Abstract
Future direct imaging missions similar to the HabEx and LUVOIR mission concepts aim to catalog and characterize Earth-mass analogs around nearby stars. The exoplanet yield of these missions ...will be dependent on the frequency of Earth-like planets, and potentially the a priori knowledge of which stars specifically host suitable planetary systems. Ground- or space-based radial velocity surveys can potentially perform the pre-selection of targets and assist in the optimization of observation times, as opposed to an uninformed direct imaging survey. In this paper, we present our framework for simulating future radial velocity surveys of nearby stars in support of direct imaging missions. We generate lists of exposure times, observation time-series, and radial velocity time-series given a direct imaging target list. We generate simulated surveys for a proposed set of telescopes and precise radial velocity spectrographs spanning a set of plausible global-network architectures that may be considered for next-generation extremely precise radial velocity surveys. We also develop figures of merit for observation frequency and planet detection sensitivity, and compare these across architectures. From these, we draw conclusions, given our stated assumptions and caveats, to optimize the yield of future radial velocity surveys supporting direct imaging missions. We find that all of our considered surveys obtain sufficient numbers of precise observations to meet the minimum theoretical white noise detection sensitivity for Earth-mass habitable-zone planets. While our detection rates and mass-sensitivity are optimistic, we have margin to explore systematic effects due to stellar activity and correlated noise in future work.
Photoevaporation is a potential explanation for several features within exoplanet demographics. Atmospheric escape observed in young Neptune-sized exoplanets can provide insight into and characterize ...which mechanisms drive this evolution and at what times they dominate. AU Mic b is one such exoplanet, slightly larger than Neptune (4.19 R⊕). It closely orbits a 23 Myr pre-main-sequence M dwarf with an orbital period of 8.46 days. We obtained two visits of AU Mic b at Lyα with Hubble Space Telescope (HST)/Space Telescope Imaging Spectrograph. One flare within the
first HST visit is characterized and removed from our search for a planetary transit. We present a nondetection in our first visit, followed by the detection of escaping neutral hydrogen ahead of the planet in our second visit. The outflow absorbed ∼30% of the star’s Lyα blue wing 2.5 hr before the planet’s white-light transit. We estimate that the highest-velocity escaping material has a column density of 1013.96 cm−2 and is moving 61.26 km s−1 away from the host star. AU Mic b’s large high-energy irradiation could photoionize its escaping neutral hydrogen in 44 minutes, rendering it temporarily unobservable. Our time-variable Lyα transit ahead of AU Mic b could also be explained by an intermediate stellar wind strength from AU Mic that shapes the escaping material into a leading tail. Future Lyα observations of this system will confirm and characterize the unique variable nature of its Lyα transit, which, combined with modeling, will tune the importance of stellar wind and photoionization.
The final assembly of terrestrial planets occurs via massive collisions, which can launch copious clouds of dust that are warmed by the star and glow in the infrared. We report the real-time ...detection of a debris-producing impact in the terrestrial planet zone around a 35-million-year-old solar-analog star. We observed a substantial brightening of the debris disk at a wavelength of 3 to 5 micrometers, followed by a decay over a year, with quasi-periodic modulations of the disk flux. The behavior is consistent with the occurrence of a violent impact that produced vapor out of which a thick cloud of silicate spherules condensed that were then ground into dust by collisions. These results demonstrate how the time domain can become a new dimension for the study of terrestrial planet formation.
