AD Leonis is anM-type star with aspectral type M3.5eV, indicating it is amain sequence star that displays emission lines in its spectrum. At a trigonometric distance of 16.2 ly (5.0 pc), it has an apparent visual magnitude of 9.43.[6][9] It has about 39–42% of theSun's mass — above the mass at which a star isfully convective[10] — and 39% of theSun's radius.[6][11] Theprojected rotation of this star is only 2.4 km/s, but it completes a rotation once every 2.227 days, indicating a relatively pole-on inclination of about12.9°.[7] It is a relatively young star with an estimated age of 25–300 million years,[4] and is considered a member of the young disk population.[12]
The variable nature of this star was first observed in 1949 by Katherine C. Gordon and Gerald E. Kron atLick Observatory.[13] AD Leonis is one of the most activeflare stars known, and the emissions from the flares have been detected across theelectromagnetic spectrum as high as theX-ray band.[14][15] The net magnetic flux at the surface is about 3 kG.[16] Besides star spots, about 73% of the surface is covered by magnetically active regions.[17] Examination of thecorona in X-ray shows compact loop structures that span up to 30% of the size of the star.[18] The average temperature of the corona is around 6.39 MK.[19]
This star is orbiting through theMilky Way galaxy with aneccentricity of 0.028 . This carries the star as close as 8.442 kpc from the galactic core, and as far as 8.926 kpc. The orbitalinclination carries it as far as 0.121 kpc from the plane of the galaxy.[20]
During a 1943proper motion study byDirk Reuyl atMcCormick Observatory, AD Leonis was suspected of having a companion. However, a 1968 study bySarah L. Lippincott atSproul Observatory was unable to confirm this result.[22]A 1997 search with a near-infrared speckle interferometer failed to detect a companion orbiting 1–10 AU from the star.[23] In 2001, an opticalcoronagraph was used to example the star, but no companion was found.[24] As of 1981, there was no sign of variability in its radial velocity, which would otherwise indicate the presence of an unseen companion.[9]
In 2018, AD Leonis was found to haveradial velocity variations with a period of 2.23 days. The star was found to rotate with the same period, suggesting that the stellar rotation may be the cause of the radial velocity signal, but it was thought possible that the signal was caused by a planet of0.24MJ in aspin-orbit resonance with the star.[25] This was listed as a candidate planet in a 2019preprint.[26] However, subsequent studies starting in 2020 refuted the planet hypothesis, finding stellar activity to be the most likely explanation for the radial velocity variations.[27][28] A 2022 study confidently ruled out planets more massive than27 M🜨 orbiting at the stellar rotation period, as well as planets more than3-6MJ with periods up to 14 years.[7]
^abcNicolet, B. (October 1978). "Catalogue of homogeneous data in the UBV photoelectric photometric system".Astronomy and Astrophysics Supplement Series.34:1–49.Bibcode:1978A&AS...34....1N.
^abKukarkin, B. V.; Kholopov, P. N.; Pskovsky, Y. P.; Efremov, Y. N.; Kukarkina, N. P.; Kurochkin, N. E.; Medvedeva, G. I. (1971). "The third edition, containing information on 20,437 variable stars discovered and designated till 1968".General Catalogue of Variable Stars (3rd ed.).Bibcode:1971GCVS3.C......0K.
^abPettersen, B. R.; Coleman, L. A. (December 1981). "Chromospheric lines in red dwarf flare stars, I - AD Leonis and GX Andromedae".Astrophysical Journal.251 (12):571–82.Bibcode:1981ApJ...251..571P.doi:10.1086/159500.
^Sciortino, S.; Maggio, A.; Favata, F.; Orlando, S. (February 1999). "X-ray spectroscopy of the active dM stars: AD Leo and EV Lac".Astronomy & Astrophysics.342 (2):502–14.Bibcode:1999A&A...342..502S.
^Crespo-Chacón, I.; Montes, D.; García-Alvarez, D.; Fernández-Figueroa, M. J.; López-Santiago, J.; Foing, B. H. (June 2006). "Analysis and modeling of high temporal resolution spectroscopic observations of flares on AD Leonis".Astronomy and Astrophysics.452 (3):987–1000.arXiv:astro-ph/0602123.Bibcode:2006A&A...452..987C.doi:10.1051/0004-6361:20053615.S2CID119092601.
^Allen, C.; Herrera, M. A. (April 1998). "The galactic orbits of nearby UV Ceti stars".Revista Mexicana de Astronomía y Astrofísica.34:37–46.Bibcode:1998RMxAA..34...37A.
^Lippincott, S. L. (March 1969). "Astrometric study of BD+20 2465 from photographs taken with the Sproul 24 inch refractor".Astronomical Journal.74:224–228.Bibcode:1969AJ.....74..224L.doi:10.1086/110795.
^Leinert, C.; Henry, T.; Glindemann, A.; McCarthy, D. W. Jr. (September 1997). "A search for companions to nearby southern M dwarfs with near-infrared speckle interferometry".Astronomy and Astrophysics.325:159–166.Bibcode:1997A&A...325..159L.
^Oppenheimer, B. R.; Golimowski, D. A.; Kulkarni, S. R.; Matthews, K.; Nakajima, T.; Creech-Eakman, M.; Durrance, S.T. (April 2001). "A coronagraphic survey for companions of stars within 8 parsecs".The Astronomical Journal.121 (4):2189–2211.arXiv:astro-ph/0101320.Bibcode:2001AJ....121.2189O.doi:10.1086/319941.S2CID119092593.
^Tuomi, M.; Jones, H. R. A.; Butler, R. P.; Arriagada, P.; Vogt, S. S.; Burt, J.; et al. (11 June 2019). "Frequency of planets orbiting M dwarfs in the Solar neighbourhood".arXiv:1906.04644 [astro-ph.EP].
^Carleo, I.; Malavolta, L.; Lanza, A. F.; Damasso, M.; Desidera, S.; Borsa, F.; et al. (2020). "The GAPS Programme at TNG XXI – A GIARPS case-study of known young planetary candidates: Confirmation of HD 285507 b and refutation of AD Leo b".Astronomy & Astrophysics.A5: 638.arXiv:2002.10562.Bibcode:2020A&A...638A...5C.doi:10.1051/0004-6361/201937369.S2CID211296466.
