  | |
| Observation data EpochJ2000 EquinoxJ2000 | |
|---|---|
| Constellation | Cassiopeia |
| HD 123A | |
| Right ascension | 00h 06m 15.81387s[1] |
| Declination | +58° 26′ 12.1073″[1] |
| Apparent magnitude (V) | 6.42[2] |
| HD 123B | |
| Right ascension | 00h 06m 15.71057s[3] |
| Declination | +58° 26′ 12.6457″[3] |
| Apparent magnitude (V) | 7.32[2] |
| Characteristics | |
| Spectral type | G3V[4] + (G8V[5] + early MV[4]) |
| B−Vcolor index | 0.70 (A), 0.97 (B)[2] |
| Astrometry | |
| HD 123A | |
| Radial velocity (Rv) | −11.7 ± 2[6] km/s |
| Proper motion (μ) | RA: 237.578[1]mas/yr Dec.: 37.174[1]mas/yr |
| Parallax (π) | 48.1027±0.0398 mas[1] |
| Distance | 67.80 ± 0.06 ly (20.79 ± 0.02 pc) |
| HD 123B | |
| Radial velocity (Rv) | −16.0 ± 5[6] km/s |
| Proper motion (μ) | RA: 237.578[3] mas/yr Dec.: 37.174[3] mas/yr |
| Parallax (π) | 47.0168 ± 0.1936 mas[3] |
| Distance | 69.4 ± 0.3 ly (21.27 ± 0.09 pc) |
| Orbit[7] | |
| Primary | HD 123A |
| Companion | HD 123B |
| Period (P) | 106.83yr |
| Semi-major axis (a) | 1.455±0.004" (29.5±0.6 AU[7]) |
| Orbit[4] | |
| Primary | HD 123Ba |
| Companion | HD 123Bb |
| Period (P) | 47.685±0.003 d |
| Eccentricity (e) | 0.610±0.024 |
| Periastronepoch (T) | MJD49891.00±0.22 |
| Argument of periastron (ω) (secondary) | 290±4° |
| Details[4] | |
| HD 123A | |
| Mass | 0.98 M☉ |
| HD 123Ba | |
| Mass | ~0.86[a] M☉ |
| Radius | ~0.87 (assumed)[7] R☉ |
| Rotational velocity (v sin i) | 4.7[5] km/s |
| HD 123Bb | |
| Mass | ~0.31[a] M☉ |
| Other designations | |
| V640 Cassiopeiae,AG+58°10,BD+57°2865,GC 88,GJ 9001,HD 123,HIP 518,HR 5,SAO 21085,PPM 25002,ADS 61 AB,CCDM J00063+5826AB,WDS J00063+5826AB,G 243-13,LTT 10022,NLTT 213,TIC 347304641,2MASS J00061575+5826128,WISEA J000616.14+582613.3, EUVE J0006+58.4,GJ 4.1, USNO-B1.0 1484-00003998[8] | |
| HD 123A:BD+57°2865A,Gaia DR3 423075173680043904,GJ 9001 A,HD 123A,ADS 61 A,WDS J00063+5826A,TIC 604446831,TYC 3664-1986-1,GJ 4.1 A, PMSC 00010+5752A[9] | |
| HD 123B:BD+57°2865B,Gaia DR3 423075173674854528,GJ 9001 B,HD 123B,ADS 61 B,WDS J00063+5826B,TYC 3664-1986-2,GJ 4.1 B, PMSC 00010+5752Bab[10] | |
| Database references | |
| SIMBAD | HD 123 |
| HD 123A | |
| HD 123B | |
HD 123 is ahierarchical triple star system in the deep northernconstellation ofCassiopeia. It consists of avisual binary between HD 123A and B, of which component B is itself aspectroscopic binary (Ba & Bb). Through the use of atelescope, the visual pair can be resolved, with a separation that varies between 0.5 and 1.6arcseconds. With a combinedapparent magnitude of 5.98, it is faintly visible to thenaked eye under dark skies as a yellow-hued star.[4] The system is located approximately 70 light-years (21 pc) distant according toHipparcosparallax measurements,[11] while theGaia EDR3 parallaxes for the individual stars point towards slightly closer distances of 67.8 ly (20.8 pc) and 69.4 ly (21.3 pc), respectively. It is trending closer towards theSolar System at a heliocentricradial velocity of −13.79 km/s.[12]
Its name, HD 123, denotes that it is the 123rd object in theHenry Draper Catalogue, included within the first volume published in 1918.[13] Alternate designations includeHR 5,ADS 61, as well as thevariable-star designation V640 Cassiopeiae, which was given in 1985[14] after it was reported to fluctuate in brightness with a one-day period in 1983,[15] but this was refuted in 1999 as the star was shown to be constant.[4]
