-
1
-
-
0000412340
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-
note
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In 1995, the Hubble Space Telescope was used to observe a 2′ patch of sky for 225 hours [R. E. Williams et al., Astron. J. 112, 1335 (1996)]. These are the deepest images ever obtained of the high-redshift universe. About 1500 sources were identified in this small field. At the same depth, it would be possible to catalog ∼ 100 billion sources over the full sky.
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2
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0040232937
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note
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-1). The use of redshift will ultimately be supplanted by "distance" and "cosmic time" once the universal parameters have been tied down to sufficient accuracy (5% or better).
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3
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0040232932
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note
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Elements heavier than helium (Z > 2) are collectively referred to as "metals." Some of these can be used to provide a cosmic clock of when the star was born. H and He were mostly formed in the Big Bang and account for 98% by mass of all baryons in the universe. Li, Be, and B are very depleted as these are fragile elements that are easily destroyed. C and heavier elements up to Fe are mostly fused in stars. Because massive stars evolve rapidly and explode as supernovae, there is a general buildup of metals (for example, [Fe/H]) with time. Ten million years after the initial starburst, through the rapid neutron capture process (r-process), the type-II supernovae from the core collapse of massive stars enhance the even Z elements (so-called alpha particles) with respect to Fe. A billion years later, other sources (for example, type-Ia supernovae and asymptotic giant branch stars) enhance the odd Z elements through slow neutron capture (the s process). The relative fractions of r- and s-process elements can be used with [Fe/H] to provide a stellar clock.
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4
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0040232933
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The key difference between rotating and pressure-supported systems is how much energy radiated away during the formation process. If the stars formed before collapse, an isolated cloud shrinks rapidly without dissipation to produce a spheroidal system. A protogalactic gas cloud is expected to collapse more slowly, dissipate a lot of energy and, with its residual angular momentum, result in a rotating disk. The net angular momentum in galaxies is linked to tidal torquing between density fluctuations in the early universe. Later in the life of a galaxy, it can undergo collisions with galaxies of comparable mass or acquire smaller mass objects. The former process increases the pressure support, whereas the latter tends to add to the net rotation.
-
-
-
-
5
-
-
0001260867
-
-
R. Schaeffer and J. Silk, Eds. Elsevier, Amsterdam
-
S. D. M. White, in Cosmology and Large-Scale Structure, Les Houches, Session LX, R. Schaeffer and J. Silk, Eds. (Elsevier, Amsterdam, 1996), p. 349.
-
Cosmology and Large-Scale Structure, Les Houches, Session LX
, vol.1996
, pp. 349
-
-
White, S.D.M.1
-
10
-
-
0040232929
-
-
note
-
When astronomers use the term "baryon," they refer to protons and neutrons, which account for most of the visible mass of the universe. Dark matter is usually believed to be nonbaryonic, that is, made up of unidentified massive particles. Here, we are referring to matter that is locked up in stars, but a small fraction of baryons exists in the form of dust and gas dispersed throughout the Milky Way. In this context, we note the remarkable correlation discovered by R. B. Tully and J. R. Fisher [Astron. Astrophys. 54, 661 (1977)]: The peak rotation speed of a galaxy (largely determined by dark matter) is directly related to its intrinsic luminosity (determined by its baryons). This relation appears to hold for almost all disk galaxies if all baryon components are included in the luminosity. The baryon to dark matter ratio is ∼5%.
-
-
-
-
11
-
-
0034614669
-
-
C. Alcock, Science 287, 74 (2000); R. Buser, Science 287, 69 (2000).
-
(2000)
Science
, vol.287
, pp. 74
-
-
Alcock, C.1
-
12
-
-
0034614681
-
-
C. Alcock, Science 287, 74 (2000); R. Buser, Science 287, 69 (2000).
-
(2000)
Science
, vol.287
, pp. 69
-
-
Buser, R.1
-
15
-
-
0039641058
-
-
H. Morrison and A. Sarajedini, Eds. Astronomical Society of the Pacific, San Francisco
-
T. C. Beers, in Formation of the Halo: Inside and Out, vol. 92 of ASP Conference Series, H. Morrison and A. Sarajedini, Eds. (Astronomical Society of the Pacific, San Francisco, 1996), p. 130.
