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GCVS Variability Types
and
Distribution Statistics of Designated Variable Stars
According to their Types of Variability
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I. GCVS Variability Types.

An improved system of variability classification is used in the fourth
edition of the GCVS, based on recent developments in classification
principles and taking into account the suggestions of a number of
specialists. Variability types are grouped according to the major
astrophysical reasons for variability, viz.,

1. eruptive (FU, GCAS, I, IA, IB, IN, INA, INB, INT, IT, IN(YY), IS, ISA,
ISB, RCB, RS, SDOR, UV, UVN, WR),
2. pulsating (ACYG, BCEP, BCEPS, CEP, CEP(B), CW, CWA, CWB, DCEP, DCEPS,
DSCT, DSCTC, GDOR, L, LB, LC, M, PVTEL, RPHS, RR, RR(B), RRAB,
RRC, RV, RVA, RVB, SR, SRA, SRB, SRC, SRD, SXPHE, ZZ, ZZA, ZZB),
3. rotating (ACV, ACVO, BY, ELL, FKCOM, PSR, SXARI),
4. cataclysmic (explosive and novalike) variables (N, NA, NB, NC, NL, NR,
SN, SNI, SNII, UG, UGSS, UGSU, UGZ, ZAND),
5. eclipsing binary systems (E, EA, EB, EW, GS, PN, RS, WD, WR, AR, D, DM,
DS, DW, K, KE, KW, SD),
6. intense variable X-ray sources (X, XB, XF, XI, XJ, XND, XNG, XP, XPR,
XPRM, XM),
7. other symbols (BLLAC, CST, GAL, L:, QSO, S, *, +, :).
8. the new variability types (ZZO, AM, R, BE, LBV, BLBOO, EP, SRS, LPB)


All of these classes include objects of a dissimilar nature that belong
to different types of light variability. On the other hand, an object
may be variable because of almost all of the possible reasons or because
of any combination of them. If a variable belongs to several types of
variability, the types are joined in the data field by a "+" sign, e.g.,
E+UG, UV+BY.

Despite considerable success in understanding stellar variability pro-
cesses, the classification adopted in the Catalogue is far from perfect.
This is especially the case for explosive, symbiotic and novalike
variables; X-ray sources; and peculiar objects.

The new variability types (ZZO, AM, R, BE, LBV, BLBOO, EP, SRS, LPB)
have been added in the Name-Lists 67- 77 and in the GCVS vol.V.

ZZO ZZ Cet type variables of the DO spectral type showing HeII and
and CIV absorpion lines in their spectra.

AM AM Her type variables; close binary systems consisting of a
dK-dM type dwarf and of a compact object with strong magnetic
field, characterized by variable linear and circular polarization
of light. The total range of light variations may reach 4-5 mag V.

R Close binary systems characterized by the presence of strong
reflection (re-radiation) of the light of the hot star
illuminating the surface of the cooler companion. Light curves
are sinusoidal with the period equal to Porb, maximum brightness
coinciding with the passage of the hot star in front of the
companion. The eclipse may be absent. The range of light
variation is about 0.5-1.0mag V (KV Vel).

BE It becomes more and more clear that, although the majority of Be
stars are photometrically variable, not all of them could be
properly called GCAS variables. Quite a number of them show
small-scale variations not necessarily related to shell events; in
some cases the variations are quasi-periodic. By now we are not
able to present an elaborated system of classification for Be
variables, but we adopt a decision that in the cases when a Be
variable cannot be readily described as a GCAS star we give simply
BE for the type of variability.

EP Stars showing eclipses by their planets. Prototype: V0376 Peg.

SRS Semiregular pulsating red giants with short period (several days to a month),
probably high-overtone pulsators. Prototype: AU Ari.

GDOR - Gamma Doradus stars. Early type F dwarfs showing (multiple) periods
from several tenths of a day to slightly in excess of one day.
Amplitudes usually do not exceed 0.1 mag. Presumably low degree g-mode
non-radial pulsators. Prototype: gamma Dor.

RPHS Very rapidly pulsating hot (subdwarf B) stars. Typical periods
are hundreds of seconds, amplitudes are within several hundredths of a
magnitude. Prototype: V361 Hya = EC 14026-2647.

LPB The comparatively long-period pulsating B stars (periods exceeding
(LBV) one day).

BLBOO The so-called "anomalous Cepheids", i.e. stars with periods
characteristic of comparatively long-period RRAB variables, but
considerably brighter by luminosity (BL Boo = NGC 5466 V19).


1. Eruptive Variable Stars

Eruptive variables are stars varying in brightness because of
violent processes and flares occurring in their chromospheres
and coronae. The light changes are usually accompanied by shell
events or mass outflow in the form of stellar winds of variable
intensity and/or by interaction with the surrounding interstellar
medium. This class includes the following types:

FU Orion variables of the FU Orionis type. Characterized by
gradual increases in brightness by about 6 mag in several months,
followed by either almost complete constancy at maximum that is
sustained for long periods of time or slow decline by 1-2 mag.
Spectral types at maximum are in the range Ae(alpha) - Gpe(alpha).
After an outburst, a gradual development of an emission spectrum
is observed and the spectral type becomes later. These variables
probably mark one of the evolutionary stages of T Tauri-type Orion
variables (INT), as evidenced by an outburst of one member, V1057
Cyg, but its decline (2.5 mag in 11 years) commenced immediately
after maximum brightness was attained. All presently known FU Ori
variables are coupled with reflecting cometary nebulae.

