J/AJ/169/41 M dwarfs binaries optical spectra & light curves (Couperus+, 2025)
The solar neighborhood.
LII. M dwarf twin binaries-presumed identical twins appear fraternal in
variability, rotation, Hα, and X-rays.
Couperus A.A., Henry T.J., Osten R.A., Jao W.-C., Vrijmoet E.H., Kar A.,
Horch E.
<Astron. J., 169, 41 (2025)>
=2025AJ....169...41C 2025AJ....169...41C
ADC_Keywords: Stars, dwarfs; Stars, M-type; Stars, double and multiple;
Optical; Photometry; Spectroscopy; Radial velocities;
Equivalent widths; Rotational velocities
Keywords: M dwarf stars ; Magnetic variable stars ; Stellar activity ;
Stellar evolution ; Stellar rotation ; Wide binary stars ; X-ray stars
Abstract:
We present an investigation into the rotation and stellar activity of
four fully convective M dwarf "twin" wide binaries. Components in each
pair have (1) astrometry confirming they are common-proper-motion
binaries, (2) Gaia BP, RP, and 2MASS J, H, and Ks magnitudes matching
within 0.10mag, and (3) presumably the same age and composition. We
report long-term photometry, rotation periods, multiepoch Hα
equivalent widths, X-ray luminosities, time series radial velocities,
and speckle observations for all components. Although it might be
expected for the twin components to have matching magnetic attributes,
this is not the case. Decade-long photometry of GJ 1183 AB indicates
consistently higher spot activity on A than B, a trend matched by A
appearing 58%±9% stronger in LX and 26%±9% stronger in Hα
on average-this is despite similar rotation periods of A=0.86d and
B=0.68d, thereby informing the range in activity for otherwise
identical and similarly rotating M dwarfs. The young β Pic Moving
Group member 2MA 0201+0117 AB displays a consistently more active B
component that is 3.6±0.5 times stronger in LX and 52%±19%
stronger in Hα on average, with distinct rotation at A=6.01d and
B=3.30d. Finally, NLTT 44989 AB displays remarkable differences with
implications for spindown evolution-B has sustained Hα emission
while A shows absorption, and B is ≥39±4 times stronger in LX,
presumably stemming from the surprisingly different rotation periods
of A=38d and B=6.55d. The last system, KX Com, has an unresolved
radial velocity companion, and is therefore not a twin system.
Description:
Our twin targets have been observed in the V-band with different
observing campaigns at the Cerro Tololo Interamerican Observatory
(CTIO) in Chile using the Small and Moderate Aperture Research
Telescope System (SMARTS):
(1) long-term optical photometry with the CTIO/SMARTS 0.9m spanning
several years (2013 to 2024) to probe for stellar activity cycles,
(2) short-term optical photometry with the CTIO/SMARTS 0.9m to capture
rotation (2022 to 2023),
(3) multiepoch (2019 to 2023) high-resolution optical spectroscopy
using the CHIRON echelle spectrograph on the CTIO/SMARTS 1.5m to
determine rotational velocities and Hα equivalent widths (EWs).
CHIRON has a fixed spectral range of 4150-8800Å.
