Groombridge 1618

Groombridge 1618 is a star in the northern constellation Ursa Major. With an apparent visual magnitude of +6.6, it lies at or below the threshold of stars visible to the naked eye for an average observer. It is relatively close to Earth, at 15.88 light years. This is a main sequence star of spectral type K7.5 Ve, having just 67% of the Sun's mass. There is a suspected planetary companion with an orbital period of 122 days.

Groombridge 1618
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Ursa Major
Right ascension 10h 11m 22.1400s[1]
Declination +49° 27′ 15.2492″[1]
Apparent magnitude (V) +6.60[2]
Characteristics
Spectral type K7.5 Ve[3]
U−B color index +1.27[2]
B−V color index +1.34[2]
Variable type BY Dra,[4] Flare star[5]
Astrometry
Radial velocity (Rv)–26.8[6] km/s
Proper motion (μ) RA: −1363.335±0.049[1] mas/yr
Dec.: −505.666±0.055[1] mas/yr
Parallax (π)205.3917 ± 0.0342[1] mas
Distance15.880 ± 0.003 ly
(4.8687 ± 0.0008 pc)
Absolute magnitude (MV)8.11[7]
Details
Mass0.670±0.033[8] M☉
Radius0.605±0.02[8] R☉
Luminosity (bolometric)0.15[9] L☉
Luminosity (visual, LV)0.046 L☉
Habitable zone inner limit0.398[10][note 1] au
Habitable zone outer limit0.755[10] au
Surface gravity (log g)4.51;[11] 4.70[8] cgs
Temperature3,970[11] K
Metallicity [Fe/H]–0.03[11] dex
Rotational velocity (v sin i)2.8[12] km/s
Age6.6[9] Gyr
Other designations
BD+50° 1725, GJ 380, HD 88230, HIP 49908, SAO 43223, LFT 696, IRAS 10082+4942[13]
Database references
SIMBADdata

Properties

This star was first identified as entry 1618 in the work A Catalog of Circumpolar Stars by Stephen Groombridge published posthumously in 1838.[14] It has such a proper motion across the sky that it guaranteed the star was quite nearby and made it an early candidate for parallax measurements. In 1884 the parallax angle was measured as 0″.322 ± 0″.023, which is larger than the modern value of 0″.205.[15]

Groombridge 1618 has a stellar classification of K8 V, which means it is a K-type main sequence star that is generating energy by fusing hydrogen at its core. It has 67% of the mass of the Sun, 61% of the Sun's radius,[8] but radiates only 15% of the Sun's energy and only 4.6% of the Sun's energy in the visible light spectrum. The effective surface temperature of the star's photosphere is about 4,000 K, giving it an orange hue.

It is a BY Draconis variable with a surface magnetic field strength of 750 G.[4] The chromosphere is relatively inactive[16] and produces star spots comparable to Sun spots. However, like UV Ceti, it has been observed to undergo increases in luminosity as a flare star.[5]

Planetary System

A search for excess infrared emission from this star by the Infrared Space Observatory came up negative, implying that Groombridge 1618 does not possess a nearby debris disk (such as Vega does).[17] However, observations using the Herschel Space Observatory showed a small excess suggesting a low-temperature debris disk. The data can be modeled by a ring of coarse, highly-reflective dust at a temperature below 22 K orbiting at least 51 AU from the host star.[9] If this star does have a companion, astrometric measurements appear to place an upper bound of 3–12 times the mass of Jupiter on such a hypothetical object (for orbital periods in the range of 5–50 years).[18]

Those observations collated by Marcy & Benitz (1989),[19] tend towards a single notable object with periodicity of 122 days as a planetary object with minimum mass 4 times that of Jupiter. This candidate planet has not been confirmed and the signal the authors had found could have been due to intrinsic stellar activity from the star's young age. If confirmed, the planet would be within the star's habitable zone.[note 1]

The unconfirmed Groombridge 1618 planetary system[19]
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(days)		 Eccentricity Inclination Radius
b (unconfirmed) ≳4 MJ 0.41 122.5 0 — —

An examination of this system in 2010 using the MMT telescope fitted with adaptive optics failed to detect a planetary companion.[20]

The habitable zone for this star, defined where liquid water could be present on an Earth-like planet, is at a radius of 0.26–0.56 AU, where 1 AU is the average distance from the Earth to the Sun.[21]

The star is among five nearby paradigms as K-type stars of a type in a 'sweet spot’ between Sun-analog stars and M stars for the likelihood of evolved life, per analysis of Giada Arney from NASA’s Goddard Space Flight Center.[22]

See also

Notes
  1. [10] when used to calculate the stellar flux reaching the outer atmosphere of an Earth-like planet orbiting Groombridge 1618 at the Inner Habitable Zone edge - the Runaway Greenhouse limit gives a of 0.9397 or 93.97% the stellar flux reaching the top of Earth's atmosphere. By applying the previously calculated stellar flux and the known 15% luminosity of Groombridge 1618 into the equation, ,[10] the distance of the Inner HZ - Runaway Greenhouse limit from Groombridge 1618 can be calculated as .

