MY Camelopardalis

MY Camelopardalis (MY Cam) is a binary star system located in the Alicante 1 open cluster, some 13 kly (4.0 kpc) away in the constellation Camelopardalis. It is one of the most massive known binary star systems and a leading candidate for a massive star merger. MY Cam is the brightest star in Alicante 1.^[1]

Artist's impression of MY Camelopardalis

MY Camelopardalis

A red band light curve for MY Camelopardalis, adapted from Lorenzo et al. (2014)[1]
Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Camelopardalis
Right ascension	03h 59m 18.2863s[2]
Declination	+57° 14′ 13.673″[2]
Apparent magnitude (V)	9.80 - 10.15[3]
Characteristics
Spectral type	O6nn[4] (O6V((f)) + O6V((f))[5])
U−B color index	−0.66[4]
B−V color index	+0.28[4]
Variable type	Ellipsoidal[3]
Astrometry
Radial velocity (Rv)	−47[1] km/s
Proper motion (μ)	RA: −2.3[6] mas/yr Dec.: −0.3[6] mas/yr
Parallax (π)	0.1333±0.0789 mas[7]
Distance	~4,000[1] pc
Absolute magnitude (MV)	−4.1[4]
Orbit[1]
Period (P)	1.175 days
Semi-major axis (a)	19.24 R☉
Eccentricity (e)	0
Inclination (i)	62.59°
Argument of periastron (ω) (secondary)	90°
Argument of periastron (ω) (primary)	270°
Semi-amplitude (K1) (primary)	335 km/s
Semi-amplitude (K2) (secondary)	400 km/s
Details[1]
A
Mass	37.7 M☉
Radius	7.60 R☉
Surface gravity (log g)	4.251 cgs
Temperature	42,000 ± 1,500 K
Rotational velocity (v sin i)	290 km/s
B
Mass	31.6 M☉
Radius	7.01 R☉
Surface gravity (log g)	4.245 cgs
Temperature	39,000 ± 1,500 K
Rotational velocity (v sin i)	268 km/s
Other designations
MY Camelopardalis, BD+56°864, Alicante 1 NM 693, 2MASS J03591829+5714137, Gaia DR2 469715181320008960, TYC 3725-498-1
Database references
SIMBAD	data

The system consists of two hot blue O-type stars with one component having a mass of 32 solar masses and the other 38 solar masses.

In 1998, the star was included in a list of suspected variable stars.^[8] John Greaves and Patrick Wils proved that it is variable, in 2004.^[9] It was given its variable star designation, MY Camelopardalis, in 2008.^[10] MY Cam is a contact binary and eclipsing binary, with an orbital period of 1.2 days, and an orbital velocity of 1,000,000 km/h (280 km/s; 620,000 mph).^[1] Both stars share a common envelope.^[1]