GCAS Eruptive irregular variables of the Gamma Cas type. These
are rapidly rotating B III-IVe stars with mass outflow from their
equatorial zones. The formation of equatorial rings or disks is
often accompanied by temporary fading. Light amplitudes may reach
1.5 mag in V.

I Poorly studied irregular variables with unknown features of light
variations and spectral types. This is a very inhomogeneous group
of objects.

IA Poorly studied irregular variables of early (O-A) spectral type.

IB Poorly studied irregular variables of intermediate (F-G) to
late (K-M) spectral type.

IN Orion variables. Irregular, eruptive variables connected with
bright or dark diffuse nebulae or observed in the regions of these
nebulae. Some of them may show cyclic light variations caused by
axial rotation. In the Spectrum-Luminosity diagram, they are
found in the area of the main sequence and subgiants. They are
probably young objects that, during the course of further
evolution, will become light-constant stars on the zero-age main
sequence (ZAMS). The range of brightness variations may reach
several magnitudes. In the case of rapid light variations having
been observed (up to 1 mag in 1-10 days), the letter "S" is added
to the symbol for the type (INS). This type may be divided into
the following subtypes:

INA Orion variables of early spectral types (B-A or Ae). They are often
characterized by occasional abrupt Algol-like fadings (T Ori);

INB Orion variables of intermediate and late spectral types, F-M or
Fe-Me (BH Cep, AH Ori). F-type stars may show Algol-like fadings
similar to those of many INA stars; K-M stars may produce flares
along with irregular light variations;

INT,IT Orion variables of the T Tauri type. Stars are assigned to
this type on the basis of the following (purely spectroscopic)
criteria: spectral types are in the range Fe-Me. The spectra of
most typical stars resemble the spectrum of the solar
chromosphere. The feature specific to the type is the presence of
the flourescent emission lines Fe II 4046, 4132 A (anomalously
intense in the spectra of these stars), emission lines [Si II] and
[O I], as well as the absorption line Li I 6707 A. These variables
are usually observed only in diffuse nebulae. If it is not
apparent that the star is associated with a nebula, the letter "N"
in the symbol for the type may be omitted, e.g., IT (RW AUR);

IN(YY) Some Orion variables (YY Ori) show the presence of absorption
components on the redward sides of emission lines, indicating the
infall of matter toward the stars' surfaces. In such cases, the
symbol for the type may be accompanied by the symbol "YY".

IS Rapid irregular variables having no apparent connection with diffuse
nebulae and showing light changes of about 0.5 - 1.0 mag within
several hours or days. There is no strict boundary between rapid
irregular and Orion variables. If a rapid irregular star is
observed in the region of a diffuse nebula, it is considered an
Orion variable and designated by the symbol INS. To attribute
a variable to the IS type, it is necessary to take much care to be
certain that its light changes are really not periodic. Quite a
number of the stars assigned to this type in the third edition of
the GCVS turned out to be eclipsing binary systems, RR Lyrae
variables, and even extragalactic BL Lac objects.

ISA Rapid irregular variables of the early spectral types, B-A or Ae;

ISB Rapid irregular variables of the intermediate and late spectral
types, F-M and Fe-Me.

RCB Variables of the R Coronae Borealis type. These are hydrogen-poor,
carbon- and helium-rich, high-luminosity stars belonging to the
spectral types Bpe-R, which are simultaneously eruptive and
pulsating variables. They show slow nonperiodic fadings by 1-9
mag in V lasting from a month or more to several hundred days.
These changes are superposed on cyclic pulsations with amplitudes
up to several tenths of a magnitude and periods in the range
30-100 days.

RS Eruptive variables of the RS Canum Venaticorum type. This type is
ascribed to close binary systems with spectra showing Ca II H and
K in emission, their components having enhanced chromospheric
activity that causes quasi-periodic light variability. The period
of variation is close to the orbital one, and the variability
amplitude is usually as great as 0.2 mag in V (UX Ari). They are
X-ray sources and rotating variables. RS CVn itself is also an
eclipsing system (see below).

SDOR Variables of the S Doradus type. These are eruptive,
high-luminosity Bpec-Fpec stars showing irregular (sometimes
cyclic) light changes with amplitudes in the range 1-7 mag in V.
They belong to the brightest blue stars of their parent galaxies.
As a rule, these stars are connected with diffuse nebulae and
surrounded by expanding envelopes (P Cyg, Eta Car).

UV Eruptive variables of the UV Ceti type, these are K Ve-M Ve stars
sometimes displaying flare activity with amplitudes from
several tenths of a magnitude up to 6 mag in V. The amplitude is
considerably greater in the ultraviolet spectral region. Maximum
light is attained in several seconds or dozens of seconds after
the beginning of a flare; the star returns to its normal
brightness in several minutes or dozens of minutes.

UVN Flaring Orion variables of spectral types Ke-Me. These are
phenomenologically almost identical to UV Cet variables observed
in the solar neighborhood. In addition to being related to
nebulae, they are normally characterized by being of earlier
spectral type and greater luminosity, with slower development of
flares (V389 Ori). They are possibly a specific subgroup of INB
variables with irregular variations superimposed by flares.

WR Eruptive Wolf-Rayet variables. Stars with broad emission features
of He I and He II as well as C II-C IV, O II-O IV, and N III-N V.
They display irregular light changes with amplitudes up to 0.1 mag
in V, which are probably caused by physical processes, in
particular, by nonstable mass outflow from their atmospheres.

2. Pulsating Variable Stars

Pulsating variables are stars showing periodic expansion and
contraction of their surface layers. The pulsations may be radial
or nonradial. A radially pulsating star remains spherical in
shape, while in the case of nonradial pulsations the star's shape
periodically deviates from a sphere, and even neighboring zones of
its surface may have opposite pulsation phases.

