CT Chamaeleontis

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[1]
Right ascension 11h 04m 09.0989s[2]
Declination −76° 27′ 19.330″[2]
Apparent magnitude (V) 11.7 to 12.9[3]
Characteristics
Evolutionary stage pre-main sequence[4]
Spectral type K7 Ve[5]
Variable type T Tauri[3]
Astrometry
Radial velocity (Rv)15.13±0.09[6] km/s
Proper motion (μ) RA: −22.223 mas/yr[2]
Dec.: +0.019 mas/yr[2]
Parallax (π)5.2645±0.0116 mas[2]
Distance620 ± 1 ly
(190.0 ± 0.4 pc)
Details
Mass0.85±0.02 or 0.96±0.02[7] M☉
Radius2.06±0.05[4] R☉
Luminosity1.41+0.17
−0.16[4] L☉
Surface gravity (log g)3.66±0.01[8] cgs
Temperature4,403+6
−10[8] K
Metallicity [Fe/H]−0.56±0.01[8] dex
Rotational velocity (v sin i)13.97+0.10
−0.15[8] km/s
Age1.26+0.41
−0.23[4] or 1.41+0.38
−0.30[4][9] Myr
Other designations
CT Cha, 2MASS J11040909−7627193, IRAS 11027−7611, NSV 5081, WDS J11042−7627AB
Database references
SIMBADCT Cha
CT Cha b

CT Chamaeleontis (CT Cha) is a T Tauri star in the constellation of Chamaeleon.[10] The star belongs to Chamaeleon I, which is part of the Chamaeleon complex.[11] It has an apparent visual magnitude which varies between 11.7 and 12.9.[3]

Characteristics

CT Cha
Disk around CT Cha with VLT/SPHERE

CT Chamaeleontis has a spectral type of K7Ve,[5] indicating that it is a late K-type star with emission lines and a main sequence luminosity class, although it has not yet reached this stage of evolution yet, with an age likely between one and two million years.[4] The star's mass has been obtained dynamically using the Keplerian rotation of its protoplanetary disk, yielding two values of 0.85±0.02 and 0.96±0.02 M☉.[7] It has a radius 2.06 times that of the Sun (R☉) and is radiating 1.4 times the Sun's luminosity (L☉) from its photosphere[4] at an effective temperature of 4,403 K. The star's iron-to-hydrogen abudance is equivalent to only 27.5% that of the Sun.[8]

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.[12] The disk around the star was directly imaged with ALMA[13] and VLT/SPHERE.[11]

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. 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's mass was estimated at 17±6 Jupiter masses (MJ) in 2008[17] and at 14–24 MJ in 2015.[18] Since these values are likely to be above the deuterium burning limit, CT Cha b was considered to be likely a brown dwarf rather than an exoplanet.[17][18] These mass estimates rely on the host star's age, which was estimated to be 2±2 million years in 2008[17] and between one and five million years in 2015.[18] However, the age was later revised ranging from 1.26+0.41
−0.32 to 3.51+0.38
−0.39 million years, while best fitting being revised downwards, ranging from 1.26+0.41
−0.32 to 1.77+0.60
−0.49 million years.[4] A recently assumed value of 1.41+0.38
−0.30 implies a mass of 9.7+1.2
−1.1 MJ, which is well within the planetary-mass regime.[9]

Already during the discovery evidence of accretion from a gas-rich circumplanetary disk was suspected from emission by Paβ.[17] 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.[18] A search with ALMA failed to detect the disk around the companion.[13] 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.[12] The following molecules were identified: acetylene (C2H2, 13CCH2), ethane (C2H6), propyne (C3H4), diacetylene (C4H2), benzene (C6H6), hydrogen cyanide (HCN) and carbon dioxide (CO2).[19][12][20] 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.[12]

The CT Chamaeleontis planetary system
Companion
(in order from star) 		Mass Semimajor axis
(AU) 		Orbital period
(days) 		Eccentricity Inclination
(°) 		Radius
protoplanetary disk[4] 6.1–9.3 AU 54.0+1.0
−0.9° 		—
protoplanetary disk[11] 64.6±4.2 AU 45.7±5.0° —
b 9.7+1.2
−1.1[9] MJ 		500+320
−150[9] 		— 0.59+0.28
−0.34[9] 		— 2.20+0.81
−0.60[17] RJ

