Advanced Composition Explorer

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National Aeronautics and Space Administration ADVANCED COMPOSITION EXPLORER Studying Near-Earth Space The Advanced Composition Explorer, or ACE, observes of radiation— and measures magnetic fields and particles in space, from the Sun, from a vantage point approximately 1/100 of the dis- from the solar tance from Earth to the Sun. Studying these energetic system, from particles contributes to NASA’s goal of understanding the galaxy— the very nature of space, which provides information that streams useful for protecting astronauts during space travel, as by. None of well as shedding light on the origins and evolution of this radiation the solar system. Thanks in part to ACE data, we now can harm hu- have a much better understanding of the zoo of space mans on Earth, particles and what causes their motion. but the biggest Artist conception of NASA’s Advanced Com- bursts of par- position Explorer. Credit: NASA Launched in 1997, ACE continues to provide key ticles from the Sun can flow into near-Earth space research about the space environment near Earth. causing a dynamic space weather system that can Its nine instruments were designed to observe the damage satellites and interfere with radio communi- wide range of particles in space, differentiating cation transmissions and navigation systems. We can between various elements, energies and charges. see such bursts erupt from afar, and even determine ACE was launched with two jobs: determine where if they are headed toward Earth —but it’s ACE that different types of particles originated and learn how feels them first, some 20 to 60 minutes before they they gained extra speed, since a large number of the impact Earth to provide us information about how individual particles in space are traveling faster than strong they were. ACE observations continue to be scientists would expect based solely on the tem- used by the US National Oceanic and Atmospheric perature of the material, suggesting that additional Administration’s Space Weather Prediction Center. acceleration processes must be at work. ACE is also capable of providing near-real-time ADDITIONAL RESOURCES: solar wind and magnetic field information that aids in forecasting space weather. ACE long served as Mission Project Home Page: Earth’s vanguard keeping an eye on space weather, http://www.srl.caltech.edu/ACE/ and paving the way for NOAA’s DSCOVR, which ACE Research: http://www.srl.caltech.edu/ACE/ launched in 2015 to take over day-to-day operations. ACENews/ACENews_Archives.html Orbiting around a point 900,000 miles away between ACE Data: http://www.srl.caltech.edu/ACE/ASC/ the Earth and our Sun, ACE records the combination FS-2019-??-???-GSFC www.nasa.gov.

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Astronomy & Astrophysics a Hipparcos Study of the Hyades
A&A 367, 111–147 (2001) Astronomy DOI: 10.1051/0004-6361:20000410 & c ESO 2001 Astrophysics A Hipparcos study of the Hyades open cluster Improved colour-absolute magnitude and Hertzsprung{Russell diagrams J. H. J. de Bruijne, R. Hoogerwerf, and P. T. de Zeeuw Sterrewacht Leiden, Postbus 9513, 2300 RA Leiden, The Netherlands Received 13 June 2000 / Accepted 24 November 2000 Abstract. Hipparcos parallaxes fix distances to individual stars in the Hyades cluster with an accuracy of ∼6per- cent. We use the Hipparcos proper motions, which have a larger relative precision than the trigonometric paral- laxes, to derive ∼3 times more precise distance estimates, by assuming that all members share the same space motion. An investigation of the available kinematic data confirms that the Hyades velocity field does not contain significant structure in the form of rotation and/or shear, but is fully consistent with a common space motion plus a (one-dimensional) internal velocity dispersion of ∼0.30 km s−1. The improved parallaxes as a set are statistically consistent with the Hipparcos parallaxes. The maximum expected systematic error in the proper motion-based parallaxes for stars in the outer regions of the cluster (i.e., beyond ∼2 tidal radii ∼20 pc) is ∼<0.30 mas. The new parallaxes confirm that the Hipparcos measurements are correlated on small angular scales, consistent with the limits specified in the Hipparcos Catalogue, though with significantly smaller “amplitudes” than claimed by Narayanan & Gould. We use the Tycho–2 long time-baseline astrometric catalogue to derive a set of independent proper motion-based parallaxes for the Hipparcos members.
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Michael Perryman
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Sdo Sdt Report.Pdf
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