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Register a new userThe Separation and H-alpha Contrasts of Massive Accreting Planets in the Gaps of Transitional Disks: Predicted H-alpha Protoplanet Yields for Adaptive Optics Surveys
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Laird M. Close
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We present a massive accreting gap (MAG) planet model that ensures large gaps in transitional disks are kept dust free by the scattering action of three co-planar quasi-circular planets in a 1:2:4 Mean Motion Resonance (MMR). This model uses the constraint of the observed gap size, and the dust-free nature of the gap, to determine within ~10% the possible orbits for 3 massive planets in an MMR. Calculated orbits are consistent with the observed orbits and H-alpha emission (the brightest line to observe these planets) for LkCa 15 b and PDS 70 b and PDS 70 c within observational errors. Moreover, the model suggests that the scarcity of detected H-alpha planets is likely a selection effect of the current limitations of non-coronagraphic, low (<10%) Strehl, H-alpha imaging with Adaptive Optics (AO) systems used in past H-alpha surveys. We predict that as higher Strehl AO systems (with high-performance custom coronagraphs; like 6.5-m Magellan Telescope MagAO-X system) are utilized at H-alpha the number of detected gap planets will substantially increase by more than tenfold. For example, we show that >25 new H-alpha gap planets are potentially discoverable by a survey of the best 19 transitional disks with MagAO-X. Detections of these accreting protoplanets will significantly improve our understanding of planet formation, planet growth and accretion, solar system architectures, and planet disk interactions.
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The mechanisms of planet formation are still under debate. We know little about how planets form, even if more than 4000 exoplanets have been detected to date. Recent investigations target the cot of newly born planets: the protoplanetary disk. At the first stages of their life, exoplanets still accrete material from the gas-rich disk in which they are embedded. Transitional disks are indeed disks that show peculiarities, such as gaps, spiral arms, and rings, which can be connected to the presence of substellar companions. To investigate what is responsible for these features, we selected all the known transitional disks in the solar neighborhood (<200 pc) that are visible from the southern hemisphere. We conducted a survey of 11 transitional disks (TDs) with the SPHERE instrument at the VLT. This is the largest Halpha survey that has been conducted so far to look for protoplanets. The observations were performed with the Halpha filter of ZIMPOL in order to target protoplanets that are still in the accretion stage. All the selected targets are very young stars, less than 20 Myr, and show low extinction in the visible. We reduced the ZIMPOL pupil stabilized data by applying the method of the angular spectral differential imaging (ASDI), which combines both techniques. The datacubes are composed of the CntHalpha and the narrow band filter Halpha, which are taken simultaneously to permit the suppression of the speckle pattern. The principal component analysis (PCA) method was employed for the reduction of the data. For each dataset, we derived the 5sigma contrast limit and converted it in upper limits on the accretion luminosity. We do not detect any new accreting substellar companions around the targeted transition disks down to an average contrast of 12 magnitudes at 0.2 arcsec from the central star (continues in the manuscript).
(Abridged) The detection of forming planets in disks around young stars remains elusive, and state-of-the-art observational techniques provide somewhat ambiguous results. It has been reported that the pre-transitional T Tauri star LkCa 15 could host three planets; candidate planet b is in the process of formation, as inferred from its H$alpha$ emission. However, a more recent work casts doubts on the planetary nature of the previous detections. We have observed LkCa 15 with ISIS/WHT. The spectrographs slit was oriented towards the last reported position of LkCa 15 b (parallel direction) and 90degr from that (perpendicular). The photocenter and full width half maximum (FWHM) of the Gaussians fitting the spatial distribution at H$alpha$ and the adjacent continuum were measured. A well-known binary (GU CMa) was used as a calibrator to test the spectro-astrometric performance of ISIS/WHT, recovering consistent photocenter and FWHM signals. However, the photocenter shift predicted for LkCa 15 b is not detected, but the FWHM in H$alpha$ is broader than in the continuum for both slit positions. Our simulations show that the photocenter and FWHM observations cannot be explained simultaneously by an accreting planet. In turn, both spectro-astrometric observations are naturally reproduced from a roughly symmetric Halpha emitting region centered on the star and extent comparable to the orbit originally attributed to the planet at several au. The extended H$alpha$ emission around LkCa 15 could be related to a variable disk wind, but additional multi-epoch data and detailed modeling are necessary to understand its physical nature. Spectro-astrometry in H$alpha$ is able to test the presence of accreting planets and can be used as a complementary technique to survey planet formation in circumstellar disks.