Objects:
----------------------------------------------------------------------------
RA (2000) DE Designation(s) (Period)
----------------------------------------------------------------------------
02 01 46.76 +01 17 16.0 2MA0201+0117A = RX J0201.7+0117A (Period=5.96d)
02 01 46.92 +01 17 05.9 2MA0201+0117B = RX J0201.7+0117B (Period=3.30d)
12 56 52.15 +23 29 50.1 KXComA = PM J12568+2329W (Period=2.54d)
12 56 52.71 +23 29 50.5 KXComBC = V* KX Com (Period=6.93d)
17 33 06.11 -30 35 08.1 NLTT44989A = LP 920-61 A (Period=38.27d)
17 33 05.77 -30 35 09.3 NLTT44989B = LP 920-61 B (Period=6.55d)
14 27 56.07 +00 22 31.1 GJ1183A = 2MASS J14275607-0022310 (Period=0.86d)
14 27 56.39 +00 22 19.1 GJ1183B = 2MASS J14275640-0022191 (Period=0.68d)
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File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table6.dat 65 109 Optical Spectra - All CHIRON Measurements
dbf5/* . 6 Long-term 0.9m light curves for the three true
twin systems (Data behind Figure 5)
dbf6/* . 8 0.9m rotation light curve data for the four twin
systems (Data behind Figure 6)
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See also:
B/simbad : Simbad objects catalogue (M.Wenger 2000)
B/sb9 : SB9: 9th Catalogue of Spectroscopic Binary Orbits (Pourbaix+ 2004-2014)
B/wds : The Washington Visual Double Star Catalog (Mason+ 2001-2020)
III/198 : Palomar/MSU nearby star spectroscopic survey (Hawley+ 1997)
II/287 : Northern Sky Variability Survey (NSVS) (Wozniak+, 2004)
II/335 : Revised catalog of GALEX UV sources (GUVcat_AIS GR6+7) (Bianchi+ 2017)
IV/34 : K2 Ecliptic Plane Input Catalog (EPIC) (Huber+, 2017)
II/358 : SkyMapper Southern Sky Survey. DR1.1 (Wolf+, 2018)
I/357 : Gaia DR3 Part 3. Non-single stars (Gaia Collaboration, 2022)
II/386 : VPHAS+ DR3 survey (Drew+, 2025)
V/122 : SB9: 9th Catalogue of Spectroscopic Binary Orbits (Pourbaix+ 2005)
VII/233 : 2MASS All-Sky Extended Source Catalog (XSC) (IPAC/UMass, 2003-2006)
J/A+A/327/1039 : Structure and evolution of low-mass stars (Chabrier+ 1997)
J/ApJ/696/L84 : Primordial circumstellar disks in binary systems (Cieza+, 2009)
J/MNRAS/407/465 : Fast-rotating M dwarfs in NGC2516 (Jackson+, 2010)
J/AJ/139/743 : Speckle interferometry in 2008-09 (Tokovinin+, 2010)
J/ApJ/743/48 : Stars with rotation periods & X-ray luminosities (Wright+, 2011)
J/ApJ/751/115 : Millimeter emission from Taurus binary systems (Harris+, 2012)
J/ApJ/754/44 : The AstraLux Large M-dwarf Survey (Janson+ 2012)
J/AcA/62/67 : ASAS photometry of ROSAT sources (Kiraga, 2012)
J/ApJ/764/3 : Hα indices in M low-mass stars (Robertson+, 2013)
J/ApJ/795/161 : Activity & rotation in Praesepe & the Hyades (Douglas+, 2014)
J/MNRAS/440/2036 : VPHAS+ survey synthetic colours (Drew+, 2014)
J/A+A/583/A85 : Binaries in beta Pic moving group (Alonso-Floriano+, 2015)
J/ApJ/798/41 : GALEX NUV observations of bright M-type stars (Ansdell+, 2015)
J/AJ/150/151 : DSSI obs. of binaries. VI. Measures in 2014 (Horch+, 2015)
J/AJ/150/6 : Solar neighborh. XXXVI. VRI variab. of M dwarfs (Hosey+, 2015)
J/AJ/152/141 : Solar neighborhood. XXXVII. RVs for M dwarfs (Benedict+, 2016)
J/ApJ/821/93 : Rotation & Galactic kinematics of mid M dwarfs (Newton+, 2016)
J/AJ/153/240 : ALMA surv. of protoplanetary disks in sigma Ori (Ansdell+, 2017)
J/AJ/154/124 : M dwarfs-long-term photometric variability (Clements+, 2017)
J/A+A/597/A47 : CARMENES input cat. of M dwarfs II (Cortes-Contreras+ 2017)
J/A+A/600/A83 : Photometry of beta Pic members (Messina+, 2017)
J/ApJ/834/85 : Hα emission in nearby M dwarfs (Newton+, 2017)
