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HD 1976
Location of HD 1976 (circled)
Observation data
Epoch J2000[1]      Equinox J2000[1]
Constellation Cassiopeia
Right ascension 00h 24m 15.65400s
Declination +52° 01′ 11.7032″
Apparent magnitude (V) 5.580 (combined)[2]
Characteristics
Spectral type (B5IV[3] + unknown) + ~B5-6IV[4]
U−B color index -0.619[5]
B−V color index -0.121[2]
J−H color index -0.102[5]
J−K color index -0.106[5]
Variable type Slowly pulsating B-type star (A; disputed)[4]
Astrometry
Radial velocity (Rv)−9.70 ± 0.49[1] km/s
Proper motion (μ) RA: 15.504[1] mas/yr
Dec.: -4.061[1] mas/yr
Parallax (π)2.4621 ± 0.33 mas[1]
Distanceapprox. 1,300 ly
(approx. 410 pc)
Orbit[6]
PrimaryHD 1976 Aa
CompanionHD 1976 Ab
Period (P)25.4163±0.0008 d
Semi-major axis (a)0.42±0.05 mas
Eccentricity (e)0.05±0.03
Inclination (i)100.7±1.2°
Longitude of the node (Ω)339.9±1.1°
Periastron epoch (T)59477±5
Argument of periastron (ω)
(secondary)		61±52°
Orbit[6]
PrimaryHD 1976 A
CompanionHD 1976 B
Period (P)171±3 yr
Semi-major axis (a)208.0±2.7 mas
Eccentricity (e)0.162±0.008
Inclination (i)62.8±0.4°
Longitude of the node (Ω)27.8±0.4°
Periastron epoch (T)33710±679
Argument of periastron (ω)
(secondary)		306.0±4°
Details[4]
HD 1976 Aa
Mass4.71+0.17
−0.16, 6.45±0.17, 6.348[6] M☉
Radius5.74+0.18
−0.16, 5.24+0.14
−0.10 R☉
Surface gravity (log g)3.59±0.01, 3.81±0.01 cgs
Temperature15534±69, 16526+100
−82 K
Rotational velocity (v sin i)178±6, 170±4 km/s
Age~60[3] Myr
HD 1976 Ab
Mass1.31, 1.87, 4.0±0.7[6] M☉
Radius1.40, 1.82 R☉
Surface gravity (log g)4.27, 4.18 cgs
Temperature6385+565
−657, 8071+266
−352 K
Rotational velocity (v sin i)165 km/s
HD 1976 B
Mass2.65±0.25, 6.10+0.27
−0.26 M☉
Radius3.40+0.29
−0.26, 4.48±0.20 R☉
Surface gravity (log g)3.80±0.03. 3.92±0.02 cgs
Temperature14750±66, 13620+154
−144 K
Rotational velocity (v sin i)63+9
−8, 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[5]
Database references
SIMBADHD 1976

HD 1976 is a hierarchical triple system in the deep northern constellation of Cassiopeia, somewhere around 1,100 light-years (340 parsecs) from Earth. It has the variable-star designation V746 Cassiopeiae (abbreviated to V746 Cas). The system is faintly visible to the naked eye under dark skies, having an apparent magnitude of 5.580. It consists of an inner pair between a B-type subgiant and a less massive unknown-type star, which is distantly orbited by another B-type subgiant. It is currently moving closer towards the Solar System at a heliocentric radial velocity of −9.70 km/s.

Measurement discrepancies

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Several measurements have been made on the distance to the star system, namely 406±54 pc,[1] 307±59 pc,[7] and 186±24 pc,[6] but all of them have large errors and differ substantially from one another. The first two agree within the wide error bars, while the third value is thought to be too low due to the noisy radial velocity orbit swaying the semi-amplitude. In a 2022 study, the total mass of the inner pair could only be constrained poorly at 9±5 M☉ because of this uncertainty, and the masses of the individual stars were estimated from a mass ratio of 1.57±0.28 and an adopted[a] mass figure of 6.348 M☉.[6]

Stellar parameter estimates via astronomical spectroscopy also yield different results depending on whether the spectral data near the Balmer lines H-β, H-γ, and H-δ is included in calculations, which are often affected by instrumental problems and rectification systematics.[4]

Stellar components

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HD 1976 Aa

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HD 1976 Aa is a B-type subgiant star with a spectral 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 the Sun (4.6 Gyr[9]). It emits 70% of the total light from the system. Two solutions exist on its mass, namely 4.71 and 6.45 M☉. The latter, deduced excluding data near the Balmer lines,[4] seems to agree better with the newer 2019 estimate of 6.348 M☉.[8]

The Aa/Ab pair is part of an SB2 spectroscopic binary with HD 1976 B, denoting that the spectral lines from both components (A, B) are visible, and is itself an SB1 spectroscopic binary, meaning that only Aa's spectral lines are visible.[3]

A light curve for V746 Cassiopeiae, plotted from TESS data.[10] One of the dominant periods, 1.065 days, is marked in red.

