David's Astronomy Pages (Projects) Eruptive Variable Stars Eclipsing Variables   Variable Stars   Home Page    Pulsating Variables

Eruptive Variables

Eruptive variables are stars varying in brightness because of violent processes and flares taking place in their chromospheres and coronae. The light changes are usually accompanied by shell events, or matter outflow in the form of stellar wind of variable intensity, or interaction with surrounding interstellar matter.

Be stars (Type BE)

Be stars showing small-scale variations, sometimes quasi-periodic, not necessarily related to shell events

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FU Orionis stars (Type FU)

FU Orionis stars, or Fuors. Similar to Orion variables (type IN), but characterised by a gradual increase in brightness by about 6 mag. in 6 months. This is followed by complete constancy at maximum light, sustained for decades, or by a slow decline of one or two magnitudes.  These variables probably mark one of the stages in the evolution of T Tauri stars (type INT), sine one T Tauri star, V1077 Cyg, showed a similar outburst, but immediately after maximum brightness had been achieved a fade began, of 2.5 mag in 2111 years. All known Fuors are associated with reflecting cometary nebulae

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FU Ori (FU variable)

FU Ori (Orion)

Annotated CCD Image  3 x 60s exposure , 2x2 binning, V Filter 2008-02-24 22:40h UT (#268180-84)

FU Ori - photometry

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Gamma Cassiopeiae stars (Type GCAS) 

Gamma Cassiopeiae stars. Rapidly rotating Be III - IV stars with outflow of matter from their equatorial zone; the formation of equatorial rings or discs is sometimes accompanied by temporary fading of the star. Light variations are irregular and may amount to as much as 1.5 mag. visually. eg Gamma Cas, 

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Irregular variables (Type I)

Poorly studied irregular variables with unknown features of light variations. A very homogeneous group of objects.

   IA - irregular variables of early spectral types
    IB - irregular variables of intermediate and later spectral types

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Orion variables (Type IN)

Orion variables. Irregular variables associated with bright or diffuse nebulae, or observed in the region of these nebulae. Some of them may show cyclic light variations due to axial rotation.  On the H-R diagram they lie in the area of the main sequence and the subgiants. They are probably young objects that are in the course of further evolution will become non-variables stars on the main sequence. The range of brightness variations may reach several magnitudes.  A star may be allocated to type INA, INB or INT based on spectral information.

    INA - Orion variables of early spectral types, Examples: T Ori
    INB -  Orion variables of intermediate and later spectral types. Examples: BH Cep, AH Ori
    INT  - T Tauri stars. Usually only observed in diffuse nebulae. Examples: T Tau, RW Aur.
    INS -  Orion variables where rapid light changes are observed observed
             (INSA - early spectral type, INSB - intermediate-late spectral type, INST - T Tau type)

T Tauri (Type INT)

Image sets of T Tauri were recorded at around 23:40h UT (2005-10-13) and 02:45h UT (2005-10-14).  Image sets comprised  3 x 15s V and 3 x 60s B.

T Tauri & adjacent nebula NGC 1555 (Taurus) [ NGC 1555 also known as Hind's variable nebula)

CCD Image  1 20 sec exposure,  C Filter 2005-10-14 02:40 h UT  (#99920)

T Tauri Photometry Baseline

CCD Image  30 sec exposure,  V Filter 2005-10-13 23:39 h UT  (#99519)

Photometry  V & B  Bands

Further observations will be made during future sessions  in order to further refine the light / colour variation.

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RR Tau (Type INSA)

RR Tau (Taurus)

Annotated CCD Image  3 x 60s exposure (average combine), 2x2 binning, C filter,   2007-03-12 21:17h UT (#182157-69)

RR Tau - reference stars

Annotated CCD Image  120s exposure, 2x2 binning, V filter,   2007-03-12 21:10h UT (#182159)

RR Tau - colour

Approximate Colour CCD Image  Blue : 3 x 120s (B) , Green : 3x60s (V),  Red : 3x30s(R)  2x2 binning 2007-03-12 21:14h UT (#182158-68)

RR Tau Variation (2007)

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Rapid irregular variables (Type IS)

Rapid irregular variables with no apparent connection with diffuse nebulae, showing light chnages by 0.5 - 1.0 mag. over several hours or days. There is no strict boundary between rapid irregular variables and Orion variables. If a rapid irregular star is observed in the region of a diffuse nebulae it is considered an Orion variable (INS).   

