Astronomy:Slow irregular variable
A slow irregular variable (ascribed the GCVS types L, LB and LC) is a variable star that exhibit no or very poorly defined periodicity in their slowly changing light emissions. These stars have often been little-studied, and once more is learnt about them, they are reclassified into other categories such as semiregular variables.
Nomenclature
Irregular variable stars were first given acronyms based on the letter "I": Ia, Ib. and Ic.[1] These were later refined so that the I codes were used "nebular" or "rapidly irregular" variable stars such as T Tauri and Orion variables. The remaining irregular stars, cool slowly varying giants and supergiants of type Ib or Ic were reassigned to Lb and Lc.[2] When the General Catalogue of Variable Stars standardised its acronyms to be all uppercase, the codes LB and LC were used.[3]
Type Lb
Slow irregular variables of late spectral types (K, M, C, S); as a rule, they are giants[3]
The GCVS also claims to give this type to slow irregular red variables where the luminosity or spectral type is not known, although it also uses the type L for slow irregular red stars where the spectral type or luminosity is unclear. The K5 star CO Cygni is given as a representative example.[3]
Type Lc
Irregular variable supergiants of late spectral types having amplitudes of about 1 mag in V[3]
The M2 supergiant TZ Cassiopeiae is given as a representative example.[3]
List
| Designation (name) | Constellation | Discovery | Apparent magnitude (Maximum)[5] | Apparent magnitude (Minimum)[5] | Range of magnitude | Spectral type | Subtype | Comment |
|---|---|---|---|---|---|---|---|---|
| U Antliae | Antlia | 8m.1 (p) | 9m.7 (p) | 1.6 | N:v | Lb | ||
| Beta Pegasi | Pegasus | Schmidt, 1847 | 2m.31 | 2m.74 | 0.43 | M2.3 II-III | Lb | |
| Epsilon Pegasi (Enif) | Pegasus | 2m.37 | 2m.45 | 0.07 | K2 Ib | Lc | ||
| TX Piscium | Pisces | 4m.79 | 5m.20 | 0.42 | C5 III | Lb | ||
| Alpha Scorpii (Antares) | Scorpius | 0m.88 | 1m.16 | 0.28 | M1.5 Iab-b | Lc | ||
| Alpha Tauri (Aldebaran) | Taurus | 0m.75 | 0m.95 | 0.20 | K5 III | Lb | ||
| Mu Geminorum | Gemini | 2m.75 | 3m.02 | 0.28 | M3 III | Lb | ||
| BE Camelopardalis | Camelopardalis | 4m.35 | 4m.48 | 0.13 | M2 II | Lc | ||
| Tau4 Eridani | Eridanus | 3m.57 | 3m.72 | 0.15 | M3 III | Lb | ||
| 13 Boötis | Bootes | 5m.29 | 5m.38 | 0.09 | M2 IIIab | Lb | ||
| Psi Virginis | Virgo | 4m.73 | 4m.96 | 0.23 | M3 III | Lb | ||
| V854 Arae | Ara | 5m.84 | 5m.99 | 0.12 | M1.5 III | Lb | ||
| 62 Sagittarii | Sagittarius | 4m.45 | 4m.62 | 0.17 | M4 III | Lb | ||
| CQ Camelopardalis | Camelopardalis | 5m.15 | 5m.27 | 0.12 | M0 II | Lc | ||
| Pi Aurigae | Auriga | 4m.24 | 4m.34 | 0.10 | M3.5 II | Lc | ||
| NO Aurigae | Auriga | 6m.06 | 6m.44 | 0.58 | M2 Iab | Lc | ||
| Omicron1 Canis Majoris | Canis Major | 3m.78 | 3m.99 | 0.21 | M2.5 Iab | Lc | ||
| Sigma Canis Majoris | Canis Major | 3m.43 | 3m.51 | 0.08 | M1.5 Iab | Lc | ||
| NS Puppis | Puppis | 4m.4 | 4m.5 | 0.1 | K3 Ib | Lc | ||
| Lambda Velorum | Vela | 2m.14 | 2m.30 | 0.16 | K4 Ib-IIa | Lc | ||
| V337 Carinae | Carina | 3m.36 | 3m.44 | 0.08 | K3 II | Lc | ||
| GZ Velorum | Vela | 3m.43 | 3m.81 | 0.38 | K3 II | Lc | ||
| RX Telescopii | Telescopium | 6m.6 | 7m.4 | 0.8 | M3 Iab | Lc | ||
| 45 G. Volantis | Volans | 5m.89 | 5m.90 | 0.01 | M1III | Lb | ||
| AF Columbae | Columba | Perryman et al., 1997 | 5m.60 | 5m.71 | 0.11 | M2 II/III | Lb |
Other irregular variables
There are a number of other types of variable stars lacking clearly detectable periods, and which are sometimes referred to as irregular variables:[4]
- γ Cassiopeiae variables, eruptive shell stars
- Orion variables, pre-main-sequence stars, including T Tauri stars and YY Orionis stars
- Rapid irregular variables, possibly similar to Orion variables with shorter period
- Poorly-defined irregular variable stars, of unknown type
In addition, many types of eruptive or cataclysmic variable are highly unpredictable.[4]
References
- ↑ Kholopov, P. N. (1959). "A Revised List of T-Associations and Their Members". Soviet Astronomy 3: 291. Bibcode: 1959SvA.....3..291K.
- ↑ Mayall, Margaret W. (1964). "Variable Star Notes- from the XII General Assembly, I.A.U.; 043274 X Camelopardalis". Journal of the Royal Astronomical Society of Canada 58: 283. Bibcode: 1964JRASC..58..283M.
- ↑ 3.0 3.1 3.2 3.3 3.4 "GCVS Variability Types". http://www.sai.msu.su/groups/cluster/gcvs/gcvs/iii/vartype.txt.
- ↑ 4.0 4.1 4.2 Samus, N. N. et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S 1: 02025. Bibcode: 2009yCat....102025S.
- ↑ 5.0 5.1 (visual magnitude, unless marked (B) (= blue) or (p) (= photographic))
External links
- Classifying variable stars - Astronomical Society of South Australia
- Why observe variable stars - British Astronomical Association
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