We have obtained projected rotation velocities (v sub(rot) sin i) of a sample of 19 ultracool dwarfs with spectral types in the interval M6.5-T8 using high-resolution, near-infrared spectra obtained ...with NIRSPEC and the Keck II telescope. Among our targets there are two young brown dwarfs, two likely field stars, and 15 likely brown dwarfs (30-72 M sub(Jup)) in the solar neighborhood. Our results indicate that the T-type dwarfs are fast rotators in marked contrast to M-type stars. We have derived v sub(rot) sin i velocities between ,15 and 40 km s super(-1) for them and have found no clear evidence for T dwarfs rotating strongly faster than L dwarfs. However, there is a hint for an increasing lower envelope on moving from mid-M to L spectral types in the v sub(rot)sin i-spectral-type diagram that was previously reported in the literature; our v sub(rot) sin i results extend it to even cooler types. Assuming that field brown dwarfs have a size of 0.08-0.1 R , we can place an upper limit of 12.5 hr on the equatorial rotation period of T-type brown dwarfs. In addition, we have compared our v sub(rot) sin i measurements to spectroscopic rotational velocities of very young brown dwarfs of similar mass available in the literature. The comparison, although model dependent, suggests that brown dwarfs lose some angular momentum during their contraction; however, their spin-down time seems to be significantly longer than that of solar-type to early M stars.
Context.
Small planets located at the lower mode of the bimodal radius distribution are generally assumed to be composed of iron and silicates in a proportion similar to that of the Earth. However, ...recent discoveries are revealing a new group of low-density planets that are inconsistent with that description.
Aims.
We intend to confirm and characterize the TESS planet candidate TOI-244.01, which orbits the bright (
K
= 7.97 mag), nearby (
d
= 22 pc), and early-type (M2.5 V) M-dwarf star GJ 1018 with an orbital period of 7.4 days.
Methods.
We used Markov chain Monte Carlo methods to model 57 precise radial velocity measurements acquired by the ESPRESSO spectrograph together with TESS photometry and complementary HARPS data. Our model includes a planetary component and Gaussian processes aimed at modeling the correlated stellar and instrumental noise.
Results.
We find TOI-244 b to be a super-Earth with a radius of
R
p
= 1.52 ± 0.12
R
⊕
and a mass of
M
p
= 2.68 ± 0.30
M
⊕
. These values correspond to a density of
ρ
= 4.2 ± 1.1 g cm
−3
, which is below what would be expected for an Earth-like composition. We find that atmospheric loss processes may have been efficient to remove a potential primordial hydrogen envelope, but high mean molecular weight volatiles such as water could have been retained. Our internal structure modeling suggests that TOI-244 b has a 479
−96
+128
km thick hydrosphere over a 1.17 ± 0.09
R
⊕
solid structure composed of a Fe-rich core and a silicate-dominated mantle compatible with that of the Earth. On a population level, we find two tentative trends in the density-metallicity and density-insolation parameter space for the low-density super-Earths, which may hint at their composition.
Conclusions.
With a 8% precision in radius and 12% precision in mass, TOI-244 b is among the most precisely characterized super-Earths, which, together with the likely presence of an extended hydrosphere, makes it a key target for atmospheric observations.
Multiband photometric transit observations (spectro-photometric) have been used mostly so far to retrieve broadband transmission spectra of transiting exoplanets in order to study their atmospheres. ...An alternative method was proposed, and has only been used once, to recover broadband transmission spectra using chromatic Rossiter–McLaughlin observations. We use the chromatic Rossiter–McLaughlin technique on archival and new observational data obtained with the HARPS and CARMENES instruments to retrieve transmission spectra of HD 189733b. The combined results cover the widest retrieved broadband transmission spectrum of an exoplanet obtained from ground-based observation. Our retrieved spectrum in the visible wavelength range shows the signature of a hazy atmosphere, and also includes an indication for the presence of sodium and potassium. These findings all agree with previous studies. The combined visible and near-infrared transmission spectrum exhibits a strong steep slope that may have several origins, such as a super-Rayleigh slope in the atmosphere of HD 189733b, an unknown systematic instrumental offset between the visible and near-infrared, or a strong stellar activity contamination. The host star is indeed known to be very active and might easily generate spurious features in the retrieved transmission spectra. Using our CARMENES observations, we assessed this scenario and place an informative constraint on some properties of the active regions of HD 189733. We demonstrate that the presence of starspots on HD 189733 can easily explain our observed strong slope in the broadband transmission spectrum.
