The Apache Point Observatory Galactic
Evolution Experiment (APOGEE)
Item Type Article
Authors Majewski, Steven R.; Schiavon, Ricardo P.; Frinchaboy, P. M.;
Prieto, Carlos Allende; Barkhouser, Robert; Bizyaev, Dmitry;
Blank, Basil; Brunner, Sophia; Burton, Adam; Carrera, R.;
Chojnowski, S. Drew; Cunha, Kátia; Epstein, Courtney; Fitzgerald,
Greg; Pérez, Ana E. García; Hearty, Fred R.; Henderson, Chuck;
Holtzman, J.; Johnson, Jennifer A.; Lam, Charles R.; Lawler,
James E.; Maseman, Paul; Mészáros, Szabolcs; Nelson, Matthew;
Nguyen, Duy Coung; Nidever, David L.; Pinsonneault, Marc;
Shetrone, M.; Smee, Stephen; Smith, Verne V.; Stolberg, Todd;
Skrutskie, Michael F.; Walker, Eric; Wilson, John C.; Zasowski,
Gail; Anders, Friedrich; Basu, Sarbani; Beland, Stephane;
Blanton, Michael R.; Bovy, Jo; Brownstein, Joel R.; Carlberg, J.
K.; Chaplin, William; Chiappini, Cristina; Eisenstein, Daniel J.;
Elsworth, Yvonne; Feuillet, Diane; Fleming, Scott W.; Galbraith-
Frew, Jessica; García, Rafael A.; García-Hernández, D. A.;
Gillespie, Bruce A.; Girardi, Léo; Gunn, James E.; Hasselquist,
Sten; Hayden, Michael R.; Hekker, Saskia; Ivans, Inese;
Kinemuchi, Karen; Klaene, Mark; Mahadevan, Suvrath; Mathur,
S.; Mosser, Benoît; Muna, Demitri; Munn, Jeffrey A.; Nichol,
Robert C.; O’Connell, Robert W.; Parejko, John K.; Robin, A. C.;
Rocha-Pinto, Helio; Schultheis, M.; Serenelli, Aldo M.; Shane,
Neville; Aguirre, Victor Silva; Sobeck, Jennifer S.; Thompson,
Benjamin; Troup, N.; Weinberg, David H.; Zamora, Olga
Citation The Apache Point Observatory Galactic Evolution Experiment
(APOGEE) 2017, 154 (3):94 The Astronomical Journal
DOI 10.3847/1538-3881/aa784d
Publisher IOP PUBLISHING LTD
The Apache Point Observatory Galactic Evolution Experiment (APOGEE)
Steven R. Majewski
1
, Ricardo P. Schiavon
2,3
, Peter M. Frinchaboy
4
, Carlos Allende Prieto
5,6
, Robert Barkhouser
7
,
Dmitry Bizyaev
8,9
, Basil Blank
10
, Sophia Brunner
1
, Adam Burton
1
, Ricardo Carrera
5,6
, S. Drew Chojnowski
1,11
, Kátia Cunha
12,13
,
Courtney Epstein
14
, Greg Fitzgerald
15
, Ana E. García Pérez
1,5
, Fred R. Hearty
1,16
, Chuck Henderson
10
, Jon A. Holtzman
11
,
Jennifer A. Johnson
14
, Charles R. Lam
1
, James E. Lawler
17
, Paul Maseman
13
, Szabolcs Mészáros
5,6,18,52
, Matthew Nelson
1
,
Duy Coung Nguyen
19
, David L. Nidever
1,20
, Marc Pinsonneault
14
, Matthew Shetrone
21
, Stephen Smee
7
, Verne V. Smith
13,22
,
Todd Stolberg
15
, Michael F. Skrutskie
1
, Eric Walker
1
, John C. Wilson
1
, Gail Zasowski
1,7
, Friedrich Anders
23
, Sarbani Basu
24
,
Stephane Beland
25,26
, Michael R. Blanton
27
, Jo Bovy
28,50,51
, Joel R. Brownstein
29
, Joleen Carlberg
1,30
, William Chaplin
31,32
,
Cristina Chiappini
23
, Daniel J. Eisenstein
33
, Yvonne Elsworth
31
, Diane Feuillet
11
, Scott W. Fleming
34,35
, Jessica Galbraith-Frew
29
,
Rafael A. García
36
, D. Aníbal García-Hernández
5,6
, Bruce A. Gillespie
7
, Léo Girardi
37,38
, James E. Gunn
39
, Sten Hasselquist
1,11
,
Michael R. Hayden
11
, Saskia Hekker
32,40
, Inese Ivans
29
, Karen Kinemuchi
8
, Mark Klaene
8
, Suvrath Mahadevan
16
, Savita Mathur
41
,
Benoît Mosser
42
, Demitri Muna
14
, Jeffrey A. Munn
43
, Robert C. Nichol
44
, Robert W. O ’Connell
1
, John K. Parejko
45
, A. C. Robin
46
,
Helio Rocha-Pinto
38,47
, Matthias Schultheis
48
