V1149 Orionis
HD 37824 is a spectroscopic binary star system in the constellation of Orion. It has the variable-star designation V1149 Orionis. With an apparent magnitude of 6.59, it is near the limit for naked eye observation from Earth, faintly visible as an orange-hued dot of light under dark skies. It is located approximately distant according to Gaia DR3 parallax measurements, and is moving further away at a heliocentric radial velocity of.
Stellar properties
HD 37824 is a single-lined spectroscopic binary, meaning only the light from the luminous primary can be observed in the system's spectra. The two stars orbit each other in a circular orbit with a period of 53.57 days. The star features prominent starspots, which are known to display the flip-flop effect; other stars that show this effect include FK Comae Berenices and HD 181809.The primary star is a chromospherically active K-type giant star in the core helium burning phase. It has a radius of and evolutionary models predict that its mass is. It is radiating times the luminosity of the Sun from its photosphere. The unseen secondary, B, is estimated to have a mass of if the orbital inclination is 90°, or with an inclination of 60°, which makes it likely to be a late-F-type or G-type main-sequence star.
Observational history
In 1973, astronomers William P. Bidelman and Darrell Jack MacConnell reported the detection of Ca II H & K emission lines in the spectra of HD 37824. As such, Douglas S. Hall et al. suspected it to be a RS [Canum Venaticorum variable]. As expected, in 1983, the star was shown to vary in brightness by 0.11 magnitudes, with photometric and orbital periods of 52.6 and 53.6 days, respectively. It was given its variable star designation in 1985.The starspots on the surface of the primary star, which are thought to cause the variability, were analyzed using photometric data taken between late 1978 and early 1990. The results were published in 1991, identifying six starspots, which each made the star dim by about 0.1 to 0.3 magnitudes and lasted for several years. The same study refined the orbital period to days.
Observations in 1992 showed a large excess of Hα emission alongside strong Ca II H & K and Hε emission lines. A follow-up study in 1997 reported a lower but still strong Hα emission, as well as a clear emission line from singly ionized helium revealed by spectral subtraction. Additional observations in 2000 discovered high variability in the profile of the Hα line.