BOSS Ancillary Targets

About 12% of all BOSS targets come from one or more of 48 ancillary target programs, designed to accomplish scientific goals in addition to those of the main BOSS target selection program. These pages describe the scientific motivation and detailed target selection criteria of each program, and indicate how to get data for ancillary program objects.

Some ancillary programs are self-contained science projects in themselves, some represent calibrations or refinements of SDSS or BOSS spectroscopic programs, and some (e.g. the SEQUELS programs) were conducted to prepare for future surveys. Ancillary programs were selected in five rounds of competitive calls for proposals among the BOSS collaboration. Note that there is often significant overlap in the scientific and/or algorithmic goals of many programs, reflecting these multiple calls.

Why observe ancillary programs?

The number density of BOSS's galaxy and quasar targets is not uniform on the sky, and in regions of lower-than-average target density, not all of the 1,000 fibers on a plate were assigned to core target categories.

Parallel ancillary target programs were solicited to provide additional targets that could be used to fill every fiber on every plate, thus maximizing the scientific output of BOSS observations.

Later, when BOSS completed its planned observations several months early, dedicated ancillary target programs were planned so that scientifically important observations would continue.

For targets selected through APOGEE ancillary targeting programs and observed in the infrared with the APOGEE spectrograph, see the APOGEE Ancillary Targets documentation.

Complete observations from twenty-three ancillary targeting programs were released as part of SDSS Data Release 10, including eight confined to the footprint of SDSS Stripe 82 (the area observed by the SDSS Supernova Survey). Data Release 12 added an additional twenty-five ancillary programs, thus completing the release of all BOSS ancillary target data.

BOSS ancillary target programs were observed using one of two strategies:

  • Parallel: observed in parallel with SDSS core target selection, a few fibers at a time as opportunities arise
  • Dedicated: observed using a complete SDSS plate after main BOSS observations were complete

Parallel ancillary target programs were intended to support studies that require no more than a few thousand fibers, but which also require fairly large samples over large regions of sky, making them difficult to complete in conventional observations at shared facilities. Thus, BOSS ancillary target programs provide opportunities to pursue studies that would be difficult to accomplish in other ways.

Complete descriptions of each ancillary target program are available in the research literature in one of two places. Targets first released in DR10 are described in the BOSS technical summary paper (Dawson et al. 2013); targets first released in DR12 are described in the DR12 data release paper (Allam et al. 2015).

Get Data for Ancillary Targets

SDSS data for ancillary targets are available in the same manner as for any other objects. Data for individual objects can be found using the SkyServer Navigate and Explore tools. Spectroscopic catalog data for multiple targets can be retrieved using SkyServer search tools or the CasJobs batch interface. Spectrum files can be downloaded in multiple formats from the Science Archive Server Advanced Search.

For all SDSS spectroscopic data, information about how that object was targeted for spectroscopy is included in the object's Target Flags. Information about whether a target was selected for one or more ancillary target programs is included in the flags ANCILLARY_TARGET1 and ANCILLARY_TARGET2. All new ancillary target programs in Data Release 12 use the ANCILLARY_TARGET2 flag.

To store targeting data most efficiently, all SDSS target flags are stored as bitmasks. For more information about working with such data, see the SDSS bitmasks page. To enable searches by flag name rather than by bit value, SkyServer and CasJobs include the lookup functions dbo.fAncillaryTarget1 and dbo.fAncillaryTarget2.

Target Selection Background

This page describes how to use SDSS ancillary targets in general; the pages linked from the lists below describe how targets were selected for specific ancillary targeting programs.

BOSS Ancillary targets were requested in three calls for proposals made to the SDSS-III collaboration: one in 2009, one in 2010, and one in 2012. Throughout SDSS observations from 2009 to 2012, ancillary targets were given a lower priority for target selection than the primary science drivers of BOSS; therefore, sample selection for the ancillary target programs is often not complete.

The SDSS photometry used for selection in these different programs typically uses PSF, model (for galaxy magnitudes), or cmodel (for galaxy colors; Abazajian et al. 2004) photometry, all corrected for Galactic extinction following Schlegel, Finkbeiner, & Davis (1998).