Abstract
We report measurements of the sky-projected spin–orbit angle for AU Mic b, a Neptune-size planet orbiting a very young (∼20 Myr) nearby pre-main-sequence M-dwarf star, which also hosts a ...bright, edge-on, debris disk. The planet was recently discovered from preliminary analysis of radial-velocity observations and confirmed to be transiting its host star from photometric data from the NASA’s TESS mission. We obtained radial-velocity measurements of AU Mic over the course of two partially observable transits and one full transit of planet b from high-resolution spectroscopic observations made with the M
inerva
-Australis telescope array. Only a marginal detection of the Rossiter–McLaughlin effect signal was obtained from the radial velocities, in part due to AU Mic being an extremely active star and the lack of full transit coverage plus sufficient out-of-transit baseline. As such, a precise determination of the obliquity for AU Mic b is not possible in this study and we find a sky-projected spin–orbit angle of
λ
=
47
−
54
+
26
°
. This result is consistent with both the planet’s orbit being aligned or highly misaligned with the spin axis of its host star. Our measurement independently agrees with, but is far less precise than observations carried out on other instruments around the same time that measure a low-obliquity orbit for the planet. AU Mic is the youngest exoplanetary system for which the projected spin–orbit angle has been measured, making it a key data point in the study of the formation and migration of exoplanets—particularly given that the system is also host to a bright debris disk.
Abstract Measurements of the carbon-to-oxygen (C/O) ratios of exoplanet atmospheres can reveal details about their formation and evolution. Recently, high-resolution cross-correlation analysis has ...emerged as a method of precisely constraining the C/O ratios of hot Jupiter atmospheres. We present two transits of the ultrahot Jupiter WASP-76b observed between 1.4 and 2.4 μ m with the high-resolution Immersion GRating INfrared Spectrometer on the Gemini-S telescope. We detected the presence of H 2 O, CO, and OH at signal-to-noise ratios of 6.93, 6.47, and 3.90, respectively. We performed two retrievals on this data set. A free retrieval for abundances of these three species retrieved a volatile metallicity of C + O H = − 0.70 − 0.93 + 1.27 , consistent with the stellar value, and a supersolar carbon-to-oxygen ratio of C/O = 0.80 − 0.11 + 0.07 . We also ran a chemically self-consistent grid retrieval, which agreed with the free retrieval within 1 σ but favored a slightly more substellar metallicity and solar C/O ratio ( C + O H = − 0.74 − 0.17 + 0.23 and C/O = 0.59 − 0.14 + 0.13 ). A variety of formation pathways may explain the composition of WASP-76b. Additionally, we found systemic ( V sys ) and Keplerian ( K p ) velocity offsets which were broadly consistent with expectations from 3D general circulation models of WASP-76b, with the exception of a redshifted V sys for H 2 O. Future observations to measure the phase-dependent velocity offsets and limb differences at high resolution on WASP-76b will be necessary to understand the H 2 O velocity shift. Finally, we find that the population of exoplanets with precisely constrained C/O ratios generally trends toward super-solar C/O ratios. More results from high-resolution observations or JWST will serve to further elucidate any population-level trends.
Abstract
Large-scale exoplanet surveys like the Transiting Exoplanet Survey Satellite (TESS) mission are powerful tools for discovering large numbers of exoplanet candidates. Single-transit events ...are commonplace within the resulting candidate list due to the unavoidable limitation of the observing baseline. These single-transit planets often remain unverified due to their unknown orbital periods and consequent difficulty in scheduling follow-up observations. In some cases, radial velocity (RV) follow up can constrain the period enough to enable a future targeted transit detection. We present the confirmation of one such planet: TOI-2010 b. Nearly three years of RV coverage determined the period to a level where a broad window search could be undertaken with the Near-Earth Object Surveillance Satellite, detecting an additional transit. An additional detection in a much later TESS sector solidified our final parameter estimation. We find TOI-2010 b to be a Jovian planet (
M
P
= 1.29
M
Jup
,
R
P
= 1.05
R
Jup
) on a mildly eccentric orbit (
e
= 0.21) with a period of
P
= 141.83403 days. Assuming a simple model with no albedo and perfect heat redistribution, the equilibrium temperature ranges from about 360 to 450 K from apastron to periastron. Its wide orbit and bright host star (
V
= 9.85) make TOI-2010 b a valuable test bed for future low-insolation atmospheric analysis.
