arXiv subjects

Tim-Oliver Husser

Publications and source records attributed to Tim-Oliver Husser.

At least 19 recordsLinked to original sources

arXiv2024

The Kinematics of 30 Milky Way Globular Clusters and the Multiple Stellar Populations within

The spectroscopic and photometric classification of multiple stellar populations (MPs) in Galactic globular clusters (GCs) has enabled comparisons between contemporary observations and formation theories regarding the initial spatial configurations of the MPs. However, the kinematics of these MPs is an aspect that requires more attention. We investigated the 3D kinematics of 30 Galactic GCs, extending to 3-5 half-light radii, as well as their MPs, in order to uncover clues of the initial conditions of GCs and the MPs within. We have combined Hubble Space Telescope and Gaia DR3 proper motions together with a comprehensive set of line-of-sight velocities to determine the 3D rotation amplitudes, rotation axes, and anisotropy profiles of the clusters. We include radial velocities from new IFU observations of NGC 5024 and an analysis of archival MUSE data of NGC 6101. We compare our kinematic results with structural and orbital parameters of each cluster, reporting the most significant correlations and common features. We find significant rotation in 21 GCs, with no significant differences between the total rotational amplitudes of the MPs, except for NGC 104. We find no significant differences in the position angles or inclination angles. We find that the 3D rotational amplitude is strongly correlated with mass, relaxation time, enriched star fraction and concentration. We determine the anisotropy profiles of each cluster and the MPs where possible. We investigate correlations with the structural parameters, orbital parameters and accretion history of the clusters, finding that the dynamically young clusters with the highest central concentrations of primordial stars show radial anisotropy in their outer regions ($>2$ half-light radii). The dynamically young clusters with a central concentration of enriched stars show significant tangential anisotropy or isotropy in their outer regions.

astro-ph.GA↗

arXiv2023

Kinematic differences between multiple populations in Galactic globular clusters

The formation process of multiple populations in globular clusters is still up for debate. Kinematic differences between the populations are particularly interesting in this respect, because they allow us to distinguish between single-epoch formation scenarios and multi-epoch formation scenarios. We analyze the kinematics of 25 globular clusters and aim to find kinematic differences between multiple populations to constrain their formation process. We split red-giant branch (RGB) stars in each cluster into three populations (P1, P2, P3) for the type-II clusters and two populations (P1 and P2) otherwise using Hubble photometry. We derive the rotation and dispersion profiles for each cluster and its populations by using all stars with radial velocity measurements obtained from MUSE spectroscopy. Based on these profiles, we calculate the rotation strength in terms of ordered-over-random motion $\left(v/σ\right)_\mathrm{HL}$ evaluated at the half-light radius of the cluster. We detect rotation in all but four clusters. For NGC~104, NGC~1851, NGC~2808, NGC~5286, NGC~5904, NGC~6093, NGC~6388, NGC~6541, NGC~7078 and NGC~7089 we also detect rotation for P1 and/or P2 stars. For NGC~2808, NGC~6093 and NGC~7078 we find differences in $\left(v/σ\right)_\mathrm{HL}$ between P1 and P2 that are larger than $1σ$. Whereas we find that P2 rotates faster than P1 for NGC~6093 and NGC~7078, the opposite is true for NGC~2808. However, even for these three clusters, the differences are still of low significance. We find that the strength of rotation of a cluster generally scales with its median relaxation time. For P1 and P2, the corresponding relation is very weak at best. We observe no correlation between the difference in rotation strength between P1 and P2 and cluster relaxation time. The MUSE stellar radial velocities that this analysis is based on are made publicly available.

astro-ph.GA↗

arXiv2022

Hazy with a chance of star spots: constraining the atmosphere of the young planet, K2-33b

Although all-sky surveys have led to the discovery of dozens of young planets, little is known about their atmospheres. Here, we present multi-wavelength transit data for the super Neptune-sized exoplanet, K2-33b -- the youngest (~10 Myr) transiting exoplanet to-date. We combined photometric observations of K2-33 covering a total of 33 transits spanning >2 years, taken from K2, MEarth, Hubble, and Spitzer. The transit photometry spanned from the optical to the near-infrared (0.6-4.5$μ$m), enabling us to construct a transmission spectrum of the planet. We find that the optical transit depths are nearly a factor of two deeper than those from the near-infrared. This difference holds across multiple datasets taken over years, ruling out issues of data analysis and unconstrained systematics. Surface inhomogeneities on the young star can reproduce some of the difference, but required spot coverage fractions (>60%) are ruled out by the observed stellar spectrum(<20%). We find a better fit to the transmission spectrum using photochemical hazes, which were predicted to be strong in young, moderate-temperature, and large-radius planets like K2-33b. A tholin haze with CO as the dominant gaseous carbon carrier in the atmosphere can reasonably reproduce the data with small or no stellar surface inhomogeneities, consistent with the stellar spectrum. The HST data quality is insufficient for the detection of any molecular features. More observations would be required to fully characterize the hazes and spot properties and confirm the presence of CO suggested by current data.

