# Gliese 581

Observation data Epoch J2000.0      Equinox J2000.0 Constellation Size of the Sun (left) and Gliese 581 (right). Libra[1] 15h 19m 26.8269s[2] −07° 43′ 20.189″[2] 10.56 to 10.58[note 1] M3V[5] 1.61[6] BY Dra[7][note 2] Radial velocity (Rv) −9.5 ± 0.5[6] km/s Proper motion (μ) RA: −1221.289±0.160[2] mas/yr Dec.: −97.237±0.105[2] mas/yr Parallax (π) 158.64 ± 0.35[2] mas Distance 20.56 ± 0.05 ly (6.30 ± 0.01 pc) Absolute magnitude (MV) 11.6[11] Mass 0.31[12] M☉ Radius 0.299±0.010[13] R☉ Luminosity (bolometric) 0.013[5] L☉ Luminosity (visual, LV) 0.002[note 3] L☉ Surface gravity (log g) 4.92±0.10[14] cgs Temperature 3,480 ± 48[14] K Metallicity [Fe/H] −0.33 ± 0.12[14] dex Rotation 132.5±6.3 d[15] Age 7 to 11[12][16] Gyr HO Librae, HO Lib, BD−07°4003, GJ 581, HIP 74995, LFT 1195, LHS 394, LPM 564, LTT 6112, NLTT 39886, TYC 5594-1093-1, Wolf 562.[6][17] SIMBAD The star e b c d f (artifact) g

Gliese 581 (/ˈɡlzə/) is a star of spectral type M3V (a red dwarf) at the center of the Gliese 581 planetary system, about 20 light years away from Earth in the Libra constellation. Its estimated mass is about a third of that of the Sun, and it is the 89th closest known star to the Sun.

## History of observations

Gliese 581 is known at least from 1886, when it was included in Eduard Schönfeld's Southern Durchmusterung (SD)—the fourth part of the Bonner Durchmusterung. The corresponding designation is BD -7 4003.[18]

## Characteristics

The name Gliese 581 refers to the catalog number from the 1957 survey Gliese Catalogue of Nearby Stars of 965 stars located within 20 parsecs of the Earth. Other names of this star include BD-07° 4003 (BD catalogue, first known publication) and HO Librae (variable star designation). It does not have an individual name such as Sirius or Procyon.[6][17] The star is a red dwarf with spectral type M3V, located 20.4 light-years away from Earth. It is located about two degrees north of Beta Librae, the brightest star in the Libra constellation. Its mass is estimated to be approximately a third that of the Sun, and it is the 89th closest known star system to the Sun.[19]

An M-class dwarf star such as Gliese 581 has a much lower mass than the Sun, causing the core region of the star to fuse hydrogen at a significantly lower rate. From the apparent magnitude and distance, astronomers have estimated an effective temperature of 3200 K and a visual luminosity of 0.2 percent of that of the Sun.[20] However, a red dwarf such as Gliese 581 radiates primarily in the near infrared, with peak emission at a wavelength of roughly 830 nm (estimated using Wien's displacement law, which assumes the star radiates as a black body), so such an estimate will underestimate the star's total luminosity.[5] (For comparison, the peak emission of the Sun is roughly 530 nm, in the middle of the visible part of the spectrum). When radiation over the entire spectrum is taken into account (not just the part that humans are able to see), something known as the bolometric correction, this star has a bolometric luminosity 1.3% of the Sun's total luminosity.[5][20] A planet would need to be situated much closer to this star in order to receive a comparable amount of energy as the Earth. The region of space around a star where a planet would receive roughly the same energy as the Earth is sometimes termed the "Goldilocks Zone", or, more prosaically, the habitable zone. The extent of such a zone is not fixed and is highly specific for each planetary system.[21] Gliese 581 is a very old star. Its slow rotation makes it very inactive, making it better suited than most red dwarfs for having habitable planets.[22]

Gliese 581 is classified as a variable star of the BY Draconis type, and has been given the variable star designation HO Librae. This is a star that exhibits variability because of the presence of star spots combined with the rotation of the star. However, the measured variability is close to the margin of error, and, if real, is most likely a long term variability.[5] Its brightness is stable to 1%.[23] Gliese 581 emits X-rays.[24]