The star was reported to show multiperiodic pulsations with periods ranging between 0.83 and 2.50 days. As such, the star was classified as a slowly pulsating B-type star (SPB). However, a 2017 study identified the two dominant photometric periods (2.503867 and 1.0649524 days) as the rotation periods of the tertiary and primary stars (albeit the latter is tentative), which, if confirmed, would throw the SPB classification into question.[4]

In 2014, it was announced that the star possessed a strong magnetic field, detected through spectropolarimetric observations,[3] though the magnetic field is now thought to belong to the third star (B) instead.[4]

HD 1976 Ab

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The only component whose spectrum cannot be directly observed, HD 1976 Ab is in a nearly circular (eccentricity 0.05) 25-day orbit with Aa.[4] Radial velocity variations caused by the star were observed as far back as 1912,[11] and its orbital parameters were first determined in 1963.[12]

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 an A-type (1.87 M☉) and F-type main-sequence star (1.31 M☉).[4] In 2022, however, a far higher mass of 4.0±0.7 M☉ was reported,[6] which resembles that of a late B-type main-sequence star.[b]

HD 1976 B

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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.[4] Its orbit was first determined in 1986, though at the time the period was underestimated at 104 years.[14] The mass estimate differs significantly depending on the aforementioned inclusion of the Balmer lines: 2.65 M☉ if included and 6.10 M☉ 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.[4]

See also

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Footnotes

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  1. ^ From Kervella et al. 2019.[8]
  2. ^ In comparison, a typical B7V star has a mass of about 3.92 M☉.[13]

References

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  1. ^ a b c d e f Brown, A. G. A.; et al. (Gaia collaboration) (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics. 649: A1. arXiv:2012.01533. Bibcode:2021A&A...649A...1G. doi:10.1051/0004-6361/202039657. S2CID 227254300. (Erratum: doi:10.1051/0004-6361/202039657e). Gaia EDR3 record for this source at VizieR.
  2. ^ a b Høg, E.; et al. (February 2000). "The Tycho-2 Catalogue of the 2.5 Million Brightest Stars". Astronomy and Astrophysics. 355 (1): L27–L30. Bibcode:2000A&A...355L..27H.
  3. ^ a b c d Neiner, C.; Tkachenko, A.; MiMeS collaboration (2014). "Discovery of a magnetic field in the B pulsating system HD 1976". Astronomy & Astrophysics. 563. EDP Sciences: L7. arXiv:1402.3245. Bibcode:2014A&A...563L...7N. doi:10.1051/0004-6361/201423595. ISSN 0004-6361.
  4. ^ a b c d e f g h i j k Harmanec, P.; Brož, M.; Mayer, P.; et al. (22 December 2017). "Improved model of the triple system V746 Cassiopeiae that has a bipolar magnetic field associated with the tertiary". Astronomy & Astrophysics. 609. EDP Sciences: A5. doi:10.1051/0004-6361/201628363. ISSN 0004-6361.
  5. ^ a b c d "HD 1976". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 10 November 2024.
  6. ^ a b c d e f g Gardner, Tyler; Monnier, John D.; Fekel, Francis C.; et al. (1 November 2022). "ARMADA. II. Further Detections of Inner Companions to Intermediate-mass Binaries with Microarcsecond Astrometry at CHARA and VLTI". The Astronomical Journal. 164 (5): 184. arXiv:2209.00669. Bibcode:2022AJ....164..184G. doi:10.3847/1538-3881/ac8eae. ISSN 0004-6256. This article incorporates text from this source, which is available under the CC BY 4.0 license.
  7. ^ van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy & Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. ISSN 0004-6361.
  8. ^ a b Kervella, Pierre; Arenou, Frédéric; Mignard, François; Thévenin, Frédéric (2019). "Stellar and substellar companions of nearby stars from Gaia DR2: Binarity from proper motion anomaly". Astronomy & Astrophysics. 623: A72. arXiv:1811.08902. Bibcode:2019A&A...623A..72K. doi:10.1051/0004-6361/201834371. ISSN 0004-6361.
  9. ^ Bonanno, A.; Schlattl, H.; Paternò, L. (2002). "The age of the Sun and the relativistic corrections in the EOS". Astronomy and Astrophysics. 390 (3): 1115–1118. arXiv:astro-ph/0204331. Bibcode:2002A&A...390.1115B. doi:10.1051/0004-6361:20020749. S2CID 119436299.
  10. ^ "MAST: Barbara A. Mikulski Archive for Space Telescopes". Space Telescope Science Institute. Retrieved 27 September 2024.
  11. ^ Adams, W. S. (1912). "The three-prism stellar spectrograph of the Mount Wilson Solar Observatory". The Astrophysical Journal. 35: 163. doi:10.1086/141924. ISSN 0004-637X.
  12. ^ Blaauw, A.; van Albada, T. S. (1963). "Radial Velocities of B-Type Stars in the Nearest Associations". The Astrophysical Journal. 137: 791. Bibcode:1963ApJ...137..791B. doi:10.1086/147556. ISSN 0004-637X.
  13. ^ Mamajek, Eric (16 April 2022). "A Modern Mean Dwarf Stellar Color and Effective Temperature Sequence". Retrieved 11 November 2024.
  14. ^ Docobo, J. A.; Costa, J. M. (1986). "First orbits for the visual double stars ADS 328, ADS 9043, and ADS 13048". The Astrophysical Journal Supplement Series. 60. American Astronomical Society: 945. Bibcode:1986ApJS...60..945D. doi:10.1086/191106. ISSN 0067-0049.
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