34 research outputs found
The Featureless Transmission Spectra of Two Super-puff Planets
The Kepler mission revealed a class of planets known as "super-puffs," with masses only a few times larger than Earth's but radii larger than Neptune, giving them very low mean densities. All three of the known planets orbiting the young solar-type star Kepler 51 are super-puffs. The Kepler 51 system thereby provides an opportunity for a comparative study of the structures and atmospheres of this mysterious class of planets, which may provide clues about their formation and evolution. We observed two transits each of Kepler 51b and 51d with the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope. Combining new WFC3 transit times with reanalyzed Kepler data and updated stellar parameters, we confirmed that all three planets have densities lower than 0.1 g cm⁻³. We measured the WFC3 transmission spectra to be featureless between 1.15 and 1.63 μm, ruling out any variations greater than 0.6 scale heights (assuming a H/He-dominated atmosphere), thus showing no significant water absorption features. We interpreted the flat spectra as the result of a high-altitude aerosol layer (pressure <3 mbar) on each planet. Adding this new result to the collection of flat spectra that have been observed for other sub-Neptune planets, we find support for one of the two hypotheses introduced by Crossfield & Kreidberg, that planets with cooler equilibrium temperatures have more high-altitude aerosols. We strongly disfavor their other hypothesis that the H/He mass fraction drives the appearance of large-amplitude transmission features
A Featureless Infrared Transmission Spectrum for the Super-puff Planet Kepler-79d
Extremely low-density planets ("super-puffs") are a small but intriguing subset of the transiting planet population. With masses in the super-Earth range (1 – 10 M_⊕) and radii akin to those of giant planets (> 4 R_⊕), their large envelopes may have been accreted beyond the water snow line and many appear to be susceptible to catastrophic mass loss. Both the presence of water and the importance of mass loss can be explored using transmission spectroscopy. Here, we present new Hubble space telescope WFC3 spectroscopy and updated Kepler transit depth measurements for the super-puff Kepler-79d. We do not detect any molecular absorption features in the 1.1 − 1.7 μm WFC3 bandpass, and the combined Kepler and WFC3 data are consistent with a flat-line model, indicating the presence of aerosols in the atmosphere. We compare the shape of Kepler-79d's transmission spectrum to predictions from a microphysical haze model that incorporates an outward particle flux due to ongoing mass loss. We find that photochemical hazes offer an attractive explanation for the observed properties of super-puffs like Kepler-79d, as they simultaneously render the near-infrared spectrum featureless and reduce the inferred envelope mass-loss rate by moving the measured radius (optical depth unity surface during transit) to lower pressures. We revisit the broader question of mass-loss rates for super-puffs and find that the age estimates and mass-loss rates for the majority of super-puffs can be reconciled if hazes move the photosphere from the typically assumed pressure of ~10 mbar to ~10 µbar
TOI-5375 B: A Very Low Mass Star at the Hydrogen-Burning Limit Orbiting an Early M-type Star
The TESS mission detected a companion orbiting TIC 71268730, categorized it
as a planet candidate, and designated the system TOI-5375. Our follow-up
analysis using radial velocity data from the Habitable-zone Planet Finder
(HPF), photometric data from Red Buttes Observatory (RBO), and speckle imaging
with NN-EXPLORE Exoplanet Stellar Speckle Imager (NESSI) determined that the
companion is a very low mass star (VLMS) near the hydrogen-burning mass limit
with a mass of 0.080\pm{0.002} M_{\Sun} (), a radius of
0.1114^{+0.0048}_{-0.0050} R_{\Sun} (1.0841), and
brightness temperature of K. This object orbits with a period of
1.721553 days around an early M dwarf star
(0.62\pm{0.016}M_{\Sun}). TESS photometry shows regular variations in the
host star's TESS light curve, which we interpreted as activity-induced
variation of 2\%, and used this variability to measure the host star's
stellar rotation period of 1.9716 days. The TOI-5375
system provides tight constraints on stellar models of low-mass stars at the
hydrogen-burning limit and adds to the population in this important region.Comment: 15 pages, 8 figures, Accepted to the Astronomical Journa
TOI-3785 b: A Low-Density Neptune Orbiting an M2-Dwarf Star
Using both ground-based transit photometry and high-precision radial velocity
(RV) spectroscopy, we confirm the planetary nature of TOI-3785 b. This
transiting Neptune orbits an M2-Dwarf star with a period of ~4.67 days, a
planetary radius of 5.14 +/- 0.16 Earth Radii, a mass of 14.95 +4.10, -3.92
Earth Masses, and a density of 0.61 +0.18, -0.17 g/cm^3. TOI-3785 b belongs to
a rare population of Neptunes (4 Earth Radii < Rp < 7 Earth Radii) orbiting
cooler, smaller M-dwarf host stars, of which only ~10 have been confirmed. By
increasing the number of confirmed planets, TOI-3785 b offers an opportunity to
compare similar planets across varying planetary and stellar parameter spaces.
