, S. L.; Horne, J. H.; Porter, A.; Duncan, D. K.; Frazer, J.; Lanning, H.; Misch, A.; Mueller, J.; Noyes, R. W.; Soyumer, D.; Vaughan, A. H.; Woodard, L. Bibcode: 1985ApJ...294..310B Altcode: The relative strength of the chromospheric Ca II H and K emission cores has been monitored on a near- nightly basis during several seasons in a variety of cool stars, predominantly those lower-main-sequence stars observed by Wilson for long-term chromospheric activity fluctuations. From initial data obtained in 1980, rotation rates had been inferred from the period of modulation of chromospheric flux. We have analyzed the rotation periods determined from three seasons of Ca II H and K emission strengths in these stars. In 12 stars we find evidence for varying periodicities in different seasons or for multiple periodicities in one season, or both. For about 10 stars, significant peaks in the power spectrum are found at two different frequencies in at least one season. Detailed analysis of the chromospheric emission with time reveals two possibilities consistent with the appearance of dual periodicities in the observed time series: two distinct periods arising from active areas rotating differentially with respect to each other because they are at different latitudes, or the growth and decay of active areas with subsequent birth of active areas occurring at a stellar longitude different from the original site of the activity. Generally, the data from only one season cannot discriminate between these two explanations of dual peaks in the power spectra. In four stars, however, differential surface rotation is a more likely explanation for the observed chromospheric fluctuations with time during the first three seasons. The fractional differential surface rotation would be at least 5% in HD 206860, 10% in HD 101501, 11% in HD 190406 and 21% in HD 114710. The analysis of the data for the GO V star HD 206860, with a relatively rapid rotation period of about 5 days, indicates an active area persisting for three years. Title: The old galactic cluster NGC 188 and the origin of the W Ursae Majoris-type contact binaries. Authors: Baliunas, S. L.; Guinan, E. F. Bibcode: 1985ApJ...294..207B Altcode: Spectroscopic observations of the four faint, short-period light variables EP Cep, EQ Cep, ER Cep, and ES Cep confirm that they are W UMa-type, or contact, binaries. The binaries EP Cep and ES Cep are members of the old open cluster NGC 188 (age about 5-10 x 10 to the 9th yr) by a radial-velocity criterion; all four are associated with the cluster by their position in space and in its color-magnitude diagram. Combined with the light curves of the variables, the inferred component radial velocities reveal spectroscopic mass ratios that characterize these binaries as "W-type' systems that are physically similar to those in the field. The high spatial incidence of these systems in a cluster of such great age suggests that these stars have evolved into the contact configuration from detached or semidetached progenitors that lose orbital angular momentum, perhaps through magnetic braking in stellar winds. The W UMa-type binaries may coalesce and form the rapidly rotating yellow giants, the FK Comae stars. Title: Book-Review - Cool Stars Stellar Systems and the Sun Authors: Baliunas, S. L.; Hartmann, L.; Vetesnik, M. Bibcode: 1985BAICz..36..128B Altcode: No abstract at ADS Title: Three Dimension Mapping of the Atmosphere of an Active K-Dwarf Star Authors: Guinan, E. F.; Wacker, S. W.; Baliunas, S. L.; Loeser, J. G. Bibcode: 1985BAAS...17..569G Altcode: No abstract at ADS Title: Combined ultraviolet studies of astronomical sources Authors: Dupree, A. K.; Baliunas, S. L.; Blair, W. P.; Hartmann, L. W.; Huchra, J. P.; Raymond, J. C.; Smith, G. H.; Soderblom, D. R. Bibcode: 1985sao..reptQ....D Altcode: Ultraviolet studies of various astronomical entities are reported. Among the specific phenomena examined were supernova remnants, dwarf novae, red giant stars, stellar winds, binary stars, and galaxies. Title: Book-Review - Cool Stars Stellar Systems and the Sun Authors: Baliunas, S. L.; Hartmann, L.; Rudiger, G. Bibcode: 1985AN....306..212B Altcode: No abstract at ADS Title: A Search for Differential Rotation in Cool Stars Using Ca II H and K Emission Authors: Porter, A. C.; Baliunas, S. L.; Horne, J. H.; Noyes, R. W.; Duncan, D. K.; Frazer, J.; Lanning, H.; Misch, A.; Mueller, J.; Soyumer, D.; Vaughan, A. H.; Woodard, L. Bibcode: 1985BAAS...17..512P Altcode: No abstract at ADS Title: Activity Cycles in the Hyades and Praesepe Authors: Baliunas, Sallie L. Bibcode: 1985iue..prop.2114B Altcode: The giant stars in the Hyades present a well-studied group of stars of spectral type KO III. Their optical properties are quite similar, if not identical. All rotate with the same, slow period. Yet their chromospheric and coronal emission is different one from another, by as much as a factor of ten. We conjecture that this disparity results from sampling during different phases of long-term activity cycles which are present among dwarf stars. Some variation on a three-year timescale has been observed, as well as during phases of rotation modulation, however, at levels too small to explain the discrepancy of the emission strengths between the stars. We propose to investigate the range of chromospheric activity from these giants which are similar in the visible three ways: (a) reobserve the Hyades to search for variability on at least a seven-year timescale; (b) reobserve another young cluster, Praesepe, with four KO III stars similar to those in the Hyades to search for variability on a five-year timescale; (c) extend the sampling to four Hyades moving group stars with similar photospheric properties. The ultraviolet spectra provided by IUE represent the longest time frame, seven years, over which to search for long-term activity variations. Title: Stellar activity cycles. Authors: Baliunas, S. L.; Vaughan, A. H. Bibcode: 1985ARA&A..23..379B Altcode: The variety of stellar chromospheric and coronal activity provides a framework for understanding solar and stellar magnetic activity. It is pointed out that the recognition of an 11-yr periodicity within the record of sunspot numbers is a relatively recent discovery of just over a century