Seventh Sloan Sky Survey Scoops Stellar Spoils
What's Hot in Physics, September/October 2010
By Simon Mitton
The publication of the Seventh Data Release (DR7) of the Sloan Digital Sky Survey (SDSS) marks the completion of the original goals of a project that commenced two decades ago. SDSS is the most ambitious optical survey of the sky in the history of astronomy. Hot Paper #9 now takes over from #10, the sixth release of SDSS, by adding a further two years of observations. Meanwhile the Physics Hot Papers leader-board is headed once again by the cosmological findings from five years of operation of the Wilkinson Microwave Anisotropy Probe, with #3 on the grid also coming from the WMAP team.
Elsewhere in the line-up this period, laboratory physics scores highly, with #2 on 100% internal quantum efficiency of solar cells, and three papers on superconductivity (#5, #7, and #8), and one on graphene at #4. Although the SDSS paper is ranked #9 for now, the citation history of the project suggests it will soar to top the rankings.
Read a Fast Breaking Paper Commentary by Eiichiro Komatsu that features
figures & descriptions of his work with WMAP.
SDSS is an enormous project that has used a dedicated 2.5m telescope to image stars, galaxies, and quasars scattered over 10,000 square degrees of the northern sky. The survey provides deep multicolor images. Its database has spectroscopic results (including redshifts) for 930,000 galaxies, 120,000 quasars, and 460,000 stars. The summary paper #9 credits 199 authors from 103 institutions. The staggering productivity of the telescope is a child of its brilliant design. During observation the telescope performs drift scans, the most efficient way to use a CCD (charge-coupled device) camera for astronomy, and its fiber-fed spectrographs can complete up to 640 spectra per plate.
DR7 includes all data from the six earlier releases, so it enables the community to examine 1.6 x 106 stars and galaxies using one-stop shopping. DR7 has plenty of value-added content compared to its predecessors. The Legacy survey of 7,500 square degrees in the North Galactic Cap is now complete, and it provides contiguous imaging and spectroscopy. The redshifts of galaxies in the Legacy survey are used to construct three-dimensional maps of the structure of the universe out to a redshift of ~0.4.
The depth of the survey is breathtaking in terms of quasars, which have been seen at record distances, and at earlier cosmic epochs. These objects probe cosmic conditions when the ionized universe had cooled sufficiently to form neutral hydrogen.
SDSS is also used in a mode that repeatedly scans selected strips of the sky. Paper #9 announces repeat surveying that has discovered almost 500 spectroscopically confirmed Type Ia supernovae, with superb light curves. That is of cosmological significance because Type Ia is a sub-category of supernovae that are standard candles for distance determination. These beacons lit the way to the discovery of dark energy and the accelerating universe. A better understanding of the astrophysics of Type Ia supernovae can only increase confidence in cosmological models.
FACT: The Wilkinson Microwave Anisotropy Probe (WMAP) is a NASA Explorer mission that launched June 2001 to make fundamental measurements of cosmology -- the study of the properties of our universe as a whole. WMAP has been stunningly successful, producing our new Standard Model of Cosmology. WMAP continues to collect high quality scientific data.
SDSS is used to probe the structure of the Milky Way by examining the positions and velocities of nearly half a million stars. Its range extends from our local neighborhood to the outer limits of the galactic halo, over 105 light years away. In the halo, SDSS data show a complex substructure, indicative of distinct families of stars. There is evidence that galactic mergers and stellar cannibalism have added to the bulk of the Milky Way.
This survey has, in a decade, spawned about 2,200 papers that use its data as a primary source, and its predecessors have accumulated some 70,000 citations. These are spectacular achievements for a project in observational astronomy, and much of the success derives from a new kind of science: publication of results by public release on websites with impressive data-mining tools. There are no restrictions whatsoever on access, so anyone can join the party.
Having met its original goals, the Sloan survey is now moving into a third phase that extends its mission to 2014. Within the Milky Way, fainter stars in the halo will be sought in order to probe the distant halo. About 11,000 bright stars will be monitored for radial velocity variations that would indicate planetary companions. And 1.75 x 106 galaxy and quasar redshifts will be measured for cosmological purposes.
Dr. Simon Mitton is a Fellow of St. Edmund’s College, Cambridge, U.K.
What's Hot in Physics | |||
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Rank | Paper |
Cites This Period Mar-Apr 10 |
Rank Last Period Jan-Feb 10 |
1 | E. Komatsu, et al., "Five-year Wilkinson Microwave Anisotropy Probe observations: Cosmological interpretation," Astrophys. J. Suppl. Ser., 180(2): 330-76, February 2009. [14 institutions worldwide] *406EI | 144 | 1 |
2 | S.H. Park, et al., "Bulk heterojunction solar cells with internal quantum efficiency approaching 100%," Nature Photonics, 3(5): 297-302, May 2009. [U. Calif., Santa Barbara; Gwangju Inst. Sci. & Tech., S. Korea; U. Laval, Quebec City, Canada] *447UY | 75 | 4 |
3 | J. Dunkley, et al., "Five-year Wilkinson Microwave Anisotropy Probe observations: Likelihoods and parameters from the WMAP data," Astrophys. J. Suppl. Ser., 180(2): 306-29, February 2009. [14 U.S. and Canadian institutions] *406EI | 66 | 2 |
4 | K.I. Bolotin, et al., "Ultrahigh electron mobility in suspended graphene," Solid State Comm., 146(9-10): 351-5, June 2008. [Columbia U., New York, NY; Natl. High Magnetic Field Lab, Tallahassee, FL; Bell Labs, Murray Hill, NJ] *312AM | 44 | 6 |
5 | F.-C. Hsu, et al., "Superconductivity in the PbO-type structure alpha-FeSe," PNAS, 105(38): 14262-4, 23 September 2008. [Acad. Sinica, Taipei, Taiwan; Natl. Tsing Hua U., Hsinchu, Taiwan; Duke U., Durham, NC] *353TY | 39 | † |
6 | O. Adriani, et al., "An anomalous positron abundance in cosmic rays with energies 1.5-100 GeV," Nature, 458(7238): 607-9, 2 April 2009. [17 institutions worldwide] *427RK | 37 | 3 |
7 | X.H. Chen, et al., "Superconductivity at 43K in SmFeAsO1-xFx," Nature, 453(7196): 761-2, 5 June 2008. [U. Sci. & Tech., Hefei, China] *308UK | 34 | 8 |
8 | Z.A. Ren, et al., "Superconductivity at 55 K in iron-based F-doped layered quaternary compound Sm[O1-xFx]FeAs," Chinese Phys. Lett., 25(6): 2215-6, June 2008. [Chinese Acad. Sci, Beijing] *306MN | 33 | † |
9 | K.N. Abazajian, et al., "The Seventh Data Release of the Sloan Digital Sky Survey," Astrophys. J. Suppl. Ser., 182(2): 543-58, June 2009. [110 institutions worldwide] *448UE | 29 | 7 |
10 | J.K. Adelman-McCarthy, et al., "The Sixth Data Release of the Sloan Digital Sky Survey," Astrophys. J. Suppl. Ser., 175(2): 297-313, April 2008. [84 institutions worldwide] *327WN | 27 | † |
SOURCE: Thomson Reuters Hot Papers Database. Read the Legend. |
KEYWORDS: Sloan Digital Sky Survey, SDSS, astronomy, cosmology, quasars, Type Ia supernovae.