astro-ph.EP↗

arXiv2022

An Isolated Stellar-Mass Black Hole Detected Through Astrometric Microlensing

We report the first unambiguous detection and mass measurement of an isolated stellar-mass black hole (BH). We used the Hubble Space Telescope (HST) to carry out precise astrometry of the source star of the long-duration (t_E~270 days), high-magnification microlensing event MOA-2011-BLG-191/OGLE-2011-BLG-0462 (hereafter designated as MOA-11-191/OGLE-11-462), in the direction of the Galactic bulge. HST imaging, conducted at eight epochs over an interval of six years, reveals a clear relativistic astrometric deflection of the background star's apparent position. Ground-based photometry of MOA-11-191/OGLE-11-462 shows a parallactic signature of the effect of the Earth's motion on the microlensing light curve. Combining the HST astrometry with the ground-based light curve and the derived parallax, we obtain a lens mass of 7.1 +/- 1.3 Msun and a distance of 1.58 +/- 0.18 kpc. We show that the lens emits no detectable light, which, along with having a mass higher than is possible for a white dwarf or neutron star, confirms its BH nature. Our analysis also provides an absolute proper motion for the BH. The proper motion is offset from the mean motion of Galactic-disk stars at similar distances by an amount corresponding to a transverse space velocity of ~45 km/s, suggesting that the BH received a 'natal kick' from its supernova explosion. Previous mass determinations for stellar-mass BHs have come from radial-velocity measurements of Galactic X-ray binaries, and from gravitational radiation emitted by merging BHs in binary systems in external galaxies. Our mass measurement is the first for an isolated stellar-mass BH using any technique.

astro-ph.SR↗

arXiv2022

pyobs -- An observatory control system forrobotic telescopes

We present a Python-based framework for the complete operation of a robotic telescope observatory. It provides out-of-the-box support for many popular camera types while other hardware like telescopes, domes, and weather stations can easily be added via a thin abstraction layer to existing code. Common functionality like focusing, acquisition, auto-guiding, sky-flat acquisition, and pipeline calibration are ready for use. A remote-control interface, a "mastermind" for truly robotic operations as well as an interface to the Las Cumbres Observatory observation portal is included. The whole system is fully configurable and easily extendable. We are currently running pyobs successfully on three different types of telescopes, of which one is a siderostat for observing the Sun. pyobs uses open standards and open software wherever possible and is itself freely available.

astro-ph.IM↗

arXiv2022

The MAVERIC Survey: The first radio and X-ray limits on the detached black holes in NGC 3201

The Galactic globular cluster NGC 3201 is the first Galactic globular cluster observed to host dynamically-confirmed stellar-mass black holes, containing two confirmed and one candidate black hole. This result indicates that globular clusters can retain black holes, which has important implications for globular cluster evolution. NGC 3201 has been observed as part of the MAVERIC survey of Galactic globular clusters. We use these data to confirm that there is no radio or X-ray detection of the three black holes, and present the first radio and X-ray limits on these sources. These limits indicate that any accretion present is at an extremely low rate and may be extremely inefficient. In particular, for the system ACS ID #21859, by assuming the system is tidally locked and any accretion is through the capture of the companion's winds, we constrain the radiative efficiency of any accretion to $\leq1.5\times10^{-5}$. We also combine the radio and X-ray source catalogues from the MAVERIC survey with the existing MUSE spectroscopic surveys and the HUGS catalogue of NGC 3201 to provide a catalogue of 42 multiwavelength sources in this cluster. We identify a new red straggler source with X-ray emission, and investigate the multiwavelength properties of the sub-subgiant population in the cluster.

