The celestial coordinates of Lalande 21185 were first published in 1801 by French astronomer Jérôme Lalande of the Paris Observatory in the star catalog Histoire Céleste Française. The catalog sequence numbers for majority of the observed stars, including this one, were introduced in its 1847 edition by Francis Baily.[6][7] Today this star, along with a few others, is still commonly referred to by its Lalande catalog number.[8]
In May 1857, Friedrich Wilhelm Argelander discovered high proper motion of the star. Sometimes it was called "Argelander's second star".[9][10][11] (The "first Argelander's star" is Groombridge 1830, whose high proper motion also was discovered by Argelander earlier—in 1842).
Friedrich August Theodor Winnecke is reported to have made the first measurement of the star's parallax of 0.511 arc seconds in 1857–58 and thus first identifying Lalande 21185 as the second-closest-known star to the Sun, after the Alpha Centauri system.Lalande 21185 is a typical type-M main-sequence star (red dwarf) with about 46% of the mass of the Sun[13] and is much cooler than the Sun at 3,828 K. It is intrinsically dim with an absolute magnitude of 10.48, emitting most of its energy in the infrared.[19] Lalande 21185 is a high-proper-motion star moving at about 5 arc seconds a year in an orbit perpendicular to the plane of the Milky Way.{{citation needed|date=May 2015}} 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),[47] which is more than twice the surface gravity of our Sun.
Lalande 21185 is listed as a BY Draconis type variable star in the General Catalogue of Variable Stars. It is identified by the variable star designation NSV 18593.[14] Several star catalogs, including SIMBAD, also classify it as a flare 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.[15]
Lalande 21185 emits X-rays.[16]
In 1951 Dutch astronomer Peter van de Kamp and his student Sarah Lippincott claimed the astrometric detection of a planetary system using photographic plates taken with the {{convert|24|in|adj=on}} refractor telescope at Swarthmore College's Sproul Observatory.[17] In 1960, Sarah Lippincott repeated the 1951 claim of a planetary system, only this time having different parameters. She used the original photographic plates and new plates taken with the same telescope.[18] Photographic plates from this observatory, taken at the same time, were used by Van de Kamp for his erroneous claim of a planetary system for Barnard's Star. The photographic plates made with the Sproul 24-inch refractor and used for these and other studies were later shown to be flawed.[19] The claims of planetary companions for both stars were refuted in 1974 with astrometric measurements made by George Gatewood of the Allegheny Observatory.[20]
Further radial velocity research with the SOPHIE échelle spectrograph and review of the original signal found that the 9.9 day period was undetectable, and instead proposed, using both datasets, that an exoplanet orbiting the star with a period of either 12.95 or 1.08 days, much more probably 12.95 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.[26]
{{OrbitboxPlanet beginThis star's measured radial velocity is so constant that astronomer and planet hunter Geoff Marcy uses it as a perfect example of "normal" red dwarf stability levels.[27] The negative results of this and other surveys do not preclude the presence of a planetary system entirely, but they do set an upper boundary on the mass of any planets that might be present. The detection limit by current technology for this star system is a little less than the mass of the planet Jupiter.{{Citation needed|date=June 2012}} New Earth- and space-based instruments will certainly lower this limit further and possibly detect any small planets that may be present.
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 0.11–0.24 AU, where 1 AU is the average distance from the Earth to the Sun.[63]
1. ^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
⊙2. ^{{cite web | url =http://www.universetoday.com/111716/14-red-dwarf-stars-to-view-with-backyard-telescopes/ | title =14 Red Dwarf Stars to View with Backyard Telescopes | last =Dickinson | first =David | date =2015-12-23 | publisher =Universe Today | access-date =2016-12-04}}
3. ^{{cite web | url =http://kencroswell.com/thebrightestreddwarf.html | title =The Brightest Red Dwarf | last =Croswell | first =Ken | date =July 2002 | website =KenCroswell.com | access-date =2016-12-04}}
4. ^
1 2 3 4 5 6 7 {{cite simbad | title=HD 95735 | access-date=2009-05-29}}
5. ^{{cite web | url=http://cdsannotations.u-strasbg.fr/annotations/simbadObject/1764001 | title=Annotations on HD 95735 object | publisher=Centre de données astronomiques de Strasbourg | accessdate=2010-04-14 }}
6. ^Baily, Francis; Lalande, Joseph Jérôme Le Français de (1847). "Catalogue of those stars in the Histoire Celeste Francaise of Jerome Delalande, for which tables of reduction to the epoch 1800 habe been published by Prof. Schumacher".
London (1847). Bibcode:
1847cshc.book.....B. Google Books id: [https://books.google.com/books?id=oc0-AAAAcAAJ oc0-AAAAcAAJ].
7. ^{{ Cite journal |title=A catalogue of those stars in the "Histoire Celeste Française" of J. De Lalande for which tables of reduction to the session define format EPOCH1 = 1800 have been published by Professor Schumacher. |journal=British Ass. Adv. Sci |volume=1847 |author=Baily, F. |date=1847 |bibcode=1950Lalan1847....0B}}
8. ^
Joseph-Jérôme de Lalande {{webarchive |url=https://web.archive.org/web/20090721084438/http://www.thomaspynchon.com/mason-dixon/extra/lalande.html |date=July 21, 2009 }}
9. ^{{cite journal |last=Lynn |first=W. T. |title=On the Parallax and Proper Motion of Lalande 21185 |date=1872 |journal=Monthly Notices of the Royal Astronomical Society |volume=33 | issue= | pages=52–54 |bibcode=1872MNRAS..33...52L |doi=10.1093/mnras/33.1.52}}
10. ^
1 {{cite journal |last=Winnecke |first=A. |title=Über die Parallaxe des zweiten Argelander'schen Sterns, von Herrn Prof. Winnecke |date=1858 |journal=Astronomische Nachrichten |volume=48 | issue=1147 | pages=289–292 |bibcode=1858AN.....48..289W|doi = 10.1002/asna.18580481903 }}
11. ^{{cite journal |last=Winnecke |first=Friedrich August Theodor |title=Bestimmung der parallaxe des zweiten Argelander-'schen sternes aus messungen AM heliometer der sternwarte zu Bonn in den jahren 1857–1858 |date=1872 |journal=Leipzig, W. Engelmann |bibcode=1872bpza.book.....W}}
12. ^{{ cite journal |title=The parallax of Lalande 21185 and γ Virginis from photographs taken at the Cambridge Observatory |bibcode=1905MNRAS..65..787R |author=Russell, H. N. |journal=Monthly Notices of the Royal Astronomical Society |volume=65 |issue=8 |date=June 1905 |pages=787–800 |doi=10.1093/mnras/65.8.787|title-link=Cambridge Observatory }}
13. ^
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14. ^
1 {{ cite web| url=http://www.sai.msu.su/groups/cluster/gcvs/cgi-bin/search.cgi?search=NSV+18593| title=NSV 18593| work=General Catalogue of Variable Stars, Sternberg Astronomical Institute, Moscow, Russia| accessdate=2009-09-09}}
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