J/A+A/708/A218 Taurus and Upper Sco brown dwarfs phot. and masses (Bouy+, 2026)
Multiplicity of young brown dwarfs and isolated planetary mass objects in
Taurus and Upper Scorpius.
Bouy H., Duchene G., Strampelli G., Aguilar J., Olivares J., Palau A.,
Barrado D., Raymond S.N., Huelamo N., Tamura M., Bertin E., Brandner W.,
Cuillandre J.-C., Galli P.A.B., Miret-Roig N.
<Astron. Astrophys. 708, A218 (2026)>
=2026A&A...708A.218B 2026A&A...708A.218B (SIMBAD/NED BibCode)
ADC_Keywords: Associations, stellar ; Stars, brown dwarf ; Exoplanets ;
Photometry, infrared ; Optical ; Stars, masses
Keywords: techniques: high angular resolution - binaries: visual -
brown dwarfs - stars: formation
Abstract:
Free-floating planetary mass objects -worlds that roam interstellar
space untethered to a parent star-challenge conventional notions of
planetary formation and migration, but also of star and brown dwarf
formation.
We focus on the multiplicity among free-floating planets. By virtue of
their low binding energy (compared to other objects formed in these
environments), these low-mass substellar binaries represent a most
sensitive probe of the mechanisms at play during the star formation
process.
We use the Hubble Space Telescope and its Wide Field Camera 3 and the
Very Large Telescope and its ERIS adaptive optics facility to search
for visual companions among a sample of 77 objects members of the
Upper Scorpius and Taurus young nearby associations with estimated
masses in the range between approximately 6-66Mjup
We report the discovery of one companion candidate around a Taurus
member with a separation of 111.9±0.4mas, or ∼18au assuming a
distance of 160pc, with an estimated primary mass in the range between
3-6Mjup and a secondary mass between 2.6-5.2MJup, depending on the
assumed age. This corresponds to an overall binary fraction of
1.8+2.6-1.3% among low-mass brown dwarfs and free-floating
planetary mass objects over the separation range >7au. Despite the
limitations of small-number statistics and variations in spatial
resolution and sensitivity, our results, combined with previous
high-spatial-resolution surveys, suggest a notable difference in the
multiplicity properties of objects below ∼30-50Mjup between Upper Sco
and Taurus. In Taurus, a binary fraction of 5.6+3.2-2.3% is found
for objects with masses below 30Mjup, and of 7.8+3.0-2.4% for
objects with masses below 50Mjup, whereas no binary were found among
80 objects over the matching luminosity range in Upper Sco,
corresponding to an upper limit of ≥1.2%.
This difference may point to intrinsically distinct formation
conditions, with warmer parental molecular clouds originally present
in Upper Sco potentially inhibiting fragmentation into the lowest-mass
brown dwarfs and free-floating planets compared to cooler environments
such as Taurus.
Description:
Position, multi-wavelength photometry and masses for objects observed
at high spatial resolution in the Taurus and Upper Sco associations.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
tablea1.dat 114 55 HST targets
tablea2.dat 75 22 VLT targets
tablec1.dat 125 95 List of Taurus late type members observed at
high spatial resolution
tablec2.dat 115 109 List of Usco late type members observed at
high spatial resolution
--------------------------------------------------------------------------------
See also:
J/ApJ/757/141 : Companion IR detection limits in young associations
(Kraus+, 2012)
J/ApJ/788/40 : Late-type targets in Taurus, Cha I, and Upper Sco
(Todorov+, 2014)
J/A+A/667/A163 : Upper Scorpius and Ophiuchus members (Miret-Roig+, 2022)
Byte-by-byte Description of file: tablea1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 19 A19 --- Object Object designation (JHHMMSS.ss+DDMMSS.s)
21- 29 F9.5 deg RAdeg Right ascension (J2000)
31- 39 F9.5 deg DEdeg Declination (J2000)
