OTS 44

OTS 44 was discovered in images taken on 1–3 March 1996 by Japanese astronomers Yumiko Oasa, Motohide Tamura, and Koji Sugitani, during a search for young stellar objects and brown dwarfs in the core of the Chamaeleon I molecular cloud.^[11]: 338 The discovery images were taken with the Cerro Tololo Inter-American Observatory's 1.5-metre (4.9 ft) telescope in Chile, which was equipped with the J, H, and K filters to measure the near-infrared colors of these objects.^{[12]: 1095 [11]: 338–339} The discoverers found 61 near-infrared-emitting objects and included them in their own catalogue,^[11]: 339 which became known as the Oasa–Tamura–Sugitani (OTS) catalogue.^{[13][1]: 565}

OTS 44 was the 44th object and one of the dimmest objects listed in the OTS catalogue.^{[11]: 337 [1]: 565} The discoverers identified OTS 44 as a brown dwarf candidate because it appeared much dimmer and redder than other young stars in Chameleon I, which meant that it should have a very low mass if it shared the same age as these stars.^{[12]: 1046 [11]: 341} The discoverers published their analysis and identification of OTS 44 as a brown dwarf candidate in the journal Science in November 1998.^[12]

In November 2004, Kevin L. Luhman, Dawn E. Peterson, and S. Thomas Megeath announced the confirmation of OTS 44 as a low-mass brown dwarf.^[14] Using spectroscopic observations by the Gemini South telescope from March 2004, the researchers determined that OTS 44's mass lay close to the ~0.012 solar mass (13 Jupiter mass) boundary between giant planets and brown dwarfs, which made OTS 44 one of the least massive free-floating brown dwarfs confirmed at the time.^{[1][15]: L53}

OTS 44 is located in the constellation Chamaeleon at a declination of approximately 76.5° south of the celestial equator.^[5] It is situated within the core of Chamaeleon I, one of the three major star-forming molecular clouds of the Chamaeleon complex.^[12][11] Chamaeleon I is one of the nearest star-forming regions to the Sun,^[11]: 336 at an estimated distance of either 160–170 parsecs (520–550 light-years) (according to 1999 parallax measurements by the Hipparcos satellite^{[16]: 580 [1]: 565}) or 192 pc (630 ly) (according to 2018 parallax measurements by the Gaia satellite^[4]: 565). Astronomers assume that OTS 44 lies at the same distance as Chamaeleon I.^{[7]: 2 [4]: 565}

As a member of Chamaeleon I, OTS 44 is inferred to share the same age as other young stellar objects in the region, which are known to be between 1 and 6 million years old.^{[2]: 13, 19} At this age, substellar objects like OTS 44 are hot and luminous.^[2]: 1–2 Observations of active accretion around OTS 44 indicate that it formed in a similar process to how stars form—via direct gravitational collapse of concentrated gas and dust.^{[6]: 1019–1020} OTS 44 will gradually cool and contract over time—becoming an L-type brown dwarf at about 10 million years of age, and then a Y dwarf after 1 billion years of age.^[6]: 1024

The near-infrared spectrum of OTS 44 exhibits deep absorption bands caused by steam (water vapor) in its atmosphere, indicating a relatively cool temperature corresponding to a late spectral type of M9.5±1.0.^[1] Additional substances including elemental sodium (Na), potassium (K), iron hydride (FeH), and carbon monoxide (CO) have been spectroscopically detected in OTS 44's atmosphere.^{[2]: 4, 7, 10} OTS 44 is estimated to have an effective temperature of 1,700 ± 100 K (1,427 ± 100 °C; 2,600 ± 180 °F), based on spectral energy distribution modeling with the object's atmospheric dust taken into account.^{[3]: 2 [2]: 17} OTS 44 stands out from cool main-sequence stars and red giants because it is much redder and brighter in near-infrared.^{[11]: 339–340} Extinction by foreground dust has been observed to cause additional reddening in OTS 44's near-infrared colors (0.3±0.3-magnitude dimming in J-band),^[1]: 567 but not in its optical colors.^[2]: 3

OTS 44 is a dim object with a luminosity between 0.001 and 0.002 times that of the Sun.^{[3]: 2 [a]} As a young and hot object, OTS 44 is expected to have a radius larger than that of Jupiter.^{[2]: 1, 19, 23} A Stefan–Boltzmann law calculation using OTS 44's luminosity and temperature suggests a "semi-empirical" radius of 3.5+0.6
−0.5 R_J, whereas a spectral energy distribution fit with OTS 44's disk taken into account suggests a radius between 3.2 and 3.6 R_J.^{[2]: 15, 17, 19} OTS 44 is estimated to be 6–17 times more massive than Jupiter,^[7] though it is more likely below 13 Jupiter masses—in the planetary mass range, where it cannot fuse deuterium unlike brown dwarfs.^[2] Hence, astronomers have also categorized OTS 44 as a free-floating planet.^[6][7]

In February 2005, a team of astronomers led by Kevin Luhman announced the discovery of a circumstellar disk around OTS 44.^[10][9] Their discovery was based on the Spitzer Space Telescope's detection of excess mid-infrared thermal emission from OTS 44, which indicated the presence of warm dust surrounding the object.^[15] As one of the least massive free-floating objects known at the time, OTS 44 claimed the record for the least massive object known to have a circumstellar disk and demonstrated that such disks could exist around planetary-mass objects.^[15]

Estimates based on OTS 44's spectral energy distribution (SED) suggests that its disk contains a total mass of about 30 Earth masses.^[3] Observations with the SINFONI spectrograph at the Very Large Telescope show that OTS 44 is accreting matter from its disk at the rate of approximately 10⁻¹¹ of the mass of the Sun per year.^[3] It could eventually develop into a planetary system.^[17]

Observations with ALMA detected OTS 44's disk in millimeter wavelengths. The observations constrained the dust mass of the disk between 0.07 and 0.63 M_🜨, but these mass estimates are limited by assumptions on poorly constrained parameters.^[7] Another work estimates the dust mass to 0.064 M_🜨 (5.2 M_☾) for dust particles of 1 mm in size and 0.295 M_🜨 (24 M_☾) for dust particles of 1 μm in size.^[4]

Other free-floating rogue planets and brown dwarfs with protoplanetary disks:

• Cha 110913-773444, rogue planet or brown dwarf surrounded by what appears to be a dusty disk
• Cha 1107−7626, a young rogue planet that underwent an episode of rapid accretion of material from its disk
• 2MASS J11151597+1937266, a young rogue planet or brown dwarf actively accreting material from its disk
• KPNO-Tau 12, another young rogue planet or brown dwarf that is actively accreting material from its disk
• J1407b, a possible disked object thought to have transited the star V1400 Centauri