Multiband photometric transit observations or low-resolution spectroscopy (spectro-photometry) are normally used to retrieve the broadband transmission spectra of transiting exoplanets in order to ...assess the chemical composition of their atmospheres. In this paper we present an alternative approach for recovering the broadband transmission spectra using chromatic Doppler tomography based on physical modeling through the
SOAP
tool: CHOCOLATE (CHrOmatiC line prOfiLe tomogrAphy TEchnique). To validate the method and examine its performance, we use observational data recently obtained with the ESPRESSO instrument to retrieve the transmission spectra of the archetypal hot Jupiter HD 209458b. Our findings indicate that the recovered transmission spectrum is in good agreement with the results presented in previous studies, which used different methodologies to extract the spectrum, achieving similar precision. We explored several atmospheric models and inferred from spectral retrieval that a model containing H
2
O and NH
3
is the preferred scenario. The CHOCOLATE methodology is particularly interesting for future studies of exoplanets around young and active stars or moderate to fast rotating stars, considering
SOAP
’s ability to model stellar active regions and the fact that the rotational broadening of spectral lines favors its application. Furthermore, CHOCOLATE will allow the broad transmission spectrum of a planet to be retrieved using high-S/N, high-resolution spectroscopy with the next generation of extremely large telescopes, where low-resolution spectroscopy will not always be accessible.
The obliquity of a terrestrial planet is an important clue about its formation and critical to its climate. Previous studies using simulated photometry of Earth show that continuous observations over ...most of a planet's orbit can be inverted to infer obliquity. However, few studies of more general planets with arbitrary albedo markings have been made and, in particular, a simple theoretical understanding of why it is possible to extract obliquity from light curves is missing. Reflected light seen by a distant observer is the product of a planet's albedo map, its host star's illumination, and the visibility of different regions. It is useful to treat the product of illumination and visibility as the kernel of a convolution. Time-resolved photometry constrains both the albedo map and the kernel, the latter of which sweeps over the planet due to rotational and orbital motion. The kernel's movement distinguishes prograde from retrograde rotation for planets with non-zero obliquity on inclined orbits. We demonstrate that the kernel's longitudinal width and mean latitude are distinct functions of obliquity and axial orientation. Notably, we find that a planet's spin axis affects the kernel – and hence time-resolved photometry – even if this planet is east–west uniform or spinning rapidly, or if it is north–south uniform. We find that perfect knowledge of the kernel at 2–4 orbital phases is usually sufficient to uniquely determine a planet's spin axis. Surprisingly, we predict that east–west albedo contrast is more useful for constraining obliquity than north–south contrast.
GJ 9827 is a bright, nearby K7V star orbited by two super-Earths and one mini-Neptune on close-in orbits. The system was first discovered using K2 data and then further characterized by other ...spectroscopic and photometric instruments. Previous literature studies provide several mass measurements for the three planets, however, with large variations and uncertainties. To better constrain the planetary masses, we added high-precision radial velocity measurements from ESPRESSO to published datasets from HARPS, HARPS-N, and HIRES and we performed a Gaussian process analysis combining radial velocity and photometric datasets from K2 and TESS. This method allowed us to model the stellar activity signal and derive precise planetary parameters. We determined planetary masses of M b = 4.28 −0.33 +0.35 M ⊕ , M c = 1.86 −0.39 +0.37 M ⊕ , and M d = 3.02 −0.57 +0.58 M ⊕ , and orbital periods of 1.208974 ± 0.000001 days for planet b, 3.648103 −0.000010 +0.000013 days for planet c, and 6.201812 ± 0.000009 days for planet d. We compared our results to literature values and found that our derived uncertainties for the planetary mass, period, and radial velocity amplitude are smaller than the previously determined uncertainties. We modeled the interior composition of the three planets using the machine-learning-based tool ExoMDN and conclude that GJ 9827 b and c have an Earth-like composition, whereas GJ 9827 d has an hydrogen envelope, which, together with its density, places it in the mini-Neptune regime.
WASP-52b is a low-density hot Jupiter orbiting a moderately active K2V star. Previous low-resolution studies have revealed a cloudy atmosphere and found atomic Na above the cloud deck. Here we report ...on the detection of excess absorption at the Na doublet, the H
α
line, and the K D
1
line. We derived a high-resolution transmission spectrum based on three transits of WASP-52b, observed with the ultra-stable, high-resolution spectrograph ESPRESSO at the Very Large Telescope array. We measured a line contrast of 1.09 ± 0.16% for Na D
1
, 1.31 ± 0.13% for Na D
2
, 0.86 ± 0.13% for H
α
, and 0.46 ± 0.13% for K D
1
, with a line FWHM range of 11–22 km s
−1
. We also found that the velocity shift of these detected lines during the transit is consistent with the planet’s orbital motion, thus confirming their planetary origin. We did not observe any significant net blueshift or redshift that could be attributed to planetary winds. We used activity indicator lines as control but found no excess absorption. However, we did notice signatures arising from the Center-to-Limb variation (CLV) and the Rossiter-McLaughlin (RM) effect at these control lines. This highlights the importance of the CLV + RM correction in correctly deriving the transmission spectrum, which, if not corrected, could resemble or cancel out planetary absorption in certain cases. WASP-52b is the second non-ultra-hot Jupiter to show excess H
α
absorption after HD 189733b. Future observations targeting non-ultra-hot Jupiters that show H
α
could help reveal the relation between stellar activity and the heating processes in the planetary upper atmosphere.