41- 45 F5.3 Msun Mass1 Mass estimated assuming 3Myr in Taurus and
5Myr in Upper Sco
46 A1 --- --- [/]
47- 51 F5.3 Msun Mass2 ? Mass estimated assuming 10Myr in Upper Sco
53- 57 F5.2 mag imag Pan-STARRS i magnitude
59- 62 F4.2 mag e_imag rms uncertainty on imag
64- 68 F5.2 mag zmag Pan-STARRS z magnitude
70- 73 F4.2 mag e_zmag rms uncertainty on zmag
75- 79 F5.2 mag F814W HST WFC3 F814W magnitude
81- 84 F4.2 mag e_F814W rms uncertainty on F814W
86- 90 F5.2 mag F850LP HST WFC3 F850LP magnitude
92- 95 F4.2 mag e_F850LP rms uncertainty on F850LP
97-101 F5.2 mag Jmag ?=99 2MASS J magnitude
103-107 F5.2 mag e_Jmag ?=99 rms uncertainty on Jmag
109-114 A6 --- Assoc [Taurus USco] Association it belongs
--------------------------------------------------------------------------------
Byte-by-byte Description of file: tablea2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 I4 --- Object Object designation
6- 14 F9.5 deg RAdeg Right ascension (J2000)
16- 24 F9.5 deg DEdeg Declination (J2000)
26- 30 F5.2 mag imag Pan-STARRS i magnitude
33- 36 F4.2 mag e_imag rms uncertainty on imag
38- 42 F5.2 mag zmag Pan-STARRS z magnitude
45- 48 F4.2 mag e_zmag rms uncertainty on zmag
50- 54 F5.2 mag Jmag 2MASS J magnitude
57- 60 F4.2 mag e_Jmag rms uncertainty on Jmag
62- 63 I2 --- strehl Strehl ratio
65- 69 F5.3 Msun Mass5 Estimated Mass at 5Myr (1)
70 A1 --- --- [/]
71- 75 F5.3 Msun Mass10 Estimated Mass at 10Myr (1)
--------------------------------------------------------------------------------
Note (1): Masses (for respectively 5 and 10Myr) from Miret-Roig et al.
(2022A&A...667A.163M 2022A&A...667A.163M, Cat. J/A+A/667/A163M).
--------------------------------------------------------------------------------
Byte-by-byte Description of file: tablec1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 23 A23 --- Name Object designation
25- 32 F8.5 deg RAdeg Right ascension (J2000)
34- 41 F8.5 deg DEdeg Declination (J2000)
43- 48 F6.3 mag imag ?=- Pan-STARRS i magnitude
50- 54 F5.3 mag e_imag ?=- rms uncertainty on imag
56- 61 F6.3 mag zmag ?=- Pan-STARRS z magnitude
63- 67 F5.3 mag e_zmag ?=- rms uncertainty on zmag
69- 73 A5 --- SpType Spectral type
75- 85 A11 --- r_SpType Reference for the spectral type (G1)
87- 89 A3 --- Multiple Multiple system?
91-125 A35 --- r_Multiple Reference for multiplicity (G1)
--------------------------------------------------------------------------------
Byte-by-byte Description of file: tablec2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 24 A24 --- Name Object designation
26- 34 F9.5 deg RAdeg Right ascension (J2000)
36- 44 F9.5 deg DEdeg Declination (J2000)
46- 51 F6.3 mag imag Pan-STARRS i magnitude
53- 57 F5.3 mag e_imag rms uncertainty on imag
59- 64 F6.3 mag zmag Pan-STARRS z magnitude
66- 70 F5.3 mag e_zmag rms uncertainty on zmag
72- 76 A5 --- SpType Spectral type
78- 88 A11 --- r_SpType Reference for the spectral type (G1)
90- 92 A3 --- Multiple Multiple system?
94-115 A22 --- r_Multiple Reference for multiplicity (G1)
--------------------------------------------------------------------------------
Global notes:
Note (G1): References as follows:
Biller2011 = Biller et al., 2011ApJ...730...39B 2011ApJ...730...39B
Bouy2006 = Bouy et al., 2006A&A...451..177B 2006A&A...451..177B
Konopacky2007 = Konopacky et al., 2007ApJ...663..394K 2007ApJ...663..394K
Kraus2012 = Kraus et al., 2012ApJ...757..141K 2012ApJ...757..141K, Cat. J/ApJ/757/141
Luhman2023 = Luhman et al., 2023AJ....165...37L 2023AJ....165...37L
Luhman2025 = Luhman et al., 2025AJ....170...19L 2025AJ....170...19L
Martin2004 = Martin et al., 2004AJ....127..449M 2004AJ....127..449M
Todorov2014 = Todorov et al., 2014ApJ...788...40T 2014ApJ...788...40T, Cat. J/ApJ/788/40
--------------------------------------------------------------------------------
Acknowledgements:
Herve Bouy, herve.bouy(at)u-bordeaux.fr
(End) Patricia Vannier [CDS] 29-Jan-2026