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HD 166473

Location of HD 166473 (circled)
Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Corona Australis
Right ascension	18 12 25.83474
Declination	−37° 45′ 09.2713″
Apparent magnitude (V)	7.953
Characteristics
Spectral type	A5pSrCrEu
B−V color index	0.42
J−H color index	-0.018
J−K color index	-0.026
Variable type	α CVn variable
Astrometry
Radial velocity (Rv)	−22.5±3.0 km/s
Proper motion (μ)	RA: -2.767 mas/yr Dec.: −12.785 mas/yr
Parallax (π)	7.1672 ± 0.0337 mas
Distance	455 ± 2 ly (139.5 ± 0.7 pc)
Absolute magnitude (MV)	1.60, 2.197
Details
Mass	2.29 M☉
Radius	2.25 R☉
Luminosity	18.03 L☉, 9.811 L☉
Surface gravity (log g)	4.00 cgs
Temperature	7760 K
Rotation	3836 ± 30 d
Age	1.00 Gyr
Other designations
CD−37° 12303, CPD−37° 7956, Gaia DR2 4037543655114296576, HD 166473, PPM 749478, TIC 368866492, TYC 7900-2776-1, GSC 07900-02776, 2MASS J18122583-3745092, V694 CrA
Database references
SIMBAD	data

HD 166473 is a rapidly oscillating Ap star (roAp star) and an α CVn variable located about 455 light-years (140 parsecs) away in the southern constellation of Corona Australis. It has the variable star designation V694 Coronae Australis (sometimes abbreviated to V694 CrA). With an apparent magnitude of 7.953, it is too faint to be seen by the naked eye from Earth, but can be observed using binoculars.

Properties

As is thought to be the case with most roAp stars, it has an overabundance of rare-earth elements as well as chromium and cobalt, solar-like levels of iron and nickel, and deficiencies in carbon and oxygen.

HD 166473 possesses one of the strongest magnetic fields of any Ap star at up to −4160±226 G, around ten thousand times stronger than Earth's magnetic field (0.25-0.65 G). The strength and orientation of the magnetic field is strongly correlated with the layer of the atmosphere specific elements land in. This can be seen in the difference in radial velocity variations caused by pulsations of the star, which are observed in the emission lines of different elements within the spectrum of the star. In particular, rare-earth elements show an amplitude as high as 110 m/s, while other elements including iron show no signs of variation at all.

It is also an extremely slow rotator, taking over a decade to rotate on its axis once. For comparison, the Sun's rotation period is only 25.38 days. Despite this, the magnetic properties of the star are essentially the same as that of Ap stars that rotate faster.

Observational history

Oscillations of the star were first discovered in 1987, with three distinct frequencies that each correspond to periods between 8.8 and 9.1 minutes and have low amplitudes between 0.25 and 0.49 millimagnitudes. Because the frequencies are not equally spaced apart, it cannot be explained using the oblique pulsator model, which is unusual since in general the model can accurately depict pulsations of roAp stars.

In 2003, the pulsations were further resolved into standing and travelling waves in the stellar atmosphere utilizing the VLT, making HD 166473 the first star other than the Sun for such observations to be conducted.

In 2020, the rotation period of the star was determined to be 3,836 days (10.50 years), making it only the fourth ever Ap star with a rotational period exceeding ten years whose magnetic field has been observed for an entire cycle or more.

See also

• Other slow-rotating Ap stars:
  • GY Andromedae (HD 9996)
  • KQ Velorum (HD 94660)
  • Przybylski's star (HD 101065)
  • HD 187474