ago. The solar activity cycle is examined, taking into account the sunspot cycle, and solar dynamo models. Time-averaged stellar chromospheric activity levels are considered along with long-term activity fluctuations of cool stars. Attention is given to the direct measurement of stellar magnetic fields, solar luminosity variations, the RS Canum Venaticorum and BY Draconis variables, continuum variations in lower main sequence stars, chromospheric variations in lower main sequence stars, and chromospheric variations in evolved stars. Title: Outer atmospheres of cool stars observed with IUE. Authors: Baliunas, S. L. Bibcode: 1984NASCP2349...64B Altcode: 1984IUE84.......64B; 1984fiue.rept...64B Ultrviolet observations of cool stars in conjuction with coronal X-ray or ground based chromospheric measurements, or both have served both to refine and define understanding of stellar activity. The sensitivity of IUE down to a reasonable limiting magnitude made accessible many different stars' ultraviolet spectra. Understanding of stellar activity throughout stellar atmospheres has progressed because observation in the ultraviolet range of particular stars can be done in great detail. Title: Betelgeuse at maximum luminosity. Authors: Dupree, A. K.; Sonneborn, G.; Baliunas, S. L.; Guinan, E. F.; Hartmann, L.; Hayes, D. P. Bibcode: 1984NASCP2349..462D Altcode: 1984IUE84......462D; 1984fiue.rept..462D Betelgeuse (Alpha Ori; M2 Iab) was extremely bright at optical wavelengths and in the Mg II resonance lines during January and February 1984 when an intrinsic brightening occurred in the photosphere and chromosphere. Linear polarization in the B-band at this time was not anomalous when compared to earlier epochs. The core of the Hα line was redshifted by about 10 km/s with respect to the photospheric lines during January/February as compared to measurements made five months previously. There may be periodic variations in the chromospheric flux. Title: Evidence for global oscillations in the K2 dwarf epsilon Eridani. Authors: Noyes, R. W.; Baliunas, S. L.; Belserene, E.; Duncan, D. K.; Horne, J.; Widrow, L. Bibcode: 1984ApJ...285L..23N Altcode: Evidence of global p-mode oscillations in the K2 V star Epsilon Eridani, based on observed time variations in the Ca II H and K emission lines, is presented. Power spectra of time series of Ca II intensity measures reveal a number of peaks spaced at about 86 and 172 micro-Hz. The 172 micro-Hz spacing is significantly larger than the corresponding spacing observed for solar p-mode oscillations but is in excellent agreement with predictions for a star of the known radius of Epsilon Eri. The amplitude of the oscillations seen in the H and K flux of this chromospherically active star is much larger than in the sun. Peak power in the H and K fluctuations occurs at periods near 10 minutes, in contrast to predictions of peak oscillation amplitude near four minutes for a K2 dwarf. Title: Activity Cycles of Lower Main-Sequence Stars: Eighteen Years of Research Authors: Baliunas, S. L.; Donahue, R. A.; Horne, J. H.; Noyes, R. W.; Porter, A.; Gilliland, R.; Duncan, D. K.; Frazer, J.; Lanning, H.; Misch, A.; Mueller, J.; Soyumer, D.; Vaughan, A. H.; Wilson, O. C.; Woodard, L. A. Bibcode: 1984BAAS...16R.899B Altcode: No abstract at ADS Title: Chromospheric emission and rotation of the Hyades lower main sequence. Authors: Duncan, D. K.; Baliunas, S. L.; Noyes, R. W.; Vaughan, A. H.; Frazer, J.; Lanning, H. H. Bibcode: 1984PASP...96..707D Altcode: The identity of chromospheric Ca II H- and K-line emission has been monitored for two seasons in a large sample of Hyades F and G dwarfs. Mean emission levels vary smoothly with spectral type, suggesting that the rotation rate at a given spectral type varies relatively little, and that the rotation rate decreases smoothly as a function of mass. In this case the mechanism which controls pre-main-sequence angular momentum loss in late-type stars must be self-regulating to a high degree. Title: Objective Characterization of Stellar Cycles Authors: Gilliland, R. L.; Baliunas, S. L. Bibcode: 1984BAAS...16..899G Altcode: No abstract at ADS Title: Flares & Activity in FF Aquarii & Lambda Andromedae Authors: Baliunas, Sallie L. Bibcode: 1984iue..prop.1765B Altcode: The serendipitous detection of an extremely energetic flare on the activechromosphere G8 IV-III star lambda And provides a unique opportunity for comparative flare studies. Our long-term investigations of A And and FF Aqr, a binary with a G8 III star reveals that the chromospheric activity in FF Aqr is more intense and extreme than in lambda And, primarily because the G8 III star FF Aqr rotates six times faster than lambda And. Some of the UV surface fluxes from FF Aqr and 20-50 times those of A And. In photometric U-band monitoring reveals flaring on the G8 III star in FF Aqr as bright as a magnitude and as frequently as once an hour. We expect, therefore, a flare more luminous than observed on lambda And. Such a flare would provide strong and extreme constraints for theoretical models of stellar flares. Title: Ultraviolet flare on lambda Andromedae. Authors: Baliunas, S. L.; Guinan, E. F.; Dupree, A. K. Bibcode: 1984ApJ...282..733B Altcode: On November 5, 6, 1982, a luminous, flarelike brightening of the ultraviolet emissions was observed with IUE from the active RS CVn type star Lambda And during the phase of rotation period corresponding to maximum area coverage of the visible hemisphere by starspots and active regions. Enhancements during the flare in the ultraviolet emission lines as large as factors of several and in the ultraviolet continuum up to 80 percent persisted for over 5 hours. The bulk of the radiative output of the flare occurred in Mg II h and k and H I Ly-alpha. Because of the long duration and extreme luminosity of the event, the energy radiated by the flare alone is in excess of 10 to the 35th ergs just in the ultraviolet region. This is the most energetic stellar flare ever recorded in the ultraviolet. In addition, it is the first ultraviolet flare observed from a giant star. In comparison to the largest solar flares, the flare on Lambda And is at least three orders of magnitude more energetic in similar emission lines. Title: Ultraviolet and visible