Chapter XI: Irregular and Doubtful Variables

Besides these well-marked classes of long-period, short-period, and Algol variables, there are some stars which seem to vary spasmodically, remaining sometimes for months or even for years without any change; and there are others whose variability is suspected but has never been confirmed. Useful work might be done by amateurs in trying to decide the status of these doubtful stars.

It must be borne in mind that red stars are notoriously difficult objects. Two observers comparing one at the same time with the same star will often come to opposite conclusions, showing how difficult it is to compare stars which differ much in colour. Whenever possible, red comparison stars should be selected to avoid this uncertainty.

The second star on the list below has a very peculiar type of variation, unlike any other except a northern star, R Coronae, and a third recently discovered. The spectra of RY Sagittarii and R Coronae are also peculiar and resemble one another.

The following are bright southern variables suspected to vary, or known to vary without recognised laws:

SOUTHERN IRREGULAR AND SUSPECTED VARIABLES

+--------------+----------+----------+-----------------------------+
| Name. | Maximum | Minimum | Remarks. |
| |Magnitude.|Magnitude.| |
+--------------+----------+----------+-----------------------------+
|Z Sculptoris | 6 | 8 | Period unknown. |
| | | | |
|RY Sagittarii | 6.5 | Fainter | Usually steady, but subject|
| | |than 11.5 | to a sudden drop at |
| | | | irregular intervals. |
| | | | Worth watching. |
| | | | |
|RT Capricorni | 6.5 | About 8 | Period probably irregular. |
| | | | Very few observations |
| | | | published. |
| | | | |
|S Phoenicis |{ 7.2 | 8.7 }| Observers differ. |
| |{ or | or }| Period irregular. |
| |{ 6.8 | 8.4 }| |
| | | | |
|W Ceti | 6.5 | 12 | Period perhaps 366 days |
| | | | |
|T Ceti | 5.4 | 6.9 | Irregular. |
| | | | |
|S Leporis | 6.5 | 7.5 | Irregular. |
| | | | |
|U Hydrae | 4.5 | 6.3 | Irregular. Red |
| | | | “carbon star.” |
| | | | |
|θ Apodis | 5.5 | 6.6 | Period probably irregular. |
| | | | |
|R Apodis | 5.5 | 6.2 | Suspected. |
| | | | |
|T Indi | 7.2 | 8.9 | No regular period found |
+--------------+----------+----------+-----------------------------+