-
(1996)
Formation of the Halo: Inside and Out, Vol. 92 of ASP Conference Series
, vol.92
, pp. 130
-
-
Beers, T.C.1
-
17
-
-
85199125120
-
-
M. R. S. Hawkins, Mon. Not. R. Astron. Soc. 206, 433 (1984). RR Lyrae stars are a class of old (>10 Ca) metal-deficient variable stars that are easy to recognize from their pattern of variability.
-
(1984)
Mon. Not. R. Astron. Soc.
, vol.206
, pp. 433
-
-
Hawkins, M.R.S.1
-
20
-
-
0039641060
-
-
note
-
That is not to say that there are no important fossils in the disk. For example, some estimates put the ages of cool white dwarfs and evolved red giants at ∼10 Ca or more [T. D. Oswalt et al., Nature 382, 692 (1996); B. Edvardsson et al., Astron. Astrophys. 275, 101 (1993)].
-
-
-
-
21
-
-
0039619748
-
-
Cambridge Univ. Press, New York
-
S. van den Bergh, Galaxy Morphology and Classification (Cambridge Univ. Press, New York, 1998); A. Sandage, Carnegie Atlas of Galaxies (Carnegie Institution of Washington, Washington, DC, 1994).
-
Galaxy Morphology and Classification
, vol.1998
-
-
Van Den Bergh, S.1
-
22
-
-
0003771519
-
-
Carnegie Institution of Washington, Washington, DC
-
S. van den Bergh, Galaxy Morphology and Classification (Cambridge Univ. Press, New York, 1998); A. Sandage, Carnegie Atlas of Galaxies (Carnegie Institution of Washington, Washington, DC, 1994).
-
(1994)
Carnegie Atlas of Galaxies
-
-
Sandage, A.1
-
24
-
-
0008541840
-
-
T. X. Thuan, C. Balkowski, J. Tran Thanh Van, Eds. Editions Frontieres, Paris
-
K. C. Freeman, in Physics of Nearby Galaxies: Nature or Nurture, T. X. Thuan, C. Balkowski, J. Tran Thanh Van, Eds. (Editions Frontieres, Paris, 1992), p. 201.
-
Physics of Nearby Galaxies: Nature or Nurture
, vol.1992
, pp. 201
-
-
Freeman, K.C.1
-
27
-
-
0039641056
-
-
thesis, Observatoire de Paris
-
C. Alard, thesis, Observatoire de Paris (1996).
-
(1996)
-
-
Alard, C.1
-
28
-
-
0039641057
-
-
L Blitz and P. Teuben, Eds. Reidel, Dordrecht, Netherlands
-
J. E. Norris, in Unsolved Problems in the Milky Way, L Blitz and P. Teuben, Eds. (Reidel, Dordrecht, Netherlands, 1996), pp. 353-366.
-
(1996)
Unsolved Problems in the Milky Way
, pp. 353-366
-
-
Norris, J.E.1
-
38
-
-
0039641055
-
-
F. Hammer et al., Eds. (Editions Frontieres, Paris, in press)
-
L. D. Matthews, W. van Driel, J. S. Gallagher, in Building Galaxies: From the Primordial Universe to the Present, F. Hammer et al., Eds. (Editions Frontieres, Paris, in press).
-
Building Galaxies: From the Primordial Universe to the Present
-
-
Matthews, L.D.1
Van Driel, W.2
Gallagher, J.S.3
-
39
-
-
0040827514
-
-
D. L. Block, I. Puerari, A. Stockton, D. Ferreira, Eds. (Kluwer, Dordrecht, Netherlands, in press)
-
K. C. Freeman, in Toward a New Millennium in Morphology, D. L. Block, I. Puerari, A. Stockton, D. Ferreira, Eds. (Kluwer, Dordrecht, Netherlands, in press).
-
Toward a New Millennium in Morphology
-
-
Freeman, K.C.1
-
42
-
-
0037852982
-
-
J. Couture, R. Racine, W. Harris, S. Holland, Astron. J. 109, 2050 (1995).
-
(1995)
Astron. J.
