A wide planetary-mass companion to a young low-mass brown dwarf in Ophiuchus

We present the discovery of a planetary-mass companion to CFHTWIR-Oph 98, a low-mass brown dwarf member of the young Ophiuchus star-forming region, with a wide 200 au separation (1farcs46). The companion was identified using Hubble Space Telescope images, and confirmed to share common proper motion with the primary using archival and new ground-based observations. Based on the very low probability of the components being unrelated Ophiuchus members, we conclude that Oph 98 AB forms a binary system. From our multiband photometry, we constrain the primary to be an M9–L1 dwarf, and the faint companion to have an L2–L6 spectral type. For a median age of 3 Myr for Ophiuchus, fits of evolutionary models to measured luminosities yield masses of 15.4 ± 0.8 MJup for Oph 98 A and 7.8 ± 0.8 MJup for Oph 98 B, with respective effective temperatures of 2320 ± 40 K and 1800 ± 40 K. For possible system ages of 1–7 Myr, masses could range from 9.6–18.4 MJup for the primary, and from 4.1–11.6 MJup for the secondary. The low component masses and very large separation make this binary the lowest binding energy system imaged to date, indicating that the outcome of low-mass star formation can result in such extreme, weakly bound systems. With such a young age, Oph 98 AB extends the growing population of young free-floating planetary-mass objects, offering a new benchmark to refine formation theories at the lowest masses

A novel survey for young substellar objects with the W-band filter III: Searching for very low-mass brown dwarfs in Serpens South and Serpens Core

We present CFHT photometry and IRTF spectroscopy of low-mass candidate members of Serpens South and Serpens Core (∼430 pc, ∼0.5 Myr), identified using a novel combination of photometric filters, known as the W-band method. We report SC182952+011618, SS182959-020335 and SS183032-021028 as young, low-mass Serpens candidate members, with spectral types in the range M7-M8, M5-L0 and M5-M6.5 respectively. Best-fit effective temperatures and luminosities imply masses of < 0.12M⊙ for all three candidate cluster members. We also present Hubble Space Telescope imaging data (F127M, F139M and F850LP) for six targets in Serpens South. We report the discovery of the binary system SS183044-020918AB. The binary components are separated by ≈45 AU, with spectral types of M7-M8 and M8-M9, and masses of 0.08-0.1 and 0.05-0.07M⊙. We discuss the effects of high dust attenuation on the reliability of our analysis, as well as the presence of reddened background stars in our photometric sample

Using HARPS-N to characterise the long-period planets in the PH-2 and Kepler-103 systems

We present confirmation of the planetary nature of PH-2b, as well as the first mass estimates for the two planets in the Kepler-103 system. PH-2b and Kepler-103c are both long-period and transiting, a sparsely-populated category of exoplanet. We use {\it Kepler} light-curve data to estimate a radius, and then use HARPS-N radial velocities to determine the semi-amplitude of the stellar reflex motion and, hence, the planet mass. For PH-2b we recover a 3.5-$\sigma$ mass estimate of $M_p = 109^{+30}_{-32}$ M$_\oplus$ and a radius of $R_p = 9.49\pm0.16$ R$_\oplus$. This means that PH-2b has a Saturn-like bulk density and is the only planet of this type with an orbital period $P > 200$ days that orbits a single star. We find that Kepler-103b has a mass of $M_{\text{p,b}} = 11.7^{+4.31}_{-4.72}$ M$_{\oplus}$ and Kepler-103c has a mass of $M_{\text{p,c}} = 58.5^{+11.2}_{-11.4}$ M$_{\oplus}$. These are 2.5$\sigma$ and 5$\sigma$ results, respectively. With radii of $R_{\text{p,b}} = 3.49^{+0.06}_{-0.05}$ R$_\oplus$, and $R_{\text{p,c}} = 5.45^{+0.18}_{-0.17}$ R$_\oplus$, these results suggest that Kepler-103b has a Neptune-like density, while Kepler-103c is one of the highest density planets with a period $P > 100$ days. By providing high-precision estimates for the masses of the long-period, intermediate-mass planets PH-2b and Kepler-103c, we increase the sample of long-period planets with known masses and radii, which will improve our understanding of the mass-radius relation across the full range of exoplanet masses and radii.The HARPS-N project has been funded by the Prodex Program of the Swiss Space Office (SSO), the Harvard University Origins of Life Initiative (HUOLI), the Scottish Universities Physics Alliance (SUPA), the University of Geneva, the Smithsonian Astrophysical Observatory (SAO), and the Italian National Astrophysical Institute (INAF), the University of St Andrews, Queen’s University Belfast, and the University of Edinburgh. AM acknowledges support from Senior Kavli Institute Fellowships at the University of Cambridge. ACC acknowledges support from the Science & Technology Facilities Council (STFC) consolidated grant number ST/R000824/1. AV’s and RDH’s work was performed under contract with the California Institute of Technology/Jet Propulsion Laboratory funded by NASA through the Sagan Fellowship Program executed by the NASA Exoplanet Science Institute. LM acknowledges support from PLATO ASI-INAF agreement n.2015-019-R.1-2018 This publication was made possible through the support of a grant from the John Templeton Foundation. The opinions expressed in this publication are those of the authors and do not necessarily reflect the views of the John Templeton Foundation. This material is partly based upon work supported by the National Aeronautics and Space Administration under grants No. NNX15AC90G and NNX17AB59G issued through the Exoplanets Research Program. Some of this work has been carried out in the frame of the National Centre for Competence in Research ‘PlanetS’ supported by the Swiss National Science Foundation (SNSF)

