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SEGUE Target Selection
Using the photometry from SDSS, the SEGUE survey designed a series of color, magnitude, and proper motion criteria to identify stellar targets that were of particular interest. Each photometric target is labeled with distinctive hexadecimal codes (bitmasks) which indicate which stellar types they are associated with. For each individual stellar category, a certain number of photometric targets that fulfill the selection criteria are observed spectroscopically. For example, around 25 stars that meet the SEGUE White Dwarf criteria are observed along each line-of-sight.
Below, we list the different selection criteria for the different programs in the SEGUE survey. The SEGUE sample consists of three different surveys, SEGUE-1, SEGUE-2, and SDSS stellar targeting originating from the SDSS Legacy Program. Each of these also consists of different observing programs, with different targeting goals and a different target-selection algorithm. For example, low latitude plates focus on K giants, with different criteria than K giants observed as part of the segue and seguefaint programs.
In addition to variation from program-to-program, the target selection algorithm for SEGUE-1 plates evolved over time. More detailed information on the evolution of target criteria is available on the Past Versions page. Here we list the most current version of the target selection algorithm. The target identification for each star listed in sppParams, SpecObjAll, and segueTargetAll is based on the latest version of the selection criteria.
Finally, the photometry and proper motions for SDSS stars has evolved over time. SEGUE-1 selected targets for spectroscopic based on a series of SEGUE imaging stripes in conjunction with proper motions from various astrometric catalogs (see Getting Started with SEGUE: Target Selection Differences and Yanny et al. 2009 for more detail). SEGUE-2 selects targets based on photometry and astrometry from SDSS DR7. These data sets have changed for DR9. Targets that may have fulfilled the criteria for a SEGUE target type in DR7 may no longer, thanks to photometric errors, among other things. Thus, there is variation in the number of targets for each category between DR7 and DR9 (due to the astrometry errors in SDSS DR8, this SEGUE data set should not be used).
Below, we detail the different targets examined in SEGUE-1, SEGUE-2, and SDSS stellar targeting originating from the SDSS Legacy Program. Each program has a table with summary information for each target type and a description of the different targeting criteria. Finally, we also include a brief summary of the calibration fiber identifications.
Jump to Summary Tables for:
SEGUE-1 Target Selection
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| Example color-color diagram of SEGUE 1 target selection categories. |
Each star observed in photometry (g < 21 or z < 21) is assigned a bitmask, segue1_target1, which indicates the different selection criteria it fulfills, regardless of whether or not it receives a SEGUE fiber. These are in segueTargetAll. There is also a segue1_target1 parameter in sppParams and SpecObjAll; however, rather than listing all of the different target categories a star belongs to, this parameter indicates why each of the observed stars received a spectroscopic fiber. For example, if a star fulfills the selection criteria of both the G-dwarf and low-metallicity categories but is assigned a fiber as a G dwarf, segueTargetAll.segue1_target1 will mark the stars as both types, whereas sppParams.segue1_target1 and specObjAll.segue1_target1 will indicate the G-dwarf category alone.
The SEGUE-1 survey consisted of a number of different programs, which utilize different target-selection algorithms. Each of the programs and their associated plates are listed here. Plates in the segue or seguefaint programs make up the majority of the observations. The segcluster, segpointed, and segpointedf plates focused on open and globular clusters and Milky Way substructure. Any additional spectroscopic fibers not used for these were assigned to stars according to the target selection categories of segue and seguefaint. For a uniform SEGUE-1 sample over a large portion of the sky, only use the plates targeted under the segue and seguefaint programs.
These target selection criteria have evolved over time. We have the latest version (v4.6) here. However, for information about how these have evolved over time, please see Past Versions.