, Aldo M. Serenelli
49
, Neville Shane
1
, Victor Silva Aguirre
32
, Jennifer S. Sobeck
1
,
Benjamin Thompson
4
, Nicholas W. Troup
1
, David H. Weinberg
14
, and Olga Zamora
5,6
1
Department of Astronomy, University of Virginia, Charlottesville, VA 22904-4325, USA
2
Gemini Observatory, 670 N. A’Ohoku Place, Hilo, HI 96720, USA
3
Astrophysics Research Institute, Liverpool John Moores University, 146 Brownlow Hill, Liverpool, L3 5RF, UK
4
Department of Physics and Astronomy, Texas Christian University, Fort Worth, TX 76129, USA
5
Instituto de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, Spain
6
16 Departamento de Astrofísica, Universidad de La Laguna, E-38206 La Laguna, Tenerife, Spain
7
Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218, USA
8
Apache Point Observatory and New Mexico State University, P.O. Box 59, Sunspot, NM, 88349-0059, USA
9
Sternberg Astronomical Institute, Moscow State University, Universitetsky prosp. 13, Moscow, Russia
10
Pulse Ray Machining & Design, 4583 State Route 414, Beaver Dams, NY 14812 USA
11
New Mexico State University, Las Cruces, NM 88003, USA
12
Observatório Nacional, Rio de Janeiro, RJ 20921-400, Brazil
13
Steward Observatory, University of Arizona, Tucson, AZ 85721, USA
14
The Ohio State University, Columbus, OH 43210, USA
15
New England Optical Systems, 237 Cedar Hill Street, Marlborough, MA 01752 USA
16
Department of Astronomy & Astrophysics, The Pennsylvania State University, 525 Davey Laboratory,
University Park PA 16802, USA
17
Department of Physics, University of Wisconsin-Madison, 1150 University Avenue, Madison, WI 53706, USA
18
ELTE Gothard Astrophysical Observatory, H-9704 Szombathely, Szent Imre Herceg St. 112, Hungary
19
Dunlap Institute for Astronomy and Astrophysics, University of Toronto, Toronto, Ontario, Canada
20
Department of Astronomy, University of Michigan, Ann Arbor, MI 48109, USA
21
University of Texas at Austin, McDonald Observatory, Fort Davis, TX 79734, USA
22
National Optical Astronomy Observatories, PO Box 26732, Tucson, AZ 85719, USA
23
Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, D-14482 Potsdam, Germany
24
Department of Astronomy, Yale University, PO Box 208101, New Haven, CT 06520-8101 USA
25
Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO 80303, USA
26
Center for Astrophysics and Space Astronomy, University of Colorado Boulder, Boulder, CO 80303, USA
27
Center for Cosmology and Particle Physics, Department of Physics, New York University,
4 Washington Place, New York, NY 10003, USA
28
Institute for Advanced Study, Einstein Drive, Princeton, NJ 08540, USA
29
Department of Physics and Astronomy, University of Utah, 115 S 1400 E #201 Salt Lake City, UT 84112 USA
30
NASA Goddard Space Flight Center, Code 667, Greenbelt, MD 20771, USA
31
School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT, UK
32
Stellar Astrophysics Centre (SAC), Department of Physics and Astronomy, Aarhus University,
Ny Munkegade 120, DK-8000 Aarhus C, Denmark
33
Harvard-Smithsonian Center for Astrophysics, 60 Garden St., MS #20, Cambridge, MA 02138, USA
34
Computer Sciences Corporation, 3700 San Martin Dr, Baltimore, MD 21218, USA
35
Space Telescope Science Institute, 3700 San Martin Dr, Baltimore, MD 21218, USA
36
Laboratoire AIM, CEA/DSM—CNRS— Univ. Paris Diderot—IRFU/SAp, Centre de Saclay,
