HD 20782

Short description: Star in the constellation Fornax

HD 20782  Observation data
Equinox J2000.0]] (ICRS)

Constellation | Fornax
Right ascension |  03h 20m 03.57776s[1]
Declination | −28° 51′ 14.6604″[1]
Apparent magnitude (V) | 7.38[2]
Characteristics
Spectral type | G1.5 V[3]
B−V color index | +0.65[2]
Astrometry
Radial velocity (Rv)| 40.7±0.99[4] km/s
Proper motion (μ)|  RA: +349.054[1] mas/yr
Dec.: −65.305[1] mas/yr
Parallax (π)| 27.8760 ± 0.0172[1] mas
Distance| 117.00 ± 0.07 ly
(35.87 ± 0.02 pc)
Absolute magnitude (MV)| +4.61[5]
Details
Mass| 0.96+0.02−0.01[6] M☉
Radius| 1.17±0.03[7] R☉
Luminosity| 1.262+0.005−0.006[1] L☉
Surface gravity (log g)| 4.35+0.05−0.08[8] cgs
Temperature| 5,741±41[6] K
Metallicity [Fe/H]| −0.06±0.02[9] dex
Rotational velocity (v sin i)| 3.0±0.6[10] km/s
Age| 8.5+2.5−2.0[9] Gyr
Other designations

CD−29°1231, CPD−29°382, HD 20782, HIP 15527, SAO 168469, WDS J03201-2851A, LTT 1582[11]

Database references
SIMBAD| data
Exoplanet Archive| data
Extrasolar Planets
Encyclopaedia| data

HD 20782 (HIP 15527; LTT 1582) is the primary of a wide binary system located in the southern constellation Fornax. It has an apparent magnitude of 7.38,[2] making it readily visible in binoculars but not to the naked eye. The system is located relatively close at a distance of 117 light-years based on Gaia DR3 parallax measurements,[1] but it is receding with a heliocentric radial velocity of 40.7 km/s.[4] At its current distance, HD 20782's brightness is diminished by 0.12 magnitudes due to interstellar extinction[12] and it has an absolute magnitude of +4.61.[5]

## Contents

* 1 Properties
* 2 Binary system
* 3 Planetary system
* 4 See also
* 5 References
* 6 External links

## Properties

HD 20782 has a stellar classification of G1.5 V,[3] indicating that it is an ordinary G-type main-sequence star like the Sun. It has also been given a cooler class of G3 V. It has 96% the mass of the Sun[6] and 1.17 times the radius of the Sun.[7] It radiates 1.262 times the luminosity of the Sun[1] from its photosphere at an effective temperature of 5,741 K,[6] which is 35 K cooler than the Sun's temperature. When viewed in the night sky. the star has a yellow hue. HD 20782 is slightly metal deficient with an iron abundance 87.1% that of the Sun's or [Fe/H] = −0.06,[9] and it is estimated to be 8.5 billion years old,[9] which is nearly twice of the Sun's age. It spins modestly with a projected rotational velocity of 3.0 km/s.[10]

## Binary system

HD 20781 is a G or K-type main-sequence star with a very large angular separation of 252 arcsec, corresponding to 9080 AU at the distance of HD 20782.[13] In 2011, two Neptune-mass planets were announced around the nearby HD 20781, and initially they too were believed to be in eccentric orbits, but less so.[14] However, later more detailed observations on this system revealed not only two more planets but also that all the planets in this system, in stark contrast to HD 20782, are likely in low eccentricity orbits. The binary star system has a total of five known planets around both stars.[15]

## Planetary system

An extremely eccentric extrasolar planet was announced around HD 20782 in 2006.[16][17] In 2009 this planet's orbit was narrowed down, and it was found to have the highest eccentricity of all known exoplanets; this distinction has stood since 2012.

The HD 20782 planetary system  Companion
(in order from star) | Mass | Semimajor axis
(AU) | Orbital period
(days) | Eccentricity | Inclination | Radius

|
|
|
|
|
|

b | ≥1.49±0.11[15] MJ | 1.3649+0.0466−0.0495[15] | 597.065±0.043[18] | 0.956±0.004[18] | —  | —

## See also

* Struve 1341
* Kepler-16

Other systems with multiple planet-hosting stars:

* 55 Cancri
* HD 133131
* WASP-94
* XO-2

## References

1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 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.
2. ↑ 2.0 2.1 2.2 Cousins, A. W. J.; Stoy, R. H. (1962). "Photoelectric magnitudes and colours of Southern stars.". Royal Greenwich Observatory Bulletins 64: 103. Bibcode: 1962RGOB...64..103C.
3. ↑ 3.0 3.1 Gray, R. O.; Corbally, C. J.; Garrison, R. F.; McFadden, M. T.; Bubar, E. J.; McGahee, C. E.; O'Donoghue, A. A.; Knox, E. R. (2 June 2006). "Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 pc--The Southern Sample". The Astronomical Journal 132 (1): 161–170. doi:10.1086/504637. ISSN 0004-6256. Bibcode: 2006AJ....132..161G.
4. ↑ 4.0 4.1 Valenti, Jeff A.; Fischer, Debra A. (July 2005). "Spectroscopic Properties of Cool Stars (SPOCS). I. 1040 F, G, and K Dwarfs from Keck, Lick, and AAT Planet Search Programs". The Astrophysical Journal Supplement Series 159 (1): 141–166. doi:10.1086/430500. ISSN 0067-0049. Bibcode: 2005ApJS..159..141V.
5. ↑ 5.0 5.1 Anderson, E.; Francis, Ch. (May 2012). "XHIP: An extended hipparcos compilation". Astronomy Letters 38 (5): 331–346. doi:10.1134/S1063773712050015. ISSN 1063-7737. Bibcode: 2012AstL...38..331A.
6. ↑ 6.0 6.1 6.2 6.3 Ramírez, I.; Fish, J. R.; Lambert, D. L.; Allende Prieto, C. (13 August 2012). "Lithium Abundances in nearby FGK Dwarf and Subgiant Stars: Internal Destruction, Galactic Chemical Evolution, and Exoplanets". The Astrophysical Journal 756 (1): 46. doi:10.1088/0004-637X/756/1/46. ISSN 0004-637X. Bibcode: 2012ApJ...756...46R.
7. ↑ 7.0 7.1 van Belle, Gerard T.; von Braun, Kaspar (March 23, 2009). "Directly Determined Linear Radii and Effective Temperatures of Exoplanet Host Stars". The Astrophysical Journal (American Astronomical Society) 694 (2): 1085–1098. doi:10.1088/0004-637x/694/2/1085. ISSN 0004-637X. Bibcode: 2009ApJ...694.1085V.
8. ↑ Stassun, Keivan G. et al. (9 September 2019). "The Revised TESS Input Catalog and Candidate Target List". The Astronomical Journal 158 (4): 138. doi:10.3847/1538-3881/ab3467. Bibcode: 2019AJ....158..138S.
9. ↑ 9.0 9.1 9.2 9.3 Ghezzi, L.; Cunha, K.; Smith, V. V.; de Araújo, F. X.; Schuler, S. C.; de la Reza, R. (19 August 2010). "Stellar Parameters and Metallicities of Stars Hosting Jovian and Neptunian Mass Planets: A Possible Dependence of Planetary Mass on Metallicity". The Astrophysical Journal 720 (2): 1290–1302. doi:10.1088/0004-637X/720/2/1290. ISSN 0004-637X. Bibcode: 2010ApJ...720.1290G.
10. ↑ 10.0 10.1 Gonzalez, G.; Carlson, M. K.; Tobin, R. W. (April 11, 2010). "Parent stars of extrasolar planets - X. Lithium abundances and v sin i revisited". Monthly Notices of the Royal Astronomical Society (Oxford University Press (OUP)) 403 (3): 1368–1380. doi:10.1111/j.1365-2966.2009.16195.x. ISSN 0035-8711. Bibcode: 2010MNRAS.403.1368G.
11. ↑ "HD 20782". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=HD+20782.
12. ↑ Gontcharov, George A.; Mosenkov, Aleksandr V. (28 September 2017). "Verifying reddening and extinction for Gaia DR1 TGAS main sequence stars". Monthly Notices of the Royal Astronomical Society 472 (4): 3805–3820. doi:10.1093/mnras/stx2219. ISSN 0035-8711. Bibcode: 2017MNRAS.472.3805G.
13. ↑ Desidera, S.; Barbieri, M. (October 24, 2006). "Properties of planets in binary systems". Astronomy & Astrophysics (EDP Sciences) 462 (1): 345–353. doi:10.1051/0004-6361:20066319. ISSN 0004-6361. Bibcode: 2007A&A...462..345D.
14. ↑ "The HARPS search for southern extra-solar planets XXXIV. Occurrence, mass distribution and orbital properties of super-Earths and Neptune-mass planets". 2011. arXiv:1109.2497 [astro-ph].
15. ↑ 15.0 15.1 15.2 Udry, S.; Dumusque, X. et al. (2019). "The HARPS search for southern extra-solar planets". Astronomy & Astrophysics 622: A37. doi:10.1051/0004-6361/201731173. ISSN 0004-6361. Bibcode: 2019A&A...622A..37U.
16. ↑ Jones, Hugh R. A. et al. (2006). "High-eccentricity planets from the Anglo-Australian Planet Search". Monthly Notices of the Royal Astronomical Society 369 (1): 249–256. doi:10.1111/j.1365-2966.2006.10298.x. Bibcode: 2006MNRAS.369..249J.
17. ↑ Schneider, J. "Notes for HD 20782". Extrasolar Planets Encyclopaedia. http://exoplanet.eu/star.php?st=HD+20782.
18. ↑ 18.0 18.1 Kane, Stephen R. et al. (2016). "Evidence for Reflected Light from the Most Eccentric Exoplanet Known". The Astrophysical Journal 821 (1): 65. doi:10.3847/0004-637X/821/1/65. Bibcode: 2016ApJ...821...65K.

## External links

* "Planet HD 20782 b". Extrasolar Planets Encyclopaedia. https://exoplanet.eu/catalog/hd_20782_b--319/. Retrieved 2021-02-23.

Coordinates:  03h 20m 03.5776s, −28° 51′ 14.656″

Template:HD20781HD20782

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Fornax constellation

Stars (list)|

| Bayer|

* α (Dalim)
* β
* γ1
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* η1
* η2
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* ι1
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* κ
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|

Variable|

* R
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HR|

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HD|

* 12596
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* 20868
* 22333

Other|

* HIP 13044
* LP 944-20
* 2MASS J02431371−2453298
* UDF 19
* UDF 366
* UDF 2457

Star clusters|

| Globular|

* NGC 1049

|

Nebulae|

| Planetary|

* NGC 1360

|

Galaxies|

| NGC|

* 686
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* 727
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* 1459

|

Other|

* ESO 358-63
* Fornax Dwarf
* HUDF-JD2
* IC 335
* IC 1993
* UDF 423
* UDF 2457
* UDFj-39546284
* UDFy-38135539

Galaxy clusters|

* Fornax Cluster

Other|

* Chandra Deep Field South
* Hubble Legacy Field
* SN 1992bd
* SN 1999eu
* SN 2003B

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