J/AJ/169/246 TOI-5389 & TOI-5610 photometry & radial velocities (Larsen+, 2025)
Searching for GEMS: Discovery and characterization of two brown dwarfs around
M dwarfs.
Larsen A., Swaby T.N., Kobulnicky H.A., Canas C.I., Kanodia S.,
Libby-Roberts J., Monson A., Gupta A.F., Cochran W., Mahadevan S.,
Bender C., Diddams S.A., Halverson S., Lin A.S.J., Moe M., Ninan J.,
Robertson P., Roy A., Schwab C., Stefansson G.
<Astron. J., 169, 246 (2025)>
=2025AJ....169..246L 2025AJ....169..246L
ADC_Keywords: Stars, brown dwarf; Radial velocities; Photometry; Optical;
Spectra, infrared; Stars, dwarfs; Stars, M-type
Keywords: Brown dwarfs ; Transits ; Photometry ; Transit photometry ;
Spectroscopy ; Substellar companion stars
Abstract:
Brown dwarfs bridge the gap between stars and planets, providing
valuable insight into both planetary and stellar-formation mechanisms.
Yet the census of transiting brown-dwarf companions, in particular
around M-dwarf stars, remains incomplete. We report the discovery of
two transiting brown dwarfs around low-mass hosts using a combination
of space- and ground-based photometry along with near-infrared radial
velocities. We characterize TOI-5389Ab (68.0-2.2+2.2MJ) and
TOI-5610b (40.4-1.0+1.0MJ), two moderately massive brown dwarfs
orbiting early M-dwarf hosts (Teff=3569±59K and 3618±59K,
respectively). For TOI-5389Ab, the best fitting parameters are period
P=10.40046±0.00002d, radius RBD=0.824-0.031+0.033RJ, and low
eccentricity e=0.0962-0.0046+0.0027. In particular, this
constitutes one of the most extreme substellar-stellar
companion-to-host mass ratios of q=0.150. For TOI-5610b, the
best-fitting parameters are period P=7.95346±0.00002d, radius
RBD=0.887-0.031+0.031RJ, and moderate eccentricity
e=0.354-0.012+0.011. Both targets are expected to have shallow,
but potentially observable, occultations: ≤500ppm in the Johnson K
band. A statistical analysis of M-dwarf/BD systems reveals for the
first time that those at short orbital periods (P<13d) exhibit a
dearth of 13MJ<MBD<40MJ companions (q<0.1) compared to those at
slightly wider separations.
Description:
The Red Buttes Observatory (RBO) is a 0.6m telescope owned by the
University of Wyoming located 10km south of Laramie, Wyoming. All
observations were conducted using the Bessell I filter (798nm) and a
240s exposure time while slightly defocused. We successfully observed
TOI-5389Ab on the local nights of 2023 February 28 and 2024 February 6
as well as TOI-5610b on the local nights of 2024 January 2 and 2024
February 11. Observations lasted 5-8 hr each and captured two full
transits for each target. Observation times had to be converted from
JDUTC into BJDTDB as described in Eastman+ (2010PASP..122..935E 2010PASP..122..935E).
The Habitable-zone Planet Finder (HPF) is a high-resolution,
near-infrared, fiber-fed, stabilized (∼1mK) spectrograph with
resolution R∼55,000 and wavelength coverage 8080-12780Å. It is
located on the 10m Hobby-Eberly Telescope at the McDonald Observatory
in Texas. We obtained two 945s exposures on each of 10 nights for
TOI-5389A and 12 nights for TOI-5610 between 2022 November and 2023
December. Only the wavelength intervals 8600-8900Å and
9900-10600Å were retained for radial velocity analysis.
TOI-5389A was identified via the TESS Science Processing Operations
Center (SPOC) and was observed in 1800s cadence in Sector 22 from 2020
February 18 to 2020 March 18 and Sector 48 in 600s cadence from 2022
January 28 to 2022 February 26. TOI-5610 was identified via the TESS
Faint Star Search (Kunimoto+2022, J/ApJS/259/33) and was observed in
Sector 21 in 1800s cadence from 2020 January 21 to 2020 February 18
and Sector 48 in 600s cadence from 2022 January 28 to 2022 February
26. The specific TESS data analyzed can be accessed via the Mikulski
Archive for Space Telescopes at the Space Telescope Science Institute.
There are clear transit signatures at dominant periodicities of
∼10.40d and ∼7.95d and approximate depths of ∼4%-5% and ∼2%-3%
for TOI-5389A and TOI-5610, respectively.
TOI-5389A and TOI-5610 were observed with the NN-Explore Exoplanet
Stellar Speckle Imager (NESSI) on the WIYN 3.5m telescope on 2023
January 28. For each target, a set of diffraction-limited frames was
taken simultaneously with the red and blue NESSI cameras in the Sloan
Digital Sky Survey (SDSS) z' and r' filters.