Depending on the period value, on the mass and evolutionary status
of the star, and on the scale of pulsational phenomena, the
following types of pulsating variables may be distinguished:

ACYG Variables of the Alpha Cygni type, which are nonradially pulsating
supergiants of Bep-AepIa spectral types. The light changes with
amplitudes of the order of 0.1 mag often seem irregular, being
caused by the superposition of many oscillations with close
periods. Cycles from several days to several weeks are observed.

BCEP Variables of the Beta Cephei type (Beta Cep, Beta CMa), which are
pulsating O8-B6 I-V stars with periods of light and
radial-velocity variations in the range of 0.1 - 0.6 days and light
amplitudes from 0.01 to 0.3 mag in V. The light curves are similar
in shape to average radial-velocity curves but lag in phase by a
quarter of the period, so that maximum brightness corresponds to
maximum contraction, i.e., to minimum stellar radius. The
majority of these stars probably show radial pulsations, but some
(V469 Per) display nonradial pulsations; multiperiodicity is
characteristic of many of these stars.

BCEPS A short-period group of Beta Cep variables. The spectral types are
B2-B3 IV-V; periods and light amplitudes are in the ranges 0.02 -
0.04 days and 0.015 - 0.025 days, respectively, i.e., an order of
magnitude smaller than the normally observed ones.

CEP Cepheids. Radially pulsating, high luminosity (classes Ib-II) vari-
ables with periods in the range of 1-135 days and amplitudes from
several hundredths to 2 mag in V (in the B band, the amplitudes
are greater). Spectral type at maximum light is F; at minimum,
the types are G-K. The longer the period of light variation,
the later is the spectral type. The maximum of the surface-layer
expansion velocity almost coinciding with maximum light.

CEP(B) Cepheids (TU Cas, V 367 Sct) displaying the presence of two or
more simultaneously operating pulsation modes (usually the
fundamental tone with the period P0 and the first overtone P1).
The periods P0 are in the range from 2 to 7 days, with the ratio
P1/P0 approx. 0.71.

CW Variables of the W Virginis type. These are pulsating variables of
the galactic spherical component (old disk) population with
periods of approximately 0.8 to 35 days and amplitudes from 0.3 to
1.2 mag in V. They obey a period-luminosity relation different
from that for Delta Cep variables (see DCEP). For an equal period
value, the W Vir variables are fainter than the Delta Cep stars by
0.7 - 2 mag. The light curves of W Vir variables for some period
intervals differ from those of Delta Cep variables for
corresponding periods either by amplitudes or by the presence of
humps on their descending branches, sometimes turning into broad
flat maxima. W Vir variables are present in globular clusters and
at high galactic latitudes. They may be separated into the
following subtypes:

CWA W Vir variables with periods longer than 8 days (W Vir);

CWB W Vir variables with periods shorter than 8 days (BL Her).

DCEP These are the classical cepheids, or Delta Cep-type variables. Com-
paratively young objects that have left the main sequence and
evolved into the instability strip of the Hertzsprung-Russell
(H-R) diagram, they obey the well-known Cepheid period-luminosity
relation and belong to the young disk population. DCEP stars are
present in open clusters. They display a certain relation between
the shapes of their light curves and their periods.

DCEPS These are Delta Cep variables having light amplitudes <0.5 mag in
V (<0.7 mag in B) and almost symmetrical light curves (M-m
approx. 0.4 - 0.5 periods); as a rule, their periods do not exceed
7 days. They are probably first-overtone pulsators and/or are in
the first transition across the instability strip after leaving
the main sequence (SU Cas).

Traditionally, both Delta Cep and W Vir stars are quite often called
Cepheids because it is often impossible to discriminate between
them on the basis of the light curves for periods in the range 3 -
10 days. However, these are distinct groups of entirely different
objects in different evolutionary stages. One of the significant
spectral differences between W Vir stars and Cepheids is the
presence, during a certain phase interval, of hydrogen-line
emission in the former and of Ca II H and K emission in the
latter.

DSCT Variables of the Delta Scuti type. These are pulsating variables of
spectral types A0-F5 III-V displaying light amplitudes from 0.003
to 0.9 mag in V (usually several hundredths of a magnitude) and
periods from 0.01 to 0.2 days. The shapes of the light curves,
periods, and amplitudes usually vary greatly. Radial as well as
nonradial pulsations are observed. The variability of some
members of this type appears sporadically and sometimes completely
ceases, this being a consequence of strong amplitude modulation
with the lower value of the amplitude not exceeding 0.001 mag
in some cases. The maximum of the surface layer expansion does not
lag behind the maximum light for more than 0.1 periods. DSCT stars are
representatives of the galactic disk (flat component) and are
phenomenologically close to the SX Phe variables.

DSCTC Low amplitude group of Delta Sct variables (light amplitude <0.1
mag in V). The majority of this type's representatives are stars
of luminosity class V; objects of this subtype generally are
representative of the Delta Sct variables in open clusters.

L Slow irregular variables. The light variations of these stars show no
evidence of periodicity, or any periodicity present is very poorly
defined and appears only occasionally. Like for the type I, stars are
often attributed to this type because of being insufficiently studied.
Many type L variables are really semiregulars or belong to other types.

LB Slow irregular variables of late spectral types (K, M, C, S); as a
rule, they are giants (CO Cyg). This type is also ascribed, in
the GCVS, to slow red irregular variables in the case of unknown
spectral types and luminosities.

LC Irregular variable supergiants of late spectral types having amplitudes
of about 1 mag in V (TZ Cas).