We explore the transit timing variations (TTVs) of the young (22 Myr) nearby AU Mic planetary system. For AU
Mic b, we introduce three Spitzer (4.5 μm) transits, five TESS transits, 11 LCO transits, ...one PEST transit, one
Brierfield transit, and two transit timing measurements from Rossiter–McLaughlin observations; for AU Mic c, we
introduce three TESS transits. We present two independent TTV analyses. First, we use EXOFASTv2 to jointly
model the Spitzer and ground-based transits and obtain the midpoint transit times. We then construct an O − C
diagram and model the TTVs with Exo-Striker. Second, we reproduce our results with an independent
photodynamical analysis. We recover a TTV mass for AU Mic c of -10.8+2.22.3 M⊕. We compare the TTV-derived
constraints to a recent radial velocity (RV) mass determination. We also observe excess TTVs that do not appear to
be consistent with the dynamical interactions of b and c alone or due to spots or flares. Thus, we present a
hypothetical nontransiting “middle-d” candidate exoplanet that is consistent with the observed TTVs and candidate
RV signal and would establish the AU Mic system as a compact resonant multiplanet chain in a 4:6:9 period
commensurability. These results demonstrate that the AU Mic planetary system is dynamically interacting,
producing detectable TTVs, and the implied orbital dynamics may inform the formation mechanisms for this
young system. We recommend future RV and TTV observations of AU Mic b and c to further constrain the masses
and confirm the existence of possible additional planet(s).
Abstract
We report the discovery of a highly eccentric long-period Jovian planet orbiting the hot-Jupiter host HD 83443. By combining radial velocity data from four instruments (AAT/UCLES, ...Keck/HIRES, HARPS, Minerva-Australis) spanning more than two decades, we find evidence for a planet with
m
sin
i
=
1.35
−
0.06
+
0.07
M
J
, moving on an orbit with
a
= 8.0 ± 0.8 au and eccentricity
e
= 0.76 ± 0.05. We combine our radial velocity analysis with Gaia eDR3 /Hipparcos proper motion anomalies and derive a dynamical mass of
1.5
−
0.2
+
0.5
M
Jup
. We perform a detailed dynamical simulation that reveals locations of stability within the system that may harbor additional planets, including stable regions within the habitable zone of the host star. HD 83443 is a rare example of a system hosting a hot Jupiter and an exterior planetary companion. The high eccentricity of HD 83443c suggests that a scattering event may have sent the hot Jupiter to its close orbit while leaving the outer planet on a wide and eccentric path.
Abstract We present the discovery of TOI-1994b, a low-mass brown dwarf transiting a hot subgiant star on a moderately eccentric orbit. TOI-1994 has an effective temperature of 7700 − 410 + 720 K, V ...magnitude of 10.51 mag and log( g ) of 3.982 − 0.065 + 0.067 . The brown dwarf has a mass of 22.1 − 2.5 + 2.6 M J , a period of 4.034 days, an eccentricity of 0.341 − 0.059 + 0.054 , and a radius of 1.220 − 0.071 + 0.082 R J . TOI-1994b is more eccentric than other transiting brown dwarfs with similar masses and periods. The population of low-mass brown dwarfs may have properties similar to planetary systems if they were formed in the same way, but the short orbital period and high eccentricity of TOI-1994b may contrast this theory. An evolved host provides a valuable opportunity to understand the influence stellar evolution has on the substellar companion’s fundamental properties. With precise age, mass, and radius, the global analysis and characterization of TOI-1994b augments the small number of transiting brown dwarfs and allows the testing of substellar evolution models.
We present 11.7 km observations of nine late-type dwarfs obtained at the Keck I 10 m telescope in 2002 December and 2003 April. Our targets were selected for their youth or apparent IRAS 12 km ...excess. For all nine sources, excess infrared emission is not detected. We find that stellar wind drag can dominate the circumstellar grain removal and plausibly explain the dearth of M dwarf systems older than 10 Myr with currently detected infrared excesses. We predict that M dwarfs possess fractional infrared excesses on the order of L sub(IR)/L* 6 10 super(-6) and that this may be detectable with future efforts.
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