SEGUE-1 v4.6 Target Selection: segue and seguefaint programs
| Category | Hex | Integer | Binary | Criteria | Per LoS | Total* |
|---|---|---|---|---|---|---|
| F/G | 0x80000200 | -2147483136 | 29 | g < 20.2 0.2 < (g-r) < 0.48 | 50 | 55189 |
| Main Sequence/White dwarf pairs** | 0x80001000 | -2147479552 | 212 | 15.0 < g < 20 (u-g) < 2.25 -0.2 < (g-r) < 1.2 0.5 < (r-i) < 2.0 (g-r) > -19.78(r-i)+11.13 (g-r) < 0.95(r-i)+0.5 (i-z) > 0.5 for (r-i) > 1 (i-z) > 0.68(r-i)-0.18 for (r-i) ≤ 1 | 5 | 338 |
| A/Blue Horizontal Branch | 0x80002000 | -2147475456 | 213 | g < 20.5 0.8 < (u-g) < 1.5 -0.5 < (g-r) < 0.2 u detection Color-gravity index condition | 150 | 15626 |
| K giants (l and red) | 0x80004000 | -2147467264 | 214 | r < 20.2 0.35 < (g-r) < 0.8 0.15 < (r-i) < 0.6 l-color > 0.07 PMtotal < 11 mas/yr good PM | 70 | 17924 |
| K dwarf | 0x80008000 | -2147450880 | 215 | 14.5 < r < 19.0 0.55 < (g-r) < 0.75 | 95 | 28580 |
| Low Metallicity | 0x80010000 | -2147418112 | 216 | 14 < r < 19.0 -0.5 < (g-r) < 0.75 0.6 < (u-g) < 3.0 l-color > 0.135 u detection | 150 | 21741 |
| Cool White Dwarf | 0x80020000 | -2147352576 | 217 | 14.5 < r < 20.5 (g-i) > -2 (g-i) < 1.7 if no neighbor with g > 22 within 7'' Otherwise, (g-r) < 0.12 good PM Hg > 16.05+2.9(g-i) Hg > 17.5 | 10 | 789 |
| G dwarf | 0x80040000 | -2147221504 | 218 | 14.0 < r < 20.2 0.48 < (g-r) < 0.55 | 375 | 43339 |
| White Dwarf | 0x80080000 | -2146959360 | 219 | g < 20.3 -1 < (g-r) < -0.2 -1 < (u-g) < 0.7 (u-g) + 2(g-r) < -0.1 | 25 | 2997 |
| Metal-poor main sequence turnoff, subdwarfs | 0x80100000 | -2146435072 | 220 | g < 20.3 -0.7 < P1(s) < -0.25 0.4 < (u-g) < 1.4 0.2 < (g-r) < 0.7 | 200 | 35617 |
| L, T brown dwarfs | 0x80200000 | -2145386496 | 221 | z < 19.5 (i-z) > 1.7 u > 21 g > 22 r > 21 | 5 | 59 |
| M subdwarfs | 0x80400000 | -2143289344 | 222 | 14.5 < r < 19.0 (g-r) > 1.6 0.95 < (r-i) < 1.3 | 5 | 238 |
| AGB | 0x80800000 | -2139095040 | 223 | 14.0 < r < 19.0 2.5 < (u-g) < 3.5 0.9 < (g-r) <1.3 s-color < -0.06 u detection | 10 | 198 |
| Extreme M subdwarfs* | 0x81000000 | -2130706432 | 224 | (r-i) < 0.787(g-r)-0.356 (r-i) < 0.9 Hr >17 1.8 < (g-i) < 2.4 | 40 | 596 |
*This is the number of unique SEGUE-1 observations of this type on segue or seguefaint plates. We use the bitmasks from the DR9 segueTargetAll table. Individual stars can belong to multiple categories.
**All magnitudes for MS/WD pairs are the reddened values
Notes:
- All ugriz magnitudes listed below are dereddened PSF mags, unless otherwise specified. This means that a check of objc_flag[2] indicates the target has no bright, no edge, no bad interp, no bad deblends
- For selections which involve u band, we require that the u flags indicate a u band detection.