flare observations of EQ Pegasi B. Authors: Baliunas, S. L.; Raymond, J. C. Bibcode: 1984ApJ...282..728B Altcode: EQ Peg AB (dM43+dM5.5e) was monitored in the visible at the Whipple Observatory and ultraviolet with IUE on September 2, 1981. In the visible spectrophotometry of EQ Peg B the H-beta emission strengthened by a factor of 2 relative to the nearby stellar continuum within a few minutes and decayed over an hour. This flare in EQ Peg B was coincident with the enhancement of ultraviolet emission lines of C IV 1550 A, He II 1640 A, and C II 1335 A in the combined light of EQ Peg AB. The ultraviolet fluxes during the flare can be interpreted as similar to those either in the thermal phases of large two-ribbon solor flares where radiative cooling balances thermal conduction or in gas cooling quickly from X-ray emitting temperatures. The appearance of the ultraviolet continuum at 1700-1900 A and ratio of H-alpha to H-beta fluxes during the flare are consistent with models producing these emissions in the chromosphere. Title: PM. 04 Stars, Atmospheres, and Shells: Potential for High-Resolution Imaging Authors: Dupree, A. K.; Baliunas, S. L.; Guinan, E. F. Bibcode: 1984BAAS...16..797D Altcode: Substantial progress in stellar physics can result from one- or two-dimensional imaging at a spatial resolution of 10-3 to 10-5arc sec. The direct measurement of stellar diameters, surface and atmospheric features, and extended shells can significantly advance the knowledge of stellar structure, activity, and evolution. A dwarf star - the sun - and a supergiant star - Alpha Orionis - are used to illustrate the possibilities of measurements with high spatial resolution. In addition, magnetically sensitive lines can trace the distribution of activity across a stellar surface. Title: Rotation, convection, and magnetic activity in lower main-sequence stars. Authors: Noyes, R. W.; Hartmann, L. W.; Baliunas, S. L.; Duncan, D. K.; Vaughan, A. H. Bibcode: 1984ApJ...279..763N Altcode: Rotation periods are reported for 14 main-sequence stars, bringing the total number of such stars with well determined rotation periods to 41. It is found that the mean level of their Ca II H and K emission (averaged over 15 years) is correlated with rotation period, as expected. However, there is a further dependence of the emission on spectral type. When expressed as the ratio of chromospheric flux to total bolometric flux, the emission is well correlated with the parameter P(obs)/tau(c), where P(obs) is the observed rotation period and tau(c)(B - V) is a theoretically-derived convective overturn time, calculated assuming a mixing length to scale height ratio alpha of about 2. This finding is consonant with general predictions of dynamo theory, if the relation between chromospheric emission and dynamo-generated magnetic fields is essentially independent of rotation rate and spectral type for the stars considered. The dependence of mean chromospheric emission on rotation and spectral type is essentially the same for stars above and below the Vaughan-Preston (1980) 'gap', thus casting doubt on explanations of the gap in terms of a discontinuity in dynamo characteristics. Title: A study of the dependence of MG II emission on the rotational periodsof main-sequence stars. Authors: Hartmann, L.; Baliunas, S. L.; Duncan, D. K.; Noyes, R. W. Bibcode: 1984ApJ...279..778H Altcode: International Ultraviolet Explorer satellite measurements of the Mg II chromospheric emission from a sample of late-type dwarfs with known rotational periods are presented. The ratio of chromospheric to photospheric luminosity for the late-G and K type stars in this sample can be fitted within the probable errors by a single function of rotational period. The chromospheric emission of early-G and F dwarfs appears to depend upon rotation in a qualitatively different way, which suggests that the rapid variation of convective zone properties in this spectral range affects the dissipation of energy in the chromosphere. Mg II h and k emission correlates fairly well with Ca II emission. However, the data sample is not large enough at present to show conclusively that Mg II emission exhibits precisely the same dependence on rotation and spectral type as the Ca II H and K line fluxes. Title: Chromospheric Activity and Rotation in the Giant Stars in the Hyades and Praesepe Clusters Authors: Baliunas, S. L.; Horne, J.; Noyes, R. W.; Duncan, D. K.; Frazer, J.; Lanning, H.; Misch, A.; Soyumer, T.; Woodard, L. Bibcode: 1984BAAS...16..508B Altcode: No abstract at ADS Title: Stars, atmospheres, and shells: potential for high-resolution imaging. Authors: Dupree, A. K.; Baliunas, S. L.; Guinan, E. F. Bibcode: 1984BAAS...16..558D Altcode: No abstract at ADS Title: Book-Review - Cool Stars Stellar Systems and the Sun Authors: Baliunas, S. L.; Hartmann, L.; Schrijver, C. J. Bibcode: 1984SSRv...39..375B Altcode: No abstract at ADS Title: Cool Stars, Stellar Systems, and the Sun Authors: Baliunas, Sallie L.; Hartmann, Lee Bibcode: 1984LNP...193.....B Altcode: 1984csss....3.....B No abstract at ADS Title: Evolution of Rotation in Main-Sequence Stars Authors: Baliunas, Sallie L. Bibcode: 1984LNP...193..114B Altcode: 1984csss....3..114B A review of the classical and modern measurements of axial rotation and their implications for the evolution of rotation of stars on the lower main sequence is given. From stars of main-sequence spectral type A through early K, the dependence of rotation on mass and age is investigated, from results for stars in open clusters and in the field. The high-mass, single, normal dwarf stars of spectral type A display a common mean projected rotational velocity dependent on their masses and re gardless of their ages. The angular momentum per unit mass in this range decreases slowly with decreasing mass. Title: Time Series Measurements of Chromospheric Emission and Possible Evidence for Differential Rotation Authors: Horne, J. H.; Baliunas, S. L.; Noyes, R. W.; Duncan, D. K.; Vaughan, A. H. Bibcode: 1984LNP...193..143H Altcode: 1984csss....3..143H No abstract at ADS Title: Four W Ursae Majoris Contact Binaries in the Old Galactic Cluster NGC 188 Authors: Baliunas, Sallie L.; Guinan, Edward F. Bibcode: 1984LNP...193..223B Altcode: 1984csss....3..223B