FY Canis Majoris
Variable star in the constellation Canis Major
From Wikipedia, the free encyclopedia
FY Canis Majoris (FY CMa), also known as HD 58978, is a star about 1,800 light years from the Earth, in the constellation Canis Major (very near the border of Puppis). It is usually a 5th magnitude star, so it will be visible to the naked eye of an observer far from city lights. It is a Gamma Cassiopeiae variable star, whose brightness varies from magnitude 4.8 to 6.25.
  | |
| Observation data Epoch J2000.0 Equinox ICRS | |
|---|---|
| Constellation | Canis Major |
| Right ascension | 07h 26m 59.48269s[1] |
| Declination | −23° 05′ 09.6897″[1] |
| Apparent magnitude (V) | 4.8 - 6.25[2] |
| Characteristics | |
| Spectral type | B0.5 IVe[3] |
| Variable type | γ Cas[2] |
| Astrometry | |
| Proper motion (μ) | RA: −6.692±0.038[1] mas/yr Dec.: +4.054±0.078[1] mas/yr |
| Parallax (π) | 1.7919±0.0645 mas[1] |
| Distance | 1,820 ± 70 ly (560 ± 20 pc) |
| Absolute magnitude (MV) | −2.23[4] |
| Orbit[5] | |
| Primary | Be star |
| Name | subdwarf |
| Period (P) | 37.257±0.003 d |
| Inclination (i) | >66[6]° |
| Periastron epoch (T) | 2448529.64±0.15 |
| Semi-amplitude (K1) (primary) | 14.4±0.9 km/s |
| Semi-amplitude (K2) (secondary) | 128.2±2.2 km/s |
| Details | |
| Be star | |
| Mass | 10-13[6] M☉ |
| Radius | 6.8[6] R☉ |
| Luminosity | 26,915[6] L☉ |
| Temperature | 27,500±3,000[5] K |
| Rotational velocity (v sin i) | 340±40[5] km/s |
| subdwarf | |
| Mass | 1.1-1.5[6] M☉ |
| Radius | 0.81[6] R☉ |
| Luminosity | 2,399[6] L☉ |
| Temperature | 45,000±5,000[5] K |
| Rotational velocity (v sin i) | 41±5[5] km/s |
| Other designations | |
| HD 58978, HIP 36168, HR 2855, SAO 173752, BD−22 1874[7] | |
| Database references | |
| SIMBAD | data |
In 1967, Alejandro Feinstein detected low amplitude (0.14 magnitude) variability in HD 58978's brightness, from photoelectric observations at La Plata Observatory.[10] The star was given the variable star designation FY Canis Majoris in 1973.[11] During an outburst in 2009, the star brightened to magnitude 4.8, its historical peak brightness.[2] TESS data show that FY CMa pulsates at many different frequencies, with periods ranging from 1.07 hours to 5.8 days.[12]
In 1905, Edward King noted that FY CMa has a peculiar spectrum with an unusually bright Hβ (and other) emission lines.[13] Paul Merrill et al. listed it as a Be star in 1925.[14] Spectra taken by various observers over several decades of the 20th century showed that the strength and relative intensities of the star's emission line are variable,[3] and could change on a timescale of just a few days.[15]
In 2008, Geraldine Peters et al. obtained high resolution spectra from the IUE and found that the Be star has a hot, far less massive hot subdwarf companion star, with which it forms a spectroscopic binary.[5]
Hui-Lau Cao calculated that FY CMa is losing mass at a rate of about 6 × 10−8 M☉/year via a stellar wind with a terminal velocity of about 750 km/sec.[16]