J/AJ/163/168 Photometry and radial velocity of LTT 1445A (Winters+, 2022)
A Second Planet Transiting LTT1445A and a Determination of the Masses of Both
Worlds.
Winters J.G., Cloutier R., Medina A.A., Irwin J.M., Charbonneau D.,
Astudillo-Defru N., Bonfils X., Howard A.W., Isaacson H., Bean J.L.,
Seifahrt A., Teske J.K., Eastman J.D., Twicken J.D., Collins K.A.,
Jensen E.L.N., Quinn S.N., Payne M.J., Kristiansen M.H., Spencer A.,
Vanderburg A., Zechmeister M., Weiss L.M., Wang S.X., Wang G., Udry S.,
Terentev I.A., Sturmer J., Stefansson G., Shporer A., Shectman S.,
Sefako R., Schwengeler H.M., Schwarz R.P., Scarsdale N., Rubenzahl R.A.,
Roy A., Rosenthal L.J., Robertson P., Petigura E.A., Pepe F., Omohundro M.,
Murphy J.M.A., Murgas F., Mocnik T., Montet B.T., Mennickent R., Mayo A.W.,
Massey B., Lubin J., Lovis C., Lewin P., Kasper D., Kane S.R., Jenkins J.M.,
Huber D., Horne K., Hill M.L., Gorrini P., Giacalone S., Fulton B.,
Forveille T., Figueira P., Fetherolf T., Dressing C., Diaz R.F.,
Delfosse X., Dalba P.A., Dai F., Cortes C.C., Crossfield I.J.M., Crane J.D.,
Conti D.M., Collins K.I., Chontos A., Butler R.P., Brown P., Brady M.,
Behmard A., Beard C., Batalha N.M., Almenara J.-M.
<Astron. J., 163, 168 (2022)>
=2022AJ....163..168W 2022AJ....163..168W
ADC_Keywords: Stars, M-type; Exoplanets; Spectra, optical; Photometry;
Radial velocities
Keywords: Exoplanets ; Solar neighborhood ; Multiple stars ; M dwarf
stars
Abstract:
LTT1445 is a hierarchical triple M-dwarf star system located at a
distance of 6.86pc. The primary star LTT1445A (0.257M☉) is known
to host the transiting planet LTT1445Ab with an orbital period of
5.36days, making it the second-closest known transiting exoplanet
system, and the closest one for which the host is an M dwarf. Using
Transiting Exoplanet Survey Satellite data, we present the discovery
of a second planet in the LTT1445 system, with an orbital period of
3.12days. We combine radial-velocity measurements obtained from the
five spectrographs, Echelle Spectrograph for Rocky Exoplanets and
Stable Spectroscopic Observations, High Accuracy Radial Velocity
Planet Searcher, High-Resolution Echelle Spectrometer, MAROON-X, and
Planet Finder Spectrograph to establish that the new world also orbits
LTT1445A. We determine the mass and radius of LTT1445Ab to be
2.87±0.25M⊕ and 1.304-0.060+0.067R⊕, consistent
with an Earth-like composition. For the newly discovered LTT 1445Ac,
we measure a mass of 1.54-0.19+0.20M⊕ and a minimum radius
of 1.15R⊕, but we cannot determine the radius directly as the
signal-to-noise ratio of our light curve permits both grazing and
nongrazing configurations. Using MEarth photometry and ground-based
spectroscopy, we establish that star C (0.161M☉) is likely the
source of the 1.4day rotation period, and star B (0.215M☉) has a
likely rotation period of 6.7days. We estimate a probable rotation
period of 85days for LTT1445A. Thus, this triple M-dwarf system
appears to be in a special evolutionary stage where the most massive M
dwarf has spun down, the intermediate mass M dwarf is in the process
of spinning down, while the least massive stellar component has not
yet begun to spin down.
