ABSTRACT
In this study, we consider chromospheric heating models for 55 Cancri in conjunction with observations. The theoretical models, previously discussed in Paper I, are self-consistent, ...non-linear, and time-dependent ab-initio computations encompassing the generation, propagation, and dissipation of waves. Our focus is the consideration of both acoustic waves and longitudinal flux tube waves amounting to two-component chromosphere models. 55 Cancri, a K-type orange dwarf, is a star of low activity, as expected by its age, which also implies a relatively small magnetic filling factor. The Ca ii K fluxes are computed (multi-ray treatment) assuming partial redistribution and time-dependent ionization. The theoretical Ca ii H+K fluxes are subsequently compared with observations. It is found that for stages of lowest chromospheric activity the observed Ca ii fluxes are akin, though not identical, to those obtained by acoustic heating, but agreement can be obtained if low levels of magnetic heating – consistent with the expected photospheric magnetic filling factor – are considered as an additional component; this idea is in alignment with previous proposals conveyed in the literature.
Abstract
The transmission spectrum of the ultrahot Jupiter KELT-9b (
T
eq
∼ 4000 K) exhibits absorption by several metal species. We searched for atomic and molecular lines in its emission spectrum ...by observing partial phase curves with the Calar Alto high-Resolution search for M dwarfs with Exoearths with Near-infrared and optical Echelle Spectrographs (
R
∼ 80,000–95,000). We find evidence for emission by Si
i
in the atmosphere of KELT-9b for the first time. Additionally we find evidence for emission by Mg
i
and Ca
ii
, which were previously detected in transmission, and confirmed earlier detections of Fe
i
emission. Conversely, we find no evidence for dayside emission from Al
i
, Ca
i
, Cr
i
, FeH, Fe
ii
, K
i
, Li
i
, Mg
ii
, Na
i
, OH, Ti
i
, TiO, V
i
, V
ii
, VO, and Y
i
. By employing likelihood mapping, we find indications of there being little variation in emission line contrast between the day- and nightsides—suggesting that KELT-9b may harbor iron emission on its nightside. Our results demonstrate that high-resolution ground-based emission spectroscopy can provide valuable insights into exoplanet atmospheres.
Abstract
We present high-resolution near-infrared spectra taken during eight transits of 55 Cancri e, a nearby low-density super-Earth with a short orbital period (<18 hr). While this exoplanet’s ...bulk density indicates a possible atmosphere, one has not been detected definitively. Our analysis relies on the Doppler cross-correlation technique, which takes advantage of the high spectral resolution and broad wavelength coverage of our data, to search for the thousands of absorption features from hydrogen-, carbon-, and nitrogen-rich molecular species in the planetary atmosphere. Although we are unable to detect an atmosphere around 55 Cancri e, we do place strong constraints on the levels of HCN, NH
3
, and C
2
H
2
that may be present. In particular, at a mean molecular weight of 5 amu, we can rule out the presence of HCN in the atmosphere down to a volume mixing ratio (VMR) of 0.02%, NH
3
down to a VMR of 0.08%, and C
2
H
2
down to a VMR of 1.0%. If the mean molecular weight is relaxed to 2 amu, we can rule out the presence of HCN, NH
3
, and C
2
H
2
down to VMRs of 0.001%, 0.0025%, and 0.08%, respectively. Our results reduce the parameter space of possible atmospheres consistent with the analysis of Hubble Space Telescope/WFC3 observations by Tsiaras et al. and indicate that if 55 Cancri e harbors an atmosphere, it must have a high mean molecular weight or clouds.
