Lalande 21185 (also known asBD+36 2147,Gliese 411, andHD 95735[3]) is a star in the south ofUrsa Major. It is theapparent brightestred dwarf in the northern hemisphere.[nb 2][9][10] Despite this, and being relatively close by, it is very dim (as are all red dwarfs), being onlymagnitude 7.5 invisible light and thus too faint to be seen with the unaided eye. Thestar is visible through asmall telescope orbinoculars.[11]
Distances of thenearest stars from 20,000 years ago until 80,000 years in the future
Thecelestial coordinates of Lalande 21185 were first published in 1801 by French astronomerJérôme Lalande of theParis Observatory in the star catalogHistoire céleste française. The catalog sequence numbers for majority of the observed stars, including this one, were introduced in its 1847 edition byFrancis Baily.[15][16] Today this star is one of just a few that are still commonly referred to by their Lalande catalog number.[17]
In May 1857,Friedrich Wilhelm Argelander discovered the highproper motion of the star. It was sometimes called "Argelander's second star".[18][19][20] (The "first Argelander's star" isGroombridge 1830, whose high proper motion was discovered by Argelander earlier—in 1842). A large proper motion was recognised as an indicator for stars which lay close to the Sun, leading Argelander to request that itsparallax be measured.
As per this request,Friedrich August Theodor Winnecke made the first measurement of the star'sparallax of 0.511arc seconds in 1857–58 and thus first identifying Lalande 21185 as the second-closest-known star to theSun, after theAlpha Centauri system.[19] Since that time better measurements have placed the star farther away, but it remained the second-closest-known star system until theastrophotographic discovery of two dim red dwarfs, Wolf 359 and Barnard's Star, in the early 20th century.[21]
An X-raylight curve for a flare on NSV 18593, adapted from Pyeet al. (2015)[22]The position of Lalande 21185 on aradar map among all stellar objects orstellar systems within 9 light years (ly) from the map's center, the Sun (Sol). The diamond-shapes are their positions entered according toright ascension inhours angle (indicated at the edge of the map's reference disc), and according to theirdeclination. The second mark shows each's distance from Sol, with theconcentric circles indicating the distance in steps of one ly.
Lalande 21185 is a typicaltype-Mmain-sequence star (red dwarf) with about 39% of the mass and radius of the Sun. It is also much cooler than the Sun with a surface temperature of 3,550 K. With just 2.2% of the Sun's luminosity,[6] it is intrinsically dim with anabsolute magnitude of 10.48, emitting most of its energy in theinfrared.[5] The proportion of elements other than hydrogen and helium is estimated based on the ratio of iron to hydrogen in the star when compared to the Sun. The logarithm of this ratio is −0.20, indicating that the proportion of iron is about 10−0.20, or 63% of the Sun. The surface gravity of this relatively compact star is approximately 65 times greater than the gravity at Earth's surface (log g = 4.8 cgs),[23] which is more than twice the surface gravity of the Sun.
Lalande 21185 is listed as aBY Draconis type variable star in theGeneral Catalogue of Variable Stars. It is identified by the variable star designation NSV 18593.[4] Several star catalogs, includingSIMBAD, also classify it as aflare star. This conclusion is not supported by the primary reference these catalogs all use. The observations made in this reference show that it is rather quiet in comparison to other stars of its variable type.[24]
Lalande 21185 emits X-rays, and X-ray flares have been observed.[25][22]
Data published in 2017 from the HIRES system at theKeck Observatory onMauna Kea supported the existence of a close-in planet with an orbital period of just 9.8693±0.0016 days, being at least3.8M🜨.[26]Further radial velocity research with theSOPHIE échelle spectrograph and review of the original signal found that the 9.9 day period was undetectable, and instead proposed, using both datasets, an exoplanet orbiting the star with a period of either 12.95 or 1.08 days, much more likely 12.95, insofar as 1-day-period exoplanets seem to be rare in systems. This would give the planet a minimum mass of 2.99 Earth masses. It is too close to the star, and so therefore too hot, to be in the habitable zone, at all points within its eccentric orbit.[27] The proposed planet on 12-day orbit was confirmed byCARMENES (Calar Alto high-Resolution search for M dwarfs with Exoearths with Near-infrared and optical Echelle Spectrographs) project in 2020.[28]
A second planet with a more distant orbit was initially noticed by SOPHIE, but the baseline was not long enough to confirm the several-year-long signal. The signal was confirmed in 2021 to be a planet with mass at least18.0+2.9 −2.6M🜨,[29] a lower-bound estimate later revised to14.2±1.8 M🜨.[7]
A third planet, Gliese 411 d, is suspected to orbit between Gliese 411 b and Gliese 411 c with a period of 215 days.[7]
