# HD 40307

Observation data Characteristics Epoch J2000.0      Equinox J2000.0 (ICRS) Location of HD 40307 in the night sky. The star is marked within the red diamond below the word "Pictor". Constellation Pictor Right ascension 05h 54m 04.2409s[1] Declination −60° 01′ 24.498″[1] Apparent magnitude (V) 7.17[1] Spectral type K2.5V[1] B−V color index 0.93[1] Radial velocity (Rv) +30.4 ± 0.2[1] km/s Proper motion (μ) RA: −51.76 [1] mas/yr Dec.: −60.44 [1] mas/yr Parallax (π) 77.95 ± 0.53[1] mas Distance 41.8 ± 0.3 ly (12.83 ± 0.09 pc) Absolute magnitude (MV) 6.63[note 1] Mass 0.75+0.03 −0.04[2] M☉ Radius 0.716 ± 0.010[3] R☉ Luminosity (bolometric) 0.23[4] L☉ Luminosity (visual, LV) 0.19[note 2] L☉ Surface gravity (log g) 4.47 ± 0.16[4] cgs Temperature 4977 ± 59[4] K Metallicity [Fe/H] = −0.31 ± 0.03[4] Rotation ~48 days[4] Rotational velocity (v sin i) 3[2] km/s Age 1.2 (≥ 0.2) × 109[2] years CD−60 1303, CPD−60 508, GC 7474, GJ 2046, HIP 27887, PPM 355061, SAO 249388.[1] SIMBAD data Exoplanet Archive data ARICNS data Extrasolar Planets Encyclopaedia data

HD 40307 is an orange (K-type) main-sequence star located approximately 42 light-years away in the constellation of Pictor (the Easel), taking its primary name from its Henry Draper Catalogue designation. It is calculated to be slightly less massive than the Sun. HD 40307 was observed during or before 1900 as part of the Cape Photographic Durchmusterung.[5] The star has six known planets, three discovered in 2008[1][6] and three more in 2012. One of them, HD 40307 g, is a potential super-Earth in the habitable zone, with an orbital period of about 200 days. This object might be capable of supporting liquid water on its surface, although much more information must be acquired before its habitability can be assessed.[7][8][9][10]

## History and nomenclature

The designation HD 40307 is from the Henry Draper Catalogue, which is based on spectral classifications made between 1911 and 1915 by Annie Jump Cannon and her co-workers, and was published between 1918 and 1924.[11][12]

## Characteristics

As a K-type star, HD 40307 emits orange-tinted light.[1] It has only about three-quarters of the Sun's radius and mass.[2] Its temperature is measured at slightly under 5000 K. This is relatively high for a K-type star, approaching the temperatures normally found in G-type stars such as the Sun.[13]

The astronomers who discovered the planets orbiting HD 40307 suggested that the metallicities of stars determine whether or not the planetary bodies that orbit them will be terrestrial, like Earth, or gaseous, like Jupiter and Saturn.[14]

### Distance and visibility

Despite its relative proximity to the Sun at 42 light-years, HD 40307 is not visible to the naked eye, given its apparent magnitude of 7.17.[15] It came within 6.4 light-years of the Sun about 413,000 years ago.[16]

## Planetary system

The orbits of the inner three planets of HD 40307.

After spending five years observing the star,[17] the European Organisation for Astronomical Research in the Southern Hemisphere (ESO) announced that they had discovered three super-Earths in orbit around HD 40307 in June 2008. All three planets were detected by the radial velocity method, using the HARPS spectrograph system.[18]

In 2012, an independent analysis carried out by a team of astronomers led by Mikko Tuomi of the University of Hertfordshire confirmed the existence of these planets and found an additional three planets in the systems.[7][8]

Five of the planets orbit very close to the star,[8] with the farthest of them located twice as close to HD 40307 than is the planet Mercury is to the Sun.[19][note 3] The outermost planet orbits at a distance similar to the distance of Venus to the Sun and is situated well in the system's liquid water habitable zone.[8]

