In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the rainbow of colors interspersed with spectral lines. Each line indicates a particular chemical element or molecule, with the line strength indicating the abundance of that element. The strengths of the different spectral lines vary mainly due to the temperature of the photosphere, although in some cases there are true abundance differences. The spectral class of a star is a short code primarily summarizing the ionization state, giving an objective measure of the photosphere's temperature.
Brown dwarfs are substellar objects that have more mass than the biggest gas giant planets, but less than the least massive main-sequence stars. Their mass is approximately 13 to 80 times that of Jupiter (MJ)—not big enough to sustain nuclear fusion of ordinary hydrogen (1H) into helium in their cores, but massive enough to emit some light and heat from the fusion of deuterium (2H). The most massive ones can fuse lithium (7Li).
Teegarden's Star is an M-type red dwarf star in the constellation Aries, 12.5 light-years from the Solar System. Although it is near Earth it is a dim magnitude 15 and can only be seen through large telescopes. This star was found to have a very large proper motion of about 5 arcseconds per year. Only seven stars with such large proper motions are currently known. Teegarden's Star hosts a planetary system with at least three planets.
Van Maanen 2, or van Maanen's Star, is the closest known solitary white dwarf to the Solar System. It is a dense, compact stellar remnant no longer generating energy and has equivalent to about 68% of the Sun's mass but only 1% of its radius. At a distance of 14.1 light-years it is the third closest of its type of star after Sirius B and Procyon B, in that order. Discovered in 1917 by Dutch–American astronomer Adriaan van Maanen, Van Maanen 2 was the third white dwarf identified, after 40 Eridani B and Sirius B, and the first solitary example.
Daniel Apai is a professor and astrophysicist at The University of Arizona in Tucson, Arizona. He is known for his studies of astrobiology, extrasolar planets, and the formation of planetary systems. He is the principal investigator of the Earths in Other Solar Systems team of NASA's Nexus for Exoplanet System Studies and the Hubble Space Telescope Cloud Atlas Treasury program, and Project EDEN, a large survey for habitable planets in the immediate solar neighborhood. He is leading the Nautilus Space Observatory space telescope concept and co-leading the technology development underpinning it.
S Ori 70 or S Ori J053810.1-023626 is a mid-T type astronomical object in the foreground of the σ Orionis cluster, which is approximately 1,150 light-years from Earth. It was discovered on November 24, 2002 by M. R. Zapatero-Osorio and E. L. Martin's team at the Roque de los Muchachos Observatory. It has yet to be determined if it is a field brown dwarf or a 3-million-year-old planet that is part of a cluster. Near-infrared spectroscopy images taken three years after its discovery led to the first motion measurements for the object. Its behavior is significantly different from what may be expected; it was further described as either a low-gravity atmosphere or an atmosphere with metallicity. The object's small proper motion suggests that it is further away than expected if it were a single field T dwarf.
SZ Crateris is a binary star system in the southern constellation Crater. Both components belong to the main sequence: the primary star has a spectral classification of K5V while the secondary is a red dwarf of spectral class M0V. The radius of the primary is about 66% the radius of the Sun, while the secondary member is only about 42% of the solar radius. In 1994, the two stars were separated by 5.1 arc seconds, which is equivalent to 112.41 astronomical units.
DENIS J081730.0−615520 is a T-type brown dwarf 17 light-years away in the constellation Carina. It was discovered by Etienne Artigau and his colleagues in April 2010. The brown dwarf belongs to the T6 spectral class, with a photosphere temperature of about 1000 K. It has a mass of about 15 MJ or about 1.5% the mass of the Sun.
2MASS J09373487+2931409, or 2MASSI J0937347+293142 is a brown dwarf of spectral class T6, located in the constellation Leo about 19.96 light-years from Earth.
2MASS J00361617+1821104 is a brown dwarf, located in 28.6 light-years from Earth in the constellation Pisces. It was discovered in 2000 by I. Neill Reid et al. Kinematically, it does not belong to any known moving group, been grouped with other "field stars".
GD 165 is a binary white dwarf and brown dwarf system located in the Boötes constellation, roughly 109 light-years from Earth. Neither of the stars have any known exoplanets.
2MASS J03552337+1133437 is a nearby brown dwarf of spectral type L5γ, located in constellation Taurus at approximately 29.8 light-years from Earth.
2MASS J0523−1403 is a very-low-mass red dwarf or high-mass brown dwarf about 40 light-years from Earth in the southern constellation of Lepus, with a very faint visual magnitude of 21.05 and a low effective temperature of 2074 K. It is visible primarily in large telescopes sensitive to infrared light. 2MASS J0523−1403 was first observed as part of the Two Micron All-Sky Survey (2MASS).
2MASS J21265040−8140293, also known as 2MASS J2126−8140, is an exoplanet orbiting the red dwarf TYC 9486-927-1, 111.4±0.3 light-years away from Earth. Its estimated mass, age, spectral type (L3), and Teff are similar to the well-studied planet β Pictoris b. With an estimated distance of around 1 trillion kilometres from its host star, it is one of the largest solar systems ever found.
Emily Rice is an astronomy professor at the Macaulay Honors College at the City University of New York. In addition to her scientific contributions to the study of the atmospheric properties of low mass astronomical bodies, she has become well known for her astronomy-related public outreach projects. She is the co-founder of the astro-centric fashion shop STARtorialist, a co-founder for the public outreach series Astronomy on Tap, a parody video creator, and a current research associate for the American Museum of Natural History in New York City. She has appeared as a guest on the popular podcast StarTalk (podcast), and was a host for their spinoff show, StarTalk All-Stars. Rice also served as a public presenter at the Hayden Planetarium in New York.
Backyard Worlds: Planet 9 is a NASA-funded citizen science project which is part of the Zooniverse web portal. It aims to discover new brown dwarfs, faint objects that are less massive than stars, some of which might be among the nearest neighbors of the Solar System, and might conceivably detect the hypothesized Planet Nine. The project's principal investigator is Marc Kuchner, an astrophysicist at NASA's Goddard Space Flight Center.
WISE 2150–7520 AB is a binary brown dwarf 78.9 light-years distant from Earth in the southern constellation Octans. The system is a wide binary with a separation of 341 astronomical units. The primary of the system was discovered in 2005 as an infrared object with high proper motion and in 2008 was found to be an ultracool dwarf with a spectral type of L. The secondary, a much cooler T dwarf, was discovered by volunteers of the citizen science project Backyard Worlds: Planet 9, using data from the Wide-field Infrared Survey Explorer (WISE). The system was followed up by the project scientists with Magellan and Spitzer and a scientific paper describing the binary was published in the Astrophysical Journal in 2020.
2MASS J03480772−6022270 is a brown dwarf of spectral class T7, located in the constellation Reticulum approximately 27.2 light-years from the Sun. It was discovered by astronomer Adam Burgasser and collaborators of the 2MASS Wide-Field T Dwarf Search in 2002. With a rotation period of 1.08 hours, it is the fastest-rotating brown dwarf confirmed as of 2022. The rotational velocity at its equator is over 100 km/s (62 mi/s), approaching the predicted rotational speed limit beyond which it would break apart due to centripetal forces. As a consequence of its rapid rotation, the brown dwarf is slightly flattened at its poles to a similar degree as Saturn, the most oblate planet in the Solar System. Its rapid rotation may enable strong auroral radio emissions via charged particle interactions in its magnetic field, as observed in other known rapidly-rotating brown dwarfs.
WISE 1534–1043 is a brown dwarf, Class Y, the coolest class, visible only in the infrared. It was accidentally discovered via the Wide-field Infrared Survey Explorer.