The Transiting Exoplanet Survey Satellite (TESS) provides a continuous suite of new planet candidates that need confirmation and precise mass determination from ground-based observatories. This is ...the case for the G-type star TOI-1710, which is known to host a transiting sub-Saturn planet (Mp = 28.3 ± 4.7 M⊕) in a long-period orbit (P = 24.28 days). Here we combine archival SOPHIE and new and archival HARPS-N radial velocity data with newly available TESS data to refine the planetary parameters of the system and derive a new mass measurement for the transiting planet, taking into account the impact of the stellar activity on the mass measurement. We report for TOI-1710b a radius of Rp = 5.15 ± 0.12 R⊕, a mass of Mp = 18.4 ± 4.5 M⊕, and a mean bulk density of ρp = 0.73 ± 0.18 g cm−3, which are consistent at 1.2σ, 1.5σ, and 0.7σ, respectively, with previous measurements. Although there is not a significant difference in the final mass measurement, we needed to add a Gaussian process component to successfully fit the radial velocity dataset. This work illustrates that adding more measurements does not necessarily imply a better mass determination in terms of precision, even though they contribute to increasing our full understanding of the system. Furthermore, TOI-1710b joins an intriguing class of planets with radii in the range 4–8 R⊕ that have no counterparts in the Solar System. A large gaseous envelope and a bright host star make TOI-1710b a very suitable candidate for follow-up atmospheric characterization.
Exoplanets with relatively clear atmospheres are prime targets for detailed studies of chemical compositions and abundances in their atmospheres. Alkali metals have long been suggested to exhibit ...broad wings due to pressure broadening, but most of the alkali detections only show very narrow absorption cores, probably because of the presence of clouds. We report the strong detection of the pressure-broadened spectral profiles of Na, K, and Li absorption in the atmosphere of the super-Neptune WASP-127b, at 4.1σ, 5.0σ, and 3.4σ, respectively. We performed a spectral retrieval modeling on the high-quality optical transmission spectrum newly acquired with the 10.4 m Gran Telescopio Canarias (GTC), in combination with the re-analyzed optical transmission spectrum obtained with the 2.5 m Nordic Optical Telescope (NOT). By assuming a patchy cloudy model, we retrieved the abundances of Na, K, and Li, which are super-solar at 3.7σ for K and 5.1σ for Li (and only 1.8σ for Na). We constrained the presence of haze coverage to be around 52%. We also found a hint of water absorption, but cannot constrain it with the global retrieval owing to larger uncertainties in the probed wavelengths. WASP-127b will be extremely valuable for atmospheric characterization in the era of James Webb Space Telescope.
Ultra-hot Jupiters orbit very close to their host star and consequently receive strong irradiation, causing their atmospheric chemistry to be different from the common gas giants. Here, we have ...studied the atmosphere of one of these particular hot planets, MASCARA-2b/KELT-20b, using four transit observations with high resolution spectroscopy facilities. Three of these observations were performed with HARPS-N and one with CARMENES. Additionally, we simultaneously observed one of the transits with MuSCAT2 to monitor possible spots in the stellar surface. At high resolution, the transmission residuals show the effects of Rossiter-McLaughlin and centre-to-limb variations from the stellar lines profiles, which we have corrected to finally extract the transmission spectra of the planet. We clearly observe the absorption features of CaII, FeII, NaI, Hα, and Hβ in the atmosphere of MASCARA-2b, and indications of Hγ and MgI at low signal-to-noise ratio. In the case of NaI, the true absorption is difficult to disentangle from the strong telluric and interstellar contamination. The results obtained with CARMENES and HARPS-N are consistent, measuring an Hα absorption depth of 0.68 ± 0.05 and 0.59 ± 0.07%, and NaI absorption of 0.11 ± 0.04 and 0.09 ± 0.05% for a 0.75 Å passband, in the two instruments respectively. The Hα absorption corresponds to ~1.2 Rp, which implies an expanded atmosphere, as a result of the gas heating caused by the irradiation received from the host star. For Hβ and Hγ only HARPS-N covers this wavelength range, measuring an absorption depth of 0.28 ± 0.06 and 0.21 ± 0.07%, respectively. For CaII, only CARMENES covers this wavelength range measuring an absorption depth of 0.28 ± 0.05, 0.41 ± 0.05 and 0.27 ± 0.06% for CaII λ8498Å, λ8542Å and λ8662Å lines, respectively. Three additional absorption lines of FeII are observed in the transmission spectrum by HARPS-N (partially covered by CARMENES), measuring an average absorption depth of 0.08 ± 0.04% (0.75 Å passband). The results presented here are consistent with theoretical models of ultra-hot Jupiters atmospheres, suggesting the emergence of an ionised gas on the day-side of such planets. Calcium and iron, together with other elements, are expected to be singly ionised at these temperatures and be more numerous than its neutral state. The Calcium triplet lines are detected here for the first time in transmission in an exoplanet atmosphere.
