# APOGEE Targeting Information

Note that the APOGEE data in DR15 are identical to those in DR14, but use the DR15 documentation pages for reference.

## Spectroscopic Target Selection and Target Flags

Every 7 deg2 APOGEE field has many more objects in it than APOGEE can observe. Targeting involves the process of selecting which objects will be observed. An object may have been targeted for spectroscopy for any one of many different purposes, or for several purposes at once. To keep track of these reasons, SDSS uses target flags. Target flags can be used in catalog queries to select only objects that were (or were not) targeted for a specific set of reasons.

The majority of APOGEE-2's targeted sample is composed of red giant stars, selected with very few criteria -- this is referred to as the "main sample" or "normal targets". The other scientific sample component comprises several programs that include (among others) stars with measured parameters and abundances from other spectroscopic studies, cluster members, embedded YSOs, and targets submitted by one of the numerous ancillary science programs. Additionally, a set of early-type stars is observed in order to measure terrestrial atmospheric contamination and remove it from all of the spectra (referred to as "tellurics").

Most of the discussion below focuses on APOGEE-2 targeting with significantly expanded details presented in Zasowski et al. (2017). Details for APOGEE-1 can be found here and with the expanded descriptions found in the APOGEE-1 targeting paper (Zasowski et al. 2013).

## APOGEE Target Bitmasks in DR15

If you are not familiar with bitmasks, please see our bitmask primer. The targeting flags, also called bitmasks, can be used to identify objects that were targeted for some particular reason(s). The target bitmasks used in APOGEE-2 are called APOGEE2_TARGET1, APOGEE2_TARGET2, and APOGEE2_TARGET3. The target bitmasks used for APOGEE-1 targets are APOGEE_TARGET1 and APOGEE_TARGET2 (and an unused one called APOGEE_TARGET3). N.B. The bits within the flags are not exactly aligned between the two generations of APOGEE.

We also include a simple bitmask called EXTRATARG in the summary data files and the CAS. This allows users to quickly select primary main survey targets, which have no EXTRATARG bit set (i.e., EXTRATARG=0). This is a straightforward way to avoid ancillary targets, commissioning data, telluric correction targets, duplicated observations, etc.

Some examples of using bitmasks are provided below.

## Core Science Targets

The "Core Science" programs in APOGEE-2 are those that receive the highest priority for both scheduling and completion.

### APOGEE-2 Main Red Giant Sample

APOGEE-2's primary sample of red giant stars is selected using H-band magnitude limits, dereddened (J-Ks)0 color limits, and gravity-sensitive optical photometry (certain halo fields only).

The magnitude limits are determined by the number of complete visits (hence, amount of total exposure time) expected for a group of stars. In a given field, some stars will be observed every that time APOGEE visits the field, and some will only be observed for a subset of the visits. A group of stars observed together in the same visit(s) is called a cohort, which comes in one of three types (short, medium, long), depending on how many visits it is expected to span. The type of cohort in which a star is included in a given design is recorded in the APOGEE2_TARGET1 targeting flags as "APOGEE2_SHORT", "APOGEE2_MEDIUM", or "APOGEE2_LONG" (bit 11, 12, or 13), and the magnitude limits are chosen such that the faintest stars in each cohort will have spectra with a final (combined) signal-to-noise of 100 per pixel.

H Magnitude Limits:

Number of Visits
H Magnitude Range
1
7.01 $\lt$ H $\lt$ 11.0
3
7.01 $\lt$ H $\lt$ 12.2
6
12.2 $\lt$ H $\lt$ 12.8
12
12.8 $\lt$ H $\lt$ 13.3
24
12.8 $\lt$ H $\lt$ 13.8 or 13.3 $\lt$ H $\lt$ 13.8
1In some disk cohorts, the bright limit was reduced to H=10; stars selected this way are flagged with APOGEE2_TARGET2 bit 23.

For the dereddened color selection, we apply a reddening correction to each potential target based on its E(H-4.5$\mu$m) color excess (using the RJCE method; Majewski et al. 2011, if 4.5$\mu$m photometry is available from either Spitzer or WISE) or on its E(B-V) reddening value in the Schlegel et al. (1998) maps. The method used for a given star is encoded in the star's APOGEE_TARGET1 or APOGEE2_TARGET1 bitmask: "APOGEE_IRAC_DERED" (bit 3), "APOGEE_WISE_DERED" (bit 4), "APOGEE_SFD_DERED" (bit 5), or APOGEE_NO_DERED (bit 6) if no reddening corrections were applied (the latter is largely confined to telluric absorption calibrators and stars on certain commissioning plates).