ISA
Rapid irregular variables of early spectral types.

ISB
Rapid irregular variables of intermediate and later spectral types. 

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R Coronae Borealis stars (Type RCB)

R Coronae Borealis stars. Stars of spectral types Bpe-R of high luminosity, poor in hydrogen and rich in carbon and helium. They are simultaneously eruptive and pulsating variables. Slow non-periodic fades of 1 - 9 mag. last from months to a few years. These are superimposed by cyclic pulsations with amplitudes up to 0.4 - 0.7 mag and periods of 30 - 100 days.  Examples: R CrB,  DY Per

R CrB (RCB variable)

R CrB (Corona Borealis)

Annotated CCD Image 3 x 30s exposure (average combine), 2x2 binning, C Filter  2006-06-15 01:21 hUT (#128092-94)

Annotated CCD Image 15s exposure, 2x2 binning, R Filter  2006-09-08 20:52 hUT (#141072)

R CrB variation

R CrB  - Normal Bright State (2006-06-15)

Annotated CCD Image 3 x 30s exposure (average combine), 2x2 binning, C Filter  2006-06-15 01:21 hUT (#128092-94)

R CrB  - Low State (2008-05-02)

Annotated CCD Image 3 x 30s exposure (average combine), 2x2 binning, C Filter  2008-05-02 23:32 hUT (#285071-73)

Light Curve for R CrB

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DY Per - (RCB variable)

DY Per  (Perseus)

Annotated CCD Image 3 x 60 sec exposure (average combine), 2x2 binning, V Filter 2007-12-02  05:18h UT (#238067-73)

DY Per  - Reference Stars

Annotated CCD Image Details as above

DY Per & Reference Star details (V) : DY Per (GSC 3691:1782) (C) : GSC 3691:206  (Bt: 10.08, Vt 9.67) Comparison star B,V,R & I magnitudes based on Arne Henden  equations which provide BVRI estimates from Bt,Vt values (K) : GSC 3691:637  (Bt: 11.65, Vt 10.97)

Photometry results

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RS Canum Venaticorum stars (Type RS) 

RS Canum Venaticorum stars. Close binary systems. Their components have enhanced chromospheric activity which cause quasi - periodic light variability. The variation period is close to the orbital period an the amplitude is usually at least 0.2 mag. Example UX Ari. They are also X-ray sources and rotating variables. They may also be eclipsing variables as in the case of RS CVn itself.

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S Doradus stars (Type SDOR)

S Doradus stars. High luminosity stars showing irregular (sometimes cyclic) light changes with visual amplitude in the range 1 - 7 mag. They are amongst the most luminous of all stars. S Dor is actually in the Large Magellanic Cloud. they usually associated with diffuse nebulae and surrounded by expanding envelopes. Examples P Cyg, Eta Car.

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UV Ceti stars (Type UV)

UV Ceti stars, or flare stars. Stars sometimes showing flares of visual amplitude ranging from several tenths of a magnitude up to 6 mag. The amplitude is considerably greater in the ultraviolet. From the beginning of the flare to maximum light takes from seconds to a minute or so. To return to its normal brightness takes from several minutes up to an hour or so.

AD Leo - UV Type Variable 

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Flaring Orion variables (Type UVN)

Flaring Orion variables of spectral types Ke-Me. Their apparent behaviour resembles that of the UV Ceti stars. Besides being associated with nebulae, UVN stars on average have earlier spectral types than UV stars, greater luminosity an slower development of flares. They may a subgroup of INB variables with irregular variations superimposed by flares . Example: V389 Ori.

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Wolf Rayet variables (Type WR)

Wolf Rayet variables. Display irregular light changes with visual amplitudes up to 0.1 mag., which are probably physical (non-stable matter outflow from their surfaces) rather than geometric (rotation etc).

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