| 1. |
- Chomez, A., et al.
(författare)
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An imaged 15 MJup companion within a hierarchical quadruple system
- 2023
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Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 676, s. L10-L10
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Tidskriftsartikel (refereegranskat)abstract
- Context. Since 2019, the direct imaging B-star Exoplanet Abundance STudy (BEAST) at SPHERE@VLT has been scanning the surroundings of young B-type stars in order to ascertain the ultimate frontiers of giant planet formation. Recently, the 17+3-4 Myr HIP 81208 was found to host a close-in (∼50 au) brown dwarf and a wider (∼230 au) late M star around the central 2.6 M⊙ primary.Aims. Alongside the continuation of the survey, we are undertaking a complete reanalysis of archival data aimed at improving detection performances so as to uncover additional low-mass companions.Methods. We present here a new reduction of the observations of HIP 81208 using the patch covariance algorithm (PACO), a recent and powerful algorithm dedicated to processing high-contrast imaging datasets, as well as more classical algorithms and a dedicated point spread function subtraction approach. The combination of different techniques allowed for a reliable extraction of astrometric and photometric parameters.Results. A previously undetected source was recovered at a short separation from the C component of the system. Proper motion analysis provided robust evidence for the gravitational bond of the object to HIP 81208 C. Orbiting C at a distance of ∼20 au, this 15 MJup brown dwarf becomes the fourth object of the hierarchical HIP 81208 system.Conclusions. Among the several BEAST stars which are being found to host substellar companions, HIP 81208 stands out as a particularly striking system. As the first stellar binary system with substellar companions around each component ever found by direct imaging, it yields exquisite opportunities for thorough formation and dynamical follow-up studies.
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| 2. |
- Eriksson, Simon C., 1983-, et al.
(författare)
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Resolved near-UV hydrogen emission lines at 40-Myr super-Jovian protoplanet Delorme 1 (AB)b
- 2023
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 669
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Tidskriftsartikel (refereegranskat)abstract
- Context. Accretion at planetary-mass companions (PMCs) suggests the presence of a protoplanetary disc in the system, likely accompanied by a circumplanetary disc. High-resolution spectroscopy of accreting PMCs is very difficult due to their proximity to bright host stars. For well-separated companions, however, such spectra are feasible and they are unique windows into accretion.Aims. We have followed up on our observations of the 40-Myr, and still accreting, circumbinary PMC Delorme 1 (AB)b. We used high-resolution spectroscopy to characterise the accretion process further by accessing the wealth of emission lines in the near-UV.Methods. We have used the UVES spectrograph on the ESO VLT/UT2 to obtain Rλ ≈ 50 000 spectroscopy, at 3300–4520 Å, of Delorme 1 (AB)b. After separating the emission of the companion from that of the M5 low-mass binary, we performed a detailed emission-line analysis, which included planetary accretion shock modelling.Results. We reaffirm ongoing accretion in Delorme 1 (AB)b and report the first detections in a (super-Jovian) protoplanet of resolved hydrogen line emission in the near-UV (Hγ, Hδ, Hϵ, H8, and H9). We tentatively detect H11, H12, He I, and Ca II H/K. The analysis strongly favours a planetary accretion shock with a line-luminosity-based accretion rate of Ṁ = 2 × 10−8 MJ yr−1. The lines are asymmetric and are well described by sums of narrow and broad components with different velocity shifts. The overall line shapes are best explained by a pre-shock velocity of v0 = 170 ± 30 km s−1, implying a planetary mass of MP = 13 ± 5 MJ, and number densities of n0 ≳ 1013 cm−3 or n0 ∼ 1011 cm−3. The higher density implies a small line-emitting area of ∼1% relative to the planetary surface. This favours magnetospheric accretion, a case potentially strengthened by the presence of blueshifted emission in the line profiles.Conclusions. High-resolution spectroscopy offers the opportunity to resolve line profiles, which are crucial for studying the accretion process in depth. The super-Jovian protoplanet Delorme 1 (AB)b is still accreting at ∼40 Myr. Thus, Delorme 1 belongs to the growing family of ‘Peter Pan disc’ systems with (a) protoplanetary and/or circumplanetary disc(s) far beyond the typically assumed disc lifetimes. Further observations of this benchmark companion and its presumed disc(s) will help answer key questions about the accretion geometry in PMCs.
