Astronomy:TZ Fornacis
| Observation data Equinox J2000.0]] (ICRS) | |
|---|---|
| Constellation | Fornax[1] |
| Right ascension | 03h 14m 40.093s[2] |
| Declination | −35° 33′ 27.59″[2] |
| Apparent magnitude (V) | 6.88[1] (7.51 + 7.76)[3] |
| Characteristics | |
| Evolutionary stage | Giant + subgiant[3] |
| Spectral type | G8 III + F7 III[3] |
| B−V color index | 0.740±0.006[1] |
| Variable type | Algol[4] |
| Astrometry | |
| Radial velocity (Rv) | 18.0±2.4[5] km/s |
| Proper motion (μ) | RA: 34.598[2] mas/yr Dec.: 17.389[2] mas/yr |
| Parallax (π) | 5.4708 ± 0.0193[2] mas |
| Distance | 596 ± 2 ly (182.8 ± 0.6 pc) |
| Absolute magnitude (MV) | 0.70[1] |
| Orbit[3] | |
| Period (P) | 75.66647±0.00006 d |
| Semi-major axis (a) | 2.993±0.030 mas 0.5564±0.0001 astronomical unit|AU |
| Eccentricity (e) | 0.00002±0.00003 |
| Inclination (i) | 85.68±0.05° |
| Longitude of the node (Ω) | 65.99±0.03° |
| Argument of periastron (ω) (secondary) | 269.93±0.04° |
| Semi-amplitude (K1) (primary) | 38.90±0.01 km/s |
| Semi-amplitude (K2) (secondary) | 40.87±0.02 km/s |
| Details[3] | |
| TZ For 1 | |
| Mass | 2.057±0.001 M☉ |
| Radius | 8.28±0.22 R☉ |
| Luminosity | 37.2+1.8−1.7 L☉ |
| Surface gravity (log g) | 2.91±0.02 cgs |
| Temperature | 4,930±30 K |
| Metallicity [Fe/H] | 0.02±0.05 dex |
| Rotational velocity (v sin i) | 6.1±0.3 km/s |
| Age | 1.20±0.10 Gyr |
| TZ For 2 | |
| Mass | 1.958±0.001 M☉ |
| Radius | 3.94±0.17 R☉ |
| Luminosity | 22.9+1.5−1.6 L☉ |
| Surface gravity (log g) | 3.35±0.02 cgs |
| Temperature | 6,650±200 K |
| Rotational velocity (v sin i) | 45.7±1.0 km/s |
| Other designations | |
| Database references | |
| SIMBAD | data |
TZ Fornacis is an eclipsing binary star system in the southern constellation of Fornax. It has the designation HD 20301 from the Henry Draper Catalogue; TZ Fornacis is the variable star designation, abbreviated TZ For. This target is a challenge to view with the naked eye, having a peak apparent visual magnitude of 6.88.[1] During an eclipse, the magnitude drops to 7.05.[4] This system is located at a distance of approximately 596 light years from the Sun based on parallax measurements,[2] and is drifting further away with a radial velocity of roughly 18 km/s.[5]
In 1977, J. Andersen and B. Nordström identified HD 20301 as a double-lined spectroscopic binary star system.[7] The same year, E. H. Olsen determined this to be an eclipsing binary system that included an aging giant star. This made it of interest to astronomers because the orbital elements could be used to more precisely determine the mass and radius of an evolved star.[8] The two stars are of similar mass and both have evolved away from the main sequence, giving them an enlarged radius.[9]
The orbital plane for this system is nearly aligned with the line of sight to the Earth, so with each orbit the components are seen to eclipse each other over an orbital period of 75.67 days. However, these eclipses are shallow so there is not a complete occultation. The orbit has been circularized by tidal forces between the stars, but only the more massive component has had its rotation tidally synchronized with the orbit.[9] The system is fully detached with neither component overrunning its Roche lobe.[3]
The primary component, designated TZ Fornacis 1, has a spectrum that matches an aging G-type giant star with a stellar classification of G8 III. It is estimated to be 1.2 billion years old and is spinning in synchronicity with the orbital rotation. Based on the abundance of iron, the metallicity of this star is essentially the same as in the Sun. It has double the mass of the Sun and has expanded to over 8 times the Sun's radius. The star is radiating 37 times the luminosity of the Sun from its enlarged photosphere at an effective temperature of 4,930 K.[3]
The secondary star, designated TZ Fornacis 2, is an F-type subgiant star with a class of F7 III. Models suggest it has just left the main sequence.[3] The star is still small enough that its rotation rate hasn't been significantly impacted by tidal interaction. It has a relatively high projected rotational velocity of 46 km/s.[10] The star has nearly double the mass of the Sun and four times the Sun's radius. It is radiating 23 times the luminosity of the Sun at an effective temperature of 6,650 K, making it the hotter star in this system.[3]
References
- ↑ 1.0 1.1 1.2 1.3 1.4 Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters 38 (5): 331, doi:10.1134/S1063773712050015, Bibcode: 2012AstL...38..331A.