## Planets

The Gliese 581 planetary system[25]
Companion
(in order from star)
Mass Semimajor axis
(AU)
Orbital period
(days)
e ≥1.7 ± 0.2 M 0.02815 ± 0.00006 3.1490 ± 0.0002 0.00-0.06
b ≥15.8 ± 0.3 M 0.04061 ± 0.00003 5.3686 ± 0.0001 0.00-0.03
c ≥5.5 ± 0.3 M 0.0721 ± 0.0003 12.914 ± 0.002 0.00-0.06
g (unconfirmed) ≥2.2 M 0.13 32 0.00
d[26] (unconfirmed) 6.98 ± 0.3 M 0.21847 ± 0.00028 66.87 ± 0.13 0.00-0.25
Debris disk[27] 25 ± 12 AU–>60 AU 30° – 70°

## Notes

1. ^ Gliese 581 is classified as a BY Draconis variable in the General Catalogue of Variable Stars.[3] This catalog gives a maximum magnitude of 10.56 and minimum of magnitude 10.58 for a relatively low 20 mmag (0.020 magnitudes) variability.[4] For full data see data description and "The combined table of GCVS Vols I-III and NL 67-78 with improved coordinates, General Catalogue of Variable Stars". Sternberg Astronomical Institute. Retrieved 2009-04-27.
2. ^ In 1994 Edward Weis concluded that Gliese 581, like half the 43 dwarf M stars he studied over a multi-year period, showed long term variability (and page 1137, Fig 1 shows Gliese 581 had magnitude 10.58 in 1982 and between 10.57 and 10.56 from 1985 to 1990).[8] Bonfils noted in 2005 that Gliese 581 "has been classified as a variable star (HO Lib), but its variability (Weis 1994) is only marginally significant. If real it would be on a time scale of several years, with short term variability being at most ∼0.006 mag."[9] Measurements by MOST showed short term variability of about 5 mmag (half a percent) over a period of a few weeks.[10]
3. ^ Taking the absolute magnitude of Gliese 581, ${\displaystyle {\begin{smallmatrix}M_{V_{\ast }}=11.59\end{smallmatrix}}}$, with the absolute magnitude of the Sun, ${\displaystyle {\begin{smallmatrix}M_{V_{\odot }}=4.83\end{smallmatrix}}}$, the visual luminosity can be calculated from, ${\displaystyle {\begin{smallmatrix}{\frac {L_{V_{\ast }}}{L_{V_{\odot }}}}=10^{0.4\left(M_{V_{\odot }}-M_{V_{\ast }}\right)}\end{smallmatrix}}}$ .