- The 'regular SDSS bright end cut' is:
No spectra of objects with g,r or i fiber mag < 14.5 allowed. - Proper motions have been included for objects
which have matches to the USNO-B catalog and are used
in various selection categories. Many criteria state "good PM." This
uses parameters from the Proper Motions catalog and is defined below:
- Match = 1
- dist22 > 7.0 arcsec (i.e., the nearest neighbor brighter than 22nd magnitude is more than 7'' away)
- pmSigmaRa < 525 mas/yr
- pmSigmaDec < 525 mas/yr
- nFit = 6 (nFit is the number of measurements used in the proper motion fit)
- Low Latitude Algorithms implemented:
- AGB type objects at low latitude
- K III type objects at low latitude
- Bluetip objects at low latitude
- AMNH high proper motion objects at low latitude
- Principal component color definitions:
- l-color = -0.436u + 1.129g - 0.119r - 0.574i + 0.1984
and is a photometry metallicity indicator for stars in the color range 0.5 < (g-r) < 0.8.
Reference: Lenz et al. (1998) - s-color = -0.249u + 0.794g - 0.555r + 0.234
- P1(s) = P1 = 0.91(u-g) + 0.415(g-r) -1.280
Reference: Helmi et al. (2003) - Hg = g + 5 + 5log10(PM (arcsec/year))
- Hr = r + 5 + 5log10(PM (arcsec/year))
- l-color = -0.436u + 1.129g - 0.119r - 0.574i + 0.1984
SEGUE-1 v4.6 Target Selection: seglowlat and seglowlatf programs
| Category | Hex | Integer | Binary | Criteria | Per LoS | Total* |
|---|---|---|---|---|---|---|
| Low latitude K giant | 0x80000400 | -2147482624 | 210 | 0.55 < (g-r) < 0.9 g < 19 PMtotal < 11 mas/yr | 300 | 2699 |
| Low latitude Blue Stellar Locus | 0x80000800 | -2147481600 | 211 | (g-r) < 0.25 | 800 | 1940 |
| Low latitude AGB/M giants | 0x88000000 | -2013265920 | 227 | s-color > -0.13 3.5 > (u-g) > 2.6 0.8 < (g-r) <1.3 | 50 | 115 |
*This is the number of unique SEGUE-1 observations of this type on seglowlat plates. We use the bitmasks from the DR9 segueTargetAll table. Individual stars can belong to multiple categories.
SEGUE-1 v4.6 Target Selection: segcluster, segclusterf
A number of SEGUE plates (mostly in SEGUE-1, but also in SEGUE-2) specifically targeted known globular or open clusters. Since these clusters are generally quite bright, the exposure times of these plates were often shorter than the normal 45 min to 2 hours exposure time, in some cases as short as two minutes. Such a short exposure time can result in lack of sky signal, and the wavelength calibration for these plates as well as the spectrophotometric flux calibration must be carefully be done by hand. While we have taken many precautions in getting these calibrations correct, users are cautioned to regard these with care. The spectra and measured SSPP output parameters from these cluster stars, combined with their ugriz or other photometry is the basis for putting the log(g), [Fe/H] and Teff systems on uniform system. The list of plates targeted in this fashion with their target cluster is here.
SEGUE-1 v4.6 Target Selection: segpointed and seguepointedf
The segpointed and segpointedf programs focused on regions of the sky with probably Milky Way substructure. Any spectroscopic fibers not devoted to the substructure were assigned to targets using the selection criteria of segue and seguefaint. Just like the segcluster plates, we caution that these plates should not be used when composing a uniform SEGUE sample over the sky. The list of plates targeted in this fashion is here.
SEGUE-1 v4.6 Target Selection: segtest,segtestf
These plates were done to test the S/N and other constraints for the SEGUE target selection algorithm. While the spectra from these plates are fine, these targets should not be included in larger SEGUE samples. The list of plates targeted in this fashion is here.
