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

                    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),
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.,

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

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

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

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

       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

       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

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

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

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

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

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

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

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