Institution
Smithsonian Astrophysical Observatory
Facility•Cambridge, Massachusetts, United States•
About: Smithsonian Astrophysical Observatory is a facility organization based out in Cambridge, Massachusetts, United States. It is known for research contribution in the topics: Galaxy & Stars. The organization has 1665 authors who have published 3622 publications receiving 132183 citations. The organization is also known as: SAO.
Topics: Galaxy, Stars, Telescope, Luminosity, Star formation
Papers published on a yearly basis
Papers
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TL;DR: In this paper, the authors reported the results of deep imaging and spectrophotometry of the arcs around SN1987A and verified the nebular arcs as echoes of the light of SN 1987A near maximum.
Abstract: Direct imaging1,2 of supernova 1987A has revealed two semicircular arcs around the explosion site. Similar arcs around Nova Persei3,4 and Nova V732 Sagittarii5 have been explained as light echoes from the time of maximum luminosity of the outburst. Here we report the results of deep imaging and spectrophotometry of the arcs around SN1987A. The spectrophotometry verifies the nebular arcs as echoes of the light of SN1987A near maximum. The clouds must be at distances of 115 and 305 pc in front of SN1987A. We also observe an apparent proper motion for the inner echo of 1.8 arcsec per month which, at 16 times the speed of light, is highly superluminal.
42 citations
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TL;DR: In this paper, the Secret Lives of Cepheids (SLiC) program has been carried out at Villanova University to study aspects and behaviors of classical CEPheids that are still not well understood.
Abstract: Over the past decade, the Secret Lives of Cepheids (SLiC) program has been carried out at Villanova University to study aspects and behaviors of classical Cepheids that are still not well understood. In this, the first of several planned papers on program Cepheids, we report the current results for δ Cep, the Cepheid prototype. Ongoing photometry has been obtained to search for changes in the pulsation period, light-curve morphology, and amplitude. Combining our photometry with the times of maximum light compilation by Berdnikov et al. returns a small period change of dP/dt ≈–0.1006 ± 0.0002 s yr^-1. There is also evidence for a gradual light amplitude increase of ~0.011 mag (V band) and ~0.012 mag (B band) per decade over the last ~50 years. In addition, Hubble Space Telescope (HST) Cosmic Origins Spectrograph (COS) UV spectrophotometry and XMM-Newton X-ray data were carried out to investigate the high-temperature plasmas present above the Cepheid photospheres. In total, from the five visits (eight exposures) with XMM-Newton, δ Cep is found to be a soft X-ray source (L X (0.3-2 keV) ≈4.5-13 × 10^28 erg s^-1) with peak flux at kT = 0.6-0.9 keV. The X-ray activity is found to vary, possibly in phase with the stellar pulsations. From 2010-2013, nine observations of δ Cep were carried out with HST-COS. The UV emissions are also variable and well phased with the stellar pulsations. Maximum UV line emissions occur near, or slightly before, maximum optical light, varying by as much as 20 times. This variability shows that pulsation-induced shock heating plays a significant role in Cepheid atmospheres, possibly in addition to a quiescent, magnetic heating. The results of this study show Cepheid atmospheres to be rather complex and dynamic.
42 citations
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TL;DR: In this paper, a simple semiquantitative explanation is presented which accounts both for the presence of the azimuthal brightness variations in Saturn's ring A and for their absence in ring B.
42 citations
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TL;DR: In this article, the authors determined the Ne/O ratio from solar and Heliospheric Observatory (SOHO)/Solar Ultraviolet Measurement of Emitted Radiation (SUMER) off-disk observations of quiescent streamers over the 1996-2008 period.
Abstract: In this work we determine the Ne/O abundance ratio from Solar and Heliospheric Observatory (SOHO)/Solar Ultraviolet Measurement of Emitted Radiation (SUMER) off-disk observations of quiescent streamers over the 1996-2008 period. We find that the Ne/O ratio is approximately constant over solar cycle 23 from 1996 to 2005, at a value of 0.099 ± 0.017; this value is lower than the transition region determinations from the quiet Sun used to infer the neon photospheric abundance from the oxygen photospheric abundance. Also, the Ne/O ratio we determined from SUMER is in excellent agreement with in situ determinations from ACE/SWICS. In 2005-2008, the Ne/O abundance ratio increased with time and reached 0.25 ± 0.05, following the same trend found in the slowest wind analyzed by ACE/SWICS. Further, we measure the absolute abundance in the corona for both oxygen and neon from the data set of 1996 November 22, obtaining A o = 8.99 ± 0.04 and A Ne = 7.92 ± 0.03, and we find that both elements are affected by the first ionization potential (FIP) effect, with oxygen being enhanced by a factor of 1.4-2.1 over its photospheric abundance, and neon being changed by a factor of 0.75-1.20. We conclude that the Ne/O ratio is not constant in the solar atmosphere, both in time and at different heights, and that it cannot be reliably used to infer the neon abundance in the photosphere. Also, we argue that the FIP effect was less effective during the minimum of solar cycle 24, and that the Ne/O = 0.25 ± 0.05 value measured at that time is closer to the true photospheric value, leading to a neon photospheric abundance larger than assumed by ≈40%. We discuss the implications of these results for the solar abundance problem, for the FIP effect, and for the identification of the source regions of the solar wind.
42 citations
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TL;DR: In this article, the petrology of 20 lithic fragments is described and compared to that of other highland sites and an identification of the major types of rocks that compose the lunar terrae is attempted, and their probable petrogenesis is discussed.
42 citations
Authors
Showing all 1666 results
Name | H-index | Papers | Citations |
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Lee Hartmann | 134 | 579 | 57649 |
David W. Latham | 127 | 852 | 67390 |
Chi Lin | 125 | 1313 | 102710 |
William R. Forman | 120 | 800 | 53717 |
Edo Berger | 118 | 578 | 47147 |
Joseph Silk | 108 | 1317 | 58146 |
Jon M. Miller | 107 | 706 | 50126 |
Fabrizio Fiore | 106 | 804 | 43260 |
Randall V. Martin | 105 | 396 | 57917 |
Christopher F. McKee | 103 | 368 | 44919 |
John P. Hughes | 101 | 616 | 36396 |
Wallace L. W. Sargent | 99 | 397 | 30265 |
Bryan Gaensler | 99 | 844 | 39851 |
Alexey Vikhlinin | 99 | 367 | 35822 |
Matthew J. Holman | 99 | 320 | 46577 |