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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, 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, L, LB, LC, M, PVTEL, 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),
7. other symbols (BLLAC, CST, GAL, L:, QSO, S:, *, +).
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) have been added
in the Name-Lists 67- 72 and in the GCVS vol.V.
ZZO ZZ Cet type variables of the DO spectral type showing HeII and
and CIV absorbtion 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.
LBV For comparatively long-period pulsating B stars (periods exceeding
one day), we introduce a provisional type LBV.
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 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
(V649 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 v