Abstract
Terrestrial exoplanets orbiting M-dwarf stars are promising targets for transmission spectroscopy with existing or near-future instrumentation. The atmospheric composition of such rocky ...planets remains an open question, especially given the high X-ray and ultraviolet flux from their host M dwarfs that can drive atmospheric escape. The 1.3
R
⊕
exoplanet GJ 486b (
T
eq
∼ 700 K), orbiting an M3.5 star, is expected to have one of the strongest transmission spectroscopy signals among known terrestrial exoplanets. We observed three transits of GJ 486b using three different high-resolution spectrographs: IRD on Subaru, IGRINS on Gemini-South, and SPIRou on the Canada–France–Hawai’i Telescope. We searched for atmospheric absorption from a wide variety of molecular species via the cross-correlation method, but did not detect any robust atmospheric signals. Nevertheless, our observations are sufficiently sensitive to rule out several clear atmospheric scenarios via injection and recovery tests, and extend comparative exoplanetology into the terrestrial regime. Our results suggest that GJ 486b does not possess a clear H
2
/He-dominated atmosphere, nor a clear 100% water-vapor atmosphere. Other secondary atmospheres with high mean molecular weights or H
2
/He-dominated atmospheres with clouds remain possible. Our findings provide further evidence suggesting that terrestrial planets orbiting M-dwarf stars may experience significant atmospheric loss.
Abstract
Recent observations of the ultra-hot Jupiter WASP-76b have revealed a diversity of atmospheric species. Here we present new high-resolution transit spectroscopy of WASP-76b with GRACES at ...the Gemini North Observatory, serving as a baseline for the Large and Long Program “Exploring the Diversity of Exoplanet Atmospheres at High Spectral Resolution” (Exoplanets with Gemini Spectroscopy, or ExoGemS for short). With a broad spectral range of 400–1050 nm, these observations allow us to search for a suite of atomic species. We recover absorption features due to neutral sodium (Na
i
), and report a new detection of the ionized calcium (Ca
ii
) triplet at ∼850 nm in the atmosphere of WASP-76b, complementing a previous detection of the Ca
ii
H and K lines. The triplet has line depths of 0.295% ± 0.034% at ∼849.2 nm, 0.574% ± 0.041% at ∼854.2 nm, and 0.454% ± 0.024% at ∼866.2 nm, corresponding to effective radii close to (but within) the planet’s Roche radius. These measured line depths are significantly larger than those predicted by model LTE and NLTE spectra obtained on the basis of a pressure–temperature profile computed assuming radiative equilibrium. The discrepancy suggests that the layers probed by our observations are either significantly hotter than predicted by radiative equilibrium and/or in a hydrodynamic state. Our results shed light on the exotic atmosphere of this ultra-hot world, and will inform future analyses from the ExoGemS survey.
Abstract
Exoplanet atmosphere studies are often enriched by synergies with brown dwarf analogs. However, many key molecules commonly seen in brown dwarfs have yet to be confirmed in exoplanet ...atmospheres. An important example is chromium hydride (CrH), which is often used to probe atmospheric temperatures and classify brown dwarfs into spectral types. Recently, tentative evidence for CrH was reported in the low-resolution transmission spectrum of the hot Jupiter WASP-31b. Here, we present high spectral resolution observations of WASP-31b’s transmission spectrum from GRACES/Gemini North and UVES/Very Large Telescope. We detect CrH at 5.6
σ
confidence, representing the first metal hydride detection in an exoplanet atmosphere at high spectral resolution. Our findings constitute a critical step in understanding the role of metal hydrides in exoplanet atmospheres.
Abstract
We present high-resolution transmission spectroscopy of WASP-76b with Gemini Remote Access to CFHT ESPaDOnS Spectrograph (GRACES)/Gemini North obtained as part of the ExoGemS survey. With a ...broad spectral range of 400–1050 nm and a relatively high resolution of ∼66,000, these observations are particularly well suited to searching for atomic and molecular atmospheric species via the Doppler cross-correlation technique. We recover absorption features due to neutral iron (Fe
i
), sodium (Na
i
), and ionized calcium (Ca
ii
) at high significance (>5
σ
), and investigate possible atmospheric temperatures and wind speeds. We also report tentative (>3
σ
) detections of Li
i
, K
i
, Cr
i
, and V
i
in the atmosphere of WASP-76b. Finally, we report nondetections of a number of other species, some of which have previously been detected with other instruments. Through model injection/recovery tests, we demonstrate that many of these species are not expected to be detected in our observations. These results allow us to place GRACES and the ExoGemS survey in context with other high-resolution optical spectrographs.