Comparison to stellar atmospheric and Galactic stellar population models indicate that within APOGEE's typical magnitude range, a color limit of (J-Ks)0 $\ge$ 0.5 mag substantially reduces the dwarf contamination in the final sample. For APOGEE-1 targets, a single color limit of (J-Ks)0 $\ge$ 0.5 was applied in disk and bulge fields, and a limit of (J-Ks)0 $\ge$ 0.3 mag in halo fields (which have far fewer target candidates). APOGEE-2 halo fields are treated the same as in APOGEE-1, but for APOGEE-2 targets in disk fields, a dual color limit was used, with a defined fraction of the targets having 0.5 $\leq$ (J-Ks)0 $\le$ 0.8 and the rest with (J-Ks)0 $\ge$ 0.8 mag. The intended fraction of targets in each color bin is recorded in the apogee2Design file for each plate design.

Stars with (J-Ks) and H within the relevant limits are then randomly sampled within each cohort. Note that the final total magnitude distribution of spectroscopic targets in a field may differ significantly from the distribution of candidates, since the former also depends on the number of each type of cohort in the field as well as on the fraction of APOGEE-2's science fibers allotted to each type of cohort.

In many of APOGEE-2's halo and dSph fields, we use Washington (M and T2) and DDO51 photometry to classify stars as dwarfs or giants prior to their selection as spectroscopic targets, in addition to the reddening and magnitude limits applied for each field (e.g., Majewski et al. 2000). This is done to increase the selection efficiency of giant stars in these particular fields, which have an intrinsically higher dwarf fraction for APOGEE's magnitude range than in the disk and bulge fields. Stars targeted as photometrically classified giants are flagged as "APOGEE_WASH_GIANT" (APOGEE_TARGET1 and APOGEE2_TARGET1 bit 7) and are prioritized over photometrically classified dwarfs ("APOGEE_WASH_DWARF", APOGEE_TARGET1 and APOGEE2_TARGET1 bit 8).

### Calibration and Star Clusters

In addition to the primary target sample, a number of stars with published stellar parameters or chemical abundances derived from (usually optical) spectroscopy are observed in order to calibrate the ASPCAP pipeline. These targets are flagged in APOGEE2_TARGET2 as "APOGEE2_STANDARD_STAR" (bit 2).

Bright stars observed with the APOGEE instrument's fiber-link to NMSU's 1-meter telescope are flagged with APOGEE2_TARGET2 bit 22. These stars have different telluric correction and sky subtraction properties (see Holtzman et al. 2010 for the properties of the telescope and Holtzman et al. 2015 for a description of specific data processing for this dataset).

A number of stars with high-quality APOGEE-1 data were also observed in APOGEE-2 to check for any pipeline shifts over time. Some stars are also targeted with both APOGEE-2N and APOGEE-2S to quantify any data differences between instruments. Stars deliberately targeted for these purposes are flagged with APOGEE2_TARGET2 bit 6.

APOGEE-2's footprint overlaps with those of several other stellar surveys and we intentionally target stars in common with these surveys. Stars chosen for this purpose are flagged with APOGEE2_TARGET2 bit 5, 13, 14, 15, 16, 17, and/or 18, depending on the survey.

APOGEE-2 targeting in stellar clusters falls into two categories. One is the targeting of well-characterized clusters (mostly globular), whose members are selected as those confirmed by existing abundance, proper motion, and/or radial velocity measurements. Stars observed for this reason are flagged in APOGEE2_TARGET2 as "APOGEE2_CALIB_CLUSTER" (bit 10). There are far fewer of these than in APOGEE-1 since nearly all clusters observable from the North were completed in APOGEE-1.

The other cluster category is the targeting of candidate members of poorly studied or unverified clusters, and candidate members of well-studied clusters identified solely by their spatial proximity to the cluster or their position relative to the cluster locus in a color-magnitude diagram. Stars in this category are flagged as "APOGEE2_SCI_CLUSTER" in APOGEE2_TARGET1 (bit 9).

N.B. Stars with APOGEE-1 targeting flags are documented here.

### Asteroseismic Targets

APOGEE-2 is expanding upon APOGEE-1's asteroseismic program (APOKASC) by completing a magnitude-limited sample of Kepler targets, with and without solarlike oscillations. This sample comprises giants with $T_{\rm eff} \le 5500$K and $\log{g} \le 3.5$, and dwarfs with $5000 \leq T_{\rm eff} \leq 6500$K and $\log{g} \le 3.5$; these pre-observation temperature and gravity estimates come from the revised Kepler Input Catalog (Huber et al. 2014) and the corrected temperature scale of Pinsonneault et al. (2012). Further spatial and parameter space coverage is effected by targeting stars in the K2 footprints, drawn from the Galactic Archaeology Program's sample of asteroseismic targets.