, vol.109
, pp. 2050
-
-
Couture, J.1
Racine, R.2
Harris, W.3
Holland, S.4
-
51
-
-
0000159690
-
-
B. M. Tinsley and R. B. Larson, Eds. Yale Univ. Press, New Haven, CT
-
L. Searle, in The Evolution of Galaxies and Stellar Populations, B. M. Tinsley and R. B. Larson, Eds. (Yale Univ. Press, New Haven, CT, 1977), p. 219.
-
(1977)
The Evolution of Galaxies and Stellar Populations
, pp. 219
-
-
Searle, L.1
-
60
-
-
0033523905
-
-
A. Helmi et al., Nature 402, 53 (1999).
-
(1999)
Nature
, vol.402
, pp. 53
-
-
Helmi, A.1
-
61
-
-
0011134944
-
-
H. Morrison and A. Sarajedini, Eds. Astronomical Society of the Pacific, San Francisco
-
S. R. Majewski, S. L. Hawley, J. A. Munn, in Formation of the Halo: Inside and Out, vol. 92 of ASP Conferences Series, H. Morrison and A. Sarajedini, Eds. (Astronomical Society of the Pacific, San Francisco, 1996), p. 119.
-
(1996)
Formation of the Halo: Inside and Out, Vol. 92 of ASP Conferences Series
, vol.92
, pp. 119
-
-
Majewski, S.R.1
Hawley, S.L.2
Munn, J.A.3
-
63
-
-
0039048974
-
-
note
-
The coordinates (l, b) are Galactic coordinates defined with respect to the plane of the Milky Way. The origin is at the sun. Longitude l is measured along the plane where l = 0° points toward the Galactic center and l = +90° is the direction of the sun's motion; latitude b is measured in a plane perpendicular to the Milky Way, where b = +90° is the North Galactic Pole.
-
-
-
-
64
-
-
0001500116
-
-
R. Ibata et al., Astron. J. 113, 634 (1997).
-
(1997)
Astron. J.
, vol.113
, pp. 634
-
-
Ibata, R.1
-
69
-
-
0040232916
-
-
note
-
The total intensity of a cloud at 21 cm is related to its mass and distance. For a self-gravitating cloud, the intrinsic width of the hydrogen line is also related to the cloud's mass but with a different dependence on distance. Thus, a crude "virial" distance can be derived for clouds held together by gravity.
-
-
-
-
70
-
-
0039048973
-
-
note
-
The Local Group of galaxies is a loose collection of ∼40 galaxies that includes the Milky Way, M31, and M33.
-
-
-
-
75
-
-
0039227607
-
-
J. R. Mould, Nature 395A (supplement), 20 (1998).
-
(1998)
Nature
, vol.395 A
, Issue.SUPPL.
, pp. 20
-
-
Mould, J.R.1
-
76
-
-
0011114133
-
-
B. Gibson, T. Axelrod, M. Putman, Eds. Astronomical Society of the Pacific, San Francisco
-
G. Da Costa, in The Third Stromlo Symposium: The Galactic Halo, vol. 165 of ASP Conference Series, B. Gibson, T. Axelrod, M. Putman, Eds. (Astronomical Society of the Pacific, San Francisco, 1999), p. 153.
-
(1999)
The Third Stromlo Symposium: The Galactic Halo, Vol. 165 of ASP Conference Series
, vol.165
, pp. 153
-
-
Da Costa, G.1
-
77
-
-
33749182635
-
-
used radioactive dating (that is, isotope ratios) to put a lower age limit of 15 Ga on a halo star rich in r-processed elements
-
C. Sneden et al. [Astrophys. J. 467, 819 (1996)] used radioactive dating (that is, isotope ratios) to put a lower age limit of 15 Ga on a halo star rich in r-processed elements.
-
(1996)
Astrophys. J.
, vol.467
, pp. 819
-
-
Sneden, C.1
-
83
-
-
0002353695
-
-
S. M. Faber, Ed. Springer-Verlag, New York
-
F. Schweizer, in Nearly Normal Galaxies: From the Planck Time to the Present, S. M. Faber, Ed. (Springer-Verlag, New York, 1987), p. 18.
-
Nearly Normal Galaxies: From the Planck Time to the Present
, vol.1987
, pp. 18
-
-
Schweizer, F.1
-
87
-
-
0039641054
-
-
note
-
Tidal shocking of globular clusters occurs when the external gravitational field in which they are moving changes on a time comparable with the orbital period of stars within the cluster.