Occasionally, fiber magnitudes are also used. The selection for many programs also uses photometry from the Wide-Field Infrared Survey Explorer (WISE, Wright et al. 2010). For convenience of the user, we provide a copy of the WISE catalog in both the DR11 and DR12 contexts in the CAS database, in the tables WISE_allsky and WISE_xmatch.

WISE carried out a full-sky survey in four bands, centered at 3.6, 4.5, 12, and 22 m; the resulting photometry (which is reported on a Vega system, unlike the AB system of SDSS) is referred to as W1, W2, W3, and W4, respectively. A number of programs use a reprocessing of the WISE data (Lang 2014) or forced photometry of WISE images at positions from SDSS (Lang, Hogg, & Schlegel 2016).

BOSS Ancillary Programs in Stripe 82

The tables below gives summary statistics for each of the parallel (shared-plate) BOSS ancillary target programs that were contained entirely in the Stripe 82 survey area. Data from these programs were originally released in Data Release 9. For more information about each program, including detailed target selection information, click on the name of the program in the table below. These programs are described in the literature in Dawson et al. (2013).

Targeting data for the Stripe 82 programs are stored in both the ANCILLARY_TARGET1 and ANCILLARY_TARGET2 columns, depending on the program. The tables below give information about each program, including the bit numbers in which target flags are recorded.


The first table shows programs whose target flags are recorded in ANCILLARY_TARGET1 values:

Program Description Spectra Unique primary objects
The Transient Universe through Stripe 82 Spectra of a variety of variable objects in a 220-square-degree section of the repeated imaging of SDSS stripe 82 404 348
Host Galaxies of SDSS-II Supernovae Spectra of host galaxies of supernovae that were identified by the 2005-2008 SDSS supernova survey 4,729 3,523
High-Quality Galaxy Spectra Repeat observations of two spectroscopic plates, leading to higher signal-to-noise spectra for 2,000 luminous red galaxies 14,000 2,000
Reddened Quasars A search for quasars reddened by dust absorption (either from intervening sources or sources local to the quasar) in the 220-square-degree survey area of Stripe 82 126 56


This table shows programs whose target flags are recorded in ANCILLARY_TARGET2 values.

Program Description Spectra Unique Primary Objects
Brightest Cluster Galaxies Spectra of brightest cluster galaxies (BCGs) in the 220-square-degree stripe 82 survey area 1,407 1,302
No Quasar Left Behind An attempt to find all likely quasars in the 220-square-degree footprint of SDSS Stripe 82, selecting based only on variable source light curve data 1,510 1,394
Variability-Selected Quasars Candidate quasars in the 220-square-degree footprint of Stripe 82, selected by variability alone 639 609
K-Band Selected Sample of Quasars Quasar candidates in the 220-square-degree footprint of Stripe 82 that were selected by matching SDSS and UKIDSS photometry 192 178

BOSS Ancillary Programs on Shared Plates

The table below gives summary statistics for each of the parallel (shared-plate) ancillary target programs over the entire BOSS survey area (spectroscopic effective area 9,376 deg2). For more information about each program, including detailed target selection information, click on the name of the program.

The ancillary target programs whose flag data are stored in ANCILLARY_TARGET1, as well as the first two programs from ANCILLARY_TARGET2 are described in the literature in Dawson et al. (2013). The rest of the programs in ANCILLARY_TARGET2 are described in Alam et al. (2015).


The first table shows programs whose target flags are recorded in ANCILLARY_TARGET1 values:

Program Description Spectra Unique primary objects
Very Low-Mass Stars and Brown Dwarfs A search for M stars and L dwarfs in the BOSS survey area (9,376 square degrees) 7,784 6,803
Low-Mass Binary Stars Spectra for widely-separated binary stars of spectral class M 1,229 1,115
White Dwarfs and Hot Subdwarf Stars Spectra of white dwarf candidates in the SDSS Data Release 7 imaging area (7,430 deg2) 8,938 7,926
Distant Halo Giant Stars Spectra of class K giant stars in the outer halo of the Milky Way 10,552 7,526
Bright Galaxies A search for bright galaxies that were missed by prior SDSS spectroscopic surveys 5,616 5,273
High Energy Blazars and Optical Counterparts of Gamma-ray Sources A search for the optical counterparts of Fermi gamma-ray sources in a the SDSS Data Release 7 survey area (7,650 square degrees) 1,126 1,050
An X-Ray View of Star-Formation and Accretion in Normal Galaxies Spectra for the optical counterparts of Chandra x-ray targets in the SDSS DR7 survey area 1,367 1,268
Remarkable X-Ray Source Populations Spectra of the optical counterparts of serendipitous x-ray sources identified by XMM-Newton and/or Chandra 2,764 2,549
Star-Forming Radio Galaxies Spectra of blue star-forming galaxies with radio emission for studies of gas cooling and radio feedback 2,938 2,781
Galaxies Near SDSS Quasar Sight Lines Spectra of galaxies in the SDSS Data Release 7 imaging area (7,650 deg2) which are close on the sky to known quasars, meaning that they lie along the quasar’s line-of-sight 2,040 1,944
Luminous Blue Galaxies at 0.7 < z < 1.7 Spectra of a sample of luminous blue galaxies at 0.7 < z < 1.7 in a 143-square-degree subset of the BOSS survey area 3,661 3,515
Broad Absorption Line (BAL) Quasar Variability Survey Spectra for broad absorption lines (BAL) quasars in a 5,740 deg2 survey area 1,805 1,393
Variable Quasar Narrow-line Absorption Spectra of narrow absorption line quasars in a 7,650 square degree survey area 2,275 2,069
High-Redshift Quasars Spectra of candidate high-redshift quasars identified from SDSS imaging. Separate target selection was carried out in the 220 deg2 footprint of SDSS Stripe 82 and in the 7,650 deg2 area of DR7 imaging 4,291 3,766


Targeting data for each of these programs is stored in the ANCILLARY_TARGET2 column. The bit number values in the table below give the bit number of ANCILLARY_TARGET2 in which that targeting flag is recorded.

Program Description Spectra Unique primary objects
Double-lobed Radio Quasars Spectra of point-source objects near the midpoint of a double-lobed radio quasar in FIRST 1,197 1,132
High-Redshift Quasars from SDSS and UKIDSS Spectra of candidate high-redshift quasars seen by both the SDSS and the UKIRT Infrared Deep Sky Survey 187 171
Characterizing Low-mass M Dwarfs Using Wide Binaries Spectra of candidate binary star pairs in which one star is an M dwarf, obtained to help better characterize the ages and metallicities of M dwarfs 95 93
A Census of Nearby Galaxies Spectroscopic observations of nearby galaxies identified in Palomar Transient Factory (PTF) imaging, taken with the goal of completing a census of the local universe 178 173
Quasar Spectrophotometric Calibration An ancillary target program undertaken to improve the spectrophotometric calibration of BOSS quasars, by targeting standard stars with similar focal plane offsets to BOSS quasar observations 1,782 1,456
Spectra of H2O Maser Galaxies Spectra of H2O maser galaxies obtained with the goal of calibrating Cepheid distances, and therefore improving estimates of H0 54 50
Spectroscopy of Massive Galaxy Cluster Members Spectra obtained to find spectroscopic redshifts of massive galaxy clusters selected in x-ray imaging, with the goal of finding the three-dimensional structure of those clusters 2,828 2,762
Repeated Spectroscopy of Candidate Close Binary Massive Black Holes Second-epoch spectroscopy of SDSS-I/II quasars that are candidate massive black hole binaries with separations less than one parsec, selected to improve our understanding of close black hole pairs 100 90
Spectroscopy of Hard X-ray Identified AGN Spectra of hard-x-ray selected AGN from XMM, selected to help constrain the dark matter halo masses of X-ray AGN as a function of redshift and luminosity 25 25
"WISE BOSS": BOSS spectra of Mid-IR bright AGN Spectra of quasars selected from the WISE All-Sky Survey, selected to study the completeness of the BOSS main quasar sample and to enable studies of the dust obscuration of quasars 21,647 20,808
Quasar Target Selection with WISE Spectra measured with the goal of enhancing the efficiency of quasar identification in SDSS 29,253 26,927
Quasar Pairs Spectra of closely-separated quasars, taken to provide a large statistical sample of quasar pairs for studies of small-scale quasar clustering 645 628

BOSS Ancillary Programs with Dedicated Plates

Because BOSS observations were proceeding ahead of schedule in 2012, a series of spectroscopic plates were added to the SDSS-III program to observe additional ancillary science programs. These plates do not have primary BOSS galaxy and quasar targets; instead, they consist entirely of ancillary science targets. The completeness of each dedicated sample is therefore typically higher than the completeness of the samples in the parallel ancillary programs listed above.