All APOKASC targets have APOGEE2_TARGET1 bit 30 set, with giants and dwarfs being further identified with APOGEE2_TARGET1 bits 27 and 28, respectively, if known.

N.B. Stars from APOGEE-1 programs are documented here.

## Goal Science Targets

Goal Science Programs are those that use the unique capabilities of APOGEE-2 to address questions that are natural extensions of our Core Science programs.

### Young Clusters

APOGEE-2 is targeting a number of deeply embedded young stellar clusters, in order to characterize the earliest stages of the older populations dominating the rest of the sample. By the end of SDSS-IV, APOGEE-2 will have observed approximately 200-1000 sources in each of $\sim$10 embedded clusters. This program is an extension of the APOGEE-1 IN-SYNC ancillary program and shares similar targeting procedures. Targets are drawn from pre-existing catalogs of young stellar objects, identified via their optical/IR photometry, IR excess, X-ray activity, Li abundance, H$\alpha$ excess, and/or variability.

Note that the ASPCAP pipeline does not include models for pre-main sequence stars, so the automated synthetic spectral fits (and subsequent Cannon results) are not likely to be meaningful for most of these sources. Sources targeted as part of the young cluster program are flagged with bit 5 of APOGEE2_TARGET3. A related ancillary program is specifically targeting young massive stars in the W3, W4, and W5 star-forming complexes.

### Kepler Objects of Interest

The APOGEE-2 Kepler Object of Interest (KOI) program contains $\sim$1000 KOIs and $\sim$200 non-planet-hosts distributed across five APOGEE-2 fields, supplemented by $\sim$200 KOIs observed in APOGEE-1. Planet hosts and KOIs were drawn from the NExScI archive using a simple magnitude limit of $H<14$ to identify all CONFIRMED or CANDIDATE targets in the fields. The non-host control sample was drawn from the Kepler Input Catalog (Brown et al. 2011), using the same $H \le 14$ magnitude limit and selected to provide the same T$_{\rm eff}$-$\log{g}$ joint density distribution as in the host+KOI sample. These control sample stars are used to fill fibers unused by the host+KOI sample.

Each APOGEE-2 KOI field is observed over 18 epochs, with cadencing sufficient to characterize a wide range of orbits. The host+KOI targets can be identified with bit 0 of APOGEE2_TARGET2, and the control sample targets with bit 2 of APOGEE2_TARGET2.

### M Dwarfs

APOGEE-1 targeted a substantial ancillary program of $\sim$1400 M dwarfs. In APOGEE-2, this sample in enhanced by known M~dwarfs in several fields, primarily in the halo and the Kepler Cygnus footprint; this extended sample contains some stars proposed as part of an APOGEE-2 ancillary program. These M dwarfs were drawn from the Kepler Input Catalog (Brown et al. 2011), with magnitude limits of $H \lt 11.5$, 12.1, and 12.5 for stars receiving 1, 2, or 3 visits.

M dwarf targets are flagged with the targeting bit 3 in APOGEE2_TARGET3 and/or any relevant ancillary program bits.

### Eclipsing Binaries

Approximately 100 EBs were targeted in APOGEE-1, predominantly in the Kepler footprint. In APOGEE-2, this sample is more than doubled to include additional Kepler-detected EBs as well as systems identified in the Kilodegree Extremely Little Telescope survey (KELT; Pepper et al. 2007). The Kepler targets are selected from the Kepler EB Catalog’s list of detached EBs (Prsa et al. 2011, Slawson et al. 2011), using a magnitude limit of $H \leq 13$. A total of ten EB targets are selected in each Kepler field, though not all may be available in the current data release. The KELT-based sample is selected from systems lying in already-planned APOGEE-2 field locations that are anticipated to be observed for eight epochs over the course of the survey. KELT itself is restricted to bright stars, so no additional magnitude cuts are required---simply the presence of a well-defined orbital period, with further preference towards those systems that have a detached morphology, are bright, and/or have shallow secondary eclipses. Up to a maximum of five KELT targets appear in any given field.

All EB targets are flagged with the bit 1 in APOGEE2_TARGET3.