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| 3. |
- Janson, Markus, et al.
(författare)
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A wide-orbit giant planet in the high-mass b Centauri binary system
- 2021
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 600:7888
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Tidskriftsartikel (refereegranskat)abstract
- Planet formation occurs around a wide range of stellar masses and stellar system architectures1. An improved understanding of the formation process can be achieved by studying it across the full parameter space, particularly towards the extremes. Earlier studies of planets in close-in orbits around high-mass stars have revealed an increase in giant planet frequency with increasing stellar mass2 until a turnover point at 1.9 solar masses (M⊙), above which the frequency rapidly decreases3. This could potentially imply that planet formation is impeded around more massive stars, and that giant planets around stars exceeding 3 M⊙ may be rare or non-existent. However, the methods used to detect planets in small orbits are insensitive to planets in wide orbits. Here we demonstrate the existence of a planet at 560 times the Sun–Earth distance from the 6- to 10-M⊙ binary b Centauri through direct imaging. The planet-to-star mass ratio of 0.10–0.17% is similar to the Jupiter–Sun ratio, but the separation of the detected planet is about 100 times wider than that of Jupiter. Our results show that planets can reside in much more massive stellar systems than what would be expected from extrapolation of previous results. The planet is unlikely to have formed in situ through the conventional core accretion mechanism4, but might have formed elsewhere and arrived to its present location through dynamical interactions, or might have formed via gravitational instability.
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| 4. |
- Viswanath, Gayathri, 1992-, et al.
(författare)
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A Statistical Search for Star–Planet Interaction in the Ultraviolet Using GALEX
- 2020
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Ingår i: Astronomical Journal. - : American Astronomical Society. - 0004-6256 .- 1538-3881. ; 159:5, s. 194-194
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Tidskriftsartikel (refereegranskat)abstract
- Most (∼82%) of the over 4000 confirmed exoplanets known today orbit very close to their host stars, within 0.5 au. Planets at such small orbital distances can result in significant interactions with their host stars, which can induce increased activity levels in them. In this work, we have searched for statistical evidence for star–planet interactions in the ultraviolet (UV) using the largest sample of 1355 Galaxy Evolution Explorer (GALEX) detected host stars with confirmed exoplanets and making use of the improved host-star parameters from Gaia DR2. From our analysis, we do not find any significant correlation between the UV activity of the host stars and their planetary properties. We further compared the UV properties of planet host stars to that of chromospherically active stars from the RAdial Velocity Experiment (RAVE) survey. Our results indicate that the enhancement in chromospheric activity of host stars due to star–planet interactions may not be significant enough to reflect in their near- and far-UV broadband flux.
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| 5. |
- Viswanath, Gayathri, 1992-
(författare)
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A Window into the Cradle of Planets : Direct detection and characterisation of young sub-stellar objects using high-contrast tools
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Ever since we first laid eyes on the twinkling lights in the night sky, our species began its age-old quest to understand how we came into existence as a planet and what the future holds for it. Most of the traditional formation theories of planets were anchored on the examples drawn from our own solar system. With the surprising and emerging trends among the yet incomplete exoplanet demographics, we are at the wake of a rigorous revision of our theoretical understanding of how planets form and evolve. To form accurate theories however, it is necessary to base them on a planet population that spans the complete range of parameter space not only in terms of its physical properties like mass and orbital separation, but also with respect to the type of stars that host these planets and their age. In this regard, direct detection, whereby you measure photons coming from the planet, helps one get closer to the whole picture since the ideal target population for this technique are young, giant planets in wide orbits that are generally difficult to observe with other detection techniques. Over the last few years, the sensitivity reached by direct imaging observations has seen tremendous improvement owing to the use of high-contrast tools like coronagraphy and adaptive optics. The development of high-resolution spectrographs together with advanced post-processing techniques have recently, for the first time, enabled witnessing planets while in the process of being born, helping us understand how they grow by devouring material from the planetary nursery — a mechanism known as accretion. This is an exciting era for planetary science, with many ongoing as