Objects:
-------------------------------------------------------------------------
RA (2000) DE Designation(s) (Period)
-------------------------------------------------------------------------
11 15 12.39 +39 21 33.0 TOI-5389Ab = TOI-5389.01 (Period=10.40d)
10 24 05.50 +48 14 54.9 TOI-5610b = TOI-5610.01 (Period=7.95d)
-------------------------------------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 35 171 TOI-5389Ab RBO photometric data
table2.dat 35 224 TOI-5610b RBO photometric data
table3.dat 20 18 Barycentric HPF radial velocity measurements for
TOI-5389Ab
table4.dat 20 22 Barycentric HPF radial velocity measurements for
TOI-5610b
--------------------------------------------------------------------------------
See also:
I/357 : Gaia DR3 Part 3. Non-single stars (Gaia Collaboration, 2022)
VII/233 : 2MASS All-Sky Extended Source Catalog (XSC) (IPAC/UMass, 2003-2006)
V/130 : Geneva-Copenhagen Surv. of Solar neighbourhood III (Holmberg+, 2009)
J/ApJ/640/1051 : 25pc sample of Sun-like stars (Grether+, 2006)
J/AJ/132/1221 : VJHK and SDSS photometry of DA white dwarfs (Holberg+, 2006)
J/AJ/142/19 : Speckle observations of KOI (Howell+, 2011)
J/A+A/525/A95 : Search for brown-dwarf companions of stars (Sahlmann+, 2011)
J/ApJ/730/128 : Spectroscopy of DA WD from the SDSS-DR4 (Tremblay+, 2011)
J/ApJ/757/112 : Stellar diameters. II. K and M-stars (Boyajian+, 2012)
J/ApJ/771/129 : Submillimetric Class II sources of Taurus (Andrews+, 2013)
J/A+A/549/A109 : HARPS XXXI. The M-dwarf sample (Bonfils+, 2013)
J/ApJ/788/48 : X-ray through NIR photometry of NGC 2617 (Shappee+, 2014)
J/ApJ/807/45 : Potentially habitable planets orbit. M dwarfs (Dressing+, 2015)
J/ApJ/814/130 : Planet occurrence rates calculated for KOIs (Mulders+, 2015)
J/ApJ/831/125 : ALMA 887um obs. of ChaI star-forming region (Pascucci+, 2016)
J/A+A/587/A64 : Physical properties of giant exoplanets (Santerne+, 2016)
J/A+A/603/A30 : Evidence for 2 distinct giant planet population (Santos+, 2017)
J/MNRAS/475/1960 : ESPaDOnS spectropolarimeter obs. of M dwarfs (Fouque+, 2018)
J/MNRAS/474/4322 : Orbital parameters of 341 new binaries (Murphy+, 2018)
J/AJ/158/75 : Mid-type M dwarfs planet occurr. rates (Hardegree-Ullman+, 2019)
J/AJ/158/13 : The first 300 stars observed by the GPIES (Nielsen+, 2019)
J/ApJ/901/93 : Model atmos. analysis of hot WDs from SDSS DR12 (Bedard+, 2020)
J/MNRAS/491/5216 : Rot. periods for 107 M dwarfs from APACHE (Giacobbe+, 2020)
J/AJ/159/100 : Flux & RVs of the dwarf G9-40 with K2 & HPF (Stefansson+, 2020)
J/A+A/652/A127 : 13-150MJ eclipsing binaries transiting comp. (Grieves+, 2021)
J/A+A/645/A7 : Determining true mass of RV exoplanets with Gaia (Kiefer+, 2021)
J/A+A/650/A201 : 10 parsec sample in the Gaia era first update (Reyle+, 2021)
J/ApJS/259/33 : Faint-star TOIs from the TESS Primary Mission (Kunimoto+, 2022)
J/A+A/658/A194 : Stellar parameters of 18 M dwarfs (Passegger+, 2022)
J/AJ/167/109 : TOI-1994 radial velocities with MINERVA & CHIRON (Page+, 2024)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 17 F17.9 d BJD [2460004/2460348] Barycentric Julian Date at TDB
19- 26 F8.6 --- Flux [0.9/1.1] Normalized flux (Bessell I)
28- 35 F8.6 --- e_Flux [0.008/0.042] Uncertainty in Flux
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 17 F17.9 d BJD [2460312/2460353] Barycentric Julian Date at TDB
19- 26 F8.6 --- Flux [0.93/1.08] Normalized flux (Bessell I)
28- 35 F8.6 --- e_Flux [0.008/0.058] Uncertainty in Flux
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 11 F11.3 d BJD [2459921/2460307] Barycentric Julian Date at TDB
13- 17 I5 m/s RVel [2424/22399] Barycentric-corrected radial
velocity
19- 20 I2 m/s e_RVel [15/81] Uncertainty in RVel
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table4.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 11 F11.3 d BJD [2459897/2460305] Barycentric Julian Date at TDB
13- 17 I5 m/s RVel [37125/49730] Barycentric-corrected radial
velocity
19- 20 I2 m/s e_RVel [5/23] Uncertainty in RVel
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Prepared by [AAS], Robin Leichtnam [CDS] 23-Jan-2026