The discovery of a very cool binary system Burningham, Ben; Leggett, S. K.; Lucas, P. W. ...
Monthly notices of the Royal Astronomical Society,
June 2010, Letnik:
404, Številka:
4
Journal Article
Recenzirano
Odprti dostop
We report the discovery of a very cool d/sdL7+T7.5p common proper motion binary system, SDSS J1416+13AB, found by cross-matching the United Kingdom Infrared Telescope (UKIRT) Infrared Deep Sky Survey ...(UKIDSS) Large Area Survey Data Release 5 (UKIDSS LAS DR4) against the Sloan Digital Sky Survey Data Release 7. The d/sdL7 is blue in J−H and H−K and has other features suggestive of low metallicity and/or high gravity. The T7.5p displays spectral peculiarity seen before in earlier type dwarfs discovered in UKIDSS LAS DR4, and referred to as CH4-J-early peculiarity, where the CH4-J index, based on the absorption to the red side of the J-band peak, suggests an earlier spectral type than the H2O-J index, based on the blue side of the J-band peak, by ∼2 subtypes. We suggest that CH4-J-early peculiarity arises from low metallicity and/or high gravity, and speculate as to its use for classifying T dwarfs. UKIDSS and follow-up United Kingdom Infrared Telescope/Wide Field CAMera (UKIRT/WFCAM) photometry shows the T dwarf to have the bluest near-infrared colours yet seen for such an object with H−K=−1.31 ± 0.17. Warm Spitzer IRAC photometry shows the T dwarf to have extremely red H−4.5= 4.86 ± 0.04, which is the reddest yet seen for a substellar object. The lack of parallax measurement for the pair limits our ability to estimate parameters for the system. However, applying a conservative distance estimate of 5–15 pc suggests a projected separation in range 45–135 au. By comparing H−K:H−4.5 colours of the T dwarf to spectral models, we estimate that Teff= 500 K and M/H∼− 0.30, with log g∼ 5.0. This suggests a mass of ∼30 MJupiter for the T dwarf and an age of ∼10 Gyr for the system. The primary would then be a 75 MJupiter object with log g∼ 5.5 and a relatively dust-free Teff∼ 1500 K atmosphere. Given the unusual properties of the system we caution that these estimates are uncertain. We eagerly await parallax measurements and high-resolution imaging which will constrain the parameters further.
Aims. We aim at detecting water vapor in the atmosphere of the hot Jupiter HD 209458 b and perform a multi-band study in the near infrared with CARMENES. Methods. The water vapor absorption lines ...from the atmosphere of the planet are Doppler-shifted due to the large change in its radial velocity during transit. This shift is of the order of tens of km s−1, whilst the Earth’s telluric and the stellar lines can be considered quasi-static. We took advantage of this shift to remove the telluric and stellar lines using SYSREM, which performs a principal component analysis including proper error propagation. The residual spectra contain the signal from thousands of planetary molecular lines well below the noise level. We retrieve the information from those lines by cross-correlating the residual spectra with models of the atmospheric absorption of the planet. Results. We find a cross-correlation signal with a signal-to-noise ratio (S/N) of 6.4, revealing H2O in HD 209458 b. We obtain a net blueshift of the signal of –5.2 −1.3+2.6 $^{+2.6}_{-1.3}$ −1.3+2.6 km s−1 that, despite the large error bars, is a firm indication of day- to night-side winds at the terminator of this hot Jupiter. Additionally, we performed a multi-band study for the detection of H2O individually from the three near infrared bands covered by CARMENES. We detect H2O from its 0.96–1.06 μm band with a S/N of 5.8, and also find hints of a detection from the 1.06–1.26 μm band, with a low S/N of 2.8. No clear planetary signal is found from the 1.26–1.62 μm band. Conclusions. Our significant H2O signal at 0.96–1.06 μm in HD 209458 b represents the first detection of H2O from this band individually, the bluest one to date. The unfavorable observational conditions might be the reason for the inconclusive detection from the stronger 1.15 and 1.4 μm bands. H2O is detected from the 0.96–1.06 μm band in HD 209458 b, but hardly in HD 189733 b, which supports a stronger aerosol extinction in the latter, in line with previous studies. Future data gathered at more stable conditions and with larger S/N at both optical and near-infrared wavelengths could help to characterize the presence of aerosols in HD 209458 b and other planets.