M Mira (Omicron) Ceti-type variables. These are long-period variable
giants with characteristic late-type emission spectra (Me, Ce, Se) and
light amplitudes from 2.5 to 11 mag in V. Their periodicity is
well pronounced, and the periods lie in the range between 80 and
1000 days. Infrared amplitudes are usually less than in the
visible and may be <2.5 mag. For example, in the K band they
usually do not exceed 0.9 mag. If the amplitudes exceed 1 - 1.5
mag , but it is not certain that the true light amplitude exceeds 2.5
mag, the symbol "M" is followed by a colon, or the star is
attributed to the semiregular class with a colon following the
symbol for that type (SR).

PVTEL Variables of the PV Telescopii type. These are helium supergiant
Bp stars with weak hydrogen lines and enhanced lines of He and C.
They pulsate with periods of approximately 0.1 to 1 days, or vary
in brightness with an amplitude of 0.1 mag in V during a time
interval of about a year.

RR Variables of the RR Lyrae type, which are radially-pulsating giant A-F
stars having amplitudes from 0.2 to 2 mag in V. Cases of variable
light-curve shapes as well as variable periods are known. If
these changes are periodic, they are called the "Blazhko effect."

Traditionally, RR Lyrae stars are sometimes called short-period
Cepheids or cluster-type variables. The majority of these stars belong
to the spherical component of the Galaxy; they are present, sometimes in
large numbers, in some globular clusters, where they are known as
pulsating horizontal-branch stars. Like Cepheids, maximum
expansion velocities of surface layers for these stars practically
coincide with maximum light.

RR(B) RR Lyrae variables showing two simultaneously operating pulsation
modes, the fundamental tone with the period P0 and the first
overtone, P1 (AQ Leo). The ratio P1/P0 is approximately 0.745;

RRAB RR Lyrae variables with asymmetric light curves (steep ascending
branches), periods from 0.3 to 1.2 days, and amplitudes from 0.5
to 2 mag in V;

RRC RR Lyrae variables with nearly symmetric, sometimes sinusoidal, light
curves, periods from 0.2 to 0.5 days, and amplitudes not greater
than 0.8 mag in V (SX UMa).

RV Variables of the RV Tauri type. These are radially pulsating
supergiants having spectral types F-G at maximum light and K-M at
minimum. The light curves are characterized by the presence of
double waves with alternating primary and secondary minima that
can vary in depth so that primary minima may become secondary and
vice versa. The complete light amplitude may reach 3-4 mag in V.
Periods between two adjacent primary minima (usually called formal
periods) lie in the range 30-150 days (these are the periods
appearing in the Catalogue). Two subtypes, RVA and RVB, are
recognized:

RVA RV Tauri variables that do not vary in mean magnitude (AC Her);

RVB RV Tauri variables that periodically (with periods from 600 to
1500 days and amplitudes up to 2 mag in V) vary in mean
magnitude (DF Cyg, RV Tau).

SR Semiregular variables, which are giants or supergiants of intermediate
and late spectral types showing noticeable periodicity in their
light changes, accompanied or sometimes interrupted by various
irregularities. Periods lie in the range from 20 to >2000 days,
while the shapes of the light curves are rather different and
variable, and the amplitudes may be from several hundredths to
several magnitudes (usually 1-2 mag in V).

SRA Semiregular late-type (M, C, S or Me, Ce, Se) giants displaying
persistent periodicity and usually small (<2.5 mag in V) light
amplitudes (Z Aqr). Amplitudes and light-curve shapes generally
vary and periods are in the range of 35-1200 days. Many of these
stars differ from Miras only by showing smaller light amplitudes;

SRB Semiregular late-type (M, C, S or Me, Ce, Se) giants with poorly
defined periodicity (mean cycles in the range of 20 to 2300 days)
or with alternating intervals of periodic and slow irregular changes,
and even with light constancy intervals (RR CrB, AF Cyg). Every star
of this type may usually be assigned a certain mean period
(cycle), which is the value given in the Catalogue. In a number
of cases, the simultaneous presence of two or more periods of
light variation is observed;

SRC Semiregular late-type (M, C, S or Me, Ce, Se) supergiants (Mu Cep) with
amplitudes of about 1 mag and periods of light variation from 30 days to
several thousand days;

SRD Semiregular variable giants and supergiants of F, G, or K spectral
types, sometimes with emission lines in their spectra. Amplitudes
of light variation are in the range from 0.1 to 4 mag, and the range of
periods is from 30 to 1100 days (SX Her, SV UMa).

SXPHE Phenomenologically, these resemble DSCT (Delta Sct) variables and
are pulsating subdwarfs of the spherical component, or old disk
galactic population, with spectral types in the range A2-F5. They
may show several simultaneous periods of oscillation, generally in
the range 0.04-0.08 days, with variable-amplitude light changes
that may reach 0.7 mag in V. These stars are present in globular
clusters.

ZZ ZZ Ceti variables. These are nonradially pulsating white dwarfs that
change their brightnesses with periods from 30 s to 25 min and
amplitudes from 0.001 to 0.2 mag in V. They usually show several
close period values. Flares of 1 mag are sometimes observed;
however, these may be explained by the presence of close UV Ceti
companions.

These variables are divided into the following subtypes:

ZZA ZZ Cet-type variables of DA spectral type (ZZ Cet) having only
hydrogen absorption lines in their spectra;

ZZB ZZ Cet-type variables of DB spectral type having only helium
absorption lines in their spectra.

