CT Chamaeleontis

CT Chamaeleontis (CT Cha) is a T Tauri star - a primary of the star system in the constellation of Chamaeleon.^[8] The star belongs to Chamaeleon I, which is part of the Chamaeleon complex.^[9] It has an apparent visual magnitude which varies between 12.31 and 12.43.^[2] Observations with JWST MIRI did show that the disk around CT Cha A does not contain any carbon molecules. Emission lines of water and OH were identified. The low energy emission by water comes from cold (≲200 K (−73 °C; −100 °F)) water.^[10] The disk around the star was directly imaged with ALMA^[11] and VLT/SPHERE.^[9]

CT Chamaeleontis

CT Chamaeleontis and its companion (faint object on the upper right near the star) Credit: NASA/ESA/CSA JWST; Ya-Lin Wu et al.; processing: Meli_thev
Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Chamaeleon
Right ascension	11h 04m 09.0989s[1]
Declination	−76° 27′ 19.327″[1]
Apparent magnitude (V)	12.31 to 12.43[2]
Characteristics
A
Evolutionary stage	T Tauri star
Spectral type	K7 Ve[3]
Variable type	INB[2]
b
Spectral type	M8–L0[4]
Astrometry
Radial velocity (Rv)	15.13±0.09[5] km/s
Proper motion (μ)	RA: −22.209±0.039[1] mas/yr Dec.: −0.175±0.035[1] mas/yr
Parallax (π)	5.2144±0.0211 mas[1]
Distance	625 ± 3 ly (191.8 ± 0.8 pc)
Position (relative to CT Chamaeleontis)
Component	b
Epoch of observation	2006–2007
Angular distance	2.670″ [4]
Position angle	300.7° [4]
Projected separation	~440 AU [4]
Details[4][6]
A
Mass	0.796+0.015 −0.014 M☉
Radius	2.06±0.05 R☉
Luminosity	1.41+0.17 −0.16 L☉
Surface gravity (log g)	4.5+0.7 −1.2 cgs
Temperature	4402+151 −166 K
Age	2±2[4] Myr
b
Mass	17±6[4] MJup
Radius	2.20+0.81 −0.60 RJup
Luminosity	0.002 L☉
Surface gravity (log g)	3.5 cgs
Temperature	2500±100[7] K
Age	2±2[4] Myr
Other designations
CT Cha, 2MASS J11040909−7627193, IRAS 11027−7611, NSV 5081, WDS J11042−7627AB
Database references
SIMBAD	data
	B

Disk around CT Cha with VLT/SPHERE

Cuno Hoffmeister discovered that CT Chamaeleontis is a variable star in 1962.^[12] It was given its variable star designation in 1981.^[13]

Planetary system/Brown dwarf

A visual band light curve for CT Chamaeleontis, plotted from ASAS data^[14]

In 2006 and 2007, a faint companion was observed 2.7 arcseconds away from CT Chamaeleontis, using the Very Large Telescope at the European Southern Observatory. Since the object shares common proper motion with CT Chamaeleontis, it is believed to be physically close to the star, with a projected separation of approximately 440 astronomical units. It is estimated to have a mass of approximately 17 Jupiter masses and is probably a brown dwarf or a planet.^[4] The companion has been either designated as CT Chamaeleontis b^[15] or as CT Chamaeleontis B, sometimes erroneously as low-mass star.^[16] The companion was proven to be most likely in the brown dwarf mass range in 2015.^[7]

Already during the discovery evidence of accretion from a gas-rich circumplanetary disk was suspected from emission by Paβ.^[4] Later it was found that the emission in the r-band is overluminous, indicating Hα emission. This team estimated an accretion rate of ~6 × 10⁻¹⁰ M_☉/yr.^[7] A search with ALMA failed to detect the disk around the companion.^[11] Observations with JWST MIRI medium resolution spectroscopy found that the disk is rich in carbon chemistry. Seven carbon-bearing molecules were found inside the disk.^[10] The following molecules were identified: acetylene (C₂H₂, ¹³CCH₂), ethane (C₂H₆), propyne (C₃H₄), diacetylene (C₄H₂), benzene (C₆H₆), hydrogen cyanide (HCN) and carbon dioxide (CO₂).^[17][10][18] This carbon-rich disk is similar to disks around isolated planetary-mass objects and other low-mass objects that show a transition from oxygen-rich disk to carbon-rich disk in their lifetime. This result will give insights into the formation of exomoons around giant planets.^[10]

The CT Chamaeleontis planetary system^[6][9][4]

Companion (in order from star)	Mass	Semimajor axis (AU)	Orbital period (days)	Eccentricity	Inclination	Radius
protoplanetary disk[6]	6.1–9.3 AU				54.0+1.0 −0.9°	—
protoplanetary disk[9]	64.6±4.2 AU				45.7±5.0°	—
b	17±6[4] MJ	507	—	—	—	2.20+0.81 −0.60[4] RJ