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Norwegian Astronomical Society - Variable Star Section
***** Sequence for the RV Tauri Type Variable Star AC Herculis *****
Compiled by Bjorn H. Granslo (version 2003 June 4)
1826+21 AC Her [R.A. = 18h30m16s.2, Decl. = +21o52'01" (2000.0)]
AC Herculis = HD 170756. GCVS (Kholopov et al. 1985) has mag.
6.85 - 9.0 V, type RVA, period 75.01d and spectrum F2pIb-K4e(C0,0).
GCPD (Mermilliod et al.) has B-V from +0.59 to +0.84; mean values
derived from the Tycho-2 catalogue (Hog et al. 2000) are V = 7.64
and B-V = +0.68.
*** 1. Sequence Stars ***
This list contains stars with B-V from -0.1 to 0.6 and should serve as
a suitable set of non-red comparison stars for AC Herculis.
Id R.A. (2000.0) Decl. Star Name V-mag sV B-V sB-V Source
h m s o ' "
A 18 29 35.7 +23 51 58 HR 6943 5.89 0.01 -0.10 0.01 GCPD
B 18 18 07.7 +18 07 54 HR 6852 6.24 0.01 0.01 0.02 GCPD
C 18 34 19.6 +20 27 59 HR 6975 6.57 0.01 0.12 0.01 GCPD
D 18 36 37.0 +22 06 27 HD 171948 6.77 0.02 0.05 0.02 See note
E 18 34 47.0 +21 29 10 HD 171569 7.22 0.02 0.06 0.02 See note
F 18 25 56.7 +21 36 21 HD 169888 7.68 0.02 0.22 0.02 Tycho2
G 18 29 51.4 +22 00 40 HD 170671 8.24 0.02 0.21 0.02 Tycho2
H 18 33 54.1 +21 49 39 HD 171426 8.52 0.02 0.15 0.02 Tycho2
K 18 29 58.7 +21 31 23 HD 170697 8.81 0.02 0.11 0.03 Tycho2
L 18 30 58.9 +21 29 34 HD 170898 8.99 0.02 0.51 0.03 Tycho2
M 18 33 34.0 +21 56 41 HD 171342 9.26 0.03 0.62 0.03 Tycho2
N 18 28 55.4 +21 56 08 HD 170509 9.61 0.03 0.07 0.04 Tycho2
P 18 30 57.5 +21 22 24 HD 342408 10.08 0.04 0.57 0.05 Tycho2
*** 2. Other Reference Stars ***
These moderately red stars (B-V between 0.8 and 1.2) may be used as
colour calibrators and alternative comparison stars.
Id R.A. (2000.0) Decl. Star Name V-mag sV B-V sB-V Source
h m s o ' "
R 18 30 41.7 +20 48 54 HR 6950 6.48 0.02 0.79 0.01 GCPD
S 18 31 44.9 +21 54 08 HD 171046 6.92 0.02 1.16 0.02 Tycho2
T 18 30 59.0 +21 39 17 HD 170897 7.40 0.02 1.06 0.02 Tycho2
U 18 27 40.3 +21 27 33 HD 170266 8.25 0.02 1.06 0.03 Tycho2
W 18 29 17.0 +21 48 53 HD 170561 8.85 0.02 1.16 0.04 Tycho2
X 18 31 07.3 +21 56 59 HD 342394 9.26 0.03 1.15 0.05 Tycho2
Notes:
Stars A-C and R: V magnitudes and B-V colours are mean values derived
from data obtained at GCPD, The Lausanne Photometric Database.
Stars D-P and S-X: V magnitudes and B-V colours are derived from
Tycho2 BT and VT photometry (Hog et al. 2000) by using the correction
procedure of Bessell (2000).
Stars D-E: Photometry is mean of WBVR (Kornilov et al. 1991) and Tycho2.
Star D: ASAS-3 has V = 6.81 (+/- 0.04) from 17 observations.
Star E: ASAS-3 has V = 7.20 (+/- 0.03) from 17 observations.
Star F: Listed as a possible eclipser (V990 Her, type EA:). Hipparcos
satellite (HIP, ESA 1997) detected a single fade of 0.2 mag. in 1990,
but variability is not confirmed from other sources; ASAS-3 has
V = 7.68 (+/- 0.03) from 27 observations.
Star G: ASAS-3 has V = 8.24 (+/- 0.03) from 17 observations.
Star H: ASAS-3 has V = 8.51 (+/- 0.02) from 17 observations.
Star K: Possible variable NSV 10932, HIP has a scatter of >0.07 mag;
ASAS-3 has V = 8.78 (+/- 0.03) from 17 observations.
Star L: ASAS-3 has V = 8.98 (+/- 0.03) from 17 observations.
Star R: Possible variable NSV 24480, constant according to HIP.
Star S: ASAS-3 has V = 6.95 (+/- 0.01) from 17 observations.
Star T: Preston et al. (1963) have V = 7.405, B-V = 1.069; possible
variable NSV 10958, HIP has a scatter of >0.04 mag; ASAS-3 has
V = 7.42 (+/- 0.02) from 17 observations.
Tycho2 is the source of astrometry. Identifications are from "The
Bright Star Catalogue" [HR] and "Henry Draper Catalogue" [HD].
Acknowledgements:
The VizieR Service at Centre de Donnees astronomiques de Strasbourg,
The Lausanne General Catalogue of Photometric Data (GCPD) and The All
Sky Automated Survey (ASAS) web site have been used in preparing this
sequence. I would also like to thank Brian Skiff, Lowell Observatory,
Flagstaff, Arizona, USA for helpful advice.
References:
Bessell, M.: 2000, "The Hipparcos and Tycho Photometric System
Passbands", Publ. Ast. Soc. Pacific, 112, 961.
Cannon A. J., Pickering E. C.: 1918-1924, "Henry Draper Catalogue
and Extension", Harv. Ann. 91-100. [HD]
European Space Agency: 1997, "The Hipparcos and Tycho Catalogues",
ESA SP-1200. [HIP]
Hoffleit D., Warren Jr W. H.: 1991, "The Bright Star Catalogue, 5th
Revised Edition", Astronomical Data Center, NSSDC/ADC. Star
identifications [HR] are Harvard Revised Number = Bright Star Number.
Hog, E. et al.: 2000, "The Tycho-2 Catalogue of the 2.5 Million
Brightest Stars", Astron. Astrophys. 355, L27. [Tycho2]
Kholopov P. N. et al.: 1985, "General Catalogue of Variable Stars,
4th Edition", Nauka, Moscow. The most updated version of GCVS is at
http://www.sai.msu.su/groups/cluster/gcvs/gcvs/ . [GCVS]
Kornilov, V. G. et al.: 1991, "The WBVR Photometric Catalog",
Tr. Gos. Astron. Inst. Shternberga, Tom 63. [WBVR]
Mermilliod, J.-C., Hauck, B., Mermilliod, M.: "The General Catalogue of
Photometric Data", University of Lausanne, Switzerland.
URL: http://obswww.unige.ch/gcpd/gcpd.html . [GCPD]
Pojmansky G.: "The All Sky Automated Survey". V magnitudes derived
from measurements with the ASAS-3 system.
URL: http://www.astrouw.edu.pl/~gp/asas/asas.html .
Preston, G. W. et al.: 1963, "A Spectroscopic and Photoelectric Survey
of the RV Tauri Stars", Astrophys. Journ., 137, 401.
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