### Substellar Companions

A number of stars are repeatedly targeted by APOGEE-2 in order to characterize substellar companions; this program focuses on red giant stars, for whom less is known about companion systems than for dwarf hosts. To maximize the number of final epochs available to characterize companion orbits, APOGEE-2's substellar companion search focuses on stars with a large number of RV measurements already taken with APOGEE-1. More specifically, this program selected five fields based on the number of epochs, position in the sky, and diversity of Galactic environment. These fields are planned to be observed numerous times to reach a final count of $\geq$24 epochs for all targets in this class. Within each field, the stars are selected from those targeted by APOGEE-1, prioritized first by the number of APOGEE-1 epochs and then by brightness, with brighter stars receiving higher priority.

Stars targeted as part of this class have targeting bit 4 set in APOGEE2_TARGET3.

### K2 Campaign Field Spectroscopic Follow-Up

APOGEE-2 is targeting several thousand giant stars in select K2 Mission Campaign fields, largely from the K2 Galactic Archaeology Program’s (GAP) sample of asteroseismic targets. These stars are selected from the pool of GAP candidates based purely on their magnitude, with additional non-GAP stars selected as oscillators based on K2 data. The total sample is observed over tens of visits divided among the campaigns, all or nearly all of which are being observed from the North.

The stars of this goal science program have targeting bit 6 set in APOGEE2_TARGET3.

## NMSU 1-meter Programs

The science programs that use the NMSU 1-meter generally require observations of stars that are brighter than the bright limit for the primary survey on the 2.5-meter. Generally, these programs augment Core or Goal science with APOGEE observations of bright, nearby, and, often, well-studied stars or by obtaining multiple epoch observations for variable sources. These programs are executed in a single-object observing mode and require slightly different data processing as is described by Holtzman et al. (2015).

All targets observed with the NMSU 1-meter have 1-m target flag (APOGEE2_TARGET2 bit 22) set, as well as any other relevant targeting flags. The programs are organized by the program title instead of the field name.

RR Lyrae
Motivated by future targeting in the survey, particularly in APOGEE-2 South, a small number of RR Lyrae (RRL) observations were made by APOGEE-2 and are available in this release. These stars were selected as bright sources accessible with the 1-m telescope at APO and observed for a varying number of epochs.

All pre-selected RRL stars have the APOGEE2_TARGET1 bit 24 set and others, if applicable.

M Dwarf
This program targets known M Dwarf stars with the aim of establishing an empirical metallicity scale and spectral atlas for M-dwarfs in the APOGEE spectral range.
Calibration
This program targets a number of stars with known parameters drawn from a variety of sources, such as those with angular diameters, asteroseismic measurements, Gaia targets, and optical abundance measurements.
Be Stars
This program targets known Be stars observable from the Northern hemisphere and too bright for the 2.5m.
Hipparcos
This program targets stars with distances from Hipparcos parallaxes and with complementary high resolution optical spectroscopy.
Moving Groups
This program targets known stars in nearby moving groups.
RCB
This program targets known hydrogen deficient carbon (HdC) and R Coronae Borealis (RCB) stars.
DQ Tau
This program targets a T Tauri binary system.

## Ancillary Targets

Targets observed as part of APOGEE-2's approved ancillary science programs are indicated in APOGEE2_TARGET3 as "APOGEE2_ANCILLARY" (bit 8) in addition to a bit set in APOGEE2_TARGET3 for each individual program. See the list below for a summary. Note that not all programs may have targets in DR15, which depends on the date of the observation, but all are included here for completeness. Questions about the targeting for these programs should be directed to the PIs and their colleagues.

N.B. Stars from APOGEE-1 ancillary programs are documented here.

### QSOs (APOGEE2_TARGET3 bit 10)

PI: F. Albareti (UAM/CSIC)
A selection of high-redshift quasars (z=2-2.4) to detect H$\beta$-[OIII] emission shifted into the near-IR.

Starting with 297,301 quasars of the SDSS-III/BOSS-DR12Q catalogue (Paris et al. 2015), we select 71,587 quasars that have a visual redshift in the range $2.06\le z \le 2.38$. This sample is further restricted by requiring Vega H-band magnitudes $<20$. However, only 20,796 quasars have H-band flux measurements from UKIDSS. For the remaining ones, we studied the correlation between UKIDSS H-band measurements and z-band SDSS magnitudes using quasars with UKIDSS H-band magnitude $<21$ (19,993 in total). Thus, for those quasars without H-band measurements we require z-band SDSS magnitude $<21.27$. Alternatively, we demand the H-band magnitude obtained either from UKIDSS or estimated from z-band SDSS measurements to be $<20$. In this way, we obtain a sample of 61,075 quasars. Only 971 are located in the APOGEE-2N halo fields (within a radius of 1.4 degrees from the center of the field). In each plate, our targets are prioritized by their H-band magnitudes.