## References

1. ^ Smith, Yvette. "NASA and NSF-Funded Research Finds First Potentially Habitable Exoplanet". nasa.gov. NASA. Retrieved 9 June 2016.
2. Brown, A. G. A.; et al. (2016). "Gaia Data Release 1. Summary of the astrometric, photometric, and survey properties". Astronomy and Astrophysics. 595. A2. arXiv:1609.04172. Bibcode:2016A&A...595A...2G. doi:10.1051/0004-6361/201629512.Gaia Data Release 1 catalog entry
3. ^ Lopez-Morales, M.; et al. (2006). "Limits to Transits of the Neptune-mass planet orbiting Gl 581". Publications of the Astronomical Society of the Pacific. 118 (849): 1506–1509. arXiv:astro-ph/0609255. Bibcode:2006PASP..118.1506L. doi:10.1086/508904. V* HO Lib … BY Draconis (page 2 of pre-print submitted 9 September 2006)
4. ^ "General Catalogue of Variable Stars Query results". Sternberg Astronomical Institute. Retrieved 2009-04-27.
5. Bonfils, X.; et al. (2005). "The HARPS search for southern extra-solar planets VI: A Neptune-mass planet around the nearby M dwarf Gl 581". Astronomy and Astrophysics Letters. 443 (3): L15–L18. arXiv:astro-ph/0509211. Bibcode:2005A&A...443L..15B. doi:10.1051/0004-6361:200500193.
6. ^ a b c d "GJ 581". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2008-08-21.
7. ^ 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.
8. ^ Weis, E. W. (1994). "Long term variability in dwarf M stars". The Astronomical Journal. 107 (3): 1138. Bibcode:1994AJ....107.1135W. doi:10.1086/116925.
9. ^ Bonfils page L15
10. ^ Matthews, J. M.; et al. (2007). "MOST Exoplanet System Photometry" (PDF). p. 80. Retrieved 2009-04-27.
11. ^ From apparent magnitude and parallax.
12. ^ a b "Star: Gliese 581". Extrasolar Planets Encyclopaedia. Archived from the original on 4 July 2012. Mass 0.31 MSun, Age 8+3
−1
Gyr
13. ^ von Braun, Kaspar; et al. (2011). "Astrophysical Parameters and Habitable Zone of the Exoplanet Hosting Star GJ 581". The Astrophysical Journal Letters. 729 (2). L26. arXiv:1102.0237. Bibcode:2011ApJ...729L..26V. doi:10.1088/2041-8205/729/2/L26.
14. ^ a b c Bean, J. L; Benedict, G. F.; Endl, M. (2006). "Metallicities of M Dwarf Planet Hosts from Spectral Synthesis". Astrophysical Journal Letters. 653 (1): L65–L68. arXiv:astro-ph/0611060. Bibcode:2006ApJ...653L..65B. doi:10.1086/510527.
15. ^ Suárez Mascareño, A.; et al. (September 2015), "Rotation periods of late-type dwarf stars from time series high-resolution spectroscopy of chromospheric indicators", Monthly Notices of the Royal Astronomical Society, 452 (3): 2745–2756, arXiv:1506.08039, Bibcode:2015MNRAS.452.2745S, doi:10.1093/mnras/stv1441.
16. ^ Selsis 3.4-page 1382 "lower limit of the age that, considering the associated uncertainties, could be around 7 Gyr", "preliminary estimate", "should not be above 10–11 Gyr"
17. ^ a b "Entry 5594-1093-1". The Hipparcos and Tycho Catalogues. Centre de données astronomiques de Strasbourg. ID I/239.
18. ^ Schönfeld, Eduard; et al. (1886). "BD -7 4003". Southern Durchmusterung.
19. ^ "The One Hundred Nearest Star Systems". Research Consortium On Nearby Stars, Georgia State University. 1 January 2009. Retrieved 2010-06-04.
20. ^ a b Udry, S; et al. (2007). "The HARPS search for southern extra-solar planets XI: Super-Earths (5 and 8 M) in a 3-planet system" (PDF). Astronomy and Astrophysics Letters. 469 (3): L43–L47. arXiv:0704.3841. Bibcode:2007A&A...469L..43U. doi:10.1051/0004-6361:20077612.
21. ^ Selsis, F.; et al. (2007). "Habitable planets around the star Gl 581?". Astronomy and Astrophysics. 476 (3): 1373–1387. arXiv:0710.5294. Bibcode:2007A&A...476.1373S. doi:10.1051/0004-6361:20078091.
22. ^ "Gliese 581 and the Stellar Activity Problem". 3 July 2014.
23. ^ Dragomir, D.; et al. (2012). "A Search for Transits of GJ 581e and Characterization of the Host Star Variability Using MOST Space Telescope Photometry". The Astrophysical Journal. 759 (1): 2f. arXiv:1211.0577. Bibcode:2012ApJ...759....2D. doi:10.1088/0004-637X/759/1/2.
24. ^ Schmitt, J. H. M. M; Fleming, T. A; Giampapa, M. S. (1995). "The X-Ray View of the Low-Mass Stars in the Solar Neighborhood". Astrophysical Journal. 450 (9): 392–400. Bibcode:1995ApJ...450..392S. doi:10.1086/176149.
25. ^ Robertson, Paul; Mahadevan, Suvrath; Endl, Michael; Roy, Arpita (3 July 2014). "Stellar activity masquerading as planets in the habitable zone of the M dwarf Gliese 581". Science. 345 (6195): 440–444. arXiv:1407.1049. Bibcode:2014Sci...345..440R. doi:10.1126/science.1253253. Retrieved 8 July 2014.
26. ^ "Reanalysis of data suggests 'habitable' planet GJ 581d really could exist". Astronomy Now. 9 March 2015. Retrieved 27 May 2015.
27. ^ J.-F. Lestrade; et al. (2012). "A DEBRIS Disk Around The Planet Hosting M-star GJ581 Spatially Resolved with Herschel". Astronomy and Astrophysics. 548: A86. arXiv:1211.4898. Bibcode:2012A&A...548A..86L. doi:10.1051/0004-6361/201220325.