Groombridge 1618

Groombridge 1618

Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Ursa Major
Right ascension	10^h 11^m 22.14051^s[1]
Declination	+49° 27′ 15.2567″[1]
Apparent magnitude (V)	+6.60[2]
Characteristics
Spectral type	K8 V[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: –1362.32[1] mas/yr Dec.: –504.52[1] mas/yr
Parallax (π)	205.21 ± 0.54[1] mas
Distance	15.89 ± 0.04 ly (4.87 ± 0.01 pc)
Absolute magnitude (MV)	8.11[7]
Details
Mass	0.670 ± 0.033[8] M☉
Radius	0.605 ± 0.02[8] R☉
Luminosity (bolometric)	0.15[9] L☉
Luminosity (visual, LV)	0.046 L☉
Habitable zone inner limit	0.398[10][note 1] au
Habitable zone outer limit	0.755[10] au
Surface gravity (log g)	4.51;[11] 4.70[8] cgs
Temperature	3,970[11] K
Metallicity [Fe/H]	–0.03[11] dex
Rotational velocity (v sin i)	2.8[12] km/s
Age	6.6[9] Gyr
Other designations
BD+50 1725, GCTP 2390.00, GJ 380, HD 88230, HIP 49908, IRAS 10082+4942, LFT 696, LHS 280, LTT 12732, SAO 43223.[3]
Database references
SIMBAD	data

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 located close to Earth, at a distance of less than 16 light years. This is an main sequence star of spectral type K8 V, having just 67% of the Sun's mass. There is a suspected planetary companion with an orbital period of 122 days.

Properties

This star was first identified as entry number 1618 in the work A Catalog of Circumpolar Stars, published posthumously by Stephen Groombridge in 1838.^[13] It has a high proper motion across the sky, which is normally taken as an indicator that the star is located nearby—making it an early candidate for parallax measurement of its distance. In 1884 the parallax angle was measured as 0″.322 ± 0″.023, which is larger than the modern value of 0″.205.^[14]

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^[15] and possesses star spots comparable to Sun spots. However, like the star UV Ceti, it has been observed to undergo increases in luminosity as a flare star.^[5] It has a greater luminosity than most flare stars, which are typically red dwarfs, but is less active. The level of activity suggests that this is a somewhat youthful star.

System

A search for an excess amount of infrared emission from this star by the Infrared Space Observatory came up negative, implying that Groombridge 1618 does not possess a debris disk (such as Vega).^[16] However, observations using the Herschel Space Observatory showed a small excess suggesting the presence of 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).^[17]

According to Marcy & Benitz (1989),^[18] a possible periodicity of 122 days has been detected, inferring the potential presence of a massive 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 located within the star's habitable zone.^{[note 1]}

The unconfirmed Groombridge 1618 planetary system^[18]

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.^[19]

The habitable zone for this star, defined as the locations 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.^[20]

See also

• Stephen Groombridge
• List of nearest stars
• Groombridge 1618 in fiction

Notes

1. $\scriptstyle S_{eff_{\ast}}= S_{eff_{\odot}} + aT_{\ast} + bT_{\ast}^2 + cT_{\ast}^3 + dT_{\ast}^4$ ^[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 $\scriptstyle S_{eff_{\ast}}$ 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, $\scriptstyle {d = {\left(\frac{{L_{\ast}}/{L_{\odot}}}{S_{eff_{\ast}}} \right)^{0.5} AU}}$,^[10] the distance of the Inner HZ - Runaway Greenhouse limit from Groombridge 1618 can be calculated as $\scriptstyle{0.4 AU}$.

References

1. van Leeuwen, F. (November 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. Argue, A. N. (1966), "UBV photometry of 550 F, G and K type stars", Monthly Notices of the Royal Astronomical Society, 133: 475–493, Bibcode:1966MNRAS.133..475A, doi:10.1093/mnras/133.4.475
3. "NSV 4765 -- Flare Star". SIMBAD. Centre de Données astronomiques de Strasbourg. Retrieved 2013-08-01.
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, 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: 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. 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.
14. Ball, Robert S. (1884). "On the Annual Parallax of Groombridge 1618". Dunsink Observatory Publications. 5 (2): 187–217. Bibcode:1884DunOP...5..187B.
15. 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.
16. Laureijs, R. J.; et al. (2002). "A 25 micron search for Vega-like disks around main-sequence stars with ISO". Astronomy & Astrophysics. 387 (1): L285–L293. Bibcode:2002A&A...387..285L. doi:10.1051/0004-6361:20020366.
17. 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.
18. 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.
19. 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.
20. 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.

Notes

External links

• "Groombridge 1618". Sol Company. Retrieved 2007-06-24.
• "ARICNS 4C00785". Astronomisches Rechen-Institut. Archived from the original on 2007-06-10. Retrieved 2007-06-24.