The visible components, A and Ba, are bothG-type main-sequence stars like theSun but slightly less massive, A being the brighter, hotter, and more massive of the two. Weber & Strassmeier (1998) assumed a radius of 0.87R☉ for B, corresponding to a typical late G-type star.[7] One of the G stars exhibit highchromospheric activity while the other is quiescent,[b] an oddity seen in some othersolar-like binaries such asHD 137763/HD 137778,37 Ceti, andZeta Reticuli.[16] Bb, on the other hand, is thought to be ared dwarf, having approximately three-tenths themass of the Sun.
The A and B components have anorbital period of 106.83 years spaced about 30 AU apart, while B itself consists of the pair Ba/Bb, which revolve around each other every 47.685 days in aneccentric orbit (eccentricity 0.610).
On 25 May 1782, astronomerWilliam Herschel discovered that HD 123 was a double star, which he designated H I 39. He remarked that the two stars appeared "red," referring to a latespectral type in modern terms.F. G. W. Struve was the second to observe the object from the 1820s through the 1830s, correctly noting that the stars bore a yellowish hue. Owing to the rapidly shiftingposition angle, a solution for the visual orbit was calculated as early as 1841, and had been refined to near-modern values by 1867, with an obtained period of 106.83 years and an eccentricity of ~0.45. The largeproper motion of the star was noticed in 1869, which, even then, was seen as an indication of its relatively close distance fromEarth. However, it took until the 1960s for a solid consensus to emerge on its parallax, which was determined to be close to 0.050 arcseconds.[4]
The possibility that HR 5 may be composed of more than two stars was raised by several authors such as Volet (1937), who suggested a 22-year secondary orbital period (though admitted it was unconvincing), andDorrit Hoffleit, who noted in the 1982 edition of the Bright Star Catalogue[17] that a 6.9-year period companion to B may exist. In 1951, H. Roth argued that component B was multiple, since the mass ratio indicated that B was apparently more massive despite being fainter. This was followed up by Lippincott (1963), refining the ratio MB/(MA+MB) to 0.546 ± 0.006, which meant B was about 20% more massive than A.[c] This has been used in subsequent studies, such as Griffin (1999) who derived a total mass of the Ba/Bb pair of 1.17M☉.[4]
In 1983, Brettman et al. reported that HR 5 was avariable star with a period of 1.082 ± 0.002 days. They were unable to distinguish which of the visible components displayed this variability, but theorized that one of them could be either a rapidlyrotating star with unevenly distributedstarspots, or aspectroscopic binary with a 1.082-day period.[15] Weber & Strassmeier (1998) additionally found radial velocity variations in HR 5B with a period of 1.026 days, and reasoned that Ba must be the variable component.[7] In 1999, however, a comprehensive study by Griffin showed that the star exhibited no signs ofphotometric variability and that while the radial velocity variations of component B did exist, the reported one-day period was analias of the true period of 47.685 days.[4] TheAAVSO lists HD 123 as a reflection variable (a binary system in which brightness variations are seen because one component reflects light from the other) with the small brightness range of magnitude 5.966 to 5.981.[18]