References

  1. ^ Roman, Nancy G. (1987). "Identification of a constellation from a position". Publications of the Astronomical Society of the Pacific. 99 (617): 695. Bibcode:1987PASP...99..695R. doi:10.1086/132034. Constellation record for this object at VizieR.
  2. ^ a b c d Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
  3. ^ a b c "VSX : Detail for CT Cha". vsx.aavso.org. Retrieved 2026-05-06.
  4. ^ a b c d e f g h i Sheehan, Patrick D.; Wu, Ya-Lin; Eisner, Josh A.; Tobin, John J. (2019). "High Precision Dynamical Masses of Pre-Main Sequence Stars with ALMA and Gaia". The Astrophysical Journal. 874 (2): 136. arXiv:1903.00032. Bibcode:2019ApJ...874..136S. doi:10.3847/1538-4357/ab09f9. S2CID 119218828.
  5. ^ a b Torres, C. A. O.; Quast, G. R.; da Silva, L.; de la Reza, R.; Melo, C. H. F.; Sterzik, M. (12 September 2006). "Search for associations containing young stars (SACY)". Astronomy & Astrophysics. 460 (3): 695–708. arXiv:astro-ph/0609258. Bibcode:2006A&A...460..695T. doi:10.1051/0004-6361:20065602. eISSN 1432-0746. ISSN 0004-6361.
  6. ^ Nguyen, Duy Cuong; Brandeker, Alexis; van Kerkwijk, Marten H.; Jayawardhana, Ray (6 January 2012). "Close Companions to Young Stars. I. A Large Spectroscopic Survey in Chamaeleon I and Taurus-Auriga". The Astrophysical Journal. 745 (2): 119. arXiv:1112.0002. Bibcode:2012ApJ...745..119N. doi:10.1088/0004-637X/745/2/119. eISSN 1538-4357. ISSN 0004-637X.
  7. ^ a b Premnath, Pranav H.; Wu, Ya-Lin; Bowler, Brendan P.; Sheehan, Patrick D. (July 2020). "Dynamical Masses of Young Stars Inferred from Two Transitions of CO with ALMA". Research Notes of the American Astronomical Society. 4 (7): 100. arXiv:2012.12690. Bibcode:2020RNAAS...4..100P. doi:10.3847/2515-5172/aba125. ISSN 2515-5172.
  8. ^ a b c d e Swastik, C.; Banyal, Ravinder K.; Narang, Mayank; Manoj, P.; Sivarani, T.; Reddy, Bacham E.; Rajaguru, S. P. (March 2021). "Host Star Metallicity of Directly Imaged Wide-orbit Planets: Implications for Planet Formation". The Astronomical Journal. 161 (3): 114. arXiv:2012.13694. Bibcode:2021AJ....161..114S. doi:10.3847/1538-3881/abd802. ISSN 0004-6256.
  9. ^ a b c d e Lazzoni, Cecilia; Zurlo, Alice; Desidera, Silvano; Bernardi, Andrea; Pérez, Sebastian; Mesa, Dino; Barbato, Domenico; Nogueira, Pedro Henrique; Dasgupta, Anuroop (2026-03-25). "SaNDi-SHoP: Searching for Satellites'N'Disks with a Star-Hopping Program I. Analysis of the close surroundings of DI companions". arXiv:2603.24796 [astro-ph.EP].
  10. ^ "CT+Cha". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved October 1, 2008.
  11. ^ a b c Ginski, C.; Garufi, A.; Benisty, M.; Tazaki, R.; Dominik, C.; Ribas, á.; Engler, N.; Birnstiel, T.; Chauvin, G.; Columba, G.; Facchini, S.; Goncharov, A.; Hagelberg, J.; Henning, T.; Hogerheijde, M.; van Holstein, R. G.; Huang, J.; Muto, T.; Pinilla, P.; Kanagawa, K.; Kim, S.; Kurtovic, N.; Langlois, M.; Manara, C.; Milli, J.; Momose, M.; Orihara, R.; Pawellek, N.; Pinte, C.; Rab, C.; Schmidt, T. O. B.; Snik, F.; Wahhaj, Z.; Williams, J.; Zurlo, A. (May 2024). "The SPHERE view of the Chamaeleon I star-forming region: The full census of planet-forming disks with GTO and DESTINYS programs". Astronomy & Astrophysics. 685: A52. arXiv:2403.02149. Bibcode:2024A&A...685A..52G. doi:10.1051/0004-6361/202244005.
  12. ^ a b c d Cugno, Gabriele; Grant, Sierra L. (2025). "A carbon-rich disk surrounding a planetary-mass companion". arXiv:2509.15209 [astro-ph.EP].
  13. ^ a b Wu, Ya-Lin; Bowler, Brendan P.; Sheehan, Patrick D.; Andrews, Sean M.; Herczeg, Gregory J.; Kraus, Adam L.; Ricci, Luca; Wilner, David J.; Zhu, Zhaohuan (May 2020). "ALMA 0.88 mm Survey of Disks around Planetary-mass Companions". The Astronomical Journal. 159 (5): 229. arXiv:1903.00032. Bibcode:2019ApJ...874..136S. doi:10.3847/1538-3881/ab818c. ISSN 0004-6256.
  14. ^ "ASAS All Star Catalogue". The All Sky Automated Survey. Retrieved 8 December 2021.
  15. ^ "Planet CT Cha b". Encyclopaedia of exoplanetary systems / Exoplanet.eu. Retrieved 2024-08-20.
  16. ^ "CT Cha b". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved October 1, 2008.
  17. ^ a b c d e Schmidt, T. O. B.; Neuhäuser, R.; Seifahrt, A.; Vogt, N.; Bedalov, A.; Helling, Ch.; Witte, S.; Hauschildt, P. H. (2008). "Direct evidence of a sub-stellar companion around CT Chamaeleontis". Astronomy & Astrophysics. 491 (1): 311–320. arXiv:0809.2812. Bibcode:2008A&A...491..311S. doi:10.1051/0004-6361:20078840. S2CID 17161561.
  18. ^ a b c d Wu, Ya-Lin; Close, Laird M.; Males, Jared R.; Barman, Travis S.; Morzinski, Katie M.; Follette, Katherine B.; Bailey, Vanessa; Rodigas, Timothy J.; Hinz, Philip; Puglisi, Alfio; Xompero, Marco; Briguglio, Runa (2015). "New Extinction and Mass Estimates from Optical Photometry of the Very Low Mass Brown Dwarf Companion CT Chamaeleontis B with the Magellan AO System". The Astrophysical Journal. 801 (1): 4. arXiv:1501.01396. Bibcode:2015ApJ...801....4W. doi:10.1088/0004-637X/801/1/4. S2CID 96467798.
  19. ^ "HITRANonline line-by-line search: 1. Select Molecules". hitran.org. Retrieved 2024-12-10.
  20. ^ "Webb studies moon-forming disc around massive planet". www.esa.int. 2025-09-29. Retrieved 2025-09-29.

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