-
-
-
-
89
-
-
0011123235
-
-
A. Blaauw and M. Schmidt, Eds. Univ. of Chicago Press, Chicago
-
J. Oort, in Galactic Structure, A. Blaauw and M. Schmidt, Eds. (Univ. of Chicago Press, Chicago, 1965), p. 455.
-
Galactic Structure
, vol.1965
, pp. 455
-
-
Oort, J.1
-
90
-
-
0011145395
-
-
G. H. Smith and J. P. Brodie, Eds. Astronomical Society of the Pacific, San Francisco
-
B. W. Carney, in The Globular Cluster-Galaxy Connection, vol 48 of ASP Conference Series, G. H. Smith and J. P. Brodie, Eds. (Astronomical Society of the Pacific, San Francisco, 1993), p. 234.
-
(1993)
The Globular Cluster-Galaxy Connection, Vol 48 of ASP Conference Series
, vol.48
, pp. 234
-
-
Carney, B.W.1
-
92
-
-
0033523901
-
-
Y.-W. Lee et al. Nature 402, 55 (1999).
-
(1999)
Nature
, vol.402
, pp. 55
-
-
Lee, Y.-W.1
-
94
-
-
4243216575
-
-
in press
-
M. S. Yun et al., Astrophys. J., in press (available at http://xxx.lanl.gov/abs/astro-ph/9909361).
-
Astrophys. J.
-
-
Yun, M.S.1
-
97
-
-
0040232914
-
-
note
-
Hipparcos was launched by the European Space Agency (ESA) on an Ariane rocket in August 1989 and was switched off 4 years later.
-
-
-
-
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-
-
note
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Proper motion accuracy of 1 milli-arc sec per year is extremely slow, that is, 30 billion times slower than the hour hand when you check your analog wrist-watch and 5 million times slower than human hair growth seen from a distance of 1 m. Future astrometric satellites will have a sensitivity that is 1000 times more accurate.
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-
-
-
103
-
-
0040143488
-
-
P. T. de Zeeuw, R. Hoogewerf, J. H. J. de Bruijne, A. G. A. Brown, A. Blaauw, Astron. J. 117, 354 (1999).
-
(1999)
Astron. J.
, vol.117
, pp. 354
-
-
De Zeeuw, P.T.1
Hoogewerf, R.2
De Bruijne, J.H.J.3
Brown, A.G.A.4
Blaauw, A.5
-
104
-
-
0039048969
-
-
A. Helmi and S. D. M. White, available at http:// xxx.lanl.gov/abs/astro-ph/9901102.
-
-
-
Helmi, A.1
White, S.D.M.2
-
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-
-
note
-
There are four astrometric missions planned for the next decade. These are the proposed German DIVA (Deutsches Interferometer für Vielkanalphotometrie und Astrometrie) mission (∼2003); the approved U.S. FAME (Full-sky Astrometric Mapping Explorer) mission (∼2005); the pointed SIM (Space Interferometry Mission) (∼2005); and the proposed ESA GAIA mission (∼2009), which will observe 1 billion stars to mag 20, with accuracy 10 micro-arc sec at a V magnitude of 15. Information on these missions is available at the following addresses, respectively: http://www.aip.de: 8080/~preprint/preprints/1997/1997_roe1.html, http://aa.usno.navy.mil/FAME/, http://sim.jpl.nasa.gov/, and http://astro.estec.esa.nl/GAIA.
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There are two microwave background space missions planned for the next decade. These are the U.S. MAP (Microwave Anisotropy Probe) mission (Fall 2000) and the ESA Planck Surveyor mission (∼2004). Information on these missions is available at http://map.gsfc.nasa.gov/ and http://aether. lbl.gov/www/projects/cosa/, respectively.
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At present, the ages of metal-poor stars cannot be tied down to better than 1 Ga, the time elapsed between z = 6 and z = 3. This is a particular handicap to identifying free-fall collapse in the early universe from the stellar record. A bigger concern is whether there really is a well defined correlation between age and metallicity. If star formation in the early universe was unevenly distributed on large scales, we would expect young stars today within these metal-poor regions (for example, voids) to reflect the metal abundance of the surrounding ISM.
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To Olin Eggen, who discovered moving star groups in the galactic halo and kept the flame alive for almost 40 years.
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