No abstract at ADS Title: Stellar rotation in lower main-sequence stars measured from time variations in H and K emission-line fluxes. II. Detailed analysis of the 1980 observing season data. Authors: Baliunas, S. L.; Hartmann, L.; Noyes, R. W.; Vaughan, H.; Preston, G. W.; Frazer, J.; Lanning, H.; Middelkoop, F.; Mihalas, D. Bibcode: 1983ApJ...275..752B Altcode: For a sample of 47 lower main-sequence stars, including the Sun, and eight evolved stars, the relative strength of the Ca II H and K emission cores has been measured daily over a nearly continuous interval during 1980 July through October at Mount Wilson. From these time series measurements of chromospheric emission, rotation rates have been inferred with quantitative estimates of both the reality and precision of the rotation periods. We find rotation rates easily for the main-sequence stars with strong emission or those later than about spectral type K0. With this technique, rotation rates can be measured precisely for the first time for equatorial velocities as slow as 1 km s-1 and independently of the aspect of the rotation axis. In a limited range of spectral type, a small sample of stars indicates that chromospheric emission decreases smoothly as a function of rotation period. No conclusion can be drawn on the question of the reality of a discontinuity in chromospheric emission as a function of time (the "Vaughan-Preston" gap for stars in the solar neighborhood).

In our sample of giant stars, the G2 III star HD 218658 shows a persistent fluctuation of 4.6 days, a period that is inconsistent with stellar rotation. The G0 III star HD 6903 is a previously unreported FK Comae-type star.

For a few main-sequence stars, measurements continued beyond 1980 October suggest the presence of active longitudes (if not individual active regions) persisting through the observing season 1981. Title: Combined ultraviolet studies of astronomical sources Authors: Dupree, A. K.; Giampapa, M. S.; Huchra, J. P.; Noyes, R. W.; Hartmann, L. W.; Raymond, J. C.; Blair, W. P.; Bothun, G. D.; Patterson, J. O.; Baliunas, S. L. Bibcode: 1983sao..reptR....D Altcode: Ultraviolet spectra of non-radiataive shock waves grain destruction and elemental abundances in interstellar shocks, carbon abundance in M33 and M31 from supernova remnants, determination of the mass function in the large Magellanic cloud, UV spectra of white dwarf pulsars, stellar flares, availability of the double quasar Q 0957 + 56' AB, spectra of late-F dwarfs and their relation to rotation, dynamics of hot gas surrounding hybrid stars, high resolution study of epsilon coronae Austriual, active regions on solar-type dwarfs as a function of rotation rate and age, coordinated chromospheric synoptic observations of selected late-type stars, the two-component atmosphere of Lambda Andromedae, and activity in Hyades giants are discussed. Title: Progress in stellar chromospheres observed with the International Ultraviolet Explorer satellite. Authors: Baliunas, S. L. Bibcode: 1983PASP...95..532B Altcode: The historical knowledge gathered over the past two decades of visible spectrum studies, predominantly at Ca II H and K, combined with detailed theoretical models and high spectrum-and spatial-resolution work on the solar atmosphere from space provide the framework for ultraviolet measurements from IUE for furthering our understanding of the solar-and-stellar activity connection. Quantitative measurements of the behavior of stellar chromospheric and coronal emission can be investigated as a function of stellar parameters such as age, rotation rate, and mass. Together the visible and ultraviolet spectra probe the stellar atmospheres as a function of height and reveal the energy budget in a variety of late-type stars. Atmospheric inhomogeneities such as stellar active areas, spots, and flares can be profitably studied in the ultraviolet and visible. At high spectrum resolutions with IUE, the dynamics of the outer atmospheres, including stellar winds and mass outflows, yield constraints on global models for mass loss in late-type stars. Title: Binary Star Evolution in the Old, Open Cluster NGC 188 Authors: Baliunas, S. L.; Guinan, E. F. Bibcode: 1983BAAS...15..924B Altcode: No abstract at ADS Title: Ca II H and K emission and rotation of the Hyades lower main sequence. Authors: Duncan, D. K.; Baliunas, S. L.; Noyes, R. F.; Vaughan, A. H. Bibcode: 1983PASP...95..589D Altcode: No abstract at ADS Title: Chromospheric and coronal emissions from the giants in the Hyades. Authors: Baliunas, S. L.; Hartmann, L.; Dupree, A. K. Bibcode: 1983ApJ...271..672B Altcode: 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. Title: Observations of the RS CVn Star HD 26337 with the International Ultraviolet Explorer Satellite Authors: Baliunas, S. L.; Blair, W. P.; Guinan, E. F. Bibcode: 1983IBVS.2323....1B Altcode: No abstract at ADS Title: Identification and properties of the M giant/X-ray system HD 154791 =2A 1704+241. Authors: Garcia, M.; Baliunas, S. L.; Doxsey, R.; Elvis, M.; Fabbiano, G.; Koenigsberger, G.; Patterson, J.; Schwartz, D.; Swank, J.; Watson, M. G. Bibcode: 1983ApJ...267..291G Altcode: The Aerial V X-ray source 2A 1704+241 (= 4U 1700+24 = 3A 1703+241) is identified with the M3 II star HD 154791. The identification is based on a precise X-ray position determined by the HEAO 1 scanning modulation collimator and the Einstein Observatory imaging proportional counter, together with a spectrum measured by the International Ultraviolet Explorer. The ultraviolet spectrum shows strong emission of C IV 1550 A, N v 1238 A, and Mg II 2800 A, which is very unusual among M giants. This is the first X-ray detection of an M giant which has a completely normal optical spectrum. The X-ray luminosity reaches three orders of magnitude above the mean upper limit for the coronal X-ray flux from M giants. Although there is no direct evidence for a binary system, since radial velocity variations have not been observed, it is shown that a plausible neutron star binary model can be constructed. Title: Rotation, Convection, and Solar-Stellar Dynamos Authors: Noyes, R. W.; Baliunas, S. L.; Duncan, D. K.; Hartmann, L. W.; Vaughan, A. H. Bibcode: 1983BAAS...15Q.698N Altcode: No abstract at ADS Title: Vertical