3. Rotating Variable Stars

Variable stars with nonuniform surface brightness and/or
ellipsoidal shapes, whose variability is caused by axial rotation
with respect to the observer. The nonuniformity of surface
brightness distributions may be caused by the presence of spots or
by some thermal or chemical inhomogeneity of the atmosphere caused
by a magnetic field whose axis is not coincident with the rotation
axis. These stars are subdivided into the following types:

ACV Alpha2 Canum Venaticorum variables. These are main-sequence stars
with spectral types B8p-A7p and displaying strong magnetic fields.
Spectra show abnormally strong lines of Si, Sr, Cr, and rare
earths whose intensities vary with rotation. They exhibit magnetic
field and brightness changes (periods of 0.5-160 days or more). The
amplitudes of the brightness changes are usually withine 0.01-0.1 mag
in V.

ACVO Rapidly oscillating Alpha2 CVn variables. These are nonradially
pulsating, rotating magnetic variables of Ap spectral type (DO
Eri). Pulsation periods are in the range of 6-12 mmag (0.004-0.01
days), while amplitudes of light variation caused by the pulsation
are about 0.01 mag in V. The pulsational variations are superposed
on those caused by rotation.

BY BY Draconis-type variables, which are emission-line dwarfs of dKe-dMe
spectral type showing quasiperiodic light changes with periods
from a fraction of a day to 120 days and amplitudes from several
hundredths to 0.5 mag in V. The light variability is caused by
axial rotation of a star with a variable degree of nonuniformity
of the surface brightness (spots) and chromospheric activity.
Some of these stars also show flares similar to those of UV Cet
stars, and in those cases they also belong to the latter type and
are simultaneously considered eruptive variables.

ELL Rotating ellipsoidal variables (b Per, Alpha Vir). These are close
binary systems with ellipsoidal components, which change combined
brightnesses with periods equal to those of orbital motion because
of changes in emitting areas toward an observer, but showing no
eclipses. Light amplitudes do not exceed 0.1 mag in V.

FKCOM FK Comae Berenices-type variables. These are rapidly rotating
giants with nonuniform surface brightnesses, which have G-K spectral
types with broad H and K Ca II emission and sometimes Halpha.
They may also be spectroscopic binary systems. Periods of light
variation (up to several days) are equal to rotational periods,
and amplitudes are several tenths of a magnitude. It is not
excluded that these objects are the product of further evolution
of EW (W UMa) close binary systems (see below).

PSR Optically variable pulsars (CM Tau), which are rapidly rotating
neutron stars with strong magnetic fields, radiating in the radio,
optical, and X-ray regions. Pulsars emit narrow beams of
radiation, and periods of their light changes coincide with
rotational periods (from 0.004 to 4 s), while amplitudes of the
light pulses reach 0.8 mag.

SXARI SX Arietis-type variables. These are main-sequence B0p-B9p stars
with variable-intensity He I and Si III lines and magnetic fields.
They are sometimes called helium variables. Periods of light and
magnetic field changes (about 1 day) coincide with rotational
periods, while amplitudes are approximately 0.1 mag in V. These
stars are high-temperature analogs of the ACV variables.

4. Cataclysmic (Explosive and Novalike) Variables

These are variable stars showing outbursts caused by thermonuclear
burst processes in their surface layers (novae) or deep in their
interiors (supernovae). We use the term "novalike" for
variables that show novalike outbursts caused by rapid energy
release in the surrounding space (UG-type stars - see
below) and also for objects not displaying outbursts but
resembling explosive variables at minimum light by their spectral
(or other) characteristics. The majority of explosive and
novalike variables are close binary systems, their components
having strong mutual influence on the evolution of each star. It
is often observed that the hot dwarf component of the system is
surrounded by an accretion disk formed by matter lost by the
other, cooler, and more extended component. This category is
subdivided into the following types:

N Novae. Close binary systems with orbital periods from 0.05 to 230
days. One of the components of these systems is a hot dwarf star
that suddenly, during a time interval from one to several dozen or
several hundred days, increases its brightness by 7-19 mag in V,
then returns gradually to its former brightness over several
months, years, or decades. Small changes at minimum light may be
present. Cool components may be giants, subgiants, or dwarfs of
K-M type. The spectra of novae near maximum light resemble A-F
absorption spectra of luminous stars at first. Then broad
emission lines (bands) of hydrogen, helium, and other elements
with absorption components indicating the presence of a rapidly
expanding envelope appear in the spectrum. As the light
decreases, the composite spectrum begins to show forbidden lines
characteristic of the spectra of gas nebulae excited by hot
stars. At minimum light, the spectra of novae are generally
continuous or resemble the spectra of Wolf-Rayet stars. Only
spectra of the most massive systems show traces of cool
components.

Some novae reveal pulsations of hot components with periods of
approximately 100 s and amplitudes of about 0.05 mag in V after an
outburst. Some novae eventually turn out to be eclipsing
systems. According to the features of their light variations,
novae are subdivided into fast (NA), slow (NB), very slow (NC),
and recurrent (NR) categories.