### Cepheids (APOGEE2_TARGET3 bit 11)

PI: R. Beaton (OCIS/Princeton)
A set of Galactic Cepheids throughout the disk, to obtain multi-species abundances.

Targets were selected by cross-matching the General Catalog of Variable Stars (GCVS; Samus et al. 2007-2012), restricted to those stars of normal Cepheid and delta Cepheid types (CEP and DCEP designations in the GCVS, respectively), to the APOGEE-2N field footprint. The GCVS Cepheid catalog is further restricted to those stars with H magnitudes between 6.5 and 11 to ensure that S/N of 100 is safely obtained in 1 hour (to avoid problems of co-adding spectra during different phases). While only those stars with periods longer than 7 days are expected to show a MIR-color metallicity relationship, sources with periods less than 7 days were included in the target selection to increase overlap with the Genovali et al. (2014, 2015).

### Low Extinction Disk (APOGEE2_TARGET3 bit 12)

PI: J. Bovy (U Toronto)
A sample of luminous giants in low-extinction windows, in order to sample the far reaches of the Milky Way's disk.

For each pointing, targets are selected in the region of the field for which $A_H(D=7{\rm kpc}) \le 1.4$. This $A_H$ is computed from Marshall et al. (2006)'s 3D extinction map, using linear interpolation in distance and assuming $A_H/A_{Ks}=0.46/0.31$. Targets in this region are selected from the 2MASS catalog using the same 2MASS quality cuts and RJCE dereddening as the standard APOGEE disk targets. All potential targets are obtained by selecting stars with $(J?K_s)_0 \ge 0.8$ and $12 \le H \le 13$. A random subset of these are observed. Targets at the top of the list that were already observed as part of the regular disk sample in the $l = 34^\circ$ and $l = 64^\circ$ midplane fields are flagged, but not re-observed.

### Emission Line Stars (APOGEE2_TARGET3 bit 13)

PI: S. D. Chojnowski (NMSU)
Multi-epoch spectroscopy of a variety of B-type emission line stars, including several rare subtypes.

Our targets were selected according to very simple and somewhat subjective criteria. First, we obtained comprehensive lists of known OBA emission-line stars via SIMBAD, VIZIER catalogues, and papers. Next, we identified the stars falling in planned APOGEE-2 fields and assembled additional data for them, including spectral types and 2MASS magnitudes. For stars with suitable H magnitudes, we checked the literature and attempted to sort by sub-type, e.g. classical Be star, B[e] star, unclassified emission star, etc. Rare and unusual Be subtypes were targeted first, followed by the 6 members of NGC 7419.

### Moving Groups (APOGEE2_TARGET3 bit 14)

PI: J.J.Downes (UNAM)
Known members of Nearby Young Moving Groups, to characterize the groups and to generate high-quality young stellar spectral templates.

We made an all-sky catalogue including all currently known members of Nearby Young Moving Groups, comprising more than 2000 stars across the sky. Of these, we selected stars with $7 \le H \le 12.2$ falling within planned APOGEE-2 fields, resulting in 9 stars with a variety of spectral types. We also selected 22 bright stars ($H \le 9.2$) with $\delta \ge -10$, filling in the gaps in spectral type, to be observed with the NMSU 1-m telescope.

### Populations in NGC6791 (APOGEE2_TARGET3 bit 15)

PI: D. Geisler (Universidad de Concepcion)
A search for evidence of multiple stellar populations in the unusual open cluster NGC 6791, by targeting several dozen member stars.

All of our targets lie in the existing APOGEE field K21_071+10 and have $H \le 12$. They are drawn from several sources in order of priority: First, all stars observed optically by Geisler et al. (2012) meeting our S/N requirements were included, excluding those which already have APOGEE-1 spectra from DR12 or earlier, as none of these show evidence for the Na-O anticorrelation. The three Na-poor stars from Geisler et al. (2012) have been given top priority on our target list. Additional candidates were drawn from literature studies which provide membership information (Platais et al. 2011, Tofflemire et al. 2014, Bragaglia et al. 2014), excluding all known non-members. The remaining targets were drawn from 2MASS point sources which fall on the cluster upper RGB or RC in the color-magnitude diagram (again excluding known non-members from the above studies), and these are sorted in order of increasing radius from the cluster center out to the approximate tidal radius of ~24 arcmin (Dalessandro et al. 2015

### External Survey Calibrators (APOGEE2_TARGET3 bit 16)

PI: M.K.Ness (MPIA)
A sample of stars that fill in parameter space for a Cannon training set and increase the calibration overlap with other surveys.