This section describes each of these dedicated-plate ancillary science program, again sorted roughly by the distance to the targets. Note that a number of the programs include multiple target classes, each indicated by a separate bit. See the individual program pages for descriptions of each bit. For a table of bit values, see the Bitmasks page.

Program Description Spectra Unique Primary Objects Plates
Star Formation in the Orion and Taurus Molecular Clouds A program to collect spectra of candidate young stellar objects (YSOs) in the Orion and Taurus molecular clouds first seen in 2MASS, Spitzer, and WISE imaging 4,679 3,945 7257
Stars Across the SDSS A spectroscopic survey designed to derive stellar parameters for stars seen in multiple SDSS surveys using consistent methods 13,088 12,815 7253-7256
A Galaxy Sample Free of Fiber Collisions Galaxies that had previously been missed from CMASS and LOWZ target selection due to fiber collisions were observed as part of this ancillary target program (See program page) 6373-6398
Quantifying BOSS Galaxy Incompleteness With a WISE-Selected Sample Spectra of galaxies with a wider range of colors than those selected in the CMASS sample 10,157 9,163 6373-6398
Exploring z > 0.6 LRGs from SDSS and WISE A spectroscopic survey of distant (z > 0.6) luminous red galaxies (LRGs) selected using WISE photometry, with the goal of better calibrating photometric redshifts of these galaxies, and therefore improving distance estimates 13,454 10,911 6373-6398
Tests of eBOSS Target Selection in CFHT-LS W3 Field A survey designed to improve target selection of galaxies and quasars for the future eBOSS survey of SDSS-IV 5,068 4,192 7027-7032
eBOSS ELG Target Selection with Deep Photometry Photometry deeper than SDSS was used to assess algorithms for selection of Emission Line Galaxies (ELG) for spectroscopic observations 2,699 2,589 6391-6933
The TDSS/SPIDERS/eBOSS Pilot Survey A pilot survey designed to find targets in optical and x-ray imaging useful for planning future phases of the SDSS 1,705 1,469 6369
Follow-up spectroscopy of wide-area XMM Fields A spectroscopic survey of AGN, selected from X-ray data, conducted to better characterize AGN population properties 3,132 3,062 7235-7238
Multi-Object Reverberation Mapping A multi-epoch spectroscopic survey designed to enable use of the reverberation mapping technique to study the structure of broad-line regions in AGN and quasars 25,470 841 7338-7340
Variability-selected Quasars at 1 < z < 4 to g = 22.5 Spectra of quasars in SDSS stripe 82, selected by color and variability 9,084 2,395 6370
Faint End of the Quasar Luminosity Function A survey of quasars designed to extend BOSS quasar selection to include fainter quasars 3,600 2,660 7334-7337
SDSS-III Observations of LOFAR Sources This ancillary program was intended to target radio sources identified in deep LOFAR observations of the ELAIS-N1 region 2,256 2,160 7562-7565

SEQUELS: Sloan Extended Quasar, ELG, and LRG Survey

SEQUELS covers several hundred square degrees within the BOSS footprint, targeting LRGs, QSOs, and emission line galaxies (ELGs). SEQUELS serves both as a pilot program for the eBOSS survey of SDSS-IV and as a stand-alone science program.

For details on target selection in SEQUELS, see the SEQUELS Ancillary Target page.

The DR12 documentation on this site includes an index of the values of ANCILLARY_TARGET1 and ANCILLARY_TARGET2 that correspond to each ancillary target program.


Abazajian, K., et al. 2004, AJ, 128, 502

Alam, S., et al. 2015, ApJS, 219, 12

Dawson, K. S., et al. 2013, AJ, 145, 10

Lang, D. 2014, AJ, 147, 108

Lang, D., Hogg, D. W., & Schlegel, D. J. 2016, AJ, 151, 36

Schlegel, D. J., Finkbeiner, D. P., & Davis, M. 1998, ApJ, 500, 525

Wright, E. L., et al. 2010, AJ, 140, 1868