Context.
The nearby ultra-compact multiplanetary system YZ Ceti consists of at least three planets, and a fourth tentative signal. The orbital period of each planet is the subject of discussion in ...the literature due to strong aliasing in the radial velocity data. The stellar activity of this M dwarf also hampers significantly the derivation of the planetary parameters.
Aims.
With an additional 229 radial velocity measurements obtained since the discovery publication, we reanalyze the YZ Ceti system and resolve the alias issues.
Methods.
We use model comparison in the framework of Bayesian statistics and periodogram simulations based on a method by Dawson and Fabrycky to resolve the aliases. We discuss additional signals in the RV data, and derive the planetary parameters by simultaneously modeling the stellar activity with a Gaussian process regression model. To constrain the planetary parameters further we apply a stability analysis on our ensemble of Keplerian fits.
Results.
We find no evidence for a fourth possible companion. We resolve the aliases: the three planets orbit the star with periods of 2.02 d, 3.06 d, and 4.66 d. We also investigate an effect of the stellar rotational signal on the derivation of the planetary parameters, in particular the eccentricity of the innermost planet. Using photometry we determine the stellar rotational period to be close to 68 d and we also detect this signal in the residuals of a three-planet fit to the RV data and the spectral activity indicators. From our stability analysis we derive a lower limit on the inclination of the system with the assumption of coplanar orbits which is
i
min
= 0.9 deg. From the absence of a transit event with TESS, we derive an upper limit of the inclination of
i
max
= 87.43 deg.
Conclusions.
YZ Ceti is a prime example of a system where strong aliasing hindered the determination of the orbital periods of exoplanets. Additionally, stellar activity influences the derivation of planetary parameters and modeling them correctly is important for the reliable estimation of the orbital parameters in this specific compact system. Stability considerations then allow additional constraints to be placed on the planetary parameters.
ABSTRACT
Developing an effective automatic classifier to separate genuine sources from artifacts is essential for transient follow-ups in wide-field optical surveys. The identification of transient ...detections from the subtraction artifacts after the image differencing process is a key step in such classifiers, known as real-bogus classification problem. We apply a self-supervised machine learning model, the deep-embedded self-organizing map (DESOM) to this ‘real-bogus’ classification problem. DESOM combines an autoencoder and a self-organizing map to perform clustering in order to distinguish between real and bogus detections, based on their dimensionality-reduced representations. We use 32 × 32 normalized detection thumbnails as the input of DESOM. We demonstrate different model training approaches, and find that our best DESOM classifier shows a missed detection rate of $6.6{{\ \rm per\,cent}}$ with a false-positive rate of $1.5{{\ \rm per\,cent}}$. DESOM offers a more nuanced way to fine-tune the decision boundary identifying likely real detections when used in combination with other types of classifiers, e.g. built on neural networks or decision trees. We also discuss other potential usages of DESOM and its limitations.
ABSTRACT
The typical detection rate of ∼1 gamma-ray burst (GRB) per day by the Fermi Gamma-ray Burst Monitor (GBM) provides a valuable opportunity to further our understanding of GRB physics. ...However, the large uncertainty of the Fermi localization typically prevents rapid identification of multiwavelength counterparts. We report the follow-up of 93 Fermi GRBs with the Gravitational-wave Optical Transient Observer (GOTO) prototype on La Palma. We selected 53 events (based on favourable observing conditions) for detailed analysis, and to demonstrate our strategy of searching for optical counterparts. We apply a filtering process consisting of both automated and manual steps to 60 085 candidates initially, rejecting all but 29, arising from 15 events. With ≈3 GRB afterglows expected to be detectable with GOTO from our sample, most of the candidates are unlikely to be related to the GRBs. Since we did not have multiple observations for those candidates, we cannot confidently confirm the association between the transients and the GRBs. Our results show that GOTO can effectively search for GRB optical counterparts thanks to its large field of view of ≈40 deg2 and its depth of ≈20 mag. We also detail several methods to improve our overall performance for future follow-up programmes of Fermi GRBs.
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