### Faint Asteroseismic Giants (APOGEE2_TARGET3 bit 17)

PI: M. Pinnsonneault (OSU)
A sample of faint Kepler targets with asteroseismic measurements to probe stars at farther distances in the halo.

### Star Forming Complex in W3/4/5 (APOGEE2_TARGET3 bit 18)

PI: Alexandre Roman Lopes (Universidad de La Serena)
A study of embedded and/or massive stars in the W3, W4, and W5 star-forming regions.

The massive star sample was selected from a combination of near- to mid-infrared color-magnitude (CMD) and color-color (CCM) selection criteria, which are described in detail by Roman-Lopes (2016). The derived catalog was then cross-matched with known OB stars, using the SIMBAD database together with the catalogs of spectral classification of stars in the direction of W3-4-5.

The YSO sources were selected based on two different approaches. The first used Spitzer colors combined with X-ray detections, where available, to identify probable young star members. These are traditionally subdivided into three categories: Class I sources (deeply embedded protostars with large IR excesses), Class II sources (those with IR excesses typified by the presence of disks), and Class III sources (those lacking IR excesses, having had their disks dispersed). Targets were selected based on these criteria from the catalogues produced by Koenig et al. (2008), Koenig & Allen (2011), and Chauhan et al. (2011) for W5, and Rivera-Ingraham et al. (2011), Bik et al. (2012), and Roman-Zuniga et al. (2015) for W3-4.

### Evolved Stars (APOGEE2_TARGET3 bit 19)

PI: G. Stringfellow (UC Boulder)
A study of the hottest, most massive luminous evolved stars, to understand the variability of their emission line spectra.

A comprehensive search of all APOGEE-2N survey plate fields remaining to be drilled at the time of the ancillary call was conducted to locate rare stars within these fields for study. The focus was on massive high luminosity stars with early spectral types, and included supergiant and emission line stars, along with other rare objects. The search utilized Simbad and and the online WR star catalogue. A final subset of 15 stars in the range $6.5 \le H \le 12$ were selected, with an emphasis on observing all visits to study spectral variability of the stars.

### Dust Reddening Laws (APOGEE2_TARGET3 bit 20)

PI: E. Schlafly (LBNL)
A survey of typical red giant stars behind high dust column densities, to study the variations in the dust extinction law.

The APOGEE Reddening Survey target selection is designed to be as similar to the main APOGEE target selection as possible, to allow these two surveys to be statistically compatible. We adopt the exact same criteria as for ordinary APOGEE targets, as detailed in Zasowski et al. 2013; we use only stars with $9 \le H \le 11.4$ mag, so that S/N of about 100 can be reached in a single visit to a plate. In addition: (1) we prioritize targets in regions of high or interesting reddening, (2) we demand that the targets have optical magnitudes from PanSTARRS-1 in at least two of the griz bands, to allow the optical reddening law to be studied, and (3) we demand that the RJCE $E(J-K_s)$ reddening estimate is greater than 0.2, to avoid looking at unreddened stars.

### M Dwarfs in Kepler (APOGEE2_TARGET3 bit 21)

PI: V. Smith (NOAO)
A sample of M dwarfs, the most common stars in the Galaxy, to study their rich NIR spectra and extract stellar abundances.

The Kepler Exoplanet Archive was searched for all Kepler and Kepler Objects of Interest (KOI) systems having input catalog effective temperatures of $T_e \le 4300$K. The primary emphasis for this project is to push abundance analyses to the M-dwarfs, but some overlap is allowed with late K-dwarfs. A $T_e$ cut at 4300K will include types K6 and K7, and these targets will provide overlap with abundance analyses from optical high-resolution spectra. SNRs were calculated for the number of planned visits given for each of the APOGEE-2 fields, and only those targets expected to yield a SNR $\ge 70$ were then included in the target list.

### AGB Stars (APOGEE2_TARGET3 bit 22)

PI: O. Zamora (IAS)
A study of the chemical abundances of a sample of galactic carbon-rich asymptotic giant branch (AGB) stars, post-AGB stars, and planetary nebulae (PNe).

The targets were selected using four different sources: the General Catalogue of Galactic Carbon stars (Alknis et al. 2001), the Strasbourg-ESO Catalogue of Galactic Planetary Nebulae (Acker et al. 1992), the Torun catalogue of Galactic post-AGB and related objects (Szczerba et al. 2007), and the PhD thesis of Pedro Garcia-Lario (1992, unpublished). A cross-match with the APOGEE-2N fields was performed, finally selecting the targets with 2MASS H-band magnitude $7.0 \le H \le 13.5$.