J/ApJ/856/23 : BANYAN. XI. The BANYAN Σ algorithm (Gagne+, 2018)
J/AJ/155/265 : The solar neighborhood. XLIV. RECONS discoveries (Henry+, 2018)
J/AJ/156/140 : 4 new eclipsing mid M-dwarf systems from MEarth (Irwin+, 2018)
J/AJ/156/217 : Stellar properties for M dwarfs in MEarth-South (Newton+, 2018)
J/ApJ/871/63 : How to constrain M dwarf. II. Nearby binaries (Mann+, 2019)
J/A+A/627/A97 : Early disc dispersal in close binaries (Messina, 2019)
J/ApJS/249/18 : The ZTF catalog of periodic variable stars (Chen+, 2020)
J/ApJS/247/66 : SUPERWIDE: wide binaries in Gaia & SUPERBLINK (Hartman+, 2020)
J/MNRAS/492/1164 : Abundances of Gaia DR2 wide binaries (Hawkins+, 2020)
J/ApJ/895/140 : EvryFlare. II. Param. of 122 cool flare stars (Howard+, 2020)
J/AJ/160/215 : Solar neighborhood.XLVI. New M dwarf binaries (Vrijmoet+, 2020)
J/AJ/161/277 : Sample of 45 HαEW outliers (Kiman+, 2021)
J/AJ/162/176 : The solar neighborhood. XLVIII. (Paredes+, 2021)
J/ApJ/916/77 : K2 rotation periods for SDSS & Gaia M dwarfs (Popinchalk+, 2021)
J/A+A/649/A3 : Gaia Early Data Release 3 photometric passbands (Riello+, 2021)
J/A+A/661/A29 : First eROSITA study of nearby M dwarfs (Magaudda+, 2022)
J/ApJ/935/104 : Catalog of Stellar Flares in 219 M-dwarfs (Medina+, 2022)
J/AJ/163/278 : Stellar populations in IC 2602 and IC 2391 (Nisak+, 2022)
J/AJ/163/178 : Solar Neighborhood. XLIV. M dwarfs with SOAR (Vrijmoet+, 2022)
J/AJ/165/192 : Mdwarfs Ha luminosity & phot. amplitudes (Garcia Soto+, 2023)
J/AJ/166/63 : Mind the Gap. I. Ha activity for M-Dwarfs (Jao+, 2023)
J/AJ/165/265 : Properties of 363 M-dwarfs from TESS (Ment+, 2023)
J/AJ/166/16 : Radial velocities of 123 active stars (Pass+, 2023)
J/AJ/166/11 : Stellar properties & RV variability for M-dwarfs (Pass+, 2023)
J/AJ/165/180 : SOAR Speckle Surv, nearby hierarchical systems (Tokovinin, 2023)
J/AJ/167/196 : The solar neighborhood LI. RECONS & TESS obs. (Kar+, 2024)
J/other/NatAs/8.223 : Stellar spin-down law (Lu+, 2024)
Byte-by-byte Description of file: table6.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 13 A13 --- Name Target name (1)
15- 23 F9.4 yr Epoch [2019/2023.4] Julian epoch of observation (2)
25 A1 --- Flare Flag identifying Hα flares, y=flare (3)
27- 32 F6.2 0.1nm EW-Ha [-15.1/0.31] Equivalent width of H-alpha line;
Angstroms
34- 37 F4.2 0.1nm e_EW-Ha [0.01/0.13] Uncertainty in EW-Ha
39- 44 F6.2 km/s RVel [-49.1/43.8] Radial velocity
46- 49 F4.2 km/s e_RVel [0.03/0.71] Uncertainty in RVel
51- 55 F5.2 km/s vsini [1.4/15.9] Projected rotational velocity (4)
57- 60 F4.2 km/s e_vsini [0.1/2.4] Uncertainty in vsini
62- 65 F4.1 --- SNR [14.7/39.6] Continuum signal-to-noise ratio
near Ha line
--------------------------------------------------------------------------------
Note (1): Target occurrences as follows:
2MA0201+0117A = 11 occurrences
2MA0201+0117B = 10 occurrences
GJ1183A = 10 occurrences
GJ1183B = 10 occurrences
KXComA = 8 occurrences
KXComBC = 30 occurrences
NLTT44989A = 15 occurrences
NLTT44989B = 15 occurrences
Note (2): Values are 2000.0 plus the number of Julian years since J2000.
Note (3): Flags as follows:
n = No; Hα flare not observed; 103 occurrences
y = Yes; Hα flare observed; 6 occurrences
Note (4): Any vsini values less than 10 km/s are potentially unreliable,
with weaker confidence as the value decreases.
--------------------------------------------------------------------------------
History:
From electronic version of the journal
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(End) Prepared by [AAS], Robin Leichtnam [CDS] 12-Nov-2025