F-91191 Gif-sur-Yvette Cedex, France
37
Osservatorio Astronomico di Padova—INAF, Vicolo dell’Osservatorio 5, I-35122 Padova, Italy
38
Laboratório Interinstitucional de e-Astronomia—LIneA, Rua Gal. José Cristino 77, Rio de Janeiro, RJ—20921-400, Brazil
39
Department of Astrophysical Sciences, Peyton Hall, Princeton University 08544, USA
40
Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, D-37077 Göttingen, Germany
41
Space Science Institute, 4750 Walnut street, Suite 205, Boulder, CO 80301 USA
42
LESIA, CNRS, Université Pierre et Marie Curie, Universit Denis Diderot, Observatoire de Paris,
F-92195 Meudon Cedex, France
43
US Naval Observatory, Flagstaff Station, 10391 West Naval Observatory Road, Flagstaff, AZ 86005-8521, USA
44
Institute of Cosmology and Gravitation, University of Portsmouth, Portsmouth, UK
45
Department of Physics, Yale University, 260 Whitney Ave, New Haven, CT 06520, USA
46
Institut Utinam, CNRS UMR6213, Université de Franche-Comté, OSU THETA Franche-Comté-Bourgogne,
Observatoire de Besançon, BP 1615, F-25010 Besançon Cedex, France
47
Universidade Federal do Rio de Janeiro, Observatório do Valongo, Ladeira do Pedro Antônio 43,
20080-090 Rio de Janeiro, Brazil
The Astronomical Journal, 154:94 (46pp), 2017 September https://doi.org/10.3847/1538-3881/aa784d
© 2017. The American Astronomical Society. All rights reserved.
1
48
Université de Nice Sophia-Antipolis, CNRS, Observatoire de Côte d’Azur, Laboratoire Lagrange, F-06304 Nice Cedex 4, France
49
Institute of Space Sciences (CSIC-IEEC) Campus UAB, Torre C5 parell 2 Bellaterra, E-08193 Spain
50
Department of Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON M5S 3H4, Canada
Received 2015 September 16; revised 2017 June 6; accepted 2017 June 6; published 2017 August 14
Abstract
The Apache Point Observatory Galactic Evolution Experiment (APOGEE), one of the programs in the Sloan
Digital Sky Survey III (SDSS-III), has now completed its systematic, homogeneous spectroscopic survey sampling
all major populations of the Milky Way. After a three-year observing campaign on the Sloan 2.5 m Telescope,
APOGEE has collected a half million high-resolution (R∼22,500), high signal-to-noise ratio (>100), infrared
(1.51–1.70 μm) spectra for 146,000 stars, with time series information via repeat visits to most of these stars. This
paper describes the motivations for the survey and its overall design—hardware, field placement, target selection,
operations—and gives an overview of these aspects as well as the data reduction, analysis, and products. An index
is also given to the complement of technical papers that describe various critical survey components in detail.
Finally, we discuss the achieved survey performance and illustrate the variety of potential uses of the data products
by way of a number of science demonstrations, which span from time series analysis of stellar spectral variations
and radial velocity variations from stellar companions, to spatial maps of kinematics, metallicity, and abundance
patterns across the Galaxy and as a function of age, to new views of the interstellar medium, the chemistry of star
clusters, and the discovery of rare stellar species. As part of SDSS-III Data Release 12 and later releases, all of the
APOGEE data products are publicly available.