## APOGEE Telluric Correction and Sky Targets

The APOGEE wavelength range contains a number of contaminant spectral features from Earth's atmosphere, such as CO2, H2O, and CH4 absorption bands and OH airglow emission lines. The APOGEE reduction pipeline (Nidever et al 2015) attempts to remove these features using observations of hot stars to characterize the telluric absorption. The stars that are used for the telluric absorption correction are chosen from amongst the bluest stars in the field (uncorrected for reddening) and are distributed spatially as evenly as possible across the field. Generally, the same set of about 15 stars is used for each visit to a given field (note the reduction from 35 tellurics used for APOGEE-1). These targets are flagged as "APOGEE2_TELLURIC" in APOGEE_TARGET2 (bit 9).

The data reduction pipeline also uses observations of star-less sky (i.e., sky positions with no 2MASS sources within 6 arcsec) to monitor the airglow and other emission. These "targets" are flagged in APOGEE2_TARGET2 as "APOGEE2_SKY" (bit 4). The resulting sky spectra are available in DR15, but only through the individual exposure stage, because sky subtraction is performed on an exposure-by-exposure basis.

N.B. Stars with APOGEE-1 targeting flags are documented here.

## Sample Targeting Bitmask Usage

Here are some examples of using the APOGEE2_TARGET1/2/3 targeting flags to identify subsamples of targets.

Which stars are in the main sample?
To select stars observed as part of APOGEE-2's "normal" sample (regardless of whether they overlap an ancillary or other special sample), look for stars identified as "APOGEE_SHORT", "APOGEE_MEDIUM", or "APOGEE_LONG" cohort members (see below; APOGEE2_TARGET1 flags 11, 12, 13). For example, using SQL syntax:


((apogee2_target1 & power(2,11)) != 0) | ((apogee2_target1 & power(2,12)) != 0) | ((apogee2_target1 & power(2,13)) != 0)


or using predefined constants in the CAS:


((apogee2_target1 & dbo.fApogeeTarget1('APOGEE2_SHORT'))  != 0) | ((apogee2_target1 & dbo.fApogeeTarget1('APOGEE2_MEDIUM')) != 0) | ((apogee2_target1 & (dbo.fApogeeTarget1('APOGEE2_LONG')) != 0)


or python:

(apogee2_target1 & 2**11 != 0) | (apogee2_target1 & 2**12 != 0) | (apogee2_target1 & 2**13 != 0)


Alternatively, there is a bitmask for the "normal" sample (APOGEE2_TARGET1 flag 14):

(apogee2_target1 & 2**14 != 0)

Which stars have literature parameters?
Another example might be to select stars that were targeted because they have pre-existing stellar parameter values in the literature. These targets have "APOGEE2_STANDARD_STAR" (APOGEE2_TARGET2 bit 2) set, corresponding to the SQL requirement:

(apogee2_target2 & power(2,2)) != 0


or in the CAS:

(apogee2_target2 & dbo.fApogeeTarget2('APOGEE_STANDARD_STAR')) != 0


or in python:

(apogee2_target2 & 2**2 != 0)


Note that this identifies stars that were targeted because they had existing literature parameters, not every star in the sample that has been studied elsewhere!

How do I get rid of the telluric calibrators?
One may be interested in removing all of the telluric calibrator targets from a given sample. This can be done by restricting the sample to all stars meeting the requirement that the APOGEE2_TARGET2 flag "APOGEE2_TELLURIC" (bit 9) is not set, in SQL:

(apogee2_target2 & power(2,9)) = 0


or python:

(apogee2_target2 & 2**9 == 0)


Of course, objects can (and often do) have multiple targeting bits set, and selections can be made on multiple criteria.

Which pre-known globular cluster members are photometric giants?
For example, to identify globular cluster members that are also photometrically classified as giants, impose the requirement that APOGEE2_TARGET2 flag "APOGEE2_CALIB_CLUSTER" (bit 10) and APOGEE2_TARGET1 flag "APOGEE2_WASH_GIANT" (bit 7) both be set, in SQL:

((apogee2_target2 & power(2,10)) != 0) && ((apogee2_target1 & power(2,7)) != 0)


or python:

(apogee_target2 & 2**10 != 0) & (apogee_target1 & 2**7 != 0)

