  | |
| Observation data EpochJ2000 EquinoxJ2000 | |
|---|---|
| Constellation | Cassiopeia[1] |
| Right ascension | 00h 24m 15.65400s[2] |
| Declination | +52° 01′ 11.7032″[2] |
| Apparent magnitude (V) | 5.580 (combined)[3] |
| Characteristics | |
| Spectral type | (B5IV[4] + unknown) + ~B5-6IV[5] |
| U−Bcolor index | −0.619[6] |
| B−Vcolor index | −0.121[3] |
| J−Hcolor index | −0.102[6] |
| J−Kcolor index | −0.106[6] |
| Variable type | Slowly pulsating B-type star (A; disputed)[5] |
| Astrometry | |
| Radial velocity (Rv) | −9.70±0.49[2] km/s |
| Proper motion (μ) | RA: 15.504[2]mas/yr Dec.: −4.061[2]mas/yr |
| Parallax (π) | 2.4621±0.33 mas[2] |
| Distance | approx. 1,300 ly (approx. 410 pc) |
| Absolute magnitude (MV) | −1.76[1] |
| Orbit[7] | |
| Primary | HD 1976 Aa |
| Companion | HD 1976 Ab |
| Period (P) | 25.4163±0.0008d |
| Semi-major axis (a) | 0.42±0.05mas |
| Eccentricity (e) | 0.05±0.03 |
| Inclination (i) | 100.7±1.2° |
| Longitude of the node (Ω) | 339.9±1.1° |
| Periastronepoch (T) | 59477±5 |
| Argument of periastron (ω) (secondary) | 61±52° |
| Orbit[7] | |
| Primary | HD 1976 A |
| Companion | HD 1976 B |
| Period (P) | 171±3 yr |
| Semi-major axis (a) | 208.0±2.7mas |
| Eccentricity (e) | 0.162±0.008 |
| Inclination (i) | 62.8±0.4° |
| Longitude of the node (Ω) | 27.8±0.4° |
| Periastronepoch (T) | 33710±679 |
| Argument of periastron (ω) (secondary) | 306.0±4° |
| Details[5] | |
| HD 1976 Aa | |
| Mass | 6.45±0.17, 6.348[7] M☉ |
| Radius | 5.24+0.14 −0.10 R☉ |
| Surface gravity (log g) | 3.81±0.01 cgs |
| Temperature | 16526+100 −82 K |
| Rotational velocity (v sin i) | 170±4 km/s |
| Age | ~60[4] Myr |
| HD 1976 Ab | |
| Mass | 1.83,4.0±0.7[7] M☉ |
| Radius | 1.83 R☉ |
| Surface gravity (log g) | 4.18 cgs |
| Temperature | 8071+266 −352 K |
| Rotational velocity (v sin i) | 165 km/s |
| HD 1976 B | |
| Mass | 6.10+0.27 −0.26 M☉ |
| Radius | 4.48±0.20 R☉ |
| Surface gravity (log g) | 3.92±0.02 cgs |
| Temperature | 13620+154 −144 K |
| Rotational velocity (v sin i) | 73+6 −5 km/s |
| Other designations | |
| V746 Cassiopeiae,AG+51°39,BD+51°62,Gaia DR3 418916648901801728,GC 476,HD 1976,HIP 1921,HR 91,SAO 21366,PPM 25297,WDS J00243+5201AB,TIC 202418751,TYC 3260-2342-1,GSC 03260-02342,2MASS J00241564+5201119,ADS 328[6] | |
| Database references | |
| SIMBAD | HD 1976 |
HD 1976 is ahierarchical triple system in the deep northernconstellation ofCassiopeia, somewhere around 1,100 light-years (340 parsecs) fromEarth. It has thevariable-star designationV746 Cassiopeiae (abbreviated to V746 Cas). The system is faintly visible to thenaked eye under dark skies, having anapparent magnitude of 5.580. It consists of an inner pair between aB-typesubgiant and a less massive unknown-type star, which is distantly orbited by another B-type subgiant. It is currently moving closer towards theSolar System at a heliocentricradial velocity of −9.70 km/s.
Several measurements have been made on the distance to the star system, namely406±54 pc,[2]307±59 pc,[8] and186±24 pc,[7] but all of them have largeerrors and differ substantially from one another. The first two agree within the wideerror bars, while the third value is thought to be too low due to the noisyradial velocity orbit swaying thesemi-amplitude. In a 2022 study, the total mass of the inner pair could only be constrained poorly at9±5M☉ because of this uncertainty, and the masses of the individual stars were estimated from a mass ratio of1.57±0.28 and an adopted[a] mass figure of 6.348M☉.[7]
Stellar parameter estimates viaastronomical spectroscopy also yield different results depending on whether the spectral data near theBalmer lines H-β, H-γ, and H-δ is included in calculations, which are often affected by instrumental problems and rectification systematics.[5]
HD 1976 Aa is a B-type subgiant star with aspectral type of B5IV. It is thought to be very young, at only about 60 million years old, a little over one-eightieth the age of theSun (4.6Gyr[10]). It emits 70% of the total light from the system. Two solutions exist on its mass, namely 4.71 and 6.45M☉. The latter, deduced excluding data near the Balmer lines,[5] seems to agree better with the newer 2019 estimate of 6.348M☉.[9]
The Aa/Ab pair is part of an SB2spectroscopic binary with HD 1976 B, denoting that thespectral lines from both components (A, B) are visible, and is itself an SB1 spectroscopic binary, meaning that only Aa's spectral lines are visible.[4]
HD 1976 was found to be avariable star when theHipparcos data was analyzed. It was given its variable star designation in 1999.[12] The star was reported to show multiperiodic pulsations with periods ranging between 0.83 and 2.50days. As such, the star was classified as aslowly pulsating B-type star (SPB). However, a 2017 study identified the two dominantphotometric periods (2.503867 and 1.0649524 days) as therotation periods of the tertiary and primary stars (albeit the latter is tentative), which, if confirmed, would throw the SPB classification into question.[5]
In 2014, it was announced that the star possessed a strongmagnetic field, detected throughspectropolarimetric observations,[4] though the magnetic field is now thought to belong to the third star (B) instead.[5]
The only component whosespectrum cannot be directly observed, HD 1976 Ab is in a nearly circular (eccentricity 0.05) 25-day orbit with Aa.[5] Radial velocity variations caused by the star were observed as far back as 1912,[13] and its orbital parameters were first determined in 1963.[14]
As is the case with the other two stars, its physical properties are very uncertain. A 2017 study presented two sets of possible characteristics, each corresponding to anA-type (1.87M☉) andF-type main-sequence star (1.31M☉).[5] In 2022, however, a far higher mass of4.0±0.7M☉ was reported,[7] which resembles that of a lateB-type main-sequence star.[b]
HD 1976 B is a B-type subgiant much like HD 1976 Aa but slightly less luminous, radiating about 30% of the total light from the system. It distantly orbits the inner Aa/Ab pair at a period of about 170 years.[5] Its orbit was first determined in 1986, though at the time the period was underestimated at 104 years.[16] The mass estimate differs significantly depending on the aforementioned inclusion of the Balmer lines: 2.65M☉ if included and 6.10M☉ if not. The star has a strong bipolar magnetic field that varies with a period of 2.504 days, which is most likely its rotational period.[5]
This article incorporates text from this source, which is available under theCC BY 4.0 license.| Stars |
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