J/AJ/169/225 RVs & light curves of WASP-193 from TESS, PFS, & LCRO (Yee+, 2025)
The super-puff WASP-193 b is on a well-aligned orbit.
Yee S.W., Stefansson G., Thorngren D., Monson A., Hartman J.D.,
Charbonneau D.B., Teske J.K., Butler R.P., Crane J.D., Osip D.,
Shectman S.A.
<Astron. J., 169, 225 (2025)>
=2025AJ....169..225Y 2025AJ....169..225Y
ADC_Keywords: Exoplanets; Radial velocities; Spectroscopy; Photometry; Optical;
Infrared; Spectra, optical
Keywords: Exoplanet astronomy ; Hot Jupiters ; Exoplanets
Abstract:
The "super-puffs" are a population of planets that have masses
comparable to that of Neptune but radii similar to Jupiter, leading to
extremely low bulk densities (ρp≤0.2g/cm3) that are not easily
explained by standard core accretion models. Interestingly, several of
these super-puffs are found in orbits significantly misaligned with
their host stars' spin axes, indicating past dynamical excitation that
may be connected to their low densities. Here, we present new
Magellan/Planet Finder Spectrograph radial velocity measurements of
WASP-193, a late F star hosting one of the least dense transiting
planets known to date (Mp=0.112-0.034+0.029MJ,
Rp=1.319-0.048+0.056RJ, ρp=0.060±0.019g/cm3). We refine
the bulk properties of WASP-193 b and use interior structure models to
determine that the planet can be explained if it consists of roughly
equal amounts of metals and H/He, with a metal fraction of Z=0.42. The
planet is likely substantially reinflated due to its host star's
evolution, and expected to be actively undergoing mass loss. We also
measure the projected stellar obliquity using the Rossiter-McLaughlin
effect, finding that WASP-193 b is on an orbit well aligned with the
stellar equator, with λ=16-15+16degrees. WASP-193 b is the
first Jupiter-sized super-puff on a relatively well-aligned orbit,
suggesting a diversity of formation pathways for this population of
planets.
Description:
We observed the WASP-193 system with the Planet Finder Spectrograph
(PFS), a high-resolution echelle spectrograph on the Magellan Clay
telescope at Las Campanas Observatory in Chile that covers wavelengths
from 391 to 734nm. We obtained a sequence of spectroscopic
observations during a transit of WASP-193 b on the night of 2024
February 27. Observations began at 00:42UT and continued for 6.5hr,
covering the entirety of the 4.25hr transit event and an
out-of-transit baseline comprising 0.75hr pre-ingress and 1.5hr
post-egress. A total of 36 exposures were taken, with the first two
having an exposure time of 900s and the remainder being 600s
exposures. We also observed WASP-193 on 13 additional epochs between
2023 December 22 and 2024 June 2, with the goal of refining the
spectroscopic orbit of WASP-193 b. These observations were taken in
the same instrument configuration and with 600s exposure times.
In addition to the in-transit spectroscopic observations on 2024
February 27, we also obtained simultaneous time-series photometry. We
observed with the Three-hundred MilliMeter Telescope (TMMT) and the
305mm Las Campanas Remote Observatory (LCRO) robotic telescope, both
at Las Campanas Observatory in Chile, in I (9000Å) and g'
(4770Å) bands respectively. However, we noted that the TMMT data
were affected by systematics on timescales similar to the transit
ingress and egress duration, resulting in poor constraints on the
transit timing. As such, we only used the LCRO data in our final
analysis.
We made use of archival spectroscopic and photometric data in our
analysis. Barkaoui+ (2024NatAs...8..909B 2024NatAs...8..909B; hereafter B24) published RV
measurements in the optical from the High Accuracy Radial velocity
Planet Searcher (HARPS) and CORALIE spectrographs, both located in La
Silla, Chile. We included the HARPS RVs in our analysis but not the
CORALIE measurements. B24 also published several follow-up transit
light curves obtained from the optical TRAnsiting Planets and
PlanetesImals Small Telescope-South (TRAPPIST-S) and the
near-infrared Search for habitable Planets EClipsing ULtra-cOOl Stars
(SPECULOOS) facilities in Chile, dating back to 2015. We jointly fit
these data in our analysis to extend the baseline of the transit data
and precisely determine the transit ephemeris.
WASP-193 was observed by NASA's Transiting Exoplanet Survey Satellite
(TESS, IV/39) in Sectors 9, 36, and 63, with the transits of WASP-193 b
clearly detected in the TESS light curves. We obtained the 2min
cadence light curves reduced by the TESS Science Processing Operations
Center for sectors 36 and 63 from the Mikulski Archive for Space
Telescopes (MAST). These data were also previously analyzed by B24. In
TESS Sector 9, WASP-193 was not one of the targets selected for 2min
cadence observations, and so was only observed in the 30min cadence
full-frame images. We performed an independent extraction for this
sector.
A search of archival survey data around WASP-193 revealed a faint,
nearby star with a sky separation of 4.25", also noted by B24. This
star is identified in the Gaia (I/355), 2MASS (II/246), and WISE
(II/311) surveys. Given this star has nearly identical parallax and
proper motion compared with WASP-193, the two components are almost
certainly bound. Indeed, the pair of stars appears in the
El-Badry+2021 (2021MNRAS.506.2269E 2021MNRAS.506.2269E) catalog of stellar binaries from
Gaia EDR3.
