15 Andromedae

Lore & Background

15 Andromedae was first included in a list of variable, microvariable and suspected variable stars by Rufener and Bartholdi in 1982, based on multicolor photometry from the 1960s and 1970s, though they could not conclusively prove variability. Proof of variability, along with a light curve and a period estimate of 63 minutes, was published by Paunzen and Handler in 1996. The star received its variable star designation, V340 Andromedae, in 1997.

The star's classification is disputed: it has been described as a giant star (A1 III), an A-type main-sequence star (A1 Va), or a Lambda Boötis star (kA1hA3mA0.5 Va+). It is a Delta Scuti variable that changes brightness by 0.03 magnitude, with two observed variability cycles of 0.0403 and 0.0449 days, a common feature for Lambda Boötis stars. The star is about 130 million years old, rotates rapidly with a projected rotational velocity of 105 km/s, has 2.7 times the Sun's mass, and radiates 27 times the Sun's luminosity at an effective temperature of 9,225 K.

An excess emission of infrared radiation suggests the presence of an orbiting disk of dust at a distance of roughly 50 AU from the host star.

Reader's Guide

15 Andromedae holds significance as a variable star whose variability was long suspected but only confirmed in 1996 by Paunzen and Handler, who provided the first light curve and a period estimate of 63 minutes. Its variable star designation, V340 Andromedae, was assigned the following year. The star's disputed classification—as a giant, main-sequence, or Lambda Boötis star—reflects ongoing uncertainty in stellar taxonomy. Its two variability periods (0.0403 and 0.0449 days) are noted as common among Lambda Boötis stars, linking it to that peculiar class. The detection of an infrared excess implies a circumstellar dust disk at about 50 AU, making it a candidate for studies of debris disks around intermediate-mass stars. The star's high rotation rate (105 km/s) and young age (130 million years) are consistent with its Delta Scuti pulsations. Its legacy lies in illustrating the process of confirming low-amplitude variability and in highlighting the connection between pulsation, rotation, and circumstellar material in A-type stars.

Did You Know?

• 15 Andromedae was included in a 1982 list of suspected variables by Rufener and Bartholdi but variability was not proven until 1996.
• The star has two variability cycles with periods of 0.0403 and 0.0449 days.
• An infrared excess suggests a dust disk orbiting at about 50 AU from the star.