Are the same bits always used to retrieve particular groups of targets observed in both APOGEE-1 and APOGEE-2?
As noted above, certain target classes were observed in both APOGEE-1 and APOGEE-2 and the corresponding targeting bits should be employed for selection. Efforts were made to have the same bits set in both APOGEE-1 and APOGEE-2 for these common groups of stars. Yet, there are occasional departures. For example, different bits are set for the APOKASC program stars that were observed in APOGEE-1 as opposed to those that were observed in APOGEE-2. In SQL, users would do:

(apogee_target1 & power(2,27)) != 0 (for APOGEE-1 APOKASC program stars)
(apogee2_target1 & power(2,30)) != 0 (for APOGEE-2 APOKASC program stars)


or python:

(apogee_target1 & 2**27 != 0) (for APOGEE-1 APOKASC program stars)
(apogee2_target1 & 2**30 != 0) (for APOGEE-2 APOKASC program stars)


The set of flags one needs to check depends on the particular query requirements. The tables at APOGEE2_TARGET1, APOGEE2_TARGET2, and APOGEE2_TARGET3, along with the APOGEE-1 flags APOGEE_TARGET1 and APOGEE_TARGET2, summarize what the available target flags mean.

## Targeting-Related Files

DR15 includes four types of files containing useful information on the stars (both targeted and non-targeted) in APOGEE-2's fields and on the fields themselves, the designs, and the plates in which the targets are organized (see further details on this organizational structure in Zasowski et al. 2013 and Zasowski et al. 2017. ).

File How Many?
apogee2Object one per field contains photometric and proper motion information on the candidate targets in the APOGEE-2 fields
N.B. Stars with observations in APOGEE-1 may or may not have data in an apogee2Object file.
apogee2Field single file contains information on the spatial fields, such as central coordinates
apogee2Design single file contains information on the individual designs, or groups of stars, like color limits and cohort fiber allocations
apogee2Plate single file contains information on the physical plates, such as drill angle

N.B. APOGEE-1 targeting files are documented here.

## Caveats and Special Notes

This section contains only items unique to APOGEE-2. Caveats and issues with APOGEE-1 observations are documented here.

### Overlap with MaNGA

APOGEE-2 observes during MaNGA time, using plates drilled for both surveys simultaneously. APOGEE-2 does not control the location of these pointings and, thus, they are "MaNGA-led". Due to the dither pattern used by MaNGA, and the resulting flux loss in APOGEE-2's single fibers, the faint limit for MaNGA-led fields is $H \le 11.5$, instead of the usual 12.2 for a 3-visit plate. Stars observed in a MaNGA-led design have APOGEE2_TARGET1 bit 15 set.

### Disk Bright Limit

During the early stages of the survey, the bright limit for a number of disk fields was changed from $H=7$ to $H=10$. This was done to avoid bright nearby stars that met the color criteria. Stars selected in designs that used this new limit are flagged with APOGEE2_TARGET2 bit 23.

### Proper Motion Catalogs

Many special targets (especially for the ancillary programs) have proper motions gathered from catalogs other than those in UCAC (used for the main survey targets), particularly for projects where high-accuracy proper motions were required. Here we give the references for these sources, identified by the PM_CAT tag for each star.

Catalog
Reference
KIC, KEPLER
(Kepler Input Catalog) Brown et al., 2011, AJ, 142, 112; see MAST site
CPS
(California Planet Survey) Target source only, proper motions from van Leeuwen, 2007, A&A, 474, 653
LSPM, LSPMN, LSPM-N, LSPMd
Lépine & Shara, 2005, AJ, 129, 1483
LG11
Lépine & Gaidos, 2011, AJ, 142, 138
N188
Platais et al., 2003, AJ, 126, 2922
Schodel+09
Schödel et al., 2009, A&A, 502, 91
CRD, JNKS, LUCY, MRTH, VSINI
Target source catalogs only; proper motions drawn from LSPM or LG11 (above)
Faherty_2009
Faherty et al., 2009, AJ, 137, 1
Jameson_2008
Jameson et al., 2008, MNRAS, 384, 1399
Kraus07
Kraus & Hillenbrand, 2007, AJ, 134, 2340
MTLS
Bonfils et al., 2005, A&A, 442, 635
PPMXL
The PPMXL Catalog
URAT, URAT-1
USNO Robotic Astrometric Telescope
HIP, Hipparcos
Hipparcos Proper Motion Catalog
Bouy
Bouy et al., 2015, A&A, 577, 148; catalog
GagneWebList2014
drawn from this source
HSOY
Gaia DR1 positions combined with the PPMXL catalog this source
prelim_PS1-2MASS
preliminary proper motions derived from comparing PanSTARRS1 and 2MASS positions
IGSL
Initial Gaia Source List