The minimum masses of the planets in the system ranges from three to ten times the mass of the Earth, placing them somewhere between Earth and gas giants like Uranus and Neptune.[8] Dynamical analysis of the innermost planets suggests that planet b is unstable at its age unless it is an ice giant, having migrated from further away. That implies similar for the other planets, even further out.[20] The most recent discovery also indicates via dynamical analysis that the true planetary masses can not be much higher than their minimum masses.[8]

The HD 40307 system[8]
Companion
(in order from star)
Mass Semimajor axis
(AU)
Orbital period
(days)
b ≥ 4.0 +0.8
−0.7
M
0.0468 +0.0023
−0.0024
4.3123 +0.0011
−0.0012
0.20 +0.16
−0.14
c ≥ 6.6 +1.1
−1.0
M
0.0799 ± 0.0040 9.6184 +0.0050
−0.0049
0.06 +0.06
−0.11
d ≥ 9.5 +1.7
−1.5
M
0.1321 +0.0066
−0.0064
20.432 +0.022
−0.024
0.07 +0.11
−0.07
e ≥ 3.5 ± 1.4 M 0.1886 +0.083
−0.0104
34.62 +0.21
−0.20
0.15 +0.13
−0.15
f ≥ 5.2 +1.5
−1.6
M
0.247 +0.011
−0.014
51.76 +0.50
−0.46
0.02 +0.20
−0.02
g ≥ 7.1 ± 2.6 M 0.600 +0.034
−0.033
197.8 +9.0
−5.7
0.29 +0.31
−0.29

## Notes

1. ^ From apparent magnitude and parallax: $\scriptstyle M_V = m_V - 5 \log_{10} \left( \frac{100}{\mathrm{parallax\ in\ milliarcseconds}} \right)$
2. ^ Using the absolute visual magnitude of HD 40307 $\scriptstyle M_{V_{\ast}}=6.63$ and the absolute visual magnitude of the Sun $\scriptstyle M_{V_{\odot}}=4.83$, the visual luminosity can be calculated by $\scriptstyle \frac{L_{V_{\ast}}}{L_{V_{\odot}}}=10^{0.4\left(M_{V_{\odot}} - M_{V_{\ast}}\right)}$
3. ^ Mercury orbits at approx. 0.39 AU