Structure of the Atmospheres of Active G-Giant Stars Authors: Baliunas, Sallie L. Bibcode: 1983iue..prop.1409B Altcode: Two G8 giants in binary systems present a unique opportunity to measure the vertical scale height of emitting regions through the extended atmospheres of these stars. For lambda And, geometrically extended regions will be mapped as an active area which either appears or disappears over the stellar limb. In FF Aqr, the hot, sdO binary companion will be used to probe geometrically-extended inhomogeneities during eclipse through the late-type giant atmosphere. Study of the similarities and differences between atmospheric inhomogeneities as a function of temperature and height may reveal separable data on localized "active" areas, compared to non-localized background emission. With a comparison of these two stars with ostensibly similar photospheres but widely different rotation rates we hope to investigate the interplay of rotation with the coronal structure and coronal heating rates. Title: Stellar activity and calcium emission variability Authors: Baliunas, S. L. Bibcode: 1983ASSL..102..195B Altcode: 1983ards.proc..195B; 1983IAUCo..71..195B Findings on the long-term behavior, intermediate timescale variations, and short-term variations obtained through time series analysis of fluctuations of Ca II H and K chromospheric emission are summarized. Many of the dwarfs in the spectrum type range F-G-K-early M undergo long-term variations. Forty percent show smooth fluctuations which appear to be cyclic with periods of 5-10 years or slightly longer. Forty percent show erratic variations and the remainder show little observable fluctuations. Rotation in open-cluster dwarfs slows with decreasing Ca II emission strength, and no good correlation exists between rotation period and activity cycle period. The success rate for determining rotation in the chromospherically more active stars can be over 80 percent. Flarelike events in chromospheric emission similar to those seen in flare stars and large solar flares have been observed in HD 22049 and other G-K stars. Title: Stellar activity measured at Ca II H and K. Authors: Baliunas, S. L. Bibcode: 1982SAOSR.392B..31B Altcode: 1982csss....2...31B No abstract at ADS Title: Ultraviolet and optical spectrum studies of lambda Andromedae : evidence for atmospheric inhomogeneities. Authors: Baliunas, S. L.; Dupree, A. K. Bibcode: 1982ApJ...252..668B Altcode: To pursue the study of solar phenomena in cool stars, chromospheric activity in Lambda Andromedae (HD 222107 has been investigated). This binary, whose primary star is G7-G8 IV-III, shows strong chromospheric emissions and is related to the RS CVn-type systems. The first quantitative measurements of chromospheric and solar-type transition-region emissions as a function of the variable starspot and active-region phenomena in an RS CVn star are presented. The presence of optically darker starspots in Lambda And coincides with the brightening of both Ca II K emission and the ultraviolet transition-region lines. The ultraviolet and optical spectra show attributes of starspots, active regions, and mass flow. Analogies to solar activity are successful in explaining these observations. Title: Stellar Flares Authors: Baliunas, Sallie L. Bibcode: 1982iue..prop.1057B Altcode: Flares on dMe stars have been observed In optical continuum radiation for many years. IUE has made it possible to observe these flares in ultraviolet emission lines and continuum. We wish to monitor two stars in both the ultraviolet and optical spectrum regions to study the energy released by flares and the nature of the continuum radiation. We will employ density diagnostics and emission measure analysis techniques developed for solar observations. The He II A 1840 line will be used to infer the flare luminosity at 56 < hv < 100 eV. Title: Activity in the Hyades Giants Authors: Baliunas, Sallie L. Bibcode: 1982iue..prop.1063B Altcode: The giant stars In the Hyades present a well-studied group of stars of spectral type KO Ill. Their optical properties are quite similar, If not Identical. All appear to be slow rotators. Yet their chromospherIc and coronal emission Is different one from the other, by more than a factor of ten. We conjecture that this disparity results from different activity cycles - much as Is present In dwarf stars. We propose to reobserve these giants to search for variability on a three year time scale. Title: The Two Component Atmosphere of Lambda Andromedae Authors: Baliunas, Sallie L. Bibcode: 1982iue..prop.1071B Altcode: From optical and ultraviolet observations, Lambda Andromedae has been found to show a clear dichotomy In the structure of its atmosphere which is strikingly similar to that found in the Sun between active regions and the quiet Sun or coronal holes. We propose to measure at high resolution the widths, fluxes and asymmetries of ultraviolet lines formed in the extended atmosphere of the primary to detect the presence and character of a stellar wind and the change in atmospheric structure when active regions and/or spots are present. Frequent observations In the Mg II transition will be made in an attempt to detect the high chomosphere equivalent of the rapid (~ 5 minutes) fluctuations discovered in the Ca K emission cores suggesting impulsive events. Title: Stellar rotation in lower main-sequence stars measured from time variations in H and K emission-line fluxes. I. Initial results. Authors: Vaughan, A. H.; Baliunas, S. L.; Middelkoop, F.; Hartmann, L. W.; Mihalas, D.; Noyes, R. W.; Preston, G. W. Bibcode: 1981ApJ...250..276V Altcode: Fluxes at 1 Å bands at the centers of the H and K lines in 46 lower main sequence field stars, and in eight selected subgiants and giant stars, have been measured at nightly intervals in the course of a nearly continuous 14-week observing run. In 19 stars we have found clear evidence of rotational modulation, from which values of the rotational periods can be assigned by inspection. In nine others, periods have been found by an autocorrelation analysis of the flux records. The periods obtained imply rotation velocities that are in good accord with spectroscopically determined values of V sin i in the literature for 13 of the stars we have observed.

