HR 273

HR 273 is a chemically peculiar spectroscopic binary system in the northern circumpolar constellation of Cassiopeia. It has an apparent visual magnitude of 5.9 making it faintly visible to the naked eye from dark suburban skies. Parallax measurements with the Hipparcos spacecraft put this system at a distance of roughly 350 light years.^[1]

HR 273

Location of HR 273 (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Cassiopeia
Right ascension	00h 58m 31.06245s[1]
Declination	+66° 21′ 06.4522″[1]
Apparent magnitude (V)	5.97[2]
Characteristics
Spectral type	A0 III[3]
U−B color index	−0.13[2]
B−V color index	−0.02[2]
Astrometry
Radial velocity (Rv)	−10.3[4] km/s
Proper motion (μ)	RA: +43.81[1] mas/yr Dec.: −13.62[1] mas/yr
Parallax (π)	9.31 ± 0.33 mas[1]
Distance	350 ± 10 ly (107 ± 4 pc)
Absolute magnitude (MV)	0.3[5]
Orbit[6]
Period (P)	6.82054 days
Eccentricity (e)	0
Inclination (i)	20.5°
Semi-amplitude (K1) (primary)	24.60 km/s
Semi-amplitude (K2) (secondary)	38.43 km/s
Details
A
Mass	2.5[6] M☉
Surface gravity (log g)	4.0[7] cgs
Temperature	11,400[7] K
B
Surface gravity (log g)	4.5[7] cgs
Temperature	7,800[7] K
Rotational velocity (v sin i)	3.2+0.3 −1.9[7] km/s
Other designations
HR 273, HD 5550, HIP 4572, BD+65°115
Database references
SIMBAD	data

The primary, HR 273 A, is an Ap star^[8] and the secondary is an Am star, making this a very unusual binary system. The primary has a magnetic field of 65 gauss, amongst the weakest seen in any Ap star. The magnetic field in the secondary is too weak to detect.^[7]

Component A has a spectral type of A0 III, and has unusually strong lines of strontium, chromium, and europium so it is known as a SrCrEu star.^[6] Although some spectral lines of the secondary star can be clearly distinguished, its spectral type cannot be clearly assigned. It is thought to be a late class A star, cooler than the primary. The primary star has been rotationally braked so that its rotational period closely matches its orbital period.^[7]

References

1. van Leeuwen, F. (November 2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. S2CID 18759600.
2. Ducati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". CDS/ADC Collection of Electronic Catalogues. 2237. Bibcode:2002yCat.2237....0D.
3. Cowley, A.; Cowley, C.; Jaschek, M.; Jaschek, C. (1969). "A study of the bright a stars. I. A catalogue of spectral classifications". Astronomical Journal. 74: 375. Bibcode:1969AJ.....74..375C. doi:10.1086/110819.
4. Wilson, Ralph Elmer (1953). "General catalogue of stellar radial velocities". Washington. Bibcode:1953GCRV..C......0W.
5. Gomez, A. E.; Luri, X.; Grenier, S.; Figueras, F.; North, P.; Royer, F.; Torra, J.; Mennessier, M. O. (1998). "The HR-diagram from HIPPARCOS data. Absolute magnitudes and kinematics of BP - AP stars". Astronomy and Astrophysics. 336: 953. Bibcode:1998A&A...336..953G.
6. Carrier, F.; North, P.; Udry, S.; Babel, J. (2002). "Multiplicity among chemically peculiar stars. II. Cool magnetic Ap stars". Astronomy and Astrophysics. 394: 151–169. arXiv:astro-ph/0208082. Bibcode:2002A&A...394..151C. doi:10.1051/0004-6361:20021122. S2CID 14223227.
7. Alecian, E.; Tkachenko, A.; Neiner, C.; Folsom, C. P.; Leroy, B. (2016). "The magnetic field of the double-lined spectroscopic binary system HD 5550". Astronomy & Astrophysics. 589: A47. arXiv:1601.07762. Bibcode:2016A&A...589A..47A. doi:10.1051/0004-6361/201527355. S2CID 54858999.
8. Renson, P.; Manfroid, J. (2009). "Catalogue of Ap, Hg Mn and Am stars". Astronomy and Astrophysics. 498 (3): 961. Bibcode:2009A&A...498..961R. doi:10.1051/0004-6361/200810788.