ABSTRACT
We report on the high-resolution spectroscopic observations of two planetary transits of the hot Jupiter KELT-7b (Mp = 1.28 ± 0.17MJup, Teq = 2028 K) observed with the High Optical ...Resolution Spectrograph (HORuS) mounted on the 10.4-m Gran Telescopio Canarias (GTC). A new set of stellar parameters are obtained for the rapidly rotating parent star from the analysis of the spectra. Using the newly derived stellar mass and radius, and the planetary transit data of the Transiting Exoplanet Survey Satellite (TESS) together with the HORuS velocities and the photometric and spectroscopic data available in the literature, we update and improve the ephemeris of KELT-7b. Our results indicate that KELT-7 has an angle λ = −10.55 ± 0.27 deg between the sky projections of the star’s spin axis and the planet’s orbital axis. By combining this angle and our newly derived stellar rotation period of 1.38 ± 0.05 d, we obtained a 3D obliquity ψ = 12.4 ± 11.7 deg (or 167.6 deg), thus reinforcing that KELT-7 is a well-aligned planetary system. We search for the presence of Hα, Li i, Na i, Mg i, and Ca ii features in the transmission spectrum of KELT-7b but we are only able to determine upper limits of 0.08–1.4 per cent on their presence after accounting for the contribution of the stellar variability to the extracted planetary spectrum. We also discuss the impact of stellar variability on the planetary data. Our results reinforce the importance of monitoring the parent star when performing high-resolution transmission spectroscopy of the planetary atmosphere in the presence of stellar activity.
We report the discovery of two planetary systems, namely G 264–012, an M 4.0 dwarf with two terrestrial planets (
M
b
sin
i
=2.50
−0.30
+0.29
M
⊕
and
M
c
sin
i
=3.75
−0.47
+0.48
M
⊕
), and Gl 393, a ...bright M 2.0 dwarf with one terrestrial planet (
M
b
sin
i
= 1.71 ± 0.24
M
⊕
). Although both stars were proposed to belong to young stellar kinematic groups, we estimate their ages to be older than about 700 Ma. The two planets around G 264–012 were discovered using only radial-velocity (RV) data from the CARMENES exoplanet survey, with estimated orbital periods of 2.30 d and 8.05 d, respectively.Photometric monitoring and analysis of activity indicators reveal a third signal present in the RV measurements, at about 100 d,caused by stellar rotation. The planet Gl 393 b was discovered in the RV data from the HARPS, CARMENES, and HIRES instruments. Its identification was only possible after modelling, with a Gaussian process (GP), the variability produced by the magnetic activity of the star. For the earliest observations, this variability produced a forest of peaks in the periodogram of the RVs at around the 34 d rotation period determined from
Kepler
data, which disappeared in the latestepochs. After correcting for them with this GP model, a significant signal showed at a period of 7.03 d. No significant signals in any of our spectral activity indicators or contemporaneous photometry were found at any of the planetary periods. Given the orbital and stellar properties, the equilibrium temperatures of the three planets are all higher than that for Earth. Current planet formation theories suggest that these two systems represent a common type of architecture. This is consistent with formation following the core accretion paradigm.
Context.
The study of exoplanet atmospheres is essential for understanding the formation, evolution, and composition of exoplanets. The transmission spectroscopy technique is playing a significant ...role in this domain. In particular, the combination of state-of-the-art spectrographs at low- and high-spectral resolution is key to our understanding of atmospheric structure and composition.
Aims.
We observed two transits of the close-in sub-Saturn-mass planet, WASP-127b, with ESPRESSO in the frame of the Guaranteed Time Observations Consortium. We aim to use these transit observations to study the system architecture and the exoplanet atmosphere simultaneously.
Methods.
We used the Reloaded Rossiter-McLaughlin technique to measure the projected obliquity
λ
and the projected rotational velocity
v
eq
⋅sin(
i
*
). We extracted the high-resolution transmission spectrum of the planet to study atomic lines. We also proposed a new cross-correlation framework to search for molecular species and we applied it to water vapor.
Results.