Much of the short term scatter in H-K flux observed by Wilson appears to be caused by rotational modulation, although variations on other time scales are also present.

As many as 80% of the chromospherically active (i.e., young) stars display prominent rotational modulation, and in some cases the phase of the modulation remained unchanged for the entire observing period, suggesting that markedly asymmetric and long-lived distributions of active regions are common in such stars.

At a given (B - V) < 1.0, the strength of H-K emission is shown to vary as a function of rate of rotation, suggesting that rotation, rather than initial conditions or age per se, is the chief parameter influencing chromospheric output.

From data on stellar activity cycles available at present, it is suggested that periodic cycles resembling the Sun's are almost exclusively found in stars with rotation periods in excess of about 20 days; and, except for this threshold effect, the cycle periods are uncorrelated with rotation rate. Title: Short time-scale variability of chromospheric CaII in late-type stars. Authors: Baliunas, S. L.; Hartmann, L.; Vaughan, A. H.; Liller, W.; Dupree, A. K. Bibcode: 1981ApJ...246..473B Altcode: The short time-scale variability of singly ionized calcium chromospheric emission has been investigated in a few late-type stars. Emission-line variations with time scales of a few minutes to hours are seen in Alpha Tau (K5 III), Lambda And (G8 III-IV), and Epsilon Eri (K2 V). The existence of substantial chromospheric flux changes (10 to the 30th to 10 to the 32nd ergs) over short periods of time suggests that the calcium emission arises from a few small, coherent regions. Frequencies present in the data are discussed in the context of acoustic wave predictions and estimated acoustic cutoff frequencies for giants and dwarfs. Title: IUE - ultraviolet and optical chromospheric studies of late-type giants in the Hyades cluster. Authors: Baliunas, S. L.; Hartmann, L.; Dupree, A. K. Bibcode: 1981NASCP2171..325B Altcode: 1981uviu.nasa..325B; 1980IUE80......325B; 1981NASCP3171..325B Ultraviolet and optical observations of four bright, late-type giants in the Hyades cluster detected with IUE are presented in order to study chromospheric and coronal activity in stars of the same age. Two of the giants, 77 Tau and gamma Tau, clearly exhibit emission in the high temperature ions such as N V, C IV, and Si IV at levels several times larger than the upper limits for the other two giants, delta Tau and epsilon Tau. Comparison of the Mg II h and k fluxes and the Ca II K emission strengths shows that 77 Tau and gamma Tau have larger chromospheric radiative losses than delta Tau, epsilon Tau, and beta Gem, a field giant which also displays low upper limits to emission from high temperature ions. Coronal X-ray emission indicates that the surface flux in X-rays is an order of magnitude brighter in 77 Tau than in delta Tau. The results indicate that a parameter other than age, temperature, gravity or metallicity determines the amount of chromospheric and coronal emission in late-type giants. Title: Optical identification of H 0123+07.5 and 4U 1137-65 : hard X-ray emission from RS CVn systems. Authors: Garcia, M.; Baliunas, S. L.; Conroy, M.; Johnston, M. D.; Ralph, E.; Roberts, W.; Schwartz, D. A.; Tonry, J. Bibcode: 1980ApJ...240L.107G Altcode: No abstract at ADS Title: Ultraviolet and Optical Chromospheric Activity in Lambda-Andromedae - Evidence for Starspots and Active Regions Authors: Baliunas, S. L.; Dupree, A. K. Bibcode: 1980SAOSR.389..101B Altcode: 1980csss....1..101B No abstract at ADS Title: Optical and Ultraviolet Studies of Stellar Chromospheres of Lambda Andromedae and Other Late-Type Stars. Authors: Baliunas, S. L. Bibcode: 1980PhDT........10B Altcode: Chromospheric studies of the outer atmospheres of several late-type stars are presented along with a comprehensive study of (lamda) Andromedae, an "active chromosphere" star. Investigations were made of the chromospheric features of Ca II H and K, Mg II h and k, and other, high-temperature emissions accessible to the Copernicus and IUE satellites. Analogues to solar activity are consistent with the spectral behavior of the chromospheric indicators. The chromospheric activity and variability in Ca II H and K in (lamda) And are similar to sunspot and solar flare activity. In addition, a search was begun for short-timescale (few minutes) fluctuations in the H and K cores in several late-type stars. Calibrated spectrophotometry for the Ca II K profiles and additional constraints provided by H(alpha) and the ultraviolet observations of Mg II and the high-temperature transition-region emissions were employed in the construction of semi-empirical chromospheric models of (lamda) And, (alpha) Aur, and (alpha) Boo. A prescription is given for models of active-chromosphere stars, which may also be useful for other late-type stars. Title: Silicon lines as spectral diagnostics - The effect of charge transfer Authors: Baliunas, S. L.; Butler, S. E. Bibcode: 1980ApJ...235L..45B Altcode: The paper discusses the importance of charge transfer as an ionization source in astrophysical plasmas. The effect of the rapid charge transfer reactions Si(+) + H(+) yields Si(+2) + H - 2.74 eV and SI(2+) + He(+) yields Si(+3) + He - 8.88 eV on the ionization equilibrium of silicon is calculated. The dominant ionization stage of silicon in a coronal plasma is shown to be Si(+2) for temperatures as low as 20,000 K in contrast to