astro-ph.HE↗

arXiv2021

Central kinematics of the Galactic globular cluster M80

We use spectra observed with the integral-field spectrograph MUSE to reveal the central kinematics of the Galactic globular cluster Messier 80 (M80, NGC 6093). Using observations obtained with the recently commissioned narrow-field mode of MUSE, we are able to analyse 932 stars in the central 7.5 arcsec by 7.5 arcsec of the cluster for which no useful spectra previously existed. Mean radial velocities of individual stars derived from the spectra are compared to predictions from axisymmetric Jeans models, resulting in radial profiles of the velocity dispersion, the rotation amplitude, and the mass-to-light ratio. The new data allow us to search for an intermediate-mass black hole (IMBH) in the centre of the cluster. Our Jeans model finds two similarly probable solutions around different dynamical cluster centres. The first solution has a centre close to the photometric estimates available in the literature and does not need an IMBH to fit the observed kinematics. The second solution contains a location of the cluster centre that is offset by about 2.4 arcsec from the first one and it needs an IMBH mass of $4600^{+1700}_{-1400}$ solar masses. N-body models support the existence of an IMBH in this cluster with a mass of up to 6000 solar masses in this cluster, although models without an IMBH provide a better fit to the observed surface brightness profile. They further indicate that the cluster has lost nearly all stellar-mass black holes. We further discuss the detection of two potential high-velocity stars with radial velocities of 80 to 90 km/s relative to the cluster mean.

astro-ph.GA↗

arXiv2020

The MUSE-Faint survey: I. Spectroscopic evidence for a star cluster in Eridanus 2 and constraints on MACHOs as a constituent of dark matter

We aim to provide spectroscopic evidence regarding the nature of the putative star cluster in Eridanus 2 and to place constraints on the mass and abundance of massive astrophysical compact halo objects (MACHOs) as a constituent of dark matter. Methods. We present spectroscopic observations of the central square arcminute of Eridanus 2 from MUSE-Faint, a survey of ultra-faint dwarf galaxies with the Multi Unit Spectroscopic Explorer on the Very Large Telescope. We derive line-of-sight velocities for possible member stars of the putative cluster and for stars in the centre of Eridanus 2. We discuss the existence of the cluster and determine new constraints for MACHOs using the Fokker-Planck diffusion approximation. Results. Out of 182 extracted spectra, we identify 26 member stars of Eridanus 2, seven of which are possible cluster members. We find intrinsic mean line-of-sight velocities of $79.7^{+3.1}_{-3.8}\,\mathrm{km}\,\mathrm{s}^{-1}$ and $76.0^{+3.2}_{-3.7}\,\mathrm{km}\,\mathrm{s}^{-1}$ for the cluster and the bulk of Eridanus 2, respectively, and intrinsic velocity dispersions of ${<}7.6\,\mathrm{km}\,\mathrm{s}^{-1}$ (68-$\%$ upper limit) and $10.3^{+3.9}_{-3.2}\,\mathrm{km}\,\mathrm{s}^{-1}$, respectively. This indicates the cluster most likely exists as a distinct dynamical population hosted by Eridanus 2, without surplus of dark matter over the background distribution. Among the member stars in the bulk of Eridanus 2, we find possible carbon stars, alluding to the existence of an intermediate-age population. We derive constraints on the fraction of dark matter that can consist of MACHOs with a given mass between $1$-$10^5\,M_\mathrm{sun}$. For dark matter consisting purely of MACHOs, the mass of the MACHOs must be less than ${\sim}7.6\,M_\mathrm{sun}$ and ${\sim}44\,M_\mathrm{sun}$ at a $68$- and $95$-$\%$ confidence level, respectively. (Abridged)

astro-ph.GA↗

arXiv2020

A stellar census in globular clusters with MUSE -- Extending the CaT-metallicity relation below the horizontal branch and applying it to multiple populations

Aims. We use the spectra of more than 30,000 red giant branch (RGB) stars in 25 globular clusters (GC), obtained within the MUSE survey of Galactic globular clusters, to calibrate the Ca II triplet (CaT) metallicity relation and derive metallicities for all individual stars. We investigate the overall metallicity distributions as well as those of the different populations within each cluster. Methods. The Ca II triplet in the near-infrared at 8498, 8542, and 8662 AA is visible in stars with spectral types between F and M and can be used to determine their metallicities. In this work, we calibrate the relation using average cluster metallicities from literature and MUSE spectra, and extend it below the horizontal branch - a cutoff that has traditionally been made to avoid a non-linear relation - using a quadratic function. In addition to the classic relation based on V-VHB we also present calibrations based on absolute magnitude and luminosity. The obtained relations are then used to calculate metallicities for all the stars in the sample and to derive metallicity distributions for different populations within a cluster, which have been separated using so-called "chromosome maps" based on HST photometry. Results. We show that, despite the relatively low spectral resolution of MUSE (R=1900-3700) we can derive single star metallicities with a mean statistical intra-cluster uncertainty of ~0.12 dex. We present metallicity distributions for the RGB stars in 25 GCs, and investigate the different metallicities of the populations P3 (and higher) in so-called metal-complex or Type II clusters, finding metallicity variations in all of them. We also detected unexpected metallicity variations in the Type I cluster NGC 2808 and confirm the Type II status of NGC 7078.