SEGUE-2 Target Selection
The SEGUE-2 survey consisted only of the segue2 program. This focused on different target categories than the various programs in SEGUE-1. In contrast to SEGUE-1 stars, the parameter segue2_target1 in sppParams and SpecObjAll identifies all of the different stellar categories each star fulfills at the time of target selection (e.g., using DR7 photometry). It does not exclusively reflect why a star received a fiber. segueTargetAll.segue2_target1 lists all of the different SEGUE-2 categories each photometric target (g < 21 or z < 21) fulfills in DR9 data, regardless of whether it was observed spectroscopically or as part of SEGUE-1. SEGUE-2 plates are listed here.
SEGUE-2 Target Selection
| Category | Hex | Integer | Binary | Criteria | Per LoS | Total* |
|---|---|---|---|---|---|---|
| MS turnoff | 0x80000001 | -2147483647 | 20 | 18 < g < 19.5 0.1 < (g-r) < 0.48 psfmagerr(g,r,i) < 0.05 | 100 | 35466 |
| Red K giants | 0x80000002 | -2147483646 | 21 | 15.5 < g < 18.5 r > 15 psfmagerr(g,r,i) < 0.05 good PM 0.8 < (g-r) < 1.3 (u-g) > 0.84(g-r)+1.758 (u-g) < 2.4(g-r)+0.73 PMtotal < 11 mas/yr | < 50 | 805 |
| l-color K giants | 0x80000004 | -2147483644 | 22 | 15.5 < g < 18.5 r > 15 psfmagerr(g,r,i) < 0.05 good PM 0.7 < (u-g) < 3 0.5 < (g-r) < 0.8 l-color > 0.09 0.1 < (r-i) < 0.6 PMtotal < 11 mas/yr | 100 | 16016 |
| Proper motion only K giants | 0x80000008 | -2147483640 | 23 | 15.5 < g < 18.5 r > 15 psfmagerr(g,r,i) < 0.05 good PM 0.8 < (u-g) < 1.2 PMtotal < 7 mas/yr (u-g) > 2.375(g-r)-0.45 (u-g) < 0.84(g-r)+1.758 | 150 | 14729 |
| Low Metallicity | 0x80000010 | -2147483632 | 24 | 0.3 < (g-r) < 0.8 0.5 < (u-g) < 2.0 15.5 < g < 18 r > 15 psfmagerr(g,r,i) < 0.05 psfmagerr(u) < 0.2 l-color > 0.115 good PM | 100 | 17020 |
| Hypervelocity | 0x80000020 | -2147483616 | 25 | 17 < g < 20 PMtotal > 8 mas/yr good PM Box 1 criteria or Box 2 criteria | <5 | 226 |
| Cool Extreme and Ultra Subdwarfs** | 0x80000040 | -2147483584 | 26 | g > 15.5 (g-r) > 1.4 (r-i) > 0.4 15 < r < 20 (r-i) < 3.0(g-r)-3.5 PMtotal < 10 mas/yr Hr > 10.0+2.5(g-r) psfmagerr(r,i) < 0.05 good PM | 50 | 7396 |
| M giants | 0x80000080 | -2147483520 | 27 | (g-r) > 1.3 (u-g) > 1.8+0.9(g-r) i > 14.5 15.5 < g < 19.25 PMtotal < 11 mas/yr psfmagerr(g,r) < 0.05 good PM | <50 | 344 |
| Halo high velocity | 0x80000100 | -2147483392 | 28 | 17 < g < 20 0.1 < (g-r) < 0.48 Vtan > 300 km/s Vtan/ σ(Vtan) > 3.0 | <5 | 3432 |
| Blue Horizontal Branch | 0x80002000 | -2147475456 | 213 | 15.5 < g < 20.3 -0.5 < (g-r) < 0.1 0.8 < (u-g) < 1.5 | < 100 | 8602 |
| Ultra-Cool CIA White Dwarfs | 0x80020000 | -2147352576 | 217 | 15.5 < r < 20.5 g > 15.5 -2.0 < (g-i) > 1.7 good PM Hg > 17.5 Hg > 16.05+2.9(g-i) | < 10 | 107 |
*This is the number of unique SEGUE-2 observations of this type on segue2 plates. We use the bitmasks from the DR9 segueTargetAll table. Individual stars can belong to multiple categories.