Detection and characterisation of young planetary-mass objects: novel techniques and optimised survey strategies

Young, low-mass brown dwarfs can be similar in size and composition to young, giant exoplanets. Many exist without host stars and are uncontaminated by starlight, making them useful analogues for studying planets in solar systems. Increasing the population of well-studied brown dwarfs and exoplanets will improve our understanding of the underlying distribution of planets, and of which formation scenarios are viable. Young star-forming regions, such as Serpens and Taurus, are ideal targets when looking for populations of planetary-mass brown dwarfs, as they are relatively nearby, young and active in star formation. In this thesis, I present surveys, past and future, of nearby star-forming regions, conducted in the hope of finding new, very low-mass brown dwarf and planetary-mass members. I also focus on the characterisation of newly-identified individual objects, and of populations as a whole. I aim to demonstrate how custom-designed narrowband photometric filters can be incredibly effective at selecting brown dwarf members of young regions for spectroscopic follow-up. In Chapter 2, I present a survey of the Serpens star-forming region using the novel W-band technique. I obtain photometry using the Wide-field Infrared Camera (WIRCAM) on the Canada-France-Hawaii Telescope (CFHT), and the custom-designed W-band filter, which is centred on the 1.45 µm absorption feature present in brown dwarf atmospheres. I then describe a spectroscopic follow-up campaign, covering J−, H− and K−bands. Finally, I describe a subset of observations using the Hubble Space Telescope (HST), obtained to identify possible low-mass companions or binary components. Using this photometric, spectroscopic, and high-resolution imaging data, I identify five likely-members of Serpens Core and Serpens South, four of which are consistent with having spectral types of M5 or later. In Chapter 3, I describe a future direct imaging survey, optimised to detect young, giant planets using a custom filter and a target list informed by our current understanding of the underlying planet distribution. The survey will use the Near Infrared Camera System (NIX), a high-contrast imager, part of the Enhanced Resolution Imager and Spectrograph (ERIS) instrument that has recently been installed at the Very Large Telescope (VLT). I present the ‘spectral shape’ technique, which uses the custom-designed K−peak filter to efficiently identify promising targets for follow-up observations. I discuss possible targets for such a survey, and conclude that a nearby, young star-forming region is an ideal target to maximise the yield of planet and brown dwarf detections. Finally, in Chapter 4 I use an additional W-band data set to investigate the the form of the initial mass function (IMF) in the Taurus star-forming region, and the question of the possible environmental dependence of the IMF. I combine CFHT and Gaia photometry to isolate likely Taurus members from field contaminants. Using the isolated cluster population, I run multiple Monte Carlo Markov Chain simulations to assess the likely form of the IMF. I use different IMF functional forms (broken power law and log-normal) and Taurus star-formation histories, and find evidence for a spread of stellar ages in Taurus from 1–10 Myr. I also find that both functional forms provide a reasonable fit to the data (with a slight preference for the broken power law), and that the best-fit IMF parameters extracted are consistent with literature values for other clusters and the general Galactic population, supporting the theory of a universal IMF

