HD 74180

This article is about b Velorum. For B Velorum, see HD 70930.

HD 74180 is a single^[13] star in the constellation Vela. It is a yellow-white F-type supergiant with a mean apparent magnitude of +3.81 and a spectral classification F8Ib. Estimates of its distance to Earth vary between 3,200 and 8,300 light-years.

b Velorum

Location of b Vel (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Vela[1]
Right ascension	08h 40m 37.57017s[2]
Declination	−46° 38′ 55.4770″[2]
Apparent magnitude (V)	3.81[3]
Characteristics
Evolutionary stage	Yellow supergiant or yellow hypergiant
Spectral type	F8 Ib,[4] F0Ia+[5] or F0Ia[6]
U−B color index	+0.34[3]
B−V color index	+0.67[7]
Variable type	suspected α Cyg[5]
Astrometry
Radial velocity (Rv)	−25.3[8] km/s
Proper motion (μ)	RA: −6.124[9] mas/yr Dec.: +4.473[9] mas/yr
Parallax (π)	0.431±0.101 mas[10]
Distance	3,230 – 8,250[a] ly (990[4][b] – 2,532[10][c] pc)
Absolute magnitude (MV)	−6.50[4]
Details
Mass	12.63[4]–21.4±2.3[11] M☉
Radius	186[4][d] R☉
Luminosity	34,040[4][e] L☉
Surface gravity (log g)	1.38[4] cgs
Temperature	5,750[4] – 7,839[12] K
Metallicity [Fe/H]	0.56[12] dex
Rotational velocity (v sin i)	21.7±6[7] km/s
Age	7.4±0.8[11][f] Myr
Other designations
b Velorum, HR 3445, HD 74180, CD−46°4438, FK5 1226, HIP 42570, SAO 220265
Database references
SIMBAD	data

Properties

A light curve for HD 74180, adapted from van Leeuwen et al. (1998)^[5]

b Velorum has been classified as a suspected α Cygni variable star which varies by only 0.06 magnitude. There are possible periods near 53, 80, and 160 days, but the variation is largely irregular.^[5] It lies less than a degree from the small open cluster NGC 2645, but is not a member.^[4]

Several studies have considered b Velorum to be a highly luminous supergiant or hypergiant with an early F spectral type, for example F2 Ia⁺,^[5] F0 Ia,^[6] and F4 I.^[14] There were corresponding luminosity estimates of several hundred thousand L_☉. A 2015 study used the Barbier-Chalonge-Divan (BCD) system to derive a luminosity of 34,000 L_☉ and a cooler less luminous F8 Ib spectral type.^[4]

Distance and size

Multiple papers give different distances for b Velorum. Bailer-Jones et al. (2021) give a distance of about 2,530 pc (8,300 ly).^[10] The Hipparcos spacecraft give a parallax of 0.67±0.16 mas, translating into a distance of 1,492.5 pc (4,868 ly).^[2] Aidelman et al. (2015) give a distance of 990 pc (3,200 ly).^[4] At the Hipparcos distance, b Velorum has its apparent brightness diminished by 1.11 magnitudes due to interstellar extinction.^[12]

b Velorum has an angular diameter estimated at 1.824 mas.^[15] The physical size depends on the star's distance, and could be 190 R_☉ assuming the distance of Aidelman et al., 290 R_☉ assuming the Hipparcos distance, or even 500 R_☉ assuming the Bailer-Jones et al. distance.^[16]

In chinese astronomy

In Chinese, 天社 (Tiān Shè), meaning Celestial Earth God's Temple, refers to an asterism consisting of Kappa Velorum, Gamma² Velorum, b Velorum and Delta Velorum.^[17] Consequently, Kappa Velorum itself is known as 天社五 (Tiān Shè wǔ), "the Fifth Star of Celestial Earth God's Temple".^[18]

Notes

1. Margin of error of ⁺¹⁹⁶⁰
   ₋₁₂₉₀ for the second value
2. This distance applies is b Velorum has spectral type F8Ib.
3. Margin of error of ⁺⁶⁰⁰
   ₋₃₉₇ for the second value
4. Applying the Stefan–Boltzmann law with a nominal solar effective temperature of 5,772 K:

   ${\displaystyle {\sqrt {(5772/5750)^{4}*34,040}}=185.91\ R\odot }$

5. From L = 10^{(0.4*(4.74−(M_bol))}, where L is the luminosity and M_bol the bolometric magnitude
6. Assuming 21.4 M_☉ as the mass