Zeta Herculis Moving Group Explained

Zeta Herculis Moving Group is a set of stars that share a common motion through space.

The existence of this moving group was first published in 1958 by Olin J. Eggen. Based upon the high velocity motion of the star Zeta Herculis through space, he searched for stars that were following a similar velocity and direction. A total of 22 candidate members were identified. Among the group members he included β Hydri, ρ Persei, η Reticuli, φ¹ Lupi, ζ Herculis and ε Octantis. He estimated the group velocity at 74.5 km/s.^[1] In 1970, Richard Woolley refined the list to ten stars, including φ² Pavonis and ζ¹/ζ² Reticuli as members of this cluster.^[2]

The parallel motion of the stars in this group implies a common origin, and hence a similar age and composition. The membership of ζ Herculis and HD 158614 came into question because their composition appeared to show they were much younger than other members of the group. The average age was estimated as, while ζ Herculis was estimated as 6.3 billion years in age.^[3] However, a statistical analysis of the metallicity for stars in this group showed no difference from a comparison sample, indicating that it may not be possible to determine more information about this group based on the composition of its members.^[4]

Members of the ζ Her moving group (1958 version)

Name	Constellation	B	F	HD	HIP	vis. mag.	Dist. (ly)	Sp. class	Notes
		ζ	40	150680	81693	2.81	35	F9IV
		β		2151	2021	2.82	24	G2IV
		ρ	25	19058	14354	3.32	325	M3IIIvar	Gorgonea Tertia
		φ^1	88	136422	75177	3.57	326	K5III
			47	2411	2219	5.01	490	M3IIIvar	TV Psc
		ε		210967	110256	5.09	268	M6III	BO Oct
		η		28093	20384	5.24	380	G7III
			84	119425	66936	5.35	217	K1III
				71377	41395	5.52	268	K1/K2III
				43899	29842	5.54	302	K2III
		C^1		100733	56518	5.64	652	M3III	V763 Cen
				150275	80850	6.35	408	K1III
			29	90250	51047	6.49	413	K1III
				221354	116085	6.76	55	K2V	Gliese 895.4
				9166	7166	6.81	485	K3III
				30455	22349	6.96	100	G2V...
			71	98824	55533	7.03	773	K1III
				219829	115112	8.09	106	K0V...
				68788	40848	8.35	101	K1V
				209134		9.11		K3V
				89668	50657	9.42	106	F8V
				106364		10.03		K2III+...

Members of the ζ her moving group (1970 version)

Name	Constellation	B	F	HD	HIP	vis. mag.	Dist. (ly)	Sp. class	Notes
		ζ	40	150680	81693	2.81	35	F9IV
		β		2151	2021	2.82	24	G2IV
		φ^2		196378	101983	5.11	79	F8V
		ζ^2		20807	15371	5.24	39	G1V
				158614	85667	5.31	54	G8IV-V	Gliese 678
		ζ^1		20766	15330	5.53	40	G2V
			1	70958	41211	5.61	89	F3V
				14680	10977	8.79	100	F3V
					59198	11.69	94	K7	Gliese 456

Notes and References

1. Stellar groups. II. The ζ Herculis, ε Indi and 61 Cygni groups of high-velocity stars . . 118 . 2 . 1958 . 154– . 1958MNRAS.118..154E . 10.1093/mnras/118.2.154 . Eggen . O. J. . free .
2. Richard van der Reit . Woolley . Box Orbits of Nearby Stars . Galactic Astronomy: Proceedings . 95–160 . Gordon and Breach . 1970 .
3. Porto de Mello, G. F. . da Silva, L. . On the physical existence of the Zeta HER moving group - A detailed analysis of Phi exp 2 Pavonis . . 102 . 1816–1825 . November 1991 . 10.1086/116006 . 1991AJ....102.1816P . free .
4. Taylor . B. J. . A statistical analysis of the metallicities of nine old superclusters and moving groups . . 362 . 2000 . 563–579 . 2000A&A...362..563T.