well as planned future surveys with both ground and space-based telescopes dedicated to unravelling the mysteries surrounding the origin of planets. In this thesis, I provide an overview of direct detection as a tool to study sub-stellar objects – a categorisation that includes both planets and brown dwarfs, and whose blurred lines of distinction is a point of contention in astronomy today. I concentrate my discussion on two techniques, high-contrast imaging and high-resolution spectroscopy, both of which have proven significant in the race for planet detection and characterisation. Three scientific research works are carried out as a part of this thesis, using which I highlight the benefits of these techniques in constraining the physical properties of planets and brown dwarfs, as well as obtaining clues to their formation mechanism. In Paper I, I search for a Jupiter-like planet around a nearby Sun-like star that has long eluded imaging surveys, revealing its presence only via its influence on the parent star. I show how the brightness constraints at various separations and multiple wavelengths from the parent star help set a lower limit on the vaguely defined age of the system, in the absence of detection of the planet in our observations. In Paper II, I report the discovery of two low-mass companions to a massive, bright, young star, infer their orbital dynamics from multi-epoch imaging data, and constrain their physical properties using simultaneous low-resolution spectroscopy. In Paper III, I use a high-resolution spectrograph to observe for the first time, resolved Hydrogen and Helium emission lines from a young, isolated planetary-mass object in the midst of formation. Based on analysis of these line profiles, I obtain clues to the possible accretion mechanism at play in this nebulous cosmic phenomenon.
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| 6. |
- Viswanath, Gayathri, 1992-, et al.
(författare)
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BEAST detection of a brown dwarf and a low-mass stellar companion around the young bright B star HIP 81208
- 2023
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Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 675, s. A54-A54
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Tidskriftsartikel (refereegranskat)abstract
- Recent observations by the B-star Exoplanet Abundance Study (BEAST) illustrate the existence of substellar companions around very massive stars. Here, we present the detection of two lower mass companions to a relatively nearby (148.7−1.3+1.5 pc), young (17−4+3 Myr), bright (V = 6.632 ± 0.006 mag), 2.58 ± 0.06 M⊙ B9V star HIP 81208 residing in the Sco-Cen association using the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument at the Very Large Telescope (VLT) in Chile. Our analysis of the photometry obtained gives mass estimates of 67−7+6 MJ for the inner companion and 0.135−0.013+0.010 M⊙ for the outer companion, indicating that the former is most likely a brown dwarf and the latter a low-mass star. The system is compact but unusual, as the orbital planes of the two companions are likely close to orthogonal. The preliminary orbital solutions we derive for the system indicate that the star and the two companions are likely in a Kozai resonance, rendering the system dynamically very interesting for future studies.
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| 7. |
- Viswanath, Gayathri, et al.
(författare)
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Constraints on the nearby exoplanet ϵ Indi Ab from deep near- and mid-infrared imaging limits
- 2021
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 651
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Tidskriftsartikel (refereegranskat)abstract
- The past decade has seen increasing efforts in detecting and characterising exoplanets using high-contrast imaging in the near- and mid-infrared, which is the optimal wavelength domain for studying old, cold planets. In this work, we present deep adaptive optics imaging observations of the nearby Sun-like star E Ind A with the NaCo (L ') and NEAR (10-12.5 microns) instruments at VLT in an attempt to directly detect its planetary companion, whose presence has been indicated from radial velocity (RV) and astrometric trends. We derive brightness limits from the non-detection of the companion with both instruments and interpret the corresponding sensitivity in mass based on both cloudy and cloud-free atmospheric and evolutionary models. For an assumed age of 5 Gyr for the system, we get detectable mass limits as low as 4.4 M-J in NaCo L ' and 8.2 M-J in NEAR bands at 1.5 ' ' from the central star. If the age assumed is 1 Gyr, we reach even lower mass limits of 1.7 M-J in NaCo L ' and 3.5 M-J in NEAR bands at the same separation. However, based on the dynamical mass estimate (3.25 M-J) and ephemerides from astrometry and RV, we find that the non-detection of the planet in these observations puts a constraint of 2 Gyr on the lower age limit of the system. NaCo offers the highest sensitivity to the planetary companion in these observations, but the combination with the NEAR wavelength range adds a considerable degree of robustness against uncertainties in the atmospheric models. This underlines the benefits of including a broad set of wavelengths for the detection and characterisation of exoplanets in direct imaging studies.