Strong atmospheric escape has been detected in several close-in exoplanets. As these planets consist mostly of hydrogen, observations in hydrogen lines, such as Ly-alpha and H-alpha, are powerful diagnostics of escape. Here, we simulate the evolution of atmospheric escape of close-in giant planets and calculate their associated Ly-alpha and H-alpha transits. We use a one-dimensional hydrodynamic escape model to compute physical properties of the atmosphere and a ray-tracing technique to simulate spectroscopic transits. We consider giant (0.3 and 1M_jup) planets orbiting a solar-like star at 0.045au, evolving from 10 to 5000 Myr. We find that younger giants show higher rates of escape, owing to a favourable combination of higher irradiation fluxes and weaker gravities. Less massive planets show higher escape rates (1e10 -- 1e13 g/s) than those more massive (1e9 -- 1e12 g/s) over their evolution. We estimate that the 1-M_jup planet would lose at most 1% of its initial mass due to escape, while the 0.3-M_jup planet, could lose up to 20%. This supports the idea that the Neptunian desert has been formed due to significant mass loss in low-gravity planets. At younger ages, we find that the mid-transit Ly-alpha line is saturated at line centre, while H-alpha exhibits transit depths of at most 3 -- 4% in excess of their geometric transit. While at older ages, Ly-alpha absorption is still significant (and possibly saturated for the lower mass planet), the H-alpha absorption nearly disappears. This is because the extended atmosphere of neutral hydrogen becomes predominantly in the ground state after ~1.2 Gyr.
We present a spectroscopic analysis of the H-alpha profiles of hydrogen-rich type II supernovae. A total of 52 type II supernovae having well sampled optical light curves and spectral sequences were analyzed. Concentrating on the H-alpha P-Cygni profile we measure its velocity from the FWHM of emission and the ratio of absorption to emission (a/e) at a common epoch at the start of the recombination phase, and search for correlations between these spectral parameters and photometric properties of the V-band light curves. Testing the strength of various correlations we find that a/e appears to be the dominant spectral parameter in terms of describing the diversity in our measured supernova properties. It is found that supernovae with smaller a/e have higher H-alpha velocities, more rapidly declining light curves from maximum, during the plateau and radioactive tail phase, are brighter at maximum light and have shorter optically thick phase durations. We discuss possible explanations of these results in terms of physical properties of type II supernovae, speculating that the most likely parameters which influence the morphologies of H-alpha profiles are the mass and density profile of the hydrogen envelope, together with additional emission components due to circumstellar interaction.
Aims: We want to detect and quantify observables related to accretion processes occurring locally in circumstellar disks, which could be attributed to young forming planets. We focus on objects known to host protoplanet candidates and/or disk structures thought to be the result of interactions with planets. Methods: We analyzed observations of 6 young stars (age $3.5-10$ Myr) and their surrounding environments with the SPHERE/ZIMPOL instrument on the VLT in the H$alpha$ filter (656 nm) and a nearby continuum filter (644.9 nm). Results: We re-detect the known accreting M-star companion HD142527 B with the highest published signal to noise to date in both H$alpha$ and the continuum. We derive new astrometry ($r = 62.8^{+2.1}_{-2.7}$ mas and $text{PA} = (98.7,pm1.8)^circ$) and photometry ($Delta$N_Ha=$6.3^{+0.2}_{-0.3}$ mag, $Delta$B_Ha=$6.7pm0.2$ mag and $Delta$Cnt_Ha=$7.3^{+0.3}_{-0.2}$ mag) for the companion in agreement with previous studies, and estimate its mass accretion rate ($dot{M}approx1-2,times10^{-10},M_odottext{ yr}^{-1}$). A faint point-like source around HD135344 B (SAO206462) is also investigated, but a second deeper observation is required to reveal its nature. No other companions are detected. In the framework of our assumptions we estimate detection limits at the locations of companion candidates around HD100546, HD169142 and MWC758 and calculate that processes involving H$alpha$ fluxes larger than $sim8times10^{-14}-10^{-15},text{erg/s/cm}^2$ ($dot{M}>10^{-10}-10^{-12},M_odottext{ yr}^{-1}$) can be excluded. Furthermore, flux upper limits of $sim10^{-14}-10^{-15},text{erg/s/cm}^2$ ($dot{M}<10^{-11}-10^{-12},M_odot text{ yr}^{-1}$) are estimated within the gaps identified in the disks surrounding HD135344B and TW Hya.
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