AC Herculis, is an RV Tauri variable and spectroscopic binary star in the constellation of Hercules. It varies in brightness between apparent magnitudes 6.85 and 9.0.
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Hercules |
| Right ascension | 18h 30m 16.23850s[1] |
| Declination | +21° 52′ 00.6080″[1] |
| Apparent magnitude (V) | 6.85 - 9.00[2] |
| Characteristics | |
| Evolutionary stage | Post-AGB star[3] |
| Spectral type | F2pIb-K4e(C0,0)[2] |
| U−B color index | +0.17 - +0.94[4] |
| B−V color index | +0.52 - +1.09[4] |
| Variable type | RVa[2] |
| Astrometry | |
| Radial velocity (Rv) | −30.00[5] km/s |
| Proper motion (μ) | RA: -2.82 ± 1.12[1] mas/yr Dec.: -0.18 ± 1.16[1] mas/yr |
| Parallax (π) | 0.7843±0.0289 mas[6] |
| Distance | 4,200 ± 200 ly (1,280 ± 50 pc) |
| Orbit[7] | |
| Period (P) | 1,187.7 days |
| Semi-major axis (a) | 2.83 au (2.01 mas) |
| Eccentricity (e) | 0.206 |
| Inclination (i) | 142.9° |
| Longitude of the node (Ω) | 155.1° |
| Periastron epoch (T) | MJD 59023.1 |
| Argument of periastron (ω) (primary) | 118.6° |
| Semi-amplitude (K1) (primary) | 10.5 km/s |
| Details | |
| A | |
| Mass | 0.73[7] M☉ |
| Radius | 47.1+4.7 −4.1[8] R☉ |
| Luminosity | 2475+183 −209[8] L☉ |
| Surface gravity (log g) | 0.65[9] cgs |
| Temperature | 5900[8] K |
| Metallicity [Fe/H] | −1.5[9] dex |
| B | |
| Mass | 1.40[9] M☉ |
| Other designations | |
| AC Her, GSC 01581-01726, HD 170756, HIP 90697, BD+21°3459, 2MASS J18301623+2152007, IRAS 18281+2149, AAVSO 1826+21 | |
| Database references | |
| SIMBAD | data |
AC Her is an RVa star, meaning it is an RV Tauri variable whose maximum and minimum magnitudes do not slowly vary over hundreds of days. It also is a very clear example of a common type of RV Tauri light curve where the maximum following a deep minimum is brighter than the maximum following a shallow minimum. In each period of 75.46 days[8] it has two maxima and two minima.[10]
AC Her is also a binary star, its companion was detected with spectroscopy and long baseline interferometry. Interferometric observations from the CHARA Array enabled its three dimensional orbit with a semimajor axis of 2.01 ± 0.01 mas, equivalent to 2.83 ± 0.08 au.[7] The orbit has an inclination of 142.9 ± 1.1 degrees and a longitude of the ascending node of 155.1 ± 1.8 degrees. The invisible secondary is more massive (1.40 ± 0.12 M☉) than the supergiant primary ( 0.73 ± 0.13 M☉). The orbital period is 1187.7 days. The two stars are also surrounded by a dusty disc filling the region between 34 and 200 astronomical units (AU).[9]
Little is known of the secondary star except that its mass is around 1.4 M☉, deduced from the mass ratio of the binary system and the modelled mass of the primary star. The primary itself is calculated to have a mass of 0.73 M☉, but a luminosity of 2,500 L☉. It is slightly cooler than the sun, although this varies by over a thousand K as the star pulsates.[4]
The total system mass can be estimated from the dynamics of the disc, and this gives a value of 1.5 M☉, slightly lower than from other methods.[3]
References
edit- 1 2 3 4 van Leeuwen, F. (2007). "Validation of the New Hipparcos Reduction". Astronomy and Astrophysics. 474 (2): 653–64. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. S2CID 18759600.
- 1 2 3 Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S. 1. Bibcode:2009yCat....102025S.
- 1 2 Bujarrabal, V.; Castro-Carrizo, A.; Alcolea, J.; Van Winckel, H. (2015). "Detection of Keplerian dynamics in a disk around the post-AGB star AC Herculis". Astronomy & Astrophysics. 575: 4. arXiv:1502.01607. Bibcode:2015A&A...575L...7B. doi:10.1051/0004-6361/201525742. S2CID 118426089.
- 1 2 3 Dawson, D. W. (1979). "A photometric investigation of RV Tauri and yellow semiregular variables". Astrophysical Journal Supplement Series. 41: 97. Bibcode:1979ApJS...41...97D. doi:10.1086/190610.
- ↑ Gontcharov, G. A. (2006). "Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system". Astronomy Letters. 32 (11): 759–771. arXiv:1606.08053. Bibcode:2006AstL...32..759G. doi:10.1134/S1063773706110065. S2CID 119231169.
- ↑ 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.
- 1 2 3 Anugu, N.; Kluska, K.; Gardner, T.; Monnier, J. D. (2023). "Three-dimensional Orbit of AC Her Determined: Binary-induced Truncation Cannot Explain the Large Cavity in This Post-AGB Transition Disk". Astrophysical Journal. 950 (2): 149. arXiv:2305.02408. Bibcode:2023ApJ...950..149A. doi:10.3847/1538-4357/acd1e6.
- 1 2 3 4 Bódi, A.; Kiss, L. L. (2019), "Physical Properties of Galactic RV Tauri Stars from Gaia DR2 Data", The Astrophysical Journal, 872 (1): 60, arXiv:1901.01409, Bibcode:2019ApJ...872...60B, doi:10.3847/1538-4357/aafc24, S2CID 119099605
- 1 2 3 4 Hillen, M.; De Vries, B. L.; Menu, J.; Van Winckel, H.; Min, M.; Mulders, G. D. (2015). "The evolved circumbinary disk of AC Herculis: A radiative transfer, interferometric, and mineralogical study" (PDF). Astronomy & Astrophysics. 578: A40. arXiv:1503.03984. Bibcode:2015A&A...578A..40H. doi:10.1051/0004-6361/201425372. S2CID 53554889.
- ↑ Preston, G. W.; Krzeminski, W.; Smak, J.; Williams, J. A. (1963). "A Spectroscopic and Photoelectric Survey of the RV Tauri Stars". Astrophysical Journal. 137: 401. Bibcode:1963ApJ...137..401P. doi:10.1086/147520.