23 Sextantis

Lore & Background

Early spectroscopic and photometric observations of 23 Sextantis were reported after the star was designated RS Sextantis in the seventh supplement of the General Catalogue of Variable Stars. The star was described as spectral type B3 with an absolute magnitude of about −2.0, and earlier photoelectric observations suggested it might belong to the β Canis Majoris (β Cephei) class with a period of roughly four hours. Spectroscopic observations were obtained at Mount Wilson Observatory, while photometric measurements were carried out at Lick Observatory. The study also reported mean radial velocities of about +5 to +6 km/s from earlier catalogues, although the available photometric data at the time were considered insufficient to establish the star’s variability firmly.

Photometric measurements indicate a small variation in brightness between visual magnitudes 6.64 and 6.68, with an amplitude of only a few hundredths of a magnitude. The measured photometric period of approximately 0.1353 days (about 3.25 hours) places the star among short-period pulsating variables. Because its observed properties overlap with those of both β Cephei variables and slowly pulsating B-type stars of the 53 Persei class, 23 Sextantis has been described as a possible candidate for either type.

Spectroscopic studies of the sightline toward 23 Sextantis indicate the presence of intervening interstellar material associated with a molecular cloud. The stellar spectrum exhibits absorption features corresponding to neutral and ionised metals as well as simple molecules. Analysis of the Na I profile reveals several distinct velocity components, including a dominant feature near −1.6 km/s and additional components extending from approximately −20 to +20 km/s. The absorbing material is associated with a compact molecular cloud identified as DBB 354 at an estimated distance of about 1 kpc, with a characteristic size of roughly 0.08 pc and particle densities of several thousand per cubic centimetre. Infrared observations link this cloud to an IRAS source, suggesting it may represent a previously unrecognized high-latitude molecular cloud.

Reader's Guide

23 Sextantis holds significance as a variable star candidate that bridges two established classes of pulsating B-type stars: the Beta Cephei variables and the 53 Persei variables. Its short photometric period of about 3.25 hours and small amplitude of a few hundredths of a magnitude place it among short-period pulsators, but its overlapping characteristics prevent a definitive classification. This ambiguity makes it a valuable object for studying the continuum between these variable types.

The star also serves as a useful background probe of the interstellar medium. The sightline toward 23 Sextantis reveals a multi-component interstellar structure associated with the compact molecular cloud DBB 354, located at roughly 1 kpc. The detection of both atomic and molecular absorption features, along with the identification of an IRAS counterpart, suggests that this cloud may be a previously unrecognized high-latitude molecular cloud. Thus, 23 Sextantis contributes not only to stellar pulsation studies but also to the mapping of diffuse interstellar material at high Galactic latitudes.

Its inclusion in major catalogues—HD 89688, HIP 50684, HR 4064, SAO 118248—ensures its accessibility for further research. The star's designation as RS Sextantis in the General Catalogue of Variable Stars formalizes its variable status, even though early photometric data were insufficient to firmly establish variability at the time of its initial study.

Did You Know?

• 23 Sextantis has a photometric period of about 0.1353 days, or roughly 3.25 hours.
• The star's brightness varies between visual magnitudes 6.64 and 6.68.
• The intervening molecular cloud DBB 354 has a characteristic size of about 0.08 pc and particle densities of several thousand per cubic centimetre.