ORCID Profile
0000-0002-9464-8101
Current Organisation
University of Chicago
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Publisher: American Astronomical Society
Date: 22-01-2021
Publisher: EDP Sciences
Date: 04-2021
DOI: 10.1051/0004-6361/202039144
Abstract: Recently detected coherent low-frequency radio emission from M dwarf systems shares phenomenological similarities with emission produced by magnetospheric processes from the gas giant planets of our Solar System. Such beamed electron-cyclotron maser emission can be driven by a star-planet interaction or a breakdown in co-rotation between a rotating plasma disk and a stellar magnetosphere. Both models suggest that the radio emission could be periodic. Here we present the longest low-frequency interferometric monitoring c aign of an M dwarf system, composed of twenty-one ≈8 h epochs taken in two series of observing blocks separated by a year. We achieved a total on-source time of 6.5 days. We show that the M dwarf binary CR Draconis has a low-frequency 3 σ detection rate of 90 −8 +5 % when a noise floor of ≈0.1 mJy is reached, with a median flux density of 0.92 mJy, consistent circularly polarised handedness, and a median circularly polarised fraction of 66%. We resolve three bright radio bursts in dynamic spectra, revealing the brightest is elliptically polarised, confined to 4 MHz of bandwidth centred on 170 MHz, and reaches a flux density of 205 mJy. The burst structure is mottled, indicating it consists of unresolved sub-bursts. Such a structure shares a striking resemblance with the low-frequency emission from Jupiter. We suggest the near-constant detection of high brightness temperature, highly-circularly-polarised radiation that has a consistent circular polarisation handedness implies the emission is produced via the electron-cyclotron maser instability. Optical photometric data reveal the system has a rotation period of 1.984 ± 0.003 days. We observe no periodicity in the radio data, but the s ling of our radio observations produces a window function that would hide the near two-day signal.
Publisher: American Astronomical Society
Date: 03-2023
Abstract: The Transiting Exoplanet Survey Satellite (TESS) mission searches for new exoplanets. The observing strategy of TESS results in high-precision photometry of millions of stars across the sky, allowing for detailed asteroseismic studies of in idual systems. In this work, we present a detailed asteroseismic analysis of the giant star HD 76920 hosting a highly eccentric giant planet ( e = 0.878) with an orbital period of 415 days, using five sectors of TESS light curve that cover around 140 days of data. Solar-like oscillations in HD 76920 are detected around 52 μ Hz by TESS for the first time. By utilizing asteroseismic modeling that takes classical observational parameters and stellar oscillation frequencies as constraints, we determine improved measurements of the stellar mass (1.22 ± 0.11 M ⊙ ), radius (8.68 ± 0.34 R ☉ ), and age (5.2 ± 1.4 Gyr). With the updated parameters of the host star, we update the semimajor axis and mass of the planet as a = 1.165 ± 0.035 au and M p sin i = 3.57 ± 0.22 M Jup . With an orbital pericenter of 0.142 ± 0.005 au, we confirm that the planet is currently far away enough from the star to experience negligible tidal decay until being engulfed in the stellar envelope. We also confirm that this event will occur within about 100 Myr, depending on the stellar model used.
Publisher: American Astronomical Society
Date: 09-2021
Publisher: Springer Science and Business Media LLC
Date: 09-01-2023
DOI: 10.1038/S41586-022-05677-Y
Abstract: Transmission spectroscopy 1–3 of exoplanets has revealed signatures of water vapour, aerosols and alkali metals in a few dozen exoplanet atmospheres 4,5 . However, these previous inferences with the Hubble and Spitzer Space Telescopes were hindered by the observations’ relatively narrow wavelength range and spectral resolving power, which precluded the unambiguous identification of other chemical species—in particular the primary carbon-bearing molecules 6,7 . Here we report a broad-wavelength 0.5–5.5 µm atmospheric transmission spectrum of WASP-39b 8 , a 1,200 K, roughly Saturn-mass, Jupiter-radius exoplanet, measured with the JWST NIRSpec’s PRISM mode 9 as part of the JWST Transiting Exoplanet Community Early Release Science Team Program 10–12 . We robustly detect several chemical species at high significance, including Na (19 σ ), H 2 O (33 σ ), CO 2 (28 σ ) and CO (7 σ ). The non-detection of CH 4 , combined with a strong CO 2 feature, favours atmospheric models with a super-solar atmospheric metallicity. An unanticipated absorption feature at 4 µm is best explained by SO 2 (2.7 σ ), which could be a tracer of atmospheric photochemistry. These observations demonstrate JWST’s sensitivity to a rich ersity of exoplanet compositions and chemical processes.
