Zeta Doradus (ζ Dor) is a young star system that lies approximately 38 light-years away. The system consists of two widely separated stars, with the primary being bright enough to be observed with the naked eye but the secondary being much a much fainter star that requires telescopic equipment to be observed.

## Components

Zeta Doradus A is a bright, high proper motion star with a spectral type of F7V, meaning that it is a main sequence star that is hotter and brighter than the Sun. With an apparent magnitude of 4.82, it is approximately the eight brightest star in the constellation of Dorado.

Though it has been known that Zeta Doradus B is a nearby star since at least the Gliese Catalogue of Nearby Stars, the connection that it is a common proper motion companion to Zeta Doradus A was only made much more recently thanks to HIPPARCOS data. The two stars form a wide binary, with a physical separation between the components of about 0.018 parsecs (0.06 light-years) which is approximately 12400 AU.[3] This is comparable to the 15000 AU separation between Alpha Centauri AB and Proxima Centauri.

Both components of the system show considerable activity: The log R'HK of the stars are -4.373 and -4.575,[9] respectively, whereas a star is "quiet" when it has a Log R'HK of <-4.8. This indicates that the system is young; indeed, the estimated age for Zeta Doradus A is only 0.58 billion years,[7] about an eighth of the solar age.

It is not unusual for a young star to possess a debris disk; Zeta Doradus A is no exception, as it has been found to have an infra-red excess indicative of a disk of small bodies like comets re-emitting absorbed light at a redder wavelength. For Zeta Doradus A, the dust disk has a luminosity of 6.0 x 10−6 times the solar luminosity[6] and a temperature of 91 ± 12 Kelvin,[10] indicating that it lies at a separation of several AU.

## Planet searches

Stars of early spectral type (>F8) are often ignored by radial velocity (RV)-based planet searches due to issues with precision: their high temperature decreases the depth of their spectral lines and they tend to be fast rotators, which broadens their spectral lines. Still, it is still sometimes possible to reach levels of precision capable of the detection of planets in AF-type stars, so Zeta Doradus A was included in a sample early-type stars observed with HARPS.[11] The star was found to be RV-stable to 17 m/s with internal uncertainties of 3 m/s, which indicates that the star does not have any close-in high mass companions, but does not preclude the presence of sub-Jovian mass planets.

## References

1. van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357.
2. Ammler-von Eiff, M.; et al. (2012). "New measurements of rotation and differential rotation in A-F stars: are there two populations of differentially rotating stars?". arXiv:1204.2459. Bibcode:2012A&A...542A.116A. doi:10.1051/0004-6361/201118724.
3. ^ a b c Shaya, Ed J.; Olling, Rob P. (January 2011), "Very Wide Binaries and Other Comoving Stellar Companions: A Bayesian Analysis of the Hipparcos Catalogue", The Astrophysical Journal Supplement, 192 (1): 2, arXiv:1007.0425, Bibcode:2011ApJS..192....2S, doi:10.1088/0067-0049/192/1/2
4. ^ Flower, Phillip J. (September 1996). "Transformations from Theoretical Hertzsprung-Russell Diagrams to Color-Magnitude Diagrams: Effective Temperatures, B-V Colors, and Bolometric Corrections". The Astrophysical Journal. 469: 355. Bibcode:1996ApJ...469..355F. doi:10.1086/177785.
5. ^ Torres, Guillermo (November 2010). "On the Use of Empirical Bolometric Corrections for Stars". The Astronomical Journal. 140 (5): 1158–1162. arXiv:1008.3913. Bibcode:2010AJ....140.1158T. doi:10.1088/0004-6256/140/5/1158. Lay summary.
6. ^ a b Bryden, G.; et al. (2006). "Frequency of Debris Disks around Solar-Type Stars: First Results from a Spitzer MIPS Survey". arXiv:astro-ph/0509199. Bibcode:2006ApJ...636.1098B. doi:10.1086/498093.
7. ^ a b Maldonado, J.; et al. (May 2012). "Metallicity of solar-type stars with debris discs and planets". Astronomy & Astrophysics. 541: A40. arXiv:1202.5884. Bibcode:2012A&A...541A..40M. doi:10.1051/0004-6361/201218800.
8. ^ Bailer-Jones, C. A. L.; et al. (2011). "Bayesian inference of stellar parameters and interstellar extinction using parallaxes and multiband photometry". arXiv:1009.2766. Bibcode:2011MNRAS.411..435B. doi:10.1111/j.1365-2966.2010.17699.x.
9. ^ Gray, R. O.; et al. (2006). "Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 pc-The Southern Sample". arXiv:astro-ph/0603770. Bibcode:2006AJ....132..161G. doi:10.1086/504637.
10. ^ Dodson-Robinson, Sarah E.; et al. (2011). "A Spitzer Infrared Spectrograph Study of Debris Disks Around Planet-host Stars". arXiv:1010.3292. Bibcode:2011AJ....141...11D. doi:10.1088/0004-6256/141/1/11.
11. ^ Lagrange, A. -M.; et al. (2009). "Extrasolar planets and brown dwarfs around A-F type stars. VI. High precision RV survey of early type dwarfs with HARPS". arXiv:0809.4636. Bibcode:2009A&A...495..335L. doi:10.1051/0004-6361:200810105.

## Notes

1. ^ From knowing the absolute visual magnitude of Zeta Doradus ${\displaystyle \scriptstyle M_{V_{\ast }}=4.38}$ and using the temperature and B-V color index of the star to derive its bolometric correction of ${\displaystyle \scriptstyle BC=-0.025}$,[4] the bolometric magnitude can be calculated as ${\displaystyle \scriptstyle M_{bol_{\ast }}=4.355}$. The bolometric magnitude of the Sun is ${\displaystyle \scriptstyle M_{bol_{\odot }}=4.73}$,[5] and so therefore Zeta Doradus' bolometric luminosity can be calculated through ${\displaystyle \scriptstyle {\frac {L_{bol_{\ast }}}{L_{bol_{\odot }}}}=10^{0.4\left(M_{bol_{\odot }}-M_{bol_{\ast }}\right)}}$
2. ^ From knowing the absolute visual magnitude of Zeta Doradus ${\displaystyle \scriptstyle M_{V_{\ast }}=4.38}$ and the absolute visual magnitude of the Sun ${\displaystyle \scriptstyle M_{V_{\odot }}=4.83}$, the visual luminosity can be calculated by ${\displaystyle \scriptstyle {\frac {L_{V_{\ast }}}{L_{V_{\odot }}}}=10^{0.4\left(M_{V_{\odot }}-M_{V_{\ast }}\right)}}$