Key words: Galaxy: abundances – Galaxy: evolution – Galaxy: formation – Galaxy: kinematics and dynamics –
Galaxy: stellar content – Galaxy: structure
1. Introduction
1.1. Galactic Archaeology Surveys
Modern astrophysics has taken two general observational
approaches to understand the evolution of galaxies. On the one
hand, increasingly larger aperture telescopes, on the ground and
in space, give access to the high-redshift universe and offer
“low-resolution” snapshots of ever earlier phases of galaxy
evolution. On the other hand, increasingly efficient, multi-
plexing photometric and spectroscopic instrumentation, often
on smaller, workhorse telescopes, has made possible enormous,
definitive surveys of nearby galaxies, yielding a “high-
resolution (HR)” view of the present state of these systems.
These data can be tested against “end state” predictions for the
growth of large structures in the universe to provide critical
constraints on cosmological models—so-called “near-field
cosmology”. These two observational approaches—overviews
of global properties at high redshift versus more detailed
information at low redshift—provide complementary informa-
tion that must be accommodated by evolutionary theories.
The highest-granularity information about galaxy evolution
is provided by stars in our own Milky Way, whose present
spatial distributions, ages, chemistry, and kinematics contain
fossilized clues to its formation. Guided by detailed models for
the chemical and dynamical evolution of stellar populations,
critical telltale signatures and correlations within the above
observables provide constraints on the model predictions for
physical quantities that cannot be observed directly, such as the
history of star formation, the early stellar initial mass function
(IMF), and the merger history of Galactic subsystems. This
“Galactic archaeology” remains the principal basis by which
models for the formation and chemodynamical evolution of the
Milky Way and analogous systems are formulated and refined.
The vast literature on Milky Way stellar populations as tools
for understanding Galactic evolution has been reviewed in the
past by, e.g., Gilmore et al. (1989), Majewski (1993), and
Freeman & Bland-Hawthorn (2002), and more recently by
Ivezić et al. (2012), Rix & Bovy (2013), and Bland-Hawthorn
& Gerhard (2016).
These efforts are of course greatly aided by access to
expansive, carefully designed, homogeneous, and precise
databases of properties for stellar samples that span large
regions of the Galaxy and include all of the principal stellar
populations. Modern archetypes of such databases are large
photometric surveys like the Two Micron All-Sky Survey
(2MASS; Skrutskie et al. 2006) and the Sloan Digital Sky
Survey (SDSS; York et al. 2000). Over the past decade, these
photometric catalogs have been widely exploited for insights
into the nature of the Milky Way and probing the complexities
of Galactic structure—e.g., halo substructure (e.g., Majewski
et al. 2003; Rocha-Pinto et al. 2004; Belokurov et al. 2006;
Grillmair 2009), satellite galaxies (e.g., Willman et al. 2005;
Belokurov et al. 2007), the warp of the disk (e.g., López-
Corredoira et al. 2002; Reylé et al. 2009)
, and the still
unresolved, composite anatomy of the bulge (e.g., Robin et al.
2012), which includes the recently found X-shaped feature (e.g.
, McWilliam & Zoccali 2010; Nataf et al. 2010) and one or
more central bars (e.g., Hammersley et al. 2000; Alard 2001;
Cabrera-Lavers et al. 2007). Follow-on, low- and medium-
resolution (MR) spectroscopic programs provide additional
dynamical discrimination of, and context for, these structures
as well as general information on their chemical makeup (e.g.,
mean metallicities and, in some cases, an additional dimension
of chemistry, such as [α/Fe]); these broad brushstrokes
represent an important step in characterizing stellar populations
and constraining galactic evolution models.
Meanwhile, HR stellar spectroscopy has become an increas-
ingly indispensable tool for providing the necessary detail to
discriminate galaxy evolution models. Accurate multi-element
chemical abundances provide insight into the stellar IMFs, and
histories of star formation and chemical enrichment of stellar
populations, which, in turn, fuel ever more sophisticated
galactic dynamical and chemodynamical models (e.g.,
51
John Bahcall Fellow.