References

1. ^ 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. ^ Bychkov, V.D.; et al. (July 2021), "Stellar magnetic rotational phase curves. II", Vizier Online Data Catalog, Centre de Donnees Strasbourg (CDS), Bibcode:2021yCat..36520031B, doi:10.26093/CDS/VIZIER.36520031, retrieved 15 October 2024
3. 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.
4. ^ "HD 166473". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 15 October 2024.
5. ^ Glagolevskij, Yu. V. (2019). "On Properties of Main Sequence Magnetic Stars". Astrophysical Bulletin. 74 (1). Pleiades Publishing Ltd: 66–79. Bibcode:2019AstBu..74...66G. doi:10.1134/s1990341319010073. ISSN 1990-3413. Record for this source at VizieR.
6. ^ Scholz, R.-D.; et al. (August 2019), "Gaia DR2-based catalogue of 237 Ap stars", Vizier Online Data Catalog, Centre de Donnees Strasbourg (CDS), Bibcode:2019yCat..36280081S, doi:10.26093/CDS/VIZIER.36280081, retrieved 15 October 2024
7. Zarenski, Ed (2004). "Limiting Magnitude in Binoculars" (PDF). Cloudy Nights. Archived (PDF) from the original on 21 July 2011. Retrieved 6 May 2011.
8. Gelbmann, M.; et al. (April 2000). "Abundance analysis of roAp stars. V. HD 166473". Astronomy and Astrophysics. 356: 200–208. Bibcode:2000A&A...356..200G.
9. ^ Järvinen, S P; et al. (28 September 2020). "The anomalous atmospheric structure of the strongly magnetic Ap star HD 166473". Monthly Notices of the Royal Astronomical Society. 499 (2). Oxford University Press (OUP): 2734–2743. arXiv:2009.10553. doi:10.1093/mnras/staa2887. ISSN 0035-8711.
10. Finlay, C. C.; et al. (December 2010). "International Geomagnetic Reference Field: the eleventh generation". Geophysical Journal International. 183 (3): 1216–1230. Bibcode:2010GeoJI.183.1216F. doi:10.1111/j.1365-246X.2010.04804.x. hdl:20.500.11850/27303.
11. Mathys, G.; et al. (6 August 2007). "Pulsation in the presence of a strong magnetic field: the roAp star HD 166473★". Monthly Notices of the Royal Astronomical Society. 380 (1). Oxford University Press (OUP): 181–198. Bibcode:2007MNRAS.380..181M. doi:10.1111/j.1365-2966.2007.12080.x. ISSN 0035-8711.
12. Williams, D. R. (1 July 2013). "Sun Fact Sheet". NASA Goddard Space Flight Center. Archived from the original on 15 July 2010. Retrieved 12 August 2013.
13. ^ Mathys, G.; et al. (2020). "The 10.5 year rotation period of the strongly magnetic rapidly oscillating Ap star HD 166473". Astronomy & Astrophysics. 636. EDP Sciences: A6. arXiv:2002.11689. Bibcode:2020A&A...636A...6M. doi:10.1051/0004-6361/201936624. ISSN 0004-6361.
14. ^ Kurtz, D. W.; et al. (1987). "The discovery and analysis of oscillations with periods between 8.8 and 9.1 min in the cool magnetic Ap star HD 166473". Monthly Notices of the Royal Astronomical Society. 226 (1). Oxford University Press (OUP): 187–193. doi:10.1093/mnras/226.1.187. ISSN 0035-8711.
15. Martinez, Peter (June 1996). "The p-mode spectra of the roAp stars". Bulletin of the Astronomical Soceity of India. 24: 359. Bibcode:1996BASI...24..359M.
16. Kurtz, D. W.; et al. (21 July 2003). "New heights in asteroseismology: VLT spectroscopy of the roAp star HD 166473". Monthly Notices of the Royal Astronomical Society. 343 (1). Oxford University Press (OUP): L5–L9. Bibcode:2003MNRAS.343L...5K. doi:10.1046/j.1365-8711.2003.06817.x. ISSN 0035-8711.

v t e Variable stars
Pulsating	Cepheids and cepheid-like Type I (Classical cepheids, Delta Scuti) Type II (BL Herculis, W Virginis, RV Tauri) RR Lyrae Rapidly oscillating Ap SX Phoenicis Blue-white with early spectra Alpha Cygni Beta Cephei Slowly pulsating B-type PV Telescopii Blue large-amplitude pulsator Long-period Mira Semiregular Slow irregular Other Gamma Doradus Solar-like oscillations White dwarf
Eruptive	Protostar and PMS Herbig Ae/Be Orion FU Orionis T Tauri Giants and supergiants Luminous blue variable R Coronae Borealis (DY Persei) Yellow hypergiant Eruptive binary Double periodic FS Canis Majoris RS Canum Venaticorum Other Flare Gamma Cassiopeiae Lambda Eridani Wolf–Rayet
Cataclysmic	AM Canum Venaticorum Dwarf nova Luminous red nova Nova Polar Intermediate Supernova Hypernova SW Sextantis Symbiotic Symbiotic nova Z Andromedae
Rotating	Non-spherical Rotating ellipsoidal Stellar spots BY Draconis FK Comae Berenices Magnetic fields α Canum Venaticorum Pulsar SX Arietis
Eclipsing	Algol Beta Lyrae Planetary transit W Ursae Majoris
Star portal * List

v t e Constellation of Corona Australis
List of stars in Corona Australis Corona Australis in Chinese astronomy
Stars	Bayer α (Meridiana) β γ δ ε ζ η η θ κ κ λ μ σ Tel Variable R S T V TY WX V686 V691 V692 V701 V718 HR 6749 6750 6786 6862 6910 6931 6937 6942 6948 7031 7122 7177 7232 7257 7281 HD 166473 166724 Other RX J1856.5−3754
Exoplanets HD 177565 b
Star clusters Coronet Cluster NGC 6541
Nebulae NGC 6729
Category

• Rapidly oscillating Ap stars
• A-type stars
• Corona Australis
• Alpha2 Canum Venaticorum variables
• Henry Draper Catalogue objects
• Objects with variable star designations
• Durchmusterung objects
• 2MASS objects