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| 8. |
- Viswanath, Gayathri, 1992-, et al.
(författare)
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Exoplanet Accretion Monitoring Spectroscopic Survey (ENTROPY).I — Evidence for magnetospheric accretion in the young isolated planetary-mass object 2MASS J11151597+1937266
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Accretion among planetary mass companions is a poorly understood phenomenon, mainly due to the lack of observational studies that shed light on the process. Detection of emission lines from accreting gas giants facilitate detailed investigations into their formation mechanisms. This work adds another young, sub-stellar candidate to the sample of few planetary-mass objects with observed emission lines − an isolated L2ϒ dwarf 2MASS J11151597+1937266 with a mass between 7 and 21 MJup and an age of 5−45 Myr, located at 45.49±2.14 pc. We obtained the first high-resolution (R~50,000) spectrum of the target with VLT/UVES, an echelle spectrograph operating in the near-UV to visible wavelengths (3200−6800 Å). We report on several resolved H I (H3−H7) and He I emission lines (λ5875.6 Å ) in the spectrum. Based on the asymmetric line profiles of Hα and Hβ, the 10% width of Hα emission (198±5 km s-1), tentative He I emission at 6678 Å and indications of a disk from MIR excess, we confirm ongoing accretion at this object. We revise the physical parameters of the target based on the more accurate Gaia parallax-based distance measurement and derive a mass accretion rate of MJup yr-1 for 2MASS J11151597+1937266 based on the HI line luminosities using planetary scaling relations for Lline‾Lacc. Analysis of the observed H I profiles within the framework of planet-surface shock model implies a pre-shock gas velocity of v0= km s-1 and a pre-shock density of n0=1013 cm-3. The line-emitting area of the planet predicted from planet-surface shock model is very small (~0.09%), and points to a shock at the base of a magnetospherically induced funnel. The Hα profile exhibits a much stronger flux than predicted by the best-fitting model to the rest of the H I profiles, indicating that another mechanism than shock emission contributes to, or even dominates, the Hα emission. On comparison of line fluxes and mass accretion rate from this UVES epoch with those from archival low-resolution SDSS DR9 and DR12 spectra, we cannot exclude variability in accretion at 2MASS J11151597+1937266.
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| 9. |
- Viswanath, Gayathri, 1992-
(författare)
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High-Contrast Investigation of the ε Ind system
- 2021
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This licentiate thesis provides a broad introduction into the methodology of detecting and characterising exoplanets, with the main focus on the method of high-contrast imaging (HCI). Developments in theoretical knowledge as well as instrumentation have, in the past decade, pushed the boundaries of what HCI can achieve, both in terms of detection sensitivity and constraining planet properties. Direct imaging surveys in the near infrared (NIR) and longward wavelengths have proven particularly useful in detecting younger giant planets at wide orbital separations.The scientific work presented as part of this thesis is one such result of an imaging pursuit of the young giant planet, ϵ Ind Ab, which has long eluded NIR imaging surveys in the past, yet revealing its existence via radial velocity trends and astrometry of the parent star. It resides in the very interesting ϵ Ind stellar system, revolving around the primary star ϵ Ind A which is a Sun-like star only ∼12 light years away and visible in the night sky to the naked eye. With the combination of imaging data from two mid infrared (MIR) instruments, advanced post-processing techniques as well as comparative analysis using different planet atmospheric models, this work was able to place tight constraints on the age of the system and mass of the planet, although no detection was achieved. The new constraints set a firm foundation for MIR imaging surveys for the planet in future, especially with the upcoming more sensitive, advanced instruments in the later half of the decade.MIR imaging surveys have gained increasing significance in the recent years, due to their ability to detect colder/ smaller planets. It plays an important role in covering the missing gaps in the planet parameter space, ultimately aiding in improving our knowledge on planet formation and evolution.
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