Parallax measurements by theGaia spacecraft suggest a distance of around 8,000 light years, although an earlier analysis of nearby luminousmain sequence stars forming a looseopen cluster suggest a distance closer to 5,400 light years if HD 18391 is a member.[5]
HD 18391 lies close to theinstability strip, an area of theH-R Diagram wherevariable stars pulsate in a regular manner with periods related to their luminosity. It is slightly hotter and more luminous thanclassical Cepheid variable stars on the strip and its pulsations are somewhat less regular. The main pulsation period is 123 days, but with a secondary period of 178 days. The amplitude of the light variations is smaller than mostCepheid variables at less than 0.1 magnitudes. If the secondary period represents thefundamental mode, then it corresponds closely to the period expected for a Cepheid variable of similar luminosity.[5]
^ab"NSV 15616".International Variable Star Index. Retrieved2025-03-13.
^Keenan, Philip C.; McNeil, Raymond C. (1989). "The Perkins Catalog of Revised MK Types for the Cooler Stars".The Astrophysical Journal Supplement Series.71: 245.Bibcode:1989ApJS...71..245K.doi:10.1086/191373.