NA Fast novae displaying rapid light increases and then, having achieved
maximum light, fading by 3 mag in 100 or fewer days (GK Per);

NB Slow novae that fade after maximum light by 3 mag in >= 150 days (RR
Pic). Here the presence of the well-known "dip" in the light
curves of novae similar to T Aur and DQ Her is not taken into
account: The rate of fading is estimated on the basis of a smooth
curve, its parts before and after the "dip" being a direct
continuation of one another;

NC Novae with a very slow development and remaining at maximum light for
more than a decade, then fading very slowly. Before an outburst
these objects may show long-period light changes with amplitudes
of 1-2 mag in V (RR Tel); cool components of these systems are
probably giants or supergiants, sometimes semiregular variables,
and even Mira variables. Outburst amplitudes may reach 10 mag.
High excitation emission spectra resemble those of planetary
nebulae, Wolf-Rayet stars, and symbiotic variables. The
possibility that these objects are planetary nebulae in the
process of formation is not excluded;

NL Novalike variables, which are insufficiently studied objects
resembling novae by the characteristics of their light changes or
by spectral features. This type includes, in addition to
variables showing novalike outbursts, objects with no bursts ever
observed; the spectra of novalike variables resemble those of old
novae, and small light changes resemble those typical for old
novae at minimum light. However, quite often a detailed
investigation makes it possible to reclassify some representatives
of this highly inhomogeneous group of objects into other types;

NR Recurrent novae, which differ from typical novae by the fact that two
or more outbursts (instead of a single one) separated by 10-80
years have been observed (T CrB).

SN Supernovae (B Cas, CM Tau). Stars that increase, as a result of an
outburst, their brightnesses by 20 mag and more, then fade slowly.
The spectrum during an outburst is characterized by the presence
of very broad emission bands, their widths being several times
greater than those of the bright bands observed in the spectra of
novae. The expansion velocities of SN envelopes are in the
thousands of km/s. The structure of a star after outburst alters
completely. An expanding emission nebula results and a (not
always observable) pulsar remains at the position of the original
star. According to the light curve shape and the spectral
features, supernovae are subdivided into types I and II.

SNI Type I supernovae. Absorption lines of Ca II, Si, etc., but no
hydrogen lines are present in the spectra. The expanding envelope
almost lacks hydrogen. During 20-30 days following maximum light,
the brightness decreases by approximately 0.1 mag per day, then
the rate of fading slows and reaches a constant value of
0.014/day;

SNII Type II supernovae. Lines of hydrogen and other elements are
apparent in their spectra. The expanding envelope consists mainly
of H and He. Light curves show greater diversity than those of
type I supernovae. Usually after 40-100 days since maximum light,
the rate of fading is 0.1 mag per day.

UG U Geminorum-type variables, quite often called dwarf novae. They are
close binary systems consisting of a dwarf or subgiant K-M star
that fills the volume of its inner Roche lobe and a white dwarf
surrounded by an accretion disk. Orbital periods are in the range
0.05-0.5 days. Usually only small, in some cases rapid, light
fluctuations are observed, but from time to time the brightness of
a system increases rapidly by several magnitudes and, after an
interval of from several days to a month or more, returns to the
original state. Intervals between two consecutive outbursts for a
given star may vary greatly, but every star is characterized by a
certain mean value of these intervals, i.e., a mean cycle that
corresponds to the mean light amplitude. The longer the cycle,
the greater the amplitude. These systems are frequently sources
of X-ray emission. The spectrum of a system at minimum is
continuous, with broad H and He emission lines. At maximum these
lines almost disappear or become shallow absorption lines. Some
of these systems are eclipsing, possibly indicating that the
primary minimum is caused by the eclipse of a hot spot that
originates in the accretion disk from the infall of a gaseous
stream from the K-M star. According to the characteristics of the
light changes, U Gem variables may be subdivided into three types:
SS Cyg, SU UMa, and Z Cam.

UGSS SS Cygni-type variables (SS Cyg, U Gem). They increase in
brightness by 2-6 mag in V in 1-2 days and in several subsequent
days return to their original brightnesses. The values of the
cycle are in the range 10 days to several thousand;

UGSU SU Ursae Majoris-type variables. These are characterized by the
presence of two types of outbursts called "normal" and
"supermaxima". Normal, short outbursts are similar to those of
UGSS stars, while supermaxima are brighter by 2 mag, are more than
five times longer (wider), and occur several times less frequently.
During supermaxima the light curves show superposed periodic
oscillations (superhumps), their periods being close to the
orbital ones and amplitudes being about 0.2-0.3 mag in V. Orbital
periods are shorter than 0.1 days; companions are of dM spectral
type;

UGZ Z Camelopardalis-type stars. These also show cyclic outbursts,
differing from UGSS variables by the fact that sometimes after an
outburst they do not return to the original brightness, but during
several cycles retain a magnitude between maximum and minimum.
The values of cycles are from 10 to 40 days, while light
amplitudes are from 2 to 5 mag in V.

ZAND Symbiotic variables of the Z Andromedae type. They are close
binaries consisting of a hot star, a star of late type, and an
extended envelope excited by the hot star's radiation. The
combined brightness displays irregular variations with amplitudes
up to 4 mag in V. A very inhomogeneous group of objects.

5. Close Binary Eclipsing Systems

We adopt a triple system of classifying eclipsing binary systems:
according to the shape of the combined light curve, as well as to
physical and evolutionary characteristics of their components.
The classification based on light curves is simple, traditional,
and suits the observers; the second and third classification
methods take into account positions of the binary-system
components in the (MV ,B-V) diagram and the degree of inner Roche
lobe filling. Estimates are made by applying the simple criteria
proposed by Svechnikov and Istomin (1979). The symbols for the
types of eclipsing binary systems that we use are given below.

a) Classification based on the shape of the light curve

E Eclipsing binary systems. These are binary systems with orbital planes
so close to the observer's line of sight (the inclination i of the
orbital plane to the plane orthogonal to the line of sight is
close to 90 deg) that the components periodically eclipse each other.
Consequently, the observer finds changes of the apparent combined
brightness of the system with the period coincident with that of the
components' orbital motion.