Thehabitable zone for this star, defined as the locations where liquid water could be present on an Earth-like planet, is at a radius of 0.11–0.24 AU, where 1 AU is the average distance from the Earth to the Sun.[30] The planet b has an equilibrium temperature of 370.1+5.8 −6.8K. Other known planets are outside HZ boundaries too, but undetected low-mass ones may be orbiting in this region of this system as well.[28]
Dutch astronomerPeter van de Kamp wrote in 1945 that Lalande 21185 possessed an "unseen companion" of 0.06 M☉ (about60MJ).[31] In 1951van de Kamp and his studentSarah Lippincott claimed theastrometric detection of a planetary system using photographic plates taken with the 24-inch (610 mm)refractor telescope atSwarthmore College'sSproul Observatory.[32] In the summer of 1960, Sarah Lippincott altered the 1951 claim, to a planet of 0.01 M☉ (that is,10MJ), an 8-year orbital period, eccentricity of 0.3, a semi-major axis[nb 3] of0.083 AU.[33] She used the original photographic plates and new plates taken with the same telescope.[34] Photographic plates from this observatory, taken at the same time, were used by Van de Kamp for his erroneous claim of a planetary system forBarnard's Star. The plates made with the Sproul 24-inch refractor and used for these and other studies were in 1973 shown to be flawed;[35] as they were the next year with astrometric measurements made byGeorge Gatewood of theAllegheny Observatory.[36]
In 1996 the same Gatewood prominently announced at anAAS meeting[37] and to the popular press[38] the discovery of multiple planets in this system, detected by astrometry. The initial report was based on a very delicate analysis of the star's position over the years, which suggested reflex orbital motion due to one or more companions. Gatewood claimed that such companions would usually appear more than 0.8 arcseconds from the red dwarf itself. Though, a paper by Gatewood published only a few years earlier[39] and later searches by others, usingcoronagraphs and multifilter techniques to reduce the scattered-light problems from the star, did not positively identify any such companions,[40] and so his claim remains unconfirmed and is now in doubt.
Before the 1980s, finding the radial velocity ofred dwarfs was neither very accurate nor consistent, and so due to its apparent brightness and because it does not have a companion, this star, along with eleven other similar red dwarf stars, were chosen to have theirradial velocity measured, to unprecedented high accuracy, by planet hunterGeoff Marcy.[41] No companion was detected around this star in this nor other contemporary surveys, and such early equipment would have picked up any planet exceeding0.7MJ in an extremely close orbit of 5 days or less; or exceeding10MJ at about Jupiter's orbital distance.[41]
^abcdeOja, T. (August 1985), "Photoelectric photometry of stars near the north Galactic pole. II",Astronomy and Astrophysics Supplement Series,61:331–339,Bibcode:1985A&AS...61..331O
^abJohnson, H. M.; Wright, C. D. (November 1983), "Predicted infrared brightness of stars within 25 parsecs of the Sun",Astrophysical Journal Supplement Series,53:643–711,Bibcode:1983ApJS...53..643J,doi:10.1086/190905
^abcdefHurt, Spencer A.; Fulton, Benjamin; Isaacson, Howard; Rosenthal, Lee J.; Howard, Andrew W.; Weiss, Lauren M.; Petigura, Erik A. (2021), "Confirmation of the Long-Period Planet Orbiting Gliese 411 and the Detection of a New Planet Candidate",The Astronomical Journal,163 (5): 218,arXiv:2107.09087,Bibcode:2022AJ....163..218H,doi:10.3847/1538-3881/ac5c47,S2CID236134034
^Kemmer, J.; Lafarga, M.; Fuhrmeister, B.; Shan, Y.; Schöfer, P.; Jeffers, S. V.; Caballero, J. A.; Quirrenbach, A.; Amado, P. J. (2025-04-11). "The CARMENES search for exoplanets around M dwarfs. Cluster analysis of signals from spectral activity indicators to search for shared periods".Astronomy and Astrophysics.697.arXiv:2504.08363.Bibcode:2025A&A...697A.225K.doi:10.1051/0004-6361/202347056.
^Baily, F. (1847). "A catalogue of those stars in the "Histoire céleste française" of J. De Lalande for which tables of reduction to the session define format EPOCH1 = 1800 have been published by Professor Schumacher".British Ass. Adv. Sci.1847.Bibcode:1950Lalan1847....0B.
^Winnecke, Friedrich August Theodor (1872). "Bestimmung der parallaxe des zweiten Argelander-'schen sternes aus messungen AM heliometer der sternwarte zu Bonn in den jahren 1857–1858".Leipzig, W. Engelmann. Astronomische Gesellschaft, Leipzig. Publication11. Leipzig.Bibcode:1872bpza.book.....W.hdl:2027/nnc1.cu50717758.
^Cayrel de Strobel, G.; et al. (1992), "A catalogue of Fe/H determinations",Astronomy and Astrophysics Supplement Series,95 (2) (1991 ed.):273–336,Bibcode:1992A&AS...95..273C,ISSN0365-0138
^From knowing the absolute visual magnitude of Lalande 21185,, and the absolute visual magnitude of the Sun, =, the visual luminosity of Lalande 21185 can therefore be calculated: = 0.005495 Lv⊙
.png)
