Editing Red dwarf (section)

==Spectral standard stars==
[[File:Gliese 623.jpg|right|thumb|[[Gliese 623]] is a pair of red dwarfs, with GJ&nbsp;623a on the left and the fainter GJ&nbsp;623b to the right of center.]]
The spectral standards for M&nbsp;type stars have changed slightly over the years, but settled down somewhat since the early 1990s. Part of this is due to the fact that even the nearest red dwarfs are fairly faint, and their colors do not register well on [[photographic emulsion]]s used in the early to mid 20th century. The study of mid- to late-M&nbsp;dwarfs has significantly advanced only in the past few decades, primarily due to development of new [[astrograph]]ic and [[spectroscopic]] techniques, dispensing with photographic plates and progressing to charged-couple devices (CCDs) and infrared-sensitive arrays.

The revised Yerkes Atlas system (Johnson & Morgan, 1953)<ref name="adsabs.harvard.edu">{{cite journal |bibcode=1953ApJ...117..313J |title=Fundamental stellar photometry for standards of spectral type on the revised system of the Yerkes spectral atlas |journal=Astrophysical Journal |volume=117 |pages=313 |last1=Johnson |first1=H.L. |last2=Morgan |first2=W.W. |year=1953 |doi=10.1086/145697}}</ref> listed only two M&nbsp;type spectral standard stars: [[HD&nbsp;147379]] (M0V)
and HD&nbsp;95735/[[Lalande 21185]] (M2V). While HD&nbsp;147379 was not considered a standard by expert classifiers in later compendia of standards, [[Lalande 21185]] is still a primary standard for M2V. Robert Garrison<ref name="Garrison">{{cite web |url=http://www.astro.utoronto.ca/~garrison/mkstds.html |title=MK anchor-point standards table |first=Robert F. |last=Garrison |website=astro.utoronto.ca |publisher=University of Toronto |department=Department of Astronomy & Astrophysics |access-date=2011-12-18 |archive-date=2019-06-25 |archive-url=https://web.archive.org/web/20190625094716/http://www.astro.utoronto.ca/~garrison/mkstds.html |url-status=dead }}</ref> does not list any "anchor" standards among the red dwarfs, but [[Lalande 21185]] has survived as a M2V standard through many compendia.<ref name="adsabs.harvard.edu"/><ref name="Keenan89">{{cite journal |bibcode=1989ApJS...71..245K |title=The Perkins catalog of revised MK types for the cooler stars |journal=Astrophysical Journal Supplement Series |volume=71 |pages=245 |last1=Keenan |first1=Philip C. |last2=McNeil |first2=Raymond C. |year=1989 |doi=10.1086/191373|s2cid=123149047 }}</ref><ref name="ReferenceA">{{cite journal |bibcode=1991ApJS...77..417K |title=A standard stellar spectral sequence in the red / near-infrared - Classes&nbsp;K5 to M9 |journal=Astrophysical Journal Supplement Series |volume=77 |pages=417 |last1=Kirkpatrick |first1=J.D. |last2=Henry |first2=Todd J. |last3=McCarthy |first3=Donald W. |year=1991 |doi=10.1086/191611|doi-access=free }}</ref> The review on MK classification by Morgan & Keenan (1973) did not contain red dwarf standards. 

In the mid-1970s, red dwarf standard stars were published by Keenan & McNeil (1976)<ref>{{cite book |last1=Keenan |first1=Philip Childs |last2=McNeil |first2=Raymond C. |year=1976 |title=An atlas of spectra of the cooler stars: Types G, K, M, S, and C. Part&nbsp;1: Introduction and tables |place=Columbus, OH |publisher=Ohio State University Press |bibcode=1976aasc.book.....K}}</ref> and Boeshaar (1976),<ref>{{cite thesis |last1=Boeshaar |first1=P.C. |year=1976 |title=The spectral classification of M&nbsp;dwarf stars |degree=Ph.D. |publisher=Ohio State University |place=Columbus, OH |bibcode=1976PhDT........14B}}</ref> but there was little agreement among the standards. As later cooler stars were identified through the 1980s, it was clear that an overhaul of the red dwarf standards was needed. Building primarily upon the Boeshaar standards, a group at Steward Observatory (Kirkpatrick, Henry, & McCarthy, 1991)<ref name="ReferenceA"/> filled in the spectral sequence from K5V to M9V. It is these M&nbsp;type dwarf standard stars which have largely survived as the main standards to the modern day. There have been negligible changes in the red dwarf spectral sequence since 1991. Additional red dwarf standards were compiled by Henry et al. (2002),<ref>{{cite journal |bibcode=2002AJ....123.2002H |title=The Solar neighborhood. VI.&nbsp;New southern nearby stars identified by optical spectroscopy |journal=The Astronomical Journal |volume=123 |issue=4 |page=2002 |last1=Henry |first1=Todd J .|author-link2=Lucianne Walkowicz |last2=Walkowicz |first2=Lucianne M. |last3=Barto |first3=Todd C. |last4=Golimowski |first4=David A. |year=2002 |doi=10.1086/339315 |arxiv = astro-ph/0112496|s2cid=17735847 }}</ref> and D. Kirkpatrick has recently
reviewed the classification of red dwarfs and standard stars in Gray & Corbally's 2009 monograph.<ref>{{cite book |last1=Gray |first1=Richard O. |last2=Corbally |first2=Christopher |year=2009 |title=Stellar Spectral Classification |publisher=Princeton University Press |bibcode=2009ssc..book.....G}}</ref> The M&nbsp;dwarf primary spectral standards are: [[GJ 270]] (M0V), [[GJ 229A]] (M1V), [[Lalande 21185]] (M2V), [[Gliese 581]] (M3V), [[Gliese 402]] (M4V), [[GJ 51]] (M5V), [[Wolf 359]] (M6V), [[van Biesbroeck 8]] (M7V), [[VB 10]] (M8V), [[LHS 2924]] (M9V).