astro-ph.SR↗

arXiv2020

An Eclipsing Substellar Binary in a Young Triple System discovered by SPECULOOS

Mass, radius, and age are three of the most fundamental parameters for celestial objects, enabling studies of the evolution and internal physics of stars, brown dwarfs, and planets. Brown dwarfs are hydrogen-rich objects that are unable to sustain core fusion reactions but are supported from collapse by electron degeneracy pressure. As they age, brown dwarfs cool, reducing their radius and luminosity. Young exoplanets follow a similar behaviour. Brown dwarf evolutionary models are relied upon to infer the masses, radii and ages of these objects. Similar models are used to infer the mass and radius of directly imaged exoplanets. Unfortunately, only sparse empirical mass, radius and age measurements are currently available, and the models remain mostly unvalidated. Double-line eclipsing binaries provide the most direct route for the absolute determination of the masses and radii of stars. Here, we report the SPECULOOS discovery of 2M1510A, a nearby, eclipsing, double-line brown dwarf binary, with a widely-separated tertiary brown dwarf companion. We also find that the system is a member of the $45\pm5$ Myr-old moving group, Argus. The system's age matches those of currently known directly-imaged exoplanets. 2M1510A provides an opportunity to benchmark evolutionary models of brown dwarfs and young planets. We find that widely-used evolutionary models do reproduce the mass, radius and age of the binary components remarkably well, but overestimate the luminosity by up to 0.65 magnitudes, which could result in underestimated photometric masses for directly-imaged exoplanets and young field brown dwarfs by 20 to 35%.

astro-ph.SR↗

arXiv2020

How stellar rotation shapes the colour magnitude diagram of the massive intermediate-age star cluster NGC 1846

We present a detailed study of stellar rotation in the massive 1.5 Gyr old cluster NGC 1846 in the Large Magellanic Cloud. Similar to other clusters at this age, NGC 1846 shows an extended main sequence turn-off (eMSTO), and previous photometric studies have suggested it could be bimodal. In this study, we use MUSE integral-field spectroscopy to measure the projected rotational velocities (vsini) of around 1400 stars across the eMSTO and along the upper main sequence of NGC 1846. We measure vsini values up to ~250 km/s and find a clear relation between the vsini of a star and its location across the eMSTO. Closer inspection of the distribution of rotation rates reveals evidence for a bimodal distribution, with the fast rotators centred around vsini = 140 km/s and the slow rotators centred around vsini = 60 km/s. We further observe a lack of fast rotating stars along the photometric binary sequence of NGC 1846, confirming results from the field that suggest that tidal interactions in binary systems can spin down stars. However, we do not detect a significant difference in the binary fractions of the fast and slowly rotating sub-populations. Finally, we report on the serendipitous discovery of a planetary nebula associated with NGC 1846.

astro-ph.SR↗

arXiv2019

The peculiar kinematics of the multiple populations in the globular cluster Messier 80 (NGC 6093)

We combine MUSE spectroscopy and Hubble Space Telescope ultraviolet (UV) photometry to perform a study of the chemistry and dynamics of the Galactic globular cluster Messier 80 (M80, NGC 6093). Previous studies have revealed three stellar populations that not only vary in their light-element abundances, but also in their radial distributions, with concentration decreasing with increasing nitrogen enrichment. This remarkable trend, which sets M80 apart from the other Galactic globular clusters, points towards a complex formation and evolutionary history. To better understand how M80 formed and evolved, revealing its internal kinematics is key. We find that the most N-enriched population rotates faster than the other two populations at a 2 sigma confidence level. While our data further suggest that the intermediate population shows the least amount of rotation, this trend is rather marginal (1 - 2 sigma). Using axisymmetric Jeans models, we show that these findings can be explained from the radial distributions of the populations if they possess different angular momenta. Our findings suggest that the populations formed with primordial kinematical differences.