## References

1. HD 40307, entry, SIMBAD. Accessed online June 18, 2008.
2. ^ a b c d HD 40307, database entry, Geneva-Copenhagen Survey of Solar neighbourhood, J. Holmberg et al., 2007, CDS database V/117A, accessed November 19, 2008; described in The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of ~14 000 F and G dwarfs, B. Nordström, M. Mayor, J. Andersen, J. Holmberg, F. Pont, B. R. Jørgensen, E. H. Olsen, S. Udry, and N. Mowlavi, Astronomy and Astrophysics 418 (May 2004), pp. 989–1019, Bibcode2004A&A...418..989N, doi:10.1051/0004-6361:20035959.
3. ^ HD 40307, entry, CDS database J/A+A/450/735; described in Effective temperature scale and bolometric corrections from 2MASS photometry, E. Masana, C. Jordi, and I. Ribas, Astronomy and Astrophysics 450, #2 (May 2006), pp. 735–746. Bibcode2006A&A...450..735M. doi:10.1051/0004-6361:20054021.
4. M. Mayor, S. Udry, C. Lovis, F. Pepe, D. Queloz, W. Benz, J.-L. Bertaux, F. Bouchy, C. Mordasini, D. Segransan (2009). "The HARPS search for southern extra-solar planets. XIII. A planetary system with 3 Super-Earths (4.2, 6.9, & 9.2 Earth masses)". Submitted to Astronomy and Astrophysics 493 (2): 639. arXiv:0806.4587. Bibcode:2009A&A...493..639M. doi:10.1051/0004-6361:200810451.
5. ^ CPD−60 508, database entry, Cape Photographic Durchmusterung (CPD), D. Gill and J. C. Kapetyn, 1895–1900, CDS ID I/108.
6. ^ Three super-Earths found around one star, Jeanna Bryner, MSNBC, June 16, 2008. Accessed on line June 18, 2008.
7. ^ a b Possible Earth-like planet could hold water; scientists cautious, Amina Khan, Los Angeles Times, November 7, 2012. Accessed on line November 8, 2012.
8. Tuomi, Anglada-Escude, Gerlach, Jones, Reiners, Rivera, Vogt, Butler, Mikko, Guillem, Enrico, Hugh R. R., Ansgar, Eugenio J., Steven S., R. Paul (2012). "Habitable-zone super-Earth candidate in a six-planet system around the K2.5V star HD 40307". arXiv:1211.1617v1 [astro-ph].
9. ^ Wall, Mike (November 7, 2012). "'Super-Earth' Alien Planet May Be Habitable for Life". Space.com. Retrieved November 8, 2012.
10. ^ Tate, Karl (November 7, 2012). "Super-Earth Planet: Potentially Habitable Alien World Explained (Infographic)". Space.com. Retrieved November 8, 2012.
11. ^ pp. 214–215 in The Henry Draper Memorial, Annie J. Cannon, Journal of the Royal Astronomical Society of Canada 9, #5 (May–June 1915), pp. 203–215, Bibcode1915JRASC...9..203C.
12. ^ The Henry Draper Catalogue, Annie J. Cannon and Edward C. Pickering, Annals of Harvard College Observatory;
hours 0 to 3, 91 (1918), Bibcode1918AnHar..91....1C;
hours 4 to 6, 92 (1918), Bibcode1918AnHar..92....1C;
hours 7 to 8, 93 (1919), Bibcode1919AnHar..93....1C;
hours 9 to 11, 94 (1919), Bibcode1919AnHar..94....1C;
hours 12 to 14, 95 (1920), Bibcode1920AnHar..95....1C;
hours 15 to 16, 96 (1921), Bibcode1921AnHar..96....1C;
hours 17 to 18, 97 (1922), Bibcode1922AnHar..97....1C;
hours 19 to 20, 98 (1923), Bibcode1923AnHar..98....1C;
hours 21 to 23, 99 (1924), Bibcode1924AnHar..99....1C.
13. ^ "Properties of Stars". Astronomy Notes. Jodrell Bank Centre for Astrophysics. 2007. Archived from the original on June 22, 2008. Retrieved 27 November 2008.
14. ^ M. Mayor, S. Udry, C. Lovis, F. Pepe, D. Queloz, W. Benz, J.-L. Bertaux, F. Bouchy, C. Mordasini, D. Segransan (2009). "The HARPS search for southern extra-solar planets. XIII. A planetary system with 3 Super-Earths (4.2, 6.9, & 9.2 Earth masses)". Submitted to Astronomy & Astrophysics 493 (2): 639. arXiv:0806.4587. Bibcode:2009A&A...493..639M. doi:10.1051/0004-6361:200810451.
15. ^ "Stellar Magnitudes". Astrophysics 162 Unit. University of Tennessee. 2008. Retrieved 20 November 2008.
16. ^ Bobylev, Vadim V. (March 2010). "Searching for Stars Closely Encountering with the Solar System". Astronomy Letters 36 (3): 220–226. arXiv:1003.2160. Bibcode:2010AstL...36..220B. doi:10.1134/S1063773710030060.
17. ^ "HD 40307 / CD-60 1303". SolStation. Sol Company. 2008. Retrieved 27 November 2008.
18. ^ Mayor et al. (2008-06-16). "Trio of 'super-Earths' discovered". BBC news. Retrieved 2008-06-16.
19. ^ "Mercury Fact Sheet". NASA Goddard Space Flight Center. November 30, 2007. Retrieved 2008-11-12.
20. ^ Barnes, Rory; Jackson, Brian; Raymond, Sean N.; West, Andrew A.; Greenberg, Richard (January 13, 2009). "The HD 40307 Planetary System: Super-Earths or Mini-Neptunes?". The Astrophysical Journal 695 (2): 1006. arXiv:0901.1698. Bibcode:2009ApJ...695.1006B. doi:10.1088/0004-637X/695/2/1006.