J/AJ/163/288 Absolute & relative astrometry for ε Indi B (Chen+, 2022)
Precise Dynamical Masses of ε Indi Ba and Bb; Evidence of Slowed
Cooling at the L/T Transition.
Chen M., Li Y., Brandt T.D., Dupuy T.J., Cardoso C.V., McCaughrean M.J.
<Astron. J., 163, 288 (2022)>
=2022AJ....163..288C 2022AJ....163..288C
ADC_Keywords: Exoplanets; Stars, double and multiple; Stars, dwarfs;
Positional data; Photometry, infrared
Keywords: Exoplanet astronomy ; Brown dwarfs ; T dwarfs ; Exoplanet
dynamics ; Orbit determination ; Astrometry
Abstract:
We report individual dynamical masses of 66.92±0.36 MJup and
53.25±0.29MJup for the binary brown dwarfs ε Indi Ba and
Bb, measured from long-term (∼10yr) relative orbit monitoring and
absolute astrometry monitoring data on the Very Large Telescope (VLT).
Relative astrometry with NACO fully constrains the Keplerian orbit of
the binary pair, while absolute astrometry with FORS2 measures the
system's parallax and mass ratio. We find a parallax consistent with
the Hipparcos and Gaia values for ε Indi A, and a mass ratio
for ε Indi Ba to Bb precise to better than 0.2%. ε
Indi Ba and Bb have spectral types T1-1.5 and T6, respectively. With
an age of 3.5-1.0+0.8Gyr from ε Indi A's activity, these
brown dwarfs provide some of the most precise benchmarks for
substellar cooling models. Assuming coevality, the very different
luminosities of the two brown dwarfs and our moderate mass ratio imply
a steep mass-luminosity relationship (L∝M5.37±0.08) that
can be explained by a slowed cooling rate in the L/T transition, as
previously observed for other L/T binaries. Finally, we present a
periodogram analysis of the near-infrared photometric data, but find
no definitive evidence of periodic signals with a coherent phase.
Description:
We measure the relative positions of ε Indi Ba and Bb using
nine years of monitoring by the Nasmyth Adaptive Optics System (NAOS)
+ Near-Infrared Imager and Spectrograph (CONICA), NACO for short. We
use images taken by the S13 Camera on NACO in the J, H, and Ks
passbands. The S13 camera on NACO has a field of view (FOV) of 14x14"
and a plate scale of ∼13.2mas/pix.
The long-term absolute position of ε Indi B was monitored with
the FOcal Reducer and low dispersion Spectrograph (FORS) installed on
ESO's UT1 telescope at the Very Large Telescope (VLT). The FORS system
consists of twin imagers and spectrographs FORS1 and FORS2,
collectively covering the visual and near UV wavelength. The absolute
astrometry monitoring was done with the FORS2 imager coupled with two
mosaic MIT CCDs; the camera has a pixel scale of 0.126/pixel in its
unbinned mode and a field of view (FOV) of ∼8.6'x8.6'.
Objects:
-------------------------------------------------------
RA (2000) DE Designation(s)
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22 04 10.60 -56 46 58.2 epsilon Indi B = * eps Ind B
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 19 84 Absolute astrometry data from FORS2
table3.dat 38 32 Relative astrometry results
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See also:
B/pastel : The PASTEL catalogue (Soubiran+, 2016-)
IX/10 : ROSAT All-Sky Bright Source Catalogue (1RXS) (Voges+ 1999)
I/259 : The Tycho-2 Catalogue (Hog+ 2000)
I/311 : Hipparcos, the New Reduction (van Leeuwen, 2007)
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
J/A+A/348/897 : Ages of main-sequence stars (Lachaume+, 1999)
J/AJ/132/161 : NStars project; The southern sample. I. (Gray+, 2006)
J/A+A/509/A52 : Search for companions with VLT/NACO (Chauvin+, 2010)
J/A+A/510/A99 : Epsilon Indi Ba and Bb IR spectra (King+, 2010)
J/A+A/512/A37 : Velocities of 43 nearby L dwarfs (Seifahrt+, 2010)
J/MNRAS/428/2824 : Rapid optical variability in ultracool dwarfs (Koen, 2013)
J/A+A/551/L8 : Chromospheric activity of field stars (Pace, 2013)
J/A+A/552/A78 : Solar like stars radial velocities (Zechmeister+, 2013)
J/AJ/147/94 : Solar neighborhood. XXXII. L and M dwarfs (Dieterich+, 2014)
J/ApJS/231/15 : Astrometric monitoring ultracool dwarf binaries (Dupuy+, 2017)
J/ApJ/837/30 : 25yrs monitoring of stellar orbits in the GC (Gillessen+, 2017)
J/ApJ/842/118 : Brown dwarfs with spectral type later than T6 (Leggett+, 2017)
J/A+A/615/A76 : Spectroscopic parameters of stars (SPECIES). I. (Soto+, 2018)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 4 I4 yr Obs.Y [2005/2016] Astrometry date, year
6- 7 I2 "month" Obs.M Astrometry date, numeric month
9- 10 I2 d Obs.D Astrometry date, day in month
12- 13 I2 --- Nframes [1/30] Number of frames
15- 15 A1 --- Band [I] Band
17- 19 I3 s Texp [20/600] Total integration
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 8 F8.3 yr Epoch [2004/2014] Epoch, Besslian fractional year
10- 16 F7.5 arcsec Sep [0.14/0.95] Separation
18- 24 F7.5 arcsec e_Sep [0.001/0.003] Uncertainty in Sep
26- 32 F7.3 deg PA [12.9/340] Position angle, east of north
34- 38 F5.3 deg e_PA [0.04/0.6] Uncertainty in PA
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History:
From electronic version of the journal
(End) Prepared by [AAS], Fix Coralie [CDS], 07-Oct-2022