**The magnitudes used for cool extreme and ultra subdwarfs are uncorrected for extinction (i.e., reddened).
Notes:
- All ugriz magnitudes listed below are dereddened PSF mags, unless otherwise specified. This means that a check of objc_flag[2] indicates the target has no bright, no edge, no bad interp, no bad deblends
- For selections which involve u band, we require that the u flags indicate a u band detection.
- The 'regular SDSS bright end cut' is:
No spectra of objects with g,r or i fiber mag < 14.5 allowed. - Proper motions have been included for objects
which have matches to the USNO-B catalog and are used
in various selection categories. Many criteria state "good PM." This
uses parameters from the Proper Motions catalog and is defined below:
- Match = 1
- dist22 > 7.0 arcsec (i.e., the nearest neighbor brighter than 22nd magnitude is more than 7'' away)
- pmSigmaRa < 525 mas/yr
- pmSigmaDec < 525 mas/yr
- nFit = 6 (nFit is the number of measurements used in the proper motion fit)
- Principal component color definitions:
- l-color = -0.436u + 1.129g - 0.119r - 0.574i + 0.1984
and is a photometry metalicity indicator for stars in the color range 0.5 < (g-r) < 0.8.
Reference: Lenz et al. (1998) - s-color = -0.249u + 0.794g - 0.555r + 0.234
- P1(s) = P1 = 0.91(u-g) + 0.415(g-r) -1.280
Reference: Helmi et al. (2003) - Hg = g + 5 + 5log10(PM (arcsec/year)) is the reduced proper motion with respect to g.
- Hr = r + 5 + 5log10(PM (arcsec/year)) is the reduced proper motion with respect to r.
- Vtan is the tangential velocity, computed from the measured proper motions and an estimated distance from photometric parallax.
- σ(Vtan) is the error on the tangential velocity calculation, based on the errors of the proper motions and distances.
- l-color = -0.436u + 1.129g - 0.119r - 0.574i + 0.1984
SDSS Stellar Targeting - Legacy
Approximately 200,000 stars were spectroscopically observed as part of the SDSS and SDSS-II Legacy program. These targets are briefly described in Yanny et al. 2009,and the target categories are explained in Stoughton et al. 2002 There is a brief description of the overall Legacy target selection algorithm here.
The table below lists the possible legacy1_target1 (located in the sppParams and SpecObjAll tables) bit settings available on each spectrum if this object was a Legacy target. Unlike SEGUE-1 and SEGUE-2, every target in the Legacy component is identified by the target type criteria it fulfills, rather than why it was assigned a fiber.
| Category | Hex | Integer | Binary | Color, Mag Cuts | Total Fibers |
|---|---|---|---|---|---|
| ROSAT C | 0x00000800 | 2048 | 211 | r < 16.5 ROSAT X-ray source within 60'' (u-g) < 1.1 | 8000 |
| BHB Star | 0x00002000 | 8192 | 213 | -0.4 < (g-r) < 0 0.8 < (u-g) < 1.8 | 19887 |
| Carbon Star | 0x00004000 | 16384 | 214 | (g-r) > 0.85 (r-i) > 0.05 (i-z) > 0 (r-i) < -0.4+0.65(g-r) (g-r) > 1.75 | 4453 |
| Brown Dwarf | 0x00008000 | 32768 | 215 | z < 19 psfmagerr(i) < 0.3 (r-i) > 1.8 (i-z) > 1.8 | 667 |
| Subdwarf | 0x00010000 | 65536 | 216 | (g-r) > 1.6 0.95 < (r-i) < 1.6 psfmagerr(g) < 0.1 | 1482 |
