Slowly irregularly changing star

Slowly irregularly changing stars are giants or supergiants with a medium to late spectral type and, in contrast to semi-regular variable stars, show little or no signs of periodic light changes .

definition

This class of stars is defined as variable stars in whose light changes no or at best only slight signs of periodicity are observed. The stars are often only provisionally assigned to this group, as the observation material was only covered for a short period of time and / or only relatively few observations were made, which results in a large spread of data. With a long-term study of the change in light, the stars would therefore possibly be assigned to the semi-regularly changing stars .

In addition to the light curves, these two classes of variable stars do not differ systemically in other properties.

Subgroups

There are two subgroups of the irregularly variable stars:

• Lb: Slowly irregular stars of the late spectral type (K, M, C, S), mostly red giants . This subgroup is also assigned to red variable stars in the General Catalog of Variable Stars , whose spectral type and light change are not known.
• Lc: Irregular light change later supergiant with an amplitude of about 1  like in  V . Large convection cells are assumed to be the cause of the irregular light change . This assumption is supported by the observation that the light curves of these stars, in addition to the irregular light change, often also show a cyclical portion of low amplitude.

Occurrence in star catalogs

The General Catalog of Variable Stars currently lists over 3000 stars with the abbreviations L , LB , and LC , which means that just over 5% of all stars in this catalog belong to the class of slowly irregularly changing stars.

Examples

• Aldebaran
• U Antliae
• Gamma Phoenicis
• Enif

literature

• Cuno Hoffmeister , G. Richter, W. Wenzel: Variable stars . JABarth Verlag, Leipzig 1990, ISBN 3-335-00224-5 .
• John R. Percy: Understanding Variable Stars . Cambridge University Press, Cambridge 2007, ISBN 978-0-521-23253-1 .
• T. Lebzelter, M. Obbrugger: How semiregular are irregular variables? In: Astrophysics. Solar and Stellar Astrophysics . 2009, arxiv : 0902.4096 .
• Ming Yang and BW Jiang: Red Supergiant Stars in the Large Magellanic Cloud: I. The Period-Luminosity Relation . In: Astrophysics. Solar and Stellar Astrophysics . 2010, arxiv : 1011.4998v1 .

Individual evidence

1. ↑ Variability types General Catalog of Variable Stars, Sternberg Astronomical Institute, Moscow, Russia. Retrieved May 12, 2019 .