52
Premium Postdoctoral Fellow of the Hungarian Academy of Sciences.
2
The Astronomical Journal, 154:94 (46pp), 2017 September Majewski et al.
Chiappini et al. 2001, 2003; Sellwood & Binney 2002; Abadi
et al. 2003; Bournaud et al. 2009; Schönrich & Binney 2009;
Minchev & Famaey 2010; Bird et al. 2013; Minchev et al.
2013, 2014; Kubryk et al. 2015). Coupled with orbital
information derived from precise radial velocities, these data
probe the role of dynamical phenomena such as large-scale
dissipative collapses, mergers, gas flows, bars, spiral arms,
dynamical heating, and radial migration.
Conventional echelle spectroscopy programs to deliver HR
spectroscopic data useful for Galactic archaeology demand
substantial resources, often on the world’ s largest telescopes.
Consequently, while heroic efforts have been devoted to
surveying stars in a wide variety of environments—including,
e.g., dwarf spheroidals, globular clusters, the Magellanic
Clouds, tidal streams, and the Galactic bulge—until very
recently the solar neighborhood was the only region for which
multiple hundreds or thousands of observations had been
assembled for “Galactic field stars” (e.g., Edvardsson et al.
1993; Bensby et al. 2003; Fuhrmann 2004; Venn et al. 2004;
Nissen & Schuster 2010; Soubiran et al. 2010; Adibekyan et al.
2012, 2013; Bensby et al. 2014). These studies traditionally
relied on kinematically selected samples to harvest from the
nearby stars of accessible apparent brightnesses a broad spread
of stellar ages and population classes. For stellar populations
not represented in the solar neighborhood, like the Galactic
bulge, and for in situ studies of field stars outside of the solar
neighborhood, HR observations are only now generating
samples with hundreds of stars. In the inner Galaxy where
foreground dust obscuration is a formidable challenge, many
previous samples were concentrated to a handful of low
extinction sight lines, such as Baade ’s Window. Unfortunately,
the aggregate of these piecemeal collections of spectroscopic
data, heterogeneously assembled, can give a biased and
incomplete view of the Milky Way.
Truly comprehensive evolutionary models for the Milky
Way must be informed and constrained by statistically reliable,
complete, or at least unbiased Galactic archaeology studies,
which require the construction of large, truly systematic, and
homogeneous chemokinematical surveys covering expansive
volumes of the Milky Way and sampling all stellar populations,
including, in particular, those dust-obscured inner regions
where the bulk of the Galactic stellar mass is concentrated. A
number of ambitious “Galactic archaeology” spectroscopic
surveys that aim to
fill this need (1) have been previously
undertaken, such as RAVE (Steinmetz et al. 2006), SEGUE-1
(Yanny et al. 2009), SEGUE-2 (Rockosi et al. 2009), and
ARGOS (Freeman et al. 2013), (2) are currently underway,
such as LAMOST (Cui et al. 2012), Gaia/ESO (Gilmore et al.
2012), GALAH (Zucker et al. 2012), and Gaia (Perryman et al.
2001), (3) or are envisaged, e.g., those associated with the
WEAVE (Dalton et al. 2014), 4MOST (de Jong et al. 2014),
and MOONS (Cirasuolo et al. 2014) instruments. Although
each of these surveys focuses on large samples of 100,000
stars, all of the past and ongoing endeavors are based on optical
observations and are therefore strongly hampered by interstellar
obscuration in the Galactic plane (Figure 1, bottom); this makes
it challenging to sample significant numbers of stars within the
very dusty regions of the Milky Way that are both central to
constraining formation models and encompass most of the
Galactic stellar mass (and some projects, like the RAVE,
SEGUE, and GALAH surveys, specifically avoid low Galactic
latitudes). Therefore, with optical wavelength surveys, it is
challenging to assemble a systematic census having compar-
able or sufficient representation of all Galactic stellar popula-
tions and across wide expanses of the Galactic disk and bulge.