- ↑ 2.0 2.1 2.2 2.3 2.4 Vallenari, A. et al. (2022). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy & Astrophysics. doi:10.1051/0004-6361/202243940 Gaia DR3 record for this source at VizieR.
- ↑ 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 Gallenne, A. et al. (February 2016), "The Araucaria Project: High-precision orbital parallax and masses of the eclipsing binary TZ Fornacis", Astronomy & Astrophysics 586: id. A35, doi:10.1051/0004-6361/201526764, Bibcode: 2016A&A...586A..35G.
- ↑ 4.0 4.1 Samus, N. N. et al. (2017), "General Catalogue of Variable Stars", Astronomy Reports, GCVS 5.1 61 (1): 80–88, Bibcode: 2017ARep...61...80S.
- ↑ 5.0 5.1 Gontcharov, G. A. (2006), "Pulkovo compilation of radial velocities for 35495 stars in a common system", Astronomy Letters 32 (11): 759–771, doi:10.1134/S1063773706110065, Bibcode: 2006AstL...32..759G.
- ↑ "TZ For". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=TZ+For.
- ↑ Andersen, J.; Nordström, B. (September 1977), "Bright southern stars of astrophysical interest", Astronomy and Astrophysics, Supplement Series 29: 309–312, Bibcode: 1977A&AS...29..309A.
- ↑ Olsen, E. H. (August 1977), "HD 20301: an Eclipsing, Double-Lined Early G Giant", Information Bulletin on Variable Stars 1317: 1, Bibcode: 1977IBVS.1317....1O.
- ↑ 9.0 9.1 Andersen, J. et al. (June 1991), "TZ Fornacis : stellar and tidal evolution in a binary with a fully-fledged red giant (absolute dimensions of eclipsing binaries. XVII).", Astronomy and Astrophysics 246: 99, Bibcode: 1991A&A...246...99A.
- ↑ Higl, J. et al. (September 2018), "An analysis of the TZ Fornacis binary system", Astronomy & Astrophysics 617: id. A36, doi:10.1051/0004-6361/201833112, Bibcode: 2018A&A...617A..36H.
Further reading
- Claret, A. (August 2022), "Exploratory scenarios for the differential nuclear and tidal evolution of TZ Fornacis", Astronomy & Astrophysics 664: id. A101, doi:10.1051/0004-6361/202243573, Bibcode: 2022A&A...664A.101C.
- Valle, G. et al. (April 2017), "Statistical errors and systematic biases in the calibration of the convective core overshooting with eclipsing binaries. A case study: TZ Fornacis", Astronomy & Astrophysics 600: id. A41, doi:10.1051/0004-6361/201628240, Bibcode: 2017A&A...600A..41V.
- Claret, A. (February 2011), "Peculiar rotation in evolved binary systems: stellar and tidal evolution of TZ Fornacis", Astronomy and Astrophysics 526: id. A157, doi:10.1051/0004-6361/201015128, Bibcode: 2011A&A...526A.157C.
- Claret, A.; Gimenez, A. (April 1995), "Stellar and tidal evolution of TZ Fornacis: a case of asynchronism", Astronomy and Astrophysics 296: 180, Bibcode: 1995A&A...296..180C.
- Clausen, J. V. et al. (June 1991), "Four-colour photometry of eclipsing binaries. XXXIII. Light curves of TZ Fornacis", Astronomy and Astrophysics, Supplement Series 88: 535, Bibcode: 1991A&AS...88..535C.
- Andersen, J. et al. (1984), Maeder, Andre; Renzini, Alvio, eds., "A New Test Case for Normal Giant Evolution - TZ-Fornacis", Observational Tests of the Stellar Evolution Theory. International Astronomical Union Symposium No. 105, held in Geneva, Switzerland, September 12–16, 1983 (Dordrecht, The Netherlands, Boston, MA, Hingham, MA.: D. Reidel Publishing Company): p. 397, Bibcode: 1984IAUS..105..397A.
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