Delorme 1

Delorme 1 (2MASS J01033563-5515561) is a binary star with a planetary-mass companion (PMC) or protoplanet in a circumbinary orbit.^[4] The PMC is notable for showing signs of accretion, despite being 30-45 Myr old, making it similar to Peter Pan disks.^[1][5][6] These disks show characteristics of a gas-rich disk at unexpected high ages.^[7]

Delorme 1 (AB)

The binary Delorme 1 (AB) is in the center and the companion is the source on the upper right. Credit: NASA/ESA Hubble WFC3; Daniel Apai et al.
Observation data Epoch J2000      Equinox J2000
Constellation	Phoenix
Right ascension	01h 03m 35.6551s
Declination	−55° 15′ 56.243″
Apparent magnitude (V)	15.40 ±0.05
Characteristics
Evolutionary stage	red dwarf
Spectral type	M5/6+M5/6+L0(VLG)[1]
Variable type	flare star[1]
Astrometry
Radial velocity (Rv)	5.2 ±1.6[2] km/s
Proper motion (μ)	RA: 111.6 ±3.6 mas/yr[2] Dec.: -43.8 ±8.1 mas/yr[2]
Parallax (π)	21.18±1.37 mas[3]
Distance	154 ± 10 ly (47 ± 3 pc)
Details[4]
Delorme 1A
Mass	0.19 ±0.02 M☉
Delorme 1B
Mass	0.17 ±0.02 M☉
Position (relative to Delorme 1A)[4]
Component	Delorme 1B
Epoch of observation	2012
Angular distance	0.249 ±0.003″
Projected separation	12 AU
Other designations
SCR J0103-5515, ** DLR 1AB, DENIS J010335.6-551556, WDS J01036-5516AB, WISE J010335.75-551556.6, 2MASS J01033563-5515561
Database references
SIMBAD	data
Exoplanet Archive	data

The binary system

The star was resolved in 2013 with the Very Large Telescope NACO instrument by Delorme et al. A spectrum of the binary was taken with GMOS at Gemini South, which showed a spectral type of M5.5/M6 and strong Hydrogen-alpha emission. The astrometry showed that this star belongs to the Tucana-Horologium association. The binary is separated by around 12 astronomical units (AU).^[4] In 2014 Riedel et al. found a better match with the Carina association, which has a similar age as Tuc-Hor. They also found the system to be over-luminous, which might either hint at a younger age or further multiplicity.^[3] Other searches do, however, find a better match with Tuc-Hor.^[2] Because the Washington Double Star Catalog named the binary ** DLR 1 after the first author of the discovery paper in 2013, Eriksson et al. suggested the name Delorme 1 for the binary.^[1] The binary is named after Philippe Delorme.^[8]

The circumstellar companion

The binary companion was discovered in 2013 as an object with a mass between 12 and 14 M_J and a separation of 84 AU from the central binary. It had a spectrum similar to early L-dwarfs, but redder than field L-dwarfs.^[4] In 2020 Eriksson et al. discovered Hydrogen-alpha, -beta and Helium I lines from Delorme 1 (AB)b using MUSE. This is seen as a clear sign of accretion on a planetary-mass object. The spectral type of this object was determined to be L0 with very low gravity due to stronger than expected vanadium oxide absorption.^[1] H-alpha can be influenced by chromospheric activity, complicating its interpretation. Betti et al. discovered Paschen and Brackett lines in Delorme 1 (AB)b in the near-infrared, using TripleSpec at SOAR. These observations are in agreement with planetary-shock accretion.^[5] In 2023 Ringqvist et al. observed Delorme 1 (AB)b with the VLT UVES, detecting neutral hydrogen in the ultraviolet.^[6] Both near-infrared and ultraviolet observations show an accretion rate of about ${\displaystyle (2-4)\times 10^{-8}M_{J}yr^{-1}}$ (about 1.2 to 2.3 the mass of 10 Hygiea per year).^[5][6] The circumplanetary disk that fuels this accretion around Delorme 1 (AB)b is not detected (as of August 2024).^[6] The planet and the star were observed with MIRI/IFU in August 2023, which should reveal any disk around the planet or star in a future work.^[9]

Delorme 1 (AB)b has been called a protoplanet candidate and a super-Jupiter.^[5][6] The researchers found that the high accretion is in better agreement with a formation via disk fragmentation, hinting that it might have formed from a circumstellar disk.^[5] Giant planets and brown dwarfs are thought to form via disk fragmentation in rare cases in the outer regions of a disk (r>50 AU).^[10] Teasdale et al. modelled three formation scenarios in which the planet could have formed. In the first two scenarios the planet forms in a massive disk via gravitational instability. The first two scenarios produce planets that have accretion and separation comparable to the observed ones, but the resulting planets are more massive than Delorme 1 (AB)b. In a third scenario the planet forms via core accretion in a less massive disk much closer to the binary. In this third scenario the mass and accretion are similar to the observed ones, but the separation is smaller.^[11]

The Delorme 1 (AB) planetary system^[4][12]

Companion (in order from star)	Mass	Semimajor axis (AU)	Orbital period (years)	Eccentricity	Inclination	Radius
b	12 to 14 MJ	102+47 −27	1682+1308 −628	0.32+0.27 −0.23	127+17 −8°	1.5764[5] RJ