the temperature of 35,000 K determined from earlier ionization equilibrium calculations. The Si(+3) abundance is also substantially modified. For the quiet-sun transition region, the effect of charge transfer upon the emissivity of the Si III lambda 1892 emission line is calculated. The peak emissivity occurs at a temperature a factor of 2 lower and is an order of magnitude higher than implied by calculations neglecting the silicon charge-transfer process. The results have widespread importance for the interpretation of solar, stellar, interstellar, and extragalactic silicon lines. Title: Optical and ultraviolet studies of stellar chromospheres of lambda Andromedae and other late-type stars Authors: Baliunas, Sallie Louise Bibcode: 1980PhDT.......212B Altcode: No abstract at ADS Title: Optical observations of SS 433. Authors: Noyes, R.; Liller, W.; Davis, M.; Baliunas, S.; Sternberg, A.; Tokarz, S. Bibcode: 1979BAAS...11..732N Altcode: No abstract at ADS Title: Chromospheric Event in alpha Aquarii Authors: Dupree, A. K.; Baliunas, S. Bibcode: 1979IAUC.3435....1D Altcode: 1979IAUC.3435....0D A. K. Dupree and S. Baliunas, Center for Astrophysics, report that IUE observations of alpha Aqr (G2Ib) on Nov. 11 show substantial changes in the Mg II line profile from measurements 11 months earlier. The flux in the short-wavelength emission peaks at 279.5 and 280.2 nm has increased and is accompanied by a broadening of the profile and an increased absorption by the extended stellar wind. The terminal wind velocity remained constant. The flux of C II (133.5 nm) and O I (135.7 nm) increased by a factor of about 2 as compared to the previous measurements, whereas C IV (155.0 nm) and Si IV (140 nm) increased by lesser amounts. High-dispersion Ca II K profiles obtained with an intensified Reticon detector and echelle spectrograph at Mt. Hopkins Observatory reveal a change in the peak line asymmetry with the blue emission peak becoming substantially stronger than the red peak between Nov. 4 and 11. By Dec. 8, the blue emission had weakened again, becoming comparable to the red emission peak. This is the first quantitative evidence of chromospheric variability in such a supergiant atmosphere, and the star should be monitored, for it may be in a phase of activity resulting from the passage of enhanced flux regions across its disk. Title: Optical Observations of SS 433 Authors: Liller, W.; Noyes, R.; Davis, M.; Baliunas, S.; Sternberg, A.; Tokarz, S. Bibcode: 1979BAAS...11..732L Altcode: No abstract at ADS Title: High-pressure transition regions in stellar model chromospheres. Authors: Baliunas, S. L.; Avrett, E. H.; Hartmann, L.; Dupree, A. K. Bibcode: 1979ApJ...233L.129B Altcode: The implications of recent ultraviolet observations of stellar transition-region lines for calculations of the Ca II and Mg II resonance lines are investigated. It is found that the adoption of high transition-region pressures for stars with active chromospheres, such as Lambda And and Alpha Aur, can be consistent with observed Ca II fluxes, contrary to the results obtained by Kelch et al. (1978) for Alpha Aur. Furthermore, the adoption of the high-pressure models removes a long-standing difficulty in the line profile calculations, since the deep central absorption present in earlier calculations is less pronounced or absent, in closer agreement with observations. The apparent contradiction between these models and the recent density diagnostic of Doschek et al. (1978) is also discussed. Title: Optical Observations of SS 433. Authors: Noyes, R.; Liller, W.; Davis, M.; Baliunas, S.; Sternberg, A.; Tokarz, S. Bibcode: 1979BAAS...11..786N Altcode: No abstract at ADS Title: SS 433 Authors: Baliunas, S.; Noyes, R.; Liller, W.; Tokarz, S. Bibcode: 1979IAUC.3410....1B Altcode: S. Baliunas, R. Noyes, W. Liller and S. Tokarz, Harvard-Smithsonian Center for Astrophysics, report that the central intensity of H-alpha relative to the continuum in SS 433 showed factor-of-two increases on Apr. 29 and June 20, each lasting about two days. Observations over five nights during these times, plus additional observations on 14 other nights throughout the interval Apr. 28 to June 24, showed all the data to be commensurate with the 13.1-day period reported by Crampton et al. (IAUC 3388). Comparison with other photometric data indicates that the ratio increases represent increases of absolute H-alpha-emission-line intensity. The data were obtained with the digital spectrograph at the Mount Hopkins 1.5-m telescope. Title: What tides and flares do to RS Canum Venaticorum binaries. Authors: Decampli, W. M.; Baliunas, S. L. Bibcode: 1979ApJ...230..815D Altcode: The effects that anisotropic mass should have on the orbital and spin states of RS Canum Venaticorum binaries are discussed. In the absence of magnetic fields, orbital period changes reported for several RS Canum Venaticorum systems require dM/dt of about 0.000001 solar masses/yr. Magnetic braking can lower this required rate if the surface magnetic fields are not less than 1000 gauss. However, this requires a method much more powerful than tidal torques to convert spin angular momentum loss to orbital angular momentum loss. This possibility is important when interpreting the complicated light curves of these systems, and may contradict the Hall's 'drifting star spot' hypothesis. In addition, large mass-loss rates may result in significant self-absorption of quiescent soft X-rays observed from several of these binaries. Title: High-Pressure Transition