HR 3600
HR 3600 is a bluish-white hued variable star in the southern constellation of Vela. It has the variable-star designation IZ Velorum. With an apparent magnitude of about 5.54, it is faintly visible to the naked eye under dark skies. It is located approximately distant according to Gaia EDR3 parallax measurements, and is receding from the Solar System at a heliocentric radial velocity of 22.8 km/s.
Physical properties
This is a hot, luminous B-type main-sequence star with a mass of 4.0 and a radius of 3.2. With an effective temperature of, it shines at an absolute bolometric magnitude of −2.08, meaning it radiates 535 from its photosphere; and an absolute visual magnitude of −0.71, that is 151 released in the visual band of the UBV photometric system.This star was initially given the stellar classification B5III in 1978, indicative of a blue giant, but was reclassified as a main-sequence star of the same spectral type by Burki et al. due to similarities to other stars such as 32 Orionis, Lambda Columbae, HW Velorum, and HD 186837, all of type B5V. They simultaneously reported that it was a slowly pulsating B-type star with three tentative periods of 9.64 days, 14.4 days, and 10.7 days, all of them with amplitudes of several mmag that produce a combined peak-to-peak amplitude of roughly 0.03 mag.
File:IZVelLightCurve.png|thumb|left|A light curve for IZ Velorum, plotted from Transiting Exoplanet [Survey Satellite|TESS] data. The 0.905 day period derived by Balona is marked in red.
In 1986, Balona & Laing stated that HR 3600 in fact only had a single period of 1.10 days, an alias of the 9.64-day period presented by Burki et al. Citing the variable radial velocity of the star and the low projected rotational velocity, they argued that it was more likely a rotating ellipsoidal variable, in which case the system would consist of a close binary orbiting each other every 2.20 days. In 1994, Balona, who continued to observe the variable, revised the period to 0.905 days, which was another alias of the 9.64-day period. The 14.4-day period could not be detected. The low rotational velocity contradicts the hypotheses that the variability is caused by either binarity or rotational modulation, so the exact nature of this star has yet to be determined.