SETI [ASTRO] The Suns Of M67


Larry Klaes (lklaes@bbn.com)
Wed, 02 Jun 1999 14:39:55 -0400


>X-Authentication-Warning: brickbat12.mindspring.com: majordom set sender to owner-astro using -f >Date: Tue, 1 Jun 1999 14:38:49 GMT >From: Ron Baalke <BAALKE@kelvin.jpl.nasa.gov> >To: astro@lists.mindspring.com >Subject: [ASTRO] The Suns Of M67 >Sender: owner-astro@brickbat12.mindspring.com >Reply-To: Ron Baalke <BAALKE@kelvin.jpl.nasa.gov> > >National Optical Astronomy Observatory >Tucson, Arizona > >EMBARGOED FOR RELEASE: 9:20 a.m., CDT, June 1, 1999 > >RELEASE NO: NOAO 99-07 > >THE SUNS OF M67 > >Dr. Mark Giampapa of the National Science Foundation's National Solar >Observatory in Tucson, Arizona, has determined that the Sun is in a >relatively moderate state of activity. Giampapa's observations of >Sun-like stars in M67 suggest that about 40% of the time the Sun is >likely to be either significantly more, or significantly less, active. A >change to either of these states is likely to cause significant changes >in the Earth's climate. These same observations also indicate excursions >in the luminosity of the Sun from about 0.2% - 0.5% are possible, compared >with the 0.1% variations that have been measured with modern satellite >instruments during the 1980s and 1990s. Any variation in what is >considered typical or normal solar activity must be taken into account >in the study of long-term behavior of the global climate. > >Using the WIYN (Wisconsin, Indiana, Yale, National Optical Astronomy >Observatories) 3.5-meter telescope on Kitt Peak, Arizona, Dr. Giampapa >and colleagues studied chromospheric emission lines in 106 Sun-like >stars in the galactic cluster M67. Two fields of about 50 stars each in >M67 were observed for nearly 20 hours from 1996 - 1998 with the Hydra >multi-object fiber spectrometer. Interpreting the range of Ca II H and K >emission observed in Sun-like stars in M67 as indicative of possible >amplitudes of cycle-related variability that can occur in the Sun itself >indicates about 42% of the solar-type stars in M67 exhibit levels of >activity that are either greater than that seen at solar maximum or >less than that seen at solar minimum. Giampapa's analysis shows that >between 10-15% of the sun-like stars in M67 are distinguished by >exceptionally quiescent levels of magnetic activity analogous to the >so-called 'Maunder-minimum' episode of the Sun during A.D. 1645 - >1715 when visible manifestations of solar activity vanished. > >This period corresponded to a time of reduced average global >temperatures on the Earth known as the "Little Ice Age." About 30% >of the M67 Suns are in a state of enhanced activity compared to that >seen at solar maximum. It is possible that the so-called `Medieval >warm period' during A.D. 900 - 1200 corresponded to a time of >enhanced activity on our Sun. > >M67 is an appropriate target of observations for the study of solar- >type stars since it is approximately the same age and has the same >chemical composition as the Sun. This method of observing a galactic >cluster for variability in Sun-like stars allows us to 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. > >Variability on the scale observed could have consequences for the >amplitude of irradiance variability that the Sun can exhibit and hence >potentially influence global climate. Excursions in the activity itself >could have an impact on the near-earth orbital environment with >consequences for space operations. > >Image Caption: [http://www.noao.edu/outreach/press/images/9907a.tif] > >M67 is an open star cluster in the constellation Cancer. One of the oldest >known such clusters, M67 is believed to be 5 billion years old. It contains >approximately 500 stars within its 12 light year diameter and is located >some 2800 light years away. More than 100 Sun-like stars in M67 were >observed and analyzed by Giampapa. > >Image Caption: [http://www.noao.edu/outreach/press/images/9907b.tif] > >A histogram of the normalized index RHK, indicative of magnetic activity, >for the contemporary Solar Cycle, Solar Twins in M67 (0.63 < B-V < 0.67), >and Solar Type stars in M67 (0.60 < B-V < 0.76). > >For more information, contact these astronomers at the National Optical >Astronomy Observatories, Tucson, Arizona: > >Suzanne H. Jacoby >NOAO Press Officer >(520) 318-8364 >email: sjacoby@noao.edu > >Dr. Mark Giampapa >NSO Deputy Director >(520) 318-8236 >email: mgiampapa@noao.edu > >Dr. R. R. Radick, (AFGL) >(505) 434-7035 >email: radick@sunspot.noao.edu > >Dr. S. L. Baliunas, (SAO) >(617) 495-7415 >email: baliunas@cfa.harvard.edu > >EDITORS: High resolution versions of the images are available via the >internet at http://www.noao.edu/outreach/press/ > >The National Solar Observatory and Kitt Peak National Observatory are >divisions of the National Optical Astronomy Observatories (NOAO). NOAO >is operated by the Association of Universities for Research in Astronomy, >Inc. under cooperative agreement with the National Science Foundation. > > >



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