binary star
(binary, binary system)
(system of two stars co-orbiting)
A binary star is a pair of stars that orbit each
other. Double star means the same thing except
that it also includes stars that are not orbiting
and not close together but happen to be on the
same line of sight from Earth, referred to as apparent binary
or optical double stars.
Binary (or more) star systems are said to be common:
the most convincingly cited number I've found is that roughly third of
all star systems have two or more stars.
They are extremely useful in the study of stellar physics, both
to use the orbital dynamics for stellar parameter determination,
and for those close enough to interact further,
giving additional situations to observe,
to infer and test the physics of stellar structure.
A system can have three or more stars,
termed a higher-order multiple star system,
or sometimes the terms multiple star system and multiple star
are used specifically for three or more.
A common classification of binary stars is based on the method by which
they were determined to be binary:
- visual binary - separate stars can be seen or photographed.
- eclipsing binary - a periodic variation in luminosity suggesting a star passing in front of its companion.
- spectrum binary - a star whose spectrum looks like the combined spectrum of two stars.
- astrometric binary - measurement of the star's position in the sky over time suggests an orbit-like movement around an unseen companion.
- spectroscopic binary - measurement of the spectrum over time shows an apparent Doppler shift signifying the type of radial motion that orbiting a companion would produce.
Another classification is based upon how close
they are and how much they interact:
- compact binary - small orbits: one criteria is that they rotate in five days or less.
- close binary star - similar meaning: close enough to consider their cross-influence and interaction.
- detached binary - sufficiently distant that the stars are (basically) spherical.
- semidetached binary - sufficiently close that one of the stars transfers mass to the other, but not touching.
- contact binary - touching; at minimum, both stars "stretched" by gravity to a contact point.
A binary star's mass ratio (μ) is the ratio
of the two masses, i.e., 1 for stars of equal
mass. When the total mass can also be determined,
e.g., from the orbital period and size,
the mass of each star is evident.
Binary stars generally have similar composition
(as shown by their spectra),
as if they were formed together.
Binaries formed together are known as primordial binaries,
another sign being aligned rotation axes.
A capture requires the coincidence of stars passing close to each other,
plus something to change their velocity, such as a third
star, or with just two, tidal forces
between them (i.e., tidal-capture binaries).
The "close pass" is more likely in areas with a very high
density of stars such as the center of globular clusters or galaxies.
Given the large range of distances between the stars and the
different sizes/spectral types of the individual stars,
binary stars show a wide variety and interactions between them
produce characteristics unseen in non-binary stars.
For example:
- barium star - a star showing unexpected barium absorption lines, often apparently a red giant that previously received mass from a companion carbon star.
- X-ray binary (XRB) or binary X-ray system - includes an accreting neutron star or black hole, whose high gravitational potential energy provides the energy to produce X-rays (through shock). With a strong magnetic field, it might be an X-ray pulsar. These may be low-mass X-ray binaries (LMXB), intermediate-mass X-ray binaries (IMXB), or high-mass X-ray binaries (HMXB or massive X-ray binaries, MXRB) according to the mass of the companion star to the BH/neutron-star. Some are X-ray bursters, with bursts thought to stem from changing levels of accretion, such a transient termed an X-ray burst or X-ray nova. A Be X-ray binary (BeXRB) is a such a binary including a Be star.
- VV Cephei systems - (like VV Cephei) consisting of a giant star and a hot star forming a long-period, interacting eclipsing binary.
- ζ Aurigae systems - (or Zeta Aurigae systems, like the star ζ Aurigae) are analogous to VV Cephei systems but with a different class of giant.
- Algol.
- post-common envelope binary (PCEB).
The commonly-used system for designating the individual stars of a
binary/multiple star system consist of adding letters to the star
system's designator, with letter "A" for the brightest,
"B" for the second
brightest, then "C" and so on.
For example, the two stars making up Sirius are termed
"Sirius A" and "Sirius B".
If two are very close and a third is distant, the two
close stars might use lower-case suffixes, i.e., "Aa" and "Ab",
with the further member called "B".
(star type,binary stars,double stars)
Further reading:
http://en.wikipedia.org/wiki/Binary_star
Referenced by pages:
accretion
accretion disk
Aitken Double Star Catalogue (ADS)
ALMA-PILS Survey
Alpha Centauri (α Centauri)
Am star
apsis
astrometric binary
Black Widow Pulsar (B1957+20)
Burnham Double Star Catalogue (BDS)
black hole binary (BHB)
black hole merger
blended spectra
binary neutron star (BNS)
BPASS
brown dwarf (BD)
carbon star (C)
candidate companion (CC)
methylidyne (CH)
circumbinary planet
common envelope
COMPAS
contact binary
core collapse
chemically peculiar star (CP star)
CRIRES
double-line spectroscopic binary (SB2)
double star
double star designation
dwarf nova (DN)
eclipsing binary (E)
EF Eridani
extra-solar planet
failed binary
galactic binary
GG Tau
globular cluster (GC)
gravitational lensing
GRO J1655-40
Guide Star Catalog (GSC)
gravitational wave (GW)
GW detection (GW)
hardness
HD 133131
HD 189733 b
heartbeat star
Heggie-Hills law
helium burning
helium planet
helium star
high-velocity star
Hipparcos
instability region
J1713-0747
Kepler Telescope
Kepler-16b
Kepler radius
Laplace-Lagrange secular theory
LB-1
Luhman 16
Luyten 726-8
mass function
mass loss
mass ratio (μ)
mass transfer
gravitational microlensing
minimum mass (m sin i)
main-sequence lifetime (MS lifetime)
multiplicity fraction
neutron star (NS)
nova (N)
optical double
orbital inclination
orbit plot
post-common envelope binary (PCEB)
planet
planetary system
probability mass function (PMF)
P-Pdot diagram
Procyon
proper motion (PM)
Hulse-Taylor Binary (PSR B1913+16)
pulsar timing array (PTA)
pulsar (PSR)
radial velocity (RV)
redshift (z)
Rigel
Roche lobe
Rossiter-McLaughlin effect (RM effect)
Catalogue of Southern Double Stars
radial velocity method
Scholz's Star
Sirius
solar system
spectroscopic binary (SB)
spectrum binary
stellar population synthesis (SPS)
SS 433
star system
StarTrack
stellar-mass black hole
stellar distance determination
stellar evolution
stellar kinematics
stellar parameter determination
subdwarf (sd)
sunspot
surface gravity
symbiotic binary (SS)
tidal capture
tidal migration
transient
transit
transiting planet
T Tauri
transit timing variations (TTV)
turn-off point (TO)
Type Ia supernova
variable star
visual binary
Vogt-Russell theorem (VR theorem)
wide binaries (WB)
WR 140
X-ray burster (XRB)
ZTF J1539+5027
Index