Abstract
Theory suggests that the orbits of some close-in giant planets should decay due to tidal interactions with their host stars. To date, WASP-12b is the only hot Jupiter reported to have a ...decaying orbit, at a rate of 29 ± 2 ms yr
−1
. We analyzed data from NASA’s Transiting Exoplanet Survey Satellite (TESS) to verify that WASP-12b’s orbit is indeed changing. We find that the TESS transit and occultation data are consistent with a decaying orbit with an updated period of 1.091420090 ± 0.000000041 days and a decay rate of 32.53 ± 1.62 ms yr
−1
. We find an orbital decay timescale of
. If the observed decay results from tidal dissipation, the modified tidal quality factor is
, which falls at the lower end of values derived for binary star systems and hot Jupiters. Our result highlights the power of space-based photometry for investigating the orbital evolution of short-period exoplanets.
Abstract
Orbital dynamics provide valuable insights into the evolution and diversity of exoplanetary systems. Currently, only one hot Jupiter, WASP-12b, is confirmed to have a decaying orbit. ...Another, WASP-4b, exhibits hints of a changing orbital period that could be caused by orbital decay, apsidal precession, or the acceleration of the system toward the Earth. We have analyzed all data sectors from NASA’s Transiting Exoplanet Survey Satellite together with all radial velocity (RV) and transit data in the literature to characterize WASP-4b’s orbit. Our analysis shows that the full RV data set is consistent with no acceleration toward the Earth. Instead, we find evidence of a possible additional planet in the WASP-4 system, with an orbital period of ∼7000 days and
M
c
sin
(
i
)
of
5.47
−
0.43
+
0.44
M
Jup
. Additionally, we find that the transit timing variations of all of the WASP-4b transits cannot be explained by the second planet but can be explained with either a decaying orbit or apsidal precession, with a slight preference for orbital decay. Assuming the decay model is correct, we find an updated period of 1.338231587 ± 0.000000022 days, a decay rate of −7.33 ± 0.71 ms yr
−1
, and an orbital decay timescale of
τ
=
P
/
∣
P
̇
∣
= 15.77 ± 1.57 Myr. If the observed decay results from tidal dissipation, we derive a modified tidal quality factor of
Q
⋆
′
=
5.1
±
0.9
×
10
4
, which is an order of magnitude lower than values derived for other hot Jupiter systems. However, more observations are needed to determine conclusively the cause of WASP-4b’s changing orbit and to confirm the existence of an outer companion.
From previous ground-based observations, the hot Jupiter exoplanet XO-6b was reported to exhibit apparently periodic transit timing variations (TTVs), with a semi-amplitude of 14 minutes and a period ...of about 450 days. These variations were interpreted as being due to a resonant perturbation between XO-6b and a hitherto unknown low-mass planet orbiting the same star. To understand this enigmatic planetary system better, we analyzed three sectors of data, spanning over seven months, from the Transiting Exoplanet Survey Satellite (TESS), which produces high-quality light curves that are well suited to characterizing exoplanets and searching for TTVs. Here we present an updated orbital period of 3.7649893 0.0000037 days and a transit epoch of 2456652.7157 0.0022 BJDTDB. The planetary parameters we report, while consistent with their discovery values, have greatly improved precision. Notably, we find no evidence for TTVs: we can rule out TTVs 2.5 minutes at the 3 level. Therefore, the TESS data have sufficient precision and time baseline to readily reveal the previously reported TTVs of approximately 10 minutes. Our findings highlight the capability of TESS for robust follow-up, and confirm that TTVs are rarely seen in hot Jupiters, unlike is the case with small planets.
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