Regions in Stellar Model Chromospheres Authors: Baliunas, S. L.; Avrett, E. H.; Hartmann, L. W.; Dupree, A. K. Bibcode: 1979BAAS...11..448B Altcode: No abstract at ADS Title: Ultraviolet and optical spectroscopic studies of lambda Andromedae: the chromosphere and interstellar medium. Authors: Baliunas, S. L.; Dupree, A. K. Bibcode: 1979ApJ...227..870B Altcode: Chromospheric lines of, and interstellar lines toward, the spectroscopic binary Lambda And (primary component G7-G8 III-IV) have been observed in the ultraviolet with the spectrometer and telescope on board the Copernicus satellite. An extensive, high-resolution spectroscopic study of the Ca II H and K profiles has also been undertaken. Some of these optical spectra were obtained simultaneously with the ultraviolet data. The ultraviolet emission lines of Lamba And are compared to the sun and to stars of similar spectral type. The star Lamba And resembles the active sun in surface brightness of chromospheric emissions and in appearance of the Mg II and Ca II profiles. The largest variations in the integrated calcium emission cores amount to an 80% increase in the K core and a corresponding 40% increase in the H core between observations two years apart. Variations in the cores may show a dependence on spectroscopic phase, and may be contributed to by circumstellar matter in the binary system. Previously unreported, transient emission features have also been observed, at a velocity of -70 km/s with respect to the Ca II emission cores. Title: Photometric and Spectroscopic Varability of Ca II H and K in G- and K-Type Giants. Authors: Baliunas, S. L.; Hartmann, L. W.; Liller, W.; Vaughan, A. H., Jr.; Avrett, E. H.; Dupree, A. K. Bibcode: 1978BAAS...10..461B Altcode: No abstract at ADS Title: Detection of [Fe XIV] emission in HD 153919 (3U 1700-37). Authors: Dupree, A. K.; Baliunas, S. L.; Lester, J. B. Bibcode: 1977ApJ...218L..71D Altcode: Spectra of HD 153919 show a previously unreported broad emission line near 5293 A that is present at phases 0.2 and 0.8 and is absent or weaker at other phases, including the time of eclipse of the X-ray source. Approximate calculations suggest identification of this feature with the forbidden Fe XIV transition at 5303 A. This line may arise in the extended atmosphere of the primary ionized by the compact X-ray source or may occur in a high-temperature corona. Further monitoring is needed. Title: Deuterium and hydrogen in the local interstellar medium. Authors: Dupree, A. K.; Baliunas, S. L.; Shipman, H. L. Bibcode: 1977ApJ...218..361D Altcode: Densities of neutral hydrogen and deuterium are found from observation with the Copernicus satellite of the Ly-alpha line toward two nearby stars. The hydrogen density is 0.03 + or - 0.01 per cu cm toward Alpha Aur (Capella) and 0.20 + or - 0.05 per cu cm in the direction of Alpha Cen A, values indicating that the nearby (less than 14 pc) interstellar medium is inhomogeneous and can be of low density in certain directions. The ratios of deuterium to hydrogen - 3.9 (+5.7, -1.7) by 10 to the -5th power and 0.24 (+0.12, -0.07) by 10 to the -5th power for Alpha Aur and Alpha Cen A, respectively - suggest that variations in the deuterium abundance may exist. Title: Possible Detection of Fe XIV in the X-Ray Binary HD 153919. Authors: Baliunas, S. L.; Dupree, A. K.; Lester, J. B. Bibcode: 1977BAAS....9..298B Altcode: No abstract at ADS Title: Interstellar Density of Deuterium and Hydrogen Towards Alpha Aurigae. Authors: Dupree, A. K.; Baliunas, S. L. Bibcode: 1976BAAS....8..551D Altcode: No abstract at ADS Title: Optical and Ultraviolet Observations of Lambda Andromedae Authors: Baliunas, S. L.; Dupree, A. K.; Lester, J. B. Bibcode: 1976BAAS....8..353B Altcode: No abstract at ADS Title: The chromosphere and corona of Capella. Authors: Dupree, A. K.; Baliunas, S. Bibcode: 1976BAAS....8..397D Altcode: No abstract at ADS Title: Halpha and Hbeta photoelectric photometry of gamma Cassiopeiae. Authors: Baliunas, S. L.; Guinan, E. F. Bibcode: 1976PASP...88...10B Altcode: Photoelectric observations of gamma Cas (B0 IVe) were made using two pairs of wide- and narrow-band interference filters centered near the rest wavelengths of the hydrogen Balmer alpha and beta lines. H-alpha and H-beta indices were obtained on 19 nights from February 1972 to February 1975. Variations in the H-alpha and H-beta indices were found with a range of 0.18 and 0.10 min, respectively. Title: Halpha and Hbeta photoelectric photometry of bright Be stars. Authors: Baliunas, S. L.; Ciccone, M. A.; Guinan, E. F. Bibcode: 1975PASP...87..969B Altcode: Ha and H photoelectric observations of 33 early-type standard stars and 23 Be stars were obtained at the Villanova University Observatory on 27 nights between January 1972 and February 1973. The data permit separation of the stronger-lined Be stars from the normal stars and reveal variations in the Be star Cas. When compared with earlier data obtained by others, the Villanova data show longer-term variations in five other Be stars as well: w Ori, Tau, K Dra, 23 Tau, and Per. Key words: Be stars - emission - narrow-band photometry Title: Photoelectric Study of the Bright Be Stars γ Cas, 48 Per, ψ Per, and φ Per. Authors: Baliunas, S. D.; Ciccone, M. A.; Guinan, E. F.; Miskinis, P. Bibcode: 1975BAAS....7Q.252B Altcode: No abstract at ADS Title: Hα and Hβ Photoelectric Photometry of Bright Be Stars. Authors: Baliunas, S. L.; Ciccone, M.; Guinan, E. F. Bibcode: 1973BAAS....5..317B Altcode: No abstract at ADS