EA Algol (Beta Persei)-type eclipsing systems. Binaries with spherical
or slightly ellipsoidal components. It is possible to specify, for
their light curves, the moments of the beginning and end of the
eclipses. Between eclipses the light remains almost constant or
varies insignificantly because of reflection effects, slight
ellipsoidality of components, or physical variations. Secondary
minima may be absent. An extremely wide range of periods is
observed, from 0.2 to >= 10000 days. Light amplitudes are also
quite different and may reach several magnitudes.

EB Beta Lyrae-type eclipsing systems. These are eclipsing systems having
ellipsoidal components and light curves for which it is impossible
to specify the exact times of onset and end of eclipses because of
a continuous change of a system's apparent combined brightness
between eclipses; secondary minimum is observed in all cases, its
depth usually being considerably smaller than that of the primary
minimum; periods are mainly longer than 1 day. The components
generally belong to early spectral types (B-A). Light amplitudes
are usually <2 mag in V.

EW W Ursae Majoris-type eclipsing variables. These are eclipsers with
periods shorter than 1 days, consisting of ellipsoidal components
almost in contact and having light curves for which it is
impossible to specify the exact times of onset and end of
eclipses. The depths of the primary and secondary minima are
almost equal or differ insignificantly. Light amplitudes are
usually <0.8 mag in V. The components generally belong to
spectral types F-G and later.

b) Classification according to the components' physical
characteristics

GS Systems with one or both giant and supergiant components; one of the
components may be a main sequence star.

PN Systems having, among their components, nuclei of planetary nebulae
(UU Sge).

RS RS Canum Venaticorum-type systems. A significant property of these
systems is the presence in their spectra of strong Ca II H and K
emission lines of variable intensity, indicating increased
chromospheric activity of the solar type. These systems are also
characterized by the presence of radio and X-ray emission. Some
have light curves that exhibit quasi sine waves outside eclipses,
with amplitudes and positions changing slowly with time. The
presence of this wave (often called a distortion wave) is
explained by differential rotation of the star, its surface being
covered with groups of spots; the period of the rotation of a spot
group is usually close to the period of orbital motion (period of
eclipses) but still differs from it, which is the reason for the
slow change (migration) of the phases of the distortion wave
minimum and maximum in the mean light curve. The variability of
the wave's amplitude (which may be up to 0.2 mag in V) is
explained by the existence of a long-period stellar activity cycle
similar to the 11-year solar activity cycle, during which the
number and total area of spots on the star's surface vary.

WD Systems with white-dwarf components.

WR Systems having Wolf-Rayet stars among their components (V 444 Cyg).

c) Classification based on the degree of filling of inner Roche
lobes

AR Detached systems of the AR Lacertae type. Both components are
subgiants not filling their inner equipotential surfaces.

D Detached systems, with components not filling their inner Roche lobes.

DM Detached main-sequence systems. Both components are main-sequence
stars and do not fill their inner Roche lobes.

DS Detached systems with a subgiant. The subgiant also does not fill its
inner critical surface.

DW Systems similar to W UMa systems in physical properties (KW, see
below), but not in contact.

K Contact systems, both components filling their inner critical surfaces.

KE Contact systems of early (O-A) spectral type, both components being
close in size to their inner critical surfaces.

KW Contact systems of the W UMa type, with ellipsoidal components of F0-K
spectral type. Primary components are main-sequence stars and
secondaries lie below and to the left of the main sequence in the
(MV,B-V) diagram.

SD Semidetached systems in which the surface of the less massive com-
ponent is close to its inner Roche lobe.

The combination of the above three classification systems for
eclipsers results in the assignment of multiple classifications
for object types. These are separated by a solidus ("/") in the
data field. Examples are: E/DM, EA/DS/RS, EB/WR, EW/KW, etc.

6. Optically Variable Close Binary Sources of Strong, Variable
X-ray Radiation (X-ray Sources)

X Close binary systems that are sources of strong, variable X-ray emis-
sion and which do not belong to or are not yet attributed to any
of the above types of variable stars. One of the components of
the system is a hot compact object (white dwarf, neutron star, or
possibly a black hole). X-ray emission originates from the infall
of matter onto the compact object or onto an accretion disk
surrounding the compact object. In turn, the X-ray emission is
incident upon the atmosphere of the cooler companion of the
compact object and is reradiated in the form of optical
high-temperature radiation (reflection effect), thus making that
area of the cooler companion's surface an earlier spectral type.
These effects lead to quite a peculiar complex character of
optical variability in such systems. These objects may be
subdivided into the following types:

XB X-ray bursters. Close binary systems showing X-ray and optical
bursts, their duration being from several seconds to ten minutes,
with amplitudes of about 0.1 mag in V (V 801 Ara, V 926 Sco);

XF Fluctuating X-ray systems showing rapid variations of X-ray (Cygnus
X-1 = V1357 Cyg) and optical (V821 Ara) radiation on time scales
of dozens of milliseconds;

XI X-ray irregulars. Close binary systems consisting of a hot compact
object surrounded by an accretion disk and a dA - dM-type dwarf.
These display irregular light changes on time scales of minutes
and hours, and amplitudes of about 1 mag in V. Superposition of a
periodic variation because of orbital motion is possible (V818
Sco);

XJ X-ray binaries characterized by the presence of relativistic jets
evident at X-ray and radio wavelengths, as well as in the optical
spectrum in the form of emission components showing periodic
displacements with relativistic velocities (V1343 Aql);

XND X-ray, novalike (transient) systems containing, along with a hot
compact object, a dwarf or subgiant of G-M spectral type. These
systems occasionally rapidly increase in brightness by 4-9 mag
in V, in the visible simultaneously with the X-ray range, with no
envelope ejected. The duration of the outburst may be up to
several months (V616 Mon);