Description:
We combined 136 RVs of LTT1445A from five high-resolution
spectrographs taken over roughly two years. We acquired 19 spectra of
LTT1445A with the Echelle Spectrograph for Rocky Exoplanets and Stable
Spectroscopic Observations (ESPRESSO) spectrograph on the Very Large
Telescope (VLT) from UT 2020 July 04 to September 03. ESPRESSO is an
ultrastable, fiber-fed echelle spectrograph with resolving power
R=140000 in the high-resolution (1-UT) configuration and a wavelength
range of 378.2-788.7nm. We acquired 45 spectra of LTT1445A with the
High Accuracy Radial Velocity Planet Searcher (HARPS) spectrograph on
the La Silla 3.6m telescope from UT 2019 March 04 to October 21. HARPS
is a fiber-fed echelle spectrograph with resolving power R=115000 and
a wavelength range of 378-691nm. We acquired 39 spectra of LTT1445A
with the High-Resolution Echelle Spectrometer (HIRES) on the 10m Keck
telescope on Maunakea, Hawaii, on nights between UT 2019 August 14 and
2020 February 28. HIRES is an optical echelle spectrograph with
resolving power R∼55000. We used the MAROON-X spectrograph on the 8.1m
Gemini-North telescope to measure RVs of LT 1445A during three
observing runs of two weeks each between 2019 December and 2020
November. MAROON-X is a stabilized, fiber-fed echelle spectrograph
with resolving power R∼85000 and a wavelength range of 500-920nm in
two camera arms. We acquired 25 spectra (15 when binned by night) of
LTT1445A with the Planet Finder Spectrograph (PFS), mounted on the
6.5m Magellan II telescope at Las Campanas Observatory in Chile, from
UT 2019 July 20 to 2020 November 4. PFS covers 391-734nm, and the
subsequent RVs are calibrated using the iodine method. The default
0.3" slit provides a resolving power R∼127000.
For the purpose of determining the rotation periods of A and BC, we
gathered photometric monitoring observations using MEarth-South
telescope 6 at Cerro Tololo Inter-American Observatory (CTIO), Chile,
beginning UT 2019 February 14; observations are ongoing at the time of
writing. The data set used in the present analysis includes 330 nights
of data ending 2021 October 7.
Objects:
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RA (2000) DE Designation(s)
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03 01 51.39 -16 35 36.1 LTT1445 = BD-17 588
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File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 37 136 Radial velocities for LTT1445A
fig2a.dat 150 17987 *MEarth light curve data for of LTT1445A
fig2bc.dat 150 17987 *MEarth light curve data for of LTT1445BC
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Note on fig2*.dat: These tables present the light curve in a standard
format used in MEarth public data releases. Some of the columns are
not relevant in the present publication, but for consistency of the
format with other public MEarth datasets, we have left it unaltered.
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See also:
I/337 : Gaia DR1 (Gaia Collaboration, 2016)
IV/38 : TESS Input Catalog - v8.0 (TIC-8) (Stassun+, 2019)
J/ApJ/757/112 : Stellar diameters. II. K and M-stars (Boyajian+, 2012)
J/ApJS/208/9 : Intrinsic colors and temperatures of PMS stars (Pecaut+, 2013)
J/A+A/575/A119 : HARPS RV and stellar activity (Astudillo-Defru+, 2015)
J/ApJ/804/64 : Empirical and model parameters of 183 M dwarfs (Mann+, 2015)
J/A+A/584/A72 : Transiting rocky planet at 6.5pc from the Sun (Motalebi+ 2015)
J/AJ/152/141 : Solar neighborhood. XXXVII. RVs for M dwarfs (Benedict+, 2016)
J/A+A/585/A134 : HD1461, HD40307, and HD204313 radial velocities (Diaz+, 2016)
J/ApJ/821/93 : Rotation & Galactic kinematics of mid M dwarfs (Newton+, 2016)
J/A+A/600/A13 : HARPS Mdwarf sample magnetic activity (Astudillo-Defru+, 2017)
J/ApJ/834/17 : Mass & radius of planets, moons, low mass stars (Chen+, 2017)
J/A+A/600/A30 : Limb-darkening for TESS satellite (Claret, 2017)
J/A+A/608/A35 : K2-18 HARPS time-series (Cloutier+, 2017)
J/ApJ/834/85 : Hα emission in nearby M dwarfs (Newton+, 2017)
J/MNRAS/474/2094 : Inferring probabilistic stellar Prots (Angus+, 2018)