The planet is orbiting its slowly rotating host star (
v
eq
⋅sin(
i
*
) = 0.53
−0.05
+0.07
km s
−1
) on a retrograde misaligned orbit (
λ
= −128.41
−5.46
+5.60
°). We detected the sodium line core at the 9-
σ
confidence level with an excess absorption of 0.34 ± 0.04%, a blueshift of 2.74 ± 0.79 km s
−1
, and a full width at half maximum of 15.18 ± 1.75 km s
−1
. However, we did not detect the presence of other atomic species but set upper limits of only a few scale heights. Finally, we put a 3-
σ
upper limit on the average depth of the 1600 strongest water lines at equilibrium temperature in the visible band of 38 ppm. This constrains the cloud-deck pressure between 0.3 and 0.5 mbar by combining our data with low-resolution data in the near-infrared and models computed for this planet.
Conclusions.
WASP-127b, with an age of about 10 Gyr, is an unexpected exoplanet by its orbital architecture but also by the small extension of its sodium atmosphere (~7 scale heights). ESPRESSO allows us to take a step forward in the detection of weak signals, thus bringing strong constraints on the presence of clouds in exoplanet atmospheres. The framework proposed in this work can be applied to search for molecular species and study cloud-decks in other exoplanets.
We present the discovery of a transiting mini-Neptune around TOI-1201, a relatively bright and moderately young early M dwarf (
J
≈ 9.5 mag, ~600–800 Myr) in an equal-mass ~8 arcsecond-wide binary ...system, using data from the Transiting Exoplanet Survey Satellite, along with follow-up transit observations. With an orbital period of 2.49 d, TOI-1201 b is a warm mini-Neptune with a radius of
R
b
= 2.415 ± 0.090
R
⊕
. This signal is also present in the precise radial velocity measurements from CARMENES, confirming the existence of the planet and providing a planetary mass of
M
b
= 6.28 ± 0.88
M
⊕
and, thus, an estimated bulk density of 2.45
−0.42
+0.48
g cm
−3
. The spectroscopic observations additionally show evidence of a signal with a period of 19 d and a long periodic variation of undetermined origin. In combination with ground-based photometric monitoring from WASP-South and ASAS-SN, we attribute the 19 d signal to the stellar rotation period (
P
rot
= 19–23 d), although we cannot rule out that the variation seen in photometry belongs to the visually close binary companion. We calculate precise stellar parameters for both TOI-1201 and its companion. The transiting planet is anexcellent target for atmosphere characterization (the transmission spectroscopy metric is 97
−16
+21
) with the upcoming
James Webb
Space Telescope. It is also feasible to measure its spin-orbit alignment via the Rossiter-McLaughlin effect using current state-of-the-art spectrographs with submeter per second radial velocity precision.
Context.
Despite swift progress in the characterisation of exoplanet atmospheres in composition and structure, the study of atmospheric dynamics has not progressed at the same speed. While ...theoretical models have been developed to describe the lower layers of the atmosphere, and independently, the exosphere, little is known about the intermediate layers up to the thermosphere.
Aims.
We aim to provide a clearer picture of atmospheric dynamics for the class of ultra-hot Jupiters, which are highly irradiated gas giants, based on the example of WASP-76 b.
Methods.
We jointly analysed two datasets that were obtained with the HARPS and ESPRESSO spectrographs to interpret the resolved planetary sodium doublet. We then applied the MERC code, which retrieves wind patterns, speeds, and temperature profiles on the line shape of the sodium doublet. An updated version of MERC, with added planetary rotation, also provides the possibility of modelling the latitude dependence of the wind patterns.
Results.
We retrieve the highest Bayesian evidence for an isothermal atmosphere, interpreted as a mean temperature of 3389 ± 227 K, a uniform day- to nightside wind of 5.5
−2.0
+1.4
km s
−1
in the lower atmosphere with a vertical wind in the upper atmosphere of 22.7
−4.1
+4.9
km s
−1
, switching atmospheric wind patterns at 10
−3
bar above the reference surface pressure (10 bar).
Conclusions.
Our results for WASP-76 b are compatible with previous studies of the lower atmospheric dynamics of WASP-76 b and other ultra-hot Jupiters. They highlight the need for vertical winds in the intermediate atmosphere above the layers probed by global circulation model studies to explain the line broadening of the sodium doublet in this planet. This work demonstrates the capability of exploiting the resolved spectral line shapes to observationally constrain possible wind patterns in exoplanet atmospheres. This is an invaluable input to more sophisticated 3D atmospheric models in the future.
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