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HgMn star; Microscopium From Wikipedia, the free encyclopedia
HD 194783 (HR 7817; 2 G. Microscopii) is a solitary star located in the southern constellation Microscopium near the border with Sagittarius. It is barely visible to the naked eye as a bluish-white-hued point of light with an apparent magnitude of 6.08.[2] The object is located relatively far at a distance of 740 light-years based on Gaia DR3 parallax measurements,[1] but it is drifting closer with a heliocentric radial velocity of −9.7 km/s.[6] At its current distance, HD 194783's brightness is diminished by an interstellar extinction of 0.31 magnitudes[14] and it has an absolute magnitude of either −0.59 or −1.10,[7][8] depending on the source.
Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
---|---|
Constellation | Microscopium |
Right ascension | 20h 28m 46.74360s[1] |
Declination | −35° 35′ 45.1068″[1] |
Apparent magnitude (V) | 6.08±0.01[2] |
Characteristics | |
Spectral type | B8 II/III[3] or B9pHgMn[4] |
B−V color index | −0.11[5] |
Astrometry | |
Radial velocity (Rv) | −9.7±1.2[6] km/s |
Proper motion (μ) | RA: +2.959 mas/yr[1] Dec.: −21.638 mas/yr[1] |
Parallax (π) | 4.3936 ± 0.0714 mas[1] |
Distance | 740 ± 10 ly (228 ± 4 pc) |
Absolute magnitude (MV) | −0.59[7] or −1.10[8] |
Details | |
Mass | 4.03±0.05[1] M☉ |
Radius | 4.19±0.21[9] R☉ |
Luminosity | 390±12[1] L☉ |
Surface gravity (log g) | 3.75[10] cgs |
Temperature | 14,028[8] K |
Metallicity [Fe/H] | −0.20[10] dex |
Rotation | 6 d[11] |
Rotational velocity (v sin i) | ≤30[11] km/s |
Age | 70[8] Myr |
Other designations | |
Database references | |
SIMBAD | data |
HD 194783 has a stellar classification of B8 II/III,[3] indicating that it is an evolved B-type star with the blended luminosity class of a bright giant and a lower luminosity giant star. It has also been given a class of B9pHgMn,[4] indicating that it is a chemically peculiar mercury-manganese star. It has 4.03 times the mass of the Sun[1] and a slightly enlarged radius 4.19 times that of the Sun's.[9] It radiates 390 times the luminosity of the Sun[1] from its photosphere at an effective temperature of 14,028 K.[8] The heavy metal (iron) to hydrogen ratio–what astronomers dub as the star's metallicity–is 63% that of the Sun's.[10] HD 194783 is estimated to be approximately 70 million years old.[8]
In 1989, HD 194783 was reported to be a spectrum variable with a period of 6 days. The projected rotational velocity of the star is not known, but it is said to be no higher than 30 km/s.[11] HD 194783 was also observed to have a relatively weak magnetic field of about −43 gauss.[15]
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