Publisher: American Astronomical Society
Date: 04-09-2020
Publisher: Springer Science and Business Media LLC
Date: 09-01-2023
DOI: 10.1038/S41586-022-05674-1
Abstract: The Saturn-mass exoplanet WASP-39b has been the subject of extensive efforts to determine its atmospheric properties using transmission spectroscopy 1–4 . However, these efforts have been h ered by modelling degeneracies between composition and cloud properties that are caused by limited data quality 5–9 . Here we present the transmission spectrum of WASP-39b obtained using the Single-Object Slitless Spectroscopy (SOSS) mode of the Near Infrared Imager and Slitless Spectrograph (NIRISS) instrument on the JWST. This spectrum spans 0.6–2.8 μm in wavelength and shows several water-absorption bands, the potassium resonance doublet and signatures of clouds. The precision and broad wavelength coverage of NIRISS/SOSS allows us to break model degeneracies between cloud properties and the atmospheric composition of WASP-39b, favouring a heavy-element enhancement (‘metallicity’) of about 10–30 times the solar value, a sub-solar carbon-to-oxygen (C/O) ratio and a solar-to-super-solar potassium-to-oxygen (K/O) ratio. The observations are also best explained by wavelength-dependent, non-grey clouds with inhomogeneous coverageof the planet’s terminator.
Publisher: American Astronomical Society
Date: 07-2022
DOI: 10.3847/PSJ/AC75B5
Abstract: Based on the occurrence rates implied by the discoveries of 1I/‘Oumuamua and 2I/Borisov, the forthcoming Rubin Observatory Legacy Survey of Space and Time (LSST) should detect ≥one interstellar object every year. We advocate for future measurements of the production rates of H 2 O, CO 2 , and CO in these objects to estimate their carbon-to-oxygen ratios, which trace formation locations within their original protoplanetary disks. We review similar measurements for solar system comets, which indicate formation interior to the CO snow line. By quantifying the relative processing in the interstellar medium and solar system, we estimate that production rates will not be representative of primordial compositions for the majority of interstellar comets. Preferential desorption of CO and CO 2 relative to H 2 O in the interstellar medium implies that measured C/O ratios represent lower limits on the primordial ratios. Specifically, production rate ratios of Q (CO)/ Q (H 2 O) 0.2 and Q (CO)/ Q (H 2 O) 1 likely indicate formation interior and exterior to the CO snow line, respectively. The high C/O ratio of 2I/Borisov implies that it formed exterior to the CO snow line. We provide an overview of the currently operational facilities capable of obtaining these measurements that will constrain the fraction of ejected comets that formed exterior to the CO snow line. This fraction will provide key insights into the efficiency of and mechanisms for cometary ejection in exoplanetary systems.
Publisher: American Astronomical Society
Date: 04-2022
Abstract: All stars produce explosive surface events such as flares and coronal mass ejections. These events are driven by the release of energy stored in coronal magnetic fields, generated by the stellar dynamo. However, it remains unclear if the energy deposition in the magnetic fields is driven by direct or alternating currents. Recently, we presented observational measurements of the flare intensity distributions for a s le of ∼10 5 stars across the main sequence observed by TESS, all of which exhibited power-law distributions similar to those observed in the Sun, albeit with varying slopes. Here we investigate the mechanisms required to produce such a distribution of flaring events via direct current energy deposition, in which coronal magnetic fields braid, reconnect, and produce flares. We adopt a topological model for this process, which produces a power-law distribution of energetic flaring events. We expand this model to include the Coriolis effect, which we demonstrate produces a shallower distribution of flare energies in stars that rotate more rapidly (corresponding to a weaker decline in occurrence rates toward increasing flare energies). We present tentative evidence for the predicted rotation-power-law index correlation in the observations. We advocate for future observations of stellar flares that would improve our measurements of the power-law exponents, and yield key insights into the underlying dynamo mechanisms that underpin the self-similar flare intensity distributions.
Publisher: American Astronomical Society
Date: 07-05-2020
No related grants have been discovered for Adina Feinstein.