An optimized survey strategy for the ERIS/NIX imager: searching for young giant exoplanets and very low mass brown dwarfs using the K-peak custom photometric filter

International audienceWe present optimal survey strategies for the upcoming NIX imager, part of the Enhanced Resolution Imager and Spectrograph instrument to be installed on the Very Large Telescope. We will use a custom 2.2 µm K-peak filter to optimize the efficiency of a future large-scale direct imaging survey, aiming to detect brown dwarfs and giant planets around nearby stars. We use the results of previous large-scale imaging surveys (primarily SPHERE SHINE and Gemini GPIES) to inform our choice of targets, as well as improved planet population distributions. We present four possible approaches to optimize survey target lists for the highest yield of detections: (i) targeting objects with anomalous proper motion trends, (ii) a follow-up survey of dense fields from SPHERE SHINE and Gemini GPIES, (iii) surveying nearby star-forming regions, and (iv) targeting newly discovered members of nearby young moving groups. We also compare the predicted performance of NIX to other state-of-the-art direct imaging instruments

A Novel Survey for Young Substellar Objects with the W-band Filter. V. IC 348 and Barnard 5 in the Perseus Cloud

International audienceWe report the discovery of substellar objects in the young star cluster IC 348 and the neighboring Barnard 5 dark cloud, both at the eastern end of the Perseus star-forming complex. The substellar candidates are selected using narrowband imaging, i.e., on and off photometric technique with a filter centered around the water absorption feature at 1.45 μm, a technique proven to be efficient in detecting water-bearing substellar objects. Our spectroscopic observations confirm three brown dwarfs in IC 348. In addition, the source WBIS 03492858+3258064, reported in this work, is the first confirmed brown dwarf discovered toward Barnard 5. Together with the young stellar population selected via near- and mid-infrared colors using the Two Micron All Sky Survey and the Wide-field Infrared Survey Explorer, we diagnose the relation between stellar versus substellar objects with the associated molecular clouds. Analyzed by Gaia EDR3 parallaxes and kinematics of the cloud members across the Perseus region, we propose the star formation scenario of the complex under influence of the nearby OB association

A Novel Survey for Young Substellar Objects with the W-band Filter. VI. Spectroscopic Census of Substellar Members and the IMF of the σ Orionis Cluster

Low-mass stars and substellar objects are essential in tracing the initial mass function (IMF). We study the nearby young σ Orionis cluster ( d ∼ 408 pc, age ∼ 1.8 Myr) using deep near-infrared (NIR) photometric data in the J , W , and H bands from WIRCam on the Canada–France–Hawaii Telescope. We use the water absorption feature to select brown dwarfs photometrically and confirm their nature spectroscopically with IRTF-SpeX. Additionally we select candidate low-mass stars for spectroscopy and analyze their membership and those of literature sources using astrometry from Gaia DR3. We obtain NIR spectra for 28 very-low-mass stars and brown dwarfs and estimate their spectral type between M3 and M8.5 (masses ranging between 0.3 and 0.01 M _⊙ ). Apart from these, we also identify five new planetary-mass candidates which require further spectroscopic confirmation of youth. We compile a comprehensive catalog of 170 spectroscopically confirmed members in the central region of the cluster, for a wide mass range of ∼19–0.004 M _☉ . We estimate the star-to-brown-dwarf ratio to be ∼4, within the range reported for other nearby star-forming regions. With the updated catalog of members we trace the IMF down to 4 M _Jup and we find that a two-segment power law fits the substellar IMF better than a log-normal distribution

A Novel Survey for Young Substellar Objects with the W -band Filter. II. The Coolest and Lowest Mass Members of the Serpens-South Star-forming Region

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