References
  1. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  2. Argue, A. N. (1966), "UBV photometry of 550 F, G and K type stars", Monthly Notices of the Royal Astronomical Society, 133 (4): 475–493, Bibcode:1966MNRAS.133..475A, doi:10.1093/mnras/133.4.475
  3. Lépine, Sébastien; et al. (2013), "A Spectroscopic Catalog of the Brightest (J < 9) M Dwarfs in the Northern Sky", The Astronomical Journal, 145 (4): 102, arXiv:1206.5991, Bibcode:2013AJ....145..102L, doi:10.1088/0004-6256/145/4/102.
  4. Gudel, M. (October 1992), "Radio and X-ray emission from main-sequence K stars", Astronomy and Astrophysics, 264 (2): L31–L34, Bibcode:1992A&A...264L..31G.
  5. Andrillat, Y.; Morguleff, N. (1967), Hack, Margherita (ed.), "Three potassium-flare stars", Proceedings of the Colloquium, held in Trieste, June 13–17, 1966, Trieste, p. 160, Bibcode:1967lts..conf..160A.
  6. Holmberg, J.; Nordstrom, B.; Andersen, J. (July 2009). "The Geneva-Copenhagen survey of the solar neighbourhood. III. Improved distances, ages, and kinematics". Astronomy and Astrophysics. 501 (3): 941–947. arXiv:0811.3982. Bibcode:2009A&A...501..941H. doi:10.1051/0004-6361/200811191.
  7. Holmberg, J.; et al. (July 2009), "The Geneva-Copenhagen survey of the solar neighbourhood. III. Improved distances, ages, and kinematics", Astronomy and Astrophysics, 501 (3): 941–947, arXiv:0811.3982, Bibcode:2009A&A...501..941H, doi:10.1051/0004-6361/200811191.
  8. Ségransan, D.; Kervella, P.; Forveille, T.; Queloz, D. (January 2003). "First radius measurements of very low mass stars with the VLTI". Astronomy and Astrophysics. 397 (3): L5–L8. arXiv:astro-ph/0211647. Bibcode:2003A&A...397L...5S. doi:10.1051/0004-6361:20021714.
  9. Eiroa, C.; et al. (December 2011), "Herschel discovery of a new class of cold, faint debris discs", Astronomy & Astrophysics, 536: L4, arXiv:1110.4826, Bibcode:2011A&A...536L...4E, doi:10.1051/0004-6361/201117797.
  10. Kopparapu, R. K.; Ramirez, R.; Kasting, J.F.; Eymet, V.; Robinson, T. D.; Mahadevan, S.; Terrien, R.C.; Domagal-Goldman, S.; Meadows, R.; Deshpande, V. (March 2013). "Habitable Zones around Main-sequence Stars: New Estimates". The Astrophysical Journal. 765 (2): 16. arXiv:1301.6674. Bibcode:2013ApJ...765..131K. doi:10.1088/0004-637X/765/2/131.
  11. Woolf, Vincent M.; Wallerstein, George (January 2005). "Metallicity measurements using atomic lines in M and K dwarf stars". Monthly Notices of the Royal Astronomical Society. 356 (3): 963–968. arXiv:astro-ph/0410452. Bibcode:2005MNRAS.356..963W. doi:10.1111/j.1365-2966.2004.08515.x. See table 3.
  12. López-Morales, Mercedes (May 2007). "On the Correlation between the Magnetic Activity Levels, Metallicities, and Radii of Low-Mass Stars". The Astrophysical Journal. 660 (1): 732–739. arXiv:astro-ph/0701702. Bibcode:2007ApJ...660..732L. doi:10.1086/513142.
  13. "NSV 4765 -- Flare Star". SIMBAD. Centre de Données astronomiques de Strasbourg. Retrieved 2013-08-01.
  14. Dyson, F. W.; Thackeray, W. G.; Christie, W. H. M. (1905). "New reduction of Groombridge's catalogue of circumpolar stars". Proceedings of the Royal Society of Edinburgh. Bibcode:1905Gmb...C......0D.
  15. Ball, Robert S. (1884). "On the Annual Parallax of Groombridge 1618". Dunsink Observatory Publications. 5 (2): 187–217. Bibcode:1884DunOP...5..187B.
  16. Byrne, P. B.; Doyle, J. G. (November 1990), "Activity in late-type stars. VII - Chromospheric and transition region line fluxes in 2 dM and 1 dM(e) stars", Astronomy and Astrophysics, 238 (1–2): 221–226, Bibcode:1990A&A...238..221B.
  17. Laureijs, R. J.; et al. (2002). "A 25 micron search for Vega-like disks around main-sequence stars with ISO" (PDF). Astronomy & Astrophysics. 387 (1): L285–L293. Bibcode:2002A&A...387..285L. doi:10.1051/0004-6361:20020366. hdl:1887/7333.
  18. Hershey, J. L.; Borgman, E. R. (1978). "Upper Limits on the Mass of a Dark Companion of Groombridge 1618 from the 40-year Sproul Plate Series". Bulletin of the American Astronomical Society. 10: 630. Bibcode:1978BAAS...10..630H.
  19. Marcy, Geoffrey W.; Benitz, Karsten J. (1989). "A search for substellar companions to low-mass stars". Astrophysical Journal, Part 1. 344 (1): 441–453. Bibcode:1989ApJ...344..441M. doi:10.1086/167812.
  20. Heinze, A. N.; et al. (May 2010). "Constraints on Long-period Planets from an L'- and M-band Survey of Nearby Sun-like Stars: Observations". The Astrophysical Journal. 714 (2): 1551–1569. arXiv:1003.5340. Bibcode:2010ApJ...714.1551H. doi:10.1088/0004-637X/714/2/1551.
  21. Cantrell, Justin R.; et al. (October 2013), "The Solar Neighborhood XXIX: The Habitable Real Estate of Our Nearest Stellar Neighbors", The Astronomical Journal, 146 (4): 99, arXiv:1307.7038, Bibcode:2013AJ....146...99C, doi:10.1088/0004-6256/146/4/99.
  22. Bill Steigerwald (2019-03-07). ""Goldilocks" Stars May Be "Just Right" for Finding Habitable Worlds". NASA. Retrieved 2020-05-12. 'I find that certain nearby K stars like 61 Cyg A/B, Epsilon Indi, Groombridge 1618, and HD 156026 may be particularly good targets for future biosignature searches,' said Arney.

Notes
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