Editing Brown dwarf (section)

=== Role of other physical properties in the mass estimate ===
While spectroscopic features can help to distinguish between [[Red dwarf|low-mass stars]] and brown dwarfs, it is often necessary to estimate the mass to come to a conclusion. The theory behind the mass estimate is that brown dwarfs with a similar mass form in a similar way and are hot when they form. Some have spectral types that are similar to low-mass stars, such as [[2M1101AB]]. As they cool down the brown dwarfs should retain a range of [[Luminosity|luminosities]] depending on the mass.<ref>{{cite journal |last1=Saumon |first1=Didier |last2=Marley |first2=Mark S. |date=December 2008 |title=The Evolution of L and T Dwarfs in Color-Magnitude Diagrams |journal=Astrophysical Journal |volume=689 |issue=2 |pages=1327–1344 |doi=10.1086/592734 |arxiv=0808.2611 |bibcode=2008ApJ...689.1327S |s2cid=15981010 |issn=0004-637X }}</ref><!-- See Figure 2 for example --> Without the age and luminosity, a mass estimate is difficult; for example, an L-type brown dwarf could be an old brown dwarf with a high mass (possibly a low-mass star) or a young brown dwarf with a very low mass. For Y dwarfs this is less of a problem, as they remain low-mass objects near the [[sub-brown dwarf]] limit, even for relatively high age estimates.<ref name=":2">{{cite journal |last1=Marocco |first1=Federico |last2=Kirkpatrick |first2=J. Davy |last3=Meisner |first3=Aaron M. |last4=Caselden |first4=Dan |last5=Eisenhardt |first5=Peter R. M. |last6=Cushing |first6=Michael C. |last7=Faherty |first7=Jacqueline K. |last8=Gelino |first8=Christopher R. |last9=Wright |first9=Edward L. |year=2020 |title=Improved infrared photometry and a preliminary parallax measurement for the extremely cold brown dwarf CWISEP J144606.62-231717.8 |journal=The Astrophysical Journal |volume=888 |issue=2 |pages=L19 |arxiv=1912.07692 |bibcode=2020ApJ...888L..19M |doi=10.3847/2041-8213/ab6201 |s2cid=209386563 |doi-access=free}}</ref> For L and T dwarfs it is still useful to have an accurate age estimate. The luminosity is here the less concerning property, as this can be estimated from the [[spectral energy distribution]].<ref>{{cite journal |last1=Filippazzo |first1=Joseph C. |last2=Rice |first2=Emily L. |last3=Faherty |first3=Jacqueline K.|author3-link=Jackie Faherty |last4=Cruz |first4=Kelle L. |last5=Van Gordon |first5=Mollie M. |last6=Looper |first6=Dagny L. |date=September 2015 |title=Fundamental Parameters and Spectral Energy Distributions of Young and Field Age Objects with Masses Spanning the Stellar to Planetary Regime |journal=Astrophysical Journal |volume=810 |issue=2 |pages=158 |doi=10.1088/0004-637X/810/2/158 |arxiv=1508.01767 |bibcode=2015ApJ...810..158F |s2cid=89611607 |issn=0004-637X }}</ref> The age estimate can be done in two ways. Either the brown dwarf is young and still has spectral features that are associated with youth, or the brown dwarf co-moves with a star or stellar group ([[star cluster]] or [[Stellar association|association]]), where age estimates are easier to obtain. A very young brown dwarf that was further studied with this method is [[2M1207]] and the companion [[2M1207b]]. Based on the location, [[proper motion]] and spectral signature, this object was determined to belong to the ~8-million-year-old [[TW Hydrae association]], and the mass of the secondary was determined to be 8 ± 2 {{Jupiter mass|link=true}}, below the [[deuterium]] burning limit.<ref>{{cite journal |last1=Mohanty |first1=Subhanjoy |last2=Jayawardhana |first2=Ray |last3=Huélamo |first3=Nuria |last4=Mamajek |first4=Eric |date=March 2007 |title=The Planetary Mass Companion 2MASS 1207-3932B: Temperature, Mass, and Evidence for an Edge-on Disk |journal=Astrophysical Journal |volume=657 |issue=2 |pages=1064–1091 |doi=10.1086/510877 |arxiv=astro-ph/0610550 |bibcode=2007ApJ...657.1064M |s2cid=17326111 |issn=0004-637X }}</ref> An example of a very old age obtained by the co-movement method is the brown dwarf + [[white dwarf]] binary COCONUTS-1, with the white dwarf estimated to be {{Val|7.3|2.8|1.6}} [[billion years]] old. In this case the mass was not estimated with the derived age, but the co-movement provided an accurate distance estimate, using [[Gaia (spacecraft)|Gaia]] [[parallax]]. Using this measurement the authors estimated the radius, which was then used to estimate the mass for the brown dwarf as {{Val|15.4|0.9|0.8}} {{Jupiter mass}}.<ref name=":3">{{cite journal |last1=Zhang |first1=Zhoujian |last2=Liu |first2=Michael C. |last3=Hermes |first3=James J. <!-- https://www.bu.edu/cas/ar/2018/7/ a.k.a. "Jota Jota" (https://jjhermes.es), full name James Joseph Hermes Jr. https://repositories.lib.utexas.edu/bitstream/handle/2152/21608/HERMES-DISSERTATION-2013.pdf -->|last4=Magnier |first4=Eugene A. |last5=Marley |first5=Mark S. |last6=Tremblay |first6=Pier-Emmanuel |last7=Tucker |first7=Michael A. |last8=Do |first8=Aaron |last9=Payne |first9=Anna V. |last10=Shappee |first10=Benjamin J. |date=February 2020 |title=COol Companions ON Ultrawide orbiTS (COCONUTS). I. A High-Gravity T4 Benchmark around an Old White Dwarf and A Re-Examination of the Surface-Gravity Dependence of the L/T Transition |journal=The Astrophysical Journal |volume=891 |issue=2 |page=171 |doi=10.3847/1538-4357/ab765c |arxiv=2002.05723 |bibcode=2020ApJ...891..171Z |s2cid=211126544 |doi-access=free }}</ref>