Rho Herculis

Rho Herculis (ρ Her, ρ Herculis) is a double star in the constellation of Hercules. The apparent magnitudes of the components are 4.510 and 5.398, respectively. Parallax measurements published in Gaia Data Release 2 put the system at some 360-390 light-years (111-121 parsecs) away.

Rho Herculis

Observation data Epoch J2000      Equinox J2000
Constellation	Hercules
ρ Her A
Right ascension	17^h 23^m 40.972^s[1]
Declination	+37° 08′ 45.33″[1]
Apparent magnitude (V)	4.510[1]
ρ Her B
Right ascension	17^h 23^m 40.718^s
Declination	+37° 08′ 48.44″[1]
Apparent magnitude (V)	5.398[1]
Characteristics
ρ Her A
Spectral type	A0IIIpHgMn[2]
U−B color index	−0.06[3]
B−V color index	+0.00[3]
ρ Her B
Spectral type	B9.5IVn[2]
Astrometry
ρ Her A
Radial velocity (Rv)	−21.0 ± 2[4] km/s
Proper motion (μ)	RA: −38.6[5] mas/yr Dec.: 9.2[5] mas/yr
Parallax (π)	8.3380 ± 0.3358[6] mas
Distance	390 ± 20 ly (120 ± 5 pc)
ρ Her B
Radial velocity (Rv)	−19.3 ± 2[4] km/s
Proper motion (μ)	RA: −38.6[1] mas/yr Dec.: 9.2[1] mas/yr
Parallax (π)	9.0354 ± 0.1135[7] mas
Distance	361 ± 5 ly (111 ± 1 pc)
Details
A
Mass	4.00/2.93[8] M☉
Temperature	9,118[6] K
Metallicity [Fe/H]	0.0[9] dex
Rotational velocity (v sin i)	75[10] km/s
B
Mass	3.27[8] M☉
Surface gravity (log g)	3.6[9] cgs
Temperature	8,755[7] K
Rotational velocity (v sin i)	291[10] km/s
Other designations
BD+37° 2878, HIP 85112, ADS 10526 AB, CCDM J17236+3708AB
ρ Her A: HD 157779, HR 6485, SAO 66001
ρ Her B: HD 157778, HR 6484, SAO 66000
Database references
SIMBAD	ρ Her
	ρ Her A
	ρ Her B

The two stars of Rho Herculis are separated by four arcseconds, and are known as Rho Herculis A and B, respectively. A is an A-type giant star, while B is a B-type subgiant star.[2] They are also referred to, rarely, as Rho¹ Herculis and Rho² Herculis. Rho Herculis A is itself a close binary which has been resolved using speckle interferometry, with the two components separated by 0.252″.[11]

The two visual components have very similar spectral types, between A0 and B9. Rho Herculis A is generally assigned a giant luminosity class, with Rho Herculis B most often considered to be a main sequence star.[12] Rho Herculis A has been considered to be an Ap star, with unusually strong silicon or mercury and manganese absorption lines in its spectrum,[2][13] but this is now considered to be dubious.[14]

References

1. Høg, E.; et al. (2000). "The Tycho-2 catalogue of the 2.5 million brightest stars". Astronomy and Astrophysics. 355: L27–L30. Bibcode:2000A&A...355L..27H.
2. Abt, Helmut A.; Morrell, Nidia I. (1995). "The Relation between Rotational Velocities and Spectral Peculiarities among A-Type Stars". The Astrophysical Journal Supplement Series. 99: 135. Bibcode:1995ApJS...99..135A. doi:10.1086/192182.
3. Johnson, H. L. (1966). "UBVRIJKL Photometry of the Bright Stars". Communications of the Lunar and Planetary Laboratory. 4: 99. Bibcode:1966CoLPL...4...99J.
4. Wilson, Ralph Elmer (1953). "General catalogue of stellar radial velocities". Carnegie Institute Washington D.C. Publication: 0. Bibcode:1953GCRV..C......0W.
5. Zacharias, N. (2012). "The fourth US Naval Observatory CCD Astrograph Catalog (UCAC4)". VizieR On-line Data Catalog. Bibcode:2012yCat.1322....0Z.
6. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
7. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
8. "Multiple Star Catalog". Cerro Tololo Inter-American Observatory. Retrieved 2018-11-30.
9. Gebran, M.; Farah, W.; Paletou, F.; Monier, R.; Watson, V. (2016). "A new method for the inversion of atmospheric parameters of A/Am stars". Astronomy and Astrophysics. 589: A83. arXiv:1603.01146. Bibcode:2016A&A...589A..83G. doi:10.1051/0004-6361/201528052.
10. Royer, F.; Grenier, S.; Baylac, M. -O.; Gómez, A. E.; Zorec, J. (2002). "Rotational velocities of A-type stars in the northern hemisphere. II. Measurement of v sin I". Astronomy and Astrophysics. 393 (3): 897–911. Bibcode:2002A&A...393..897R. doi:10.1051/0004-6361:20020943.
11. Mason, Brian D.; Hartkopf, William I.; Gies, Douglas R.; Henry, Todd J.; Helsel, John W. (2009). "The High Angular Resolution Multiplicity of Massive Stars". The Astronomical Journal. 137 (2): 3358. arXiv:0811.0492. Bibcode:2009AJ....137.3358M. doi:10.1088/0004-6256/137/2/3358.
12. Skiff, B. A. (2014). "VizieR Online Data Catalog: Catalogue of Stellar Spectral Classifications (Skiff, 2009-2016)". VizieR On-line Data Catalog. Bibcode:2014yCat....1.2023S.
13. Abt, H. A.; Cardona, O. (1984). "The nature of the visual companions of AP and AM stars". The Astrophysical Journal. 276: 266. Bibcode:1984ApJ...276..266A. doi:10.1086/161610.
14. Renson, P.; Manfroid, J. (2009). "Catalogue of Ap, HgMn and Am stars". Astronomy and Astrophysics. 498 (3): 961. Bibcode:2009A&A...498..961R. doi:10.1051/0004-6361/200810788.