astro-ph.SR↗

arXiv2019

The binary content of multiple populations in NGC 3201

We investigate the binary content of the two stellar populations that coexist in the globular cluster NGC 3201. Previous studies of binary stars in globular clusters have reported higher binary fractions in their first populations (P1, having field-like abundances) compared to their second populations (P2, having anomalous abundances). This is interpreted as evidence for the latter forming more centrally concentrated. In contrast to previous studies, our analysis focuses on the cluster centre, where comparable binary fractions between the populations are predicted because of the short relaxation times. However, we find that even in the centre of NGC 3201, the observed binary fraction of P1 is higher, (23.1 +/- 6.2)% compared to (8.2 +/- 3.5)% in P2. Our results are difficult to reconcile with a scenario where the populations only differ in their initial concentrations, but instead suggests that the populations also formed with different fractions of binary stars.

astro-ph.SR↗

arXiv2019

A stellar census in globular clusters with MUSE: A spectral catalogue of emission-line sources

Globular clusters produce many exotic stars due to a much higher frequency of dynamical interactions in their dense stellar environments. Some of these objects were observed together with several hundred thousands other stars in our MUSE survey of 26 Galactic globular clusters. Assuming that at least a few exotic stars have exotic spectra, that means spectra that contain emission lines, we can use this large spectroscopic data set of over a million stellar spectra as a blind survey to detect stellar exotica in globular clusters. To detect emission lines in each spectrum, we model the expected shape of an emission line as a Gaussian curve. This template is used for matched filtering on the differences between each observed 1D spectrum and its fitted spectral model. The spectra with the most significant detections of H$α$ emission are checked visually and cross-matched with published catalogues. We find 156 stars with H$α$ emission, including several known cataclysmic variables (CV) and two new CVs, pulsating variable stars, eclipsing binary stars, the optical counterpart of a known black hole, several probable sub-subgiants and red stragglers, and 21 background emission-line galaxies. We find possible optical counterparts to 39 X-ray sources, as we detect H$α$ emission in several spectra of stars that are close to known positions of Chandra X-ray sources. This spectral catalogue can be used to supplement existing or future X-ray or radio observations with spectra of potential optical counterparts to classify the sources.

astro-ph.SR↗

arXiv2019

A stellar census in globular clusters with MUSE: Binaries in NGC 3201

We utilize multi-epoch MUSE spectroscopy to study binaries in the core of NGC 3201. Our sample consists of 3553 stars with 54883 spectra in total comprising 3200 main-sequence stars up to 4 magnitudes below the turn-off. Each star in our sample has between 3 and 63 (with a median of 14) reliable radial velocity (RV) measurements within five years of observations. We introduce a statistical method to determine the probability of a star showing RV variations based on the whole inhomogeneous RV sample. Using HST photometry and an advanced dynamical MOCCA simulation of this specific GC we overcome observational biases that previous spectroscopic studies had to deal with. This allows us to infer a binary frequency in the MUSE FoV and enables us to deduce the underlying true binary frequency of (6.75+-0.72) % in NGC 3201. The comparison of the MUSE observations with the MOCCA simulation suggests a significant fraction of primordial binaries. We can also confirm a radial increase of the binary fraction towards the GC centre due to mass segregation. We discovered that in our sample at least (57.5+-7.9) % of blue straggler stars (BSS) are in a binary system. For the first time in a study of GCs, we were able to fit Keplerian orbits to a significant sample of 95 binaries. We present the binary system properties of eleven BSS and show evidence that two BSS formation scenarios, the mass transfer in binary (or triple) star systems and the coalescence due to binary-binary interactions, are present in our data. We also describe the binary and spectroscopic properties of four sub-subgiant (or red straggler) stars. Furthermore, we discovered two new black hole (BH) candidates with minimum masses (Msini) of (7.68+-0.50) M_sun, (4.4+-2.8) M_sun, and refine the minimum mass estimate on the already published BH to (4.53+-0.21) M_sun. These BHs are consistent with an extensive BH subsystem hosted by NGC 3201.

astro-ph.SR↗

arXiv2019

No evidence for intermediate-mass black holes in the globular clusters $ω$ Cen and NGC 6624