Objects:
------------------------------------------------------------------
RA (2000) DE Designation(s) (Period)
------------------------------------------------------------------
10 57 23.85 -29 59 49.6 WASP-193 = WASP-193 (Per=6.246d)
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File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 30 49 PFS radial velocities for WASP-193
fig1.dat 36 1797 TESS light curves of WASP-193
fig4a.dat 52 341 LCRO g'-band in-transit photometric data of WASP-193
fig4b.dat 62 463 TMMT I-band in-transit photometric data of WASP-193
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See also:
II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)
II/311 : WISE All-Sky Data Release (Cutri+ 2012)
IV/38 : TESS Input Catalog - v8.0 (TIC-8) (Stassun+, 2019)
IV/39 : TESS Input Catalog version 8.2 (TIC v8.2) (Paegert+, 2021)
I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)
I/357 : Gaia DR3 Part 3. Non-single stars (Gaia Collaboration, 2022)
VI/120 : High-resolution synthetic stellar library (Coelho+, 2005)
J/ApJS/159/141 : Spectroscopic properties of cool stars. I. (Valenti+, 2005)
J/A+A/529/A75 : Limb-darkening coefficients (Claret+, 2011)
J/ApJ/831/64 : Mass-metallicity relation for giant planets (Thorngren+, 2016)
J/MNRAS/456/2070 : Eccentricity distribution of wide binar. (Tokovinin+, 2016)
J/A+A/600/A30 : Limb-darkening for TESS satellite (Claret, 2017)
J/AJ/153/96 : Standard Galactic field RR Lyrae. I. Photometry (Monson+, 2017)
J/ApJS/245/13 : CDIPS. I. LCs from TESS sectors 6 and 7 (Bouma+, 2019)
J/AJ/161/70 : RVs for WASP-107 with HIRES & CORALIE (Piaulet+, 2021)
J/A+A/649/A3 : Gaia Early Data Release 3 photometric passbands (Riello+, 2021)
J/AJ/161/119 : The TESS-Keck survey. IV. Rvel for WASP-107 (Rubenzahl+, 2021)
J/ApJ/931/L15 : Obs. of two transits of GJ 3470b with NEID (Stefansson+, 2022)
J/AJ/168/185 : HATS-38b & WASP-139b: LCs & RVs (Espinoza-Retamal+, 2024)
J/A+A/690/A379 : Obliquities of exoplanet host stars (Knudstrup+, 2024)
J/AJ/167/199 : WIRC light curves of TOI-1420b (Vissapragada+, 2024)
http://archive.stsci.edu/index.html : MAST website
http://zenodo.org/records/4435257 : Binar. cat. from Gaia EDR3 (El-Badry+2021)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 13 F13.5 --- BJD [2460300/2460464] Barycentric Julian Date of
midpoint; TDB
15- 20 F6.2 m/s RVel [-57.7/63.5] Relative radial velocity
22- 25 F4.2 m/s e_RVel [4.6/8] Uncertainty in RVel
27- 30 I4 s Exp [600/900] Exposure time
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Byte-by-byte Description of file: fig1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 A3 --- Sector TESS Sector identifier (1)
5- 18 F14.6 d BJD [2458549/2460040] Barycentric Julian Date; TDB
20- 27 F8.6 --- Flux [0.98/1.01] Relative flux
29- 36 F8.6 --- e_Flux [7e-4/2.6e-3] Uncertainty in Flux
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Note (1): Dates of observation for each sector as follows:
S9 = from February 28 to the March 26, 2019 (51 occurrences)
S36 = from March 7 to April 1, 2021 (216 occurrences)
S63 = from March 10 to April 6, 2023 (1530 occurrences)
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Byte-by-byte Description of file: fig4a.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 14 F14.6 d BJD [2460367/2460370] Barycentric Julian Date of
midpoint; TDB
16- 23 F8.6 --- Flux [0.96/1.01] Relative flux; LCRO g' band
(477nm)
25- 32 F8.6 --- e_Flux [2e-3/2.2e-3] Uncertainty in Flux
34- 42 F9.6 --- Flip [-0.68/1] Detrending Variable 1; Meridian
Flip
44- 52 F9.6 --- BJD-Norm [-0.98/1] Detrending Variable 2; Normalized
BJD
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Byte-by-byte Description of file: fig4b.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 14 F14.6 d BJD [2460367/2460371] Barycentric Julian Date of
midpoint; TDB
16- 23 F8.6 --- Flux [0.95/1.02] Relative flux; TMMT I-band (900nm)
25- 32 F8.6 --- e_Flux [2.8e-3/5.1e-3] Uncertainty in Flux
34- 42 F9.6 --- Flip [-0.71/1] Detrending Variable 1; Meridian
Flip
44- 52 F9.6 --- BJD-Norm [-0.93/1] Detrending Variable 2; Normalized
BJD
54- 62 F9.6 --- X-T1 [-0.76/1] Detrending Variable 3; X pixel
position
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History:
From electronic version of the journal
(End) Prepared by [AAS], Robin Leichtnam [CDS] 16-Jan-2026