XNG X-ray, novalike (transient) systems with an early-type supergiant or
giant primary component and a hot compact object as a companion.
Following the main component's outburst, the material ejected by
it falls onto the compact object and causes, with a significant
delay, the appearance of X rays. The amplitudes are about 1-2 mag
in V (V725 Tau);

XP X-ray pulsar systems. The primary component is usually an ellipsoidal
early-type supergiant. The reflection effect is very small and
light variability is mainly caused by the ellipsoidal primary
component's rotation. Periods of light changes are between 1 and
10 days; the period of the pulsar in the system is from 1 s to 100
min. Light amplitudes usually do not exceed several tenths of a
magnitude (Vela X-1 = GP Vel);

XPR X-ray pulsar systems featuring the presence of the reflection effect.
They consist of a dB-dF-type primary and an X-ray pulsar, which
may also be an optical pulsar. The mean light of the system is
brightest when the primary component is irradiated by X rays; it
is faintest during a low state of the X-ray source. The total
light amplitude may reach 2-3 mag in V (HZ Her);

XPRM, X-ray systems consisting of a late-type dwarf (dK-dM) and a pulsar
XM with a strong magnetic field. Matter accretion on the compact
object's magnetic poles is accompanied by the appearance of
variable linear and circular polarization; hence, these systems
are sometimes known as "polars". The amplitudes of the light
changes are usually about 1 mag in V but, provided that the
primary component is irradiated by X rays, the mean brightness of
a system may increase by 3 mag in V. The total light amplitude may
reach 4-5 mag in V (AM Her, AN UMa).

If the beam of X-ray emission originating at the magnetic poles of
the rotating hot compact object does not pass through the
observer's position and the system is not observed as a pulsar,
the letter "P" in the above symbols for X-ray- system types is not
used. If an X-ray system is also an eclipsing or an ellipsoidal
variable, the X-ray symbol is preceded by "E" or "ELL" joined with
the X-ray symbol by a "+" sign (e.g., E+X, ELL+X).

7. Other Symbols

In addition to the variable-star types described above, certain
other symbols that need to be explained will be found in the
Type data field:

BLLAC Extragalactic BL Lacertae-type objects. These are compact
quasistellar objects showing almost continuous spectra with weak
emission and absorption lines and relatively rapid irregular light
changes with amplitudes up to 3 mag in V or more. Sources of
strong X-ray radiation and radio waves, their emission displays
strong and variable linear polarization in the visible and
infrared spectral regions. Some objects of this type, considered
erroneously to be variable stars and designated in the GCVS
system, will probably sometimes be included in the main table of
the Catalogue in the future, too.

CST Nonvariable stars, formerly suspected to be variable and hastily
designated. Further observations have not confirmed their
variability.

GAL Optically variable quasistellar extragalactic objects (active
galactic nuclei [AGNs]) considered to be variable stars by
mistake.

L: Unstudied variable stars with slow light changes.

QSO Optically variable quasistellar extragalactic sources (quasars) that
earlier were erroneously considered to be variable stars.

S Unstudied variable stars with rapid light changes.

* Unique variable stars outside the range of the classifications de-
scribed above. These probably represent either short stages of
transition from one variability type to another or the earliest
and latest evolutionary stages of these types, or they are
insufficiently studied members of future new types of variables.

+ If a variable star belongs to several types of light variability
simultaneously, the types are joined in the Type field by a "+"
sign (e.g., E+UG, UV+BY).

: Uncertainty flag on Type of Variability


-------------------------------------------------------------------------------------------------------------------------


II. Distribution Statistics of Designated Variable Stars
According to their Types of Variability
(GCVS I-III and NL 67 - 79).


Type Numb. Stars
---------------------------
| | 576
|* | 85
|ACV | 569
|AM | 17
|BCEP | 149
|BE | 267
|BLLAC | 5
|BY | 580
|CEP | 192
|CST | 162
|CW | 194
|DCEP | 547
|DSCT | 544
|E | 493
|E+AM: | 31
|E/DM | 214
|E: | 303
|EA | 4059
|EB | 941
|ELL | 148
|EP | 8
|EW | 1111
|FKCOM: | 14
|FU | 14
|GAL | 9
|GCAS: | 155
|GDOR | 60
|I | 162
|I: | 48
|IA | 56
|IB | 17
|IN | 1630
|IS | 225
|IT | 59
|L | 534
|L: | 143
|LB | 3069
|LC | 111
|LPB | 140
|M | 6287
|M+NB: | 3
|M: | 1300
|N | 57
|N+UG:+EA | 1
|N: | 32
|NA | 182
|NB | 40
|NC | 11
|NL | 100
|NR | 8
|PSR | 1
|PVTEL | 15
|QSO | 6
|R | 10
|R/PN | 1
|R: | 4
|RCB | 42
|RPHS | 28
|RR | 6884
|RS | 205
|RV | 133
|S: | 181
|SDOR | 20
|SN | 7
|SR | 6063
|SXARI | 64
|UG | 431
|UV | 1597
|WR | 34
|X | 2
|X+BE | 2
|XB | 14
|XF | 3
|XI | 9
|XJ: | 1
|XM | 48
|XN | 26
|XP | 16
|ZAND | 66
|ZZ | 63
---------------------
Total 41638

========================================================================
(End) N.N. Samus [Moscow Inst. Astron.], O.V. Durlevich [Sternberg
Astron. Inst., Moscow] 12-Feb-2009