We compare the results of a large grid of N-body simulations with the surface brightness and velocity dispersion profiles of the globular clusters $ω$ Cen and NGC 6624. Our models include clusters with varying stellar-mass black hole retention fractions and varying masses of a central intermediate-mass black hole (IMBH). We find that an $\sim 45,000$ M$_\odot$ IMBH, whose presence has been suggested based on the measured velocity dispersion profile of $ω$ Cen, predicts the existence of about 20 fast-moving, $m>0.5$ M$_\odot$ main-sequence stars with a (1D) velocity $v>60$ km/sec in the central 20 arcsec of $ω$ Cen. However no such star is present in the HST/ACS proper motion catalogue of Bellini et al. (2017), strongly ruling out the presence of a massive IMBH in the core of $ω$ Cen. Instead, we find that all available data can be fitted by a model that contains 4.6% of the mass of $ω$ Cen in a centrally concentrated cluster of stellar-mass black holes. We show that this mass fraction in stellar-mass BHs is compatible with the predictions of stellar evolution models of massive stars. We also compare our grid of $N$-body simulations with NGC 6624, a cluster recently claimed to harbor a 20,000 M$_\odot$ black hole based on timing observations of millisecond pulsars. However, we find that models with $M_{IMBH}>1,000$ M$_\odot$ IMBHs are incompatible with the observed velocity dispersion and surface brightness profile of NGC 6624,ruling out the presence of a massive IMBH in this cluster. Models without an IMBH provide again an excellent fit to NGC 6624.

astro-ph.GA↗

arXiv2019

Discovery of an old nova remnant in the Galactic globular cluster M 22

A nova is a cataclysmic event on the surface of a white dwarf in a binary system that increases the overall brightness by several orders of magnitude. Although binary systems with a white dwarf are expected to be overabundant in globular clusters (GCs) compared to the Galaxy, only two novae from Galactic globular clusters have been observed. We present the discovery of an emission nebula in the Galactic globular cluster M 22 (NGC 6656) in observations made with the integral-field spectrograph MUSE. We extract the spectrum of the nebula and use the radial velocity determined from the emission lines to confirm that the nebula is part of NGC 6656. Emission-line ratios are used to determine the electron temperature and density. It is estimated to have a mass of 1 to $17 \times 10^{-5}$ solar masses. This mass and the emission-line ratios indicate that the nebula is a nova remnant. Its position coincides with the reported location of a 'guest star', an ancient Chinese term for transients, observed in May 48 BCE. With this discovery, this nova may be one of the oldest confirmed extrasolar events recorded in human history.

astro-ph.SR↗

arXiv2018

The atmosphere of WASP-17b: Optical high-resolution transmission spectroscopy

High-resolution transmission spectroscopy is a method for understanding the chemical and physical properties of upper exoplanetary atmospheres. Due to large absorption cross-sections, resonance lines of atomic sodium D-lines (at 5889.95 $Å$ and 5895.92 $Å$) produce large transmission signals. Our aim is to unveil the physical properties of WASP-17b through an accurate measurement of the sodium absorption in the transmission spectrum. We analyze 37 high-resolution spectra observed during a single transit of WASP-17b with the MIKE instrument on the 6.5 meter Magellan Telescopes. We exclude stellar flaring activity during the observations by analyzing the temporal variations of H$_α$ and Ca II infra-red triplet (IRT) lines. Then we obtain the excess absorption light curves in wavelength bands of 0.75, 1, 1.5 and 3 $Å$ around the center of each sodium line (i.e., the light curve approach). We model the effects of differential limb-darkening, and the changing planetary radial velocity on the light curves. We also analyze the sodium absorption directly in the transmission spectrum, which is obtained through dividing in-transit by out-of-transit spectra (i.e., the division approach). We then compare our measurements with a radiative transfer atmospheric model. Our analysis results in a tentative detection of exoplanetary sodium: we measure the width and amplitude of the exoplanetary sodium feature to be $σ_{\mathrm{Na}}$ = (0.128 $\pm$ 0.078) $Å$ and A$_{\mathrm{Na}}$ = (1.7 $\pm$ 0.9)% in the excess light curve approach and $σ_{\mathrm{Na}}$ = (0.850 $\pm$ 0.034) $Å$ and A$_{\mathrm{Na}}$ = (1.3 $\pm$ 0.6)% in the division approach. By comparing our measurements with a simple atmospheric model, we retrieve an atmospheric temperature of 1550 $^{+170} _{-200}$ K and radius (at 0.1 bar) of 1.81 $\pm$ 0.02 R$_{\rm Jup}$ for WASP-17b.

astro-ph.EP↗