?          Uncertain
A          Atoll source (neutron star)
AGN        Active galactic nuclei
AGN?       Possible active galactic nuclei
AXP        Anomalous X-ray pulsar
B          Burster (neutron star)
Be         B-type emission-line star
Be?        Possible B-type emission-line star
BH         Black hole (confirmed mass evaluation)
BHC        Black hole candidate
BHC?       Possible black hole candidate
Cluster    Cluster of galaxies
Cluster?   Possible cluster of galaxies
CV         Cataclysmic variable
CV?        Possible cataclysmic variable
D          Dipping source
G          Globular Cluster X-ray source
HMXB       High-mass X-ray binary
HMXB?      Possible high-mass X-ray binary
LMXB       Low-mass X-ray binary
LMXB?      Possible low-mass X-ray binary
Mol Cloud  Molecular cloud
Mol Cloud? Possible molecular cloud
NS         Neutron star
NS?        Possible neutron star
PSR        Radio pulsar
PWN        Pulsar wind nebula
QSO        Quasar
SGR        Soft gamma-ray repeater
SNR        Supernova remnant
Sy         Seyfert galaxy
Sy1?       Possible Seyfert 1 galaxy
Sy1        Seyfert 1 galaxy
Sy1h       Broad polarized Balmer lines detected
Sy1i       Broad Paschen lines observed in the infrared
Sy1.2      Intermediate Seyfert galaxy
Sy1.5      Intermediate Seyfert galaxy
Sy1.9      Intermediate Seyfert galaxy
Sy2        Seyfert 2 galaxy
Symb       Symbiotic star
T          Transient source
U          Ultrasoft source
XB         Galactic X-ray binary
XB?        Possible galactic X-ray binary
XP         X-ray pulsar
Z          Z-type source (neutron star)