| Cataclysmic Variable* | 0x00020000 | 131072 | 217 | g < 19.5 (u-g) < 0.45 (g-r) < 0.7 (r-i) > 0.3 (i-z) > 0.4 (u-g)-1.314(g-r) < 0.61 (r-i) > 0.91 (i-z) > 0.49 | 8959 |
| Red Dwarf | 0x00040000 | 262144 | 218 | i < 19.5 psfmagerr(i) < 0.2 (r-i) > 1.0 (r-i) > 1.8 | 14649 |
| White Dwarf | 0x00080000 | 524288 | 219 | (g-r) < -0.15 (u-g)+2(g-r) < 0 (r-i) < 0 Hg > 19 Hg > 16.136 + 2.727(g-i) (g-i) > 0 | 6059 |
| Serendipity Blue | 0x00100000 | 1048576 | 220 | (u-g) < 0.8 (g-r) < -0.05 | 81937 |
| Serendipity FIRST | 0x00200000 | 2097152 | 221 | FIRST radio source within 1.5'' | 14689 |
| Serendipity Red* | 0x00400000 | 4194304 | 222 | (r-i) > 2.7 (i-z) > 1.6 | 4179 |
| Serendipity Distant* | 0x00800000 | 8388608 | 223 | (g-r) > 2 (r-i) < 0 | 11820 |
| ROSAT E | 0x08000000 | 134217728 | 227 | ROSAT source within 60'' | 8000 |
| PN Star | 0x10000000 | 268435456 | 228 | (g-r) > 0.4 (r-i) < -0.6 (i-z) > -0.2 16 < r < 20.5 | 20 |
*The magnitudes for these targets are not dereddened.
Calibration Fibers in SEGUE
A number of stellar targets are assigned fibers for calibration purposes. This is indicated in the parameter segue1_target2 in the SpecObjAll and sppParams tables for SEGUE-1 targets and in segue2_target2 for SEGUE-2.
The bitmask assignments for segue1_target2 are listed below:
| Category | Hex | Integer | Binary |
|---|---|---|---|
| Science Target | 0x40000000 | 1073741824 | 230 |
| Reddening Standard | 0x2 | 2 | 21 |
| QA Duplicate Observation* | 0x8 | 8 | 23 |
| Sky | 0x10 | 16 | 24 |
| Spectrophotometric Standard | 0x20 | 32 | 25 |
The bitmask assignments for segue2_target2 are listed below:
| Category | Hex | Integer | Binary |
|---|---|---|---|
| Light Trap | 0x80000001 | -2147483647 | 20 |
| Reddening Standard | 0x80000002 | -2147483646 | 21 |
| Test | 0x80000004 | -2147483644 | 22 |
| QA Duplicate Observation* | 0x80000008 | -2147483640 | 23 |
| Sky | 0x80000010 | -2147483632 | 24 |
| Spectrophotometric Standard | 0x80000020 | -2147483616 | 25 |
| Guide Star | 0x80000040 | -2147483584 | 26 |
| Bundle Hole | 0x80000080 | -2147483520 | 27 |
| Quality Hole | 0x80000100 | -2147483392 | 28 |
| Hot Standard | 0x80000200 | -2147483136 | 29 |
| Stellar Cluster Target | 0x80000400 | -2147482624 | 210 |
| Stetson Standard | 0x80000800 | -2147481600 | 211 |
*QA duplicate observations are no longer marked in segue1_target2 bitmasks. These are only marked in sourcetype in SpecObjAll.
The bitmask assignments for legacy_target2 are listed below:
| Category | Hex | Integer | Binary |
|---|---|---|---|
| Light Trap | 0x80000001 | -2147483647 | 20 |
| Reddening Standard | 0x80000002 | -2147483646 | 21 |
| Test | 0x80000004 | -2147483644 | 22 |
| QA Duplicate Observation* | 0x80000008 | -2147483640 | 23 |
| Sky | 0x80000010 | -2147483632 | 24 |
| Spectrophotometric Standard | 0x80000020 | -2147483616 | 25 |
| Guide Star | 0x80000040 | -2147483584 | 26 |
| Bundle Hole | 0x80000080 | -2147483520 | 27 |
| Quality Hole | 0x80000100 | -2147483392 | 28 |
| Hot Standard | 0x80000200 | -2147483136 | 29 |
| Southern Survey Target | 0x80000000 | -2147483648 | 231 |