J/A+A/618/A142 : Radial velocity for GJ 1132 (Bonfils+, 2018)
J/AJ/155/265 : Solar neighborhood. XLIV. RECONS discoveries (Henry+, 2018)
J/AJ/155/180 : A catalog of cool dwarf targets for the TESS (Muirhead+, 2018)
J/AJ/156/102 : TESS Input Catalog and Candidate Target List (Stassun+, 2018)
J/A+A/629/A111 : L 98-59 (TOI 175) HARPS observations (Cloutier+, 2019)
J/A+A/628/A39 : Radial velocities of GJ 357 (Luque+, 2019)
J/AJ/160/3 : Radial velocities M-dwarf LTT3780 with HARPS (Cloutier+, 2020)
J/AJ/160/22 : TOI-1235 Rvel & optical spectroscopy (Cloutier+, 2020)
J/A+A/642/A236 : GJ 3473 (TOI-488) radial velocity curve (Kemmer+, 2020)
J/AJ/159/290 : RVs of 12 spectroscopic binaries M-dwarfs (Winters+, 2020)
J/AJ/162/79 : HARPS radial velocity follow up of TOI-1634 (Cloutier+, 2021)
J/AJ/161/23 : Rvel & light curve of low mass star TOI 540 (Ment+, 2021)
J/AJ/161/63 : Mdwarfs masses 0.1≲M/M☉≲0.3 within 15pc (Winters+, 2021)
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 14 F14.6 d BJD [2458546/2459190] Barycentric Julian Date of
mid-exposure, TDB system
16- 23 F8.2 m/s RVel [-5464/5.08] Barycentric radial velocity
25- 28 F4.2 m/s e_RVel [0.1/3] Uncertainty in RVel
30- 37 A8 --- Inst Instrument used (1)
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Note (1): RVel for ESPRESSO and HARPS are absolute, while those for
HIRES, MAROON-X, and PFS are relative.
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Byte-by-byte Description of file: fig2a.dat fig2bc.dat
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Bytes Format Units Label Explanations
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1- 14 F14.6 d BJD [2458528/2459495] Barycentric Julian Date at
mid-exposure
16- 26 F11.6 mag Dmag [-0.8/1.61] Differential magnitude
28- 38 F11.6 mag e_Dmag [0.002/0.2] Uncertainty in differential magnitude
40- 46 F7.3 s Texp [4.034] Exposure time
48- 54 F7.4 mag mag0 [-3.98/0.25] Frame magnitude zero point offset
56- 61 F6.3 pix FWHM [-1/5.26] FWHM of stellar images (1)
63- 67 F5.3 -- Ell [0.005/0.37] Ellipticity of stellar images (1)
69- 75 F7.5 -- Airmass [1.02/2.06] Airmass at mid-exposure
77- 85 F9.3 pix X [625/1427] X pixel coordinate of star
87- 95 F9.3 pix Y [756/1288] Y pixel coordinate of star
97-103 F7.2 deg Angle [-180/0.04] Angle relative to reference image
105-112 F8.2 --- Sky [1.77/4677] Local sky background level
114-118 I5 --- Peak [691/21273] Peak counts in object, including sky
120-121 I2 -- Seg [1/2] Segment number (2)
123-124 I2 -- Vers [4] Instrument version number
126-126 I1 -- Status [0/2] Realtime status flag (3)
128-128 I1 -- Flags [0] Flags (4)
130-138 F9.6 mag CM [-0.02/0.01] Common-mode differential mag (5)
140-150 F11.6 mag mag [-0.8/1.61] Corrected differential magnitude (6)
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Note (1): Negative FWHM values indicate that no estimates of FWHM and
Ellipticity could be made due to there being too few detected stellar
sources on the image.
Note (2): Used to identify which side of the meridian the image was taken
on. Possible values are 1 or 2 for the present light curve.
Note (3): Non-zero if the data point was taken in response to a real-time
trigger. Values are 1 or 2, corresponding to two stages of the
real-time detection process: confirmation (R=1), or high-cadence
followup (R=2).
Note (4): Flags as follows:
2 = Aperture contains known bad pixels
4 = Possible saturation detected.
Note (5): Gives the "common mode" interpolated to the Julian date of the
exposure. Derived from the average differential magnitude of all the
M-dwarfs observed by all 8 MEarth telescopes in a given time interval.
This should be scaled and subtracted from mag to correct for
variations in precipitable water vapor.
Note (6): Detrended differential photometry using a simple baseline model
consisting of one magnitude zero-point for each side of the meridian,
and linear decorrelation against CM and FWHM. Not used in the present
publication.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Coralie Fix [CDS], 27-Apr-2022