While other surveys, such as BRAVA (Rich et al. 2007),
ARGOS (Freeman et al. 2013), and Gonzalez et al. ( 2011) aim
to fill at least part of this void by specifically focusing on the
Galactic bulge, they utilize target selection criteria that differ
from those of surveys of other parts of the Milky Way, which
makes it difficult to generate a holistic picture of stellar
populations and their potential connections. Moreover, apart
from GALAH and the Gaia/ESO survey, these other studies
are limited to MR spectroscopy (R<10,000; Figure 1), and so
they are unable to provide reliably the kind of detailed
elemental abundance information that is now a key input to the
models, while at the same time the moderate velocity precisions
can limit their sensitivity to more subtle, second-order
dynamical effects (e.g., perturbations by spiral arms and the
bar, dynamical resonances, velocity-coherent moving groups
and streams).
1.2. APOGEE: Basic Architecture and Motivations
In contrast to previous and ongoing surveys, the Apache
Point Observatory Galactic Evolution Experiment (APOGEE)
in Sloan Digital Sky Survey III (SDSS-III) was designed to
Figure 1. APOGEE in the context of other Galactic archaeology surveys, past,
present, and future. The top panel shows the number of Milky Way stars,
observed or anticipated, as a function of survey resolution. For those surveys
with at least a resolution of R=10,000, the bottom panel shows the expected
nominal depth of the survey for a star with
=-
M 1
V
in the case of no
extinction (right end of arrows) and in the case of
=
A
10
V
(left end of arrows).
In both panels, already completed surveys are shown in black, ongoing surveys
in dark gray, and planned surveys in light gray. For surveys with multiple
resolution modes, data in the top panel are plotted separately for high resolution
(HR), medium resolution (MR), and/ or low resolution (LR). For the Gaia/
ESO survey, data for the “Inner Galaxy” and “Halo” subsamples are shown
separately as well. “Gaia-RV” includes Gaia HR spectra of enough S/Nto
deliver radial velocities, whereas “Gaia” indicates only those with S/N high
enough for abundance work. For Gaia, we adopted
A
A
GV
from Jordi et al.
(2010), assuming
-=()VI 1.7;
C 0
sample numbers were taken from http://
www.cosmos.esa.int/web/gaia/science-performance.
3
The Astronomical Journal, 154:94 (46pp), 2017 September Majewski et al.
![Figure 3. Summary of the S/N experiments described in Appendix B for each of the 15 chemical elements. For each, the minimum required S/N to measure 0.1 dex precision abundances is plotted for a variety of resolutions from R=15,000 to 30,000, and for three metallicities, = -[ ]Fe H 2, −1, and 0. For Al, Si, and Mg, the data points for all three modeled metallicities fall on top of one another.](/figures/figure-3-summary-of-the-s-n-experiments-described-in-2ev51d1a.webp)
![Figure 29. APOGEE-derived metallicity and [α/Fe] (using the reliable individual DR12 elements O+Ca+Si as α) as a function of Galactocentric radius for 29 clusters in two age regimes: blue (orange) points denote clusters younger (older) than 1 Gyr. The light gray region in the upper panel shows a gradient in [Fe/H] of −0.06 dex kpc−1 within =R 15 kpcGC and hints at a flat distribution (admittedly based on very few data points) beyond with a spread of 0.2 dex. A shallower, positive gradient, of +0.007 kpc−1 dex, is seen in [α/Fe] (lower panel), consistent with previous literature-based open cluster studies (e.g., Yong et al. 2012). Additional individual element abundance gradients are explored in P. M. Frinchaboy et al. (2017, in preparation).](/figures/figure-29-apogee-derived-metallicity-and-a-fe-using-the-ft9g0wdd.webp)
![Figure 9. Comparison of a section of the APOGEE spectra for two stars of the same temperature (approximately 4060 K) with about a 100×ratio in the abundance of iron. The red (top) spectrum is for a star that has [Fe/H]=−1.68 and =glog 0.40. The black (bottom) spectrum is for a star that has [Fe/H]=+0.28 and =glog 1.39 (DR12 values).](/figures/figure-9-comparison-of-a-section-of-the-apogee-spectra-for-2bz1kye5.webp)