Moreover, with a high transmission spectroscopy metric (TSM) of ~150 combined
with a relatively cool equilibrium temperature of 582 +/- 16 K and an inactive
host star, TOI-3785 b is one of the more promising low-density M-dwarf Neptune
targets for atmospheric follow-up. Future investigation into atmospheric mass
loss rates of TOI-3785 b may yield new insights into the atmospheric evolution
of these low-mass gas planets around M-dwarfs.Comment: 22 pages, 6 figures, 6 tables, Submitted to A
NEID Reveals that The Young Warm Neptune TOI-2076 b Has a Low Obliquity
TOI-2076 b is a sub-Neptune-sized planet () that transits a young () bright
() K-dwarf hosting a system of three transiting planets. Using
spectroscopic observations with the NEID spectrograph on the WIYN 3.5 m
Telescope, we model the Rossiter-McLaughlin effect of TOI-2076 b, and derive a
sky-projected obliquity of . Using the size of
the star (), and the stellar rotation period
( days), we estimate a true obliquity of
( at 95% confidence),
demonstrating that TOI-2076 b is on a well-aligned orbit. Simultaneous
diffuser-assisted photometry from the 3.5 m Telescope at Apache Point
Observatory rules out flares during the transit. TOI-2076 b joins a small but
growing sample of young planets in compact multi-planet systems with
well-aligned orbits, and is the fourth planet with an age Myr in
a multi-transiting system with an obliquity measurement. The low obliquity of
TOI-2076 b and the presence of transit timing variations in the system suggest
the TOI-2076 system likely formed via convergent disk migration in an initially
well-aligned disk.Comment: Submitted to ApJL, 13 pages, 4 figures, 3 table
TOI-4201: An Early M-dwarf Hosting a Massive Transiting Jupiter Stretching Theories of Core-Accretion
We confirm TOI-4201 b as a transiting Jovian mass planet orbiting an early M
dwarf discovered by the Transiting Exoplanet Survey Satellite. Using ground
based photometry and precise radial velocities from NEID and the Planet Finder
Spectrograph, we measure a planet mass of 2.59 M,
making this one of the most massive planets transiting an M-dwarf. The planet
is 0.4\% the mass of its 0.63 M host and may have a heavy
element mass comparable to the total dust mass contained in a typical Class II
disk. TOI-4201 b stretches our understanding of core-accretion during the
protoplanetary phase, and the disk mass budget, necessitating giant planet
formation to either take place much earlier in the disk lifetime, or perhaps
through alternative mechanisms like gravitational instability.Comment: To be submitted to AAS journals on 14th July 202
TOI-5205b: A Jupiter transiting an M dwarf near the Convective Boundary
We present the discovery of TOI-5205b, a transiting Jovian planet orbiting a
solar metallicity M4V star, which was discovered using TESS photometry and then
confirmed using a combination of precise radial velocities, ground-based
photometry, spectra and speckle imaging. The host star TOI-5205 sits near the
eponymous `Jao gap', which is the transition region between partially and
fully-convective M dwarfs. TOI-5205b has one of the highest mass ratio for M
dwarf planets with a mass ratio of almost 0.3, as it orbits a host star
that is just . Its planetary radius is , while the mass is . Additionally, the large size
of the planet orbiting a small star results in a transit depth of ,
making it one of the deepest transits of a confirmed exoplanet orbiting a
main-sequence star. The large transit depth makes TOI-5205b a compelling target
to probe its atmospheric properties, as a means of tracing the potential
formation pathways. While there have been radial velocity-only discoveries of
giant planets around mid M dwarfs, this is the first transiting Jupiter with a
mass measurement discovered around such a low-mass host star. The high mass of
TOI-5205b stretches conventional theories of planet formation and disk scaling
relations that cannot easily recreate the conditions required to form such
planets.Comment: Submitted to ApJ. Comments are welcome. arXiv admin note: text
overlap with arXiv:2203.0717
TOI-2015b: A Warm Neptune with Transit Timing Variations Orbiting an Active mid M Dwarf
We report the discovery of a close-in () warm Neptune with clear transit timing variations (TTVs)
orbiting the nearby () active M4 star, TOI-2015. We
characterize the planet's properties using TESS photometry, precise
near-infrared radial velocities (RV) with the Habitable-zone Planet Finder (HP)
Spectrograph, ground-based photometry, and high-contrast imaging. A joint
photometry and RV fit yields a radius , mass , and
density for TOI-2015b,
suggesting a likely volatile-rich planet. The young, active host star has a
rotation period of and
associated rotation-based age estimate of . Though
no other transiting planets are seen in the TESS data, the system shows clear
TTVs of super period and
amplitude . After considering multiple likely
period ratio models, we show an outer planet candidate near a 2:1 resonance can
explain the observed TTVs while offering a dynamically stable solution.
However, other possible two-planet solutions -- including 3:2 and 4:3 resonance
-- cannot be conclusively excluded without further observations. Assuming a 2:1
resonance in the joint TTV-RV modeling suggests a mass of
for TOI-2015b and
for the outer candidate.
Additional transit and RV observations will be beneficial to explicitly
identify the resonance and further characterize the properties of the system.Comment: 28 pages, 15 figures, 6 tables. As submitted to AAS Journal
TOI-3984 A b and TOI-5293 A b: two temperate gas giants transiting mid-M dwarfs in wide binary systems
We confirm the planetary nature of two gas giants discovered by TESS to
transit M dwarfs with stellar companions at wide separations. TOI-3984 A
() is an M4 dwarf hosting a short-period (
days) gas giant ( and
) with a wide separation white dwarf companion.
TOI-5293 A () is an M3 dwarf hosting a short-period ( days) gas giant ( and
) with a wide separation M dwarf companion. We
characterize both systems using a combination of ground-based and space-based
photometry, speckle imaging, and high-precision radial velocities from the
Habitable-zone Planet Finder and NEID spectrographs. TOI-3984 A b
( K and ) and TOI-5293 A b
( K and ) are two of the coolest
gas giants among the population of hot Jupiter-sized gas planets orbiting M
dwarfs and are favorable targets for atmospheric characterization of temperate
gas giants and three-dimensional obliquity measurements to probe system
architecture and migration scenarios.Comment: Submitted to AJ, 42 pages, 14 figures. arXiv admin note: substantial
text overlap with arXiv:2201.0996